Al-induced fullerene-like nanostructures in C-Al-N thin films

The role of aluminium incorporated into growing carbon nitride (CN_x) films prepared by reactive dc-magnetron sputtering was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). XPS analyses revealed the formation of Al-N bonding besides C-C and C-N bonds. With increasing Al concentrations above 11.8 at.%, a structural transformation from essentially amorphous (a-) (CN_x, AlN) phase to locally ordered microstructure comprising of fullerene-like (FL-) CN_x nanostructures surrounded by a-(CN_x, AlN) matrices was evidenced by Raman and HRTEM. The effect of aluminium in triggering FL-CN_x nanostructures was elucidated from thermodynamic considerations.     

Ti–Al–Si–N nanocrystalline composite films synthesized by reactive magnetron sputtering

A series of Ti–Al–Si–N nanocrystalline composite films with different Si contents were synthesized in a mixture gas composed of Ar, N₂ and SiH₄ by reactive magnetron sputtering. Energy dispersive spectroscopy, Auger electron spectroscopy, X-ray diffraction and transmission electron microscopy were employed to characterize the microstructures of these films; a nanoindenter was used to measure their mechanical properties. The results show that by changing the SiH₄ partial pressure in the mixture gas, Si content in the films can be easily controlled. After Si is added into the films, an interface phase TiSi_x appears. It prevents (Ti,Al)N and AlN grains from growing, as a result, the (Ti,Al)N and AlN phases exist as nanocrystals. Correspondingly, the films' hardness and elastic modulus arrive at their maximum values of 36.0 and 400 GPa, respectively, at 3.5 at.% Si. With a further increase of Si content, the films' mechanical properties decrease gradually.     

In2O3 films prepared by thermal oxidation of amorphous InSe thin films

In₂O₃ thin films were prepared by the thermal oxidation of amorphous InSe films in air atmosphere. The structure, morphology and composition of the thermal annealed products were characterized by X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive spectroscopy, respectively. The XRD patterns indicate that the as-deposited InSe films were amorphous and they fully transformed into polycrystalline In₂O₃ films with a cubic crystal structure in the preferential (222) orientation at a temperature around 600 °C. The optical energy gap of 3.66 eV was determined at room temperature by transmittance and reflectance measurements using UV-vis-NIR spectroscopy. A preliminary characterization shows that these films have a promising response towards NO₂ gas at a working temperature around 180 °C.     

Effect of negative bias voltage on the microstructures of AlN thin films fabricated by reactive r.f. magnetron sputtering

Aluminium nitride thin films have been fabricated on silicon wafers by reactive r.f. magnetron sputtering in mixed Ar-N2 discharge with variation of negative bias voltage. The effect of negative bias voltage on the microstructures of AlN thin films have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), stress measurement, Auger electron spectroscopy (AES), etc. While the negative bias voltage was varied in the range 0 to −45 V, highly c-axis oriented film can be fabricated at −30 V, and the grain size and compressive stress increase with the negative bias voltage. From the plasma analysis, the dominant positive chemical species is identified as N+2 ions. The above results can be understood considering that at the kinetic energy transfer and flux of N+2 ions increase with increasing negative bias voltage. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optical properties of erbium oxide thin films deposited by electron beam evaporation

Erbium oxide thin films were deposited by electron beam evaporation on substrates heated to 300 °C. The effect of the introduction of oxygen on the structural, chemical and optical properties of the films was investigated. The films were characterized using X-ray diffraction, X-ray photoelectron spectroscopy and normal-incidence transmittance and reflectance. The films had microcrystallites embedded in an amorphous matrix, and their stoichiometry was dependent on the oxygen partial pressure. The transmittance spectra of the films revealed that they were optically inhomogeneous. A model based on an inhomogeneous layer was applied to extract the refractive index and extinction coefficient from the transmittance and reflectance spectra.     

Microstructure-Property relationships in thin film ITO

Polycrystalline tin-doped indium oxide (ITO) thin films were prepared by pulsed laser deposition (PLD) with an ITO (In₂O₃-10 wt.% SnO₂) target and deposited on borosilicate glass substrates. By changing independently the deposition temperature and the oxygen pressure, a variety of microstructures were deposited. These different microstructures were mainly investigated not only by transmission electron microscopy (TEM) with cross-section and plan-view electron micrographs, but also by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction. Composition changes in ITO thin films grown under different deposition conditions were characterized by energy dispersive X-ray spectroscopy (EDX). The optical and electrical properties were studied respectively by UV-visible spectrophotometry and a four-point probe. The best compromise in terms of high transmittance (T) in the visible range and low resistivity (ρ) was obtained for films deposited between 0.66 and 2 Pa oxygen pressure (P_O2) at 200 °C substrate temperature (T_s). The influence of P_O2 and T_s on the microstructure and ITO film properties is discussed.     

