氧气氛中p-GaN/Ni/Au电极在相同温度不同合金时间下的欧姆接触形成机制和扩散行为

用卢瑟福背散射/沟道技术研究了p-GaN上的Ni/Au电极在氧气氛下相同合金温度(500℃)不同合金时间后的微结构演化,以揭示欧姆接触的形成机制.利用背散射随机谱和RUMP模拟程序研究了电极金属之间的互扩散,用沟道谱探测了电极金属中的氧分布.结合不同合金时间下比接触电阻ρ_c的变化,发现随着合金时间的延长比接触电阻持续降低,在合金时间60 s后降低的速度减慢, Au扩散到GaN的表面,在p-GaN上形成外延结构,O向电极内部扩散反应生成NiO对降低ρ_{关键词： GaN 卢瑟福背散射/沟道 欧姆接触}     

用卢瑟福背散射/沟道技术研究ZnO/Zn0.9 Mg0.1 O/ZnO异质结的弹性应变

利用卢瑟福背散射/沟道技术对射频等离子体辅助分子束外延法生长在蓝宝石衬底上的ZnO/Zn0.9Mg0.1O/ZnO异质结进行了组分分析,并得到了异质结弹性应变随深度的变化,应变由界面向表面逐渐释放,并由负变正,且在ZnO与Zn0.9Mg0.1O界面处轻微增大.负的应变是由于ZnO与衬底的晶格失配和热失配,而逐渐变为正值是Zn0.9Mg0.1O与ZnO的晶格常数差异及弹性应变的逐渐释放所致.     

用卢瑟福背散射/沟道技术研究ZnO/Zn0.9Mg0.1O/ZnO异质结的弹性应变

利用卢瑟福背散射/沟道技术对射频等离子体辅助分子束外延法生长在蓝宝石衬底上的ZnO/Zn_0.9Mg_0.1O/ZnO异质结进行了组分分析，并得到了异质结弹性应变随深度的变化，应变由界面向表面逐渐释放，并由负变正，且在ZnO与Zn_0.9Mg_0.1O界面处轻微增大.负的应变是由于ZnO与衬底的晶格失配和热失配，而逐渐变为正值是Zn_0.9Mg_0.1O与ZnO的晶格常数差异及弹性应变的 关键词： 异质结 卢瑟福背散射/沟道 弹性应变 ZnMgO     

用卢瑟福背散射/沟道技术及高分辨X射线衍射技术分析不同Al和In含量的AlInGaN薄膜的应变

利用卢瑟福背散射/沟道技术对在蓝宝石衬底上用金属有机化学气相沉积方法生长的有GaN缓冲层(>2μm)的一系列不同Al和In含量的AlInGaN薄膜进行组分及结晶品质的测量；并结合高分辨X射线衍射技术，通过对AlInGaN的对称(0002)面，及非对称(1015)面的θ—2θ扫描及倒空间扫描，可以精确测定AlInGaN外延层的晶格常数及水平和垂直方向的应变.实验结果表明AlInGaN 薄膜中不同含量Al和In对其应变有较大的影响，结合Vegard定理，对这一现象给出了理论的解释. 关键词： AlInGaN 高分辨X射线衍射 卢瑟福背散射/沟道 弹性应变     

Si(111)衬底上生长有多缓冲层的六方GaN晶格常数计算和应变分析

利用卢瑟福背散射/沟道技术和高分辨率X射线衍射技术对在Si(111)衬底上利用金属有机化合物气相外延技术(MOVPE)生长有多缓冲层的六方GaN外延膜进行结晶品质计算、晶格常数计算和应变分析. 实验结果表明：GaN外延膜的结晶品质为χ_min=1.54%，已达到完美晶体的结晶品质(χ_min=1%—2%)；GaN外延膜的水平方向和垂直方向晶格常数分别为：a_epi＝0.31903nm，c_epi=0.51837nm，基本达到G 关键词： GaN 高分辨X射线衍射 卢瑟福背散射/沟道 弹性应变     

