Structural and optical properties of Al-doped SnO2 nanowires

We report a facile thermal evaporation method for the syntheses of Al-doped SnO₂ nanowires using Al-doped SnO₂ nanoparticles as precursors. High-density, single-crystalline Al-doped SnO₂ nanowires were directly grown on the 6H-SiC substrates without any catalyst. X-ray diffraction patterns show that the Al dopants are incorporated into the rutile SnO₂ nanowires. The X-ray photoelectron spectra confirm the SnO₂ nanowires doped with 5 at.% Al. The photoluminescence spectra of the Al-doped SnO₂ nanowires exhibit that the large blue shift of the emission band can be observed in the Al-doped SnO₂ nanowires compared with undoped nanowires. The distortion of the crystal lattices caused by incorporation of Al atoms at the interstitials should be responsible for the large blue shift of the emission band.     

不同衬底上溅射TiO2薄膜的光学性能研究

在硅片和石英上利用射频溅射法沉积了TiO2薄膜,并分别在空气中进行了退火处理。利用椭偏光谱仪对硅片上薄膜进行了椭偏测试,利用紫外-可见分光光度计对石英上薄膜进行了透射光谱测试。利用解谱软件对椭偏谱和透射谱进行了建模解谱,获得了不同基片上薄膜在不同退火温度下的折射指数和消光系数,发现和TiO2块材的光学常数也有明显的区别。通过计算得到了系列薄膜的光学带隙,带隙值范围从3.35～3.88eV,可以为薄膜态TiO2体系的光学应用、设计和相关理论研究提供一定的依据。     

Structural and optical properties of layer-by-layer solution deposited Cu2SnS3 films

Cu₂SnS₃ (CTS) is a simple and potential material for low-cost thin film solar cells. The present work incorporates the study of changes in structural and optical properties of layer-by-layer solution deposited CTS films with annealing. Raman spectroscopy is used to ascertain structural modification upon annealing. Increase in annealing temperature leads to a structural transition from tetragonal to cubic phase. Effect of annealing on optical properties of the films is evaluated in the wavelength range of 400–2,400 nm. It is proposed that layer-by-layer growth method fundamentally defines the optical behaviour of these films. Optical constants and parameters such as refractive indices, dielectric constants and electron energy loss function are calculated from transmittance and reflectance data. The refractive indices, n and k are determined to be in ranges of 1.8–2.2 and 0.18–1.2, respectively. The real and imaginary dielectric constants vary from 1.5 to 4.6 and 0.7 to 5, respectively. Dispersion of refractive index is analyzed using two different theoretical models of Wemple–diDomenico and Spitzer–Fan.     

Structural and optical properties of single-crystalline ultraviolet-emitting needle-shaped ZnO nanowires

Well-crystallized with excellent optical properties, needle-shaped ZnO nanowires have been synthesized on silicon substrate in a high density via the thermal evaporation of metallic zinc powder without the use of catalysts or additives. Extensive structural analysis showed that the grown nanowires are highly crystalline with the wurtzite hexagonal phase, grown along the [0001] in the c-axis direction. The presence of an optical-phonon E₂ mode in Raman spectrum at 437 cm^{− 1} and sharp and strong UV emission at 379 nm with no green emission in the room-temperature photoluminescence (PL) spectrum confirms good crystallinity with the excellent optical properties for the deposited nanowires.     

脉冲电压沉积制备金属Ni纳米线阵列及磁性能

以硫酸溶液为电解质,采用两步电化学阳极氧化法制备了氧化铝有序多孔膜,孔径为20nm,孔间距为50nm左右,孔洞密度为4.5×1010个/cm2.以此多孔膜为模板,以脉冲信号为沉积电压制备了金属Ni纳米线阵列,单根纳米线直径为15～20nm,择优取向为Ni(220)晶面.磁滞回线结果表明垂直于膜面的方向为易磁化方向,当磁场垂直于膜面时,矩形比高达90.5%,矫顽力为63.84kA/m.     

Fabrication and optical emission of TiO2-sheathed ZnO nanowires

The ZnO nanowires were synthesized by using vapor-liquid-solid mechanism and then the ZnO nanowires were sheathed with TiO2 by metal organic chemical vapor deposition. The coaxial nanowires were 30-200 nm in diameter and up to 0.2 microm in length. Transmission electron microscopy and X-ray diffraction analysis results showed that the ZnO cores and TiO2 shells of the core-shell nanowires had wurtzite and amorphous structures, respectively. Photoluminescence measurement showed that TiO2 coating increased and decreased the near-band edge (NBE) and deep-level emissions of the ZnO nanowires in intensity, respectively. However, it appeared that subsequent annealing was undesirable since it decreased the NBE emission in intensity.     

