Tomas Vystavel - Academia.edu (original) (raw)

Papers by Tomas Vystavel

ISTFA 2021: Conference Proceedings from the 47th International Symposium for Testing and Failure Analysis

The physical limits of CMOS scaling, as predicted by Moore's Law, should have already been re... more The physical limits of CMOS scaling, as predicted by Moore's Law, should have already been reached several years ago. However, the scaling of transistors is still ongoing due to continuous improvements in material quality enabling the fabrication of complex device structures with nm-size dimensions. More than ever, the structural properties and the eventual presence of crystalline defects in the various semiconductor materials (SiGe, III/V) play a critical role. Electron channeling contrast imaging (ECCI) is a powerful defect analysis technique developed in recent years. The technique allows for fast and non-destructive characterizations with the potential for extremely low detection limits. The analysis of lowly defective materials requires measurements over large areas to obtain statistically relevant data. Automated ECCI mapping routines enable the quantification of crystalline defect densities as low as ~1e5 cm-2, e.g., Si0.75Ge0.25 strain relaxed buffers (SRB) epitaxially g...

ECS Meeting Abstracts

For future scaling of CMOS technology beyond the 10 nm node it is necessary to integrate high mob... more For future scaling of CMOS technology beyond the 10 nm node it is necessary to integrate high mobility semiconductors including (Si)Ge and III/V compounds on silicon substrates. The lattice mismatch between these materials and the Silicon platform can lead to the formation of defects which will cause a degradation of the final device performance. Therefore, a metrology technique is needed to monitor the presence and density of defects in blanket layer as well as in patterned structures such as fins. There are several techniques for defect metrology including optical methods, X-ray diffraction or transmission electron microscopy, however, expected defect densities (<105 cm-2) make them ineffective for this task. Electron channeling contrast imaging (ECCI) is scanning electron microscopy (SEM) technique used for the visualization and characterization of crystalline defects including dislocations or stacking faults. Distortions of the crystal lattice of a material due to the presenc...

MRS Proceedings, 2002

The thermal stability of nanocrystalline ultra-soft magnetic (Fe98Zr2)1-xNxfilms with x=0.10-0.25... more The thermal stability of nanocrystalline ultra-soft magnetic (Fe98Zr2)1-xNxfilms with x=0.10-0.25 was studied using high-resolution transmission electron microscopy (HRTEM), positron beam analysis (PBA) and thermal desorption spectrometry (TDS). The results demonstrate that grain growth during the heat treatment is accompanied by an increase of the free volume, by nitrogen reallocation and desorption. All this can drastically deteriorate the ultra-soft magnetic properties. The desorption starts already at slightly elevated temperatures, below 100°C. However, most of the nitrogen leaves the sample at a temperature above 500°C.

European Microscopy Congress 2016: Proceedings, 2016

ISTFA 2018: Conference Proceedings from the 44th International Symposium for Testing and Failure Analysis, 2018

As semiconductor devices continue to shrink, novel materials (e.g. (Si)Ge, III/V) are being teste... more As semiconductor devices continue to shrink, novel materials (e.g. (Si)Ge, III/V) are being tested and incorporated to boost device performance. Such materials are difficult to grow on Si wafers without forming crystalline defects due to lattice mismatch. Such defects can decrease or compromise device performance. For this reason, non-destructive, high throughput and reliable analytical techniques are required. In this paper Electron Channeling Contrast Imaging (ECCI), large area mapping and defect detection using deep learning are combined in an analytical workflow for the characterization of the defectivity of “beyond Silicon” materials. Such a workflow addresses the requirements for large areas 10-4 cm2 with defect density down to 104 cm-2.

