Analytical electron microscopy of a reaction-bonded Si3N4-based ceramic containing oxide additions

The microstructure of a silicon nitride (Si₃N₄)-based ceramic, prepared by a process combining direct nitridation and reactive liquid phase sintering of silicon/ceramic oxide powder compacts, has been characterised using analytical transmission electron microscopy. The presence of the reactive liquid phase, promoted by the addition of oxides from the CaO-Al₂O₃-SiO₂ ternary system, resulted in an as-fired microstructure containing a mixture of crystalline phases based on -Si₃N₄, β-Si₃N₄ and Si₂ N₂O, and distinct amorphous regions rich in Si, Al and Ca. X-ray microanalysis revealed the calcium to be wholly partitioned to the glassy phase, while significant concentrations of aluminium were detected in both β-Si₃N₄ and Si₂N₂O. The observed compositions of these phases, together with measured lattice parameters systematically in excess of those of the pure compounds, imply that they are in fact β- and O-sialons respectively. Semi-quantitative energy dispersive X-ray spectroscopy, using an ultra-thin window detector, is demonstrated to be capable of distinguishing clearly between these phases according to their oxygen content and of determining the aluminium content of both phases to within ± 1 equ.%, even at concentration levels of <5 equ.%.     

Structural and photoluminescence properties of Si nanoclusters obtained by ion implantation into Si3N4 films

In the present paper we report structural and photoluminescence (PL) results from samples obtained by Si implantation into stoichiometric silicon nitride (Si₃N₄) films. The Si excess was introduced in the matrix by 170 keV Si implantation performed at different temperatures with a fluence of Φ=1×10¹⁷ Si/cm². The annealing temperature was varied between 350 and 900 °C in order to form the Si precipitates. PL measurements, with a 488 nm Ar laser as an excitation source, show two superimposed broad PL bands centered around 760 and 900 nm. The maximum PL yield is achieved for the samples annealed at 475 °C. Transmission electron microscopy (TEM) measurements show the formation of amorphous nanoclusters and their evolution with the annealing temperature.     

Chlorination of Si surfaces with gaseous hydrogen chloride at elevated temperatures

Silicon wafers of different orientations were treated with gaseous hydrogen chloride at elevated temperatures in a chemical vapor deposition (CVD) reactor to generate chlorinated surfaces. After the chlorination process, a smooth surface morphology with single layer steps was observed on Si(1 1 1) surfaces. X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering (RBS) measurements showed that the chlorine coverage is directly affected by the Si surface orientation. The surface chlorine is highly reactive with moisture and alcoholic compounds, which provides a new route for organic molecular functionalization of silicon surfaces.     

Molecular recognition of chromophore molecules to amine terminated surfaces

We report the design and characterization of quartz surfaces that can bind to three retinal based chromophores. The amine terminated surfaces were engineered in order to mimic the environment of the opsin protein that accommodates binding of chromophore molecules in the human eye. Each surface coupling step was characterized by water contact angle measurements, ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, and transmission infrared spectroscopy. The spectroscopic techniques confirmed that the three chromophore molecules can bind to the surface using a Schiff base mode. Our data suggests that the availability of the amine groups on the surface is critical in the accommodation of the binding of different chromophores.     

Si3N4/Si表面Si生长过程的扫描隧道显微镜研究

利用原位扫描隧道显微镜和低能电子衍射分析了Si的纳米颗粒在Si₃N₄/Si(111)和Si₃N₄/Si(100)表面生长过程的结构演变.在生长早期T为350—1075K范围内,Si在两种衬底表面上都形成高密度的三维纳米团簇,这些团簇的大小均在几个纳米范围内,并且在高温退火时保持相当稳定的形状而不相互融合.当生长继续时,Si的晶体小面开始显现.在晶态的Si₃N₄(0001)/S 关键词： 氮化硅 扫描隧道显微镜 纳米颗粒     

Observing the effect of water vapor on post-irradiated surface morphology of SiO2 and Si3N4 insulators by atomic force microscopy

