The effect of SiO2 on TiO2 up-conversion photoluminescence film

In order to increase the photoelectric conversion efficiency of silicon solar cell, the up-conversion film has been tried to enhance the response of the solar cells to the infrared band. Yb³⁺, Er³⁺ co-doped SiO₂/TiO₂ composite films with different Ti/Si molar ratio were deposited on the glass substrate with sol–gel method and spin-coating technique. The effect of different molar ratio of Ti/Si on the film’s morphology and optical properties was investigated. The morphology, the absorption spectra and photoluminescence (PL) spectra of the film were tested and analyzed. After the film was annealed at 900 °C, the XRD diffraction pattern indicated that rare earths ions have evenly dispersed into the matrix lattice. The FT-IR showed that Si ions entered into the lattice of titanium dioxide, and the Ti–O–Si bonds came into being. When the film pumped with a laser of 980 nm, there were a dominant red emission and several weak green peaks. In addition, with the increase of the mole ratio of Si/Ti, the intensity of the film’s up-conversion luminescence increases at first and then decreases. When the molar ratio of Si/Ti is 1/8, the sample had the highest intensity of up-conversion luminescence.     

Abnormal photoluminescence of ZnO thin film on ITO glass

The photoluminescence (PL) properties of ZnO thin films on ITO glass substrate deposited by rf magnetron sputtering with different oxygen partial pressures were studied. It was found that the exciton related emission of ZnO thin films depends on oxygen partial pressure, and that the visible emission related to intrinsic defects has no obvious change with various oxygen partial pressures. Abnormal UV-PL characteristics were observed, and its intensity was obviously enhanced. The emission position has a strong red-shift with increasing excitation intensity, and the emission intensity increases notably with increasing excitation cycle.     

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.     

Effect of annealing and hydrogen plasma treatment on the luminescence of hydrothermally grown bulk ZnO

The optical properties of hydrothermally grown bulk ZnO is investigated by low temperature photoluminescence (PL) spectroscopy. The effects of annealing in an argon atmosphere, as well as the influence of hydrogen plasma exposure, on the PL of as-grown material are studied. The 11 K PL spectrum of the as-grown ZnO shows different excitonic lines in the NBE region: several bound exciton lines are clearly visible. The origin of these bound excitons is discussed, as well as the influence of annealing on these lines. A shift in the deep level emission (DLE) is also observed with an increase in annealing temperature: a red shift is detected when the annealing temperature is increased up to 650 °C, while a subsequent blue shift is observed upon an increase in the annealing temperature. The involvement of Li and Cu in this phenomenon will be discussed and the effect of hydrogen on this DLE will also be studied.     

Effects of annealing on the photoluminescence of ZnSe nanorods coated with Au

Au-functionalized ZnSe nanorods were synthesized by the thermal evaporation of ZnSe powder followed by Au sputter-deposition and thermal annealing. Photoluminescence (PL) showed that the intensity of near-band edge (NBE) emission of ZnSe nanorods was enhanced remarkably by Au-coating and annealing in a H₂ atmosphere. The intensity ratio of NBE emission to the deep level emission, I_NBE/I_DL of Au-coated ZnSe nanorods after annealing in a H₂ atmosphere was ∼68 times higher than that of the pristine (unannealed, uncoated) ZnSe nanorods. The increase in I_NBE/I_DL might be due to a combination of carrier transfer from the defect level to the Fermi level of Au nanoparticles, surface plasmon resonance in Au nanoparticles and hydrogen passivated deep level defects.     

Fabrication of highly oriented (002) ZnO film on glass by sol-gel method

In this study high quality (002) ZnO films were deposited on glass substrate by a sol-gel spin coating process. The as-coated films were post-annealed at different temperatures in air to investigate the effect of annealing temperature in particular. The chemical composition of the precursor sol and the intermediates produced in the films heating process were analyzed by thermo gravimetric analysis/differential thermal analysis (TGA/DTA). The microstructure and its optical properties of ZnO films were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence. TGA/DTA showed that a significant weight loss occurred at around 200-300 °C and the weight stabilized at 300 °C. An extremely sharp (002) diffracted peak in XRD patterns indicated the high preference in crystallinity of these films. FESEM micrographs revealed that the films were filled with particulates with size ranging from 10 to 25 nm as post annealing temperature increased from 400 to 500 °C and turned into porous films at 600 °C. UV-Vis has shown that the films were highly transparent under visible light and had a sharp absorption edge in the ultraviolet region at 380 nm. The measured optical band gap values of the ZnO thin films were around 3.24-3.26 eV. Photoluminescence spectra revealed a strong UV emission centered at about 390 nm corresponding to the near-band-edge emission with a weak defect-related emission at about 520 nm. The intensity of UV emission increased with the annealing temperature. This may be attributed to a higher quality ZnO film while annealed at higher temperature.     

