Determination of the size and phase composition of silver nanoparticles in a gel film of bacterial cellulose by small-angle X-ray scattering,electron diffraction,and electron microscopy

The nanoscale structural features in a composite (gel film of Acetobacter Xylinum cellulose with adsorbed silver nanoparticles, stabilized by N-polyvinylpyrrolidone) have been investigated by small-angle X-ray scattering. The size distributions of inhomogeneities in the porous structure of the cellulose matrix and the size distributions of silver nanoparticles in the composite have been determined. It is shown that the sizes of synthesized nanoparticles correlate with the sizes of inhomogeneities in the gel film. Particles of larger size (with radii up to 100 nm) have also been found. Electron microscopy of thin cross sections of a dried composite layer showed that large particles are located on the cellulose layer surface. Electron diffraction revealed a crystal structure of silver nanoparticles in the composite.     

Particulate erosion of glass surfaces at subsonic velocities

The erosion of borosilicate glass plates through multiple collisions with 70–290 μm glass beads and 1.8 mm water drops is described. The basic element for the initiation of erosion damage by rounded solid particles is the cone fracture. The diameter of the ring and penetration of the conical fracture surface extending into the glass specimens have been measured for various impact conditions. The material removal process near the velocity threshold for cone fracture formation is dependent on the radius of the impacting particle. At intermediate velocities in the subsonic range the damage due to a single water drop impact is much more difficult to identify compared to solid-particle impingement. The observed damage is not coherent and fracture surfaces approximating circular arcs only begin to become evident at velocities considerably higher than that required for preferential erosion of the specimen's surface.     

LBO晶体超光滑表面抛光机理

胶体SiO2抛光LBO晶体获得无损伤的超光滑表面,结合前人对抛光机理的认识,探讨了超光滑表面抛光的材料去除机理,分析了化学机械抛光中的原子级材料去除机理.在此基础上,对胶体SiO2抛光LBO晶体表面材料去除机理和超光滑表面的形成进行了详细的描述,研究抛光液的pH值与材料去除率和表面粗糙度的关系.LBO晶体超光滑表面抛光的材料去除机理是抛光液与晶体表面的活泼原子层发生化学反应形成过渡的软质层,软质层在磨料和抛光盘的作用下很容易被无损伤的去除.酸性条件下,随抛光液pH值的减小抛光材料的去除率增大;抛光液pH值为4时,获得最好的表面粗糙度.     

Influence of LPE process technological conditions on Si ELO layers morphology

Epitaxial lateral overgrowth (ELO) is a suitable method which makes it possible to obtain thin layers for applications in the thin film solar cells technology. Due to the method it is possible to save the material which is used in production to make PV modules more economical. Moreover, an ELO layer is partly separated from the growth substrate by an SiO₂ cover which prevents propagation of defects into the ELO layer from the substrate. It means that even poor quality silicon substrates can be used to fabricate good quality solar cells. Growing a continuous thin silicon layer on a specially prepared growth silicon substrate is the first step to obtain photovoltaic (PV) modules. The morphology as well as the layer quality and the density of defects depend on various factors: growth temperature, cooling rate, growth time, atmosphere, substrate type, etc. This work presents an analysis of silicon ELO layers growth in different conditions using a horizontal LPE setup. The results can be used to determine the best conditions of growth in order to obtain optimal Si layers for PV applications.     

Evidence of nucleation and growth of metal Cu and Ag nanoparticles in lustre: AFM surface characterization

Lustre is one of the most interesting ancient ceramic decorations. Recent studies demonstrated that lustre correspond to a nanostructured thin layer formed by metallic copper and metallic silver nanocrystals embedded in a glass matrix. The aim of this paper is to improve the comprehension of lustre nature and the mechanisms of its formation focusing special attention on glaze surface nanotopography and the crystalline particles size and distribution. Lustre reproductions were studied during the lustre formation process and compared to medieval lustre layers. Lustre reproductions and ancient lustre surfaces were observed by means of White Light Interferometry, Atom Forces Microscopy, X-ray Diffraction and Electron Microprobe. These observations shown that lustre layer does not appear as a superimposed layer on the top of the glaze but as a surface roughness resulting by the nanocrystals growth inside the glassy matrix. Chemical Microprobe Analysis of lustre reproductions indicates that Cu and (later) Ag are introduced into the glaze by ion-exchange with alkalis (Na and K) from the glaze. White Light Interferometry and Atomic Forces Microscopy showed that surface roughness increase during the lustre formation process as a result of metal nanoparticles growth. Silver particles appear heterogeneously distributed and have a smaller size and higher roughness than copper particles on ancient lustre. This paper confirmed that lustre formation process involves two steps process: ion exchange and crystallization (nucleation and crystal growth) of Cu and Ag metal nanoparticles inside the glassy matrix.     

