摘要:

We have investigated the segregational properties of polycrystalline Al(Cu) alloys in the composition range of 0.04 to 0.5 at. % Cu using medium energy ion scattering. While Cu does not segregate to the bare surface, significant quantities of Cu are found at the interface between the Al(Cu) and aluminum oxide. By measuring the interfacial Cu concentration as a function of temperature, we have determined that the segregational energy is 0.21±0.03 eV. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115672

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Lanthanum modified lead zirconate titanate (PLZT) ceramics with a Zr/Ti ratio of 85/15 were investigated as a function of La content by dielectric spectroscopy, Sawyer–Tower polarization techniques, and electron microscopy. Tweedlike structures were found to evolve from normal &mgr;m‐sized ferroelectric domains with increasing La content above 4 at. %. For a composition with 6 at. % La, an incommensurate antiferroelectric state was found to coexist with a polar nanodomain state, where the size of the nanodomains was approximately equal to the value of the incommensurate modulation wavelength. For this composition, P–E studies revealed double hysteresis characteristics, whereas dielectric investigations revealed relaxorlike ferroelectric behavior. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115673

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Several sets of diamond films were grown by microwave plasma enhanced chemical vapor deposition (CVD) using a CH4–H2gas mixture. The growth conditions were systematically changed in order to obtain different film morphologies, preferential orientations, and crystal qualities. In particular, the substrate temperatureTsand the CH4concentration in the gas mixture were varied in the ranges 850–950 °C and 0.4%–2.0%, respectively. The resulting films were characterized by x‐ray diffraction, Raman spectroscopy, and scanning electron microscopy. Room‐temperature cathodoluminescence has been investigated in the energy range 1.55–6.20 eV (200–800 nm). A clear correlation of the 2.85 eV (435 nm) emission band, the so‐called band A, with both the substrate temperature and CH4content in the gas mixture during deposition, was observed. An explanation is given in terms of crystal defects and diamond film texturing induced by the growth process. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115674

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

X‐ray photoelectron spectroscopy and atomic force microscopy are employed in the characterization of the first stages in the growth of carbon layers on a (001) Si substrate which is not scratched with diamond powder before placing it in an Ar–2%CH4–H2plasma discharge. Results show that the first layers could be formed in SiC grains where the carbon diamond particles nucleate. The high nucleation density of 1.109–5.109nuclei. cm−2and the low aggregates density lead to a smooth surface. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115675

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter, we describe the formation and ultralow friction mechanisms of a surface film on boron carbide (B4C). This film results from sequential reactions between B4C and oxygen and between the resulting boron oxide (B2O3) and moisture; it can afford friction coefficients of 0.03 to 0.05 to sliding steel surfaces. At temperatures above 600 °C, B4C undergoes oxidation and forms a layer of boron oxide (B2O3) in the upper surface. During cooling to room temperature, the B2O3reacts with moisture in the air to form a secondary film, boric acid (H3BO3). The sliding friction coefficient of 440C steel balls against this film is 0.04, compared to 0.7 against the bare B4C surfaces. Mechanistically, we propose that the ultralow friction behavior of the heat‐treated B4C surface is due mainly to the layered‐crystal structure of the H3BO3film that forms on the sliding surface. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115676

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Core‐level photoabsorption has been used to determine thesp2andsp3bonding content of nanocrystalline diamond thin films grown using C60or CH4precursors. The C(1s) absorption spectra show clear bulk diamond excitonic andsp3features with little evidence ofsp2bonding, while the Raman spectra measured from these same films are ambiguous and indeterminate. This result can be attributed to the local structure (near‐neighbor bonding) sensitivity of core‐level photoabsorption that is insensitive to domain size, unlike Raman spectroscopy. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115677

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The thermal stability in vacuum of amorphous tetrahedrally coordinated carbon (a‐tC) films grown on Si has been assessed byinsituRaman spectroscopy. Films were grown in vacuum on room‐temperature substrates using laser fluences of 12, 22, and 45 J/cm2and in a background gas of either hydrogen or nitrogen using a laser fluence of 45 J/cm2. The films grown in vacuum at high fluence (≳20J/cm2) show little change in thea‐tC Raman spectra with temperature up to 800 °C. Above this temperature the films convert to glassy carbon (nanocrystalline graphite). Samples grown in vacuum at lower fluence or in a background gas (H2or N2) at high fluence are not nearly as stable. For all samples, the Raman signal from the Si substrate (observed through thea‐tC film) decreases in intensity with annealing temperature indicating that the transparency of thea‐tC films is decreasing with temperature. These changes in transparency begin at much lower temperatures (∼200 °C) than the changes in thea‐tC Raman band shape and indicate that subtle changes are occurring in thea‐tC films at lower temperatures. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115891

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the realization of a bright and stable electroluminescent Schottky diode based on aluminum‐porous silicon junction. White light, visible in normal daylight, is emitted when a reverse bias is applied to the device, promoting the junction breakdown. The device has a fast (100 ns) rise time of the light emission. An excellent stability, tested over more than one month of continuous operation at a high bias level, is achieved by the complete encapsulation of the active porous silicon under a transparent alumina layer. The external power efficiency of light emission is 0.01%. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115892

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter we present photoluminescence results on &bgr;‐FeSi2/Si using excitation energies above and below the silicon band gap. These results show that the luminescence emission observed at 1.5 &mgr;m can be firmly attributed to band edge related emission from the &bgr;‐FeSi2. This result confirms the potential of &bgr;‐FeSi2as a strong contender for a silicon compatible optoelectronics technology that matches the conventional optical fiber transmission wavelength at 1.5 &mgr;m. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115893

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have prepared an electrically tunable and adaptive 3‐pole half‐wave bandpass coplanar waveguide filter incorporating a 1.2‐&mgr;m‐thick paraelectric SrTiO3bottom layer and a 0.4‐&mgr;m‐thick superconducting YBa2Cu3O7−xtop electrode layer on a LaAlO3substrate. By applying a separate bias voltage on each pole and also on each coupling capacitance of the device at 4 and 76 K, the filter response is not only fine tuned to achieve symmetric and optimized filter characteristics with less than 2% bandwidth centered around 2.5 GHz, but also broadband tuned to shift the passband by more than 15%. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115894

出版商:AIP    

年代:1996

数据来源: AIP