摘要:

The x‐ray standing wave (XSW) technique was applied to determine the lattice location of Si impurity atoms in GaAs(100) crystals. The synchrotron radiation of X24A at the national synchrotron light source was utilized to set up backreflection XSW, an experimental geometry which drastically relaxes the otherwise stringent requirement on the lattice perfection. Specifically, the lattice sites were determined with respect to the [311] reflection planes which differentiate a Ga site from an As site. With the aid of an appropriate choice of the x‐ray fluorescence filter, we were able to study GaAs(100) samples with very low levels of Si impurities. On a sample doped with 4×1018cm−3Si during the molecular‐beam epitaxy growth, we found that the Si atoms predominantly occupied the Ga sites. On both an ion‐implanted sample after annealing and a sample with Si impurities introduced by thermal diffusion, about 30% of the Si atoms occupied the Ga sites, and the rest occupied random sites. The As site occupation was less than 6%. Suggestions are made for further experiments with improved sensitivity.

ISSN:0021-8979    

DOI:10.1063/1.353430

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A laboratory x‐ray diffractometer for surface and thin‐film studies is presented.Exsitustructural characterization of FeSi2films epitaxially grown on Si(111) is reported. Both specular and nonspecular reflectivities are measured on &bgr;‐FeSi2films grown by solid‐phase epitaxy and reactive deposition epitaxy techniques. A detailed comparison is performed of the electron density profile of the films normal to the surface, as well as of their surface roughness. In‐plane diffraction is also measured at grazing incidence. For the &bgr;‐FeSi2sample investigated, the (110) epitaxy on Si(111) is clearly shown. For a film grown by molecular‐beam‐epitaxy codeposition at 550 °C, the existence of a new metastable phase which is in registry with silicon along the Si⟨1¯ 10⟩ direction and slightly out of registry, (3.0±1.0)% compressed along the Si⟨112¯⟩ direction, is reported.

ISSN:0021-8979    

DOI:10.1063/1.353431

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Soda‐lime‐silicate glass has been implanted with 500 keV Er ions at fluences between 8.6×1014and 1.8×1016/cm2with the aim to optically dope the material in the near surface region. The ion range was 100 nm, and Er concentrations in the range 0.09—1.9 at. % were obtained. The characteristic photoluminescence (PL) of Er3+around 1.54 &mgr;m is observed at room temperature in as‐implanted glass. The PL intensity increases by an order of magnitude after annealing above 500 °C, as a result of annihilation of implantation‐induced defects. Annealing causes an increase in PL lifetime. As a function of Er fluence, the PL intensity first increases, but levels off above ∼6×1015Er/cm2(0.6 at. % Er peak concentration). The PL lifetime decreases from 13 to 1.5 ms for increasing Er concentration. The decrease in PL efficiency with concentration is attributed to concentration quenching caused by Er‐Er interactions. The optimal combination of PL intensity and lifetime is reached at ≊0.4 at. % peak concentration, for which the lifetime is 6 ms. For high Er concentrations and high pump intensities (∼3 kW/cm2) an additional, intensity dependent quenching mechanism (possibly cooperative upconversion) is observed.

ISSN:0021-8979    

DOI:10.1063/1.353432

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have found definite evidence which proves that radiation damage in SiO2/Si induced by low‐energy electrons is caused by plasmon excitation in SiO2. The SiO2/Si sample was irradiated by accelerated thermoelectrons, and the flat‐band voltage shift, &Dgr;VFB, of the sample was measured by theC‐Vmethod. The effective charge generation yield,Rf, in SiO2/Si was evaluated from the &Dgr;VFBand the electron dose. The effective positive charges were measured inp‐type SiO2/Si, and the effective negative charges were measured inn‐type SiO2/Si. This is because interface states behave like positive charges inp‐type SiO2/Si and negative charges inn‐type SiO2/Si. TheRfinp‐type SiO2/Si oscillated as a function of the incident electron energy of 5–150 eV with several clear peaks. These peaks correspond to the quantum energy of a bulk plasmon or a surface plasmon. Both plasmons decay into electron‐hole pairs. The holes that escape from recombination with the electrons are trapped at the SiO2/Si interface and cause effective positive charges. TheRfwas maximum when the SiO2thickness was 20 nm, independent of the incident electron energy. This is because the plasmon region extends to about 20 nm in SiO2, and the hole‐trapping efficiency is expected to be maximum at a SiO2thickness of 20 nm.

ISSN:0021-8979    

DOI:10.1063/1.353433

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Scanning probe studies of electromigration in 4‐&mgr;m‐wide by 1‐&mgr;m‐thick electroplated Au wires reveal changes in surface morphology. Features that develop on a submicrometer length scale were observed using current densities up to 7.5×106A/cm2and temperatures up to 280 °C for time intervals ranging from a few minutes up to a few days. Scanning probe images of thesamearea taken before, during, and after current stressing reveal substantial changes in surface morphology. Both hillock growth and void formation have been observedinsitu. Changes in surface morphology caused by electromigration can be quantitatively described from the scanning probe images and new techniques for studying mass flow due to electromigration are now possible.