Ultramicroscopy

Nowadays electron channeling contrast imaging (ECCI) is widely used to characterize crystalline d... more Nowadays electron channeling contrast imaging (ECCI) is widely used to characterize crystalline defects on blanket semiconductors. Its further application in the semiconductor industry is however challenged by the emerging rise of nanoscale 3D heterostructures. In this study, an angular multi-segment detector is utilized in backscatter geometry to investigate the application of ECCI to the defect analysis of 3D semiconductor structures such as III/V nano-ridges. We show that a low beam energy of 5 keV is more favorable and that the dimension of 3D structures characterized by ECCI can be scaled down to ~ 28 nm. Furthermore, the impact of device edges on the collected ECCI image is investigated and correlated with tool parameters and cross-section profiles of the 3D structures. It is found that backscattered electrons (BSE) emitted from the device edge sidewalls and generating the bright edges (edge effects), share a similar angular distribution to those emitted from the surface. We show that the collection of low angle BSEs can suppressed the edge effects, however, at the cost of losing the defect contrast. A positive stage bias suppresses edge effects by removing the inelastically backscattered electrons from the sidewalls, but low loss BSEs from the sidewalls still contribute to the ECCI micrographs. On the other hand, if segments of an angular backscatter (ABS) detector are properly aligned with the nano-ridges, BSEs emitted from the sidewall and the surface can be separated, thus leading to the completely absence of one bright edge on the surface without compromise of the defect contrast. The merging of two such ECCI images reveals the nano-ridge surface without edge effects.

Ultramicroscopy

In this study, an annular multi-segment backscattered electron (BSE) detector is used in back sca... more In this study, an annular multi-segment backscattered electron (BSE) detector is used in back scatter geometry to investigate the influence of the angular distribution of BSE on the crystalline defect contrast in electron channeling contrast imaging (ECCI). The study is carried out on GaAs and Ge layers epitaxially grown on top of silicon (Si) substrates, respectively. The influence of the BSE detection angle and landing energy are studied to identify the optimal ECCI conditions. It is demonstrated that the angular selection of BSEs exhibits strong effects on defect contrast formation with variation of beam energies. In our study, maximum defect contrast can be obtained at BSE detection angles 53-65° for the investigated energies 5, 10 and 20 keV. In addition, it is found that higher beam energy is favorable to reveal defects with stronger contrast whereas lower energy ( ≤ 5 keV) is favorable for revealing crystalline defects as well as with topographic features on the surface. Our study provides optimal ECCI conditions, and therefore enables a precise and fast detection of threading dislocations in lowly defective materials and nanoscale 3D semiconductor structures where signal to noise ratio is especially important. A comparison of ECCI with BSE and secondary electron imaging further demonstrates the strength of ECCI in term of simultaneous detection of defects and morphology features such as terraces with atomic step heights.

ECS Transactions

Semiconductor heterostructures represent the key building blocks for most nanoelectronics and pho... more Semiconductor heterostructures represent the key building blocks for most nanoelectronics and photonics devices. However, the performance and reliability of these devices is often limited by the presence of extended defects arising from plastic relaxation of misfit strain. Hence, metrology for assessing the nature, density and distribution of such defects is of crucial importance in order to support the development and fabrication of novel semiconductor devices. Electron Channeling Contrast Imaging (ECCI) has emerged as the method of choice for analyzing the crystalline quality of semiconductor heterostructures with excellent precision even at low defect densities. The present paper discusses the most relevant theoretical and experimental aspects one needs to consider to obtain high-quality ECCI micrographs. Moreover, the capabilities of the methodology are illustrated on the example of various different defect types in the most relevant semiconductor material systems and structures.

Microscopy and Microanalysis

Nanoscale, Jan 19, 2018

Semiconductor heterostructures are at the heart of most nanoelectronic and photonic devices such ... more Semiconductor heterostructures are at the heart of most nanoelectronic and photonic devices such as advanced transistors, lasers, light emitting diodes, optical modulators and photo-detectors. However, the performance and reliability of the respective devices are often limited by the presence of crystalline defects which arise from plastic relaxation of misfit strain present in these heterogeneous systems. To date, characterizing the nature and distribution of such defects in 3D nanoscale devices precisely and non-destructively remains a critical metrology challenge. In this paper we demonstrate that electron channeling contrast imaging (ECCI) is capable of analyzing individual dislocations and stacking faults in confined 3D nanostructures, thereby fulfilling the aforementioned requirements. For this purpose we imaged the intensity of electrons backscattered from the sample under test under controlled diffraction conditions using a scanning electron microscope (SEM). In contrast to ...

