ZnO thin films deposited by capillaritron ion beam sputtering deposition

ZnO thin films were deposited by capillaritron ion beam sputtering deposition. The crystalline quality, stoichiometry and photoluminescence properties of as-deposited and annealed ZnO thin films were studied. The as-deposited ZnO films show no preferred crystallographic orientations while annealed films exhibit a strong single ZnO (0 0 2) diffraction peak at 34.50°. The stoichiometry of ZnO films were found to be dependent on both beam energy and annealing conditions that the atomic percent ratio of Zn/O can be controlled between 0.95 and 1.10. ZnO films deposited with 4 keV ion beam and annealed at 800 °C in oxygen shows the lowest defect related deep level visible emission, while 80% of oxygen atoms are still located in fully oxidized stoichiometric ZnO matrixes.     

Growth, characterization and effect of substrate bias on ZnO prepared by reactive capillaritron ion beam sputtering deposition

ZnO thin films have been deposited on Si substrates by reactive ion beam sputtering deposition utilizing a capillaritron ion source. All the as-deposited ZnO films exhibit a preferred (0 0 2) growth direction while the grain size increases as oxygen partial flow rate increases. An optimum photoluminescence result was achieved using oxygen partial flow rate of ∼40% that the ratio of integrated deep level emission to that of integrated near-band-edge emission is less than 1.5. The atomic percentage ratio of Zn:O remains at 55/45, regardless of oxygen partial flow rates. With the applied substrate bias, the atomic percentage ratio of Zn/O changes to 40/60, indicating that stoichiometric ZnO may be achieved by selecting appropriate substrate bias. With the substrate bias applied, increased amount of oxygen atoms were found located in oxygen deficient matrixes, likely due to the bombardment of secondary ions.     

Recovery of the luminescence property in sulfur-implanted ZnO thin film

The recovery behavior of defect implanted in highly oriented ZnO thin films, deposited on (1 1 2̄ 0) alumina by chemical vapor deposition is studied as a function of annealing time at 800 °C using the photoluminescence technique. The band-edge emission of the film is completely extinguished by behavior implantation. The recovery of the luminescence at 800 °C is observed as weak violet and intense visible emissions. A weak violet emission is observed in samples annealed for 15–60 min. An intense visible emission shifted from 511 to 525 nm for the duration of 15–300 min. Analyses by secondary ion mass spectrometry revealed that the sulfur concentration decreases with increasing annealing time, and indicated, in the high lateral resolution image, that the sulfur in ZnO thin film has a heterogeneous distribution. The emissions due to the recovery are discussed together with the behavior of sulfur in ZnO thin film during annealing.     

Effects of Deposition Temperature on the Properties of Fluorinated Amorphous Carbon Films

Fluorinated amorphous carbon films (a-C:F) were prepared at different temperatures using a microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) reactor with CHF3 and C2H2 as source gases. Films were annealed at 500℃ in vacuum ambience inorder to investigate the relationship of their thermal stability, optical and electrical propertieswith deposition temperature. Results indicate that the films deposited at high temperature have a less CFx bonding and a more cross-linking structure thus a better thermal stability. They also have a lower bandgap, higher dielectric constant and higher leakage current.     

Studies of effect of deposition parameters on the ZnO films prepared by PLD

Thin films of zinc oxide (ZnO), having different thicknesses were prepared by pulsed laser deposition (PLD) technique onto silicon Si(1 1 1) and quartz (SiO₂) substrates at different partial pressures of oxygen. Rutherford back scattering (RBS) analysis was carried out in order to investigate effect of deposition parameters on thickness of films. Quality of the films was investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) analyses. The thickness of the film was found to increase with oxygen partial pressure for both Si and SiO₂ substrates.     

Nanoscratch study of ZnO thin films deposited using radio frequency magnetron sputtering

In this study, a radio frequency magnetron sputtering system was used to deposit zinc oxide (ZnO) thin films onto langasite substrates. The thickness of the ZnO film increased from 0.3 to 1.2 μm upon increasing the deposition power from 100 to 200 W. The predominant growth orientation was along the c-axis (0 0 2); the intensities of the signals in the X-ray diffraction spectrum increased significantly upon increasing the film thickness. Scanning electron microscopy images revealed columnar structures in the ZnO films and the morphology of ZnO grains is found to be continuous and dense. It is attributed that oxygen chemisorbs on the target and cases a surface layer of adsorbed oxygen. We suggest that the more neutral ion bombardment on the growing film which induces the higher sputtering rate of the growing film. From in situ imaging of scratched tracks, measurement of the coefficient of friction was an effective means of detecting the occurrence of structural defects in the microstructures. We also found that the chemical compositions of ZnO films prepared under various deposition powers could be investigated using X-ray photoelectron spectroscopy.     

