摘要:

We measure the pump power dependence of efficiency and signal-to-background ratio in wavelength conversion using four-wave mixing in semiconductor optical amplifiers, for different lengths of the device. We show that the efficiency for a 1-mm-long amplifier is about 40 dB larger and the signal-to-noise ratio is about 23 dB larger than for a 0.25 mm amplifier. We also show that, unlike the efficiency, for constant ratio between pump- and signal-power, the signal-to-background ratio monotonically increases with the pump power. We show theoretically that this behavior holds for any range of pump-power values. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118400

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A normal-mode formalism is developed to describe the nonspecular effects of a finite-aperture ultrasonic beam incident onto layered elastic media. Analytical expressions for the reflected field have been obtained for various structures. This model proposed a unique physical picture and resolved the conflict between various explanations made for the nonspecular reflection phenomena. Novel features of leaky wave fields were observed at interfaces of liquid-solid and liquid-solid-liquid structures. These results may be helpful for nondestructive evaluation of layered structures and determination of material signatures in the acoustic microscope. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118401

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate the application of an ultrashort x-ray source as an external probe to measure plasma dynamics. The plasma is generated by a 100-fs Ti:sapphire laser focused onto thin metallic films. Time-resolved spectroscopy of the gold x-ray probe transmission through a perturbed 1000 Å aluminum film reveals redshifts of theL-shell photoabsorption edge. We show that the dynamic behavior of this shift is consistent with the relaxation of the aluminum following the compression generated by a shock wave traveling through the film. An analytic plasma model, with comparison to a numerical hydrodynamics model, indicates compression up to 1.4 times solid density. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118392

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Cubic-boron nitride (c-BN) thin films were grown by dual ion beam sputter deposition and the growth mechanism was studied using angle resolvedin-situXPS (x-ray photoelectron spectroscopy) analysis. The&pgr;bond shake-up satellite of the B 1speak, which is observed only in a hexagonal boron nitride (h-BN) phase, appeared in the XPS spectrum obtained for the surface layer of the c-BN film. This can be a clear evidence that the c-BN phase grows via the transformation of an initially formed h-BN phase and the transformation is induced by the compressive stress accumulated in the subsurface region during ion bombardment. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118402

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The microstructure of Al lines resolidified in an amorphous groove pattern, is investigated by backscatter Kikuchi diffraction, x-ray diffraction, and transmission electron microscopy (TEM). If a temperature gradient is present during cooling, the Al lines do not have the common (111) fiber texture. Instead, the (111) crystal planes are parallel to the vertical sidewalls of the grooves and the crystal lattice shows a remarkable, constant curvature over the entire line length of 1 cm. TEM revealed parallel dislocations in the bulk of the line and small crystallites at the interfaces. It is suggested that the (111) sidewall texture is a consequence of the sidewall area being larger than the bottom area. The observed lattice curvature is explained by a nonisotropic movement of dislocations during cooling. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118403

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dielectric superlattices of (Sr,Ca)TiO3/(Ba,Sr)TiO3have been formed by a pulsed laser ablation technique. The crystal structure is controlled with atomic order accuracy and a large lattice stress of 0.5–1 GPa can be introduced periodically at the interfaces owing to the lattice mismatch of the constituent layers. The(Sr0.3Ba0.7)TiO3/(Sr0.48Ca0.52)TiO3superlattice shows dramatically large dielectric constant of 900 even at film thickness of 500 Å. The optimum pressure for inducing tetragonality in the (Ba,Sr)TiO3layers and enhanced dielectric properties occurs at a lattice mismatch of 2.5–3&percent;. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118202

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Si0.84Ge0.16/Siheterostructures with variable finite lateral dimensions (10–300 &mgr;m) and different layer thicknesses grown by selective low pressure chemical vapor deposition epitaxy at a temperature of 700 °C were investigated with regard to relaxation by formation of misfit dislocations. While in small structures only nucleation and propagation occur, the dislocation–dislocation interaction (mainly multiplication) becomes more and more important in larger structures. Therefore it was possible to separate the three different mechanisms which play a role in relaxation, i.e., nucleation, propagation, and multiplication, and to study them independently. From the analysis of the misfit dislocations at the initial stage of relaxation it was possible to determine the nucleation site density and an activation energy of 2.8 eV for the heterogeneous nucleation of misfit dislocations. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118404

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Oxygen precipitates at various grain boundaries in crystalline silicon, formed after prolonged high temperature annealing, grow within a narrow size distribution. This narrow size distribution appears to depend on the specific grain boundary. On the basis of this observation a model is derived which is based on the energy balance between grain boundary energy,Si/SiO2interface energy, and an additional term describing the energy of the ledges of the faceted precipitates. This model predicts an energy minimum for a defined size of the precipitates. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118405

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ballistic electron emission microscopy (BEEM) measurements on GaN grown on sapphire substrates reveal a second conduction band minimum ∼340 meV above the absolute band minimum at the zone center (&Ggr; point). A significant lateral variation of the energy difference between the two band minima, ±50 meV, was observed which may result from nonuniform strain in the material. The existence of two conduction bands in close proximity may affect device applications, i.e., GaN based lasers and electronic devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118406

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new approach to three-dimensional nanostructures is discussed with the goal of fabricating vertical, ultrasmall tunneling junctions suitable for single electron devices. Pillars consisting of multiple layers of polycrystalline silicon (polysilicon) (∼10 nm thick) and silicon nitride (∼2 nm thick) were laterally oxidized. The fabrication of vertically stacked silicon nanoislands, with dimensions on the order of 10 nm in all three directions, connected by thin silicon nitride layers, is demonstrated. The saturation of the polysilicon core diameter during the lateral pillar oxidation process is clearly observed, confirming the self-limiting effect for polysilicon pillars. This approach allows the fabrication of three-dimensional nanostructures using conventional silicon processing equipment. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118387

出版商:AIP    

年代:1997

数据来源: AIP