Investigations of thin films on GaAs using the proton resonant scattering technique

We have characterized a number of thermally stable thin film/GaAs systems including thin films of refractory metal suicides and nitrides as well as dielectric films on GaAs substrates using a MeV proton scattering technique. Thin films of tungsten suicides, zirconium nitride and silicon dioxide on GaAs substrates are investigated. The enhanced proton scattering cross sections of nitrogen, silicon and oxygen at their corresponding resonant energies enable us to accurately measure the compositions of these films. The advantages and disadvantages of this technique regarding depth resolution, accessible depth, and mass resolution compared to the conventional Rutherford backscattering spectrometry for thin film analysis are discussed.     

Investigations of radiative electron capture by ion channeling techniques

The unique constraints imposed on the interactions of energetic heavy ions with target atoms as a result of the channeling effect are utilized to investigate the phenomenon of radiative electron capture (REC) for 17 to 40 MeV oxygen ions. Measured cross-sections and widths of the REC radiation are compared to calculations made specifically for the channeling situation.     

Determination of the electronic energy loss of light ions in a silicon lattice by using the transmission ion channeling method

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon and oxygen at trace levels in semiconductor materials. This technique requires the knowledge of the stopping powers of these materials for channeled ions. The electronic energy loss for ions entering the crystal lattice in a random direction is well established. The electronic energy losses for protons, deuterons, ³He⁺ and ⁴He⁺ ions entering a 3.6 μm thick silicon single crystal along the 1 0 0 direction were measured by using the transmission of particles technique. Data obtained were compared with those obtained by other authors using theoretical and experimental methods.     

On the lattice location of implanted impurities in silicon

As implanted ions are brought to rest at relatively low energies, one can anticipate that their lattice sites are predominantly determined by the local chemical bond depending on the band structure of the host crystal and the electronic configuration of the implanted impurities. Consequently, one can expect that for a given pure semiconductor the occupancy of various impurity sites will vary with the valency of the impurity atoms. As an example, impurity sites of several groups of nontransition elements of the Periodic Table implanted in silicon are discussed and compared with recent experimental data. Further, a few simple rules concerning the behaviour of implanted impurities in silicon are formulated giving some insight into the nature of the electronic structure of implanted semiconductors.     

Foreign atom location by channeling in a helium irradiated Al-Mn alloy

The results of channeling experiments on single crystals are not in all cases comparable to analytical calculations with the continuum model, in which the interactions with the individual atoms surrounding the channel are smoothed out. For interpretation of angular scans it is necessary to simulate the channeling process in a Monte Carlo program on the basis of the binary collision model. Such a program which yields the energy and flux distributions of the channeled ions by calculating their collisions with the nearest target atoms in the momentum approximation was described earlier.With this program, irradiation induced interstitial-impurity complexes in a dilute Al-0.09 at.% Mn alloy are analysed on the basis of 〈111〉 and 〈110〉 symmetrical and — for the first time published — asymmetrical angular scans measured by Swanson et al. Here, He⁺ ions backscattered from the Mn atoms are assumed to be displaced in a 〈100〉, 〈110〉 or 〈111〉 direction from a normal lattice site. Displacements of this kind would occur in mixed dumbbells, where an impurity atom and a self-interstitial atom share one lattice site. The best fit to the experimental data has been obtained assuming the impurity atom to be displaced 0.14 nm in 〈100〉 direction. A 〈111〉 mixed dumbbell with a displacement of 0.22–0.27 nm might be possible, too. The evaluation needs the value of the stopping power in channel direction the knowledge of which is inaccurate. It will be shown that the results are not sensitive to the angular dependence of this stopping power.     

Theoretical critical angels of ion channeling in carbon nanotubes

We have developed a mass- and charge-dependent equation to predict theoretical critical angles for ion channeling in carbon nanotubes. We focus M (ion mass) effects how to reduce Ze (ion nucleus charge) effects on Ψ_C (critical angles). As an instance, we give theoretical critical angels of He, Ne, Ar, Kr, Xe and Rn ion channeling in carbon nanotubes. We find that for (10, 10) single-wall carbon nanotubes, Ψ_C(He) ≈ Ψ_C(Ne) ≈ Ψ_C(Ar) ≈ Ψ_C(Kr) ≈ Ψ_C(Xe) ≈ Ψ_C(Rn) ≈ 23.3 (keV/E)^1/2 deg. This is because (Z/M)^1/2 ≈ 0.66 [amu]^?1/2.     

