ZnO films grown on cotton fibers surface at low temperature by a simple two-step process

Zinc oxide (ZnO) films have been synthesized and deposited onto cotton fiber surface using a simple two-step process. At first step, the cotton fiber surface was coated with a conductive layer of zinc-cellulose complex by rinsing the fibers in zinc chloride solution. After that, the growth of ZnO films was carried out in zinc acetate aqueous solution at room temperature, with alkaline aqueous solution drops continuously added under magnetic stirring. The morphology of the as-prepared ZnO-coated cotton fibers was characterized by scanning electron microscopy. Infrared and photoluminescence spectra were used to confirm the existence of ZnO. In addition, the formation mechanism of ZnO-coated cotton fibers is discussed in detail.     

纳米ZnO低温脱除H2S工艺条件的研究

采用均匀沉淀法制备纳米ZnO,以其作为低温脱除H2S的活性组分,考察了纳米ZnO粒径、空速、反应温度、氧分压等因素对纳米ZnO脱硫性能的影响,并对脱硫剂的结构进行了表征.结果表明:在常压、低温、氧分压较低的条件下,粒径越小脱硫性能越强,260℃焙烧制得的纳米ZnO脱硫剂具有高的脱硫活性,H2S可选择性地被氧化为单质S,转化率高达100%,脱硫活性时间是分析纯ZnO的40倍.尾气中未见SO2产生.     

Pressure dependence and micro-hillock formation of ZnO thin films grown at low temperature by MOCVD

ZnO thin films were grown at a reduced growth temperature on a Si substrate by low-pressure metalorganic chemical vapor deposition. The effects of the reactor pressures and the formation of micro-hillocks on the characteristics of the film were investigated. The ZnO films grown at 210 °C showed mass-transport limited growth behavior and a faceted surface morphology. It was found that the effect of the micro-hillocks on the structural, optical, and electrical properties can be ignored. While the sample grown at 10 Torr showed transparent conductive oxide properties, the sample grown at 3 Torr showed suitable characteristics for use as an ultraviolet emitter.     

Indium doped ZnO films prepared by RF magnetron sputtering: effect of substrate temperature on the strain-induced band gap

Indium doped zinc oxide (InZnO) thin films were deposited onto corning glass substrates by RF magnetron sputtering. The dependence of crystal structure, surface morphology, optical properties and electrical conductivity on substrate temperature was investigated using XRD, AFM, UV-vis Spectrophotometer, Fluorescence Spectrophotometer and four-point probe. The films were prepared at different substrate temperatures viz, room temperature (RT), 473 K and 673 K at RF power 200 W. All the films showed preferred orientation along (002) direction. Crystallite size increased from 14 to 19 nm as the substrate temperature was increased to 473 K. With increase in substrate temperature the crystallites did not show any further growth. AFM analysis showed that the rms roughness value decreased from 60 nm to 23 nm when the substrate temperature was increased to 673 K. Optical measurements revealed maximum band gap and minimum refractive index for the film prepared at 473 K. A strong correlation between the band gap variation and the strain developed at different substrate temperatures is established.     

Room temperature paramagnetism of ZnO:Mn films grown by RF-sputtering

ZnO:Mn transparent thin films (thickness < 1 μm) with the Mn contents ranging from 1.8 to 3.25 at.% were grown by RF magnetron co-sputtering. The films are nanocrystalline, with wurtzite-structure grains of a typical size of 20 nm and with a preferential orientation of the c-axis perpendicular to the surface. According to the Raman spectroscopy data, Mn mostly substitutes Zn in the lattice sites. In spite of these factors, the nanostructure and the Mn(Zn) substitution, that are considered favorable for ferromagnetism in this material, both magnetic resonance and Faraday effect measurements show paramagnetic behavior of the ZnO:Mn films and the absence of ferromagnetic order at room temperature.     

Low temperature annealing effects on the structure and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on glass substrates at room temperature (RT) ∼500 °C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 °C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments; the grain size increased and stress relaxed for the films deposited at 200-500 °C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E_g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 °C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.     

Solution grown nanocrystalline ZnO thin films for UV emission and LPG sensing

Nanocrystalline ZnO thin films were successfully deposited by a simple and inexpensive solution growth technique. Photoluminescence (PL) and liquefied petroleum gas (LPG) sensing properties were investigated. Films were found to be uniform, pinhole free, and well adherent. As deposited and heat treated (at 673 K for 2 h) films were characterized by XRD, SEM, and EDAX. The dc electrical resistivity and LPG sensing property were measured. The change in morphology, from spherical particle to rod-like, was observed after air annealing. XRD results revealed that the obtained films were nanocrystalline and had a hexagonal wurtzite structure. The absorption edge was found to be at around 366 nm for the as-deposited film and 374 nm for the annealed film. The band gaps were found to be 3.29 and 2.9 eV for the as-deposited and annealed films, respectively. PL spectra of ZnO thin films showed strong peak at 384 nm, which corresponds to near band edge emission (UV emission) and a relatively weak peak at 471 nm. Further, the annealed film was used for detection of LPG in air. Maximum response was observed at 673 K. The maximum sensitivity of sensor was found to be 4.5 for 0.6 vol.% LPG. Sensing response got saturated after 0.6 vol.% of gas concentration. A possible mechanism of LPG sensing has been explained.     

