摘要:

Epitaxial crystal growth using an energy- and mass-analysed ion beam can provide insights into the fundamental processes involved in thin-film growth. In these experiments layers of silicon were deposited onto (001) silicon substrates using 30 eV and 50 eV28Si+ions. This Letter reports on the use of ultramicrotomy and high-resolution transmission electron microscopy to obtain lattice images of ion-beam-deposited epitaxial silicon films. The lattice images show that film growth proceeds via a competition between epitaxial and amorphous phases, similar to island (Volmer–Weber) growth. Electron energy loss and ion scattering measurements show that, although the film is epitaxial, it contains defect structures. The lattice images indicate that a sufficient amount of the native oxide layer could be removed simply using low-energy28Si+bombardment to enable epitaxial growth. In the case of samples etchedin situby low-energy chlorine ions, initial epitaxial growth gave way to an amorphous growth phase after ≈ 7·5 nm.

ISSN:0950-0839    

DOI:10.1080/09500839008206498

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

We present here a rotation matrix in five-dimensional space which connects the decagonal phase to a tetragonal crystalline related phase through a one-dimensional quasicrystals range by means of a phason-phonon coupling. Phason and phonon fields are determined in a general way and, from this result, a simple linear approximation is given. Continuous evolution density-wave patterns are shown.

ISSN:0950-0839    

DOI:10.1080/09500839008206499

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Nanometre-size semiconductor clusters trapped in glass matrices represent a novel class of nonlinear optical materials. Microstructural characterization of these materials by conventional and high-resolution transmission electron microscopy (TEM and HRTEM) shows the sensitivity of bright-field image contrast to the nature of the specific II–VI semiconductors (CdS, CdSe) precipitated in the glass matrices. An analysis based on electron-scattering intensity and structure-factor calculations is presented to account for the quality of TEM and HRTEM images observed for CdS- and CdSe-containing quantum-dot glasses.

ISSN:0950-0839    

DOI:10.1080/09500839008206500

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

GaAs current-controlled bipolar-unipolar transition negative differential resistance (NDR) transistors using n+-i-p+-i-n+structure prepared by molecular-beam epitaxy (MBE) are demonstrated. Using a base thickness of 200 Å and a highly doped sheet concentration of 1013cm−2, a NDR phenomenon is revealed at base low injection level. The peak-to-valley current ratios are about eight at room temperature. This is proposed to be due to the bipolar-unipolar transition reaction. When the base is under a high injection level, the proposed device operates just like a conventional bipolar transistor. A hypothetical model is used and confirmed by experiments.

ISSN:0950-0839    

DOI:10.1080/09500839008206501

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A new negative differential resistance (NDR) device with a bulk barrier and resonant tunnelling structure has been prepared by molecular-beam epitaxy. A peak-to-valley current ratio up to 22 and a peak current density of 10 kA cm−2are obtained at room temperature. The former is the largest value ever reported in the A1GaAs/GaAs system. Higher power output also can be expected.

ISSN:0950-0839    

DOI:10.1080/09500839008206502

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Electron microscopy of five pure type IaB diamonds (showing no trace whatever of a B′ infrared absorption peak due to {001} platelets) reveals voidite distributions unlike any reported before. In three of the crystals the voidites are distributed at random, and are not associated with degraded platelets, which themselves are not present in these specimens. These observations show that voidite formation and platelet degradation are distinct independent phenomena. The other two speamens showed only arrays of dislocations that patently resulted from plastic deformation: no voidites were seen. The non-formation of platelets in diamonds showing such an advanced stage of nitrogen aggregation is unexpected, and places these diamonds in a category distinct from that called ‘irregular’, in which platelets have indeed formed, but then experienced, to some degree, a process of transformation to perfect dislocation loops.

ISSN:0950-0839    

DOI:10.1080/09500839008206503

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The powder neutron-diffraction pattern of AgBr has been measured at 669 K and the structural disorder has been deduced by modelling both the diffuse and the Bragg scattering simultaneously using the reverse Monte Carlo technique. The density distribution of ions in the average unit cell shows considerable disorder of Ag+ions, with some Ag+ion density in the (1/4, 1/4, 1/4) interstitial site. The density distribution has been used to calculate the diffuse neutron scattering expected from a single crystal and measurements on a single-crystal sample of AgBr at 669 K are found to be in good agreement.

ISSN:0950-0839    

DOI:10.1080/09500839008206504

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor