ALD THESES

Precursor Chemistry for Atomic Layer Deposition
Author
Timo Hatanpää
Year
2019
Source of Information
Thesis pdf (written here by Riikka)
University
University of Helsinki
(Helsinki, Finland)
External Link
2019
Molecular layer deposition for applications in lithium ion batteries
Author
Kevin Van de Kerckhove
Year
2019
Abstract

Molecular layer deposition (MLD) is a thin film deposition technique that  is based on self-limiting gas-surface reactions. MLD inherits several attractive properties from its parent technique atomic layer deposition (ALD),  e.g. the sub-nanometer thickness control and excellent conformality on  complex structures. MLD distinguishes itself from ALD through the use  of organic reactants as ethylene glycol (EG) and glycerol (GL) in combination with metal-organic precursors. Organic fragments can be built into  the growing film, leading to the deposition of hybrid organic-inorganic  films called “metalcones”. MLD processes for alucone, titanicone, zincone,  zircone, and hafnicone have already been reported in the literature. An interesting property of metalcone films is that they can be transformed into  nanoporous metal oxide films by calcination in air or water etching, as was  reported by Liang et al. in 2009. Hybrid organic-inorganic films deposited  by MLD have potential applications for flexible electronics, catalysis, luminescent materials, light conversion, and lithium ion batteries.  Three research objectives were defined at the start of this thesis. The  first objective is to further study the transformation of metalcone films  into porous metal oxides. In this work, the transformation of alucone was  studied in more detail. The second objective is to develop MLD processes  that employ alkylamine metal precursors. This type of precursor is wellestablished in the ALD literature, but has never before been used for MLD.  Here, alkylamine precursors for titanium, vanadium and tin were incorporated in MLD processes for titanicone, vanadicone and tincone respectively. The final objective is to investigate the application of metalcone  films as thin film electrodes for lithium ion batteries. Before this work,  there existed only one report on the synthesis of a Li ion battery electrode  by MLD: lithium terephthalate  

Molecular layer deposition (MLD) is a thin film deposition technique that  is based on self-limiting gas-surface reactions. MLD inherits several attractive properties from its parent technique atomic layer deposition (ALD),  e.g. the sub-nanometer thickness control and excellent conformality on  complex structures. MLD distinguishes itself from ALD through the use  of organic reactants as ethylene glycol (EG) and glycerol (GL) in combination with metal-organic precursors. Organic fragments can be built into  the growing film, leading to the deposition of hybrid organic-inorganic  films called “metalcones”. MLD processes for alucone, titanicone, zincone,  zircone, and hafnicone have already been reported in the literature. An interesting property of metalcone films is that they can be transformed into  nanoporous metal oxide films by calcination in air or water etching, as was  reported by Liang et al. in 2009. Hybrid organic-inorganic films deposited  by MLD have potential applications for flexible electronics, catalysis, luminescent materials, light conversion, and lithium ion batteries.  Three research objectives were defined at the start of this thesis. The  first objective is to further study the transformation of metalcone films  into porous metal oxides. In this work, the transformation of alucone was  studied in more detail. The second objective is to develop MLD processes  that employ alkylamine metal precursors. This type of precursor is wellestablished in the ALD literature, but has never before been used for MLD.  Here, alkylamine precursors for titanium, vanadium and tin were incorporated in MLD processes for titanicone, vanadicone and tincone respectively. The final objective is to investigate the application of metalcone  films as thin film electrodes for lithium ion batteries. Before this work,  there existed only one report on the synthesis of a Li ion battery electrode  by MLD: lithium terephthalate  
Source of Information
Felix Mattelaer
University
Ghent University, Department of Solid State Physics, CoCooN research group
(Ghent, Belgium)
2019
MODIFICATION OF THE SURFACE OF NANOSTRUCTURED TITANIUM BY METHODS OF CHEMICAL ETCHING AND MOLECULAR LAYERING FOR REGULATION OF BIOMEDICAL PROPERTIES
Author
D.V. Nazarov
Year
2019
Language of the thesis
Russian
Thesis name in original language
МОДИФИКАЦИЯ ПОВЕРХНОСТИ НАНОСТРУКТУРИРОВАННОГО ТИТАНА МЕТОДАМИ ХИМИЧЕСКОГО ТРАВЛЕНИЯ И МОЛЕКУЛЯРНОГО НАСЛАИВАНИЯ ДЛЯ РЕГУЛИРОВАНИЯ БИОМЕДИЦИНСКИХ СВОЙСТВ
Source of Information
Anatoly Malygin
University
St. Petersburg State University
(Saint Petersburg, Russian)
Other notes
Scientific advisor: V. M. Smirnov
External Link
2019
Metal-Organic Frameworks by Molecular Layer Deposition
Author
Kristian Lausund
Year
2019
Abstract

Organic-inorganic hybrid materials have been prepared as thin films by molecular layer deposition (MLD) for over a decade. However, it has proven challenging to synthesize porous films or crystalline metal-organic frameworks (MOFs) through this technique, and only a few examples of such synthesis exist in the literature. MOF thin films are desirable for a large range of applications spanning from sensor materials to separation techniques or even drug delivery, but so far, they have required solventbased synthesis such as solvothermal synthesis. Using an all-gas-phase approach, however, opens for easier implementation in applications such as microelectronics with delicate parts that are not compatible with solvothermal synthesis. In this work, a new synthesis method for MOF thin films, including the exceptionally stable structure UiO-66 and a few related Zr-based structures, is presented. These structures have been formed by depositing organic-inorganic hybrid films by MLD using ZrCl4 as a precursor along with five different organic precursors. These organic precursors consist of various aromatic structures with two carboxylic acid groups, one in either end of the molecule. The films were subsequently crystallized to form the various MOF structures by heat treatment in acetic acid vapor. The developed technique is the first solvent-free synthesis method of thin films of these Zr-based MOF structures and should open for future applications of such materials where the extraordinary porosity of MOFs is utilized. During the MLD synthesis, a modulation step was included by adding an acetic acid pulse after the organic precursors. Characterizations of the films by techniques such as FTIRa , XRDb  and SEMc , show that this acetic acid modulation guides the organic precursors in forming a stronger, bidentate coordination to the metal atoms. This is one of the main findings in this thesis since it can provide a better understanding of the reaction kinetics in formation of such films and be applied for control of stoichiometry during growth. The films were amorphous as-deposited, while still being porous. Such porosity for amorphous films is not common and makes these hybrid films interesting candidates for sensor materials or membranes, particularly for applications where pinhole-free films are required. Preliminary tests show luminescent and antibacterial properties, forming a basis for future research and development. This thesis is mostly based the work included in three papers, one article on synthesis of UiO-66 thin films (Paper I), one article on synthesis of UiO-66-NH2 (Paper II), and a manuscript describing synthesis of films with two larger organic molecules (Paper III). 

