Surface and bulk thermal annealing effects on ZnO crystals

Annealing at temperatures up to 1000 °C is shown to decrease band edge photoluminescence in bulk ZnO crystals and increase deep level-related emission. The surface roughens for anneals in the range of 600-800 °C as O is lost preferentially from the surface, but at 900 °C the morphology improves as excess Zn is also lost from the surface. Splitting of the peak in the rocking curve of the ZnO (0 0 2) plane after annealing at 900-1000 °C indicates that the substrate is a mosaic of two or more crystals oriented slightly differently from one another and we are detecting differences in orientation of some of the grains in different areas or small changes due to annealing. There was no significant change in bulk conductivity of the ZnO for anneals up to 1000 °C, suggesting that ion implantation followed by annealing may be an effective approach for doping in this.     

低能Co离子注入单晶ZnO的光致发光特性

采用离子注入法研究了Co离子注入ZnO晶体的光致发光效应。 对离子注入后的样品在Ar气保护下进行退火处理, 退火温度为700 ℃, 退火时间为10 min, 在其光致发光谱中观察到了406和370 nm的紫光发射峰。 对比了Co, Cu离子分别注入的ZnO晶体的光致发光谱, 观测到二者的光致发光谱类似。 同时, 研究了Co离子注入剂量对样品发光性质的影响, 结果表明随注入剂量的增加绿色发光中心逐渐向低能边偏移, 分析认为绿色发光中心的偏移与离子注入后ZnO晶体的禁带宽度发生改变相关。 In this paper, ion implantation techniques were used to study the photoluminescence(PL) of the Co implanted crystal ZnO. After Co ion implanted, the samples were annealed at 700 ℃ for 10 min in Ar gas flow. It was observed violet emission peak of 406 and 370 nm in the PL spectrum. The PL spectra of the ZnO crystal samples which were implanted by Co ions and Cu ions, respectively, have been compared and observed that the PL spectrum of the Co implanted ZnO is similar to that of the Cu implanted ZnO. We studied the influence of implantation dose on the PL of the Co implanted ZnO and found that the green luminescence centre shifted with increasing of implantation dose. It is concluded that the shift of the green luminescence centre is related to the change of ZnO band gap which was caused by ion implantation.     

Analysis of properties of krypton ion-implanted Zn-polar ZnO thin films

The optical properties of materials are of great significance for their device applications. Different numbers of krypton ions are doped into high-quality Zn-polar Zn O films fabricated by molecular beam epitaxy(MBE) on sapphire substrates through ion implantation. Krypton is chemically inert. The structures, morphologies, and optical properties of films are measured. The x-ray diffraction(XRD) spectra confirm the wurtzite structures of Zn-polar Zn O films. Atomic force microscopy(AFM) results show that the films have pit surface structure and higher roughness after Kr ion implantation. A detailed investigation of the optical properties is performed by using the absorption spectrum, photoluminescence(PL), and spectroscopic ellipsometry(SE). The absorption spectrum is measured by UV-visible spectrophotometer and the bandgap energy is estimated by the Tauc method. The results show that the absorption increases and the bandgap decreases after Kr ion implantation. Moreover, the Kr ion implantation concentration also affects the properties of the film. The ellipsometry results show that the films' refractive index decreases with the Kr ion implantation concentration increasing. These results can conduce to the design and optimization of Kr ion-implanted polar Zn O films for optoelectronic applications.     

Photoresponse of ion implanted gallium dopants in silicon

High resolution spectral photoconductivity measurements are reported for a thin Si:Ga layer fabricated by ion implantation. The gallium ions were implanted at an energy of 3 MeV and a dose of 10¹⁴cm⁻². The measured spectral response of the layer was comparable to that of bulk Si:Ga, while the temperature range of the layer's photoresponse showed an increase when compared to that of bulk Si:Ga. These results show that ion implantation can produce useful thin, infrared active layers.     

A comparative study of the structure and cytotoxicity of polytetrafluoroethylene after ion etching and ion implantation

The ion-plasma treatment has been widely used for modifying the surface structure of polymers in order to improve their properties, but it can lead to destruction of the surface and, as a consequence, to an increase in their toxicity. A comparative study of the structure and cytotoxicity of polytetrafluoroethylene (PTFE) after the ion etching (IE) and ion implantation (II) for 10 min with energy densities of 363 and 226 J/cm², respectively, has been performed. It has been shown that, unlike the ion implantation, the ion etching results in the destruction of the polymer and in the appearance of the cytotoxicity. The factors responsible for this effect, which are associated with the bulk and surface treatment, as well as with the influence of the temperature, have been discussed.     

Ion implantation into heteroepitaxial Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Te grown by molecular-beam epitaxy

The results of investigations into the electrophysical properties of heteroepitaxial semiconductor material CdHgTe (CMT) grown by molecular-beam epitaxy (MBE) after ion implantation are reported. The major factors responsible for the differences between ion implantation in bulk CMT crystals and heteroepitaxial MBE CMT are determined. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 5–18, October, 2008.     

