Formation of titanium oxide films on the surface of porous silicon carbide

The influence of rapid thermal annealing (RTA) on the properties of a titanium film on the surface of porous silicon carbide is considered. It is shown that an increase in the RTA temperature to 900°C stabilizes the phase composition of the forming titanium oxide over the film, which is identified as rutile. Due to the formation of titanium oxide nanoclusters under the action of RTA, an additional photoluminescence band arises near 2.5 eV. Based on Auger spectrometry data, a multilayer model to calculate the optical parameters of titanium oxide films covering porous silicon carbide is suggested.     

A comparison of silicon oxide and nitride as host matrices on the photoluminescence from Er+ ions

This paper compares the properties of silicon oxide and nitride as host matrices for Er ions.Erbium-doped silicon nitride films were deposited by a plasma-enhanced chemical-vapour deposition system.After deposition,the films were implanted with Er3+ at different doses.Er-doped thermal grown silicon oxide films were prepared at the same time as references.Photoluminescence features of Er3+ were inspected systematically.It is found that silicon nitride films are suitable for high concentration doping and the thermal quenching effect is not severe.However,a very high annealing temperature up to 1200° C is needed to optically activate Er3+,which may be the main obstacle to impede the application of Er-doped silicon nitride.     

Epitaxial growth of zinc oxide by the method of atomic layer deposition on SiC/Si substrates

For the first time, zinc oxide epitaxial films on silicon were grown by the method of atomic layer deposition at a temperature T = 250°C. In order to avoid a chemical reaction between silicon and zinc oxide (at the growth temperature, the rate constant of the reaction is of the order of 10²²), a high-quality silicon carbide buffer layer with a thickness of ~50 nm was preliminarily synthesized by the chemical substitution of atoms on the silicon surface. The zinc oxide films were grown on n- and p-type Si(100) wafers. The ellipsometric, Raman, electron diffraction, and trace element analyses showed that the ZnO films are epitaxial.     

室温下掺Er富硅氧化硅和掺Er富硅氮化硅的光致发光及其退火

用磁控溅射淀积掺Er氧化硅、掺Er富硅氧化硅、掺Er氮化硅和掺Er富硅氮化硅薄膜,室温下测量这四种薄膜的光致发光（PL）谱,观察到这四种薄膜都具有1.54μm的峰位,其强度与薄膜的退火温度有关。为了确定1.54μmPL的最佳退火温度,这些薄膜都分别在600,700,800,900,1000,1100℃的温度下同时退火,发现两种富硅薄膜的最佳退火温度是800℃,不富硅的两种薄膜的最佳退火温度是900℃。样品的1.54μmPL最强,且800℃退火的掺Er富硅氧化硅薄膜的1.54μm峰强度是最强的,比不富硅的强了约20倍,还观察到这四种薄膜都具有1.38μm的PL带,且掺Er富硅氧化硅和掺Er富硅氮化硅这两种薄膜的PL在强度上1.38μm峰与1.54μm峰有一定的关系。     

磁控溅射淀积掺Er富Si氧化硅膜中Er3+ 1.54μm光致发光

用磁控溅射淀积不同富Si程度的掺Er富Si氧化硅薄膜.室温下测量其光致发光谱,观察到各谱中都含有1.54和1.38μm两个发光峰,其中1.54和1.38μm的光致发光峰分别来自Er³⁺和氧化硅中某种缺陷.系统研究了Er³⁺1.54μm光致发光峰强度对富Si程度及退火温度的依赖关系.还发现1.54μm发光峰强度与1.38μm发光峰强度相互关联,对此进行了讨论 关键词： Er 富Si氧化硅 光致发光 纳米硅     

Effect of microwave annealing on silicon dioxide/silicon carbide structures

The methods of atomic force microscopy and optical absorption spectroscopy are applied to study the effect of microwave treatment on the properties of SiO₂/SiC structures obtained by rapid thermal annealing and conventional thermal oxidation in steam. From the variation of the sample optical density with total time of microwave treatment, it is concluded that the structures prepared by rapid thermal annealing are more stable against microwave radiation. It is shown that long-term microwave treatment flattens the oxide film surface at the nanolevel regardless of the method of silicon carbide oxidation.     

Structure,composition and optical properties of ZnO:Ga films electrodeposited on flexible substrates

Thin films of ZnO:Ga are electrodeposited on stainless steel from zinc chloride solutions containing gallium with a Ga/Zn molar ratio in the range 1–10%. The surface morphology, structure, composition, and the optical properties of these films are studied using SEM, XRD, EDX, XPS, photoluminescence and transmittance spectroscopy. Results reveal that films with embedded platelets can be grown with a Ga/Zn molar ratio up to 60%. In as-grown films, Ga is present in the form of oxide, hydroxide or hydroxychloride compounds which decompose by annealing. Films annealed at 400°C are composed only from ZnO and Ga₂O₃ phases. The incorporation of Ga in ZnO films does not make a considerable change in the optical transmittance and the photoluminescence properties of the films.     

