jap banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

15 Jun 2005

Volume 97, Issue 12, Articles (12xxxx)

Page 1 of 6 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process

Riikka L. Puurunen

J. Appl. Phys. 97, 121301 (2005); http://dx.doi.org/10.1063/1.1940727 (52 pages) | Cited 158 times

Online Publication Date: 30 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Atomic layer deposition (ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions, reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.
Show PACS
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.43.Mn Adsorption kinetics
82.33.Ya Chemistry of MOCVD and other vapor deposition methods
back to top
RSS Feeds

Biexcitonic blue Stark shift in semiconductor quantum dots

S. Banerjee and K. A. Shore

J. Appl. Phys. 97, 123101 (2005); http://dx.doi.org/10.1063/1.1927705 (5 pages) | Cited 2 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The effect of biexcitons on the Stark effect in GaAs and CdS quantum dots (QDs) has been investigated theoretically using a time-dependent perturbation technique. Our results show that the redshift, which usually occurs in QD energy levels, changes to a blueshift when account is taken of biexciton effects. The results are obtained for a single-quantum dot as well as for an inhomogeneous distribution of quantum dots. A comparison has also been made between the Stark effect in GaAs and in CdS crystals and it has been found that the Stark effect in GaAs is stronger than in CdS quantum dots. This can be attributed to the difference in biexciton binding energies of the two materials.
Show PACS
78.67.Hc Quantum dots
73.21.La Quantum dots
71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
71.15.Nc Total energy and cohesive energy calculations

Facet degradation of GaN heterostructure laser diodes

Thomas Schoedl, Ulrich T. Schwarz, Volker Kümmler, Michael Furitsch, Andreas Leber, Andreas Miler, Alfred Lell, and Volker Härle

J. Appl. Phys. 97, 123102 (2005); http://dx.doi.org/10.1063/1.1929851 (8 pages) | Cited 12 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigated the degradation of cleaved facets of (Al,In)GaN laser diodes in different atmospheres. We found that operation in water-free atmospheres with sufficient oxygen shows a slow degradation. Operation in atmospheres with water vapor causes a fast degradation and an oxidation on the facet. This deposition is a permanent damage to the laser diode. If the laser diode is operated in pure nitrogen, we find a thick deposition on the facet, which shows high absorption. This deposition can be removed by either high optical output powers or by operation in atmospheres with sufficient oxygen. We also explain the influence of these coatings to the degradation behavior and see these coatings as the reason for unstable kinks in the L–I characteristics during operation.
Show PACS
81.65.Mq Oxidation
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Asymmetric, nonbroadened large optical cavity waveguide structures for high-power long-wavelength semiconductor lasers

B. S. Ryvkin and E. A. Avrutin

J. Appl. Phys. 97, 123103 (2005); http://dx.doi.org/10.1063/1.1928309 (6 pages) | Cited 12 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a simple semianalytical model for evaluating the free-carrier loss in the waveguide layer of large-cavity semiconductor lasers, which proves that these losses may become an important factor at high bias currents. It is shown that nonbroadened asymmetric waveguide structures can significantly reduce these losses when compared to broadened symmetric waveguides, with little or no degradation in threshold, near- and far-field properties, and are thus a promising configuration for high-power lasers operating high above threshold.
Show PACS
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Population inversion and threshold current densities: A comparison of GaAs/(Al,Ga)As quantum-cascade structures with different barrier heights

L. Schrottke, S. L. Lu, R. Hey, M. Giehler, H. Kostial, and H. T. Grahn

J. Appl. Phys. 97, 123104 (2005); http://dx.doi.org/10.1063/1.1929863 (4 pages) | Cited 5 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The population of the laser levels in undoped GaAs/AlxGa1−xAs quantum-cascade structures (QCSs) is investigated by interband photoluminescence spectroscopy. We compare similar QCSs with different barrier heights (x = 0.33 and x = 0.45), for which the calculated population ratios ρpca are equal. While the experimental value ρpme for x = 0.45 agrees with the theoretical one, ρpme for x = 0.33 is much smaller than ρpca. At the same time, the threshold current densities jth are significantly smaller for x = 0.45 than for x = 0.33. In the framework of a linear rate equation model, we estimate the effect of the experimentally observed reduction of the population ratio on jth. We show that the increased value of jth for x = 0.33 cannot only be attributed to a larger leakage current due to the lower barriers, but also to the reduced population ratio.
Show PACS
42.55.Px Semiconductor lasers; laser diodes
78.55.Cr III-V semiconductors

