Paramagnetic defects in diamond films synthesized by the hot filament chemical vapour deposition

Defects in nitrogen‐doped diamond films, produced by hot filament chemical vapour deposition have been studied by Electron Spin Resonance (ESR), Raman spectroscopy and Scanning Electron Microscopy (SEM). The peak‐to‐peak ESR line width (ΔH _pp) varies in the range 0.36‐0.52 mT and depends on the nitrogen concentration in the process gas. In the case of nitrogen‐doped diamond films ESR spectrum shows a hyperfine structure typical of N_S⁰ paramagnetic centre. The shape of the central ESR line shows that it is a superposition of two components: a narrower Lorentzian and a broader Gaussian one, characterized by different saturation behaviour. With increasing nitrogen concentration in process gas the ratio of integral intensities A _G/A _L (Gausian to Lorentzian) of ESR spectrum also increases. The Raman spectra show that with increasing doping level the diamond Raman line at 1332.5 cm^‐1 broadens, the broad band at about 1530 cm^‐1 becomes more pronounced what indicate on degradation of diamond crystallinity and it is in agreement with SEM observation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

直流电弧等离子体喷射化学气相沉积高质量金刚石膜残余应力分布的垃曼谱分析

不同工艺条件下在钼衬底(φ60mm)上用100 kW直流电弧等离子体喷射化学气相沉积设备进行金刚石膜的制备.金刚石膜用扫描电镜(SEM)、拉曼谱(激光激发波长为488nm)和X射线衍射来表征.研究结果表明,在直流电弧等离子体喷射化学气相沉积金刚石膜的过程中,内应力大小从金刚石膜的中央到边缘是增加的,并且应力形式是压应力.这说明了在金刚石膜中存在明显的应力不均.甲烷浓度和衬底温度都影响金刚石膜中的内应力.随着甲烷浓度和衬底温度的提高,金刚石膜中的内应力呈增加的趋势.     

Optical microscopic, synchrotron X-ray topographic and reticulographic study of homoepitaxial CVD diamond

Surface topography and crystal-lattice perfection of homoepitaxial layers deposited by microwave plasma CVD on (0 0 1) and near-(0 0 1) facets polished on HPHT synthetic diamond are described. Optical micrographic techniques included birefringence, Nomarski and 2-beam interference. The synchrotron X-ray experiments comprised Laue topography plus a recently developed sensitive misorientation-measuring technique, reticulography. Two special circumstances enhanced information yield from the experiments. First, the substrate crystal was unusually strain-free and had a very low dislocation content. Second, epilayer growth had taken place in two stages, depositing thicknesses of 10 μm and 30–34 μm, respectively. This double deposition complicated the observations, but added features of scientific and practical interest. Epilayer cracking finally present had occurred almost entirely before the second growth stage. With assistance from quantitative data provided by reticulography, the X-ray diffraction properties of the substrate and epilayers are analysed. Lattice misorientations on the untreated lower surface of the substrate were only 1 arcsec except close to growth-sector boundaries and dislocation outcrops. The final epilayer growth surface above areas where cracking in the first epilayer was absent or sparse exhibited near-perfect-crystal diffraction behaviour.     

Preparation and characterization of electrodeposited indium selenide thin films

Indium Selenide (InSe) thin films were deposited from a mixture of Indium chloride and selenium dioxide in aqueous solution by electrodeposition technique on Indium Tin oxide coated glass substrates. The effects of the parameters during deposition such as current density, deposition potential versus saturated calomel electrode, pH value and concentration of source material were studied. X‐ray diffraction studies were carried out on the films to analyze the microstructure using an x‐ray diffractometer and were examined by RAMAN spectroscopy. The Raman peak position did not change much with chemical concentrations. Raman scattering due to the (LO) phonon was observed at 211 cm^–1. Optical absorption studies were performed with a double beam ultra violet‐visible –NIR spectrophotometer in the wavelength 300–1100 nm. The surface morphology of the layer was examined using a scanning electron micrograph. The composition of the films was studied using an Energy Dispersive Analysis by X‐Rays (EDAX).     