In this work, we investigated the effect of water-vapor treatment on the surface morphology of SiO₂ and Si₃N₄ insulators before and after Co⁶⁰ gamma-ray irradiation by using the atomic force microscopy (AFM) operated under non-contact mode. Before irradiation, no apparent surface morphology change was found in SiO₂ samples even they were water vapor treated. However, bright spots were found on post-irradiated water-vapor-treated SiO₂ sample surfaces but not on those without water-vapor treatment. We attributed the bright spots to the negative charge accumulation in the oxide due to charge balancing between hydroxyl (OH⁻) ions adsorbed on SiO₂ surface and electron-hole pairs (ehps) generated during irradiation since they can be annealed out after low temperature annealing process. On the contrary, no bright spots were observed on post-irradiated Si₃N₄ samples with and without water-vapor treatment. This result confirms that Si₃N₄ is a better water-resist passivation layer than SiO₂ layer.     

Molecular functionalization of tantalum oxide surface towards development of apatite growth

We have studied the apatite growth dynamics on tantalum oxide surfaces. This nucleation is obtained via an organosilane intermediate layer between the apatite and the substrate surface. Four organosilane layers (differing by their terminal functionality) were investigated. Their characterization with atomic force microscopy and other techniques such as X-ray photoelectron spectroscopy (XPS) and wetting measurements highlighted the influence of the organosilane terminal groups on the apatite growth rates. Results revealed that apatite is indeed growing faster on phosphate terminal groups than on the three other groups studied (vinyl, hydroxyl and carboxyl).     

Thermally-induced morphological transition in WOx deposited on a ZrO2(1 0 0) substrate

A combined atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) study of tungsten oxide model catalysts is presented. The model catalysts were prepared by applying the real preparation method to a ZrO₂(1 0 0) single crystal support. AFM imaged several granular structures of scattered dimensions on the surface of ZrO₂(1 0 0) in the as prepared samples. After heating, at low loading the tungsten species rearranged into small WO_x particles strongly interacting with the substrate. At high tungsten content large WO₃ aggregates also formed. XPS analysis confirmed these changes. The estimated surface density of the interacting W-containing species closely matched that of real catalysts.     

Thickness and microstructure dependent transport and MR in La0.7Pb0.3MnO3 manganite films

Thickness dependent modifications in the structure and microstructure and their effect on the transport and magnetotransport in chemical solution deposition (CSD) grown La_0.7Pb_0.3MnO₃ (LPMO) manganite thin films grown on single crystalline LaAlO₃ (LAO) (1 0 0) substrates have been studied. X-ray diffraction (XRD) measurements show the reduction in the microstrain at the film-substrate interface with increasing thickness. Increase in grain size and island like grain growth with the reduction in surface roughness as a function of film thickness has been observed from the microstructural studies using atomic force microscopy (AFM) and lateral force microscopy (LFM) measurements. Improvement in the surface to volume ratio (D⁻¹) resulting in the modifications in transport and magnetotransport properties of the LPMO films has been discussed in detail in the light of thickness dependent microstructural effects on the resistivity and magnetoresistance (MR) behavior. The variations in intrinsic and extrinsic MR with D⁻¹ show an interesting interplay between them, which can be explained on the basis of thickness dependent grain size, grain boundary density and grain boundary nature.     

Spectroscopic ellipsometric characterization of TiAlN/TiAlON/Si3N4 tandem absorber for solar selective applications

Sputter deposited TiAlN/TiAlON/Si₃N₄ tandem absorber has been characterized by spectroscopic ellipsometry in the wavelength range of 450-1200 nm. Each layer of the tandem absorber viz., TiAlN, TiAlON and Si₃N₄ has been deposited separately on copper substrate (Cu) and ellipsometric measurements have been carried out on each of these layers. The measured ellipsometric spectra were fitted with theoretically simulated spectra and the sample structure and wavelength dispersion of optical constants of each layers have been determined. The ellipsometric measurements have also been carried out on the three-layer tandem absorber deposited on Cu substrate. By analyzing the ellipsometric data, depth profiling of the tandem absorber has been carried out using the derived optical constants of the individual layers.     