Guided-mode effects in quantum-well infrared photodetectors integrated with light-emitting diode

E. Dupont, M. Byloos, T. Oogarah, I. Sproule, and H. C. Liu

J. Appl. Phys. 97, 123105 (2005); http://dx.doi.org/10.1063/1.1931029 (5 pages) | Cited 2 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Mode-guiding effects on an infrared thermal-imaging device consisting of a quantum-well infrared photodetector integrated with a light-emitting diode have been observed. The photocurrent spectra and the integrated response are modulated even for a very large numerical aperture. In the range of device thickness explored the response changes by about 10%.
Show PACS
42.82.Et Waveguides, couplers, and arrays
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
42.79.Gn Optical waveguides and couplers

Resonant transmission of light waves in dielectric heterostructures

Ye Lu, R. W. Peng, Z. Wang, Z. H. Tang, X. Q. Huang, Mu Wang, Y. Qiu, A. Hu, S. S. Jiang, and D. Feng

J. Appl. Phys. 97, 123106 (2005); http://dx.doi.org/10.1063/1.1929847 (5 pages) | Cited 7 times

Online Publication Date: 20 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate the propagation of electromagnetic wave through dielectric heterostructures with transfer-matrix method. It is shown that if a dimerlike positional correlation (DPC) is introduced to the heterostructure, resonant transmission of light waves will definitely take place. The resonant transmissions are characterized by perfect transmission peaks in the photonic band gap, which is demonstrated by the electric-field distribution at corresponding resonant modes. The numerical calculations are in good agreement with the analytical predictions. Furthermore, by applying the SiO2/Si heterostructure with DPC, resonant modes can appear within the photonic band gap at the telecommunication wavelengths of 1.55 and 1.3 μm. This finding is expected to have potential applications in wavelength division multiplexing system.
Show PACS
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials
78.30.Hv Other nonmetallic inorganics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Low-frequency noise of GaN-based ultraviolet light-emitting diodes

S. L. Rumyantsev, S. Sawyer, M. S. Shur, N. Pala, Yu. Bilenko, J. P. Zhang, X. Hu, A. Lunev, J. Deng, and R. Gaska

J. Appl. Phys. 97, 123107 (2005); http://dx.doi.org/10.1063/1.1928310 (5 pages) | Cited 4 times

Online Publication Date: 21 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Low-frequency fluctuations of current and light intensity were measured for different types of ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths from 280 to 375 nm. These UV LEDs are suitable for studying steady-state and time-varying UV fluorescences of biological materials. The correlation coefficient between the current and light intensity fluctuations varies with the LED current and load resistance. This dependence is explained in terms of contributions to the 1/f noise from the active region and from the LED series resistance. The noise level could be reduced by operating the UV LEDs at a certain optimum current level and with large external series resistance.
Show PACS
85.60.Jb Light-emitting devices
72.70.+m Noise processes and phenomena

Optical properties of a nematic sample in the low-frequency regime of an external electric field

J. A. Reyes, C. Provenzano, G. Cipparrone, and G. Barbero

J. Appl. Phys. 97, 123108 (2005); http://dx.doi.org/10.1063/1.1935762 (6 pages)

Online Publication Date: 21 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We analyze the optical response of a nematic sample submitted to an external periodic square wave representing an electric voltage of low frequency. To this end we extend a model previously proposed by us to investigate the response to a dc electric field. We determine, analytically, the time evolution of the electrical potential across the sample and the bulk and surface densities of the ions. Our analysis is performed by assuming that the ions are identical in all the aspects, except for the sign of the electrical charge. We evaluate the characteristic times of the problem by limiting our study to the case in which the distortion induced by the electric field on the nematic liquid crystal is small. This implies that the amplitude of the applied voltage is of the order of the threshold voltage of the Freedericksz transition. The theoretical model is in reasonable agreement with our experimental data.
Show PACS
42.70.Df Liquid crystals
78.20.Jq Electro-optical effects
64.70.M- Transitions in liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
back to top
RSS Feeds

Measurement of metastable He*(2math) density in dielectric barrier discharges with two different configurations operating at around atmospheric pressure