Organic-inorganic hybrid materials have been prepared as thin films by molecular layer deposition (MLD) for over a decade. However, it has proven challenging to synthesize porous films or crystalline metal-organic frameworks (MOFs) through this technique, and only a few examples of such synthesis exist in the literature. MOF thin films are desirable for a large range of applications spanning from sensor materials to separation techniques or even drug delivery, but so far, they have required solventbased synthesis such as solvothermal synthesis. Using an all-gas-phase approach, however, opens for easier implementation in applications such as microelectronics with delicate parts that are not compatible with solvothermal synthesis. In this work, a new synthesis method for MOF thin films, including the exceptionally stable structure UiO-66 and a few related Zr-based structures, is presented. These structures have been formed by depositing organic-inorganic hybrid films by MLD using ZrCl4 as a precursor along with five different organic precursors. These organic precursors consist of various aromatic structures with two carboxylic acid groups, one in either end of the molecule. The films were subsequently crystallized to form the various MOF structures by heat treatment in acetic acid vapor. The developed technique is the first solvent-free synthesis method of thin films of these Zr-based MOF structures and should open for future applications of such materials where the extraordinary porosity of MOFs is utilized. During the MLD synthesis, a modulation step was included by adding an acetic acid pulse after the organic precursors. Characterizations of the films by techniques such as FTIRa , XRDb  and SEMc , show that this acetic acid modulation guides the organic precursors in forming a stronger, bidentate coordination to the metal atoms. This is one of the main findings in this thesis since it can provide a better understanding of the reaction kinetics in formation of such films and be applied for control of stoichiometry during growth. The films were amorphous as-deposited, while still being porous. Such porosity for amorphous films is not common and makes these hybrid films interesting candidates for sensor materials or membranes, particularly for applications where pinhole-free films are required. Preliminary tests show luminescent and antibacterial properties, forming a basis for future research and development. This thesis is mostly based the work included in three papers, one article on synthesis of UiO-66 thin films (Paper I), one article on synthesis of UiO-66-NH2 (Paper II), and a manuscript describing synthesis of films with two larger organic molecules (Paper III). 
Source of Information
Henrik Sonsteby
University
University of Oslo
(Oslo, Norway)
External Link
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2019
Inducing reversible polarization switching in HfO2-ZrO2 films for energy and memory application
Author
Keum Do Kim
Year
2019
Source of Information
Cheol Seong Hwang
University
Seoul National University
(Seoul, Korea)
2019
Growth and Leakage Current Control of High-k SrTiO3 Thin Films Grown via Atomic Layer Deposition
Author
Sang Hyeon Kim
Year
2019
Source of Information
Cheol Seong Hwang
University
Seoul National University
(Seoul, Korea)
Other notes
http://dcollection.snu.ac.kr/common/orgView/000000153980
External Link
2019
Growth and characteristics of Ru based electrodes using RuO4 precursor for DRAM capacitor
Author
Cheol Hyun An
Year
2019
Source of Information
Cheol Seong Hwang
University
Seoul National University
(Seoul, Korea)
2019
From Radical-Enhanced to Pure Thermal ALD of Gallium and Aluminium Nitrides
Author
Sourish Banerjee
Year
2019
Abstract

To continue the miniaturization trend of Silicon (Si)-based microelectronic devices in an era when we have almost fully-exploited the physical capabilities of Si, other semiconductors such as gallium nitride (GaN) and aluminium nitride (AlN) (collectively (Al)GaN) are currently being investigated. These can potentially complement Si, since in their monocrystalline form, have superior material properties to Si. Examples include direct and wider bandgap, high electron mobility and high breakdown field. Thus, combining the mature Si-based process technology with such superior (Al)GaN material properties on one platform enables microelectronic devices, in accordance with the ‘More-than-Moore’ philosophy. Exploring polycrystalline and thin film (i.e., sub-micron) (Al)GaN must also be pursued, since that broadens their applications; enabling utilization in sensors, thin film transistors (TFT), as passivation layers, etc. Atomic layer deposition (ALD) is a highly relevant technique for (Al)GaN, since the technique promises atomic-level thickness control, coupled with superb film conformality and spatial uniformity. Reports of (Al)GaN ALD are only appearing recently in the literature, suggesting the increasing relevance of this field.

This thesis investigated ALD of polycrystalline (Al)GaN, using conventional Si-technology and industrially accepted precursors. A variety of activation techniques, from thermal, to plasma, and the novel hot-wire activation were explored. Some important obtained research results were: (a) Identification of a chemical route which enables pure thermal ALD of GaN, (b) Preparation of novel GaCN composite layers with high refractive indices, (c) Selectively depositing GaN on specially-terminated substrates, (d) Tuning (Al)GaN polycrystallinity and optical properties with plasma composition and investigating the underlying causes, (e) Investigating the role of precursor-generated radicals on (Al)GaN growth, and (f) Identifying the discontinuous nature of sub-10 nm AlN with electrical and optical techniques. In conclusion, the results obtained and the suggested future work are expected to advance the state-of-the-art of Al(GaN) ALD.

To continue the miniaturization trend of Silicon (Si)-based microelectronic devices in an era when we have almost fully-exploited the physical capabilities of Si, other semiconductors such as gallium nitride (GaN) and aluminium nitride (AlN) (collectively (Al)GaN) are currently being investigated. These can potentially complement Si, since in their monocrystalline form, have superior material properties to Si. Examples include direct and wider bandgap, high electron mobility and high breakdown field. Thus, combining the mature Si-based process technology with such superior (Al)GaN material properties on one platform enables microelectronic devices, in accordance with the ‘More-than-Moore’ philosophy. Exploring polycrystalline and thin film (i.e., sub-micron) (Al)GaN must also be pursued, since that broadens their applications; enabling utilization in sensors, thin film transistors (TFT), as passivation layers, etc. Atomic layer deposition (ALD) is a highly relevant technique for (Al)GaN, since the technique promises atomic-level thickness control, coupled with superb film conformality and spatial uniformity. Reports of (Al)GaN ALD are only appearing recently in the literature, suggesting the increasing relevance of this field.This thesis investigated ALD of polycrystalline (Al)GaN, using conventional Si-technology and industrially accepted precursors. A variety of activation techniques, from thermal, to plasma, and the novel hot-wire activation were explored. Some important obtained research results were: (a) Identification of a chemical route which enables pure thermal ALD of GaN, (b) Preparation of novel GaCN composite layers with high refractive indices, (c) Selectively depositing GaN on specially-terminated substrates, (d) Tuning (Al)GaN polycrystallinity and optical properties with plasma composition and investigating the underlying causes, (e) Investigating the role of precursor-generated radicals on (Al)GaN growth, and (f) Identifying the discontinuous nature of sub-10 nm AlN with electrical and optical techniques. In conclusion, the results obtained and the suggested future work are expected to advance the state-of-the-art of Al(GaN) ALD.
Source of Information
Alexey Kovalgin
University
University of Twente
(Enschede, Netherlands)
External Link
2019
Feasibility of atomic-layer-deposited Al2O3 /SrTiO3 hetero-oxide interfaces on didoe and transistor devices
Author
Taehwan Moon
Year
2019
Source of Information
Cheol Seong Hwang
University
Seoul National University
(Seoul, Korea)
External Link
2019
Expanding the toolbox of atomic scale processing
Author
Tahsin Faraz
Year
2019
Abstract