X‐ray absorption near‐edge structure anomalous behaviour in structures with buried layers containing silicon nanocrystals

Substructure and phase composition of silicon suboxide films containing silicon nanocrystals and implanted with carbon have been investigated by means of the X‐ray absorption near‐edge structure technique with the use of synchrotron radiation. It is shown that formation of silicon nanocrystals in the films' depth (more than 60 nm) and their following transformation into silicon carbide nanocrystals leads to abnormal behaviour of the X‐ray absorption spectra in the elementary silicon absorption‐edge energy region (100–104 eV) or in the silicon oxide absorption‐edge energy region (104–110 eV). This abnormal behaviour is connected to X‐ray elastic backscattering on silicon or silicon carbide nanocrystals located in the silicon oxide films depth.     

Solvent-Induced Crystallization of PS-b-PEO-b-PS Block Copolymer Films

Solvent-induced crystallization and dewetting behaviors of polystyrene-b-poly (ethylene oxide)-b-polystyrene (PS-b-PEO-b-PS) block copolymer films deposited on three different substrates, silicon, mica, and carbon-coated mica have been studied by atomic force microscope (AFM). When the common solvent dichloromethane was used for annealing, the films on all three of the substrates exhibited dewetting behavior; the dendritic crystallization patterns were found in the dewetted regions for the films on silicon and mica substrates, while for the films on carbon-coated mica, no crystallization pattern appeared. According to the observation of the crystallization patterns formed in the films with different initial thicknesses, it is shown that the width of the dendritic branches decreases with the increase of film thickness and solvent annealing time. When the PS-selective solvent toluene was used for annealing, the dewetting process was absent, and the crystallization patterns were observed on the surface of the films on all three kinds of substrates.     

Synchrotron investigations of the electron structure of silicon nanocrystals in a SiO2 matrix

Silicon ions are implanted into silicon oxide thin films obtained by the thermal oxidation of silicon wafers in wet oxygen. The implantation dose is accumulated either once or cyclically, and the samples are annealed in dry nitrogen every time after implantation. The second series of samples is prepared in a similar way, but the technology for obtaining the oxide films includes additional annealing at 1100°C in air for three hours. X-ray absorption near-edge structure (XANES) spectra are obtained using synchrotron radiation. In all the Si L _2,3 spectra, two absorption edges are observed, the first corresponding to elemental silicon, and the second corresponding to the SiO₂ matrix. The fine structure of the first edge indicates that nanocrystalline silicon (nc-Si) can form in the SiO₂ matrix, whose atomic and electronic structure depends on the technology of its formation. In both series, the cyclic accumulation of the total dose (Φ = 10¹⁷ cm^?2) and the annealing time (2 h) gives rise to the most pronounced fine structure in the region of the absorption edge of elemental silicon. The probability of forming silicon nanocrystals decreases for the denser silicon oxide in the second series of samples.     

碳化硅薄膜脉冲激光晶化特性研究

采用XeCl准分子激光对非晶碳化硅(a-SiC)薄膜的脉冲激光晶化特性进行了研究.通过原子力显微镜（AFM）和Raman光谱技术对退火前后薄膜样品的形貌、结构及物相特性进行了分析.结果表明，选用合适的激光能量采用激光退火技术能够实现a-SiC薄膜的纳米晶化.退火薄膜中的纳米颗粒大小随着激光能量密度的增加而增大；Raman谱分析结果显示了退火后的薄膜的晶态结构特性并给出了伴随退火过程存在的物相分凝现象.根据以上结果并结合激光退火特性，对a-SiC的脉冲激光晶化机理进行了讨论. 关键词： 激光退火 晶化 碳化硅     

非晶碳化硅材料与光学微腔的制备与发光

利用等离子体化学气相沉积技术在100℃的衬底温度下,制备了具有不同组分比的系列非晶碳化硅薄膜。结合傅里叶变换红外光谱与喇曼光谱对所制备的薄膜微结构进行了表征与分析,同时,对具有不同组分比的非晶碳化硅薄膜室温光致发光性质进行了系统的研究。结果表明在Ar⁺离子激光和Xe灯紫外光的激发下,不同组分的样品显示出不同的光致发光特性,并对样品的发光特性与其微结构的联系进行了讨论。在此基础上,用碳化硅薄膜设计和制备了全固体光学微腔,研究了微腔对碳化硅发光行为的调制作用。     

Influence of the temperature on the photoluminescence of silicon clusters embedded in a silicon oxide matrix