K. Tachibana, Y. Kishimoto, and O. Sakai

J. Appl. Phys. 97, 123301 (2005); http://dx.doi.org/10.1063/1.1922581 (7 pages) | Cited 20 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have measured the density of metastable He atoms in the lowest triplet state (2math) with a diode-laser absorption spectroscopic technique in atmospheric pressure plasmas produced by dielectric barrier discharge schemes. Two different types of electrode configuration are employed: one is a conventional parallel-plate system and the other is a microdischarge integrated system with stacked metal-mesh electrodes covered by insulating films. We have analyzed the pressure-broadened spectral line corresponding to the 2math→2math (J = 0–2) transition to derive the broadening coefficient and to calibrate absolute densities. The measured density ranges from 1011 to 1012 cm−3, but the values in the mesh-type system are larger than those in the parallel-plate system by about one order of magnitude. The density, however, depends strongly on the gas flow rate, showing the influence of quenching by the Penning-ionization process with impurities. Those behaviors are consistent with the variation of the electron density estimated by millimeter-wave transmittance measurement.
Show PACS
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Vy Impurities in plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Spectroscopic measurement of radiation of high-pressure mercury discharge lamps

Ling Fu, Ralf Leutz, and Harald Ries

J. Appl. Phys. 97, 123302 (2005); http://dx.doi.org/10.1063/1.1929887 (4 pages) | Cited 1 time

Online Publication Date: 20 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Compact size and high efficiency are important features for projection systems. As the most often used sources for projection optics, short arc lamps are characterized by their impressive economy and the ability to produce extremely bright light from small dimensional sources. In this contribution the old principle of back reflection towards the sources is applied to a high-pressure mercury discharge lamp with a reflector to improve the radiance of the source by 35% at a certain reduced solid angle. Increasing the optical thickness of sources is equivalent to reducing the total phase space (etendue) of emitted radiation by the same factor, which is very useful for compacting sources. In addition, by comparing the forward radiation and the back-reflected radiation obtained from spectroscopic measurements, we calculate the absorptivity, emissivity, absorption, and emission coefficients of the plasma of the arc lamp based on Kirchhoff’s Law and Planck’s equation which is necessary for determining its temperature and pressure.
Show PACS
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Kn Thermodynamics of plasmas

Simulation of cluster formation in laser-ablated silicon plumes

Sushmita R. Franklin and R. K. Thareja

J. Appl. Phys. 97, 123303 (2005); http://dx.doi.org/10.1063/1.1931028 (6 pages) | Cited 6 times

Online Publication Date: 20 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have developed a simple model to simulate the clusters formation in laser-ablated plume in an ambient atmosphere of inert gas. The model uses the reaction-rate theory as applied to quantum oscillators in conjunction with transition state theory to synthesize and optimize the nanoparticles in the ablated plume. The evolution of cluster size is obtained by incorporating diffusion of ambient gas into an adiabatically expanding plume. Various rate constants of clustering reactions are calculated using collision rate and transition state theory. We have used the model to simulate the spatial and temporal extents of silicon nanoparticle formation in laser-ablated silicon plume generated using 248- and 532-nm irradiation in ambient atmosphere of argon. The model predicts the onset time of 3 ms with 248 nm and 1.0 Torr of argon and 2.0, 1.2, and 0.6 ms with 532-nm irradiation and argon background at 2, 5, and 10 Torr, respectively, for 1-nm clusters of silicon. The concentration of clusters decreases with an increase in distance from the target surface. The onset time dependence on ambient pressure follows a simple relation of the form {τonset∝(1/Pambient)0.91}. The reasonable agreement of simulated results with experimental observations implies that the model is adequate to simulate Si cluster formation in the ablation plume.
Show PACS
81.05.Cy Elemental semiconductors
61.82.Rx Nanocrystalline materials
52.38.Mf Laser ablation
81.07.Bc Nanocrystalline materials
66.30.-h Diffusion in solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.46.-w Structure of nanoscale materials
61.82.Fk Semiconductors
79.20.Ds Laser-beam impact phenomena

Decomposition and polymerization of perfluorinated compounds in microwave-excited atmospheric pressure plasma