SiC formation on Si(100) via C60 precursors

The interaction between C₆₀ molecules and the Si(100) surface and the preparation of silicon-carbide thin films by thermal reaction of C₆₀ molecules with the Si(100) surface have been investigated using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, reflection high-energy electron diffraction and atomic force microscopy measurements. The effects of annealing temperature and C₆₀ coverage on the SiC formation will be discussed. It is found that the C₆₀ molecules bond covalently with silicon, and the number of bonds increase upon increasing the annealing temperature. Annealing at T≥830°C entails the formation of stoichiometric silicon carbide clusters that coalesce to form a continuous SiC layer when the C₆₀ coverage is greater than one monolayer. Deep pits acting as silicon diffusion channels are present with dimensions that increase with the amounts of C₆₀.

The interaction of C₆₀ with the SiC surface was also investigated. It is found that a similar covalent interaction is present in the two systems C₆₀/Si and C₆₀/SiC.     

Formation of micro-crystals on the (100) surface of SrTiO3 at elevated temperatures

Droplet-like features and regularly shaped micro-crystals appear on the (100) surface of single-crystals of stoichiometric and doped SrTiO₃ as a result of heat treatment around 1000–1100°C under ambient pressure. Secondary ion mass spectrometry, atomic force microscopy and X-ray photoemission are employed to characterize the morphology of the modified surface. The results provide evidence of an accumulation of SrO_x on the surface in a liquid form and subsequent recrystallization as SrO on prolonged annealing. The phenomena are discussed in relation to the restructuring in the near-surface region and the loss of material at the temperatures employed, as evident from thermogravimetrical measurements.     

Effect of annealing on the nanoscratch behavior of multilayer Si0.8Ge0.2/Si films

In this study, we examined the nanoscratch behavior of annealed multilayered silicon-germanium (SiGe) films comprising alternating sublayers (Si) deposited using an ultrahigh-vacuum chemical vapor deposition (UHV/CVD) system. Annealing consisted of ex situ thermal treatment in a furnace system. We used a nanoscratch technique to investigate the nanotribological behavior of the SiGe films and atomic force microscopy (AFM) to observe deformation phenomena. Our AFM morphological studies of the SiGe films revealed that pile-up phenomena occurred on both sides of each scratch. The scratched surfaces of the SiGe films that had been subjected to various annealing conditions exhibited significantly different features, it is conjectured that cracking dominates in the case of SiGe films while ploughing dominates during the scratching process. We obtained higher coefficients of friction (μ) when the ramped force was set at 6000 μN, rather than 2000 μN, suggesting that annealing of SiGe films leads to higher shear resistance; annealing treatment not only produced misfit dislocations in the form of a significantly wavy sliding surface but also promoted scratching resistance.     

Surface analysis for LiBq4 growing on ITO and CuPc film using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS)

We have investigated the morphology and surface electron states of LiBq₄ deposited on ITO and CuPc/ITO, using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM observations indicate that LiBq₄ can form a much more uniform film on CuPc than that on ITO. Furthermore, X-ray photoelectron spectroscopy (XPS) is utilized to further demonstrate the AFM results. From the analysis of XPS, we found that LiBq₄ molecules have poor thermal stability, they are seriously oxidized during depositing; but when a CuPc layer is inserted between LiBq₄ and ITO film, the oxidation and surface contamination of LiBq₄ are significantly reduced. It is then concluded that the introduction of a CuPc buffer layer under the LiBq₄ film can improve the film quality of LiBq₄.The XPS results also testified the fact that no coordination bonds between N atoms and B atoms are formed in LiBq₄ molecules, which make LiBq₄ to be potential blue organic light-emitting material.     

