摘要:

We present results from spatially resolved photoluminescence and Raman experiments on the substrate interface region of wurtzite GaN layers. We show that the broad photoluminescence band with an intensity maximum at 2.4 eV is not an intrinsic property of GaN. We found that this photoluminescence band is strong only near the interface. Our investigations reveal that both the substrate interface and a region of structural reorientation of the layer near the interface act as a source of the photoluminescence. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115947

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Platinum (Pt) and palladium (Pd) Schottky diodes onn‐type GaN grown by metalorganic chemical vapor deposition were achieved and investigated. Aluminum was used for ohmic contacts. Barrier heights were determined to be as high as &Fgr;B=1.13 eV by the current–voltage (I–V) method and &Fgr;B=1.27 eV by the capacitance–voltage (C–V) method for the Pt/GaN diode, and &Fgr;B=1.11 eV, &Fgr;B=0.96 eV, and &Fgr;B=1.24 eV byI–V, activation energy (I–V–T), andC–Vmethods for the Pd/GaN diode, respectively. The ideality factors were obtained to ben∼1.10. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115948

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Atomic force microscopy has been used to investigate the influence of controlled oxygen incorporation on the surface morphology of GaAs films grown by metalorganic vapor phase epitaxy (MOVPE). Oxygen influences the periodic morphology observed in GaAs surfaces, with concentrations about 1018cm−3leading to a breakup of the periodicity. To account for these observations, we propose a model in which oxygen preferentially attaches at steps with a subsequent reduction in step mobility and a concomitant increase in the surface roughness. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115949

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An integrated quasioptical receiver consisting of a planar double dipole antenna, superconductor‐insulator‐superconductor mixer and a superconducting local oscillator (LO) with matching circuits has been designed, fabricated and tested in the frequency range 360–490 GHz. A flux‐flow oscillator (FFO) based on unidirectional and viscous flow of magnetic vortexes in a long Josephson tunnel junction, is employed as a local oscillator. All components of the receiver are integrated on a 4 mm×4 mm×0.2 mm crystalline quartz substrate using a single Nb–AlOx–Nb trilayer. The lowest DSB noise temperature of 470–560 K has been achieved within a frequency range of 425–455 GHz. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115950

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We studied the microstructure of Ar ion‐beam etched ramps in epitaxial DyBa2Cu3O7−&dgr;films by atomic force microscopy. Generally, ramps were well aligned (&fgr;≊0°) with one of the crystal axes of the (001) SrTiO3substrate. In those cases we observed a surface reconstruction into a regular pattern of very long (up to 0.5 &mgr;m), about 20 nm wide facets, parallel to the ramp edge. For high misorientation angles (&fgr;≳0°), the reconstruction appeared much more complex and less regular. Furthermore, we investigated the nucleation and growth of very thin barrier layers of PrBa2Cu3O7−&dgr;on well aligned ramps. We found that nucleation takes place in the shallow trenches in the ramp, where facets meet. When more material is deposited, islands coalesce to form closed domains parallel to the trenches. This causes a thickness modulation close to 100% for barrier layer thickness up to 6 nm. The conclusions drawn from this research allow for an important improvement of the technology for the fabrication of ramp‐type junctions. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115951

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effect of uniaxial mechanical stress on the magnetic properties of electroplated Ni films was measured with a magneto‐optical Kerr loop tracer. We show that the effect of stress on the coercive force is completely different for thin (20 nm) and thick (10 &mgr;m) films. The latter behaves like bulk Ni, whereas results on lower thicknesses show a continuous transition from thin film to bulklike behavior. The results are discussed by assuming different micromagnetic reversal processes for the two extremes: rotational for thin film and domain wall movement for bulk. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115952

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An electron‐beam lithography technique for fabricating submicron point contacts to planar surfaces of bulk samples is described. We have demonstrated the technique by creating a linear array of point contacts, oriented along the bisectrix axis of a bismuth single crystal, which act as emitters and collectors in multiprobe transport measurements. In a transverse electron focusing geometry, we find the expected series of periodic voltage peaks as a function of applied magnetic field at low temperatures. The lithographically fabricated contacts offer advantages over conducting‐needle probes in electrical integrity, thermal robustness, lack of damage to the contact site, ability to make multiple submicron contacts with ≤10 &mgr;m separations and ability to align the contacts precisely along crystallographic axes. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115953

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The roughening kinetics of copper films synthesized by low pressure chemical vapor deposition (LPCVD) on Si(100) substrates was investigated by scanning tunneling microscopy (STM). By applying the dynamic scaling theory to the STM images, a steady growth roughness exponent &agr;=0.81±0.05 and a dynamic growth roughness exponent &bgr;=0.62±0.09 were determined. The value of &agr; is consistent with growth model predictions incorporating surface diffusion. The value of &bgr;, while higher than expected from these models, can be related to LPCVD processing conditions favoring growth instabilities. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115954

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the synthesis of stable nanometer‐size silver‐coated polydiacetylene (PDA) particles. At first, an ethanol solution of diacetylene (DA) is dispersed into a Ag+ion containing aqueous solution. Silver ions are attracted to –CCO−anions of DA, then monomer DA vesicles coated by silver ions are formed by a long‐term ultrasonication treatment. The monomer DA vesicles are photopolymerized and the silver ions are photo‐reduced simultaneously to form coated composite particles. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115955

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Carbon nitride films on silicon (111) and (100) wafers and Ti/C substrates with nitrogen concentration up to 50 at. % have been prepared by ion beam enhanced deposition carried out in a single ion source system. The possibility of synthesis of carbon nitride films was investigated. The nitrogen concentration and the compositions of the films were analyzed by Rutherford backscattering which gave out the nitrogen concentration of the films ranging from 37 to 50 at. %, Fourier transform infrared spectroscopy, and x‐ray photoelectron spectra. The characteristics of C 1speaks at 284.6, 285.9, 287.5, 289.5, eV and N  1speaks at 396.0, 398.4, 399.9, 402.1 eV enabled us to analyze the compositions of the films. The results of the analyses indicate that various phases such as different carbon phases, a tetrahedrally bonded phase (&bgr;‐C3N4) and other carbon nitrides (the ratio of N/C varied from 0.5 to 1.1) are contained in the films. Furthermore the concentration of the tetrahedrally bonded phase increases with the increment of the nitrogen concentration. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115956

出版商:AIP    

年代:1996

数据来源: AIP