Amorphous silicon oxide thin films were prepared by co-evaporation of Si and SiO in ultra-high vacuum. Different compositions were obtained by changing the evaporation rate of silicon. After thermal annealing treatments, the dissociation of the silicon oxide in pure silicon and silicon dioxide leads to the formation of silicon clusters embedded in a silicon oxide matrix. Thus the samples were annealed to different temperatures up to 950°C. Depending on the annealing temperature and on the composition, different cluster sizes were obtained. The photoluminescence (PL) energy depends on the cluster size and a large range of wavelengths is obtained from 500 to 750 nm. The PL, attributed to a confinement effect of the electron–hole pairs in the silicon particles, is studied as a function of the temperature. It is demonstrated that the continuous decrease of PL intensity with the temperature from 77 to 500 K depends on the structure of the samples. For samples with well-separated clusters, the PL decreases rapidly with the temperature. For samples containing clusters separated by a small distance, the PL weakly depends on the temperature. No shift of the energy is observed. The results are discussed by taking into account the competition between the radiative recombination in the silicon clusters and the non-radiative escape of the carriers via a hopping mechanism.     

The effects of ambient oxygen pressure on the 1.54 μm photoluminescence of Er-doped silicon-rich silicon oxide films grown by laser ablation of a Si+Er target

We fabricated Er-doped silicon-rich silicon oxide (SRSO:Er) films by pulsed laser deposition. A Si+Er target consisting of an Er metallic strip and a silicon disk was adopted with a goal to achieve a convenient control of the Er and oxygen density in the film. We found that the photoluminescence (PL) at 1.54 m is highly dependent on the ambient oxygen pressure, which determines the relative ratio of Si-Si, SiO_x, and SiO₂ phase in the film. The PL intensity increased drastically with increase in the annealing temperature and reached the maximum intensity at 500 °C. PACS 81.15.Fg; 81.07.-b     

Effect of annealing on the structural, optical and electrical properties of ZnO thin films by spray pyrolysis

Zinc oxide thin films have been deposited on glass substrates at a substrate temperature of 673 K by spray pyrolysis. The samples are annealed in ambient atmosphere at various temperatures. The effect of annealing on structural, electrical, and optical properties of ZnO films has been investigated. X-ray diffraction patterns show that crystallinity of the ZnO films has been improved after annealing. The morphology of ZnO thin films is studied by atomic force microscopy. The tensile strain (compressive stress) is found to decrease with increase in annealing temperature which indicates the relaxation of tensile strain in ZnO thin films. A decrease in energy band gap is observed with increase of annealing temperature. The mechanism of blue-green luminescence of ZnO thin film has been analyzed. The resistivity is found to decrease with annealing temperature.     

Specific features of morphology and the structure of nanocrystalline cubic silicon carbide films grown on a silicon surface

Physics of the Solid State - The composition, surface morphology, and crystal structure of nanocrystalline cubic silicon carbide films grown on a silicon surface through chemical conversion from...     

Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Photoluminescence from Er-doped silicon rich oxide thin films

 Photoluminescence (PL) properties of Er-doped silicon rich oxide thin films deposited on Si substrate by co-evaporation of silicon monoxide and Er under different atmospheres are investigated. The samples exhibit luminescence peak at 1.54 μm which could be assigned to the recombination in intra-4f Er³⁺ transition. PL shows that this transition is highest when ammonia atmosphere is used during deposition followed by an annealing temperature at 850 °C in 95% N₂+5% H₂ gas (forming gas). In fact, we believe that the presence of the N atoms around Er ions increases the intensity of the 1.54 μm luminescence.     

Limiting step involved in the thermal growth of silicon oxide films on silicon carbide

Thermal growth of silicon oxide films on silicon carbide in O2 was investigated using oxygen isotopic substitution and narrow resonance nuclear reaction profiling. This investigation was carried out in parallel with the thermal growth of silicon oxide films on Si. Results demonstrate that the limiting steps of the thermal oxide growth are different in these two semiconductors, being diffusion limited in the case of Si and reaction limited in the case of SiC. This fact renders the growth kinetics of SiO2 on SiC very sensitive to the reactivity of the interface region, whose compositional and structural changes can affect the electrical properties of the structure.     

红荧烯薄膜生长及稳定性的研究

利用原子力显微镜研究了二氧化硅衬底上红荧烯薄膜的生长及稳定性。在较低沉积速率下,较低衬底温度时,红荧烯分子有充足的扩散时间,利于薄膜的横向生长,形成连续性、均匀性较好的薄膜。快速蒸镀及较高衬底温度使红荧烯薄膜转变为纵向生长模式,形成团粒状岛。横向生长的红荧烯薄膜在退火和空气中表现为亚稳特性,随着退火温度的升高和空气中放置时间的延长,红荧烯分子会自发地进行质量传输,发生纵向转移,转变为团粒状岛。获得了二氧化硅界面上红荧烯薄膜的生长及亚稳定机制模型。研究结果证明红荧烯分子与二氧化硅界面之间的作用力小于红荧烯分子间的作用力。