室温下GaAs中正电子迁移率的测量

用正电子湮没寿命谱方法测量了GaAs中的正电子迁移率,在低电场(小于300Vcm~(-1))和室温294K条件下测得μ_+=880±40cm~2V~(-1)s~(-1)。     

Channelling studies on the lattice location of B atoms in graphite

In order to obtain information on the lattice location of B atoms in graphite, channelling experiments have been performed at room temperature with a proton beam of an energy of 0.65-0.77 MeV for the 〈0 0 0 1〉 axial channel in highly oriented pyrolytic graphite (HOPG) crystals doped with 0.32 at.% B. The B atoms are detected by measuring α-particles which are emitted as a result of a nuclear reaction ¹¹B(p,α)αα. It is clearly demonstrated that most of B atoms are shadowed behind the 〈0 0 0 1〉 C atomic rows. Taking account of the already reported experimental results on a change of lattice parameters by B-doping, it is concluded that most of B atoms are located at substitutional sites. It is also observed that B-doping introduces lattice strain on the c-plane. In addition, the presence of a small portion of interstitial B atoms is suggested.     

Bonding effect on channeling of C ions in a carbon nanotube

The channeling phenomenon of carbon ions in single-wall carbon nanotubes (SWCNTs) is investigated by using the molecular dynamics simulation with analytical potentials.The relationship between the channeling critical angles in the SWCNT and the bonding interaction is analyzed.It was found that,at 200-5000 eV and 10°-20° of incident angle,the ions with the bonding interaction or chemical effect,have decreased dechanneling probabilities and increased critical angles,compared to that of non-bonding ions.So the bonding effect cannot be ignored in the channeling mechanism of carbon ions through a SWCNT.     

用蒙特卡洛方法计算砷化镓中的正电子迁移率

用计算机模拟的方法获得正电子在半导体材料的迁移率，讨论了正电子有效质量，杂质浓度和温度对正电子迁移率的影响。     

Measuring the magnetic moments of short-lived particles using channeling in bent crystals

A recent demonstration of spin precession using channeling in a bent crystal offers the interesting possibility of a technique to measure magnetic moments of short-lived charm baryons. There are significant differences among theoretical models of these moments. Accumulating experimental evidence indicates the tools used for hyperon magnetic moment measurements, polarized production and decay asymmetries, may also be available with heavier baryons. Useful measurements may be possible using the channeling technique but they will require challenging beam conditions.     

Investigations of the origins of deposited carbon species in gaps between divertor tiles using a kinetic code system

In order to investigate the origins of deposited carbon species in gaps, the simulations have been performed using a kinetic code system. At low plasma temperatures, the deposited carbon species mainly originate from top surfaces of the tile, while at high plasma temperatures the deposited carbon species are basically derived from side surfaces of the tile. A substantial variation of the deposition rate of carbon species originating from side surfaces is obtained due to physical sputtering and topography advantage. The deposited carbon species derived from top surfaces and side surfaces demonstrate different deposition characteristics for physical sputtering and chemical erosion: (i) for deposited carbon species from top surfaces, the deposition ratio for physical sputtering increases evidently and deposition rate virtually increases by one order of magnitude with increasing plasma temperature; and the deposition ratio for chemical erosion reduces correspondingly and deposition rate decreases gradually; (ii) for deposited carbon species from side surfaces, the deposited carbon species principally arise from physical sputtering; the deposition rates for chemical erosion are of the order of magnitude of 10¹⁵ m^?2 s^?1 for all studied plasma temperatures, and the deposition rates for physical sputtering can be two to three orders of magnitude greater than that for chemical erosion.     

