摘要:

Yielding properties of Au point contacts of nanometer‐scale dimensions have been studied using a scanning tunneling microscope supplemented by a force sensor for measuring tip–sample forces. The contacts are made by indenting the tip typically 10 nm into the substrate, whereby an adhesion neck is formed. Three consecutive deformation phases of the neck can be identified during retraction of the tip: (1) buildup of tensile stress, (2) incomplete fracture, and (3) quasicontinuous plastic flow. Finally the neck breaks when a maximum of three to four atoms are left in the contact. In the plastic flow regime, the conductance and thus the contact area shrink exponentially with elongation of the neck, suggesting that plastic deformation occurs locally within 5 to 6 atomic layers. The stress applied during plastic flow is initially of the order of 10 GPa and gradually increases to &bartil; 20 GPa shortly before the neck breaks. Accounting for a surface force contribution, an intrinsic yield strength of the order of 5 to 8 GPa is obtained, which is more than one order of magnitude larger than the macroscopic yield strength of Au. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116493

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

By using the photomixing technique we have found that the drift mobility (&mgr;d) of intrinsic hydrogenated amorphous silicon (a‐Si:H) films produced by both glow discharge and hot wire techniques increases with increasing electric field, while the lifetime (&tgr;) decreases with increasing electric field, and the &mgr;d&tgr; product is essentially independent of the electric field. We have also found an empirical relationship that a greater field dependence of the drift mobility of ana‐Si:H film in the annealed state indicates a poorer stability of the photoconductivity upon light soaking. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116494

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter we demonstrate that the anomalously low (002) x‐ray rocking curve widths for epitaxial hexagonal GaN films on (001) sapphire are a result of a specific threading dislocation (TD) geometry. Epitaxial GaN films were grown onc‐plane sapphire by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) in a horizontal flow reactor. Films were grown with (002) rocking curves (&ohgr;‐scans) widths as low as 40 arcsec and threading dislocation densities of ∼2×1010cm−2. The threading dislocations in this film lie parallel to the [001] direction and within the limit of imaging statistics, all are pure edge with Burgers vectors parallel to the film/substrate interface. These TDs will not distort the (002) planes. However, distortion of asymmetric planes, such as (102), is predicted and confirmed in (102) rocking curve widths of 740 arcsec. These results are compared with films with (002) rocking curves of ∼270 arcsec and threading dislocation densities of ∼7×108cm−2. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116495

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effect of thermal annealing on the electrical conductivities of arsenic‐ion‐implanted GaAs has been investigated by deep level transient spectroscopy and temperature‐dependent conductance measurements. For the annealed films of arsenic‐ion‐implanted GaAs a band of deep‐level defects with the activation energy of around 0.55 eV below the conduction band is found. The dense concentration of traps is able to reduce the carrier concentration from 3×1018to 2×1017cm−3. The cross section of the deep level is calculated to be 1.5×10−14cm2. The carrier‐transport mechanisms of both as‐implanted GaAs and postannealed GaAs are dominantly shown to be a separate hopping and active‐type conduction. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116496

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Using a novel photocurrent difference spectroscopy, six conduction subbands have become observable in 20‐nm‐wide In0.53Ga0.47As/In0.52Al0.48As multiquantum wells. The observed wavelength range was 0.8–1.8 &mgr;m. A proper choice of electric fields in the well on the order of 90‐170 kV/cm made it possible to magnify the photocurrent difference spectrum by 1×104, owing to the Stark shift of about 20–100 meV. The interband optical transitions were limited to the field‐sensitive ones of mostly forbidden type. As a result, conduction‐subband eigen energies in the wells were determined at room temperature. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116497

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The thermal stability of the silicon doping of (111)A GaAs, grown by molecular beam epitaxy under different As overpressures, is studied by electrical and photoluminescence measurements. Annealing treatments were performed at 1028 K for 8 hr in As‐poor conditions. It is found that the silicon doping of (111)A GaAs is unstable; annealing turns the doping fromptype tontype inp‐type doped samples and increases the compensation inn‐type doped samples. The role of the point defects in the process is discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116498

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Structural transformations produced in strain‐relaxed, low‐dislocation‐density Si0.6Ge0.4films by As+implantation and rapid thermal annealing were studied by transmission electron microscopy and x‐ray microanalysis. The type of residual defects was found to be strongly dependent on annealing temperature. Only perfect dislocation loops were observed in implanted layers after annealing at 800 °C. Annealing at higher temperature (900 °C) results in complete removal of irradiation damage accompanied by the formation of GeAs precipitates of monoclinic phase and spherical shape. The results show that the behavior of As in Si–Ge alloys during thermal processing is remarkably different from that in Si. In particular, precipitation of As atoms in Si0.6Ge0.4was found at an As concentration of 9×1020cm−3which is at least one order of magnitude lower than the critical As concentration for As precipitation in Si. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116499

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a processing technique which is conducted entirely under an ultrahigh vacuum environment, calledinsituelectron‐beam (EB) lithography, to pattern GaAs substrates on which AlGaAs/GaAs wire and box structures are subsequently regrown. In this technique a thin GaAs oxide layer is selectively formed by EB‐stimulated oxidation under a controlled oxygen atmosphere, and is then used as a mask material to define mesa stripes and mesa squares by Cl2gas etching. Subsequently, the initial mesa size is reduced by the regrowth of a GaAs layer. Finally, AlGaAs/GaAs wire and box structures are fabricated on the top of the mesas by the growth of a quantum well. These structures were characterized by cathodoluminescence measurements at 77 K. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116500

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new amorphous semiconductor, 2CdO⋅PbOx(band gap: 1.58 eV), was found. Thin films of this material were prepared by rf sputtering of a Cd2PbO4target in O2–Ar. The dc conductivity of the resulting amorphous thin films was ∼180 S cm−1at 300 K and remained almost constant down to ∼4 K. The concentration of carrier electrons and the Hall mobility in the as‐deposited state were 1×1020cm−3and 9 cm2 V−1 s−1, respectively. When the as‐deposited specimens were heated to 250 °C, which is far below the crystallization (to Cd2PbO4) temperature (460 °C), the conductivity and the carrier concentration at 300 K became approximately twice as high. The thermal O2‐desorption measurements demonstrated that carrier electrons are generated via the formation of oxygen vacancies at the initial stage (<250 °C) of thermal desorption of O2from the amorphous structure. The effective mass of carrier electrons was estimated as 0.57m0. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116501

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter, we report the synthesis of epitaxial SnxGe1−x/Ge/Si(001) with compositions up tox=0.34 by ion‐assisted molecular beam epitaxy with 30–100 eV Ar+ions produced by an electron cyclotron resonance ionization source with ion to atom flux ratios of the order of unity in the substrate temperature range of 120–200 °C. High flux low energy ion beam irradiation greatly inhibits Sn segregation without interrupting epitaxy. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116502

出版商:AIP    

年代:1996

数据来源: AIP