Showing papers on "Power density published in 1991"

Vertical‐cavity, room‐temperature stimulated emission from photopumped GaN films deposited over sapphire substrates using low‐pressure metalorganic chemical vapor deposition

Abstract: We report the first observation of near‐UV vertical‐cavity stimulated emission from a photopumped GaN epilayer at room temperature. The epilayer was deposited over AIN‐coated basal plane sapphire substrate using low‐pressure metalorganic chemical vapor deposition. Epitaxy quality of a 1.5‐μm‐thick GaN layer was high enough to achieve stimulated emission at room temperature. The observed near‐UV optical emission power was a nonlinear function of the pump power density. At threshold power density, we also observed line narrowing and a shift of the peak UV emission towards longer wavelengths. Data comparing the UV emission for the vertical‐cavity and the edge emission geometry are also presented.

High-power-density GaAs MISFETs with a low-temperature-grown epitaxial layer as the insulator

Abstract: A GaAs layer grown by molecular beam epitaxy at 200 degrees C is used as the gate insulator for GaAs MISFETs. The gate reverse breakdown and forward turn-on voltages, are improved substantially by using the high-resistivity GaAs layer between the gate metal and the conducting channel. It is shown that a reverse bias of 42 V or forward bias of 9,3 V is needed to reach a gate current of 1 mA/mm of gate width. A MISFET having a gate of 1.5*600 mu m delivers an output power of 940 mW (1.57-W/mm power density) with 4.4-dB gain and 27.3% power added efficiency at 1.1 GHz. This is the highest power density reported for GaAs-based FETs. >

Method for destruction of toxic substances with ultraviolet radiation

Abstract: A method for destruction of toxic compounds through direct ultraviolet irradiation. Continuum UV radiation from the deep region of the spectrum is applied to the target medium in pulsed fashion with a specified range of power ratios and average power. Enhanced destruction of undesirable toxins is achieved when the ratio of rms power to average power falls in characteristic range of 50:1 to 200:1; the ratio of peak power to average power falls in the characteristic range of 1000:1 to 10,000:1; and the average power density is maintained at least at a value of about 0.5 Watt/cm2 within the carrier medium.

Surface polaritons in cylindrical optical fibers

Abstract: The properties of the polariton modes associated with a resonance in the dielectric function of an optical fiber are derived. Particular attention is given to the surface polaritons, whose energy densities and power flows are concentrated close to the interface of the fiber core and its cladding. The results are illustrated with a range of dispersion curves for the two most important cases, when the fiber dielectric function has the reststrahl and plasma forms. General expressions are given and illustrated graphically for the power flow and the power density. It is shown numerically that the energy velocity, or group velocity, can have opposite sign to the phase velocity of the surface polariton.

Solid state microwave generating array material, each element of which is phase controllable, and plasma processing systems

Abstract: A solid state microwave generator energized phased antenna (10) array is utilized as the excitation source for material/plasma processes. Each antenna element (10) of the array is driven by a separate solid state microwave power source. Very close and precise control of each solid state generator's phase and amplitude is provided to control the amplitude of the composite power node, and electromagnetic field distribution produced by the array which control is not readily possible with vacuum tube devices and systems such as microwave oven magnetrons. Utilizing the concepts of the invention the total power generated by the system may be easily controlled. The phase of the individual elements may be used to control the location of the power node of the plasma within a reaction chamber (12) and to move said power node within the chamber (12) with no mechanical movement or physical alteration of the processing apparatus. Because of the degree of control possible within the overall processes system of the invention plasma processing methods may be performed which were not previously practical because a high power density plasma can be concentrated at any desired location in the reaction chamber (12) or scanned across a desired region. These control features are lacking in currently available vacuum tube microwave devices. It is also probable that the overall cost of such a solid state based microwave power generators systems will be far less than that of comparable tube type microwave generators especially as fabrication and control technology progresses.

