Effects of hydrogen flow on properties of hydrogen doped ZnO thin films prepared by RF magnetron sputtering

The hydrogen doped ZnO (ZnO:H) thin films were deposited on quartz glass substrates by radio frequency magnetron sputtering. The doping characteristics of ZnO:H thin films with varied hydrogen flow ratio were investigated. At low hydrogen flow ratio (H₂/(H₂+Ar)≤0.02), the ZnO:H thin films exhibited dominant (002) peaks from X-ray diffraction and the lattice constants became smaller. The particles were mainly a columnar structure. The particles’ size became smaller, and the island-like structure appeared on the thin films surface. In addition, the low resistivity properties of ZnO:H thin films was ascribed to the increase of the carriers concentration and carriers mobility; When the hydrogen flow ratio was more than 0.02 (M≥0.02), two absorption bands at 1400–1800 cm^?1 and 3200–3900 cm^?1 were observed from the FT-IR spectra, which indicated that the ZnO:H thin films had typical Zn–H bonding, O–H bonding (hydroxyl), and Zn–H–O bonding (like-hydroxyl). The scanning electron microscope (SEM) results show that a large number of hydroxyl agglomeration formed an island-like structure on the thin films surface. The absorption peak at about 575 cm^?1 in the Raman spectra indicated that oxygen vacancies (V_O) defects were produced in the process of high hydrogen doping. In this condition, the low resistivity properties of ZnO:H thin films were mainly due to the increasing electron concentration resulted from V_O. Meanwhile, the Raman absorption peaks at approximately 98 cm^?1 and 436 cm^?1 became weaker, and the (002) XRD diffraction peak quenched and the lattice constants increased, which shows that the ZnO:H thin films no longer presented a typical ZnO hexagonal wurtzite structure. With the increasing of hydrogen flow ratio, the optical transmittance of ZnO:H thin films in the ultraviolet band show a clear Burstein–Moss shift effect, which further explained that electron concentration was increased due to the increasing V_O with high hydrogen doping concentration. Moreover, the optical reflectance of the thin films decreased, indicating the higher roughness of the films surface. It was noteworthy that etching effect of H plasma was obvious in the process of heavy hydrogen doping.     

磁控共溅射法制备的Zn2GeO4多晶薄膜结构及其光致发光研究

用射频磁控共溅射方法在不同温度的单晶硅基片上生长薄膜,然后在800℃真空环境下对薄膜进行退火处理,成功获得了结晶状态良好的Zn₂GeO₄多晶薄膜.利用X射线衍射(XRD),X射线光电子能谱(XPS)和原子力显微镜(AFM)对薄膜进行了结构、成分和形貌分析,研究了基片温度对三者的影响. 结果显示,当基片温度升高到400℃以上时,薄膜中的Zn₂GeO₄晶粒在(220)方向上显示出了明显的择优取向. 当基片温度在500—600℃范围内,有利于GeO₂结晶相的形成. XPS显示薄膜中存在着Zn₂GeO₄,GeO₂,GeO,ZnO四种化合态. 同时,随着基片温度的升高,晶粒尺寸增大且薄膜表面趋于平整. 薄膜的光致发光在绿光带存在中心波长为530和550nm两个峰,应该归因于主体材料Zn₂GeO₄中两个不同的Ge²⁺的发光中心. 关键词： 射频磁控溅射 2GeO₄')" href="#">Zn₂GeO₄ 荧光体     

Influence of annealing temperature on the photoluminescence property of ZnO thin film covered by TiO2 nanoparticles

In this work, ZnO thin films covered by TiO₂ nanoparticles (labeled as TiO₂-ZnO thin films) were prepared by electron beam evaporation. The influence of annealing temperature on the photoluminescence property of the samples was studied. The structures and surface morphologies of the samples were analyzed by X-ray diffraction (XRD) and atomic force microscope, respectively. The photoluminescence was used to investigate the fluorescent properties of the samples. The measurement results show that the ultraviolet emission of ZnO thin films is largely enhanced after they are covered by TiO₂ nanoparticles, while the green emission is suppressed. However, when the annealing temperature is relatively high (≥500 °C), the intensity of ultraviolet emission drops off and a violet emission peak along with a blue emission peak appears. This is probably connected with the atomic interdiffusion between TiO₂ nanoparticles and ZnO thin film. Therefore, selecting a suitable annealing temperature is a key factor for obtaining the most efficient ultraviolet emission from TiO₂-ZnO thin films.     