分子束外延生长ZnO薄膜及性能研究

用分子束外延（MBE）和氧气氛方法，并改变束源炉和衬底生长温度，在Si(100)衬底上，采用Zn作缓冲层以解决ZnO层与衬底间的晶格失配问题，生长得到ZnO薄膜。在ZnO/Zn/Si(100)薄膜样品的X射线衍射（XRD）谱中，观测到ZnO的（100）、（200）、（101）和（103）等衍射峰；用原子力显微镜（AFM）观测ZnO薄膜的表面形貌，为直径约80－90mm的量子点，表明已得到具有纳米结构的ZnO薄膜。用同步辐射EXAFS技术研究了ZnO薄膜的局域结构，得到有关的几个结构参数。     

Optical and structural properties of ZnO thin films; effects of high energy electron irradiation and annealing

High energy electron irradiation (HEEI) effects on the as-grown and annealed ZnO thin films grown by electrochemical deposition were investigated. Both samples were exposed to the sequential electron irradiations of 6, 12 and 15 MeV energies at a fluence of 1 × 10¹² e⁻/cm². The results of X-ray diffraction suggest that a highly strong crystallographic structure can be produced by annealing process. Photoluminescence (PL) studies show that the EI produces violet emission which results from the zinc interstitial. Recombination lifetime (RL) values of the both films reveal that the high quality crystals are obtained. The decreasing trends of RL values with increasing electron energy have been explained by the formation of crystal defects due to the HEEI.     

原位光电子能谱研究La_2O_3/LaAlO_3/Si电子结构

在超高真空条件下,通过脉冲激光技术沉积La_2O_3/LaAlO_3/Si多层膜结构,原位条件下利用同步辐射光电子能谱研究了LaAlO_3作为势垒层的La_2O_3与Si的界面电子结构。实验结果显示,LaAlO_3中Al的2p峰在沉积和退火前后没有变化;衬底硅的芯能级峰在沉积LaAlO_3时没有变化,但在沉积La_2O_3薄膜和退火过程中,硅峰变弱;O的1S芯能级的峰由多种不用的氧化物薄膜层和反应物中的氧杂化而成。结果表明:LaAlO_3从沉积到退火当中,不参与任何反应,Si与LaAlO_3界面相当稳定;在体系中,阻挡层LaAlO_3起到阻挡硅扩散的作用,进一步表明La_2O_3与硅的界面不太稳定。     

Effects of Li ion implantation energies on the structure, photoluminescence, and ferromagnetism properties of (Li, Co) co-implanted ZnO films

Room temperature ferromagnetism was observed in (Li, Co) co-implanted ZnO films. The implantation energy for Co ions was 400 keV, while for Li ions were 50, 100 and 200 keV, respectively. The ion implantation induced defects and disorder has been observed by the XRD, PL and TEM experiments. For the co-implanted ZnO films with Li ion implantation energies of 100 and 200 keV, the band energy emission disappears and the defect related emission with wavelength of 500-700 nm dominates, which can be attributed to defects introduced by implantation. Co-implanted ZnO Films with Li ion implantation energies of 200 keV show a saturation magnetization value (M_S) of over 9 × 10⁻⁵ emu and a positive coercive field of 60 Oe. The carrier concentration is not much improved after annealing and in the order of 10¹⁶ cm⁻³, which suggests that FM does not depend upon the presence of a significant carrier concentration. The origin of ferromagnetism behavior can be explained on the basis of electrons and defects that form bound magnetic polarons, which overlap to create a spin-split impurity band.     

Positron annihilation and X-ray diffraction studies on tin oxide thin films

Positron annihilation spectroscopy along with glancing incidence X-ray diffraction have been used to investigate tin oxide thin films grown on Si by pulsed laser deposition. The films were prepared at room temperature and at 670 K under oxygen partial pressure. As-grown samples are amorphous and are found to contain large concentration of open volume sites (vacancy defects). Post-deposition annealing of as-grown samples at 970 K is found to drastically reduce the number of open volume sites and the film becomes crystalline. However, film grown under elevated temperature and under partial pressure of oxygen is found to exhibit a lower S-parameter, indicating lower defect concentration. Based on the analysis of experimental positron annihilation results, the defect-sensitive S-parameter and the overlayer thickness of tin oxide thin films are deduced. S-W correlation plots exhibit distinct positron trapping defect states in three samples.     

