摘要:

NiGeAu and PdGeTiPt ohmic contacts ton-GaAs and TiPd and PdGeTiPt ohmic contacts top+-GaAs are examined by comparing their contact resistances, chemical intermixing as determined by Auger electron microscopy, interface structure as determined by transmission electron microscopy, and surface roughness as determined by surface profiling all measured as a function of annealing time and temperature. Then-PdGeTiPt contact annealed for short times, ⩽15 s, and at low temperatures, ⩽395 °C, was superior to the NiGeAu contact because it had a comparable contact resistance, less interface mixing, better lateral homogeneity, and a smoother surface. However, its contact resistance increased substantially with the annealing time and temperature, whereas the NiGeAu contact was relatively unaffected. For all annealing times and temperatures except the one at 550 °C, the TiPd contact top+GaAs was superior as it had a lower contact resistance and a comparable amount of interface intermixing, lateral homogeneity, and surface roughness. However, it had a complete chemical breakdown at 550 °C, whereas the PdGeTiPt contact resistance remained relatively stable.

ISSN:0021-8979    

DOI:10.1063/1.365973

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dielectric constant and the reflectivity spectrum of polycrystallineRuO2films, grown by pulsed laser deposition, are presented as deduced by optical reflection and electron energy-loss spectroscopy. The similarities of these spectra with those obtained on single crystals, suggest that the production ofRuO2by laser ablation is a very good tool in obtaining films with electronic and structural characteristics equivalent to those of the bulk material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365974

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on microwave measurements of the surface impedanceZs=Rs+iXsofNb3Snsuperconducting films deposited by planar magnetron sputtering on sapphire substrates. The samples show theA15structure with maximumTc(R=0)of 17.4 K and residual resistivity ratios up to &bgr;≈3. The measurements are performed by a microstrip resonator technique using a meander line geometry. The power dependence ofZsis studied at different temperatures and frequencies in the range of 1–10 GHz using the fundamental and higher order modes of the resonator. The effect of a dc magnetic field applied with different orientations is also studied. The data are analyzed in the context of a simple model able to describe most of the reported loss mechanisms. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365975

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The room-temperature wall energy&sgr;w=4.0×10−3 J/m2of an exchange-coupledTb19.6Fe74.7Co5.7/Dy28.5Fe43.2Co28.3double layer stack can be reduced by introducing a soft magnetic intermediate layer in between both layers exhibiting a significantly smaller anisotropy compared to Tb–FeCo and Dy–FeCo.&sgr;wwill decrease linearly with increasing intermediate layer thickness,dIL,until the wall is completely located within the intermediate layer fordIL⩾dw,wheredwdenotes the wall thickness. Thus,dwcan be obtained from the plot&sgr;wversusdIL.We determined&sgr;wanddwon Gd–FeCo intermediate layers with different anisotropy behavior (perpendicular and in-plane easy axis) and compared the results with data obtained from Brillouin light-scattering measurements, where exchange stiffness,A,and uniaxial anisotropy,Ku,could be determined. With the knowledge ofAandKu,wall energy and thickness were calculated and showed an excellent agreement with the magnetic measurements. A ten times smaller perpendicular anisotropy ofGd28.1Fe71.9in comparison to Tb–FeCo and Dy–FeCo resulted in a much smaller&sgr;w=1.1×10−3 J/m2anddw=24 nmat 300 K. AGd34.1Fe61.4Co4.5with in-plane anisotropy at room temperature showed a further reduced&sgr;w=0.3×10−3 J/m2anddw=17 nm.The smaller wall energy was a result of a different wall structure compared to perpendicular layers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365947

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A set of Fe-based amorphous alloys,Fe93−x−yZr7BxCuy,withx=4,6, 8, or 12, andy=0or 2 has been systematically characterized in their ability to form nanocrystalline, magnetically soft material via annealing in the range of 430–600 °C. Conventional Mo¨ssbauer spectroscopy is used to follow the degree of bcc-Fe formation as well as changes in the hyperfine field distribution of the amorphous phase as a function of anneal temperature. Copper plays a strong role in the bcc-Fe formation forx=12but less of a role forx=8and 6. Unconventional Mo¨ssbauer studies utilizing radio frequency (rf) fields provide information on the soft magnetic nature of the alloys by observing the degree of rf-induced collapse of the hyperfine fields. The Mo¨ssbauer experiment in which the rf collapse and rf sideband effects are used allows the soft nanocrystalline bcc phase to be distinguished from magnetically harder microcrystalline &agr;-Fe. The rf Mo¨ssbauer technique, being particularly sensitive to the magnetic anisotropy, provides information on the anisotropy fields and hence on the grain size distribution. X-ray diffraction (XRD) is used to estimate the bcc-Fe grain size based on the diffraction peak linewidths. Average grain sizes of 5–14 nm are found for 500–550 °C annealed specimens where smaller grain sizes are always observed fory=2compared toy=0for fixedx.Small-angle x-ray scattering is also used to study the grain size and this method yields sizes in the range from 3 to 7 nm, consistently almost a factor of 2 smaller than those from the XRD line broadening. This discrepancy is attributed to the difference in the regions of the 20-&mgr;m-thick ribbons probed by the two methods. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365976

