摘要:

In thin metal films the phase change on reflection of incident light is dependent on the wavelength, the angle of incidence, the type of metal, and the metal thickness. These properties have been exploited to improve the performance of planar metal mirror microcavities. We model substantial alteration of peak emission wavelength and linewidth with mirror thickness. This allows the tuning of the cavity resonance wavelength by variation of metal mirror thickness. The dependence of the phase change on wavelength and angle of incidence can also be used to suppress the angular dependence of the cavity resonance wavelength. These effects are observed in silver-mirrored cavities containing the polymers poly(p-phenylene vinylene), (PPV), and a cyano-substituted derivative of PPV, MEH-CN-PPV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363940

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigated the Raman spectra of thermally reduced and untreated Y- and Ca-stabilized cubic zirconia. A substantial decrease in Raman activity was observed in the acoustic mode region upon reduction. Analyses of these spectra as a phonon density of states and of the observed spectral changes indicate that the reduced states are more ordered than the untreated one. This is consistent with a nonrandom arrangement of vacancies, which produces the superposition of periodic sequences of vacancies within domains. This, in turn, causes the increment in coherence length of phonons that is manifested as a decrease in acoustic mode activity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363941

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Melts were produced in as-grown and cleaned gold films by focused nanosecond laser pulses, with fluences too low to cause a measurable ablation. Their dynamics and solidification were followed with time-resolving transmission electron microscopy and analyzed by computer simulations. The liquids perform an oscillating flow on the time scale of 100 ns and solidify with an impurity-dependent large-scale distribution of material superimposed by nonresonant ripples. This behavior could be reproduced by simulations if impurity-dependent thermocapillarity and a new mechanism of distribution of surface active impurities were incorporated into the usual equations of energy, momentum, and mass conservation, i.e., periodically varying segregation at the crystallization front and transport by a mobile surface layer. The liquid is inferred to consist effectively of a fast-moving (⩽60 m/s) surface layer that accumulates most surface active atoms and slow (⩽1 m/s) bulk material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363942

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nitrogen plasma instabilities have been identified through fluctuations in the ion current density and substrate floating potential. The behavior of the plasma instabilities was found to be confined to the pressure regime 0.9 mTorr<P<1.6 mTorr. The onset of instabilities in the nitrogen plasmas occurred following the transition from an underdense to overdense plasma, where an overdense plasma is defined for densities greater than the critical densitync=7.4×1010cm−3. The instabilities are a consequence of the nonlinear dynamics present in electron cyclotron resonance (ECR) plasmas and indicative of a transition between plasma modes as the pressure increases from 0.9 to 1.6 mTorr. The plasma instabilities are suppressed with the introduction of silane for the deposition of silicon nitride, although the plasma still undergoes a transition from an underdense to overdense plasma at 1.0 mTorr. The transition pressure delineated regions of poor and optimum electrical properties of silicon nitride films deposited from a dilute nitrogen-silane (N2/SiH4=5) plasma. To evaluate growth conditions, the flux of energetic ions to deposited atoms was approximated by examination of the ratio of ion current density to deposition rate. This ratio was found to be well correlated to the electrical properties of ECR microwave plasma deposited silicon nitride films for pressures above the underdense to overdense transition at 1.0 mTorr. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363943

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Removal of hydrogen from the growth surface during silane plasma deposition of silicon is correlated with the transition from amorphous to microcrystalline film structure. Plasma deposition experiments were performed using a pulsed gas technique, where repeated steps of thin amorphous silicon film deposition, and atomic hydrogen (or deuterium) exposure are used to form microcrystalline and polycrystalline thin films at substrate temperatures below 250 °C. Infrared absorption and Raman spectroscopy are used to estimate the silicon-hydrogen bonding concentrations, and characterize crystal structure, respectively. Hydrogen elimination probed using real-time differentially pumped mass spectroscopy demonstrates that during atomic deuterium exposure, hydrogen abstraction by deuterium, rather than silicon etching, is the primary mechanism for hydrogen removal from the depositing surface. Polycrystalline material, with no shoulder at 480 cm−1in the Raman spectrum, and grain sizes greater than 1000 Å, as determined by transmission electron microscopy, have been formed at temperatures below 250 °C. The amorphous to crystal transition is observed at substrate temperatures as low as 25 °C, with longer hydrogen exposure required at lower temperatures. Hydrogen is shown to be preferentially abstracted from monohydride (Si–H) units as compared to dihydride (SiH2) units at or near the depositing growth surface, consistent withab initioenergy calculations of hydrogen interactions with silicon hydrides. A transition in hydrogen removal kinetics is observed upon film crystallization, where the rate of hydrogen removal is reduced for more crystalline materials. These results are valuable for understanding surface reactions in low temperature crystalline silicon deposition, for example, for fabrication of high mobility thin film transistor structures on glass. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364309