M. Nagai, M. Hori, and T. Goto

J. Appl. Phys. 97, 123304 (2005); http://dx.doi.org/10.1063/1.1931034 (5 pages) | Cited 5 times

Online Publication Date: 20 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Decompositions and polymerizations of perfluorinated compounds gases were demonstrated employing atmospheric pressure plasmas with continuous-wave microwave excitations. The atmospheric pressure plasma was generated at a low gas temperature of 520 K. Spherical-shaped particles of approximately 50–120 nm in diameter were synthesized in CF4/He and C4F8/He plasma on Si substrate with dc voltage biasing, which was set in the plasma downstream region. The gas temperature in plasma was important to generate particles because particles were not generated at a high gas temperature of 850 K. The particles were determined to consist of carbon and fluorine atom composition from an energy dispersive x-ray spectroscopy. Furthermore, the effect of H2 addition on the CF4/He plasma was investigated. The decomposition efficiency of CF4 was increased with H2 addition and obtained over 80% without emissions of carbon dioxide.
Show PACS
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.35.-x Polymers: properties; reactions; polymerization
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
52.77.-j Plasma applications

Study of the Ar metastable atom population in a hollow cathode discharge by means of a hybrid model and spectrometric measurements

N. Baguer, A. Bogaerts, Z. Donko, R. Gijbels, and N. Sadeghi

J. Appl. Phys. 97, 123305 (2005); http://dx.doi.org/10.1063/1.1929857 (12 pages) | Cited 12 times

Online Publication Date: 22 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The role of the metastable Ar atoms in a 1-cm-diameter cylindrical hollow cathode discharge (HCD) is studied self-consistently based on a hybrid model and experimental measurements in the pressure range of 0.3–1 Torr and currents of 1–10 mA. The model comprises submodels based on the principles of Monte Carlo and fluid simulations. The Monte Carlo model describes the movement of the fast electrons, fast Ar and Cu atoms, and fast Ar+ and Cu+ ions as particles, while in the fluid model, the slow electrons, Ar+, Cu+ ions, Cu, and Ar metastable atoms are treated as a continuum. The population of the two metastable states within the 3p54s configuration (math and math) were combined into one collective level, for which the continuity equation was written. Typical calculation results are, among others, the two-dimensional profiles of the production and the loss rates of Ar metastable atoms, as well as the metastable atom densities and fluxes throughout the complete HCD. Moreover, the calculated radial profiles (averaged over the axial direction) of the Ar metastable atom density are compared with experimental radial density profiles recorded by laser absorption spectroscopy. The relative importance of the different processes determining the Ar metastable population is analyzed, as well as the influence of pressure and voltage on them. Experimental results evidence the presence of the metastable atom production source at the cathode surface, probably originating from fast Ar+ ions and Ar atoms impinging on it. Comparison between experimental and calculated Ar metastable atom densities shows a good agreement at low pressures, but at 1 Torr the calculated values differ by a factor of 2 from the measured ones. Several possible explanations for this discrepancy are discussed.
Show PACS
52.80.Hc Glow; corona
52.65.Pp Monte Carlo methods
52.65.Kj Magnetohydrodynamic and fluid equation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Dg Plasma sources

Modeling of transient nonequilibrium phenomena in an inductively coupled plasma under pulsed power conditions

R. Ye and T. Ishigaki

J. Appl. Phys. 97, 123306 (2005); http://dx.doi.org/10.1063/1.1931036 (9 pages) | Cited 1 time

Online Publication Date: 22 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A time-dependent two-temperature model is developed to simulate the behavior of an argon radio frequency plasma under transient nonequilibrium conditions, with emphasis to shed light on the temporal and spatial evolution of the nonequilibrium phenomena occurring in pulsed power plasmas. The results show that the effects of changes in input power on the thermal nonequilibrium and the ionization nonequilibrium are most noticeable at the early stages of pulse on and off. The observed deviation from thermal equilibrium during pulsation is more pronounced in the fringes of the plasma and near the wall of the torch. In the central region, the influence is less significant and the plasma remains in a quasilocal thermal equilibrium state. The temporal evolution of the ionization nonequilibrium does not keep pace with that of the thermal nonequilibrium, and the relaxation process of the electron number density is slower and smoother. The effects of operating conditions on the transient behavior of the nonequilibrium situations under pulsed power conditions are also examined. It indicates that, for materials processing, a pulse duration between 2 and 10 ms is adequate for rf plasmas operated in pulse-modulated modes.
Show PACS
52.25.Kn Thermodynamics of plasmas
52.25.Jm Ionization of plasmas
52.75.Hn Plasma torches
52.65.-y Plasma simulation