Microscopy and Microanalysis

Microscopy and Microanalysis

We are presenting a new extension to our Cell and Tissue/Neurobiology large volume imaging workfl... more We are presenting a new extension to our Cell and Tissue/Neurobiology large volume imaging workflow, with the goal of increasing acquisition speed by more than five times. Instead of scanning dense square-grid frames, in the conventional way, our approach is here to explore the use of sparse scanning and inpainting techniques inspired by Compressive Sensing (CS) [1]. Sparse samples are obtained by pseudo-random scan patterns, and reconstruction algorithms are used to recover the dense volume data. The goal is to recover 3D datasets with minimum loss of information. Techniques inspired by CS gained wide attention over the last decade and are now being used in various applications where sensor bandwidth is a limiting factor. They have been recently explored for SEM and STEM applications [2][3]. In the context of nano-scale cell biology volume acquisition, we expect these techniques to ultimately increase the imaging throughput by nearly an order of magnitude. We will discuss additional advantages of this approach, such as the low-dose imaging of sensitive specimens, and the good compatibility with backscatter electron imaging. A key enabler of any sparse scan application to EM is the accurate control of scan locations. It has been shown in [2] and in our own experiments that precise positioning of the beam at the planned sampling locations is essential for a good CS reconstruction. We have developed advanced minimum-path scanning strategies to address this issue. The scanning technique is illustrated in Fig. 1, where the left two images show a conventional raster scan at 300ns dwell visiting a random set of points with the compressive sensing reconstruction obtained from such scan strategy. The right two images of Fig. 1 show an example minimum-path scan pattern and a much improved reconstruction result from images acquired with this second method. In future work we will compare pseudo-random sparse sampling, in combination with a reconstruction algorithm based on CS-inspired in-painting, to conventional grid sampling of the same effective dose, in combination with a de-noising algorithm, also based on CS. CS machine learning algorithms build patch-dictionaries, which are used as the building blocks for data representation [3]. During live acquisition runs, such dictionaries can be used to in-paint with high fidelity, the sparsely sampled datasets (Figure 2). We are implementing the new sparse scanning modules on SEM platforms, which also employ the Multi Energy Deconvolution SEM (MED-SEM) technology and Serial Block Face (SBF) imaging [4]. By incorporating CS, we will have an instrument allowing for both high-resolution isotropic imaging, and the fast acquisition of very large datasets (Figure 3).

Journal of Electron Spectroscopy and Related Phenomena

The nano-scale dispersion of ordered/disordered phases in semi-crystalline polymers can strongly ... more The nano-scale dispersion of ordered/disordered phases in semi-crystalline polymers can strongly influence their performance e.g. in terms of mechanical properties and/or electronic properties. However, to reveal the latter in scanning electron microscopy (SEM) often requires invasive sample preparation (etching of amorphous phase), because SEM usually exploits topographical contrast or yield differences between different materials. However, for pure carbon materials the secondary spectra were shown to differ substantially with increased order/disorder. The aims here is to gain an understanding of the shape of secondary electron spectrum (SES) of a widely used semi-crystalline polymer regioregular poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT, and its links to the underlying secondary electron emission mechanisms so SES can be exploited for the mapping the nanomorphology. The comparison of simulated and experimental SES shows an excellent agreement, revealing a peak (at about 0.8eV) followed by a broad shoulder (between 2eV and 4.5eV) with respective relative intensities reflecting order/disorder.

Nano letters, Jan 10, 2016

Hydride precursors are commonly used for semiconductor nanowire growth from the vapor phase and h... more Hydride precursors are commonly used for semiconductor nanowire growth from the vapor phase and hydrogen is quite often used as a carrier gas. Here, we used in situ scanning electron microscopy and spatially resolved Auger spectroscopy to reveal the essential role of atomic hydrogen in determining the growth direction of Ge nanowires with an Au catalyst. With hydrogen passivating nanowire sidewalls the formation of inclined facets is suppressed, which stabilizes the growth in the ⟨111⟩ direction. By contrast, without hydrogen gold diffuses out of the catalyst and decorates the nanowire sidewalls, which strongly affects the surface free energy of the system and results in the ⟨110⟩ oriented growth. The experiments with intentional nanowire kinking reveal the existence of an energetic barrier, which originates from the kinetic force needed to drive the droplet out of its optimum configuration on top of a nanowire. Our results stress the role of the catalyst material and surface chemis...

