摘要:

Ultraviolet laser sputtering of sapphire was observed to result in droplet ejection when done in air, pressurized air, or in 20 mTorr pressure. Such droplets were collected and studied with scanning electron microscopy and optical microscopy. The collected particles were spherical and ranged in size up to 3 &mgr;m in diameter. Some particles appeared to have been molten and splattered on the collection plate. The size of the particles was independent of the ambient pressure. However, the collection efficiency of the collection plate was ∼30 times greater at 20 mTorr pressure as compared to one atmosphere. The similar result for measurements of the sputter depth under a range of background pressure indicates that the mechanism for the laser sputtering of sapphire at 266 nm with 30 ps pulses and a fluence near 10 J/cm2is independent of the ambient pressure. Redeposition of debris onto the sputtered sample was significantly greater in one atmosphere pressure than in reduced pressure. These findings indicate that hydrodynamic sputtering is the most likely mechanism for the laser sputtering of sapphire at high sputter rates.

ISSN:0003-6951    

DOI:10.1063/1.102617

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

When illuminated by ultrashort optical pulses, large aperture planar photoconductors are shown to radiate a directional electromagnetic pulse which can be steered by varying the angle of incidence of the optical beam.

ISSN:0003-6951    

DOI:10.1063/1.102618

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report InGaAsP/InP vertical‐cavity surface‐emitting lasers (VCSELs) with an emission wavelength near 1.3 &mgr;m grown by metalorganic vapor phase epitaxy. The VCSEL structure contains a double‐heterostructure cavity, a metal mirror, and a SiO2/Si dielectric stack (three pairs) mirror with a measured reflectivity of 98%. A threshold current as low as 5 mA for 15‐&mgr;m‐diam devices with a 1‐&mgr;m‐thick active layer at 77 K was achieved, which is close to the best reported value (6 mA) within the accuracy of the pulse measurement. The highest operating temperature was 220 K.

ISSN:0003-6951    

DOI:10.1063/1.102619

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Large linear refractive index birefringence, strong dichroic behavior, and highly anisotropic &khgr;(3)have been observed for a uniaxially oriented poly (2, 5‐dimethoxy paraphenylene vinylene) film. A subpicosecond time‐resolved degenerate four‐wave mixing study reveals an unusual behavior. Along the draw direction &khgr;(3)is complex with a negative real part and has a response time that is longer than the optical pulse resolution. In contrast, &khgr;(3)along the transverse direction is largely real and positive. Its response time is much faster, and is limited by the laser pulse width of ∼400 fs.

ISSN:0003-6951    

DOI:10.1063/1.102620

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A sample of lead‐lanthanum‐zirconium‐titanate (PLZT 9/65/35) has been exposed to 6‐ns‐long laser pulses of 266 nm wavelength. The maximum output pulse energy of the laser beam was 300 &mgr;J, the output power density on the sample 5×105W/cm2, and the beam diameter 3 mm. By applying a moderate extraction voltage of several kilovolts, intense electron beam pulses are emitted from the free sample surface. Their time structure corresponds to the time structure of the laser pulse. Electron beam current intensities of up to 0.1 A and 2 A/cm2and total charges of 1 nC (corresponding to 20 nC/cm2) were measured with a simple Faraday cup. In the range where the parameters of laser intensity and of extraction voltage could be varied their influence on the emitted electron beam current amplitude was determined.

ISSN:0003-6951    

DOI:10.1063/1.102621

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Hot‐filament chemical vapor deposition (hot‐filament CVD) of silicon nitride films has been studied using silane and monomethylamine as source gases for the deposition temperature 600–800 °C. The deposition rate was about one order larger than that of thermochemical vapor deposition (thermo‐CVD) using the same gases. The activation energy of the growth rate was 0.2 eV smaller than that of thermo‐CVD. The hydrogen content was below the detection limit of infrared absorption measurements even in the film deposited at 600 °C. The film surface deposited at 700 °C had a smooth specular surface and the flatness of the hot‐filament CVD films was the same as that of thermo‐CVD films deposited at 100–200 °C higher temperatures.

ISSN:0003-6951    

DOI:10.1063/1.102622

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This letter revises the interpretation of recent experiments showing quantized conductance on GaAs/GaAlAs constrictions or point contacts in terms of coherent ballistic and sequential transport. Our calculations show by using a first iterative self‐consistent procedure that the experimental data can also be reconciled with sequential transport. The mean free path concept in the constriction is discussed in comparison with that of the reservoirs. We conclude that, for the higher modes, the former is much smaller than the latter, implying that in the constriction the transport may be sequential.

ISSN:0003-6951    

DOI:10.1063/1.102623

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Very thin copper lines for seeding of chemical copper deposition have been deposited by laser direct writing techniques, using water soluble precursor films from copper formate. Writing speeds of up to 50 mm/s could be reached. The deposition process has a strong influence on the substrate surface, thereby achieving a very stable film adhesion.

ISSN:0003-6951    

DOI:10.1063/1.102624

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Effects of the heat treatment in flowing oxygen containing ozone of 0.5–1 vol % (O3annealing) on the dielectric properties of the Ta2O5thin film (100–200 A˚) grown on the Si substrate by the chemical vapor deposition method were investigated. The leakage current was drastically reduced from more than 10−3to 10−9A/cm2in an electric field of 3 MV/cm by the O3annealing at 400 °C. It was also found that the leakage current was decreased and increased reversibly between alternate O3annealing and O2annealing (without ozone). These two states of the leakage current can be attributed to the reproducible change of the oxygen vacancies in the Ta2O5film.

ISSN:0003-6951    

DOI:10.1063/1.103323

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have demonstrated, by high‐resolution x‐ray diffraction, the presence of strained regions on the scale of about one molecular layer at each interface in lattice‐matched GaInAs/InP superlattices grown by gas source molecular beam epitaxy. The existence of these interfacial regions results only from the different group V element in each interface layer of the superlattice and the lack of any significant diffusion between atomic planes during, or subsequent to epitaxy. We have demonstrated that the intrinsic strain at the interfaces of lattice‐matched GaInAs/InP superlattices can be modified on the same near molecular layer scale by altering the beam sequence during growth.

ISSN:0003-6951    

DOI:10.1063/1.102625

出版商:AIP    

年代:1990

数据来源: AIP