Gas temperature of capacitance spark discharge in air

Ryo Ono, Masaharu Nifuku, Shuzo Fujiwara, Sadashige Horiguchi, and Tetsuji Oda

J. Appl. Phys. 97, 123307 (2005); http://dx.doi.org/10.1063/1.1938274 (7 pages) | Cited 4 times

Online Publication Date: 22 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Capacitance spark discharge has been widely used for studying the ignition of flammable gas caused by electrostatic discharge. In the present study, the gas temperature of capacitance spark discharge is measured. The gas temperature is an important factor in understanding the electrostatic ignition process because it influences the reaction rate of ignition. Spark discharge is generated in air with a pulse duration shorter than 100 ns. The discharge energy is set to 0.03–1 mJ. The rotational and vibrational temperatures of the N2 molecule are measured using the emission spectrum of the N2 second positive system. The rotational and vibrational temperatures are estimated to be 500 and 5000 K, respectively, which are independent of the discharge energy. This result indicates that most of the electron energy is consumed in the excitation of vibrational levels of molecules rather than the heating of the gas. The gas temperature after discharge is also measured by laser-induced fluorescence of OH radicals. It is shown that the gas temperature increases after discharge and reaches approximately 1000 K at 3 μs after discharge. Then the temperature decreases at a rate in the range of 8–35 K/μs depending on the discharge energy.
Show PACS
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties

Probe measurements of plasma potential nonuniformity due to edge asymmetry in large-area radio-frequency reactors: The telegraph effect

A. A. Howling, L. Derendinger, L. Sansonnens, H. Schmidt, Ch. Hollenstein, E. Sakanaka, and J. P. M. Schmitt

J. Appl. Phys. 97, 123308 (2005); http://dx.doi.org/10.1063/1.1940136 (13 pages) | Cited 9 times

Online Publication Date: 23 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In large-area radio-frequency (rf) capacitive reactors, the redistribution of rf current to maintain current continuity near asymmetric sidewalls causes a perturbation in rf plasma potential to propagate along the resistive plasma between capacitive sheaths. The damping length of the perturbation can be determined by a telegraph equation. Experiments are described using a surface array of unbiased electrostatic probes in the ground electrode to verify the theoretical model of the telegraph effect in Howling et al. [J. Appl. Phys. 96, 5429 (2004)] . The measured spatial dependence of the plasma potential rf amplitude and circulating nonambipolar current agree well with two-dimensional numerical solutions of the telegraph equation. The rf plasma potential can be made uniform by using symmetric reactor sidewalls.
Show PACS
52.70.Ds Electric and magnetic measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

A high-frequency electrospray driven by gas volume charges

Dmitri Lastochkin and Hsueh-Chia Chang

J. Appl. Phys. 97, 123309 (2005); http://dx.doi.org/10.1063/1.1927279 (4 pages) | Cited 5 times

Online Publication Date: 27 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High-frequency (>10 kHz) ac electrospray is shown to eject volatile dielectric liquid drops by an entirely different mechanism from dc sprays. The steady dc Taylor conic tip is absent and continuous spraying of submicron drops is replaced by individual dynamic pinchoff events involving the entire drop. We attribute this spraying mechanism to a normal Maxwell force produced by an undispersed plasma cloud in front of the meniscus that produces a visible glow at the spherical tip. The volume charge within the cloud is formed by electron-induced gas ionization of the evaporated liquid and produces a large normal field that is much higher than the nominal applied field such that drop ejection occurs at a voltage (at high frequencies) that is as much as ten times lower than that for dc sprays. The ejection force is sensitive to the liquid properties (but not its electrolyte composition), the ac frequency and trace amounts of inert gases, which are believed to catalyze the ionization reactions. As electroneutral drops are ejected, due to the large (>100) ratio between individual drop ejection time and the ac frequency, this mechanism can produce large (microns) electroneutral drops at relatively low voltages.
Show PACS
52.30.-q Plasma dynamics and flow
52.80.Hc Glow; corona