Estimation of the sizes of disordered surface regions of Cu and Ag thin films using the ion transmission method

The dimensions of cluster phases that form on the surfaces of free Cu and Ag films in the case of different irradiation doses are estimated for the first time. It is shown that ion implantation leads to a significant decrease in the number of ions passed through a free film. Under the same conditions of the ion implantation, the concentration of impurity atoms on the surface and their depth-distribution profile for the free film differ noticeably from those for a bulk crystal.     

ZnO压敏陶瓷缺陷结构表征及冲击老化机理研究

对多元ZnO压敏陶瓷电阻片进行了多达14000次的大电流冲击老化试验, 通过显微结构、电气性能及介电特性的测量对其缺陷结构进行了表征, 并研究了缺陷结构与大电流冲击老化之间的关系. 试验表明多次大电流冲击老化导致试样的电气性能明显下降, 发现ZnO压敏陶瓷的几何效应不仅受控于晶粒还与晶界密切相关. 另外, 通过介电谱分析观察到ZnO压敏陶瓷存在四种缺陷弛豫过程, 低温-60 ℃下的两个缺陷弛豫峰激活能约为0.24 eV和0.35 eV, 认为它们分别对应着本征的锌填隙缺陷L(Zn_i^··)和氧空位缺陷L(V_O^·)并且不受冲击老化的影响. 高温80℃以上两个松弛峰的活化能约为0.71 eV和0.84 eV, 认为它们分别对应着非本征的晶间相电子陷阱L(ingr)和晶界处界面态陷阱L(gb). 发现大电流冲击后, 仅界面态陷阱激活能从0.84 eV降低到0.76 eV, 认为界面态陷阱主要控制着ZnO压敏陶瓷的电气性能和稳定性.     

Synthesis of nano-sized SiC precipitates in Si by simultaneous dual-beam implantation of C+ and Si+ ions

Nanometer-sized SiC precipitates were synthesized in situ in Si by simultaneous implantation of two ion beams of C⁺ and Si⁺ ions. The results of simultaneous dual-beam implantation are compared with those of sequential dual-beam ion implantation and of single-beam C⁺ ion implantation. Remarkable differences are observed regarding the content and the crystal quality of SiC precipitates as well as the defect structure of the Si substrate. The SiC precipitation during dual-beam synthesis is found to depend on the ion energy of the second beam and on the implantation mode, simultaneous or sequential. For suitable implantation conditions, simultaneous dual-beam synthesis can improve the in situ SiC formation in comparison to the single-beam synthesis. A higher density of SiC precipitates with better crystal quality was observed, whereas their size was not changed. The second ion beam enables a shift in the dynamic equilibrium of constructive and destructive processes for SiC formation. A model is proposed assuming that SiC precipitation preferentially proceeds in regions with vacancy defects. The implantation process itself creates vacancy-dominated and also interstitial-dominated regions. The balance of the local point-defect composition is shifted under the second ion beam. In this way, the conditions for SiC precipitation can be modified. Received: 18 February 2002 / Accepted: 17 May 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +49-351/260-3411, E-mail: koegler@fz-rossendorf.de     

Comparison of plasma chemistries for the dry etching of bulk single-crystal zinc-oxide and rf-sputtered indium-zinc-oxide films

The dry etching characteristics of bulk, single-crystal zinc-oxide (ZnO) and rf-sputtered indium-zinc-oxide (IZO) films have been investigated using an inductively coupled high-density plasma with different plasma chemistries. The introduction of interhalogens such as ICl, IBr, BI₃, and BBr₃ to the Ar plasma produced no enhancement of the ZnO and IZO etch rates with respect to physical sputtering in a pure argon atmosphere under the same experimental conditions. In these plasma chemistries, the etch rate of both materials increased with source power and ion energy, indicating that ion bombardment plays an important role in enhancing desorption of etch products. Except in Ar/CH₄/H₂ discharges, the ZnO etch rate was very similar to that of IZO, which indicates that zinc and indium atoms are driven by a similar plasma etching dynamic. CH₄/H₂-containing plasmas produced higher etch rates for IZO than for ZnO due to the preferential desorption of the group III etch products. Application of the CH₄/H₂/Ar plasma to the etching of deep features in bulk, single-crystal ZnO produced highly anisotropic profiles although some trenches were observed near the sidewalls.     

Model of β-CO on Mo(100): Dissociative adsorption

Secondary ion production during ion bombardment is analyzed experimentally. Secondary ions consist of bulk ions and surface ions. The former originates in the bulk material and the latter in the adsorbed layer. The most probable kinetic energy of bulk ions is higher by several tens of eV than that of surface ions, In order to perform quantitative bulk analysis the surface ions should be removed from the mass spectrum by making use of the difference between these kinetic energies. Secondary ion measurements indicate that the recoil implantation of an adsorbed element occurs to a significant extent under low ion current density bombardment.     

