摘要:

A scanning tunneling microscope was used to record tip-sample displacements inferred from the tunnel current versus applied piezoelectric voltage. This provides a means to determine the range in which the mechanical system, especially the piezoelectric element, exhibits hysteretic behavior. Graphite and gold were used as the substrate samples. With graphite, reversible behavior of the displacements is observed until 2.1 Å; beyond this point, the system exhibits persistent irreversible behavior. In the gold system, irreversible behavior appears initially at 0.8 Å, but repeated cycling extends the range of reversibility to a displacement of 3–4.8 Å. Irreversible behavior dominates beyond this tip displacement range, although the system exhibits sporadic reversible behavior even for tip excursions as large as 46 Å. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365646

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe the use of micronic Hall sensors as magnetic-field profilometers with submicron resolution. The procedure involves the deconvolution of Hall voltage maps produced by scanning the field source over the sensor, with a scanning probe microscope. The response function of an infinite Hall cross is calculated analytically in the two-dimensional case, using conformal mapping techniques. Various methods of deconvolution of the Hall voltage maps are presented and compared. The calculated response function is used for the deconvolutions, and different effective sensor sizes are tried. It is shown that the remaining main uncertainties come from the ignorance of the true response function of the sensor, ascribed to the charge depletion phenomenon that is known to occur at the sensor edges. The method is applied to thin-film magnetic force microscope tips for which a precise knowledge of the tips field at sample location proves crucial to image interpretation. Maximum fields in the range 10–100 Oe are found at a distance known to be about 100 nm from the tip contact surface, depending on the tip coating thickness and magnetization direction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365623

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design of magnetic materials can be achieved with artificial magnetic molecules formed by electrically small loop antennas loaded with passive electrical circuit elements. A time derivative Lorentz material response is achieved with a series resistor and capacitor load. It is shown that the parameters of this magnetic molecule can be selected to yield a time derivative Lorentz material that acts as a highly conducting magnetic wall. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365624

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design of dielectric materials with artificial molecules formed by electrically small dipole antennas loaded with passive electrical circuit elements is considered. Variations in the antenna loads lead to known and generalizations of known dielectric material models. These artificial dielectrics are characterized in terms of their equivalent susceptibilities and polarization vectors both in the frequency and time domains. With suitable choices in the antenna loads one can design the loss and dispersion properties of the resultant materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365625

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By using an acousto-optic modulator, we have stabilized a free-running continuous wave (CW) laser diode in the presence of strong reflections from a high finesse Fabry–Perot resonator. The laser diode linewidth can be stabilized from several MHz, for high resolution spectroscopy of species at low pressures, to several hundred MHz, for lower resolution spectroscopy of species at atmospheric pressures. We demonstrated CW cavity ring-down spectroscopy of water vapor at both 1 atm and 5 Torr. We achieved ring-down repetition rates of 10–50 kHz, and a noise level of2×10−8 cm−1. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365688

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Channel optical waveguides have been formed on both GaAs and InP substrates utilizing deuterium passivation of the surface to provide planar confinement and etching to provide lateral confinement. Design criteria were established for obtaining single mode channel waveguides for the present case of small index changes and thick surface layers associated with deuterium passivation. Planar and channel waveguide operations were demonstrated and channel waveguide propagation losses have been measured. For GaAs channel waveguides, optical loss was measured as a function of channel waveguide width, ranging from 3 to 9 &mgr;m, with a minimum loss found for a width of 6.0 &mgr;m. Channel waveguide losses as low as 12.7 dB/cm for GaAs and 6.0 dB/cm for InP have been measured at &lgr;=1.3 &mgr;m. For InP this loss value is close to the limiting value imposed by free carrier absorption in the semiconductor region below the passivated region. Since the waveguide loss due to free carriers can be reduced by increasing waveguide confinement, we anticipate that lower loss optical channel waveguides could be formed by this technique. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365626

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structure of the optical phase change memory alloy, silver–vanadium–indium–antimony–tellurium (AVIST), has been investigated by the methods of optical reflectivity change, Raman spectroscopy, and electron diffraction. In order to identify each phase, Sb, AgSb, AgSbTe, and AgInTe films were also studied. The Raman spectrum of an AVIST thin film annealed at 523 K for 1 h in Ar gas, shows two main broad peaks around 116 and150 cm−1.These peaks appear to be related to Sb vibration modes in the AVIST alloy, but their relative intensities are reversed for the AVIST films in comparison with those for a Sb film. Furthermore, in AVIST, the peak at116 cm−1shifts to lower wave number when the vanadium content is increased from 0.4 to 4.7 at &percent;. The electron diffraction pattern of AVIST alloy indicates that theAgSbTe2crystalline phase dominates rather than Sb. A model of the structure of AVIST consistent with these observations is proposed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365627

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Reflection coefficients at the interface between two homogeneous, isotropic magnetoelastic media are obtained. An equation of caustic for lateral shear horizontal wave is also derived by using the method of steepest descent. These expressions are used in analyzing the relationship between magnetic field and reflection coefficient and could lead to discussions for using magnetic field in ultrasound imaging. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365628

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed two-dimensional calorimetry with infrared imaging of beam targets to optimize and measure the energy-density distribution of intense ion beams. The technique, which measures a complete energy-density distribution on each machine firing, has been used to rapidly develop and characterize two very different beams—a 400 keV beam used to study materials processing and an 80 keV beam used for magnetic fusion diagnostics. Results of measurements, using this technique, varying the diode applied magnetic field strength and geometry, anode material type and configuration, and anode-cathode gap spacing are presented and correlated with other observations. An assessment of calorimeter errors due to target ablation is made by comparison with Faraday cup measurements and computer modeling of beam-target interactions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365629

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The vacancy production in6H-SiCby 3 MeV electron irradiation at room temperature was studied using positron lifetime spectroscopy combined with annealing experiments. It was found that the trapping rates of positrons in vacancies increased linearly with the fluence in the initial stage of irradiation. After the linear increase, the trapping rates were found to be proportional to the square root of the fluence. The linear and nonlinear fluence dependences of the trapping rates are explained by the reduction of vacancies due to recombination with interstitials during irradiation. The positron trapping rate for the admixture of silicon vacancies and divacancies showed a tendency to saturate in the higher fluence range. The trapping rate for carbon vacancies decreased after reaching a maximum. These results are explained in terms of the shift of the Fermi level due to the irradiation process. It was found that, for the lightly irradiated specimen, an annealing stage caused by recombination between close vacancies and interstitials was observed. However, such an annealing stage was not observed when using a heavily irradiated specimen. These different results are explained as the reduction of interstitials due to the recombination with vacancies and long-range migration of interstitials to sinks during irradiation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365630

出版商:AIP    

年代:1997

数据来源: AIP