Fabrication and photovoltaic properties of heterostructured TiO2 nanowires

One-dimensional heterostructured TiO2 nanowires were successfully fabricated by an electrospinning technique and modified by hydrolysis. We investigated their structure, morphology, chemical composition, and optical properties by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy. In the case of the photovoltaic performance, the short-circuit current density and cell efficiency of the DSSCs employing single TiO2 nanowires and heterostructured TiO2 nanowires improve from 6.90 to 11.38 mA/cm2 and from 2.56 to 4.29%, respectively. The results show that the photoconversion efficiency of the heterostructured TiO2 nanowires could be improved by more than approximately 67% compared to that of the single TiO2 nanowires because of the enhanced specific surface area that facilitates dye adsorption.     

Structural and optical properties of chemically deposited CuInSe2 thin film in acidic medium

Thin films of nanocrystalline CuInSe2 were prepared on glass substrates using chemical bath deposition in acidic medium at room temperature. Thickness of the chemically deposited CuInSe2 thin films was approximately 100 nm which composed of closely packed irregular grains of approximately 100-120 nm in diameter. X-ray diffraction pattern of CuInSe2 thin films showed nanocrystalline structure with (112) preferential orientation. The films exhibited faint black and direct band gap energy was 0.96 eV.     

Structural,optical and magnetic properties of the Fe2TiO5 nanopowders

Iron titanate nanopowders with a particle size range of 48–70?nm could be obtained after calcinations of the dried gel at 900°C for 2?h. Fe₂TiO₅ indicates a ferrimagnetic–paramagnetic behaviour, as evidenced by using vibrating sample magnetometer at room temperature. In the temperature range of 25–300°C the empirical equation of the heat capacity C _p (J/mol?K)?=??692.328?+?1.39?T?+?3.757?×?10⁷/T ² for Fe₂TiO₅ was determined from differential scanning calorimetry. Direct optical band gap of Fe₂TiO₅ was calculated using the Tauc model by UV-Vis diffuse reflectance spectroscopy. Band gap energy of Fe₂TiO₅ was determined as 1.95?eV.     

Structural, optical and photocatalytic properties of sol-gel synthesized mesoporous TiO2 film

TiO2 surfactant-templated nanostructured film was fabricated by supramolecular templating technique using TiCl4 and P-123 as raw material and surfactant, respectively. The film was produced by sol-gel dip coating procedure. Characterization of the product was carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface areas, thermogravimetry (TG), and UV-vis absorption spectroscopy. Detailed characterization reveals that film is transparent and has a wormlike mesostructured with high surface area. It is about 2 microm thick and is composed of closely packed anatase particles. The estimated band gap value of TiO2 thin film in the present work is 3.69 eV which is about 0.3 eV larger than value reported in literature for anatase thin film. It could be due to quantum size effect arising from the small size of TiO2 nanocrystallite in this thin film. The photocatalytic activity of the prepared TiO2 film was evaluated by Crystalviolet dye degradation. The film has excellent photocatalytic efficiencies and more than 70% of dye was decolorized in 60 minutes.     

氧分压对TiO2膜结构与光学性质的影响

报道了用反应溅射法制备TiO2 膜的实验研究 .详细研究了膜的沉积、膜结构及其光学性质 ,随溅射氧分压的变化 .随氧分压由 6× 10 - 2 Pa增加到 9× 10 - 2 Pa时 ,晶体结构由金红石变到锐钛矿 ,氧分压超过 9× 10 - 2 Pa时趋向于无定形结构 .与膜结构密切相关的折射率n随氧分压的增大由 2 .4 4变到 1.96 ,禁带宽度Eg 则由大变小 ,然后再增大的变化 (3.4 1→ 3.2 6→3.4 2 ) .     

Roughness of glancing angle deposited titanium thin films: an experimental and computational study

The characterization of roughness at the nanoscale by the means of atomic force microscopy (AFM) was performed on high aspect ratio glancing angle deposited titanium thin films. With the use of scanning electron microscopy as well as x-ray photoelectron spectroscopy, it was shown that the AFM measurements gave rise to incorrect roughness values for the films consisting of the highest aspect ratio structures. By correcting for this experimental artefact, the difference between the saturated roughness value of a film grown with conventional physical vapour deposition and films grown with a glancing angle of deposition was shown to behave as a power law function of the deposition angle, with a saturated roughness exponent of κ?=?7.1?±?0.2. This power law scaling was confirmed by three-dimensional molecular dynamics simulations of glancing angle deposition, where the saturated roughness exponent was calculated to κ?=?6.7?±?0.4.     

Structural,optical and electrical properties of spray pyrolytically deposited thin films of CuInS2

CuInS₂ is a promising chalcopyrite semiconducting material for solar cell fabrication. Using aqueous solutions of cupric chloride, indium trichloride and thiourea, we deposited thin CuInS₂ films on glass at 350°C and studied their structural, optical and electrical properties. From the XRD pattern the chalcopyrite structure of these films was confirmed. The films were polycrystalline. The grain size estimated from scanning electron micrographs was found to be of the order of 1μm. Resistivity of the film was measured for temperatures ranging from 77 to 473 K. Band gap values were determined from optical transmission data. Hall mobility and carrier concentration at room temperature were calculated using Van der Pauw-Hall method.     