As we enter an era of atomic scale device dimensions, it has become imperative to  utilize deposition and etching techniques that allow for processing materials at the  atomic level. Furthermore, next-generation devices consist of various material layers  across both planar and three-dimensional (3D) layouts which has led to an additional  need for processing materials in a selective manner. As a result, it is now vitally  important to retain proper control over the thickness and properties of materials grown  or removed during fabrication of nanoscale devices with 3D geometries. Plasmaenhanced atomic layer deposition (ALD) has obtained a prominent position in  synthesizing ultra-thin films of functional materials with atomic scale precision. Uniform  and conformal film deposition even on challenging 3D substrate topographies can be  attained by virtue of the sequential and self-limiting precursor and plasma exposure  steps of plasma ALD. Highly reactive plasma radicals are generated during the plasma  step and the contribution of these electrically neutral species toward film growth is a  well-known feature of plasma ALD. However, the ions generated during plasma  exposure can also play a significant role in the deposition process which has been  relatively less explored. Furthermore, the challenges related to current plasma based  dry-etching processes provide a window of opportunity for being potentially tackled by  the etch counterpart of ALD, i.e., atomic layer etching (ALE). This dissertation  investigates plasma-enhanced atomic scale processing of functional materials and the  role of ions during these processes on planar and 3D substrate topographies, relevant  for next-generation device technologies.  In the first part of this work, a new ALD process for SiNx was developed using a  novel organosilane precursor (DSBAS) and N2 plasma. Dense and wet-etch resistant SiNx  films that can be synthesized at low temperatures serve as spacers or encapsulation  layers for protecting sensitive device components; e.g., gate stacks in 3D transistors or  magnetic tunnel junctions in emerging magnetoresistive memories. SiNx films with a  high density and low impurity content were obtained at low substrate temperatures on  planar substrates using the process developed in this work. Deposition were also  performed on high aspect ratio 3D trench nanostructures to investigate SiNx film  conformality and wet-etch resistance. Sources limiting conformality on 3D substrates  were attributed to factors occurring in the N2 plasma step. Identification of factors  associated with plasma processing conditions is a prerequisite for addressing the  challenge of growing conformal SiNx on 3D substrates. Yet, very low wet-etch rates  were observed at different regions throughout the trenches, confirming high quality SiNx could be grown at low substrate temperature on 3D substrates using the developed  process.  Next, the effects substrate biasing during plasma ALD on the properties of  materials (oxides and nitrides of Ti, Hf, and Si) grown on planar and 3D substrate  topographies were investigated. A commercial 200-mm remote plasma ALD system  equipped with RF substrate biasing was used to control the ion energy during the  plasma exposure step. This technique was demonstrated to significantly enhance the  versatility of plasma ALD processes by providing additional knobs for controlling a wide  range of material properties, appropriate for numerous applications. Substrate biasing  during plasma ALD increased the refractive index and mass density of TiOx and HfOx and  enabled control over their crystalline properties. Plasma ALD of these oxides with  substrate biasing formed crystalline films at a low temperature which would otherwise  yield amorphous films without biasing. Substrate biasing drastically reduced the  resistivity of conductive TiNx and HfNx films. Furthermore, biasing enabled the residual  stress of these materials to be altered from tensile to compressive. The properties of  SiOx were slightly improved whereas those of SiNx were degraded as a function of  substrate biasing. Plasma ALD on 3D trench nanostructures with biasing induced  differing film properties at different regions of the 3D substrate which demonstrated  the potential of this technique in enabling new approaches for topographically selective  deposition.  Ion energy characteristics on grounded and biased substrates during plasma  exposure were also measured to investigate their role in tailoring material properties.  Insights from such measurements are essential toward understanding how a given  plasma ALD process at different operating conditions can be influenced by energetic  ions. Ion flux-energy distribution functions (IFEDFs) were measured using a retarding  field energy analyzer for reactive plasmas typically used in plasma ALD (O2, H2, N2)  without and with RF biasing. The properties of materials (TiOx, HfNx, SiNx) grown using  these plasmas were analyzed as a function of the ion energy and flux parameters  derived from IFEDFs. These results have provided more insight on the relation between  energetic ions and the ensuing material properties, e.g., by providing energy maps of  material properties in terms of the ion energy dose during plasma ALD. They  demonstrate how the measurement and control of ion energy characteristics during  plasma ALD provide a platform for synthesizing ultra-thin films with the desired  properties.  In the final part of this work, past research efforts on ALE were reviewed and the  key defining characteristics of ALE identified. These include cyclic step-wise processing,  self-limiting surface chemistry, repeated removal of atomic layers (not necessarily a full monolayer) of the material, and the presence or absence of directional species that lead  to anisotropic or isotropic ALE processes, respectively. Subsequently, further parallels  were drawn with the more mature and mainstream technology of ALD from which  lessons and concepts were extracted that can be beneficial for advancing the field of  ALE.  To conclude, this dissertation elucidates important aspects associated with plasmaenhanced atomic scale processes that provide deeper insight on the fundamental and  technological opportunities afforded by these techniques, relevant for future 3D device  architectures. It serves to exemplify how the properties of functional materials can be  tailored by accurate control and optimization of plasma based processing conditions  