Property change during nanosecond pulse laser annealing of amorphous NiTi thin film

Nanosecond lasers of different intensities were pulsed into sputter-deposited amorphous thin films of near equiatomic Ni/Ti composition to produce partially crystallized highly sensitive R-phase spots surrounded by amorphous regions. Scanning electron microscopy having secondary and back-scattered electrons, field emission scanning electron microscopy, optical microscopy and X-ray diffraction patterns were used to characterize the laser treated spots. Effect of nanosecond pulse lasering on microstructure, morphology, thermal diffusion and inclusion formation was investigated. Increasing beam intensity and laser pulse-number promoted amorphous to R-phase transition. Lowering duration of the pulse incidence reduced local film oxidation and film/substrate interference.     

Properties of amorphous silicon thin films synthesized by reactive particle beam assisted chemical vapor deposition

Amorphous silicon thin films were formed by chemical vapor deposition of reactive particle beam assisted inductively coupled plasma type with various reflector bias voltages. During the deposition, the substrate was heated at 150 °C. The effects of reflector bias voltage on the physical and chemical properties of the films were systematically studied. X-ray diffraction and Raman spectroscopy results showed that the deposited films were amorphous and the films under higher reflector voltage had higher internal energy to be easily crystallized. The chemical state of amorphous silicon films was revealed as metallic bonding of Si atoms by using X-ray photoelectron spectroscopy. An increase in reflector voltage induced an increase of surface morphology of films and optical bandgap and a decrease of photoconductivity.     

Effect of cobalt doping on the structural and optical properties of TiO2 films prepared by sol-gel process

Pure and cobalt doped titanium dioxide thin films have been prepared on glass and Si (100) substrates by sol-gel spin coating method. The structural and optical properties of the films as a function of cobalt concentration (up to 15 wt.%) have been systematically studied by Rutherford backscattering spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, optical spectroscopy and spectroscopic ellipsometry methods. Rutherford backscattering studies show the presence of cobalt dopant in the films is almost equal to the precursor stoichiometry. Grazing incidence X-ray diffraction and Raman spectroscopy studies confirm the amorphous phase of the as-deposited films and crystalline anatase phase for the films annealed at 600 °C. The optical spectroscopy measurements show that the films are fully transparent in the visible region and there is a band gap narrowing upon increasing cobalt dopant concentration. The refractive index, band gap (E_g) and thickness of the films were determined from spectroscopic ellipsometry measurements. The refractive index of the films was found to increase from 2.2 to 2.7 with the increase in cobalt concentration with a simultaneous decrease of band gap from 3.1 to 2.8, which is favorable for photocatalytic applications. The packing density of the films was calculated by Clausius-Mossotti relation and is found to increase with cobalt concentration.     

Optical and structural characterization of inhomogeneities in a-Si:H TO μc-Si transition

The a-Si:H films with different thickness and microstructure have been deposited with rf-PECVD using a plasma of silane diluted with hydrogen. The structure and optical analysis were carried out by X-ray diffraction, UV-VIS and Raman spectroscopy. Spectral refractive indices, optical energy band gaps, extinction coefficients, phases ratio and grain size were determined as a function of the hydrogen dilution (R = H₂/SiH₄). Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to micro-crystalline hydrogenated silicon (μc-Si:H). XRD analysis indicated that films with R = 0 and R = 20 were amorphous and homogeneous, while films with R = 40 and higher were micro-crystalline consisting medium range ordered silicon hydride (Si₄H) and μc-Si phases with different size of crystallites, which was confirmed also by Raman spectroscopy.     

二元不互溶Cu-Ta体系非晶相的形成

利用X射线衍射(XRD)、高分辨透射电子显微术(HRTEM)和X射线能谱(EDS)研究了共溅射Cu-Ta薄膜中非晶相的形成.结果表明,共溅射Cu-Ta薄膜为非晶相,但是其中存在着纳米尺度的Cu晶粒和富Cu的非晶纳米颗粒,即存在纳米尺度的相分离.正的混合热是导致Cu-Ta二元不互溶体系非晶态薄膜相分离的本质原因.     

Negative-differential-resistance effects in amorphous CuInS2 thin film

The microstructure and the optical properties of amorphous CuInS₂ thin films deposited on glass substrates by a single source thermal evaporation technique, are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission and reflection measurements. Amorphous CuInS₂ thin films sandwiched between gold and copper electrodes, show current-controlled electronic switching. The switching is believed to be associated rather with electronic processes than the thermal ones.     

Influence of bias voltage on the optical and structural properties of nc-Si:H films grown by layer-by-layer (LBL) deposition technique

The effects of applying a positive bias of 25 to 100 V on the optical, structural and photoluminescence (PL) properties of hydrogenated nanocrystalline silicon (nc-Si:H) films produced by layer-by-layer (LBL) deposition technique has been studied. Optical characterization of the films has been obtained from UV-VIS-NIR spectroscopy measurements. Structural characterization has been performed using X-ray diffraction, micro-Raman spectroscopy and field emission scanning electron microscope (FESEM). PL spectroscopy technique has been used to investigate the PL properties of the films. In general, the films formed shows a mixed phase of silicon (Si) nanocrystallites embedded within an amorphous phase of the Si matrix. The crystalline volume fraction and grain size of the Si nanocrystallites have been shown to be strongly dependent on the applied bias voltage. High applied bias voltage enhances the growth rate of the films but reduces the refractive index and the optical energy gap of the films. Higher crystalline volume fraction of the films prepared at low bias voltages exhibits room temperature PL at around 1.8 eV (700 nm).     

Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition

We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH₃). At 185 °C, deposition rate saturated for TMA and NH₃ doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH₃ resulted in a constant growth rate of ~ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≥ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ~ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

The preparation and characterization of preferred (110) orientation aluminum nitride thin films on Si (100) substrates by pulsed laser deposition

The preferred (110) oriented aluminum nitride (AlN) thin films have been prepared by pulsed laser deposition on p-Si (100) substrates. The films were characterized with X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscope (AFM). The results indicate that the AlN thin films are well-crystallized when laser energy is higher than 300 mJ/puls. The AFM images show that the surface roughness of the deposited AlN thin films gradually increases with increasing laser energy, but the surface morphologies are still very smooth. The crystallinity and morphology of the thin films are found to be strongly dependent on the laser energy.     

A novel approach for codoping in ZnO by AlN

In the present work, we have illustrated a new idea of codoping in ZnO with AlN as codopant to achieve p-ZnO. ZnO films doped with different concentrations of AlN were grown by RF magnetron sputtering. The AlN doped ZnO (ANZO) films grown on sapphire substrate were subjected to X-ray diffraction (XRD), reflectance measurements, Hall measurements, atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis. XRD analysis reveals that all films have grown in the form of hexagonal wurtzite structure with (002) preferential orientation. The FWHM of (002) peak decreases till 1 mol% of AlN and increases for further addition of AlN indicating the incorporation of more impurities (dopants). The reflectance measurements suggest that the reflectance decreases at lower concentration and increases above 1 mol% of AlN in the visible region ranging from 400 to 800 nm. Hall measurements show that all the films are n-type. The electron concentration increases initially and then decreases for further addition of AlN (>1 mol%) suggesting the incorporation of nitrogen into the film at higher concentrations of AlN. The presence of N in the films is further confirmed by EDS analysis. The rms surface roughness measured by AFM decreases exponentially with dopant concentration. The figure of merit increases upon codoping with AlN.     

Chemical bath deposition of MoS2 thin film using ammonium tetrathiomolybdate as a single source for molybdenum and sulphur

Molybdenum disulphide, MoS₂, thin films have been deposited by chemical bath deposition method on glass and quartz substrate using ammonium tetrathiomolybdate as a single source precursor for Mo and S and subjected to vacuum heat treatment at different temperatures. X-ray diffraction of as-deposited film indicated its amorphous character and showed the development of poorly crystalline MoS₂ thin film on increasing annealing temperature. The film has been characterized by energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, scanning electron micrograph and the optical properties also have been studied.     

TiCuO薄膜的显微结构对Cu离子释放和内皮细胞行为的影响

采用直流磁控溅射技术, 在Si片和316L SS基体上制备了不同Cu含量的TiCuO薄膜。采用X射线衍射仪(XRD)、透射电镜(TEM)、X 射线能谱仪(EDS)和X射线光电子能谱(XPS)对薄膜的显微结构和化学组成进行了分析。采用电化学腐蚀和模拟体液浸泡实验评价了薄膜的腐蚀性能和Cu离子释放特性。体外静态培养内皮细胞后, 采用细胞计数试剂盒(CCK-8)评价了TiCuO薄膜的细胞活性。研究结果表明, 未掺杂的TiO₂薄膜为金红石相, 掺入Cu后的TiCuO薄膜由非晶基体上含有Cu₂O的纳米晶粒构成。薄膜中的富Cu区引起了薄膜腐蚀。含Cu量高的TiCuO薄膜更易被腐蚀, 并释放出较多Cu离子。TiCuO薄膜释放出一定浓度的Cu离子促进了内皮细胞活性。研究表明, TiCuO薄膜的含Cu量和显微结构影响了Cu离子释放, 对其内皮细胞活性起了关键作用。     

Atmospheric pressure chemical vapour deposition of thermochromic tungsten doped vanadium dioxide thin films for use in architectural glazing

Atmospheric pressure chemical vapour deposition of VCl₄, WCl₆ and water at 550 °C lead to the production of high quality tungsten doped vanadium dioxide thin films. Careful control of the gas phase precursors allowed for tungsten doping up to 8 at.%. The transition temperature of the thermochromic switch was tunable in the range 55 °C to − 23 °C. The films were analysed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their optical properties were examined using variable-temperature transmission and reflectance spectroscopy. It was found that incorporation of tungsten into the films led to an improvement in the colour from yellow/brown to green/blue depending on the level of tungsten incorporation. The films were optimized for optical transmission, thermochromic switching temperature, magnitude of the switching behaviour and colour to produce films that are suitable for use as an energy saving environmental glass product.