面向器件应用的PEDOT:PSS薄膜的光电稳定性研究

PEDOT:PSS(聚3, 4-亚乙基二氧噻吩-聚苯乙烯磺酸盐)薄膜因其良好的导电性、透光性、机械柔韧性以及溶液可加工性而被广泛应用。提高PEDOT材料的电导率以及光电稳定性对其器件应用有重要意义。在本文中,首先用旋涂法制备PEDOT:PSS薄膜,然后采用硫酸后处理技术提高其电导率,并将硫酸处理后的薄膜分别放置于空气、氧气、氮气中以及太阳光照下30 d,研究薄膜的光电稳定性及老化机制。实验结果表明:太阳光照是影响薄膜光电性能稳定性的主要因素,而硫酸处理有效地去除了过量的PSS成分,使薄膜的稳定性变好。通过比较老化前后薄膜的光吸收谱和光电子能谱(XPS)发现,在老化过程中薄膜发生了光氧化降解,这是影响薄膜光电稳定性的原因之一。     

Time evolution of surface defect states in hydrogenated amorphous silicon studied by photothermal and photocurrent spectroscopy and optical simulation

The time evolution of surface defect density and width of space charge region in thin layer of amorphous silicon is observed experimentally by Fourier transform photocurrent spectroscopy. This work reviews the assumption that photocurrent is insensitive to surface defects for samples thinner than 1500 nm. We show that correct evaluation based on simple optical model comprising layers representing surface defects and layers representing space charge region with reduced collection allows obtaining the same results as from photothermal deflection spectroscopy. Our main approach is the comparison of photocurrent or photothermal deflection spectra measured in absorptance/transmittance mode from layer and substrate side of the thin film.     

Investigation of the Crystallization Process in the Verneuil Techniques

The stability of the process of crystallization in the Verneuil techniques is analyzed, taking into account the geometrical shape of the molten layer surface and specific features of the heat and mass transfer typical for this method of crystal growth. The process is stable for crystal radii below the capillarity constant.     

溅射环境下基片表面所受到的轰击能量研究

溅射环境下基于薄膜的沉积速率和Langmuir探针测出的基片位置处离子流通量量化了单位时间内基片表面微区所接受的溅射中性原子的轰击能量Ec1和各种轰击离子传递给基片的轰击能量Ec2;Ec1和Ec2的数量级近似相同,Ec1和Ec2同时作用于基片表面微区加速了薄膜沉积过程中最表层原子的表面扩散进程,Ec1和Ec2持续作用所引起的能量积淀和温升效应可促进薄膜表层下方原子的体扩散进程。     

Novel Crosslinked PVA Without Photoinitiator for Organic Passivation Layers of Pentacene Thin-Film Transistors

We report a new polyvinyl alcohol (PVA)-tetraethoxysilane (TEOS) hybrid layer to protect an organic thin-film transistor (OTFT). PVA/TEOS hybrid thin film was successfully fabricated through hydrolysis and condensation mechanism. The surface roughness of PVA/TEOS film was measured by atomic force miscroscophy (AFM) and it showed a good surface roughness with a root-mean-squae value of about 0.23 nm. Thermally crosslinked PVA with TEOS was successfully adaped as a solution processable passivation layer for pentacene TFT. In case of well known photo-crosslinked PVA/ammonium dichromater (ADC) passivation, extremely large initial performance drop (almost 52% mobility drop) was observed after passivation. PVA/TEOS hybrid passiavtion, however, no significant initial performance drop was found after passivation process. In addition, pentacene TFT with PVA/TEOS passivation layer exhibited very stable TFT operation with almost no field mobility drop or threshold voltage shift up to 980 h.     