As we enter an era of atomic scale device dimensions, it has become imperative to  utilize deposition and etching techniques that allow for processing materials at the  atomic level. Furthermore, next-generation devices consist of various material layers  across both planar and three-dimensional (3D) layouts which has led to an additional  need for processing materials in a selective manner. As a result, it is now vitally  important to retain proper control over the thickness and properties of materials grown  or removed during fabrication of nanoscale devices with 3D geometries. Plasmaenhanced atomic layer deposition (ALD) has obtained a prominent position in  synthesizing ultra-thin films of functional materials with atomic scale precision. Uniform  and conformal film deposition even on challenging 3D substrate topographies can be  attained by virtue of the sequential and self-limiting precursor and plasma exposure  steps of plasma ALD. Highly reactive plasma radicals are generated during the plasma  step and the contribution of these electrically neutral species toward film growth is a  well-known feature of plasma ALD. However, the ions generated during plasma  exposure can also play a significant role in the deposition process which has been  relatively less explored. Furthermore, the challenges related to current plasma based  dry-etching processes provide a window of opportunity for being potentially tackled by  the etch counterpart of ALD, i.e., atomic layer etching (ALE). This dissertation  investigates plasma-enhanced atomic scale processing of functional materials and the  role of ions during these processes on planar and 3D substrate topographies, relevant  for next-generation device technologies.  In the first part of this work, a new ALD process for SiNx was developed using a  novel organosilane precursor (DSBAS) and N2 plasma. Dense and wet-etch resistant SiNx  films that can be synthesized at low temperatures serve as spacers or encapsulation  layers for protecting sensitive device components; e.g., gate stacks in 3D transistors or  magnetic tunnel junctions in emerging magnetoresistive memories. SiNx films with a  high density and low impurity content were obtained at low substrate temperatures on  planar substrates using the process developed in this work. Deposition were also  performed on high aspect ratio 3D trench nanostructures to investigate SiNx film  conformality and wet-etch resistance. Sources limiting conformality on 3D substrates  were attributed to factors occurring in the N2 plasma step. Identification of factors  associated with plasma processing conditions is a prerequisite for addressing the  challenge of growing conformal SiNx on 3D substrates. Yet, very low wet-etch rates  were observed at different regions throughout the trenches, confirming high quality SiNx could be grown at low substrate temperature on 3D substrates using the developed  process.  Next, the effects substrate biasing during plasma ALD on the properties of  materials (oxides and nitrides of Ti, Hf, and Si) grown on planar and 3D substrate  topographies were investigated. A commercial 200-mm remote plasma ALD system  equipped with RF substrate biasing was used to control the ion energy during the  plasma exposure step. This technique was demonstrated to significantly enhance the  versatility of plasma ALD processes by providing additional knobs for controlling a wide  range of material properties, appropriate for numerous applications. Substrate biasing  during plasma ALD increased the refractive index and mass density of TiOx and HfOx and  enabled control over their crystalline properties. Plasma ALD of these oxides with  substrate biasing formed crystalline films at a low temperature which would otherwise  yield amorphous films without biasing. Substrate biasing drastically reduced the  resistivity of conductive TiNx and HfNx films. Furthermore, biasing enabled the residual  stress of these materials to be altered from tensile to compressive. The properties of  SiOx were slightly improved whereas those of SiNx were degraded as a function of  substrate biasing. Plasma ALD on 3D trench nanostructures with biasing induced  differing film properties at different regions of the 3D substrate which demonstrated  the potential of this technique in enabling new approaches for topographically selective  deposition.  Ion energy characteristics on grounded and biased substrates during plasma  exposure were also measured to investigate their role in tailoring material properties.  Insights from such measurements are essential toward understanding how a given  plasma ALD process at different operating conditions can be influenced by energetic  ions. Ion flux-energy distribution functions (IFEDFs) were measured using a retarding  field energy analyzer for reactive plasmas typically used in plasma ALD (O2, H2, N2)  without and with RF biasing. The properties of materials (TiOx, HfNx, SiNx) grown using  these plasmas were analyzed as a function of the ion energy and flux parameters  derived from IFEDFs. These results have provided more insight on the relation between  energetic ions and the ensuing material properties, e.g., by providing energy maps of  material properties in terms of the ion energy dose during plasma ALD. They  demonstrate how the measurement and control of ion energy characteristics during  plasma ALD provide a platform for synthesizing ultra-thin films with the desired  properties.  In the final part of this work, past research efforts on ALE were reviewed and the  key defining characteristics of ALE identified. These include cyclic step-wise processing,  self-limiting surface chemistry, repeated removal of atomic layers (not necessarily a full monolayer) of the material, and the presence or absence of directional species that lead  to anisotropic or isotropic ALE processes, respectively. Subsequently, further parallels  were drawn with the more mature and mainstream technology of ALD from which  lessons and concepts were extracted that can be beneficial for advancing the field of  ALE.  To conclude, this dissertation elucidates important aspects associated with plasmaenhanced atomic scale processes that provide deeper insight on the fundamental and  technological opportunities afforded by these techniques, relevant for future 3D device  architectures. It serves to exemplify how the properties of functional materials can be  tailored by accurate control and optimization of plasma based processing conditions  
Source of Information
Harm Knoops
University
Eindhoven University of Technology
(Eindhoven, Netherlands)
External Link
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2019
Development of mechanical characterization methods for thin films and interfaces
Author
Jussi Aav
Year
2019
Abstract

Probably the most important thin film characteristic is its' adhesion to the used substrate. It is  very important to understand the fundamental mechanics of adhesion-related failures, and by  having suitable characterization methods to detect any problems as early as possible. Tailored or  correctly conducted quantitative analysis of adhesion is required for building reliable devices. In  many conventional test methods significant loading to the substrate is applied which can result in  problems especially with brittle substrates where the substrate can break before the film is  delaminated. The characterization of interfacial mechanical properties of increasingly thinner films  is challenging with many practical shortcomings and thus method development is needed.  In this thesis, three measurement methods where the loading to the substrate is minimized are  presented and demonstrated for the interfacial and mechanical testing of especially atomic layer  deposited (ALD) thin films. (i) Microelectromechanical system (MEMS) test chip assisted shaftloaded  blister testing through a hole in the substrate to the backside of the thin film, (ii)  microrobotic manipulation of embedded microspheres using lateral loading mostly to the thin film  and to the interface and (iii) a combination of nanoscratch and scanning nanowear for minimized  interaction volume of loading to the substrate. The relationship between adhesion and cohesion  as competing processes during film/ substrate failure is shown. When the film-interface-substrate  system is under loading the energy will dissipate through the path of least resistance. This will  happen either (i) through plastic deformation of the coating/ substrate, (ii) film fracture (decohesion) or (iii) delamination (de-adhesion) of the film. Usually, however the energy is  dissipated as a combination of these three different mechanisms, unless some of the mechanisms  is dominant in the energy release.  The presented characterization methods are mostly generic, and can be applied for the evaluation  of mechanical and interfacial properties, such as adhesion, between practically any materials of  choice with some limitations. Compared to some of the existing methods, the quantitative nature  of these characterization methods enables a more in-depth possibility for the analysis, understanding, tuning and improvement of the properties of the thin films and processes aiding  in maintaining and improving product and process quality. The main outcome of this thesis is that  the authors have demonstrated the potential and versatility of especially the MEMS test structures  and microrobotic testing systems, either on their own or as a combination as a solution to  developing new tailored interfacial and mechanical characterization methods for current and future  needs of research and the industry. 

Probably the most important thin film characteristic is its' adhesion to the used substrate. It is  very important to understand the fundamental mechanics of adhesion-related failures, and by  having suitable characterization methods to detect any problems as early as possible. Tailored or  correctly conducted quantitative analysis of adhesion is required for building reliable devices. In  many conventional test methods significant loading to the substrate is applied which can result in  problems especially with brittle substrates where the substrate can break before the film is  delaminated. The characterization of interfacial mechanical properties of increasingly thinner films  is challenging with many practical shortcomings and thus method development is needed.  In this thesis, three measurement methods where the loading to the substrate is minimized are  presented and demonstrated for the interfacial and mechanical testing of especially atomic layer  deposited (ALD) thin films. (i) Microelectromechanical system (MEMS) test chip assisted shaftloaded  blister testing through a hole in the substrate to the backside of the thin film, (ii)  microrobotic manipulation of embedded microspheres using lateral loading mostly to the thin film  and to the interface and (iii) a combination of nanoscratch and scanning nanowear for minimized  interaction volume of loading to the substrate. The relationship between adhesion and cohesion  as competing processes during film/ substrate failure is shown. When the film-interface-substrate  system is under loading the energy will dissipate through the path of least resistance. This will  happen either (i) through plastic deformation of the coating/ substrate, (ii) film fracture (decohesion) or (iii) delamination (de-adhesion) of the film. Usually, however the energy is  dissipated as a combination of these three different mechanisms, unless some of the mechanisms  is dominant in the energy release.  The presented characterization methods are mostly generic, and can be applied for the evaluation  of mechanical and interfacial properties, such as adhesion, between practically any materials of  choice with some limitations. Compared to some of the existing methods, the quantitative nature  of these characterization methods enables a more in-depth possibility for the analysis, understanding, tuning and improvement of the properties of the thin films and processes aiding  in maintaining and improving product and process quality. The main outcome of this thesis is that  the authors have demonstrated the potential and versatility of especially the MEMS test structures  and microrobotic testing systems, either on their own or as a combination as a solution to  developing new tailored interfacial and mechanical characterization methods for current and future  needs of research and the industry. 
University
Aalto University School of Chemical Engineering
(Espoo, Finland)
External Link
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2019
Atomic layer deposition of ruthenium and silver
Author
matthias minjauw
Year
2019
Language of the thesis
english
Abstract

This PhD thesis presents a study on the atomic layer deposition (ALD) of silver and ruthenium. The research was started in August 2013, and results  up to September 2018 are included. The lion’s share of the experimental  work was done within the Department of Solid State Sciences at Ghent  University.  The thesis is paper-based and contains four original research articles, published in peer-reviewed journals. The structure of this document is as  follows: First an introductory chapter is given, which provides the research  context and motivation to the reader; this is followed by the four articles  which were reformatted and included as stand-alone chapters; while in the  final chapter conclusions are made. A description of the used experimental  techniques is given in the appendix.  I hope that I have managed to present my contributions to the field of ALD  in a clear and interesting way for both the expert and the layman.