RBS study of Ti/ZnO interface

We have studied the interface stability of the Ti(overlayer)/ZnO(substrate) system. Ti thin film was grown on the Zn face of single crystal ZnO(0 0 0 1) substrate by the vacuum deposition technique. The Ti film thickness was typically 16 nm. Then the samples were annealed in air at 300 and 400 °C for 15 min, respectively. The deposition and annealing effects on the interface structure were investigated with Rutherford backscattering and channeling spectroscopy using 2 MeV He⁺ ion beam. After Ti deposition the minimum yield from the ZnO substrate increased from 2% to 7%. This suggests severe damage caused by deposition, i.e. the interface reaction between Ti and ZnO (even at room temperature). A significant amount of Zn (approximately 6.4 × 10¹⁶ atoms/cm²) moved onto the surface after post-annealing at 400 °C. Since Ti has a stronger tendency to react with O than Zn, it is expected that Ti reacts with substrate oxygen leaving behind free Zn atoms, which can easily migrate onto the surface. We discuss how the Ti/ZnO interface reaction in detail, and seek to find another good metallic contact for ZnO devices, which are attracting much attention recently for practical applications as well as scientific aspects.     

Influence of low-energy bombardment of an RF magnetron sputtering discharge on texture formation and stress in ZnO films

In an oxygen planar RF magnetron sputtering discharge, the time-averaged flux and energy of positive ions drifting out of the plasma and striking the substrate surface have been determined as a function of RF discharge power over a range of 100 to 1000 W, and as a function of chamber pressure from 0.2 to 6 Pa by measurement of ion-current density and time-averaged plasma sheath potential at the substrate. These data were related to the resulting crystal structure of the deposited ZnO films which had been studied in detail using well-known methods of X-ray diffraction. The impact energy of the positive ions bombarding the growing film varies from some 10 eV to close 50 eV depending on magnetron RF discharge power and oxygen pressure, respectively. The incident ion flux was found to be below 1× 10¹⁵ cm⁻²s⁻¹ up to 1 × 10¹⁶ cm⁻²s⁻¹, a value of the same order of magnitude as that for the condensing rate of sputtered ZnO species. The structural results obtained show that both the ion energy and the ion flux in the range mentioned above cause significant changes in the degree of crystallinity, preferred orientation and texture sharpness of the deposited ZnO films. Furthermore, positive ion bombardment during film growth has been found to alter the ZnO unit cell dimension up to 2% relative to the equilibrium bulk or powder value which is responsible for the formation of strong compressive residual stress of up to several GPa within the ZnO film. Following these results, one of the criterions for preparing highly c-axis oriented ZnO films with columnar grain structure is to decrease both the energy and the flux of the positive ion bombardment without decreasing the deposition rate of ZnO species. At a such slight-bombardment RF magnetron deposition the compressive residual stress of the ZnO film can be reduced towards zero.     

用正电子湮没实验研究PbWO4新型闪烁晶体绿光发光机理

通过正电子湮没寿命谱研究ＰｂＷＯ４晶体退火处理前后缺陷的变化,发现氧退火后,晶体正电子寿命值τ２变小,正电子捕获率ｋ增大,真空退火反之。并且ＰｂＷＯ４晶体氧退火后发光主峰位从４４０ｎｍ称到４８５ｎｍ的绿光处,而真空退火晶体发射谱谱形并未变化。从不同退火处理对晶体的影响,提出了ＰｂＷＯ４晶体中铅空位形成ＷＯ３＋Ｏ＾－发绿光的发光模型。     

Effect of O<Subscript>2</Subscript>/Ar Mixture on the Structural and Optical Properties of ZnO Thin Films Fabricated by DC Cylindrical Magnetron Sputtering

Direct Current Cylindrical Magnetron Sputtering Setup was used to deposit ZnO thin films on BK7 substrates. The effects of changing O₂/Ar reactive gas mixtures on the structural and optical properties of films were studied. Crystallinity and structure of films were obtained by X-ray diffraction (XRD). Preferential crystalline growth orientation of ZnO films detected by XRD was always along the (002) orientation. The thickness of films was measured by surface profilometer which showed thickness increasing from 68.7 to 80.8 nm for 3–6% O₂ amount respectively. The morphology and roughness of the films were investigated by Atomic Force Microscopy (AFM). As oxygen gas amount was increased, the roughness and the grain size were decreased and the deposition rate was increased. The optical transmittance of ZnO films are obviously affected by the changing of O₂/Ar reactive gas mixtures. All films exhibit a transmittance higher than 70% in the visible region. The optical band gap of films was measured by Tauc’s method. The results show that by increasing the amount of O₂ in reactive gas mixture, the optical band gap of deposited films increases.     