Formation of structure in small lead clusters under thermal effect

The thermal effect on lead clusters with radii up to 5.5 nm has been investigated by the molecular dynamics method using a modified tight-binding potential TB-SMA. The melting of Pb nanoparticles of these sizes is strictly homogeneous, without the formation of a surface liquidlike layer. The primary fcc phase in the particles is retained upon heating in the overwhelming majority of model experiments. An analysis of the structure formation during crystallization has shown that structures with pentagonal symmetry are preferred for lead clusters in this case. It is noted that an increase in the nanoparticle size leads to the dominance of the dodecahedral structure over the icosahedral one.     

Epitaxial Sn1‐xPbxS nanorods on iso‐compositional thin films

Based on SnS (Herzenbergite) – SnPbS₂ (Teallite) mixed crystals with orthorhombic layer structures, thin films and lawns of Sn_1‐xPb_xS nanorods were produced using hot wall vacuum deposition method (HWVD). The lawn was formed onto the surface of an underlying thin Sn_1‐xPb_xS film which is build by differently oriented blocks. The density of rods arranged like a lawn depends on the metal ratio and substrate temperature. X‐ray and TEM analysis of the epitaxial material showed preferential (001) orientation perpendicular to the surface of the glass substrate. The roughness of the films measured by atomic force microscopy was in the range of R_q = 49.5–86.3 nm depending on lead concentration The rods were about 500 nm high and 300 nm in diameter. As revealed by TEM‐EDX experiments the droplet at the tip of rods consists of tin. Therefore it is assumed the rods grew via a self‐consuming vapor–liquid–solid (VLS) mechanism. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Material characteristics of metalorganic chemical vapor deposition of Bi2Te3 films on GaAs substrates

Metal organic chemical vapor deposition has been investigated for growth of Bi₂Te₃ films on (0 0 1) GaAs substrates using trimethylbismuth and diisopropyltelluride as metal organic sources. The results of surface morphology, electrical and thermoelectric properties as a function of growth parameters are given. The surface morphologies of Bi₂Te₃ films were strongly dependent on the deposition temperatures. Surface morphologies varied from step-flow growth mode to island coalescence structures depending on deposition temperature. In-plane carrier concentration and electrical Hall mobility were highly dependent on precursor's ratio of VI/V and deposition temperature. By optimizing growth parameters, we could clearly observe an electrically intrinsic region of the carrier concentration at the temperature higher than 240 K. The high Seebeck coefficient (of −160 μVK⁻¹) and good surface morphology of this material is promising for Bi₂Te₃-based thermoelectric thin film and two-dimensional supperlattice device applications.     

Aging in chalcohalide glasses: Origin and consequences

The application of chalcogenide and chalcohalide glasses is limited by their uncontrolled drift in properties over time due to aging processes. In the present work, we perform aging experiments on some chalcohalide glasses in oxidizing, inert and reducing atmospheres and afterwards we measure the elemental concentration depth profiles in the surface layer of the glasses by using secondary neutral mass spectroscopy. The results show that anionic diffusion processes occur in the glasses during aging. The aging process leads to a decrease in microhardness of the studied glasses, which is attributed to both physical aging (i.e., structural relaxation) and chemical aging (i.e., compositional change of the surface layer).     

Effects of morphologies on the field emission characteristics of GaN nanorods grown on Si (0 0 1) by MBE

GaN nanorods were grown on Si (0 0 1) substrates with a native oxide layer by molecular beam epitaxy. The changes in the morphologies and their effects on the field emission characteristics of GaN nanorods were investigated by varying growth conditions, namely, growth time of low-temperature GaN buffer layer, growth time of GaN nanorods, Ga flux during growth of GaN nanorods, and growth temperature of GaN nanorods. GaN nanorods with a low aspect ratio measured by diode configuration showed better field emission characteristics than those with a high aspect ratio, which may be due to the effects of screening and the surface depletion layer. In addition, the distance between the GaN nanorods and the anode played an important role in the field emission characteristics such as turn-on field, field enhancement factor, and field distribution on the emitter surface.     

Mechanism for CuPt-type ordering in mixed III–V epitaxial layers

A model is proposed to rationalize the occurence of CuPt-type ordering in mixed III–V epitaxial layers grown on (001) substrates. It is invoked that 2× surface reconstruction occuring on group V terminated (001) surfaces produces dilated and compressed regions in sub-surface layers. The presence of these regions biases the occupation of certain sites during the growth of a layer consisting of atoms differing in their tetrahedral radii. By assuming that the reconstruction always occurs at the growing surface, it is possible to explain the evolution of CuPt-type ordering in epitaxial layers. Also, based on the model, experimental observations pertaining to the influence of growth conditions, surface misorientation and steps on ordering can be rationalized.     

