摘要:

Pulsed single mode operation of distributed feedback quantum cascade lasers is reported above room temperature at both 5.4 and 8 &mgr;m wavelengths. Peak optical powers up to 60 mW at 300 K are obtained with a tuning range of ∼60 nm from 100 to ∼320 K. The linewidth is limited by thermal drift during the pulse with a typical value of 0.3cm−1for a 10 ns long pulse at 300 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119208

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The resonance behavior of metal transmission gratings and its impact on the response of metal-semiconductor-metal (MSM) photodetectors have been studied experimentally and theoretically. The metal gratings, with finger spacings in the subwavelength region of the visible light, were fabricated usinge-beam lithography and lift-off. Strong resonances have been observed only in theSpolarization. As a result, the light transmitted through a grating is primarilySpolarized if the grating’s finger spacing is less than one-third of the wavelength of the incident light, butPpolarized otherwise. Similar phenomenon has been observed in the response of MSM photodetectors since the fingers (electrodes) of an MSM photodetector basically form a grating. Theoretical simulations employing the rigorous modal-expansion theory fairly predict the observed phenomenon. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118990

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

While short compressive stresses can readily be produced by laser ablation, the generation of pure tensile stresses is more difficult. We demonstrate that a 90° prism made of polyethylene can serve to produce short and pure tensile stresses. A compressive wave is generated by ablating a thin layer of strongly absorbing ink on one surface of the prism with aQ-switched frequency-doubled Nd:YAG laser. The compressive wave driven into the prism is reflected as a tensile wave by the polyethylene-air interface at its long surface. The low acoustic impedance of polyethylene makes it ideal for coupling tensile stresses into liquids. In water, tensile stresses up to−200 barswith a rise time of the order of 20 ns and a duration of 100 ns are achieved. The tensile strength of water is determined for pure tensile stresses lasting for 100 ns only. The technique has potential application in studying the initiation of cavitation in liquids and in comparing the effect of compressive and tensile stress transients on biological media. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118991

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The observation of electron interference effects provides direct evidence of the coherence of the electrons emitted from a carbon nanotube. To demonstrate this, the low-energy electron point source microscope has been used to mount an individual carbon nanotube onto a tungsten tip. In subsequent experiments, the electrons emitted from the nanotube were used to generate holograms. Comparison with a standard tungsten atomic point source emitter establishes a high degree of coherence for a nanotube emitter. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118978

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Hydrogenated amorphous silicon,a-Si:H, prepared with the hot-wire chemical vapour deposition technique is incorporated in thin-film transistors (TFTs). High-quality TFTs are fabricated with this type ofa-Si:H, which we deposited at a rate of 17 Å/s. TFTs with a current switching ratio of5×105,a threshold voltage of 6.3 V, and an electron field-effect mobility in the saturation regime of0.6 cm2/V sare obtained. These TFTs do not show any threshold voltage shift upon prolonged gate voltage application, in contrast to conventionala-Si:H TFTs. This has been achieved by optimizing the electronic properties of the hot-wire layer, and by optimizing the interface between the gate dielectric and the hot-wire layer. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118992

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Raman characterization of aligned carbon nanotubes of average diameter 10–15 nm, produced by chemical vapor deposition on a mesoporous substrate, has been carried out. The resonance behavior and higher-order Raman bands up to fourth order have been observed and compared with those of carbon nanotubes produced by arc discharge and highly oriented pyrolytic graphite, as well as pyrolytic graphite. The phonon properties have been analyzed with the help of high-resolution transmission electron microscope studies. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118993

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe and demonstrate a new class of devices that enabledirectthermal conductance measurements on monocrystalline nanostructures. These are possible through our newly developed techniques for three-dimensional, successive surface nanomachining of GaAs-based heterostructures. Our methods allow the patterning of complex devices comprising electrically insulating, mesoscopic thermal conductors with separate, thermal transducersin situ. Intimate thermal contact between these elements is provided by their epitaxial registry. Low-temperature thermal conductance measurements indicate that phonon boundary scattering in these initial nanometer is scale structures is partially specular. These devices offer promise for ultrasensitive bolometry and calorimetry. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118994

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have fabricated direct-injection high-Tcsuperconducting quantum interference devices (SQUIDs) with integrated YBa2Cu3O7−x(YBCO) ground planes in the upper part of structure. The YBCO/PrBa2Cu3O7−x(PBCO)/YBCO edge junctions with 10-nm-thick PBCO barriers showed RSJ-like current-voltage(I–V)characteristics before and after the ground plane formation. We measured the voltage modulations of these SQUIDs with two different hole sizes to evaluate the line inductance. At a temperature of 30 K, the estimated line inductance under the ground plane was about 1.0pH/□, while the estimated line inductance without the ground plane was 2.8pH/□. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118995

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the results of charge collection measurements on liquid encapsulated Czochralski grown semi-insulating GaAs devices for alpha particles. Experimental evidence is given which demonstrates a drastic enhancement of charge collection efficiency after prolonged illumination with 1.086&mgr;m below-gap light. The recovery of EL2 from metastable state to normal state can also be achieved by electric field at high bias voltage. The experimental result shows that the EL2 defect is practically the dominant trap for free charge carriers and together with other shallow defects responsible for the electric compensation in semi-insulating GaAs. The metastable transition of the EL2 defect is always simultaneously accompanied by the neutralization of a shallow acceptor. No change in the type of conductivity was found. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118981

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fe+ions of 200 keV in energy were implanted into Si(111) at 350 °C with a dose of7×1017 cm−2.The depth distribution of the two formed phases (&egr;-FeSi and&bgr;-FeSi2) was investigated nondestructively up to a depth of about 800 Å by depth-selective conversion-electron Mo¨ssbauer spectroscopy (DCEMS) in combination with depth-profiling (destructive) Auger electron spectroscopy (AES). Near the surface only&bgr;-FeSi2is formed, while a mixture of&bgr;-FeSi2and &egr;-FeSi is formed at larger depths. The Fe-concentration depth profile calculated from the DCEMS results is in good agreement with that measured by AES. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118996

出版商:AIP    

年代:1997

数据来源: AIP