摘要:

The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported. Thesp3fraction was found to strongly depend on the ion energy, giving a highlysp3bondeda-C denoted as tetrahedral amorphous carbon (ta-C) at ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly withsp2fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure ofa-C. The structure ofta-C was also strongly dependent on the deposition temperature, changing sharply tosp2above a transition temperature,T1, of ≈200 °C. Furthermore,T1was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to thesp3fraction. However, the optical and electrical properties were found to undergo a more gradual transition with the deposition temperature which we attribute to the medium range order ofsp2sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface aboveT1due to thermal activation, leading to the relaxation of density in context of a growth model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364000

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Silicon carbide amorphous thin films have been bombarded with 100 keV N ions. Infrared-absorption spectroscopy has been used to study the effect of increasing ion doses, up to 5×1017N+ cm−2, on the evolution of chemical bonding between Si, C, and N. The changes induced by thermal annealing at different temperatures, up to 973 K, on the stability of the bombardment induced SiCxNyphase are investigated, together with the effect of surface oxidation during the postannealing cooling of the films. The new phase is thermally stable within the temperature range investigated. At the highest implantation dose a threshold is reached above which N atoms are located as interstitial, or are weakly bonded in the host film. Annealing at high enough temperature induces migration toward the surface and subsequent loss of interstitial N. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364001

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Segregation and trapping of Er during solid-phase crystallization of amorphous Si on crystalline Si is studied in a concentration range of 1016–5×1020Er/cm3. Amorphous surface layers are prepared on Si(100) by 250 keV Er ion implantation, recrystallized at 600 °C, and then analyzed using high-resolution Rutherford backscattering spectrometry using 2 MeV He+or 100 keV H+. The segregation coefficientkdepends strongly on Er concentration. At Er interface areal densities below 6×1013Er/cm2nearly full segregation to the surface is observed, withk=0.01. At higher Er densities, segregation and trapping in the crystal are observed, withk=0.20. The results are consistent with a model in which it is assumed that defects in thea-Si near the interface act as traps for the Er. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364002

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have performed scanning tunneling microscopy (STM) in ultrahigh vacuum and transmission electron microscopy (TEM) on silver and gold clusters grown in preformed nanometer-sized pits on the surface of highly oriented pyrolytic graphite. We describe the preparation method and evaluate the three-dimensional shape of the clusters using a combination of STM and TEM applied to the same cluster sample. The nanometer-sized pits were essential to fix the clusters in position when using STM. The influence of the tip shape on the STM imaging of nanometer-sized clusters is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364003

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new and versatile model of capillary-driven microstructural evolution is described. The model operates on digital images of microstructures, and uses the local phase distribution to form an interpolated “equivalent sharp surface.’’ Local surface properties, like outward normal vectors and curvatures, are calculated and local driving forces for mass transport are determined using standard irreversible thermodynamic concepts. Mass transport kinetics are simulated using discretized rate laws for a specified path and rate-controlling step. Models of surface diffusion and of surface-attachment-limited kinetics are described and applied to several systems. Results for simple microstructures agree well with analytical predictions of transport rates and scaling laws, and useful quantitative information is extracted from simulations on more complex microstructures for which analytical predictions do not exist. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364004

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have grown stoichiometrically identical superlattices comprising a bcc transition metal (V, Cr, Fe) together with the metastable high temperature bcc &dgr;-Mn modification on Ge(001) substrates. Despite identical molecular beam epitaxial growth conditions and identical bulk crystal structures of V, Cr, and Fe with nearly identical lattice parameters, the superlattices show a very different crystallographic behavior. The lattice parameters of &dgr;-Mn are found to be strongly dependent on the thickness of the Mn layers as well as the lattice parameters of the adjacent metals. Therefore, different distortions of the cubic bcc &dgr;-Mn structure can be obtained, ranging from almost cubic structures in V/&dgr;-Mn superlattices to large tetragonal distortions(c/a≈8&percent;)in Cr/&dgr;-Mn superlattices. Nevertheless, we found that the unit cell volume of the &dgr;-Mn modification remains almost constant for thin Mn layers, and that the deduced cubic lattice parameter for &dgr;-Mn (a=2.985Å) significantly differs from previously predicted and published values. This result appears to be of great importance concerning the predicted magnetic properties of &dgr;-Mn. All presented simulations were performed using the refinement programSUPREXwritten by Schuller, Fullerton, and Bruynseraede. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364005