Http Www Theses Fr, 1999

La structure de joints de grains de flexion d'axe 110 dans le molybdene et les phenomenes de ... more La structure de joints de grains de flexion d'axe 110 dans le molybdene et les phenomenes de mouillage de ces joints par le nickel, ont ete etudies. Nous avons utilise des bicristaux de caracteristiques cristallographiques bien definies qui correspondent a des energies de joint differentes et donc a des proprietes differentes. Trois types de bicristaux d'angle differents ont ete observes : les macles coherente et incoherente et un joint de coincidence particuliere (sigma = 11). Les observations experimentales ont ete faites principalement en microscopie electronique conventionnelle, a haute resolution et par spectroscopie de pertes d'energie des electrons. Pour chaque type de bicristal, la structure du reseau de dislocations secondaires a ete determinee par microscopie conventionnelle et par diffraction electronique et interpretee dans le cadre de la theorie de bollmann. Certaines de ces dislocations ont ete observees en haute resolution et leur champ de deformation elastique calcule. La structure a l'echelle atomique de chacun des bicristaux purs a ete determinee par haute resolution. Les resultats sont en tres bon accord avec ceux calcules par simulation numerique, notamment la structure des unites structurales qui composent les differents joints. Les translations rigides paralleles et perpendiculaires au plan de joint ont ete mesurees. Les experiences de mouillage par le nickel ont ete faites a deux temperatures (1350 et 1380 degres c). Selon l'energie du joint, il se forme soit des precipites isoles de phase mo-ni, soit une couche de mouillage tres mince (1nm) et continue le long du joint. La comparaison entre les differents bicristaux montre que le joint de faible energie ne presente pas de mouillage sauf au cur des dislocations secondaires, alors que le joint de forte energie est beaucoup plus fortement mouille. De plus, a la temperature de 1380 degres c, ce joint migre vers une position asymetrique.

ISTFA 2021: Conference Proceedings from the 47th International Symposium for Testing and Failure Analysis

The physical limits of CMOS scaling, as predicted by Moore's Law, should have already been re... more The physical limits of CMOS scaling, as predicted by Moore's Law, should have already been reached several years ago. However, the scaling of transistors is still ongoing due to continuous improvements in material quality enabling the fabrication of complex device structures with nm-size dimensions. More than ever, the structural properties and the eventual presence of crystalline defects in the various semiconductor materials (SiGe, III/V) play a critical role. Electron channeling contrast imaging (ECCI) is a powerful defect analysis technique developed in recent years. The technique allows for fast and non-destructive characterizations with the potential for extremely low detection limits. The analysis of lowly defective materials requires measurements over large areas to obtain statistically relevant data. Automated ECCI mapping routines enable the quantification of crystalline defect densities as low as ~1e5 cm-2, e.g., Si0.75Ge0.25 strain relaxed buffers (SRB) epitaxially g...

ECS Meeting Abstracts

For future scaling of CMOS technology beyond the 10 nm node it is necessary to integrate high mob... more For future scaling of CMOS technology beyond the 10 nm node it is necessary to integrate high mobility semiconductors including (Si)Ge and III/V compounds on silicon substrates. The lattice mismatch between these materials and the Silicon platform can lead to the formation of defects which will cause a degradation of the final device performance. Therefore, a metrology technique is needed to monitor the presence and density of defects in blanket layer as well as in patterned structures such as fins. There are several techniques for defect metrology including optical methods, X-ray diffraction or transmission electron microscopy, however, expected defect densities (<105 cm-2) make them ineffective for this task. Electron channeling contrast imaging (ECCI) is scanning electron microscopy (SEM) technique used for the visualization and characterization of crystalline defects including dislocations or stacking faults. Distortions of the crystal lattice of a material due to the presenc...