Particle-in-cell Monte Carlo modeling of Langmuir probes in an Ar plasma

A. Cenian, A. Chernukho, A. Bogaerts, R. Gijbels, and C. Leys

J. Appl. Phys. 97, 123310 (2005); http://dx.doi.org/10.1063/1.1938275 (10 pages) | Cited 5 times

Online Publication Date: 29 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The Langmuir-probe diagnostic of a plasma is studied using a particle-in-cell Monte Carlo model. The electron-density, temperature, and potential profiles are determined for a probe immersed in an Ar plasma. The model is verified using the low-pressure results of Sternovsky et al. [J. Appl. Phys. 94, 1374 (2003)] . It was proved that the ion to electron temperature ratio may not be constant in the sheath–presheath region.
Show PACS
52.70.Ds Electric and magnetic measurements
52.65.Rr Particle-in-cell method
52.65.Pp Monte Carlo methods
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
back to top
RSS Feeds

Absorption intensities and emission cross sections of principal intermanifold and inter-Stark transitions of Er3+(4f 11) in polycrystalline ceramic garnet Y3Al5O12

Dhiraj K. Sardar, Charles C. Russell, John B. Gruber, and Toomas H. Allik

J. Appl. Phys. 97, 123501 (2005); http://dx.doi.org/10.1063/1.1928327 (6 pages) | Cited 23 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A comparative spectroscopic study is performed on Er3+(4f11) ions doped in polycrystalline ceramic garnet Y3Al5O12 (YAG) and single-crystal laser rod, both containing nominal 50 at. % of Er3+. The standard Judd–Ofelt (JO) model is applied to the room-temperature absorption intensities of Er3+(4f11) transitions in both hosts to obtain the phenomenological intensity parameters. These parameters are subsequently used to determine the radiative decay rates, radiative lifetimes, and branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds math of Er3+(4f11) in these garnet hosts. The emission cross sections of the intermanifold Er3+ math→math (1.5 μm) transition as well as the principal inter-Stark transition Y1→Z4 (1550 nm) within the corresponding multiplet manifolds have been determined. The room-temperature fluorescence lifetimes of the math→math (1.5 μm) transition in both polycrystalline ceramic and single-crystal YAG samples were measured. From the radiative lifetimes determined from the JO model and the measured fluorescence lifetimes, the quantum efficiencies for both samples were determined. The comparative study of Er3+(4f11) ions performed suggests that polycrystalline ceramic YAG is an excellent alternative to single-crystal YAG rod for certain applications.
Show PACS
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.50.Gg Ferrimagnetics
78.55.Hx Other solid inorganic materials
78.20.Jq Electro-optical effects

Ion irradiation of inhomogeneous Schottky barriers on silicon carbide

F. Roccaforte, S. Libertino, F. Giannazzo, C. Bongiorno, F. La Via, and V. Raineri

J. Appl. Phys. 97, 123502 (2005); http://dx.doi.org/10.1063/1.1928328 (9 pages) | Cited 9 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, the effects of ion irradiation on Schottky barriers formed on silicon carbide are discussed. After Si-ion irradiation at the near-interface region in Ti/4H-SiC contacts an increase of the Schottky barrier height from 1.05 to 1.21 eV was observed, accompanied by a lowering of the reverse leakage current. The combination of several methods allowed us to determine the physical properties of the Schottky barrier and to explain the mechanism responsible for the barrier height changes. In particular, the structural and electrical modifications of the interfacial region, both of Ti layer and SiC (i.e., different orientation of the Ti layer, irradiation-induced defects in the epilayer, dopant deactivation, and the consequent reduction of the surface electric field) are responsible for the increase of the Schottky barrier height and the reduction of the leakage current. The electrical characterization of the contacts at different temperatures also suggested that ion irradiation induced modifications in the inhomogeneous nature of the Ti Schottky barrier.
Show PACS
73.30.+y Surface double layers, Schottky barriers, and work functions
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
73.40.Ns Metal-nonmetal contacts

Thermal-expansion behavior of a directionally solidified NiAl–Mo composite investigated by neutron diffraction and dilatometry