Structural,optical and electrical properties of chemically deposited copper selenide films

Stoichiometric and nonstoichiometric thin films of copper selenide have been prepared by chemical bath deposition technique at temperature below 60°C on glass substrate. The effect of nonstoichiometry on the optical, electrical and structural properties of the film was studied. The bandgap energy was observed to increase with the increase in at % of copper in composition. The grain size was also observed to increase with the decrease of at % of copper in composition. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), absorption spectroscopy, and AFM. The results are discussed and interpreted.     

Structural and surface properties of TiO2 thin films doped with neodymium deposited by reactive magnetron sputtering

Thin films were deposited using modified, high energy magnetron sputtering method from Ti-Nd mosaic targets. The amount of neodymium dopant incorporated into two sets of thin films was estimated to be 0.8 and 8.5 at.%, by means of energy dispersive spectroscopy. On the basis of x-ray diffraction method, the type of crystalline structure and crystallites size were evaluated directly after the deposition process and after additional post-process annealing at 800 °C temperature. The influence of annealing on the surface properties was evaluated with the aid of atomic force microscopy. Uniformity of the dopant distribution in titanium dioxide matrix was examined with the aid of secondary ion mass spectroscopy. Additionally, using atomic force microscope, diversification and roughness of the surface was determined. Chemical bonds energy at the surface of TiO₂:Nd thin films was investigated by x-ray photoelectron spectroscopy method. Wettability measurements were performed to determine contact angles, critical surface tensions and surface free energy of prepared coatings. On the basis of performed investigations it was found, that both factors, the amount of neodymium dopant and the post-process annealing, fundamentally influenced the physicochemical properties of prepared thin films.     

稀土La3+掺杂TiO2纳米线的制备及其性能研究

采用水热法制备了钛酸钠纳米线、TiO2纳米线和La3+/TiO2纳米线。利用XRD、SEM、HREM、XPS和UV-Vis等技术手段对样品微观结构、光学性能和表面元素价态进行了分析;并以甲基橙溶液为目标污染物测试其光催化性能。研究表明,实验合成了直径为50～200nm、长度为十几微米到几十微米的钛酸钠纳米线,并通过对微观结构的分析,初步确定其分子式为Na2Ti3O7,钛酸钠纳米线经过氢离子和镧离子进行离子交换并高温烧结得到了TiO2纳米线和La3+/TiO2纳米线;钛酸钠纳米线对甲基橙溶液几乎没有光催化降解作用,而TiO2纳米线具有较高的光催化活性,其中样品La3+/TiO2纳米线光催化性能最强。     

Structural,optical and electrical properties of ion beam irradiated cadmium selenate nanowires

Present study is related to the synthesis of cadmium selenate nanowires via template-assisted electrodeposition approach and their characterization before and after lithium (Li³⁺) ion beam irradiation. Energy-dispersive X-ray analysis and X-ray diffraction study confirmed the synthesis of cadmium selenate nanowires with monoclinic structure. Electrical properties were examined with current–voltage (I–V) source meter using two-probe method. The electrical conductivity augmentation was perceptible for semiconducting nanowires with the increase in the ion beam fluence. The band gap of pristine nanowires was found to be 1.96 eV, while the red shift was observed in the optical band gap of ion irradiated nanowires and it approaches to the value of 1.31 eV at last fluence. In XRD spectra, no evidence was found of phase change or shifting in ‘2θ’ position or evolution of any new peak. However, variation in the peak intensities was noticed that could be the result of movement of plane orientation. This study revealed that the defects induced by the ion irradiation and variation in potential gradient with fluence plays a major role in the alteration of the optical and electrical properties of the semiconducting nanowires.     

Structural and optical properties of individual GaP/ZnO core–shell nanowires

Structural and optical properties of ZnO–GaP core–shell nanowires were studied by means of electron microscopy and microphotoluminescence. A thin ZnO shell layer was deposited by RF sputtering on GaP nanowires, which were grown on GaP (111)B substrates under vapour–liquid–solid mode by MOVPE. The SEM and TEM characterization showed that the ZnO shells fully covered the surface of the NWs from top to bottom. Each GaP NW core is composed of many well-defined twinned segments with the planes of twinning oriented in perpendicular to the growth direction. This was contradicted in kinked GaP NWs: their growth direction was initially perpendicular to the twinning planes, but once the NW had kinked, it changed to lie within the twinning planes. The ZnO shell deposited on the GaP core has a columnar morphology. The columns are inclined at a positive angle close to 70° with respect to the GaP growth axis. All observed columns were tilted at this angle to the growth direction. Micro-photoluminescence study showed that thermal annealing improved the quality of the ZnO crystallographic structure; the annealing made observable the photoluminescence peak related to the band-to-band transition in ZnO.