This PhD thesis presents a study on the atomic layer deposition (ALD) of silver and ruthenium. The research was started in August 2013, and results  up to September 2018 are included. The lion’s share of the experimental  work was done within the Department of Solid State Sciences at Ghent  University.  The thesis is paper-based and contains four original research articles, published in peer-reviewed journals. The structure of this document is as  follows: First an introductory chapter is given, which provides the research  context and motivation to the reader; this is followed by the four articles  which were reformatted and included as stand-alone chapters; while in the  final chapter conclusions are made. A description of the used experimental  techniques is given in the appendix.  I hope that I have managed to present my contributions to the field of ALD  in a clear and interesting way for both the expert and the layman.
University
Ghent University
(Ghent, Belgium)
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2019
Atomic Layer Deposition of Late First-Row Transition Metals: Precursors and Processes
Author
Katja Väyrynen
Year
2019
Abstract

Late first-row transition metals, namely copper, nickel, and cobalt, are pivotal materials in many modern and future applications. Because of its low resistivity, Cu has for long been the metal of choice for interconnects in microelectronic devices. Co is needed in the smallest features of the 10 nm technology node interconnects, as it is more robust than Cu toward electromigration, a phenomenon causing damage to the interconnects. Being ferromagnetic, Co and Ni are in the focal point of developing faster and more durable magnetic memories capable of handling the exponentially increasing amounts of data being generated annually. The development of faster yet smaller electronic devices requires a constant increase in computational power. To improve the performance without increasing device size, the components on integrated circuits should be shrunk and packed more closely. The shrinking is achieved by using thin films with nanoscale thicknesses preferably arranged in threedimensional forms. For downscaling to continue, accurate thin film deposition methods are needed. Atomic layer deposition (ALD) provides atomic level accuracy and is thus the number one thin film deposition technique for modern and future devices. ALD is based on a cyclically repeated alternate supply of gaseous precursors that react on a substrate and form a uniform layer of material, atom by atom, even on complex three-dimensional structures. ALD is based solely on chemistry; to benefit from the many advantages the method has to offer, suitable precursors must first be found for each of the desired materials. ALD has been employed to deposit a myriad of materials ranging from pure elements to, for example, oxides, nitrides, and chalcogenides, but the deposition of metals has been hindered by a lack of reactive precursors and reducing agents. Thermal ALD processes exist mostly for noble metals, but mere thermal activation has often proven insufficient for the reduction of the late first-row transition metals. The aim of this thesis was to find and develop new precursors and processes for the ALD of high-quality Cu, Ni, and Co thin films, thus promoting the development of better microelectronics. Within the scope of this thesis, several new metal precursors for the ALD of the late firstrow transition metals were developed and tested. Out of all of them, the diamine adducts of Co(II) and Ni(II) chlorides showed the best performance in the ALD experiments. In addition to the new metal precursors, the focus of this thesis was also on finding more efficient alternatives for the conventional reducing agents, H2 and NH3. Tert-butylhydrazine showed high reactivity to produce Cu and Ni3N by ALD, providing significant improvement on film purity and resistivity over the existing processes. Tributyltin hydride, another powerful reducing agent, was studied for the ALD of Co and Ni. Instead of producing metallic Co or Ni, intermetallic Co3Sn2 and Ni3Sn2 were deposited unveiling a new field of ALD: the ALD of intermetallics. The same approach was also applied to the ALD of Ni2Ge thin films. Postdeposition reduction of the corresponding metal oxides and nitrides was also explored as an alternative route for the preparation of metal thin films. 

Late first-row transition metals, namely copper, nickel, and cobalt, are pivotal materials in many modern and future applications. Because of its low resistivity, Cu has for long been the metal of choice for interconnects in microelectronic devices. Co is needed in the smallest features of the 10 nm technology node interconnects, as it is more robust than Cu toward electromigration, a phenomenon causing damage to the interconnects. Being ferromagnetic, Co and Ni are in the focal point of developing faster and more durable magnetic memories capable of handling the exponentially increasing amounts of data being generated annually. The development of faster yet smaller electronic devices requires a constant increase in computational power. To improve the performance without increasing device size, the components on integrated circuits should be shrunk and packed more closely. The shrinking is achieved by using thin films with nanoscale thicknesses preferably arranged in threedimensional forms. For downscaling to continue, accurate thin film deposition methods are needed. Atomic layer deposition (ALD) provides atomic level accuracy and is thus the number one thin film deposition technique for modern and future devices. ALD is based on a cyclically repeated alternate supply of gaseous precursors that react on a substrate and form a uniform layer of material, atom by atom, even on complex three-dimensional structures. ALD is based solely on chemistry; to benefit from the many advantages the method has to offer, suitable precursors must first be found for each of the desired materials. ALD has been employed to deposit a myriad of materials ranging from pure elements to, for example, oxides, nitrides, and chalcogenides, but the deposition of metals has been hindered by a lack of reactive precursors and reducing agents. Thermal ALD processes exist mostly for noble metals, but mere thermal activation has often proven insufficient for the reduction of the late first-row transition metals. The aim of this thesis was to find and develop new precursors and processes for the ALD of high-quality Cu, Ni, and Co thin films, thus promoting the development of better microelectronics. Within the scope of this thesis, several new metal precursors for the ALD of the late firstrow transition metals were developed and tested. Out of all of them, the diamine adducts of Co(II) and Ni(II) chlorides showed the best performance in the ALD experiments. In addition to the new metal precursors, the focus of this thesis was also on finding more efficient alternatives for the conventional reducing agents, H2 and NH3. Tert-butylhydrazine showed high reactivity to produce Cu and Ni3N by ALD, providing significant improvement on film purity and resistivity over the existing processes. Tributyltin hydride, another powerful reducing agent, was studied for the ALD of Co and Ni. Instead of producing metallic Co or Ni, intermetallic Co3Sn2 and Ni3Sn2 were deposited unveiling a new field of ALD: the ALD of intermetallics. The same approach was also applied to the ALD of Ni2Ge thin films. Postdeposition reduction of the corresponding metal oxides and nitrides was also explored as an alternative route for the preparation of metal thin films. 
Source of Information
website (via riikka)
University
University of Helsinki
(Helsinki, Finland)
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2019
Atomic layer deposition of catalytic materials for environmental protection
Author
Tatiana Ivanova
Year
2019
Abstract