DC Plasma Jet CVD金刚石自支撑膜体结构的控制生长及其表面粗糙度的研究

在100kW级DC Plasma Jet CVD设备上,采用Ar-H2-CH4混合气体,通过控制工艺参数,在Mo衬底上获得不同占优晶面和应力状态的膜体结构.研究表明:不同取向的晶面在膜体中的分布不同,但各晶面随沉积温度的变化规律是相似的,在900℃左右容易获得较大的(220)晶面占优的膜体结构;薄膜的内应力沿晶体生长方向逐渐减小,且随沉积温度或甲烷浓度的增大而增大;具有高取向度的膜体将获得较为平整的表面.     

Optical and spectroscopic characterization of germanium selenide glass films

A previews study of germanium selenide glass films by scanning electron microscopy and atomic force microscopy revealed a heterogeneous surface morphology consisting of granular regions 15–50 nm in size, which cause high optical losses. The present work was performed in order to further characterize such materials using spectroscopic ellipsometry, infrared (IR) and Raman spectroscopies. Chalcogenide glass films with GeSe₂, Ge₂₈Sb₁₂Se₆₀ and GeSe compositions have been deposited on single crystal silicon and silica glass substrates by vacuum thermal evaporation. The film thickness and the optical constants were obtained from spectroscopic ellipsometry using the Tauc-Lorenz dispersion formula. A model was derived for the film structure, which included a roughness layer at the surface. This top layer was found to have a thickness of 5–15 nm, of the order of the size of the granular regions previously reported. The optical bandgap of the samples increased with increasing selenium content, while the refractive index decreased. Despite a previous report of large scale phase separation in bulk Ge₂₆Sb₁₄Se₆₀ glass, the fundamental IR and Raman spectra obtained in the present work did not provide any clear evidence for such phase separation which could be associated with the heterogeneous nanostructure observed at the surface of the films.     

硬质合金表面去钴和脱碳对金刚石薄膜粘结性能的影响

金刚石涂层的粘结性能是影响CVD金刚石薄膜涂层刀具使用寿命的关键因素.本文分别对硬质合金(YG6)表面进行酸蚀去钴和原位脱碳两种不同的预处理后,在热丝CVD系统中沉积金刚石薄膜,运用压痕试验评价金刚石薄膜与硬质合金基体的粘结性能.结果表明,经过原位脱碳预处理的硬质合金表面上金刚石涂层的粘结性能比酸蚀去钴法提高了近一倍;同时分析了硬质合金表面酸蚀去钴对金刚石薄膜粘结性能的影响及其剥离机制,并讨论了硬质合金表面原位脱碳的化学机制.     

直流等离子体喷射CVD技术制备自支撑金刚石膜的新结构和新形貌

采用30kW高功率直流等离子体喷射CVD技术制备了自支撑金刚石膜的新型结构,通过使甲烷与氢气的浓度比随沉积时间变化的方法,制备了两层、三层和四层结构.扫描电镜结果显示所制备的层结构是由柱状晶和非常细晶粒组成的,而拉曼谱结果表明这层细晶粒具有纳米金刚石的激光散射特征.在甲烷与氢气的浓度比超过15;的沉积条件下,我们发现一种新形貌,这种形貌是由具有非常好的刻面的晶粒构成的.     

Role of annealing environment and partial pressure on structure and optical performance of TiO2 thin films fabricated by rf sputter method

Influences of the different annealing ambient (in air, 1 bar, 2 bar, 3 bar and 4 bar oxygen partial pressure) on the titanium dioxide (TiO₂) thin films deposited on soda lime glass by standard radio frequency (rf) magnetron reactive sputtering method at 100 watt were investigated by means of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis), and Scanning Electron Microscopy (SEM). It was found that either optical properties or energy band gaps of the films enhanced with increase in the oxygen partial pressure up to 3 bar. The energy band gaps of the films (except for the film annealed in 4 bar oxygen partial pressure) became larger than the film annealed in atmospheric pressure. The best transmission was observed for the thin film annealed in 3 bar oxygen partial pressure. Moreover, not only was grain–like structure found to be more dominant than dot–like structure but also growth of anatase phase was observed instead of that of the rutile phase with increasing oxygen partial pressure up to 3 bar. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bonding and ion-ion interactions of Mn ions in fluoride-phosphate and boro-silicate glasses probed by EPR and fluorescence spectroscopy