Effects of hydrogen flux on the properties of Al-doped ZnO films sputtered in Ar + H2 ambient at low temperature

Al-doped ZnO (AZO) transparent conductive thin films were grown by magnetron sputtering with AZO (98 wt.% ZnO, 2 wt.% Al₂O₃) ceramic target in Ar + H₂ ambient at a relatively low temperature of 100 °C. To investigate the dependence of crystalline and properties of as-grown AZO films on the H₂-flux, X-ray diffraction (XRD), X-ray photoemission spectrometer (XPS), Hall and transmittance spectra measurements were employed to analyze the AZO samples deposited with different H₂-flux. The results indicate that H₂-flux has a considerable influence on the transparent conductive properties of AZO films. The resistivity of 4.15 × 10⁻⁴ Ω cm and the average transmittance of more than 94% in the visible range were obtained with the optimal H₂-flux of 1.0 sccm. Such a low temperature growing method present here may be especially useful for some low-melting point photoelectric devices and substrates.     

The location of excess electrons on H2O/TiO2(110) surface and its role in the surface reactions

Excess electrons play a key role in many of the properties of Titanium dioxide (TiO₂). Understanding their behaviour is important for improving the performance of TiO₂ in energy-related applications. Here, we describe a DFT + U study of the locations of the unpaired electron (UPE) on rutile TiO₂(110) (R-TiO₂(110)) surface and H₂O/R-TiO₂(110) surface. Our results show that the subsurface are preferred with R-TiO₂(110) surface. In contrast to previous studies, we find that the UPE tends to migrate to the surface H₂O-Ti_5c (the five-coordinated titanium (Ti_5c) at surface with H₂O adsorption) with the increasing of H₂O coverage and UPE concentration. In addition, we have shown that the UPE plays an important role in the O-H bond dissociation and other important elementary reactions in photo-catalytic H₂O dissociation on R-TiO₂(110) such as H, OH and H₂ desorption. Specifically, it enhances the O-H bond dissociation, as well as H and H₂ desorption from bridging hydroxyl and Ti_5c-OH (the Ti_5c with OH adsorption), but hinders the OH and H desorption from Ti_5c. We believe our results afford a further understanding of the adsorbent dependent UPE migration, and the role of UPE in the surface reactions.     

Conversion of p-type to n-type conductivity in undoped ZnO films by increasing operating temperature

ZnO thin films with the thickness of about 15 nm on (0 0 0 1) sapphire substrates were prepared by pulsed laser deposition. X-ray photoelectron spectroscopy indicated that both as-grown and post-annealed ZnO thin films were oxygen-rich. H₂ sensing measurements of the films indicated that the conductivity type of both the unannealed and annealed ZnO films converted from p-type to n-type in process of increasing the operating temperature. However, the two films showed different conversion temperatures. The origin of the p-type conductivity in the unannealed and annealed ZnO films should be attributed to oxygen related defects and zinc vacancies related defects, respectively. The conversion of the conductivity type was due to the annealing out of the correlated defects. Moreover, p-type ZnO films can work at lower temperature than n-type ZnO films without obvious sensitivity loss.     

Structural properties of Al2O3 dielectrics grown on TiN metal substrates by atomic layer deposition

We investigated on the structural properties of Al₂O₃ dielectrics grown on TiN metal substrates using an atomic layer deposition technique with tri-methyl-aluminum and either O₃ or H₂O as the precursor and oxidant, respectively. The structural and morphological features of these films were examined by atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements. We find that Al₂O₃ dielectric films with the O₃ oxidant exhibit a rough morphology, a thick TiO₂ film, and a small amount of contaminants such as carbon and hydrogen. The reason for the rapid diffusion of oxygen atoms into the TiN lattice leads to the formation of TiO₂ layer on the TiN substrate. This is due to the higher oxidation potential of the O₃ compared to the H₂O.     

(TiO2)n(n=3—6)团簇吸附水分子的理论研究

给出了优化小分子在团簇表面吸附结构的遗传算法.结合经验势函数,搜寻了水分子在(TiO₂)_n(n=3—6)团簇上可能的吸附方式;利用B3LYP/6-31G^**方法对各种吸附结构进行了优化.结果表明水分子主要通过O原子以非解离方式吸附到团簇中配位数较低或位置比较凸出的Ti原子上.分子轨道分析表明,水分子与团簇之间的成键主要来自吸附位Ti原子3s3p轨道的贡献,水分子的轨道保持了气相水分子中的基本特征,但离域化程度增大 关键词： 2团簇')" href="#">TiO₂团簇 2O吸附')" href="#">H₂O吸附 遗传算法 DFT     