H. Bei, E. P. George, D. W. Brown, G. M. Pharr, H. Choo, W. D. Porter, and M. A. M. Bourke

J. Appl. Phys. 97, 123503 (2005); http://dx.doi.org/10.1063/1.1929853 (5 pages) | Cited 7 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The thermal expansion of directionally solidified NiAl–Mo eutectic alloys consisting of nanoscale Mo fibers embedded in a NiAl matrix was analyzed by neutron diffraction and dilatometry. From room temperature to 800 °C, perpendicular to the fiber direction, the NiAl and Mo phases expand independently with average coefficients of thermal expansion (CTEs) of 16.0×10−6 °C−1 and 5.8×10−6 °C−1, respectively. Parallel to the fiber direction, they coexpand up to 650 °C with an average CTE of 12.8×10−6 °C−1, but above this temperature the Mo fibers expand more than the NiAl matrix. This anomalous behavior is the result of the load transfer to the Mo fibers when the NiAl matrix softens. The average CTE of the composite parallel to the fiber direction was determined by dilatometry to be 13.0×10−6 °C−1, which is approximately 11% lower than the value predicted by a simple rule of mixtures using the CTEs of the constituent phases.
Show PACS
81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
65.40.De Thermal expansion; thermomechanical effects
81.30.Fb Solidification

Ductile relaxation in cracked metal-organic chemical-vapor-deposition-grown AlGaN films on GaN

J.-M. Bethoux and P. Vennéguès

J. Appl. Phys. 97, 123504 (2005); http://dx.doi.org/10.1063/1.1929856 (8 pages) | Cited 8 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A study of the strain relaxation of cracked (Al,Ga)N/GaN films grown by metal-organic chemical-vapor deposition on (0001) sapphire is presented. The strain measured by x-ray diffraction is shown to depend both on the film thickness and on the high-temperature exposure time (including both growth duration and annealing). These macroscopic observations are linked to the film microstructure by using transmission electron microscopy and cathodoluminescence observations. Relaxation may occur either by the introduction of long, straight, a+c misfit dislocations or by the introduction of additional cracks bordered by bowed a-type misfit dislocations. The nucleation mechanism and the efficiency in relaxing the misfit strain of these two features are discussed.
Show PACS
81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.M- Structural failure of materials
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO3 in the THz range

L. Pálfalvi, J. Hebling, J. Kuhl, Á. Péter, and K. Polgár

J. Appl. Phys. 97, 123505 (2005); http://dx.doi.org/10.1063/1.1929859 (6 pages) | Cited 47 times

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The absorption coefficient and the index of refraction of undoped and Mg-doped stoichiometric and congruent LiNbO3 crystals were determined for polarization parallel to the z axis in the far-infrared (FIR) 30−180-cm−1 frequency range for different Mg-doping levels and temperatures down to 10 K. For stoichiometric LiNbO3, smaller absorption and index of refraction were found, than for congruent samples. At a Mg content near the photorefractive threshold, the FIR absorption coefficient has the lowest value in the stoichiometric crystals, which are most suitable for efficient pulse generation in the terahertz range.
Show PACS
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
61.72.S- Impurities in crystals
78.70.Gq Microwave and radio-frequency interactions

On conductivity changes in shocked potassium chloride

N. K. Bourne, D. Townsend, and M. Braithwaite

J. Appl. Phys. 97, 123506 (2005); http://dx.doi.org/10.1063/1.1929094 (6 pages) | Cited 1 time

Online Publication Date: 16 June 2005

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A previous work has reported that shock loading of ionic crystals produces an induced polarization and changes in electrical conductivity. However, previous measurements recorded an integrated electrical signal comprising the induced electrical field and that due to current flow. For this reason a differential system was designed to separate these effects that was adapted from that used in the investigation of the conductivity of hydrogen under shock. The measurement removes voltages produced in the shock-induced electrical field, allowing determination of those resulting from resistance changes. Although the mechanical response of potassium chloride to shock has been studied extensively, the electrical response is less studied. Here, experiments are reported in which it is shocked to various stresses in order to observe conductivity changes. The range of stresses induced includes several mechanical thresholds, including the elastic-plastic transition, the B1:B2 phase transformation, and the overdriving of the shock faster than the elastic wave. The behavior observed when single crystal and targets pressed from granular material (to close to full density) are shocked around each of these thresholds is presented. The effects of loading to a particular stress in a single step or in multiple steps are discussed.
Show PACS
81.05.Rm Porous materials; granular materials
62.50.-p High-pressure effects in solids and liquids
72.80.Sk Insulators
62.30.+d Mechanical and elastic waves; vibrations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
Page 1 of 6 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close