Electron paramagnetic resonance (EPR) and fluorescence spectroscopy are sensitive and selective methods for probing coordination and bonding of Mn²⁺ ions in glasses. Both methods provide additional information on Mn-Mn ion interactions and cluster formation. Mn²⁺ was found to be tetrahedrally coordinated in boro-silicate glasses of high optical basicity, and octahedrally coordinated in low alkaline boro-silicate glasses (duran-type) as in fluoride-phosphate glasses. Broad emission bands and multicomponent fluorescence decay curves in duran glasses indicate very strong Mn-Mn ion interactions and the presence of multiple Mn²⁺ sites. Site distribution is more homogenous in metaphosphate glasses, though concentration quenching is apparent at high Mn-levels. As the Mn-content increases the EPR spectra show exchange narrowing due to a decrease in the Mn-Mn distances in the duran series, but show extreme linewidth broadening due to increased cluster sizes at constant Mn-Mn distances for metaphosphate glasses. For the fluoride-phosphate and boro-silicate systems investigated, fluorescence lifetimes are found to decrease as the wavelength of the emission maximum increases and with increasing g-values of the sextet at g = 2. For octahedral coordination of Mn²⁺ ions the EPR hyperfine splitting constant decreases linearly with increasing optical basicity, as a result of an increasing covalent character of the Mn²⁺-ligand bond.     

Influence of the deposition parameters on the microstructure and opto-electrical properties of hydrogenated nanocrystalline silicon films by HW-CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared at high deposition rates (> 13 Å/s) from pure silane without hydrogen dilution by hot wire deposition method by varying filament-to-substrate distance (d_s-f). In this study we have systematically and carefully investigated the effect of filament-to-substrate distance on structural, optical and electrical properties of the Si:H films. A variety of characterization techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FE-SEM), UV-Visible-NIR spectroscopy and electrical dark and photoconductivity measurement were used to characterize these films. Films deposited at d_s-f > 5 cm are amorphous while those deposited at d_s-f < 5 cm are biphasic; a crystalline phase and an amorphous phase with nano-sized crystallites embedded in it. Low angle X-ray diffraction analysis showed that the crystallites in the films have preferential orientation along (111) directions. Decrease in d_s-f, the crystallinity and crystalline size increases whereas hydrogen bonding shifts from mono-hydride (SiH) to di-hydride (SiH₂) and poly-hydride (SiH₂)_n complexes. The band gaps of nc-Si:H films (~ 1.9-2.0 eV) are high compared to the a-Si:H films, while hydrogen content remains < 10 at.%. We attribute the high band gap to the quantum size effect. A correlation between electrical and structural properties has been established. Finally, from the present study it has been concluded that the filament-to-substrate distance is a key process parameter to induce the crystallinity in the films by hot wire method. The ease of depositing films with variable crystallite size and its volume fraction, and tunable band gap is useful for fabrication of tandem/micro-morph solar cells.     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.     

Growth and characterization of sulphamic acid single crystals grown by Sanakaranarayanan‐Ramasamy (SR) method

By directional solidification, single crystal of Sulphamic acid (SA) was successfully grown from aqueous solution by Sankaranarayanan‐Ramasamy (SR) method. A vertically designed L‐bend was used to avoid the effect due to spurious nucleation. A vertical bottom‐seeded ampoule was used for the growth of single crystal. A seed crystal was mounted at the bottom of the ampoule. Sulphamic acid crystals of up to 40 mm in diameter and 60 mm in length have been grown with a growth up to 10 mm per day. The grown sulphamic acid single crystal was characterized using X‐ray powder diffraction analysis, Raman, FTIR, and optical transmission studies. The dielectric behaviour was measured in the frequency range of 1 kHz–10 MHz for the temperature ranges from 30 °C to 170 °C. The sulphamic acid single crystal was also grown by conventional method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical and electrical characterization of HgxCd1‐xTe polycrystalline films fabricated by two‐source evaporation technique

Two‐source thermal evaporation technique was used to prepare Hg_xCd_1‐xTe thin films onto scratch free transparent glass substrates. The structural investigations revealed that thin films were polycrystalline in nature. Transmittance measurements in the wavelength range (500‐2700 nm) were used to calculate optical constants. The analysis of the optical absorption data showed that the optical band gap was of indirect type. In the composition range 0.05 < x < 0.25 the films exhibited an optical band gap between 1.29 and 0.98 eV. In the same composition range the films were p‐type and exhibited a resistivity, which varied between 10² and 10^‐1 Ω‐cm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the substrate temperature on the structural,optical, and electrical properties of tin selenide thin films deposited by thermal evaporation method

Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (T_s) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all T_s. With the increase of T_s the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different T_s. The activation energy for films deposited at different T_s was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)