原位氧化Zn3N2制备p型ZnO薄膜的性能研究

采用射频反应溅射法在玻璃衬底上制备Zn₃N₂薄膜，然后向真空室中通入纯氧气进行热氧化制备ZnO薄膜.利用X射线衍射、扫描电子显微镜、霍尔效应测量、透射光谱和光致发光光谱等表征技术，研究了氧化温度和氧化时间对ZnO薄膜的结晶质量、电学性质和光学性能的影响.研究结果显示，450 ℃ 下氧化2 h后的样品中除含有ZnO外，还有Zn₃N₂成分，500 ℃下氧化2 h可以制备出电阻率为0.7 Ωcm，空穴载流子浓度为10^{关键词： p型ZnO薄膜 3N₂薄膜')" href="#">Zn₃N₂薄膜 射频溅射 原位氧化}     

Investigation of structural and magnetic properties of Ni, NiFe and NiFe2O4 thin films

Soft magnetic thin films of Ni, NiFe and NiFe₂O₄ were prepared using reactive magnetron sputtering in various deposition conditions. Experimentally observed soft magnetic property was compared and correlated with nanocrystalline structure evolution. Ni and NiFe deposited films are textured with fcc(111) phase preferred orientation. Accordingly, grain size and lattice parameter were calculated from X-ray diffraction (111) peak line width and 2θ peak position. Addition of reactive gas oxygen in deposition process has substantial effect on crystalline structure of film. There is phase transition from the ordered NiFe (111) structure to the NiFe₂O₄ nanocrystalline phase. The resulting film has shown small X-ray diffraction intensity peak corresponding to (311) and (400) orientation, indicating small amount of existing NiFe₂O₄ phase. The mechanism has been discussed to be responsible for nanocrystallization and amorphization of NiFe₂O₄ films. Magnetic measurement (M-H) loop reveal soft magnetic nature of films with magnetic anisotropy. The coercivity (H_c) of films is in accordance with random anisotropy model, where H_c reduced with grain size. The structural transformation was supported by Fourier transforms infrared spectroscopy measurement. The films are highly smooth with surface roughness in the range of ∼0.53-0.93 nm. NiFe₂O₄ films have shown lowest surface roughness with highest electrical resistivity values. The structural, surface, magnetic and infrared spectroscopy results are observed and analyzed.     

Synthesis,structural and ellipsometric evaluation of oxygen-deficient and nearly stoichiometric zinc oxide and indium oxide nanowires/nanoparticles

Oxygen-deficient (OD) and nearly stoichiometric (NST) ZnO and In₂O₃ nanowires/nanoparticles were synthesized by chemical vapor deposition on Au-coated silicon substrates. The OD ZnO and OD In₂O₃ nanowires were synthesized at 750 and 950°C, respectively, using Ar flow at ambient pressure. A mixture of flowing Ar and O₂ was used for synthesizing NST ZnO nanowires and NST In₂O₃ nanoparticles. Growth of OD ZnO nanowires and NST In₂O₃ nanoparticles was found to be via a vapor–solid (VS) mechanism and the growth of NST ZnO nanowires was via a vapor–liquid–solid mechanism (VLS). However, it was uncertain whether the growth of OD In₂O₃ nanowires was via a VS or VLS mechanism. The optical constants, thickness and surface roughness of the prepared nanostructured films were determined by spectroscopic ellipsometry measurements. A three-layered model was used to fit the calculated data to the experimental ellipsometric spectra. The refractive index of OD ZnO, NST ZnO nanowires and NST In₂O₃ nanoparticles films displayed normal dispersion behavior. The calculated optical band gap values for OD ZnO, NST ZnO, OD In₂O₃ nanowires and NST In₂O₃ nanoparticles films were 3.03, 3.55, 2.81 and 3.52?eV, respectively.     

Influence of growth temperature of TiO2 buffer on structure and PL properties of ZnO films

A series of ZnO films with TiO₂ buffer on Si (1 0 0) substrates were prepared by DC reactive sputtering. Growth temperature of TiO₂ buffer changed from 100 °C to 400 °C, and the influence on the crystal structures and optical properties of ZnO films have been investigated. The XRD results show that the ZnO films with TiO₂ buffer have a hexagonal wurtzite structure with random orientation, and with the increase of growth temperature of TiO₂ buffer, the residual stresses were released gradually. Specially, the UV emission enhanced distinctly and FWHMs (full width half maximum) decreased linearly with the increasing TiO₂ growth temperature. The results all come from the improvement of crystal quality of ZnO films.     