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrochromic Ni-oxide-based films were prepared by cathodic electrodeposition and, for comparison, also by reactive sputtering. The films were characterized by cyclic voltammetry, spectrophotometry, and infrared absorption spectroscopy. Explorative magnetic measurements, performed at low temperatures using SQUID technology, exhibited a well-defined Curie–Weiss behavior with a transition temperature that was depressed by proton extraction. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365977

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The magnetic properties of CoCrPt films produced by sputtering at power levels of 0.1, 0.3, 0.5, and 1 kW are studied with special emphasis placed on the structural properties we previously obtained using several x-ray experimental methods [J. Appl. Phys.77, 2321 (1995)]. In measurements on the saturated magnetic state, the saturation magnetization of the 0.1 kW film was found to be about 20&percent; lower than those of the other films. This is ascribed to the segregated structure of this film (described in the above reference). The out-of-plane magnetic anisotropy decreases as the sputtering power decreases. Its magnitude is related to the hcp(002) intensity and its orientation is slightly tilted from the normal direction. The in-plane magnetic anisotropy, on the other hand, increases sharply as the sputtering power decreases to levels below 0.5 kW. This increase is a result of the small grain structure produced by the sputtering at very low power levels. In the unsaturated magnetic state, three magnetic properties were measured: field-induced magnetic anisotropy and two types of magnetic torque loss, that is, intrinsic torque loss and field-induced torque loss related to field-induced magnetic anisotropy. The field-induced magnetic anisotropy is a consequence of the quenched magnetic domain structure produced by applying a strong external magnetic field. This anisotropy for films sputtered at 0.3, 0.5, and 1 kW is unusual in that the magnetization switching field is larger than the anisotropy field. This is ascribed to the intrinsic spatial and amplitude dispersion of the magnetization. Taking the structural and magnetic properties of CoCrPt into consideration made it clear that wall displacement rather than rotation magnetization is the major factor responsible for both types of torque loss. The rotation magnetization also made a significant contribution to intrinsic torque loss, but a limited contribution to field-induced torque loss. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365978

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

During optical excitation of spectrally sensitized silver bromide microcrystals, dye radicals are generated at the surface of the crystals. For the dyes studied in this work the radicals are oxidized dye molecules, which have a hole trapped at their doubly degenerate highest occupied molecular orbital. The dye positive holes can be detected using electron spin resonance (ESR) spectroscopy. After optical excitation the oxidized form of the dye starts to decay. A new method to acquire kinetic data of formation and decay of dye positive holes is introduced, taking into account the variation in linewidth of the ESR signal. By comparing measurements in ambient air, dry air and dry nitrogen gas it is found that moisture and not oxygen influences the kinetic behavior of the radicals. A quantitative model is suggested which is able to describe the formation of dye positive holes during optical excitation. This model allows one to predict the decay of the oxidized dye molecules, using the fitting parameters of the formation curves. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365979

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Pulsed-rf excitation of hexafluoropropylene oxide has been used to deposit poly(tetrafluoroethylene)-like thin films. Films were deposited at pulse rates of10/20,10/50,10/200,and10/400 mson/ms off and analyzed using electron spin resonance spectroscopy (ESR). All four films produced similar broad ESR spectra, with an average width at maximum slope of∼60 Gand agvalue of 2.0045. The number of free electrons in a sample decreased with increasing pulse off time. This behavior can be modeled by the reaction of a free radical with a gas species, assuming that free radicals are generated only during the pulse on time. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365980

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It is shown that at weak alternating stress the relationship between the piezoelectrically induced charge and applied stress in ferroelectric ceramics has the same form as the Rayleigh law for magnetization versus magnetic field in ferromagnetic materials. Applicability of the Rayleigh law to the piezoelectric effect is demonstrated in detail for lead zirconate titanate (PZT) ceramics. Experimental results indicate that the dominant mechanism responsible for piezoelectric hysteresis and the dependence of the piezoelectric coefficient on the applied ac stress is the pinning of non-180°domain walls. The dependence of the piezoelectric coefficient on the frequency of the driving stress is examined and is shown to be due to the frequency dispersion of both reversible and irreversible components of domain-wall displacement. Analysis of the stress dependence of the piezoelectric phase angle reveals piezoelectric hysteresis contributions that are not necessarily due to Rayleigh-type displacement of domain walls. Piezoelectric properties of a modified lead titanate composition that exhibits non-Rayleigh type behavior are examined and compared with the properties of PZT ceramics. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365981

出版商:AIP    

年代:1997

数据来源: AIP