The reduction of toxic pollutants emitted by human activities to ambient air is an important issue nowadays. The technological approach to this problem is the development of different oxidation techniques together with catalytic materials, which can convert toxic emission products to safe compounds. Current methods for the preparation of heterogeneous catalysts which fully control the structure, size and composition are limited. The atomic layer deposition (ALD) technique can create catalytic thin films with precise thickness and structure control even on complex substrates. The present work describes the development of TiO2, CeO2 and Ag-doped CeO2 catalytic thin films deposited by ALD in order to find their capacity for the decomposition of toluene and soot. TiO2 catalytic films with different thicknesses were grown to investigate their nucleation delay and changes in their polycrystalline structure and the impact of these on their photocatalytic properties. It was shown that porous glass filters coated by TiO2 in combination with a dielectric barrier discharge (DBD) reactor could decompose toluene at a concentration of 2450 ppm with the specific input energy (SIE) of 336 J/l. In CeO2 studies it was found that a deposition temperature of 300 °C changes the structural properties of the catalytic thin films. The combination of small crystallites, larger clusters and the existence of Ce3+ in CeO2 catalytic films showed 100% soot decomposition at 450°C under loose contact mode. The doping of CeO2 with Ag in the ratio of CeO2:Ag = 10:1 by ALD reduced the soot decomposition temperature to 390°C. It was proposed that Ag+ sites could promote oxygen species and reduce the Ce ions in stoichiometric CeO2 from Ce4+ to Ce3+. Most catalytic thin films prepared by ALD showed good durability after repetitive tests of soot decomposition. 

Keywords: atomic layer deposition, titanium dioxide, cerium dioxide, silver, photocatalytic activity, soot oxidation, toluene.

The reduction of toxic pollutants emitted by human activities to ambient air is an important issue nowadays. The technological approach to this problem is the development of different oxidation techniques together with catalytic materials, which can convert toxic emission products to safe compounds. Current methods for the preparation of heterogeneous catalysts which fully control the structure, size and composition are limited. The atomic layer deposition (ALD) technique can create catalytic thin films with precise thickness and structure control even on complex substrates. The present work describes the development of TiO2, CeO2 and Ag-doped CeO2 catalytic thin films deposited by ALD in order to find their capacity for the decomposition of toluene and soot. TiO2 catalytic films with different thicknesses were grown to investigate their nucleation delay and changes in their polycrystalline structure and the impact of these on their photocatalytic properties. It was shown that porous glass filters coated by TiO2 in combination with a dielectric barrier discharge (DBD) reactor could decompose toluene at a concentration of 2450 ppm with the specific input energy (SIE) of 336 J/l. In CeO2 studies it was found that a deposition temperature of 300 °C changes the structural properties of the catalytic thin films. The combination of small crystallites, larger clusters and the existence of Ce3+ in CeO2 catalytic films showed 100% soot decomposition at 450°C under loose contact mode. The doping of CeO2 with Ag in the ratio of CeO2:Ag = 10:1 by ALD reduced the soot decomposition temperature to 390°C. It was proposed that Ag+ sites could promote oxygen species and reduce the Ce ions in stoichiometric CeO2 from Ce4+ to Ce3+. Most catalytic thin films prepared by ALD showed good durability after repetitive tests of soot decomposition. Keywords: atomic layer deposition, titanium dioxide, cerium dioxide, silver, photocatalytic activity, soot oxidation, toluene.
Source of Information
David Cameron
University
Lappeenranta University of Technology
(Lappeenranta, Finland)
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2019
Atomic Layer Deposited 3D Nanostructured Materials for Efficient Energy Storage
Author
Arpan Dhara
Year
2019
Abstract

The rapid advancement in the field of nanotechnology in the past several years has promised great potential for controlling materials at the nanoscale and stimulated vast opportunities to architect materials with desirable properties. This evolution has also contributed significantly to the development in the area of energy storage, which is a crucial technology in the present time. Electrode architecture always plays an important role in the domain of energy storage. In specific, engineering at nanoscale offers exclusive properties resulting in an improvement in the performance of electrodes and electrolytes in different energy storage technologies. Accordingly, significant efforts have been put forward in recent years to accomplish the present demands of energy storage using these advanced nanostructured materials. Various nanostructured materials with larger surface area and low bulk volume are presently being studied to improve the energy and power densities together for next-generation storage devices. The main objective of this thesis is to develop three-dimensional (3D) nanostructured electrodes with superior energy density and power density for electrochemical energy storage. Controlling the thickness of the active material in a few nanometers ensures the short diffusion length and full utilization of the active material. To get the nano level control, the ALD technique is used for active material deposition. Highly conducting templates like CNTs, graphenes and metal nanostructures are utilized to anchor the active material ensuring the effective electron transportation. Three-dimensional electrodes represent a unique way to improve the storage density and rate capability without the complex process of material development. This thesis presents the synthesis of 3D hybrid nanostructured electrodes with superior energy density and power density for electrochemical energy storage using template assisted methods. Carbon nanotubes (CNT) and Cu-NWs are used as template layer because of their high surface area and electrical conductivity. The active material is being deposited on these template layers by atomic layer deposition (ALD) process because of its extreme conformal and sub-nanometer thickness control.
Due to its high theoretical capacity, energy density and excellent reversibility with Li/Li+, molybdenum oxides are one of the vastly studied electrode material in lithium-ion batteries. However, like most of the oxides, it also suffers from poor cyclic stability because of their low electrical conductivity. In 3D core-shell structure prepared by ALD coating provide superiority in nanoscale decoration because of its extreme conformality and precise thickness control on high aspect ratio surfaces. The first part of this thesis focuses on the fabrication and electrochemical activities of 3D CNT/MoOx electrodes. These electrodes exhibit much higher areal and overall cell capacity than its planer 2D counterpart. An optimal thickness of MoOx on CNT is also found out in order to attain the most stable cyclic performance of this nanostructure. A stable reversible areal capacity of 645 μAh cm-2 with a specific capacity of 915 mAh g-1 is achieved from optimized MoOx/CNT assembly.


The second part of the thesis focuses on increasing the conductivity of the MoOx layer by N-incorporation for better electrochemical performance. It is well studied that the transition metal oxynitrides have better conductivity than their pure oxide phase. This particular work highlighted three important factors, (i) synthesis, (ii) electron transportation and (iii) electrochemical performances of N-incorporated MoOx films. It is found that N-atoms are homogeneously distributed throughout the films at the deposition temperature, no post-annealing is required for diffusion. The conductivity of those films increases with increasing nitrogen concentration. The electrochemical study reveals the superior performance of N-incorporated films against Li/Li+ than that of the pristine materials. The highest discharge capacity of 1287 mAh g-1 was achieved in the first cycle at a current rate of 0.1 A g-1 and a stable capacity of 974 mAh g-1 and 610 mAh g-1 achieved when discharged at 0.1 and 2 A g-1 from the core-shell 3D CNT/MoOx:N electrodes.
In the final part, Cu-nw scaffold is used as template layer by replacing CNTs. The high abundance, low-cost and high electronic conductivity make the choice simpler to use Cu as an affordable scaffold layer. Cu/ MoOx electrode showed a stable capacity of 993 mAh g-1 at the rate of 0.1 A g-1 and retained 45% of its initial capacity with 40 times higher current rate. This kind of state-of-the-art fabrication method helps to deposit more amount of active material with less Li+ diffusion length and ease the electron/ion transportation during the charge-discharge process
 

