摘要:

A quantum interference transistor that can be fabricated by available technology and can operate at room temperature is proposed. This device uses the phase interference effect of a vacuum electron that is not influenced by thermal fluctuations, in contrast to an electron in solid‐state materials. The device consists of a field emitter, a collector, and segmented capacitors between the emitter and the collector. The capacitors control electron trajectories and the phase interference of the electron in vacuum by their electrical potential. This quantum interference effect is found not to be the same as the Aharonov–Bohm effect contrary to our expectations. We are convinced that the new transistor is capable of room‐temperature operation because the large kinetic energy of the electron in vacuum suppresses energy fluctuations caused by the field emission itself and by thermal fluctuations in the emitter material to about 50 meV. The switching time of the transistor is limited in order to average the number of electrons at the collector to allow the emitter‐collector current to be a deterministic variable against the quantum stochastic property. The threshold of the switching time is estimated to be of the order of magnitude of 10−11s for the field emitter reported by C. A. Spindt, I. Brodie, L. Hummphrey, and E. R. Westerberg [J. Appl. Phys.47, 5248 (1976)].

ISSN:0021-8979    

DOI:10.1063/1.353883

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Upper bounds are derived for the work that can be extracted from simple isothermal chemical converters (chemical engines) that operate from a finite chemical potential reservoir. The incremental gains that stem from adding an arbitrary number of engines is derived. Results are analogous to those for heat engines fed by a finite heat capacity reservoir. Systems of practical interest include chemical reactions, electrochemical cells, and solid‐state converters. The effectiveness of introducing more engines to utilize unexploited chemical potential is expressed in terms of the specific relation between mass transfer and chemical potential difference, often referred to as the device’s current‐voltage curve.

ISSN:0021-8979    

DOI:10.1063/1.353835

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Second‐order hyperpolarizabilities &bgr; of organic nonlinear optical materials were measured by a modified method of the electric‐field induced second‐harmonic generation. Since this method avoided interference between two second‐harmonic waves from a solution and cell‐window glass, &bgr; of a dilute solution was easily determined and at the same time, a third‐order hyperpolarizability &ggr; of a solvent was also evaluated. The obtained &bgr; values were constant in a wide range of the concentration.  

ISSN:0021-8979    

DOI:10.1063/1.353889

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Instability in the output of dc‐biased surface emitting lasers due to an external cavity effect was observed. The output power spectrum exhibited multiple peaks with spacing corresponding to exactly the round‐trip delay in silica fibers with length ranging from 2 m to 2 km. The magnitude of the peaks was enhanced in the spectral region centered at the laser relaxation frequency. With increased feedback, the background of the output spectrum was found to increase, indicating the presence of optical chaos. Numerical simulation based on the rate equation analysis was found to agree with the experiment, indicating the surface emitting lasers are well described by the rate equation and are susceptible to feedback as the edge emitting lasers.

ISSN:0021-8979    

DOI:10.1063/1.353880

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Surface emitting optical devices with a vertical cavity have been investigated for applications in optical interconnections. To integrate these devices into a two‐dimensional array, it is necessary to improve the conversion efficiency from electrical power to optical power. To meet this requirement, the series resistance of the distributed Bragg reflectors that form the vertical cavity must be reduced. This article demonstrates the reduction in the series resistance of the distributed Bragg reflector by introducing quasi‐graded superlattices at the heterointerfaces. By using this structure, we obtain a low series resistance distributed Bragg reflector without compromising the high reflectivity. The mechanism of the reduction in the series resistance is studied and it is found that an increase in tunneling current leads to a decrease in the resistance. The dependence of tunneling current on doping concentration of the distributed Bragg reflector and the superlattice structure is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.353893

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The classical Biot theory [J. Acoust. Soc. Am.28, 168 (1956)] predicts the existence of three waves that can propagate in a fluid‐saturated porous material: A fast compressional wave, a slow compressional wave, and a shear wave. Through use of this theory, propagation characteristics within water‐filled and air‐filled materials were compared in the 10 Hz–100 kHz band. Numerical calculations show that the ratio of fluid to solid motion for the slow compressional wave is around 2 in water‐filled sand, but greater than 300 in air‐filled sand. In addition, calculations of plane wave transmission from a fluid into a fluid‐saturated porous solid were investigated. The calculations show that when the fluid is water, nearly all of the incident energy is transferred to the reflected wave and to the transmitted fast compressional wave that is traveling mainly in the solid frame. Only a slight frequency dependence occurs in the energy transfer. When the fluid is air, however, the interaction of the waves with the boundary becomes strongly dependent upon frequency, and most of the incident energy is transferred to the reflected wave and to the transmitted slow compressional wave traveling mainly in the pores. These theoretical results justify the different approaches used to treat reflections from porous materials in underwater and aeroacoustics. For reflections, air‐filled soil or snow can be approximately modeled as a modified fluid (ignoring motion in the frame) rather than as a viscoelastic solid (ignoring motion in the pores), the approximation commonly used to model saturated undersea sediments.

ISSN:0021-8979    

DOI:10.1063/1.354035

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have used picosecond ultrasonics techniques to study the vibrations of several nanostructures composed of laterally patterned gold films on fused quartz substrates. The structures include arrays of stripes and dots with lateral repeat distance as small as 2000 A˚. The frequencies and attenuation rates of the low‐lying normal modes of these structures are measured. We compare these results with those obtained theoretically from a finite element analysis of the dynamics of the structures, and discuss the physical nature of the principal vibrational modes.

ISSN:0021-8979    

DOI:10.1063/1.353859

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A method for measuring the density of mercury in high intensity discharge (HID) lamps using x‐ray absorption is described. The method is suitable for use with lamps with any outer envelopes. Time dependent values of absolute density and cold spot temperature were obtained for a variety of HID lamp types during the period following the extinguishing of the arc. Values for the time dependent mercury mass per unit area at various locations in the lamp were obtained during the warming up of the lamps.

ISSN:0021-8979    

DOI:10.1063/1.353876

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Formaldehyde (CH2O) is a common pollutant of indoor air in residences and commercial buildings. The removal of CH2O from atmospheric pressure gas streams (N2/O2/H2O/CH2O) using plasmas generated by a dielectric barrier discharge has been theoretically investigated with the goal of cleansing indoor air. The model consists of a full accounting of the electron, ion, and neutral chemical kinetics in contaminated humid air. We find that the destruction of CH2O results dominantly from chemical attack by OH and O radicals, with the primary end products being CO and H2O. The predicted destruction rates for CH2O are typically 2–8 ppm/(mJ cm−3) (parts per million of CH2O in air/energy deposition). The elimination of the unwanted byproducts, CO and NO, using a platinum catalyst is discussed.

ISSN:0021-8979    

DOI:10.1063/1.353828

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Zn‐doped GaSb epilayers grown on GaAs and GaSb substrates by low‐pressure metal‐organic chemical vapor deposition were studied. Triethylgallium and trimethylantimony were used as Ga and Sb sources, respectively. The carrier concentrations ofp‐type GaSb epilayers were affected by V/III ratio and growth temperature. Diethylzinc(DEZn) was used as thep‐type dopant. The relationship between carrier concentrationPand mole fraction [DEZn] isP=K[DEZn]2.3. Photoluminescence for different carrier concentration was compared. There exist two different regions for the carrier concentration versus growth temperature.

ISSN:0021-8979    

DOI:10.1063/1.353829

出版商:AIP    

年代:1993

数据来源: AIP