氢气引入对宽光谱Mg和Ga共掺杂ZnO透明导电薄膜的特性影响

为适应宽光谱高效率硅基薄膜太阳电池的应用需求,本文尝试采用直流磁控溅射技术在553 K衬底温度下生长氢化Mg和Ga共掺杂ZnO(HMGZO)透明导电氧化物(TCO)薄膜.通过对薄膜微观结构、表面形貌、电学以及光学性能的测试和分析,详细地研究了氢气(H2)流量(0—16.0 sccm)对HMGZO薄膜结晶特性及光电性能的影响.实验结果表明:生长获得的HMGZO薄膜均为六角纤锌矿结构的多晶薄膜,择优取向为(002)晶面生长方向.薄膜的生长速率随着氢气流量的增加呈现逐渐减小趋势,主要归因于溅射产额的减小.适当的氢气引入会引起晶粒尺寸的增加.随着氢气流量由0增加至4.0 sccm,ZnO薄膜电阻率从177?·cm急剧减小至7.2×10-3?·cm,主要是由于H施主的引入显著地增加了载流子浓度;然而进一步增加氢气流量(4.0—16.0 sccm)造成电阻率的轻微增加,主要归因于载流子浓度的减小以及过多氢杂质引入造成杂质散射的增加.所有生长获得的HMGZO薄膜平均光学透过率在波长λ～320—1100 nm范围内可达87%以上.由于Mg的作用及Burstein-Moss效应的影响造成了带隙展宽,带隙变化范围～3.49—3.70 eV,其中最大光学带隙Eg可达～3.70 eV.     

Controlling the orientation of ZnO nanorod arrays using TiO<Subscript>2</Subscript> thin film templates dip-coated by sol–gel

The oriented ZnO nanorod arrays have been synthesized on a silicon wafer that coated with TiO₂ films by aqueous chemical method. The morphologies, phase structure and the photoluminescence (PL) properties of the as-obtained product were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and PL spectrum. The nanorods were about 100 nm in diameter and more than 1 μm in length, which possessed wurtzite structure with a c axis growth direction. The room-temperature PL measurement of the nanorod arrays showed strong ultraviolet emission. The effect of the crystal structure and the thickness of TiO₂ films on the morphologies of ZnO nanostructures were investigated. It was found that the rutile TiO₂ films were appropriate to the oriented growth of ZnO nanorod arrays in comparison with anatase TiO₂ films. Moreover, flakelike ZnO nanostructures were obtained with increasing the thickness of anatase TiO₂ films.     

Temperature dependence and the effect of hydrogen peroxide on ITO/poly-ZnO Schottky diodes fabricated by laser evaporation

Transparent and efficient poly-ZnO ultraviolet Schottky diodes grown at different temperatures with indium-tin-oxide (ITO) as the metallic contact layer were fabricated with hydrogen peroxide (H₂O₂) applied as a surface treatment at 70 °C for 20 min. Analysis via field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) demonstrated that the ZnO films underwent gradual oxidation and that H₂O₂ treatment resulted in an interfacial ZnO₂ layer that covered the ZnO surface. I–V measurements indicated that the ideality factor and the Schottky barrier height improved with increasing shunt resistance, and the trade-off between film quality and the degree of oxidation revealed that films grown at 400 °C exhibited the best diode characteristics.     

温度对ZnO/Al2O3(0001)界面的吸附、扩散及生长初期模式的影响

构建了一个ZnO沉积在α-Al₂O₃(0001)表面生长初期的模型，采用基于密度泛函理论的平面波超软赝势法进行了动力学模拟.发现在400，600和800℃的条件下界面原子有不同的扩散能力，因此温度对ZnO/α-Al₂O₃(0001)表面界面结构以及ZnO薄膜生长初期模式有决定性的影响.在整个ZnO吸附生长过程中，O原子的扩散系数大于Zn原子的扩散系数，O原子的层间扩散对薄膜的均匀生长起着重要作用.进一步从理论计算上证实了ZnO在蓝宝石(0001)上两种生长模式的存在，400℃左右生长模式主要是Zn螺旋扭曲生长，具有Zn六角平面对称特征，且有利于Zn原子位于最外表面.600℃左右呈现为比较规则的层状生长，且有利于O原子位于最外表面.模拟观察到在ZnO薄膜临近Al₂O₃基片表面处，Zn的空位缺陷明显多于O的空位缺陷. 关键词： 扩散 薄膜生长 2O₃(0001)')" href="#">α-Al₂O₃(0001) ZnO     

Core/shell structured ZnO/SiO2 nanoparticles: Preparation, characterization and photocatalytic property

ZnO nanoparticles were prepared by a simple chemical synthesis route. Subsequently, SiO₂ layers were successfully coated onto the surface of ZnO nanoparticles to modify the photocatalytic activity in acidic or alkaline solutions. The obtained particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS) and zeta potential. It was found that ultrafine core/shell structured ZnO/SiO₂ nanoparticles were successfully obtained. The photocatalytic performance of ZnO/SiO₂ core/shell structured nanoparticles in Rhodamine B aqueous solution at varied pH value were also investigated. Compared with uncoated ZnO nanoparticles, core/shell structured ZnO/SiO₂ nanoparticles with thinner SiO₂ shell possess improved stability and relatively better photocatalytic activity in acidic or alkaline solutions, which would broaden its potential application in pollutant treatment.     