The rapid advancement in the field of nanotechnology in the past several years has promised great potential for controlling materials at the nanoscale and stimulated vast opportunities to architect materials with desirable properties. This evolution has also contributed significantly to the development in the area of energy storage, which is a crucial technology in the present time. Electrode architecture always plays an important role in the domain of energy storage. In specific, engineering at nanoscale offers exclusive properties resulting in an improvement in the performance of electrodes and electrolytes in different energy storage technologies. Accordingly, significant efforts have been put forward in recent years to accomplish the present demands of energy storage using these advanced nanostructured materials. Various nanostructured materials with larger surface area and low bulk volume are presently being studied to improve the energy and power densities together for next-generation storage devices. The main objective of this thesis is to develop three-dimensional (3D) nanostructured electrodes with superior energy density and power density for electrochemical energy storage. Controlling the thickness of the active material in a few nanometers ensures the short diffusion length and full utilization of the active material. To get the nano level control, the ALD technique is used for active material deposition. Highly conducting templates like CNTs, graphenes and metal nanostructures are utilized to anchor the active material ensuring the effective electron transportation. Three-dimensional electrodes represent a unique way to improve the storage density and rate capability without the complex process of material development. This thesis presents the synthesis of 3D hybrid nanostructured electrodes with superior energy density and power density for electrochemical energy storage using template assisted methods. Carbon nanotubes (CNT) and Cu-NWs are used as template layer because of their high surface area and electrical conductivity. The active material is being deposited on these template layers by atomic layer deposition (ALD) process because of its extreme conformal and sub-nanometer thickness control.Due to its high theoretical capacity, energy density and excellent reversibility with Li/Li+, molybdenum oxides are one of the vastly studied electrode material in lithium-ion batteries. However, like most of the oxides, it also suffers from poor cyclic stability because of their low electrical conductivity. In 3D core-shell structure prepared by ALD coating provide superiority in nanoscale decoration because of its extreme conformality and precise thickness control on high aspect ratio surfaces. The first part of this thesis focuses on the fabrication and electrochemical activities of 3D CNT/MoOx electrodes. These electrodes exhibit much higher areal and overall cell capacity than its planer 2D counterpart. An optimal thickness of MoOx on CNT is also found out in order to attain the most stable cyclic performance of this nanostructure. A stable reversible areal capacity of 645 μAh cm-2 with a specific capacity of 915 mAh g-1 is achieved from optimized MoOx/CNT assembly.The second part of the thesis focuses on increasing the conductivity of the MoOx layer by N-incorporation for better electrochemical performance. It is well studied that the transition metal oxynitrides have better conductivity than their pure oxide phase. This particular work highlighted three important factors, (i) synthesis, (ii) electron transportation and (iii) electrochemical performances of N-incorporated MoOx films. It is found that N-atoms are homogeneously distributed throughout the films at the deposition temperature, no post-annealing is required for diffusion. The conductivity of those films increases with increasing nitrogen concentration. The electrochemical study reveals the superior performance of N-incorporated films against Li/Li+ than that of the pristine materials. The highest discharge capacity of 1287 mAh g-1 was achieved in the first cycle at a current rate of 0.1 A g-1 and a stable capacity of 974 mAh g-1 and 610 mAh g-1 achieved when discharged at 0.1 and 2 A g-1 from the core-shell 3D CNT/MoOx:N electrodes.In the final part, Cu-nw scaffold is used as template layer by replacing CNTs. The high abundance, low-cost and high electronic conductivity make the choice simpler to use Cu as an affordable scaffold layer. Cu/ MoOx electrode showed a stable capacity of 993 mAh g-1 at the rate of 0.1 A g-1 and retained 45% of its initial capacity with 40 times higher current rate. This kind of state-of-the-art fabrication method helps to deposit more amount of active material with less Li+ diffusion length and ease the electron/ion transportation during the charge-discharge process 
Source of Information
Arpan Dhara
University
IIT Bombay
(Mumbai, India )
External Link
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2019
ATOMIC FORСE MICROSCOPY OF COMPOSITE POLYMERIC AND SILICATE MATERIALS SYNTHESIZED BY THE METHOD OF MOLECULAR LAYERING
Author
A.S. Kochetkova
Year
2019
Language of the thesis
Russian
Thesis name in original language
АТОМНО-СИЛОВАЯ МИКРОСКОПИЯ КОМПОЗИТНЫХ ПОЛИМЕРНЫХ И СИЛИКАТНЫХ МАТЕРИАЛОВ, СИНТЕЗИРОВАННЫХ МЕТОДОМ МОЛЕКУЛЯРНОГО НАСЛАИВАНИЯ
Source of Information
Anatoly Malygin
University
Petersburg State Institute of Technology (Technical University)
(Saint Petersburg, Russian)
Other notes
Supervisor: Malygin A.A. Scientific consultant: Sosnov E.A.
External Link
2019
A Study on the Dielectric TiO2 Films for Fabrication of 3-D Structural Capacitor and Promising Electrodes for Next-generation DRAM Capacitor
Author
Cheol Jin Cho
Year
2019
Source of Information
Cheol Seong Hwang
University
Seoul National University
(Seoul, Korea)
Other notes
http://dcollection.snu.ac.kr/common/orgView/000000154523
External Link
2019
Molybdenum Sulfide Prepared by Atomic Layer Deposition: Synthesis and Characterization
Author
Steven Letourneau
Year
2020
Source of Information
Steven Letourneau
University
Boise State University
(Boise, USA)
Other notes
https://scholarworks.boisestate.edu/td/1397/
External Link
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2020
Atomic layer deposition towards novel device applications
Author
Giovanni Marin
Year
2020
Abstract

Atomic layer deposition (ALD) is a gas-phase thin film deposition technique that has gained increasing popularity in the last 20 years because of its unique properties. It is based on self-limiting chemical reactions that ensure the layer-by-layer growth of the film. This unique growth mode is fundamental to the fine control of both film thickness and structure. The film grows conformally on the substrate, following the morphology of the surface. ALD can grow films at low temperature, making possible the use of temperature-sensitive substrates. A slightly modified technique called molecular layer deposition (MLD) utilises organic precur-sors to deposit fully organic films. Hybrid inorganic-organic materials can be deposited with a combination of ALD and MLD. The aim of this research was to utilise the unique characteris-tics of ALD/MLD in two different applications, thermoelectrics and barrier coatings.

Thermoelectric devices were fabricated on flexible plastic, glass, and textile. Testing of the barrier properties of ALD-grown films were carried out on 3D printed plastic substrates. The conformality of the deposition is fundamental in both applications. The films needed to coat the single fibres within the textile substrate as well as the porous surface of the 3D printed plastic. The low deposition temperature made it possible to use cotton as well as various plas-tics as substrates. The fine control over the film thickness and structure, enabled the deposi-tion of inorganic-organic superlattice hybrid materials. Zinc oxide (ZnO) and hydroquinone (HQ) were chosen for the fabrication of the thermoelectric devices while aluminium oxide (AlOx) was the chosen barrier material. Hydroquinone was utilised as monomolecular layers within the ZnO matrix to lower thermal conductivity and enhance the thermoelectric perfor-mance.

The ALD-deposited AlOx coating was shown to successfully lower the vacuum degassing of the 3D printed plastics compared to commercial sealants. These superior performances open the way to inexpensive and personalised, 3D printed, laboratory tools coated with ALD which pro-vide degassing protection to the vacuum environment.