Ion synthesis and laser annealing of Cu nanoparticles in Al2O3

Al₂O₃ samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×10¹⁷ ion/cm² and a current density from 2.5 to 12.5 μA/cm², were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm². The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more likely to be reduced in size than to undergo oxidation. Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002     

Electroluminescence of ion-implanted Si-SiO2 structures

Specific features of the electroluminescence of ion-implanted (Ar ion implantation in oxide layer bulk) and ion-synthesized (SIMOX technology) Si-SiO₂ structures were studied. The electroluminescence from the electrolyte-insulator-semiconductor system was registered in the 250–800 nm range at room temperature. It has been found that implantation increases the concentration of centers already present in the oxide layer bulk and creates new luminescent centers. The nature and the models of the centers are discussed.     

用拉曼光谱测量离子注入引起的晶格应变

对于10个周期的AlAs/GaAs超晶格和25个周期的GaAs/Ga0.92In0.08As超晶格,在室温下进行0.28 MeV的Zn＋注入,注入剂量为5×1013~5×1014 cm-2。通过拉曼光谱测量,定量地分析了由于离子注入所引起的晶格内应变。实验结果表明：在所选用的注入剂量下,由于离子注入引起的应变小于体材料GaAs的最大非驰豫应变值0.038,说明该注入条件下,注入区的结晶态仍然保持得比较好。在较高注入剂量下应变达到饱和,说明缺陷的产生和复合达到了平衡,从而形成了均衡的应变场分布。     

First-principles study of the electronic and optical properties of ZnO nanowires

The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.     

用拉曼光谱测量离子注入引起的晶格应变

 对于10个周期的AlAs/GaAs超晶格和25个周期的GaAs/Ga0.92In0.08As超晶格,在室温下进行0.28 MeV的Zn＋注入,注入剂量为5×10¹³~5×10¹⁴ cm^-2。通过拉曼光谱测量,定量地分析了由于离子注入所引起的晶格内应变。实验结果表明：在所选用的注入剂量下,由于离子注入引起的应变小于体材料GaAs的最大非驰豫应变值0.038,说明该注入条件下,注入区的结晶态仍然保持得比较好。在较高注入剂量下应变达到饱和,说明缺陷的产生和复合达到了平衡,从而形成了均衡的应变场分布。     

Atomistic processes and the strain distribution in the early stages of thin film growth

Structural relaxations in small Co islands on the Cu(001) surface are investigated performing atomistic calculations. We demonstrate that the strain relief at the metal interface in the early stages of heteroepitaxy is more complicated than suggested by simple considerations based on the small mismatch between the Co and Cu bulk metals. We found that the strain distribution in the surface region near the islands varies strongly on an atomic scale. The effect of strain on the shape of the Co islands is revealed. Diffusion on the top of strained islands and edge diffusion are considered. Received: 10 April 2000 / Accepted: 15 May 2000 / Published online: 7 March 2001     

Photorefractive properties of optical waveguides in Fe:LiNbO<Subscript>3</Subscript> crystals produced by O<Superscript>3+</Superscript> ion implantation

The photorefractive properties of optical planar waveguides in Fe:LiNbO₃ crystals fabricated by O³⁺ ion implantation are investigated. Two-wave mixing experiments are carried out for both the waveguide and the bulk. The results show that the measured gain coefficients are almost identical for the waveguiding layer and the substrate. In the waveguide, the response time could be reduced by one order of magnitude, with respect to the bulk, at the same power level of the incident light.     

Tribological properties of chromium implanted silicon nitride ceramics correlated with microstructure

3 N₄ ceramic after chromium implantation were investigated for the dependence on implantation energy between 200 keV and 3 MeV at a fixed fluence of 10¹⁷ ions/cm². The wear of the modified material is reduced for a load of 2 N independent of ion energy accompanied by a slight increase of the friction coefficient. At higher loads only high-energy implantations result in improved wear behaviour. Structural investigations show the absence of any new phases formed by ion implantation. All energies result in an amorphous layer. For lower energies this amorphous layer reaches up to the surface whereas at higher energies it is covered by still-crystalline but damaged material. The observed wear behaviour can be explained with the amorphization of the near surface region and the stress generated by the volume swelling of the amorphous layer. Received: 25 November 1996/Accepted: 29 April 1997     

Formation of concentration profiles of implanted ions in metallic materials under polyenergetic implantation

A physical and mathematical model of mass transfer in polycrystalline metallic materials under exposure to ion beams is proposed. Alongside bulk indiffusion from the irradiated surface, diffusion along the migrating extensive defects interacting with an impurity is considered. For a polyenergetic ion beam, the contribution of bulk indiffusion is presented as an integral over energy of the product of two functions; one of them describes the energy distribution of ions in a beam and the second represents the implantation profile of monoenergetic ion beam.