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The peculiarities of high-resolution measurements in grazing-incidence diffraction (GID) are studied, both theoretically and experimentally. It is shown that complete discrimination between coherent reflection and diffuse scattering due to defects in GID requires a three-dimensional mapping of reciprocal space. These measurements can be performed using a combination of analyzer crystal and position-sensitive detector for angular analysis of scattered x-rays in mutually perpendicular planes. The equations for the resolution function of GID experiments are given and applied to the interpretation of GID measurements taken from an AlAs/GaAs superlattice. The discrimination of diffuse scattering due to interfacial roughness in the superlattice is demonstrated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363838

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of aging on Co/C multilayer x-ray mirrors is presented. One significant result is the enhancement of the reflectivity at grazing incidence with time for the Co/C multilayers with C-on-top stored in air or argon and Co-on-top stored in argon. This can be interpreted in terms of a Co–C phase-separation at Co–C interfaces due to the positive enthalpy of Co–C mixing. Results also show that oxidation of the surface of Co-on-top Co/C multilayers plays an important role in the decrease of reflectivity. The oxidation can be prevented by storing the multilayers in an oxygen-free atmosphere or by depositing amorphous carbon as the top layer. The reflectivity of tarnished multilayers can be restored by removing the oxides by wet chemical methods. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363839

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the structural and defect characteristics of GaAs and AlxGa1−xAs grown at low substrate temperature (250 °C) by molecular beam epitaxy. Using x-ray diffraction we have observed an increase in lattice parameter for all as-grown layers, with the AlxGa1−xAs layers showing a smaller expansion than the GaAs layer. However, infrared absorbtion measurements revealed that the concentration of neutral arsenic antisite defect, [AsGa]0, was not significantly affected by aluminum content(x), with only a small reduction forx=0.36. Positron beam studies showed that the low temperature layers had a higher concentration of vacancy-related defects (∼1017cm−3) than the semi-insulating substrate, with the AlxGa1−xAs layers having the highest values. After annealing (600 °C, 15 min) the lattice constants relaxed to those of conventionally grown material and [AsGa]0was reduced in all cases, with the smallest reduction occurring for thex=0.36 layer, indicating that the Al atoms strengthen the lattice against excess arsenic incorporation and hold the arsenic antisite atoms more strongly in position. X-ray photoelectron spectroscopy showed that arsenic diffused out of the surface region and was replaced by oxygen, possibly due to an insufficient overpressure of forming gas during the anneal. This oxygen penetration was greater for the GaAs layer than for the AlxGa1−xAs layers. Extra Raman peaks at 200 and 257 cm−1confirmed that the surface was very disordered. There was, nevertheless, a large increase (4&percent;) in the positronSparameter in the bulk of the annealed layers, suggesting the formation of vacancy clusters, whereas in the surface region we find evidence that AsGadiffusion proceeded at a faster rate in thex=0.36 than thex=0.2, in agreement with the vacancy-enhanced AsGadiffusion model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364105

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Structural properties of Si0.7Ge0.3alloy films grown on Si(001) substrate by molecular beam epitaxy have been characterized by means of several available techniques. Different types of buffer layers were predeposited on a clean Si(001) substrate in order to relax the lattice mismatch between the topmost Si0.7Ge0.3alloy layer and Si substrate. The effect of buffer layers on the structural quality of the overgrown Si0.7Ge0.3was investigated by x-ray diffraction, x-ray photoemission spectroscopy, photoluminescence, and cross-sectional transmission electron microscope. It is confirmed that the threading dislocation density in the alloy layer drastically decreases by using buffer layers. The samples with step buffer layers relax the strain by introducing the dislocations at the interfaces, part of which goes through the alloy layer. On the other hand, the samples with superlattice buffer layers relax the strain by introducing the dislocations in the buffer layers which terminate at the interface of the superlattice buffer layer and the topmost alloy layer. The residual strain in the alloy layers on buffer layers grown at 550 °C is relaxed upon the annealing at 700 °C, or the growth at 700 °C. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363841

出版商:AIP    

年代:1997

数据来源: AIP