Effects of annealing temperature on the structure and photoluminescence properties of ZnO films

Zinc oxide (ZnO) films with c-orientation were deposited on Si (1 1 1) substrates at room temperature (RT) by RF-magnetron sputtering. Violet (394 and 412 nm) and green (560 and 588 nm) photoluminescence (PL) were observed from the as-deposited and annealed samples. The PL intensity was increasing with increasing annealing temperature (T_a). The 412 nm violet peak shifted from 412 to 407 nm and the 394 nm violet peak shifted from 394 to 399 nm on increasing the temperature from 500 to 900 °C, whereas no shift in PL green peaks was observed over the whole range of temperature examined. The 412 nm violet luminescence is ascribed to radiative defects related to the interface traps existing at grain boundaries. With the increase of T_a, the stress in the films changed from compressive to tensile, which is believed to have resulted in the observed 412 nm violet emission peak shifts from 412-407 nm. The 394 nm violet luminescence observed is attributed to free excitonic emission, and the increase of the crystal size may result in the 394 nm violet emission peak shifts from 394 to 399 nm. The other two PL bands located at 560 and 588 nm are attributed to oxygen deficiency.     

Effect of annealing temperature and composition on photoluminescence properties of magnetron sputtered SiCN films

Silicon carbonitride (SiCN) films were prepared by means of reactive magnetron sputtering of a sintered SiC target on n-type Si (1 0 0) substrates in the reactant gas of nitrogen, and then the films were respectively annealed at 600, 800 and 1100 °C for 5 min in nitrogen ambient. The films were characterized by energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectroscopy and photoluminescence (PL) spectrophotometry. Intense PL peaks at 370, 400 and 440 nm were observed at room temperature. The results show that annealing temperature and composition play an important role in the structures and PL properties of the films. The annealing temperature of 600 °C favors the formation of the SiC (1 0 9) crystal in the SiCN films, and results in a maximal PL peak. The intensity of the 440 nm PL peak can be improved by increasing the abundance of the Si-C bond.     

The structure and photoluminescence properties of ZnO/SiC multilayer film on Si substrate

ZnO/SiC multilayer film has been fabricated on a Si (111) substrate with a silicon carbide (SiC) buffer layer using the RF (radio frequency)-magnetron technique with targets of a ceramic polycrystalline zinc oxide (ZnO) and a composite target of pure C plate with attached Si chips on the surface. The as-deposited films were annealed at a temperature range of 600–1000°C under nitrogen atmosphere. The structure and photoluminescence (PL) properties of the samples were measured using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and PL spectrophotometry. By increasing the annealing temperature to 800°C, it is found that all the ZnO peaks have the strongest intensities, and the crystallinity of ZnO is more consistent on the SiC buffer layer. Further increase of the annealing temperature allows the ZnO and SiC layers to penetrate one another, which makes the interface between ZnO and SiC layer become more and more complicated, thus reduces the crystallinities of ZnO and SiC. The PL properties of a ZnO/SiC multilayer are investigated in detail. It is discovered that the PL intensities of these bands reach their maximum after being annealed at 800°C. The PL peaks shift with an increase in the annealing temperature, which is due to the ZnO and SiC layers penetrating reciprocally. This makes the interface more impacted and complicated, which induces band structure deformation resulting from lattice deformation.     

Effect of annealing temperature on ZnO:Al/p-Si heterojunctions

Al-doped, zinc oxide (ZnO:Al) films with a 1.2 at.% Al concentration were deposited on p-type silicon wafers using a sol-gel dip coating technique to produce a ZnO:Al/p-Si heterojunction. Following deposition and subsequent drying processes, the films were annealed in vacuum at five different temperatures between 550 and 900 °C for 1 h. The resistivity of the films decreased with increasing annealing temperature, and an annealing temperature of 700 °C provided controlled current flow through the ZnO:Al/p-Si heterojunction up to 20 V. The ZnO:Al film deposited on a p-type silicon wafer with 1.2 at.% Al concentration was concluded to have the potential for use in electronic devices as a diode after annealing at 700 °C.     