Synthesis and optical characterization of ZnO and ZnO:Al nanocrystalline films obtained by the sol-gel dip-coating process

Zinc oxide is obtained by the sol-gel process. The precursor solution was deposited on quartz substrates by dip-coating. The as-deposited films are transformed into nanocrystalline pure or aluminium-doped ZnO after thermal treatment. The microstructure was studied by X-ray diffraction and the nanocrystallite size was estimated using Scherrer equation. The optical transmittance in the visible region is between 83 and 91%. A direct absorption edge is observed with bandgap energies between 3.27 and 3.31 eV for the undoped samples, and between 3.30 and 3.35 eV for the Al doped ZnO. These values correlate well with the nanocrystal sizes following two different laws for the undoped and doped samples, due to Moss-Burstein shift. The visible transmittance also increases for higher bandgap energies. The UV transmittance is greater than 50% due to the small thickness of the films, which for the undoped samples is proportional to the number of layers.     

Laser annealing of photoluminescent ZnO nanorods grown at low temperature

We report on pulsed laser annealing as an efficient method for improving the structural and optical properties of ZnO nanorods grown at low temperature. We find that the excitonic luminescence at 390 nm can be improved by as much as a factor of 8. We also show that laser annealing can be carried out in typical device structures, in particular by illumination through glass/indium-tin-oxide substrates and through polymer/indium-tin-oxide substrates.     

Electrical properties of diamond films grown at low temperature

The unique electronic properties of diamond, associated with the emergence of chemical vapour deposition (CVD) methods for the growth of thin films on non-diamond substrates, have led to considerable interest in electronic devices fabricated from this material. In our previous work, we found that polycrystalline diamond films can be deposited at 250 °C using CH₄---CO₂ gas mixtures. Studying the electrical properties and the upcoming problems of applications of low-temperature diamond films are relevant concerns.

In this work, the electrical properties of diamond films grown at low temperatures were studied and compared with those of conventional diamond films. Platinum was used as the upper electrode. The resistivity of low-temperature diamond was around three orders of magnititude lower than that of conventional diamond. However, both the low temperature and conventional growth diamond exihibited rectifying behavior when platinum was used as the upper electrode.     

Humidity sensing behaviors of nanocrystalline Al-doped ZnO thin films prepared by sol–gel process

Nanocrystalline Al-doped ZnO(AZO) thin films prepared by sol–gel method were used for studying the variation of resistance with humidity. The particle size of the films exhibits nanometer order with zincite structure and the thickness of the films increases linearly with the number of coatings. The AZO film coated five times and annealed at 500 °C exhibits the highest sensitivity for the humidity, which shows three order change in the resistance during the relative humidity variation from 20 to 90%. It is considered that the high humidity sensitivity is due to proton hopping between water molecules adsorbed on the film surfaces with capillary nanopores.     

ZnO缓冲层上低温生长Al掺杂的ZnO薄膜

采用射频磁控溅射法在ZnO缓冲层上制备了不同Al掺杂量的ZnO（AZO）薄膜。利用X射线衍射（XRD）、扫描电子显微镜（SEM）和光致发光（PL）等表征技术,研究了AZO薄膜的微观结构、表面形貌和发光特性。结果表明,随着Al掺杂量的增加,ZnO薄膜的择优取向性发生了改变,且当Al的掺杂量为0.81%（原子分数）时,（002）衍射峰与其它衍射峰强度的比值达到最大,表明适合的Al掺杂使ZnO薄膜的择优取向性得到了改善。在可见光范围内薄膜的平均透过率超过70%。通过对样品光致发光（PL）谱的研究,发现所有样品出现了3个发光峰,分别对应于以444nm（2.80eV）、483nm（2.57eV）为中心的蓝光发光峰和以521nm（2.38eV）为中心较弱的绿光峰。并对样品的发光机理进行了详细的探讨。     

Augmentation of band gap and photoemission in ZnO by Li doping

The monovalent impurity Lithium is chosen to dope with Zinc oxide (ZnO) in four concentrations by auto-combustion route. The influence of Li on the structural and optical properties of ZnO are discussed. The Li incorporation happens both as substitution and interstitial doping with an increase of grain size and the optical band gap of ZnO. The optical phonon modes are identified from Raman spectra that also gives information about the stress in the samples. The UV and visible emission characteristics of the samples are found from the fluorescence spectra. The origin of the visible emission is explained by defect chemistry. When Li lodges Zn site new acceptor levels of Li are created that causes the yellow emission that is absent in undoped ZnO. Li interstitial creates Zn interstitials that are responsible for blue emission. The green emission is explained as the outcome of the transition between Zn_i and oxygen vacancies.     