An experimental low power density rectenna

Abstract: Describes the design and performance of a 2.45-GHz rectenna that absorbs small amounts (milliwatts) of microwave power at incident power density levels that are 10000 times lower than those normally used and then, after a microwave impedance step up of 50, converts it into DC power at useful voltage levels. Several applications are discussed, including a transponder in a communications or sensor system in which the interrogating transmitter also supplies power to the transponder. >

Non-linear coupling of the lower hybrid grill in ASDEX

Abstract: Computations of the reflection coefficient based on a non-linear lower hybrid (LH) coupling theory are presented and compared with the measurements of the reflection coefficient of the ASDEX tokamak LH grill, where powers up to 4 kW/cm2 have been launched. This high LH power density modifies the electron density in front of the grill because of ponderomotive forces. Thus, the coupling and the power reflection coefficient change. To explain the observed saturation of the growth of the reflection coefficient with power, it is necessary to take into account some heating of the plasma in front of the grill by the transmitted LH power, which also leads to a poloidally inhomogeneous edge electron density.

Characterization of Hydrogenated Amorphous Silicon Films by a Pulsed Positron Beam

Abstract: A low-energy pulsed positron beam was, for the first time, applied to the characterization of hydrogenated amorphous silicon films (~1 µm in thickness) deposited by means of plasma-enhanced chemical-vapor deposition. By the use of a pulsed positron beam, positron lifetime spectra were measured on four films deposited under different rf-power densities. In two of the films prepared at the intermediate power densities, a long-lived component (τ9 ns) was observed, which indicates that a high concentration of voids exists. A component with a lifetime of 319 ps, which is due to trapped positrons at divacancies or small vacancy clusters, was observed in the film prepared at the lowest power density, while a component with a lifetime of 390 ps-440 ps, which is due to trapped positrons at large vacancy-type defects, was observed in the other films. The results clearly indicate that the defect properties are strongly influenced by the rf-power density.

Nicht-spurgebundenes Fahrzeug mit elektrodynamischem Wandler

Abstract: A motor vehicle contains a unit (2) consisting of an internal combustion engine and a generator which supplies current to electric motors (12, 16) coupled to the driving wheels (14, 18) via a power-distribution power electronics system (8). In addition there is an accumulator (22) into which power from the internal combustion engine-generator unit (2) is fed. An electronic control (20) controls the power distributor (8) depending on a running signal in accordance with boundary conditions, e.g. the lowest possible specific fuel consumption. A temporary high power requirement can be covered by the accumulator (22). During more sustained increased power consumption, the internal combustion engine, which is run when possible in a mode consuming little fuel, is speeded up to cover the increased power requirement. At the maximum power of the internal combustion engine, the power stored in the accumulator (22) can be used for additional thrust.

A Mathematical Model of a Hydrogen/Oxygen Alkaline Fuel Cell

Abstract: A mathematical model of a hydrogen/oxygen alkaline fuel cell is presented that can be used to predict polarization behavior under various potential loads. The model describes the phenomena occurring in the solid, liquid, and gaseous phases of the anode, separator, and cathode regions, assuming a macrohomogeneous, three-phase porous electrode structure. The model calculates the spatial variation of the partial pressures of oxygen, hydrogen, and water vapor, dissolved oxygen and hydrogen concentrations, electrolyte concentration, and the solid- and solution-phase potential drops. By developing a complete model of the alkaline fuel cell, the interaction of the various transport and kinetic resistances can be more accurately investigated under conditions that simulate actual fuel cells. The model predicts that the solution-phase diffusional resistance of dissolved oxygen is a major limitation to achieving high performance at low cell potentials, while the ohmic drop in the solid electrodes contributes the most resistance at high cell potentials. Other limitations to achieving high power densities are indicated, and methods to increase the maximum attainable power density are suggested. These performance indications can help future research and the design of alkaline fuel cells. The alkaline fuel cell (AFC) is capable of providing a clean, efficient,, and high-powered source of electrical energy. The relative ease of operation, low weight and volume, and reliable performance have made the alkaline fuel cell an attractive power source for the American space program, as well as for electric vehicles, defense, stationary power sources, portable generators, and small submersibles, to name a few (1-3). However, for applications that require even higher power densities, the performance of the alkaline fuel cell needs to be improved. The maximum power density obtained from alkaline fuel cells has undergone many advances in recent years due to improved catalysts and electrode materials, and also due to optimized operating conditions and fuel cell design. It has been known that in order to increase the power density in AFCs, the activation, concentration, and ohmic polarizations should be minimized (4). For example, improved electro