ISSN:0021-8979    

DOI:10.1063/1.353434

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Energy‐dispersive x‐ray diffraction studies were carried out on the III‐V compound aluminum nitride to 65 GPa using a synchrotron x‐ray source. A pressure‐induced first‐order phase transition from a wurtzite structure to a rocksalt structure was observed. The first peaks of the high‐pressure phase appeared at 14 GPa. On further loading of the diamond anvil cell, the wurtzite peaks disappeared by 20 GPa. After unloading the cell to atmospheric pressure, the rocksalt structure persisted. The equilibrium transformation pressure lies on the interval 0–14 GPa.

ISSN:0021-8979    

DOI:10.1063/1.353435

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Time‐resolved transmission electron microscopy (TEM) was applied to study phase transitions in free‐standing Ni0.75Al0.25films, induced by pulses from an Nd:YAG laser (20 ns, 532 nm). At fluences above 0.23 J/cm2melting occurred within the laser pulse, the liquid was set into violent motion during 300 ns after melting, and the film solidified 1–2 &mgr;s later. The liquid motion was triggered by expansion of the melting film. Solidification proceeded by heterogeneous nucleation of crystals at the periphery of the laser molten spot and by centripetal growth of large plates with velocities 0.9–2.4 m/s, from which a supercooling of 2–20 K at the liquid/crystal interface is inferred. The final texture consisted of large &ggr; and &ggr;’crystals plus fine‐grained Al precipitates. The dynamics were either continuously traced or intermediate stages were visualized by double‐frame TEM with exposure times of some 10 ns.

ISSN:0021-8979    

DOI:10.1063/1.353436

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A modified variant of Fisher’s model is proposed to describe the recently discovered phenomenon of fast impurity diffusion along grain boundaries (GBs) in metals as follows, (i) The fast diffusion is assumed to occur by the dissociative mechanism. Depending on the lattice dislocation density &rgr; the bulk diffusion of the impurity around GBs is either vacancy controlled [if (Dt)1/2≪&rgr;−1/2] or interstitial controlled [if (DT)1/2≫&rgr;−1/2]. In the first case the effective bulk diffusivityDdepends on the GB concentration whereas in the second caseD=const. (ii) Fast diffusers strongly segregate to GBs. The GB saturation effect is taken into account by introducing McLean’s isotherm of GB segregation. The GB penetration profiles calculated from approximate analytical solutions of the model exhibit two parts: a near‐surface part caused by the GB saturation effect and a more deeply penetrating linear segregation part with a much smaller slope. The second part of the profile either shows strong downward curvature (vacancy‐controlledD) or demonstrates normal Fisher‐like behavior (interstitial‐controlledD). Methods of profile treatment for the determination of GB diffusion parameters are presented. Based on the present model the available experimental data are critically considered and ideas of future experiments are discussed.

ISSN:0021-8979    

DOI:10.1063/1.353437

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The diffusion of boron in N2ambient is studied by usingp+polysilicon metal‐oxide‐silicon structures annealed during times long enough to allow boron diffusion through the gate oxide, up to the underlying substrate. Assuming equilibrium segregation at the interfaces, the boron diffusivity in the oxide is calculated by numerically fitting the resulting profile in the substrate. It is found that B diffuses in SiO2with an activation energy of about 3 eV. We also quantify the influence of the nitridation of the oxide, and confirm its efficiency as a diffusion barrier. However, this study reveals a strong inconsistency between the extracted diffusivity values of B in SiO2and the amount of B atoms being able to reach the Si/SiO2interface to account for the observed interface state density.

ISSN:0021-8979    

DOI:10.1063/1.353438

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

1.8 MeV He+ion backscattering and channeling was used to study various lattice matched and mismatched ScxYb1−xAs and ScyEr1−yAs films grown on GaAs (001). The lattice matching leads to excellent epitaxy with &khgr;minas low as 1.5% along the [001] direction. It is demonstrated unambiguously that the interface peaks result from the first atoms of the Ga rows of the substrate, indicating that the As sublattice is continuous across the rare‐earth monoarsenide/GaAs interface. These lattice matched heterostructures are proposed as ideal tools for studying ion channeling phenomena. Concerning the mismatched heterostructures, it is shown that the mosaic resulting from the strain relaxation, and the lattice tilt occurring for thick films can be evaluated directly from aligned spectra.

ISSN:0021-8979    

DOI:10.1063/1.353439

出版商:AIP    

年代:1993

数据来源: AIP