Incorporation of oxygen during oxidative annealing of thermally evaporated In films

The paper describes studies on compositional, morphological and optical characteristics of thin indium oxide films prepared by annealing thermally evaporated indium metal films in 423-723 K temperature range in air. The incorporation of oxygen in the films has been probed by depth profiling oxygen using ¹⁸O(p, α)¹⁵N nuclear reaction and 3.05 MeV ¹⁶O(α, α)¹⁶O resonant scattering. The morphology of the films has been examined by atomic force microscopy while their structure by glancing incidence X-ray diffraction. As grown In films are polycrystalline and consist of well-aligned (In) hillocks. The hillocks in thin films (∼12 nm) are nanosized and conical in shape while those in thicker films (∼130 nm) are micron-sized with rather flat tops. Nanosized hillocks impart films enhanced reactivity towards oxygen. Consequently thinner films contain high amount of adsorbed oxygen in as-deposited state and undergo facile oxidation. The hillocks are obliterated in the process. The enhanced reactivity is attributed to high surface energy, generally associated with nanoparticles, and residual stress. These films exhibit high transmission (>90%) on annealing beyond 473 K. Micro-sized hillocks, on the other hand lend pronounced roughness to the films. Roughness and lower surface free energy which manifests in the form of flatter hillock tops, make the films oxidation-resistant. Depth profile measurements in thicker films show that oxidation starts at the surface and proceeds into the interiors of the film with increase in the duration of annealing. The films are deficient in oxygen, even as X-ray diffraction shows the formation of polycrystalline indium oxide. These have low transmission (<30%) and their band gaps increase with the temperature and duration of annealing. The increase in band gap is attributed to the gradual oxidation of interior regions that are initially significantly deficient in oxygen and improvement in crystallinity.     

SR-XRD和EXAFS研究Mn掺杂ZnO薄膜的微观结构

用射频磁控溅射技术在蓝宝石衬底上制备了一组不同衬底温度的Mn掺杂ZnO薄膜。质子激发X射线荧光(PIXE)测量表明,薄膜中仅有含量为5 at.%的Mn,未见其它磁性杂质元素(如Fe、Co、Ni等)。同步辐射X射线衍射(SR-XRD)表明,这些Mn掺杂ZnO薄膜具有纤锌矿ZnO结构。SR-XRD和扩展X射线吸收精细结构谱(EXAFS)分析显示,薄膜中未发现Mn团簇或MnO、MnO2、Mn2O3、Mn3O4等二次相,Mn原子是通过替代Zn原子而进入了ZnO晶格。     

Phase structure of the CPD prepared CdS films before and after Ar^＋ ion irradiation

CdS films prepared with chemical pyrolysis deposition(CPD) at different temperature during film growth were characterized by XRD.Hexagon-like structrue appeared at the temperature of 350-500℃,while wurtzite phase was observed at temperature of 540℃ during film growth,Also CdS films prepared by CPD at 400℃ were undergone post annealing at different temperature of 200-600℃ or post Ar^ ion irradiation.It is found that wurtzite phase happened when the annealing temperature rose to 600℃.And hexagon-like structure existed at the annealing temperature from 25℃to near 500℃.Ar^ ion irradiation could not cause phase transformation,but induce some preferred orientations and an increase in grain size for the CdS films.     

Oxygen defects created in CeO2 irradiated with 200 MeV Au ions

CeO₂ films were irradiated with 200 MeV Au ions in order to investigate the damages created by electronic energy deposition. In the Raman spectra of the ion-irradiated films, a broad band appears at the higher frequency side of the F_2g peak of CeO₂. The band intensity increases as ion fluence increases. Furthermore, the F_2g peak becomes asymmetric with a low-frequency tail. In order to understand the origin of these spectral changes, an unirradiated CeO₂ film was annealed in vacuum at 1000 °C. By comparing the results for the irradiation and for the annealing, it is concluded that the broad band obtained for irradiated samples contains the peak observed for the annealed sample. The F_2g peak becomes asymmetric with a low-frequency tail by the irradiation as well as the annealing. Therefore, the above-mentioned changes in the Raman spectra caused by 200 MeV Au irradiation is closely related to the creation of oxygen vacancies.     

Incorporation of Nitrogen into Amorphous Carbon Films Produced by Surface-Wave Plasma Chemical Vapor Deposition

In order to study the influence of nitrogen incorporated into amorphous carbon films, nitrogenated amorphous carbon films have been deposited by using surface wave plasma chemical vapor deposition under various ratios of N2/CH4 gas flow. Optical emission spectroscopy has been used to monitor plasma features near the deposition zone. After deposition, the samples are checked by Raman spectroscopy and x-ray photo spectroscopy (XPS). Optical emission intensities of CH and N atom in the plasma are found to be enhanced with the increase in the N2/CH4 gas flow ratio, and then reach their maximums when the N2/CH4 gas flow ratio is 5%. A contrary variation is found in Raman spectra of deposited films. The intensity ratio of the D band to the G band (ID/IG) and the peak positions of the G and D bands all reach their minimums when the N2/CH4 gas flow ratio is 5%. These show that the structure of amorphous carbon films has been significantly modified by introduction of nitrogen。