快重离子辐照引起Ni/SiO2界面原子混合及相变研究

在室温下用308 MeV的Xe离子和853 MeV的Pb离子辐照Ni/SiO2样品, 用卢瑟福背散射和X射线衍射技术对样品进行了分析。 通过分析Ni/SiO2样品中元素成分分布和结构随离子辐照剂量和电子能损的变化, 探索了离子辐照在Ni/SiO2样品中引起的界面原子混合与结构相变现象。 实验结果显示, Xe和Pb离子辐照均能引起明显的Ni原子向SiO2基体的扩散并导致界面附近Ni, Si和O原子的混合。 实验观测到低剂量Xe离子辐照可产生NiSi2相, 而高剂量Xe离子辐照则导致了Ni3Si和NiO相的形成。 根据热峰模型, Ni原子的扩散和新相的形成可能由沿离子入射路径强电子激发引起的瞬间热峰过程驱动。Ni/SiO2 interface were irradiated at room temperature with 308 MeV Xe ions to 1×1012, 5×1012 Xe/cm2 and 853 MeV Pb ions to 5×1011 Pb/cm2, respectively. These samples were analyzed using Rutherford Backscattering Spectrometry (RBS) and X ray diffraction spectroscopy (XRD), from which the intermixing and phase change were investigated. The obtained results show that both Xe and Pb ions could induce diffusion of Ni atoms to SiO2 substrates and result in intermixing of Ni with SiO2. Furthermore, 1.0×1012 Xe/cm2 irradiation induced the formation of NiSi2 and 5.0×1012 Xe/cm2 irradiation created Ni3Si and NiO phases. The diffusion of Ni atoms and the formation of new phase may be driven by a transient thermal spike process induced by the intense electronic energy loss along the incident ion path.     

硅晶体中点缺陷结合过程的分子动力学研究

采用分子动力学方法模拟研究了硅晶体中的空位和间隙原子的结合过程. 研究中采用了Stilliger-Weber三体经验势描述原子间的相互作用, 系统分别在低温300K和高温1400K进行弛豫. 计算中发现空位和间隙原子倾向于通过<111>方向结合，而<110>方向上存在着势垒. 通过势垒值的计算, 对Tang和Zawadzki势垒计算值的差异进行了解释. 关键词： 分子动力学 空位与间隙原子 扩散     

北京大学1.7MV串列静电加速器的离子注入/辐照实验系统

北京大学1.7 MV串列静电加速器运行至今已有三十多年.该加速器配备有高频电荷交换负离子源和铯溅射负离子源,能够引出从H到Au之间的大部分元素的离子.离子能量可被加速至几百keV到若干MeV,主要开展离子注入/辐照实验和卢瑟福背散射(RBS)和沟道分析等离子束分析工作.基于辐照实验需求,建立了高温辐照系统,温度最高可达...     

InGaN/GaN多量子阱的组分确定和晶格常数计算

采用金属有机化学气相沉积(MOCVD)技术以蓝宝石为衬底在n型GaN单晶层上生长了InGaN/GaN多量子阱结构外延薄膜，利用高分辨X射线衍射(HRXRD)，卢瑟福背散射/沟道(RBS/channeling)，以及光致发光(PL)技术对InGaN/GaN多量子阱结构薄膜分别进行了平均晶格常数计算、In原子替位率计算和In组分的定量分析.研究表明：InGaN/GaN多量子阱的水平和垂直方向平均晶格常数分别为a_epi=0.3195nm，c_epi=0.5198nm，In原子的替位率为99.3%，利用HRXRD和RBS/channeling两种分析技术计算In的组分分别是0.023和0.026，并与样品生长时设定的预期目标相符合，验证了两种实验方法的准确性；而用室温条件下的光致发光谱(PL)来计算InGaN/GaN多量子阱中In的组分是与HRXRD和RBS/channeling的实验结果相差很大，说明用PL测试In组分的方法是不适宜的. 关键词： InGaN/GaN多量子阱 高分辨X射线衍射 卢瑟福背散射/沟道 光致发光     

铅离子辐照注碳4H—SiC的红外光谱特性研究

主要研究了铅离子辐照注碳4H—SiC样品在3个不同退火温度下傅立叶变换红外光谱的变化。从红外谱的变化可以知道铅辐照注碳4H-SiC样品在一定深度内出现了非晶层,波数在960—1450cm^-1范围内出现了干涉带,干涉带强度随着退火温度的升高而 变弱。1373K退火后样品的卢瑟福背散射分析结果显示,一定深度内硅原子的背散射产额明显减少。4H-SiC specimens were implanted with C-ions and then irradiated with Pb-ions, and subsequently annealed at three different temperatures. The samples were investigated by using Fourier transformation infrared spectrum（FTIR） and Rutherford backward scattering（RBS）. The obtained FTIR spectra showed that there is a buried amorphous layer close to the ion-incident surface and there are several interference fringes in the range from 960 to 1 450 cm ^-1. The intensity of fringes decreases with the increase of annealing temperature. The obtained RBS spectra showed that the yield of Si atoms in 4H-SiC crystal decreases in a well-defined depth region after annealing at 1 373 K.     