Etching polyimide films with continuous‐wave ultraviolet lasers

Abstract: Continuous‐wave laser radiation from an argon‐ion laser in the wavelength range 300–330 nm or 350–380 nm, when focused to a spot such that the power density is ∼10 kW/cm2, can be used to etch polyimide (DuPont KaptonTM) films with as little thermal damage as from an excimer laser (308 or 351 nm) provided the laser spot is moved over the surface at speeds at which the transit time over its own diameter is in the order of 1–1000 μs. There is an optimum speed at which the cutting action is a maximum for a given power density per unit area. The fluence (in J/cm2) at which etching occurs is comparable to results obtained with excimer laser pulses but the depth of the material that is removed per joule of incident laser is energy is ∼100‐fold less. In the present process there is no ablation and no acoustic report accompanies it. Only a fraction of the polyimide that is removed from the surface is seen as debris.

Energy Considerations in the Deposition of High‐Quality Plasma‐Enhanced CVD Silicon Dioxide

Abstract: Silicon dioxide films deposited from the plasma‐enhanced chemical vapor deposition (PECVD) reaction of silane and nitrous oxide in the presence of helium were studied to determine the effects of temperature and radio frequency (RF) power on the deposition process. Increased RF power density yielded oxides which were structurally more relaxed and homogeneous. Temperature had a more significant effect on the impurity levels in the films. The combination of elevated power density with increased susceptor temperature resulted in the deposition of films of high physical integrity.

Method of forming silicon-based thin film and method of manufacturing thin film transistor using silicon-based thin film

Abstract: Method of forming a thin film consisting of a silicon-based material includes a first step of setting a substrate (104) subjected to formation of a thin insulating film consisting of the silicon-based material in a chamber (101) having high-frequency electrodes (106) for receiving a high-frequency power while the substrate is kept heated at a predetermined temperature, a second step of supplying a process gas to the chamber, a third step of applying a high-frequency power to the high-frequency electrodes to generate a plasma, a fourth step of depositing an insulator consisting of the silicon-based material on the substrate to a predetermined thickness while gas supply in the second step and supply of the high-frequency power in the third step are kept maintained, and a fifth step of cooling the substrate on which the insulating film is formed and unloading the substrate from the chamber. In the fourth step, the substrate is kept heated within the temperature range of 230°C to 270°C, and the high-frequency power is controlled to be supplied so that an RF discharge power density falls within the range of 60 to 100 mW/cm².

Photokinetic etching of polymethyl methacrylate films by continuous wave ultraviolet laser radiation

Abstract: Continuous wave laser radiation from an argon‐ion laser in the wavelength range 300–330 nm or 350–380 nm can be used to etch doped polymethyl methacrylate (PMMA) films with as little thermal damage as from a pulsed, ultraviolet laser (308 or 351 nm) provided the laser spot is moved over the surface at speeds at which the transit time over its own diameter is in the order of 1–200 μs. The laser beam is focused to a spot so that its power density at the polymer surface is between 10 and 100 kW/cm2. There is an optimum speed at a given power density and wavelength at which the cutting action is a maximum. The material that is removed is vaporized in part and the rest collects in and around the cut channel as a low melting polymer. There is no acoustic report similar to that seen in ablative photodecomposition. The process is quite similar to the photokinetic etching that has been described in polyimide films using cw ultraviolet laser radiation. The mechanism of the process can be a thermal depolymerization ...