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In situoptical emission spectroscopy was applied to an electron assisted hot filament diamond growth process. Emission lines from the Balmer series of atomic hydrogen, molecular hydrogen, CH, CH+, and Ar were observed in the visible range when CH4, Ar, and H2were used as the input gases. The relative concentration of atomic hydrogen was estimated by using the emission line of Ar at 750.4 nm as an actinometer. The effects of deposition conditions, including filament temperature, substrate temperature, bias voltage, and methane concentration in the source gas, on the species distribution, electron temperature, and diamond film growth were investigated. The vertical spatially resolved measurements show that the concentration of atomic hydrogen decreases as the detection point moves far from the filament and suddenly drops near the substrate. The horizontal spatially resolved measurements show that the homogeneous region of reaction species and the electron temperature near the substrate define the homogeneous region of diamond film growth. Increase of filament temperature, substrate temperature, bias voltage, and the decrease of methane concentration in the feed gas increase the atomic hydrogen concentration and diamond deposition. A higher intensity ratio of CH+to Ar and a lower ratio of CH to Ar are associated with a high quality of diamond film growth. Optical emission spectroscopy showed that atomic hydrogen and CH+correlate with the formation of the diamond component, whereas the CH relates to the presence of amorphous carbon in the films. The effect of positive bias on the diamond growth results largely from the bombardment of electrons on the substrate. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363944

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An electron beam generated plasma reactor is used to decompose low concentrations (100–3000 ppm) of 1,1-dichloroethane and 1,1-dichloroethene in atmospheric pressure air streams. The energy requirements for 90&percent; and 99&percent; decomposition of each compound are reported as a function of inlet concentration. Dichloroethene decomposition is enhanced by a chlorine radical propagated chain reaction. The chain length of the dichloroethene reaction is estimated to increase with dichloroethene concentration from 10 at 100 ppm initial dichloroethene concentration to 30 at 3000 ppm. Both the dichloroethane and dichloroethene reactions seem to be inhibited by electron scavenging decomposition products. A simple analytic expression is proposed for fitting decomposition data where inhibition effects are important and simple first order kinetics are not observed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363945

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A model is presented for the steady state operation of polymer light-emitting electrochemical cells (LECs). An LEC consists of a luminescent and ionically conducting polymer, with an ionic salt added to provide ions necessary forp-type andn-type doping, sandwiched between two electrodes. Upon applying a sufficiently large voltage bias, the ions are spatially separated forming an electrical junction. Electrons injected from then-type side of the junction recombine with holes injected from thep-type side of the junction emitting light. We first describe the LEC at zero bias in which electric fields may occur in charge double layers near the contacts but in which there is a charge neutral, field free region in the device center which has an equal density of anions and cations and essentially no electrons or holes. A threshold voltage for junction formation is found, which depends on the polymer energy gap, the dissociation free energy of the salt, and the added salt density. It is generally somewhat smaller than the polymer energy gap. Below threshold, an applied bias changes the electric fields in the double charge layers near the contacts but the device center remains field free and essentially no current flows. Above threshold, the ions become spatially separated, a junction forms, and current begins to flow. Part of the applied voltage, above threshold, falls in the contact region and is necessary to establish the junction by electrochemical doping and part of the applied voltage falls across the junction. We describe the structure of the junction, which is quite different from that of a conventionalp-njunction, including the spatial profiles of the electrons, holes, and ions, and the electrostatic potential. We discuss the current-voltage and capacitance-voltage characteristics of the LECs and show how they depend on the material parameters. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363966

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A simple analytical theory is presented to explain the measured roll over and cross over behaviour of theIVcharacteristics of thin film CdTe solar cells. It involves a classical description of the CdS/CdTe junction and the CdTe/back contact structure and is extended with a new description of minority carrier current in the CdTe contact region. This extension is crucial in describing the light dependence of the forwardIVcurves, and hence cross over. The same model also explains the measuredCVcurves. It is shown that analysis of the capacitance measurement can yield additional information about the doping density of CdTe in the vicinity of the contact. A relationship between the fill factor of the solar cell and the barrier height of the back contact is derived; this relation is useful as a new, practical criterion for the quality of the back contact. The results of this simple analytical model are confirmed by full numerical calculations of the dc and ac characteristics. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363946

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A recent publication by Statman and Georges reported on the dynamics of electric-field-induced second harmonic (EFISH) in planar germanosilicate waveguides. They provided a model that examines the decay of the second harmonic signal as a result of charge migration inside the doped glass medium through dielectric relaxation and electronic drift. We present experimental results of EFISH using femtosecond laser pulses. We show here that this decay is actually due to the formation of a surface charge.

ISSN:0021-8979    

DOI:10.1063/1.363947

出版商:AIP    

年代:1997

数据来源: AIP