Preparation of TiO2 thin films from autoclaved sol containing needle-like anatase crystals

A new inorganic sol-gel method was introduced in this paper to prepare TiO₂ thin films. The autoclaved sol with needle-like anatase crystals was synthesized using titanyl sulfate (TiOSO₄) and peroxide (H₂O₂) as starting materials. The transparent anatase TiO₂ thin films were prepared on glass slides from the autoclaved sol by sol-gel dip-coating method. A wide range of techniques such as Fourier transform infrared transmission spectra (FT-IR), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), scanning electron microscopes, X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectrum were applied to characterize the autoclaved sol and TiO₂ thin films. The results indicate that the autoclaved sol is flavescent, semitransparent and stable at room temperature. The anatase crystals of TiO₂ films connect together to form net-like structure after calcined and the films become uniform with increasing heating temperature. The surface of the TiO₂ films contain not only Ti and O elements, but also a small amount of N and Na elements diffused from substrates during heat treatment. The TiO₂ films are transparent and their maximal light transmittances exceed 80% under visible light region.     

Site-blocking effects of preadsorbed H on Pt(1 1 1) probed by 1,3-butadiene adsorption and reaction

The influence of hydrogen coadsorption on hydrocarbon chemistry on transition metal surfaces is a key aspect to an improved understanding of catalytic selective hydrogenation. We have investigated the effects of H preadsorption on adsorption and reaction of 1,3-butadiene (H₂CCHCHCH₂, C₄H₆) on Pt(1 1 1) surfaces by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Preadsorbed hydrogen adatoms decrease the amount of 1,3-butadiene chemisorbed on the surface and chemisorption is completely blocked by the hydrogen monolayer (saturation) coverage (θ_H = 0.92 ML). No hydrogenation products of reactions between coadsorbed H adatoms and 1,3-butadiene were observed to desorb in TPD experiments over the range of θ_H investigated (θ_H = 0.6-0.9 ML). This is in strong contrast to the copious evolution of ethane (CH₃CH₃, C₂H₆) from coadsorbed hydrogen and ethylene (CH₂CH₂, C₂H₄) on Pt(1 1 1). Hydrogen adatoms effectively (in a 1:1 stoichiometry) remove sites from interaction with chemisorbed 1,3-butadiene, but do not affect adjacent sites. The adsorption energy of coadsorbed 1,3-butadiene is not affected by the presence of hydrogen on Pt(1 1 1). The chemisorbed 1,3-butadiene on hydrogen preadsorbed Pt(1 1 1) completely dehydrogenates to H₂ and surface carbon upon heating without any molecular desorption detected, which is identical to that observed on clean Pt(1 1 1). In addition to revealing aspects of site blocking that should have broad implications for hydrogen coadsorption with hydrocarbon molecules on transition metal surfaces in general, these results also provide additional basic information on the surface science of selective catalytic hydrogenation of butadiene in butadiene-butene mixtures.     

Characterization of ZnO thin films grown on various substrates by RF magnetron sputtering

In this study we investigated properties of ZnO thin films deposited on both oxygen-containing substrates and a substrate without oxygen content at various O₂/Ar reactant gas ratios. Deposition of ZnO on indium-tin oxide (ITO) resulted in the best crystallinity, whereas the least degree of crystallization was observed from ZnO deposited on glass. All the films were found to have compressive stress, which was relieved by annealing in O₂ environment. ZnO films deposited on glass revealed p-type conductivity when prepared at O₂/Ar ratio of 0.25 whereas those on SiN_x yielded p-type conductivity when prepared at O₂/Ar ratio of 4. In addition, shallower oxygen interstitial seemed to be found from films with better crystallinity. The largest shift in binding energy of Zn_2p3/2 was observed from ZnO prepared on glass at O₂/Ar ratio of 0.25, whereas that of O_1s was obtained from ZnO deposited on SiN_x at O₂/Ar ratio of 4. A model was proposed in terms of O₂ diffusion and hydrogen desorption in order to account for the observed property variations depending on substrates and O₂/Ar ratios.