Ray model for transmission of infrared radiation through multibent cylindrical waveguides

Abstract: An improved ray model for simulating the transmission of laser radiation through a metallic or metallic-dielectric multibent hollow cylindrical waveguide has been developed. It calculates the power transmission and the power density at any point along the curved waveguide, as a function of geometrical dimensions of the waveguide, coupling lens at the entrance, polarization (random, vertical, or perpendicular), and the 3-D trajectory of the waveguide. The theoretical calculations are compared with the experimental results.

Performance of water jet cooled silicon monochromators on a multipole wiggler beam line at NSLS

Abstract: A 27 pole wiggler on the X25 beam line at the National Synchrotron Light Source (NSLS) provides a horizontal X-ray power density of 350 W/mrad with a critical energy of 4.6 keV. Jet cooled silicon crystal monochromators are shown to be capable of almost perfect performance at the experimental position where the available power density is about 45 W/cm of beam width and the total power is about 250 W. Both Si(111) and Si(220) monochromators have been tested and the Bragg angle variation across the beam thermal footprint is shown to be only 2.5 arc sec at the highest power levels.

Effects of harmonic terminations on power and efficiency of GaAs HBT power amplifiers at 900 MHz

Abstract: Investigates and discusses the effects of harmonic termination impedances on the collector efficiency of GaAs HBTs for use in power amplifiers at 900 MHz. Collector efficiency is shown, by experiment, to vary by 38% points as harmonic terminations at both input and output are varied. An optimum collector efficiency (870 MHz) of 78% with an associated power gain of 12 dB is reported for a 100 mu m emitter length HBT at an RF output power density of 1.6 W/(mm emitter length) when 2nd and 3rd harmonics are terminated in short and open circuits respectively at both input and output.

Laser light beam synthesizing apparatus

Abstract: A laser light source in which a couple of light beams whose shapes are re-formed and whose polarizing planes are made perpendicular to each other are synthesized by a beam splitter and then the synthesized light is incident on an optical guide through a predetermined optical system, thereby generating the synthesized light having a short spot diameter and an improved power density.

High power density pulsed X-band heterojunction bipolar transistors

Abstract: Abrupt junction Npn AlGaAs/GaAs heterojunction bipolar transistors giving 10 GHz output power density of 6.2 mW/μm 2 (18.7 W per mm emitter length) are reported. Pulse length was 300 nS with 33 % duty cycle. Associated gain and power-added efficiency were 5.0 dB and 46 %, respectively. Associated peak power was 561 mW. Peak and average powers were measured as a function of pulse length at fixed duty cycle and found to increase sharply from CW values for pulse lengths less than 1000 nS

CW laser ablation velocities as a function of absorption in an experimental one-dimensional tissue model.

Abstract: One-dimensional continuous-wave laser tissue ablation models predict that the steady-state ablation velocity is independent of the optical absorption of the tissue and proportional to laser power density. This theoretical result was tested in an experimental model that approximates the one-dimensional situation. The model consists of 3 to 4 mm-diameter polyacrylamide rods irradiated at one end with an argon laser beam with uniform power density. It was found that ablation velocity is indeed independent of the light absorption coefficient in the material and proportional to the incident power density. Analysis of the relation between the experimental velocities and the power density showed that approximately 40% of the incident laser light is reflected or attenuated in the escaping vapors. Furthermore, compared to the actual absorbed laser power, heat loss caused by thermal radiation and convection from the side surface of the rod is considerable during ablation, especially at lower power densities. This heat loss is not present in a true one-dimensional geometry and creates therefore a marked difference between the rod and one-dimensional geometry. Computations show that in the pre-ablation stage the heat losses from the rod can be neglected, compared to the absorbed energy. In this case the rod is a very good approximation of the true one-dimensional situation.