生长温度对ZnO薄膜结构的影响

在不同温度下，利用射频等离子体增强型MOCVD系统，在蓝宝石C面上生长出了C轴单一取向的ZnO薄膜，并通过XRD，SEM手段对生长温度与样品的生长速度，表面结构和氧锌原子化学计量比的关系作了较为详细的研究，优化了薄膜的温度生长参数，当生长温度为520℃时，ZnO薄膜的生长速度最大且表面粗糙度较低，当温度为550℃时，可生长出O：Zn为49.99:50:01的近本征ZnO薄膜。     

退火对溅射ZnO薄膜的形貌和内应力的影响

用超高真空射频磁控溅射技术制备了高C轴取向的ZnO薄膜,用扫描电镜和X射线衍射仪分别研究了退火对ZnO薄膜形貌和内应力的影响.结果表明:适当温度退火后薄膜的形貌和内应力得到改善,通过增氧、缺陷原子的热激活和晶粒融合等可以有效地降低薄膜中由热效应、缺陷效应和粒子注入效应等引起的张应力,薄膜组织致密化并且柱状晶粒取向趋于一致.450℃退火的ZnO薄膜具有最低的张应力和最佳的结晶质量.     

Study of ZnO sol-gel films: Effect of annealing

Thin films of zinc oxide were deposited by spin coating method on different substrates. The obtained samples were thermally treated at temperatures from 400 °C up to 850 °C. The structural study was performed by XRD and FTIR techniques in order to observe the effect of the annealing temperatures. The sol-gel ZnO films showed polycrystalline hexagonal structure. The optical transmittance reached 91% and it diminished with increasing annealing temperatures.     

反应源温度对ZnO纳米线阵列定向性及发光性能的影响

以Au薄膜为催化剂、ZnO与碳混合粉末为反应源,采用碳热还原法在单晶Si衬底上制备了ZnO纳米线阵列.通过扫描电子显微镜( SEM)、X射线衍射仪(XRD)、荧光分光光度计对样品的表征,研究了反应源温度对ZnO纳米线阵列的定向性和光致发光性能的影响.样品在源温度920℃条件下沿(002)方向择优生长,定向性最好,温度过低不利于ZnO纳米线阵列密集生长,而温度过高导致Zn原子二次蒸发,因而也不利于纳米线阵列的定向和择优生长;样品在源温度880℃有最强的近紫外带边发射,表明温度过高和过低都不利于ZnO晶体结构的优化;由于ZnO纳米线在缺氧氛围下生长,氧空位是缺陷存在的主要形式,因此所有样品都有较强的绿光发射.温度升高导致纳米线生长速度提高而增加了氧空位缺陷数量,从而使样品绿峰强度增强并在源温度920℃时达最大值,但温度的进一步升高可导致ZnO纳米线表面Zn元素的蒸发而降低氧空位缺陷的数量,从而抑制绿峰强度.     

Effect of microwave remote plasma and radiofrequency plasma on the photoluminescence of (0001) epitaxial ZnO films

Photoluminescence of (0001) epitaxial ZnO films with thicknesses of 10, 30 and 100 nm on C-sapphire substrates have been studied at room temperature and after exposure to Ar, Ar–O₂, Ar–N₂ and Ar–H by remote microwave and radiofrequency plasmas. The photoluminescence are not modified by remote plasma treatments where only neutral species were involved. On the contrary, the photoluminescence signal is enhanced or quenched after radiofrequency plasma treatments when energetic ion species are involved in the surface treatment processes. Little changes of electric properties are observed, however, the optical transmission indicates that the absorption edge and probably also the index of refraction are affected. Photoluminescence peak shifts, widths and intensities changes show very strong similarities with polarized emission of ZnO single crystal where it exists a strong dichroism. The photoluminescence emission properties may then result from this optical modification. However, the plasma treatments on the different samples show very low stability in time, except, for the treatment in argon plasma alone. In this later case, in-situ monitoring of photoluminescence as a function of temperature revealed a partial recovery of the photoluminescence properties after a heat treatment at 400 °C for few minutes. These results indicate that photoluminescence of (0001) ZnO thin film, related to σ-emission polarized emission from c-axis polar surfaces, is highly affected by surface and implanted charged species.     