Investigation on the regeneration of Z‐cut KDP crystals

The regeneration of Z‐cut KDP crystals is explored by analyzing the growth of thin surface layers formed. The structural defects and crystalline perfection of the thin surface layers are evaluated by white‐beam synchrotron radiation topography and high‐resolution X‐Ray diffraction respectively. It shows that the thin surface layers have the same crystal structure as KDP crystal. There are large numbers of defects in thin surface layers and the crystalline quality is very poor. The growth velocity of thin surface layers is firstly accurately measured by a newly‐designed in‐situ crystal growth observation setup. It is found that the growth velocity of the thin surface layers strongly depends on the flow rate of the growth solution. The hindering effect of pyrophosphate (K₄P₂O₇) on the growth of the thin surface layers is discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two‐ and three‐dimensional growth modes of nitride layers

Heteroepitaxial three dimensional (3D) and two dimensional (2D) growth modes of nitride layers on sapphire substrates are discussed. It is shown that the 3D or 2D growth mode of AlGaN layers depends predominantly on the growth conditions of the underneath low temperature (LT) nucleation layer. Commonly described in literature 3D growth mode is achieved on LT GaN or AlN nucleation layer grown relatively fast. Successive growth of secondary layer at high temperature begins from separated sites, where individual 3D crystallites are formed. Threading dislocations present in crystallites bend on their facets, which reduces the quantity of dislocations. However, slight crystallographic misorientations between crystallites lead to the creation of new dislocations during coalescence of the crystallites. As a result, edge and mix dislocations appear at similar densities of about 10⁹ cm^‐2. Modification of growth conditions of LT AlN nucleation layer, especially reduction of their growth rate, leads to drastic changes in properties of the layer. Successive growth of secondary AlGaN layer at high temperature starts evenly on whole surface retaining atomic flatness. Thus growth at high temperature occurs only by 2D mode. Therefore, it is possible to grow a very thin AlGaN layers directly on top of LT nucleation layer. Such layers contain large number (10¹⁰ cm^‐2) of edge dislocations, and relatively small number (less then 10⁸ cm^‐2) of mix dislocations. It is also shown that the decisive factor determining the growth mode of AlN nucleation layer is a growth of the first few atomic layers on substrate surface. The slow growth of these few first atomic layers decide about the 2D growth mode, and the fast one about the 3D one. The model explaining this difference is presented as well. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of glass surface damaged by alumina abrasive grains

The quality of an optical glass component is influenced by the presence of surface and subsurface defects generated by machining processes, especially lapping. However, the damaged area is characterized by roughness and crack layers that contribute to reduce the component's mechanical and optical performances. Evaluation of these defects leads to the obtainment of the best finishing technique for optical glass components.In this work, the effect of the lapping technological parameters (lapping time and alumina abrasive grain size) on the glass surface roughness as well as the depth of the damaged layer were determined. Furthermore, a proportionality constant between the total height of the roughness profile (Rt) and the subsurface damage layer was calculated. The damaged depth was characterized using mechanical techniques and microscopic analysis. The obtained results show an important damage of the glass surface, since the first few seconds of contact time between the surface and the grains. The increase of the lapping time gives rise to the propagation of this damage to reach its maximum and then a material removal rate is observed. At the end of the operation, a defined final surface roughness and a subsurface damaged layer are obtained. The proportionality constant between the subsurface damage layer and the total height of the roughness profile (Rt) was found to be 6.7 ± 0.8.     

Electron microscopic study on nucleation and growth of silver particles in a thin glass film

Nucleation and crystal growth of silver particles in a thin glass film of Li₂O·2.6SiO₂ glass containing 0.1 wt% of Ag₂O were observed by transmission electron microscopy and studied by an electron diffraction technique. Anomalies of the image contrast which appeared in the heat-treated specimens were explained to be caused by phase separation of the glass. Nucleation of silver particles was found to occur on the surface of the phase-separated silica-rich droplets. As the silver particles grew, their shape changed into that of a regular cube which was covered with a thin diffusion layer of silver ions about 50 Å in thickness. The presence of this thin layer and the cubic shape suggest that the growth of silver particles proceeds by a layer-by-layer growth mechanism.