The effects of buffer growth parameters on heteroepitaxial ZnO films grown by pulsed laser deposition

The effects of buffer layer deposition conditions on subsequent ZnO epitaxy on sapphire (0001) were examined. An initial ZnO buffer layer improves surface roughness for a wide range of buffer layer growth temperatures and pressures. Changes in buffer layer growth pressure and temperature have a moderate effect on the roughness of subsequent film growth. However, the conditions for buffer layer deposition have a large impact on crystallinity of subsequent films. In particular, the out-of-plane X-ray diffraction rocking curve full-width half-maximum decreased as buffer deposition temperature or O₂/O₃ pressure increases. Carrier mobility in the subsequent thick ZnO film was enhanced with increase in buffer layer deposition temperature. Carrier concentration decreased with increasing buffer layer deposition pressure.     

Tuning the band gap of ZnO nanoparticles by ultrasonic irradiation

In this present paper, we report the tunability of ZnO nanoparticles by ultrasonic irradiation. Different sized ZnO nanoparticles viz. 2.58–2.97 nm have been synthesized with variation of ultrasonic irradiation time 75–270 min in presence of Histidine as capping agent. UV and visible spectroscopy study revealed that as ultrasonic irradiation time increases, there is increase in amount of formed ZnO nanoparticles and also there is red shift in absorption edge. This confirms the tunability of bandgap of histidine capped ZnO nanoparticles with ultrasonic irradiation. Growth mechanism for controlling the size of ZnO nanoparticles are also discussed.     

Growth and characterization of ZnMgSrO thin films lattice-matched to ZnO and with deep-UV energy band gap

Quaternary Zn_1-x-yMg_xSr_yO films were grown and characterized in detail, which were observed to be lattice matched to the ZnO by the X-ray diffraction (XRD). Cathodoluminescence measurement showed that near-band UV emission peaks of the samples move toward higher energy as concentration of Mg and Sr increases, to 3.67 eV for the Zn_0.87Mg_0.08Sr_0.05O and to 4.02 eV for the Zn_0.72Mg_0.17Sr_0.11O. It was also observed by the scanning electron microscopy and the XRD that the films are single crystalline. It is believed that the ZnMgSrO films would be one of the important candidate materials for the high quality deep-UV optoelectronic devices.     

Study on ZnO thin films deposited on sol-gel grown ZnO buffer by RF magnetron sputtering

ZnO thin films with preferential C-orientation and dense microstructure have been prepared using RF magnetron sputtering method by the insertion of a sol-gel grown ZnO buffer layer. The XRD results show that the C-orientation of the film deposited on ZnO buffer is obviously better than that deposited directly on lime-glass substrate. With an increase of the RF power from 100 to 380 W, C-orientation of the films with ZnO buffer improves and the grain size increases. When the RF power equals 550 W, the orientation of the film changes to (1 0 0) and the grain size decreases. The crystalline and microstructure quality of the films can be improved after annealing, however, the grain size is not much dependent on the annealing temperature in the range of 560-610 °C.     

Composition of alumina films grown on Si at low temperature with catalytic CVD

The X-ray photoelectron spectroscopy (XPS) measurements have been used to reveal the compositions of alumina (Al₂O₃) films formed on Si wafers using tri-methyl aluminium (TMA) and molecular oxygen (O₂) with catalytic chemical vapour deposition (Cat-CVD). The atomic ratio (O/Al) for Al₂O₃ samples formed at substrate temperature of 200-400 °C has been obtained to be 1.4 which is close to stoichiometry. The increase of growth rate at substrate temperatures below 200 °C and above 400 °C can be attributed to formation of aluminum oxides with non-stoichiometry and metallic aluminum incorporated in the films resulting from deficient oxygen. Angle resolved XPS measurements have revealed that the alumina/Si interface with no SiO₂ film has been obtained at substrate temperatures below 200 °C.     

Synthesis and characterization of ZnO nano and micro structures grown by low temperature spray pyrolysis and vapor transport

In this work we present a systematic study of ZnO micro and nanostructures grown by spray pyrolysis (SP) and by physical vapour transport (PVT) on glass and c-sapphire substrates at low temperatures. Optimised growth conditions have allowed to obtain homogeneous ZnO nanolayers composed of quasi-spherical nanoparticles in the range 2 to 8 nm by spray pyrolysis, while by PVT the selected growth conditions allow to produce a wide variety of morphologies (tripods, grains, arrows and wires) of nano and microsize dimension. Grazing incidence X-ray diffraction, field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) were used as characterization techniques in the investigation of structural, morphological and compositional nature of these nanostructures in relation with the growth method.