MRS Proceedings, 2002

The thermal stability of nanocrystalline ultra-soft magnetic (Fe98Zr2)1-xNxfilms with x=0.10-0.25... more The thermal stability of nanocrystalline ultra-soft magnetic (Fe98Zr2)1-xNxfilms with x=0.10-0.25 was studied using high-resolution transmission electron microscopy (HRTEM), positron beam analysis (PBA) and thermal desorption spectrometry (TDS). The results demonstrate that grain growth during the heat treatment is accompanied by an increase of the free volume, by nitrogen reallocation and desorption. All this can drastically deteriorate the ultra-soft magnetic properties. The desorption starts already at slightly elevated temperatures, below 100°C. However, most of the nitrogen leaves the sample at a temperature above 500°C.

European Microscopy Congress 2016: Proceedings, 2016

ISTFA 2018: Conference Proceedings from the 44th International Symposium for Testing and Failure Analysis, 2018

As semiconductor devices continue to shrink, novel materials (e.g. (Si)Ge, III/V) are being teste... more As semiconductor devices continue to shrink, novel materials (e.g. (Si)Ge, III/V) are being tested and incorporated to boost device performance. Such materials are difficult to grow on Si wafers without forming crystalline defects due to lattice mismatch. Such defects can decrease or compromise device performance. For this reason, non-destructive, high throughput and reliable analytical techniques are required. In this paper Electron Channeling Contrast Imaging (ECCI), large area mapping and defect detection using deep learning are combined in an analytical workflow for the characterization of the defectivity of “beyond Silicon” materials. Such a workflow addresses the requirements for large areas 10-4 cm2 with defect density down to 104 cm-2.

Ultramicroscopy

Nowadays electron channeling contrast imaging (ECCI) is widely used to characterize crystalline d... more Nowadays electron channeling contrast imaging (ECCI) is widely used to characterize crystalline defects on blanket semiconductors. Its further application in the semiconductor industry is however challenged by the emerging rise of nanoscale 3D heterostructures. In this study, an angular multi-segment detector is utilized in backscatter geometry to investigate the application of ECCI to the defect analysis of 3D semiconductor structures such as III/V nano-ridges. We show that a low beam energy of 5 keV is more favorable and that the dimension of 3D structures characterized by ECCI can be scaled down to ~ 28 nm. Furthermore, the impact of device edges on the collected ECCI image is investigated and correlated with tool parameters and cross-section profiles of the 3D structures. It is found that backscattered electrons (BSE) emitted from the device edge sidewalls and generating the bright edges (edge effects), share a similar angular distribution to those emitted from the surface. We show that the collection of low angle BSEs can suppressed the edge effects, however, at the cost of losing the defect contrast. A positive stage bias suppresses edge effects by removing the inelastically backscattered electrons from the sidewalls, but low loss BSEs from the sidewalls still contribute to the ECCI micrographs. On the other hand, if segments of an angular backscatter (ABS) detector are properly aligned with the nano-ridges, BSEs emitted from the sidewall and the surface can be separated, thus leading to the completely absence of one bright edge on the surface without compromise of the defect contrast. The merging of two such ECCI images reveals the nano-ridge surface without edge effects.

Ultramicroscopy

In this study, an annular multi-segment backscattered electron (BSE) detector is used in back sca... more In this study, an annular multi-segment backscattered electron (BSE) detector is used in back scatter geometry to investigate the influence of the angular distribution of BSE on the crystalline defect contrast in electron channeling contrast imaging (ECCI). The study is carried out on GaAs and Ge layers epitaxially grown on top of silicon (Si) substrates, respectively. The influence of the BSE detection angle and landing energy are studied to identify the optimal ECCI conditions. It is demonstrated that the angular selection of BSEs exhibits strong effects on defect contrast formation with variation of beam energies. In our study, maximum defect contrast can be obtained at BSE detection angles 53-65° for the investigated energies 5, 10 and 20 keV. In addition, it is found that higher beam energy is favorable to reveal defects with stronger contrast whereas lower energy ( ≤ 5 keV) is favorable for revealing crystalline defects as well as with topographic features on the surface. Our study provides optimal ECCI conditions, and therefore enables a precise and fast detection of threading dislocations in lowly defective materials and nanoscale 3D semiconductor structures where signal to noise ratio is especially important. A comparison of ECCI with BSE and secondary electron imaging further demonstrates the strength of ECCI in term of simultaneous detection of defects and morphology features such as terraces with atomic step heights.