Structural and optical properties of waveguides in YbVO4 crystals formed by 3.0 MeV Cu-ions implantation

We report on the structural and optical characterization of waveguides formed in YbVO₄ crystals by Cu²⁺-ion implantation with an energy of 3.0 MeV and doses of 3.0×10¹⁴-1.0×10¹⁵ ions/cm². The damage properties are determined by RBS/Channeling measurements with the help of simulation code RUMP. The m-line method is used to characterize the dark-mode spectroscopy in the planar waveguides. According to the reconstructed refractive index profile of the waveguide cross section, a numerical simulation is carried out to investigate the confinement of the light in the waveguides based on the beam propagation method.     

H+2，H+3团簇离子在沟道条件下的背散射 质子产额测量

采用卢瑟福背散射方法，测得了每质子能量为650 keV的H⁺₂，H+₃团簇离子在Si晶体<100>和<110>沟道条件下的质子背散射能谱.结果发现，由于H⁺₂，H⁺₃团簇在晶体中的库仑爆炸和团簇效应，H⁺₂的背散射质子产额大于H ⁺的背散射产额，而H^{+< 关键词： 团簇 沟道效应 库仑爆炸 背散射}     

Structural, electrical and optical properties of TiO2 doped WO3 thin films

TiO₂ doped WO₃ thin films were deposited onto glass substrates and fluorine doped tin oxide (FTO) coated conducting glass substrates, maintained at 500 °C by pyrolytic decomposition of adequate precursor solution. Equimolar ammonium tungstate ((NH₄)₂WO₄) and titanyl acetyl acetonate (TiAcAc) solutions were mixed together at pH 9 in volume proportions and used as a precursor solution for the deposition of TiO₂ doped WO₃ thin films. Doping concentrations were varied between 4 and 38%. The effect of TiO₂ doping concentration on structural, electrical and optical properties of TiO₂ doped WO₃ thin films were studied. Values of room temperature electrical resistivity, thermoelectric power and band gap energy (E_g) were estimated. The films with 38% TiO₂ doping in WO₃ exhibited lowest resistivity, n-type electrical conductivity and improved electrochromic performance among all the samples. The values of thermoelectric power (TEP) were in the range of 23-56 μV/K and the direct band gap energy varied between 2.72 and 2.86 eV.     

CO和O2分子与TiO2(110)表面负载Pt单原子的相互作用

Pt单原子在低温CO氧化反应中具有很高的催化活性. 利用扫描隧道显微术与密度泛函理论,研究了Pt单原子在还原性TiO₂(110)表面的吸附行为及其与CO和O₂分子的相互作用. 研究发现在80 K低温下,TiO₂表面的氧空位缺陷是Pt单原子的最优吸附位. 将CO和O₂分子分别通入Pt单原子吸附后的TiO₂表面,研究相应的吸附构型. 实验表明在低覆盖度下,单个Pt原子会俘获一个CO分子,CO分子同时与表面次近邻的五配位Ti原子(Ti_5c)成键,进而形成非对称的Pt-CO 复合物构型. 将样品从80 K升温到100 K后,TiO₂表面的CO分子会迁移到Pt-CO处形成Pt-(CO)₂的复合结构. 对于O₂分子,单个Pt原子同样会吸附一个O₂分子,O₂分子也会与最近邻或次近邻的Ti_5c原子成键形成两种Pt-O₂构型. 这些结果在单分子尺度上揭示了CO和O₂与Pt单原子的相互作用,呈现了CO与O₂反应中的初始状态.     

Mg+注入对GaN晶体辐射损伤的研究

在蓝宝石衬底上通过金属有机物化学气相沉积(metal-organic chemical vapor deposition，MOCVD)方法外延生长的GaN薄膜具有良好的结晶品质，χ_min达到2.00%. 结合卢瑟福背散射/沟道(Rutherford backscattering/channeling，RBS/C)和高分辨X射线衍射(high-resolution X-ray diffraction，HXRD)的实验测量，研究了不同剂量和不同角度Mg⁺注入GaN所造成的辐射损伤. 实验结果表明，随注入剂量的增大，晶体的辐射损伤也增大，注入剂量在1×10¹⁵atom/cm²以下，χ_min小于4.78%，1×10¹⁶atom/cm²是Mg⁺注入GaN的剂量阈值，超过这个阈值，结晶品质急剧变差，χ_min达到29.5%；随机注入比沟道注入的辐射损伤大，且在一定范围内随注入角度的增大，损伤也增大，在4×10¹⁵atom/cm²剂量下偏离〈0001〉沟道0°，4°，6°，9°时的χ_min(%)分别为6.28，8.46，10.06，10.85；经过700℃/10min+1050℃/20s两步退火和1000℃/30s高温快速退火后，晶体的辐射损伤都有一定程度的恢复，而且1000℃/30s高温快速退火的效果更好，晶体的辐射损伤可以得到更好的恢复. 关键词： GaN 卢瑟福被散射/沟道 高分辨X射线衍射 辐射损伤     

Magnetic and structural study of Cu-doped TiO2 thin films

Transparent pure and Cu-doped (2.5, 5 and 10 at.%) anatase TiO₂ thin films were grown by pulsed laser deposition technique on LaAlO₃ substrates. The samples were structurally characterized by X-ray absorption spectroscopy and X-ray diffraction. The magnetic properties were measured using a SQUID. All films have a FM-like behaviour. In the case of the Cu-doped samples, the magnetic cycles are almost independent of the Cu concentration. Cu atoms are forming CuO and/or substituting Ti in TiO₂. The thermal treatment in air promotes the CuO segregation. Since CuO is antiferromagnetic, the magnetic signals present in the films could be assigned to Cu substitutionally replacing cations in TiO₂.     

Single crystal RuO2/Ti and RuO2/TiO2 interface: LEED, Auger and XPS study

The interactions at the evolving RuO₂/titanium interface have been studied by LEED, AES and XPS. Titanium films of up to 5 monolayers were evaporated onto well ordered and ion sputtered ruthenium dioxide crystal surfaces of (110) and (100) orientation. Stabilization of the surface oxygen content under thermal treatment in UHV (up to 600°C) with increasing titanium coverage was established. After extended (up to 4 h) annealing in O₂ at 600°C an epitaxial ordering of TiO₂ on RuO₂(110) was observed. The (1 × 1) LEED patterns from the epitaxial layer exhibit a reduced background level when compared to the RuO₂ substrate itself. These findings are correlated with the XPS data and are interpreted in connection with the disappearance of the defect RuO₂ phase in the surface layer of the RuO₂. The appearance of the (1 × 2) surface reconstruction at the RuO₂(100)/Ti interface is discussed in the context of maximum cation coordination by oxygen atoms.     

Total cross sections for scattering of electrons from O2, H2O, H2, O3, CO and CO2 at 100－2000eV

A complex optical model potential rewritten by the concept of bonded atom, which considers the overlap of electron clouds, is employed to calculate the total cross sections for electron scattering from several simple molecules (O_2, H_2O, H_2, O_3, CO and CO_2) consisting of C, H and O atoms in an incident energy range of 100－2000eV by the use of the additivity rule at Hartree－Fock level. In the study, the complex optical potential composed of static, exchange, correlation polarization plus absorption contributions firstly uses the bonded-atom concept. The quantitative molecular total cross section results are compared with experimental data and with the other calculations wherever available and good agreement is obtained. It is shown that the additivity rule along with the complex optical model potential rewritten by the concept of bonded atom can be used successfully to calculate the total cross section of electron－molecule scattering above 100eV, whereas the rule together with the complex optical model potential not rewritten by the concept of bonded atom is only successfully used above 300－500eV. So, the introduction of the bonded-atom concept in the complex optical potential can improve the accuracy of the total cross section calculations.     

TiO2/SiO2多层膜的带隙结构及光催化性能

利用传输矩阵法设计了由SiO2、TiO2组成的多层膜高透射率光子晶体结构,并分析了其透射谱特性,根据等效层原理改变多层膜一维光子晶体的自身结构来提高通带内特征波长附近的透射率,获得了最佳结构参数。研究结果表明,当晶格参数为150nm,填充比为0.346,周期数为6时,400nm波长附近吸收带处的透射率最低也可达96.5%,并且不论是TM模式还是TE模式,入射角在0°～45°范围内仍保持高的透射率,该结构可望用于空气净化装置以提高SiO2、TiO2光催化剂的光催化效率。