摘要:

An anomalously large periodicity has been observed in scanning tunneling microscope images of a (00.1) graphite sample. The unusual contrast has hexagonal symmetry, a periodicity of 7.7±0.2 nm and is superimposed on the usuala=0.246 nm atomic spacing of graphite. Current‐voltage curves recorded in the scanning tunneling spectroscopy mode from the region showing the superperiodicity exhibit slightly more metallic behavior than those from neighboring normal regions. One possible explanation for the observed periodicity is that it is a rotational moire´ pattern resulting from the overlap between a misoriented layer of graphite and the underlying graphite single crystal.

ISSN:0003-6951    

DOI:10.1063/1.102906

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Very thin lead‐zirconate‐titanate films, 500 A˚ or less in thickness, have been prepared on Pt‐Ti metallized silicon wafers by a sol‐gel processing technique. Excellent ferroelectric, dielectric, and structural properties have been demonstrated. The maximum polarization and the remanent polarization at a switching voltage of 3 V on a film with a Zr/Ti ratio of about 50/50 are 33 and 12 &mgr;C/cm2, respectively. The capability of reaching a saturation polarization at a low voltage (∼3 V) on these films suggests that they are very attractive for use in radiation‐hard low‐voltage nonvolatile programmable random access memories.

ISSN:0003-6951    

DOI:10.1063/1.102891

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Structural features of TiS2were studied by scanning tunneling microscopy (STM) and single‐crystal x‐ray diffraction was applied as a complementary technique. STM images in air and at room temperature revealed, besides the trigonal symmetry of the lattice, several new features having this symmetry as well. We conclude that these features are not only to be described by structural defect phenomena which affect sites in the 1T‐CdI2structure but tetrahedral sites as well. Sample orientation determination by x‐ray diffraction provides a unique relation between feature types and sites. A model is proposed in which displaced Ti atoms account for the observed features.

ISSN:0003-6951    

DOI:10.1063/1.103250

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ge ions at 400 keV were implanted on ⟨100⟩ undoped silicon and on arsenic‐doped silicon wafers maintained at 250 °C. The arsenic concentration ranged between 1.0×1019and 1.0×1020atom/cm3. The residual damage is mainly in the form of dislocation loops as measured by channeling and transmission electron microscopy. The amount of extended defects is lower in the arsenic‐doped than in the undoped samples and it is reduced by a factor of 2 at a dopant concentration of 1×1019atom/cm3. The experimental data are accounted for by a simple model which assumes an enhanced recombination of point defects created by the ion beam, through the formation of arsenic‐point defect pairs in the doped samples.

ISSN:0003-6951    

DOI:10.1063/1.102892

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present a technique for rapid measurement of surface forces using an ac force microscope. Measurement of both the amplitude and relative phase of a cantilever probe allows simultaneous and rapid determination of static and velocity‐dependent forces of order nN over nm length scales. Using this technique, we have also demonstrated the high lateral spatial resolution of the force microscope in the measurement of surface forces.

ISSN:0003-6951    

DOI:10.1063/1.102893

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report a novel localized electrodeposition process based on localized Joule heating at a constriction and the temperature dependence of the equilibrium potential at a metal‐electrolyte interface. Assuming a local temperature rise of 50 K, a deposition rate as high as 2 &mgr;m per minute of copper is theoretically predicted in acidified copper sulfate solution, which is verified by a series of experiments. Scanning electron microscopy micrographs show that the deposited copper is dense and crystalline. As an immediate application of this novel phenomenon, a method of self‐induced repair for incipient opens, i.e., a self‐locating and self‐terminating process to treat constrictions in circuits, is established.

ISSN:0003-6951    

DOI:10.1063/1.102894

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report the first measurements of growth oscillations in high vacuum metalorganic vapor phase epitaxy (MOVPE). The reflection difference response of the surface is used for real‐time monitoring of the layer‐by‐layer growth of GaAs from triethylgallium (TEG) and arsine. The frequency of the optically detected growth oscillations is found to be proportional to the flux of TEG and to the growth rate. We expect our results to extend the more limited ranges of applicability offered by reflection high‐energy electron diffraction to allow the study of growth oscillations also in other MOVPE‐related growth techniques.

ISSN:0003-6951    

DOI:10.1063/1.102895

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thermal instability of anodic sulfide films on Hg1−xCdxTe was studied. Instead of using laser ionization or ion backscattering in studying oxidic films after heat treatment, we used x‐ray photoelectron spectroscopy (XPS) in analyzing nonaqueous sulfidization. In this case, XPS is feasible, simpler, and has the advantage of better resolution. Hg evaporation was investigated here by measuring Te(3d5/2) of Te oxide peak rather than Hg lines. Correlation between thermal instability and compositionxwas obtained.

ISSN:0003-6951    

DOI:10.1063/1.103189

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial liftoff is an alternative to lattice‐mismatched heteroepitaxial growth. Multilayer AlxGa1−xAs epitaxial films are separated from their growth substrates by undercutting an AlAs release layer in HF acid (selectivity ≳108forx≤0.4). The resulting AlxGa1−xAs films tend to bond by natural intermolecular surface forces to any smooth substrate (Van der Waals bonding). We have demonstrated GaAs thin‐film bonding by surface tension forces onto Si, glass, sapphire, LiNbO3, InP, and diamond substrates, as well as self‐bonding onto GaAs substrates. In transmission electron microscopy the substrate and thin‐film atomic lattices can be simultaneously imaged, showing only a thin (20–100 A˚) amorphous layer in between.

ISSN:0003-6951    

DOI:10.1063/1.102896

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Specially designed structures have been grown in the GaAs/GaAlAs/AlAs system, in order to get a spatial separation of photocreated electrons and holes and thus modify the band profile under illumination in a nonstandard way. The photoinduced electric field is measured by the Stark Shift of the probing quantum well luminescence. Fields as high as 25 kV/cm are obtained under 100 W/cm2cw illumination.

ISSN:0003-6951    

DOI:10.1063/1.102897

出版商:AIP    

年代:1990

数据来源: AIP