ECS Transactions

Semiconductor heterostructures represent the key building blocks for most nanoelectronics and pho... more Semiconductor heterostructures represent the key building blocks for most nanoelectronics and photonics devices. However, the performance and reliability of these devices is often limited by the presence of extended defects arising from plastic relaxation of misfit strain. Hence, metrology for assessing the nature, density and distribution of such defects is of crucial importance in order to support the development and fabrication of novel semiconductor devices. Electron Channeling Contrast Imaging (ECCI) has emerged as the method of choice for analyzing the crystalline quality of semiconductor heterostructures with excellent precision even at low defect densities. The present paper discusses the most relevant theoretical and experimental aspects one needs to consider to obtain high-quality ECCI micrographs. Moreover, the capabilities of the methodology are illustrated on the example of various different defect types in the most relevant semiconductor material systems and structures.

Microscopy and Microanalysis

Nanoscale, Jan 19, 2018

Semiconductor heterostructures are at the heart of most nanoelectronic and photonic devices such ... more Semiconductor heterostructures are at the heart of most nanoelectronic and photonic devices such as advanced transistors, lasers, light emitting diodes, optical modulators and photo-detectors. However, the performance and reliability of the respective devices are often limited by the presence of crystalline defects which arise from plastic relaxation of misfit strain present in these heterogeneous systems. To date, characterizing the nature and distribution of such defects in 3D nanoscale devices precisely and non-destructively remains a critical metrology challenge. In this paper we demonstrate that electron channeling contrast imaging (ECCI) is capable of analyzing individual dislocations and stacking faults in confined 3D nanostructures, thereby fulfilling the aforementioned requirements. For this purpose we imaged the intensity of electrons backscattered from the sample under test under controlled diffraction conditions using a scanning electron microscope (SEM). In contrast to ...

Microscopy and Microanalysis

Microscopy and Microanalysis

We are presenting a new extension to our Cell and Tissue/Neurobiology large volume imaging workfl... more We are presenting a new extension to our Cell and Tissue/Neurobiology large volume imaging workflow, with the goal of increasing acquisition speed by more than five times. Instead of scanning dense square-grid frames, in the conventional way, our approach is here to explore the use of sparse scanning and inpainting techniques inspired by Compressive Sensing (CS) [1]. Sparse samples are obtained by pseudo-random scan patterns, and reconstruction algorithms are used to recover the dense volume data. The goal is to recover 3D datasets with minimum loss of information. Techniques inspired by CS gained wide attention over the last decade and are now being used in various applications where sensor bandwidth is a limiting factor. They have been recently explored for SEM and STEM applications [2][3]. In the context of nano-scale cell biology volume acquisition, we expect these techniques to ultimately increase the imaging throughput by nearly an order of magnitude. We will discuss additional advantages of this approach, such as the low-dose imaging of sensitive specimens, and the good compatibility with backscatter electron imaging. A key enabler of any sparse scan application to EM is the accurate control of scan locations. It has been shown in [2] and in our own experiments that precise positioning of the beam at the planned sampling locations is essential for a good CS reconstruction. We have developed advanced minimum-path scanning strategies to address this issue. The scanning technique is illustrated in Fig. 1, where the left two images show a conventional raster scan at 300ns dwell visiting a random set of points with the compressive sensing reconstruction obtained from such scan strategy. The right two images of Fig. 1 show an example minimum-path scan pattern and a much improved reconstruction result from images acquired with this second method. In future work we will compare pseudo-random sparse sampling, in combination with a reconstruction algorithm based on CS-inspired in-painting, to conventional grid sampling of the same effective dose, in combination with a de-noising algorithm, also based on CS. CS machine learning algorithms build patch-dictionaries, which are used as the building blocks for data representation [3]. During live acquisition runs, such dictionaries can be used to in-paint with high fidelity, the sparsely sampled datasets (Figure 2). We are implementing the new sparse scanning modules on SEM platforms, which also employ the Multi Energy Deconvolution SEM (MED-SEM) technology and Serial Block Face (SBF) imaging [4]. By incorporating CS, we will have an instrument allowing for both high-resolution isotropic imaging, and the fast acquisition of very large datasets (Figure 3).