Lattice strain measurement of strained In0.1Ga0.9As/GaAs heterostructures by RBS and channeling

Organometallic Vapor Phase Epitaxy (OMVPE) grown layered structures of In_0.1Ga_0.9As/GaAs have been analyzed by He⁺⁺ ion backscattering and channeling. From the random spectrum, the In_xGa_1 − xAs layer thickness was determined to be around 300 Å and the composition of In to be In_0.1 within an experimental error of around 5%. The χ_min obtained from the In signal is around 7% which shows that the epilayer is of good crystallinity. The normalized yield vs. the tilt angle for the epilayer and the substrate along the off-axis (along [1 1 0] direction of the substrate) shows a shift in the minimum yield χ_min dip, which is a direct measure of the strain present. This shift is found to be 0.2 ± 0.05° corresponding to a tetragonal distortion of 0.7 ± 0.2%. Shifting of the minimum yield dip of the overlayer towards left side with respect to the substrate indicates that the strain is compressive which is what is expected. X-ray diffraction is also carried out on the same sample which gives us ϵ_⊥=1.01% and the in-plane lattice mismatch is nearly zero.     

Apparatus for magnetic moment measurement using channeling in bent crystals

A recent experiment has demonstrated spin precession using a bent channeling crystal. In the experiment defect dechanneling was studied and dechanneling from dislocation slip planes was observed for the first time. Information was gained on preparing the crystal detectors. X-ray diffraction techniques were developed for pre-alignment. Ramifications for trans-TeV channeling are explored.     

Measurement of channeling radiation using a 45 MeV betatron

An experimental setup for the measurement of channeling radiation from relativistic electrons in single crystals is described. A betatron with a maximum beam energy of 45 MeV is used as electron source. The beam divergence is tuned to less than 0.3 mrad by means of a beam optic system. Results of the measurement of channeling radiation in silicon and beryllium crystals are reported and compared with calculations.     

A study on technique to estimate impact location of loose part using Wigner-Ville distribution

Presented in this paper is a method to estimate impact location of a loose part using the Wigner-Ville distribution. The method uses dispersion characteristics of bending waves propagated in a plate. The power propagation velocity and arrival time difference of bending waves related to the dispersion characteristics can be obtained through the transformation of impact signals using the Wigner-Ville distribution. The distance from the impact location to the signal measuring point can be estimated using the information on the power propagation velocity and the arrival time difference of two bending waves. The experimental results show that the proposed method estimates the impact location with relative percentage error within 10% compared with the actual impact location.     

5.0MeV和9.5MeV快中子辐照在GaAs中产生的辐射损伤的正电子湮没研究

采用正电子湮没寿命测量方法研究了５．０ＭｅＶ和９．５ＭｅＶ快中子辐照在ＧａＡｓ中产生的辐射损伤，实验结果表明１０＾１１－１０＾１２ｎ／ｃｍ＾２注量的中子辐照只产生单空位缺陷１０＾１３ｎ／ｃｍ＾３注量的中子辐照产生单空位和双空位缺陷，１０＾１２ｎ／ｃｍ＾２注量的９．５ＭｅＶ中子辐照的ＧａＡｓ经４５０－６２０℃退火产生三空位缺陷，产生的缺陷浓度随中子能量和注量的增大而增大，但缺陷产生率对中子注量更灵敏     

The lattice location of helium implanted in α-SiC

Methods of ion channeling analysis, employing backscattering spectrometry and the ion-induced ³He(d,p)⁴He nuclear reaction, were applied to specify a lattice site of high symmetry for helium in α-SiC. Single-crystal α-SiC, held at 300 K, was implanted with ³He⁺ at 75 keV. By considering the channeling angular distributions and the crystal structure, a probable position within the unit cell was qualitatively identified. Significant clustering and random positioning were not present. A single helium atom was centrally positioned in either a substitutional site or a tetrahedral interstitial site. Limitations upon the number of available low-index channeling directions prevented precise specification of the final lattice location. The availability of α-SiC with an orientation normal to the 0001 axis would allow the two identified possible locations for the helium to be distinguished.     

Investigations on uranium carbonitrides (I): The lattice parameters of the solid solutions

The lattice parameters of the UC-UN solid solutions have been measured at room temperature as a function of composition. Equilibrium has been approached from two directions, by starting from UC + UN or from UN + graphite mixtures. After equilibrium, which was readily obtained at 1800°C, a careful chemical characterization was carried out, including chemical analyses of all major elements.     

用离子束沟道技术研究GexS1—x／Si应变超晶格

用RBS结合沟道技术对Ge_xSi_(1-x)/Si应变超晶格材料的组分和形变进行了分析。实验结果与样品生长参数记录及理论计算值符合得很好。实验表明,离子束沟道技术对于应变超晶格的结构研究是一种十分有效的分析方法。