Thermoelectric devices were fabricated on several substrates (silicon, flexible plastic, flexible glass, and textile) using the n-type ZnO as thermoelectric. On textile, the device was made with both n-type (ZnO or ZnO-HQ) and p-type (poly(3,4-ethylenedioxythiophene) - PEDOT) components to improve performance. The ZnO-HQ superlattice outperformed the bare ZnO films, proving that the hybrid approach is worth pursuing to reduce thermal conductivity. The best device fabricated on textile, produced an open-circuit voltage around 150 mV at a ΔT of 20 °C with a power output in the order of pW. These numbers, although low, are paving the way for future application of the ALD/MLD in the fabrication of thermoelectric devices inte-grated into smart clothing.

Atomic layer deposition (ALD) is a gas-phase thin film deposition technique that has gained increasing popularity in the last 20 years because of its unique properties. It is based on self-limiting chemical reactions that ensure the layer-by-layer growth of the film. This unique growth mode is fundamental to the fine control of both film thickness and structure. The film grows conformally on the substrate, following the morphology of the surface. ALD can grow films at low temperature, making possible the use of temperature-sensitive substrates. A slightly modified technique called molecular layer deposition (MLD) utilises organic precur-sors to deposit fully organic films. Hybrid inorganic-organic materials can be deposited with a combination of ALD and MLD. The aim of this research was to utilise the unique characteris-tics of ALD/MLD in two different applications, thermoelectrics and barrier coatings.Thermoelectric devices were fabricated on flexible plastic, glass, and textile. Testing of the barrier properties of ALD-grown films were carried out on 3D printed plastic substrates. The conformality of the deposition is fundamental in both applications. The films needed to coat the single fibres within the textile substrate as well as the porous surface of the 3D printed plastic. The low deposition temperature made it possible to use cotton as well as various plas-tics as substrates. The fine control over the film thickness and structure, enabled the deposi-tion of inorganic-organic superlattice hybrid materials. Zinc oxide (ZnO) and hydroquinone (HQ) were chosen for the fabrication of the thermoelectric devices while aluminium oxide (AlOx) was the chosen barrier material. Hydroquinone was utilised as monomolecular layers within the ZnO matrix to lower thermal conductivity and enhance the thermoelectric perfor-mance.The ALD-deposited AlOx coating was shown to successfully lower the vacuum degassing of the 3D printed plastics compared to commercial sealants. These superior performances open the way to inexpensive and personalised, 3D printed, laboratory tools coated with ALD which pro-vide degassing protection to the vacuum environment.Thermoelectric devices were fabricated on several substrates (silicon, flexible plastic, flexible glass, and textile) using the n-type ZnO as thermoelectric. On textile, the device was made with both n-type (ZnO or ZnO-HQ) and p-type (poly(3,4-ethylenedioxythiophene) - PEDOT) components to improve performance. The ZnO-HQ superlattice outperformed the bare ZnO films, proving that the hybrid approach is worth pursuing to reduce thermal conductivity. The best device fabricated on textile, produced an open-circuit voltage around 150 mV at a ΔT of 20 °C with a power output in the order of pW. These numbers, although low, are paving the way for future application of the ALD/MLD in the fabrication of thermoelectric devices inte-grated into smart clothing.
Source of Information
Webpage
University
Aalto University
(Espoo, Finland)
External Link
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2020
Multilayered ZnO-based thin films to control heat and electrical transport properties
Author
Fabian Krahl
Year
2021
Abstract

Interfaces between materials can have properties that differ greatly from the bulk state. In classical materials only a tiny fraction of atoms are at the interface while the vast majority is in the bulk of the material. The capability to engineer materials with an artificially high amount of interfaces opens up a pathway to amplify the interface effects and tailor the material properties by controlling the amount of interfaces. This approach to engineer materials step by step or layer by layer also allows for a controlled combination of very different materials into a hybrid material that would not form naturally and which can show fundamentally different and new properties.

In this thesis atomic layer deposition (ALD), molecular layer deposition (MLD) and pulsed laser deposition (PLD) are utilized to engineer ZnO-based thin films with high interface densities. The films are analysed with x-ray reflectivity (XRR), x-ray diffraction (XRD) and transmission electron microscopy (TEM) in regards to their internal structure. Time domain thermoreflectance (TDTR) is utilized to measure the thermal conductivity, the electrical properties are measured with a hall measurement setup. The latter is the focus in layered thin films of polycrystalline ZnO and amorphous InGaZnO4 in which a considerable increase in the charge carrier concentration following the interface density could be demonstrated.

The interfaces between a ZnO matrix, ZnO-benzene and AlOx layers are studied in detail in a hybrid ZnO/ZnO-benzene/AlOx system in which this work demonstrates, that these layers in ZnO can be as thin as a single atom/molecule, yet still form distinctive layers. However, these very thin layers of ZnO-benzene and AlOx are found to have little impact on the crystal growth of ZnO, but can act as effective barriers for ZnO crystal growth when 10 or more consecutive ALD/MLD cycles are utilized for each AlOx/benzene layer respectively. Finally the thermal conductivity in ZnO/benzene thin films is characterised, the database for the thermal conductivity in that system is significantly extended and thermal conductivities for irregularly layered structures are reported for the first time in ZnO/ZnO-benzene hybrid thin films. Analysis with multivariate data analysis of the database confirms that the interface density has the most pronounced effect on the thermal conductivity.

Interfaces between materials can have properties that differ greatly from the bulk state. In classical materials only a tiny fraction of atoms are at the interface while the vast majority is in the bulk of the material. The capability to engineer materials with an artificially high amount of interfaces opens up a pathway to amplify the interface effects and tailor the material properties by controlling the amount of interfaces. This approach to engineer materials step by step or layer by layer also allows for a controlled combination of very different materials into a hybrid material that would not form naturally and which can show fundamentally different and new properties.In this thesis atomic layer deposition (ALD), molecular layer deposition (MLD) and pulsed laser deposition (PLD) are utilized to engineer ZnO-based thin films with high interface densities. The films are analysed with x-ray reflectivity (XRR), x-ray diffraction (XRD) and transmission electron microscopy (TEM) in regards to their internal structure. Time domain thermoreflectance (TDTR) is utilized to measure the thermal conductivity, the electrical properties are measured with a hall measurement setup. The latter is the focus in layered thin films of polycrystalline ZnO and amorphous InGaZnO4 in which a considerable increase in the charge carrier concentration following the interface density could be demonstrated.The interfaces between a ZnO matrix, ZnO-benzene and AlOx layers are studied in detail in a hybrid ZnO/ZnO-benzene/AlOx system in which this work demonstrates, that these layers in ZnO can be as thin as a single atom/molecule, yet still form distinctive layers. However, these very thin layers of ZnO-benzene and AlOx are found to have little impact on the crystal growth of ZnO, but can act as effective barriers for ZnO crystal growth when 10 or more consecutive ALD/MLD cycles are utilized for each AlOx/benzene layer respectively. Finally the thermal conductivity in ZnO/benzene thin films is characterised, the database for the thermal conductivity in that system is significantly extended and thermal conductivities for irregularly layered structures are reported for the first time in ZnO/ZnO-benzene hybrid thin films. Analysis with multivariate data analysis of the database confirms that the interface density has the most pronounced effect on the thermal conductivity.
Source of Information
Webpage
University
Aalto University
(Espoo, Finland)
Other notes
Has a small section of PLD, but the main work is done with ALD/MLD
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2021