Journal of Electron Spectroscopy and Related Phenomena

The nano-scale dispersion of ordered/disordered phases in semi-crystalline polymers can strongly ... more The nano-scale dispersion of ordered/disordered phases in semi-crystalline polymers can strongly influence their performance e.g. in terms of mechanical properties and/or electronic properties. However, to reveal the latter in scanning electron microscopy (SEM) often requires invasive sample preparation (etching of amorphous phase), because SEM usually exploits topographical contrast or yield differences between different materials. However, for pure carbon materials the secondary spectra were shown to differ substantially with increased order/disorder. The aims here is to gain an understanding of the shape of secondary electron spectrum (SES) of a widely used semi-crystalline polymer regioregular poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT, and its links to the underlying secondary electron emission mechanisms so SES can be exploited for the mapping the nanomorphology. The comparison of simulated and experimental SES shows an excellent agreement, revealing a peak (at about 0.8eV) followed by a broad shoulder (between 2eV and 4.5eV) with respective relative intensities reflecting order/disorder.

Nano letters, Jan 10, 2016

Hydride precursors are commonly used for semiconductor nanowire growth from the vapor phase and h... more Hydride precursors are commonly used for semiconductor nanowire growth from the vapor phase and hydrogen is quite often used as a carrier gas. Here, we used in situ scanning electron microscopy and spatially resolved Auger spectroscopy to reveal the essential role of atomic hydrogen in determining the growth direction of Ge nanowires with an Au catalyst. With hydrogen passivating nanowire sidewalls the formation of inclined facets is suppressed, which stabilizes the growth in the ⟨111⟩ direction. By contrast, without hydrogen gold diffuses out of the catalyst and decorates the nanowire sidewalls, which strongly affects the surface free energy of the system and results in the ⟨110⟩ oriented growth. The experiments with intentional nanowire kinking reveal the existence of an energetic barrier, which originates from the kinetic force needed to drive the droplet out of its optimum configuration on top of a nanowire. Our results stress the role of the catalyst material and surface chemis...

Http Www Theses Fr, 1999

La structure de joints de grains de flexion d'axe 110 dans le molybdene et les phenomenes de ... more La structure de joints de grains de flexion d'axe 110 dans le molybdene et les phenomenes de mouillage de ces joints par le nickel, ont ete etudies. Nous avons utilise des bicristaux de caracteristiques cristallographiques bien definies qui correspondent a des energies de joint differentes et donc a des proprietes differentes. Trois types de bicristaux d'angle differents ont ete observes : les macles coherente et incoherente et un joint de coincidence particuliere (sigma = 11). Les observations experimentales ont ete faites principalement en microscopie electronique conventionnelle, a haute resolution et par spectroscopie de pertes d'energie des electrons. Pour chaque type de bicristal, la structure du reseau de dislocations secondaires a ete determinee par microscopie conventionnelle et par diffraction electronique et interpretee dans le cadre de la theorie de bollmann. Certaines de ces dislocations ont ete observees en haute resolution et leur champ de deformation elastique calcule. La structure a l'echelle atomique de chacun des bicristaux purs a ete determinee par haute resolution. Les resultats sont en tres bon accord avec ceux calcules par simulation numerique, notamment la structure des unites structurales qui composent les differents joints. Les translations rigides paralleles et perpendiculaires au plan de joint ont ete mesurees. Les experiences de mouillage par le nickel ont ete faites a deux temperatures (1350 et 1380 degres c). Selon l'energie du joint, il se forme soit des precipites isoles de phase mo-ni, soit une couche de mouillage tres mince (1nm) et continue le long du joint. La comparaison entre les differents bicristaux montre que le joint de faible energie ne presente pas de mouillage sauf au cur des dislocations secondaires, alors que le joint de forte energie est beaucoup plus fortement mouille. De plus, a la temperature de 1380 degres c, ce joint migre vers une position asymetrique.