Millimeter wave power performance of InAlAs/InGaAs/InP HEMTs

Abstract: The DC and microwave power performance of both lattice-matched and pseudomorphic InAlAs/InGaAs/InP high electron mobility transistors HEMT lattice-matched to an InP substrate yielded peak power-added efficiency of 52% with power gain of 10.5 db and power density of 0.41 W/mm. When the HEMT was biased and tuned for maximum output power, a power density of 0.78 W/mm and power-added efficiency of 44% with 10.2 dB power gain were measured. At 60 GHz, a 0.15- mu m-gate-length and 50- mu m-gate-width InP-based HEMT with a pseudomorphic channel demonstrated 41% peak power-added efficiency with 7.2 dB power gain and 0.35 W/mm power density. A similar device also exhibited peak power-added efficiency of 26% with power gain of 4.9 dB and output power density of 0.2 W/mm at 94 GHz. >

Method for growing a diamond thin film on a substrate by plasma enhanced chemical vapor deposition

Abstract: A method is provided for growing a diamond thin film on a selected substrate. First the substrate is prepared by scratching the surface thereof with diamond paste. The substrate is then confined in an enclosed space which includes high purity hydrogen and high purity methane gasses under relatively low pressure. The substrate is then irradiated with microwave energy to subject the substrate to a plasma exhibiting a first predetermined power density for a first period of time sufficient to form, on the substrate, diamond-like ball structure particles. The power density of the plasma to which the substrate is exposed is then effectively increased to a second predetermined power density and the substrate in exposed to the plasma for a second period of time sufficiently long such that (100) diamond faces grow on top of the ball structure particles. Finally, the irradiation of the substrate with the diamond-like ball structure particles thereon is continued at the second predetermined power density for a third period of time sufficient to cause the (100) faces on top of the particles to be joined together into a substantially continuous diamond film.

Excimer laser surface treatment of bulk ceramics

Abstract: Changes of surface morphology following excimer laser (KrF, ArF) irradiation were investigated for three technical ceramic materials (TZP, PSZ, Si3N4). Zirconia samples exhibit a smooth and glass-like surface at the low power density regime, while at higher power densities colour changes were observed due to changes in the chemical composition of the bulk material. In the silicon nitride samples new crystals of specific orientation are formed, which could be crystalline silicon.

Laser Induced Plasmas Observed with and Optical Imaging Spectrometer

Abstract: Laser-induced plasmas generated by a Q-switched Nd: YAG laser were observed with an optical imaging spectrometer which was assembled from a 0.32m spectrometer and a cooled CCD (charge-coupled device) detector. The ambient atmosphere, the kind of gas used and its pressure, influenced the emission intensities for both atomic lines and the continuum, and the volume of emissive regions of plasmas. The power density of the laser also affected the plasma characteristics. Tight focusing of laser radiation did not directly bring about a plasma of high emission intensity, because of the absorption of laser energy by the plasma itself. The importance of prevention of a gas breakdown before sample vaporization was also indicated. These effects are discussed from the viewpoints of initial cascade growth of electron number density, absorption of laser energy by the plasmas, and plasma expansion processes.

Thin-film power-density meter for millimeter wavelengths

Abstract: A quasi-optical power density meter for millimeter and submillimeter wavelengths has been developed. The device is a 2-cm/sup 2/ thin-film bismuth bolometer deposited on a mylar membrane. The resistance responsivity is 150 Omega /W, and the time constant is 1 min. The meter is calibrated at DC. The bolometer is much thinner than a wavelength, and can thus be modeled as a lumped resistance in a transmission-line equivalent circuit. The absorption coefficient is 0.5 for 189- Omega /square film. The power-density meter has been used to measure absolute power densities for millimeter-wave antenna efficiency measurements. Absolute power densities of 0.5 mW/cm/sup 2/ have been measured to an estimated accuracy of 5%. >

Structure characterization of plasma-deposited TiN coatings

Abstract: The plasma-assisted chemical vapour deposition of TiN on steel, silicon and glass substrates from a gaseous mixture of TiCl 4 , N 2 and H 2 has been studied. The crystallinity and density of the TiN coatings were affected by the r.f. discharge power density. X-ray diffraction revealed that the films have a strong (200) orientation which increases on increasing the discharge power density, and scanning electron micrographs of the TiN films show that the columnar structure becomes more dense. By increasing the discharge power density, the coating microhardness increases up to a maximum, after which it decreases. This effect is attributed to the different chlorine content of the films, which shows a minimum when the microhardness is maximum.