Evolution of Si0.8Ge0.2 quantum dots during Si encapsulation

Surface structure, determined by scanning tunneling microscopy (STM), surface morphology, determined by atomic force microscopy (AFM), and surface composition, determined by X-ray photoelectron spectroscopy (XPS) of 20.0 nm Si_0.8Ge_0.2 quantum dots formed at 800 °C and encapsulated with 0-10 nm of Si at 500 °C and 800 °C are presented. It is observed that the quantum dot surface morphology changes during the Si encapsulation at 800 °C by the smoothing of the quantum dots. The height of the quantum dots decreases faster than can be accounted for from the amount of Si deposited, indicating that there is movement of material out of the quantum dots during the encapsulation process. Encapsulation at 500 °C results in a retention of the quantum dot surface morphology with increased Ge segregation compared to Si encapsulation at 800 °C. We conclude that the changing surface morphology at 800 °C is not the result of Ge segregation but due to intermixing resulting from the tensile strain of Si depositing on SiGe.     

Composition depth profiles of Bi3.15Nd0.85Ti3O12 thin films studied by X-ray photoelectron spectroscopy

In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar⁺-ion sputtering changes lots of Bi³⁺ ions into Bi⁰ due to weak Bi-O bond and high etching energy.     

原子力显微镜与x射线光电子能谱对LiBq4/ITO和LiBq4/CuPc/ITO的表面分析

利用原子力显微镜对8-羟基喹啉硼化锂(LiBq₄)/铟锡氧化物和8-羟基喹啉硼化锂/酞菁铜(CuPc)/铟锡氧化物表面分别进行了扫描，显示了LiBq₄在不同衬底上的形貌差异，并进一步利用样品表面的x射线光电子能谱图验证了这一差异.实验表明，CuPc层的加入改善了LiBq₄的成膜质量，并将这种改善归因于分子构型与电子亲和势的不同. 关键词： 原子力显微镜 x射线光电子能谱 电子亲和势     

Si3N4的晶体化和ZrN/Si3N4纳米多层膜的超硬效应

研究了Si₃N₄层在ZrN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si₃N₄层厚度的ZrN/Si₃N₄纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明，由于受到ZrN调制层晶体结构的模板作用，溅射条件下以非晶态存在的Si₃N₄层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体，ZrN/Si₃N₄纳米多层膜形成共格外延生长的柱状晶，并相应地产生硬度升高的超硬效应. Si₃N₄随层厚的进一步增加又转变为非晶态，多层膜的共格生长结构因而受到破坏，其硬度也随之降低.     

Scanning tunneling microscopy of N2H4 on silicon surfaces

The chemistry of N₂H₄ on Si(100)2 × 1 and Si(111)7 × 7 has been studied using scanning tunneling microscopy. At low coverages on Si(100)2 × 1 at room temperature the adsorption sites are distributed randomly on the surface and are imaged as dark spots in the dimer row by the STM. Upon annealing the substrate at 600 K, both isolated reaction products, as well as clusters of reaction products are formed on the surface. The STM images show that the majority of the isolated reaction products are adsorbed symmetrically across the dimers. Based on previous HREELS data, these are most likely NH_x groups. However, the clusters are not well resolved. Because of this we speculate that they are not simply symmetrically adsorbed NH_x groups, but likely have a more complicated internal structure. At higher coverages, the STM images show that the predominant pathway for adsorption is with the N---N bond parallel to the surface, in agreement with HREELS studies of this system. On Si(111)7 × 7, the molecule behaves in a manner which is similar to NH₃. That is, at low coverages the molecule adsorbs preferentially at center adatoms due to the greater reactivity of these sites, while at higher coverages it also reacts with the corner adatoms.     

Crystallization of amorphous Si3N4 and superhardness effect in HfC/Si3N4 nanomultilayers

HfC/Si₃N₄ nanomultilayers with various thicknesses of Si₃N₄ layer have been prepared by reactive magnetron sputtering. Microstructure and mechanical properties of the multilayers have been investigated. The results show that amorphous Si₃N₄ is forced to crystallize and grow coherently with HfC when the Si₃N₄ layer thickness is less than 0.95 nm, correspondingly the multilayers exhibit strong columnar structure and achieve a significantly enhanced hardness with the maximum of 38.2 GPa. Further increasing Si₃N₄ layer thickness leads to the formation of amorphous Si₃N₄, which blocks the coherent growth of multilayer, and thus the hardness of multilayer decreases quickly.