高质量ZnO薄膜的退火性质研究

在LP－MOCVD中，我们利用Zn(C2H5)2作Zn源，CO2作氧源，在（0002）蓝宝石衬底上成功制备出皮c轴取向高度一致的ZnO薄膜，并对其进行500℃-800℃四个不同温度的退火。利用XRD、吸收谱、光致发光谱和AFM等手段研究了退火对ZnO晶体质量和光学性质的影响。退火后，（0002）ZnO的XRD衍射峰强度显著增强，c轴晶格常数变小，同时（0002）ZnOX射红衍射峰半高宽不断减小表明晶粒逐渐增大，这与AFM观察结果较一致。由透射谱拟合得到的光学带隙退火后变小，PL谱的带边发射则加强，并出现红移，蓝带发光被有效抑制，表明ZnO薄膜的质量得到提高。     

Effect of deposition parameters and annealing temperature on the structure and properties of Al-doped ZnO thin films

Transparent conductive films of Al-doped ZnO (AZO) were deposited onto inexpensive soda-lime glass substrates by radio frequency (rf) magnetron sputtering using a ZnO target with an Al content of 3 wt%. The Taguchi method with a L₉ orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to examine the performance characteristics of the coating operations. This study investigated the effect of the deposition parameters (rf power, sputtering pressure, thickness of AZO films, and substrate temperature) on the electrical, structural, morphological and optical properties of AZO films. The grey-based Taguchi method showed the electrical resistivity of AZO films to be about 9.15 × 10⁻³ Ω cm, and the visible range transmittance to be about 89.31%. Additionally, the films were annealed in a vacuum ambient (5.0 × 10⁻⁶ Torr) at temperatures of 400, 450, 500 and 600 °C, for a period of 30 min. It is apparent that the intensity of the X-ray peaks increases with annealing treatment, leading to improved crystallinity of the films. By applying annealing at 500 °C in a vacuum ambient for 30 min, the AZO films show the lowest electrical resistivity of 2.31 × 10⁻³ Ω cm, with about 90% optical transmittance in the visible region and a surface roughness of Ra = 12.25 nm.     

N-doped ZnO nano-arrays: A facile synthesis route, characterization and photoluminescence

Field emission scanning electron microscopy (SEM) investigation reveals that array-orderly novel nanostructures, which are nanorods with many nanoparticles on the surfaces, have been synthesized at low temperature (162 °C) via a one-step in-situ process in solution. High resolution transmission electron microscope (HRTEM) and energy-dispersive X-ray spectroscopy (EDS), coupled with X-ray powder diffraction (XRD) patterns and X-ray photoelectron spectra (XPS), reveal that the as-obtained products possess crystalline structure of N-doped ZnO. The room temperature photoluminescence (PL) spectrum has also been examined to explore the optical property. The present synthesis method possesses several advantages, which would be significant to be studied deeper in the future. It is also envisioned that this method could provide a new approach to synthesize ZnO:N and other ZnO-based adulterants at low temperature.     

Enhanced photoluminescence from polycrystalline ZnO films resulting from oxygen processing

We report studies of photoluminescence from polycrystalline ZnO films deposited on sapphire as a function of the in situ oxygen pressure during growth and ex situ annealing. The ultraviolet photoluminescence was observed to increase by more than two orders of magnitude as a result of the annealing treatment. Enhanced cathodoluminescence was observed from the same films. The role of oxygen defects is discussed.     

Effect of annealing temperature on the tribological behavior of ZnO films prepared by sol-gel method

The tribological behavior of zinc oxide (ZnO) films grown on glass and silicon (100) substrates by sol-gel method was investigated. Particularly, the as-coated films were post-annealed at different temperatures in air to investigate the effect of annealing temperature. Crystal structural and surface morphology of the films were measured by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). XRD patterns and AFM images indicated that the crystallinity and grain size of the films were enhanced and increased, respectively, with temperature. The tribological behavior of films was evaluated by sliding the ZnO films against a Si₃N₄ ball under 0.5 gf normal load using a reciprocating pin-on-plate tribo-tester. The wear tracks of the films were measured by AFM to quantify the wear resistance of the films. The results showed that the wear resistance of the films could be improved by the annealing process. The wear resistance of the films generally increased with annealing temperature. Specifically, the wear resistance of the films was significantly improved when the annealing temperature was higher than 550° C. The increase in the wear resistance is attributed to the increase in hardness and modulus of the film with annealing temperature.