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15 Oct 1999

Volume 86, Issue 8, pp. 4067-4713

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Transparent stacked organic light emitting devices. I. Design principles and transparent compound electrodes

G. Gu, G. Parthasarathy, P. E. Burrows, P. Tian, I. G. Hill, A. Kahn, and S. R. Forrest

J. Appl. Phys. 86, 4067 (1999); http://dx.doi.org/10.1063/1.371331 (9 pages) | Cited 36 times

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Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is a means for achieving full-color flat panel displays. The physics, performance, and applications of stacked OLEDs (SOLEDs) are discussed in this and the following paper (Papers I and II, respectively). In Paper I, we analyze optical microcavity effects that can distort the emission colors of SOLEDs if not properly controlled, and describe design principles to minimize these parasitic effects. We also describe the fabrication and operating characteristics of transparent contacts that are an integral part of SOLEDs. We demonstrate that both metal-containing and metal-free transparent electrodes can serve as efficient electron and hole injectors into the stacked organic semiconductor layers. Two different transparent SOLED structures (metal-containing and metal-free) that exhibit sufficient performance for many full-color display applications will be discussed in Paper II. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems
42.15.Eq Optical system design
07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.
42.86.+b Optical workshop techniques

Transparent stacked organic light emitting devices. II. Device performance and applications to displays

G. Gu, G. Parthasarathy, P. Tian, P. E. Burrows, and S. R. Forrest

J. Appl. Phys. 86, 4076 (1999); http://dx.doi.org/10.1063/1.371428 (9 pages) | Cited 29 times

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Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, respectively. The respective subpixel luminous efficiencies are 0.53, 1.44, and 1.52 cd/A, and the Commission Internationale de L’Éclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0.22). In the high transparency metal-free SOLED, an insulating layer was inserted between the two upper subpixels to allow for independent grounding of all color emitters in the stack. At operating voltages of 12–14 V, video display brightnesses were achieved with luminous efficiencies of 0.35, 1.36, and 1.05 cd/A for the R, G, and B subpixels, respectively. The respective CIE coordinates for R, G, and B emissions are (0.72, 0.28), (0.26, 0.63), and (0.17, 0.28) in the normal viewing direction, shifting inperceptibly as the viewing angle is increased to as large as 60°. Finally, we discuss addressing schemes of SOLED displays, and compare them with other strategies for achieving full-color, OLED-based displays. © 1999 American Institute of Physics.
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78.70.Bj Positron annihilation
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Rm Porous materials; granular materials

Relaxation of thermal stresses in double-coated optical fibers

Sham-Tsong Shiue and Yuan-Kuang Tu

J. Appl. Phys. 86, 4085 (1999); http://dx.doi.org/10.1063/1.371332 (6 pages) | Cited 11 times

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The thermal stresses in double-coated optical fibers are analyzed by the viscoelastic theory. A closed form solution of the thermal stresses is obtained. The thermal stresses are proportional to the temperature change, and are a function of the material’s properties of the polymeric coatings and their thicknesses. The material’s properties of the polymeric coatings include the Young’s modulus, thermal expansion coefficient, Poisson’s ratio, and relaxation time. The relaxation of thermal stresses is strongly dependent on the relaxation time of the polymeric coating. If the relaxation time of the polymeric coating is very long, the viscous behavior of the polymeric coatings will not appear, and the thermal stresses solved by the viscoelastic theory are the same as those solved by the elastic theory. On the other hand, if the relaxation time of the polymeric coating is very short, the relaxation of thermal stresses is very apparent. A compressive radial stress at the interface of the glass fiber and primary coating will result in an increase of the microbending losses, and a tensile interfacial radial stress will possibly produce the debond at the interface of the glass fiber and primary coating. To minimize this interfacial radial stress, the radii, Young’s moduli, thermal expansion coefficients, and Poisson’s ratios of polymeric coatings should be appropriately selected, and the relaxation time of the primary coating should be decreased. Finally, the thermal stresses in single- and double-coated optical fibers are discussed. © 1999 American Institute of Physics.
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42.81.Bm Fabrication, cladding, and splicing
42.79.Wc Optical coatings

Simulation of the dynamics of twisted nematic devices including flow

Jack Kelly, Syed Jamal, and Mingji Cui

J. Appl. Phys. 86, 4091 (1999); http://dx.doi.org/10.1063/1.371333 (5 pages) | Cited 14 times

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We have modeled the switching behavior of a twisted nematic cell using the one-dimensional Ericksen–Leslie equations of nematodynamics. We compare the modeling results with experimental data on transmission versus time. Excellent agreement between experiment and model is achieved at all voltages and viewing angles. To achieve this agreement, only two viscosity parameters are required; these are combinations of the Leslie viscosity coefficients, namely, α3−α2 (the rotational viscosity) and α4+α5. A fast and stable adaptive numerical algorithm, based on an effective viscosity parameter, is developed for solving the equations of motion. The viscosity parameters obtained from fitting the flow experiments are in good agreement with those obtained from dynamic light-scattering measurements. © 1999 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects

Fast polarization switching with memory effect in a vertical cavity surface emitting laser subject to modulated optical injection

D. L. Boiko, G. M. Stéphan, and P. Besnard

J. Appl. Phys. 86, 4096 (1999); http://dx.doi.org/10.1063/1.371429 (4 pages) | Cited 14 times

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The polarization state of a vertical cavity surface emitting laser (VCSEL) output was driven by means of optical injection from another VCSEL. The bistability inherent to polarization locking allowed us to generate a memory effect. The control parameter was the modulated bias current of the maser laser and effects were shown to exist at frequencies up to 1 GHz. © 1999 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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A noninvasive rf probe for the study of ionization and dissociation processes in technological plasmas

V. J. Law, A. J. Kenyon, D. C. Clary, and I. Batty

J. Appl. Phys. 86, 4100 (1999); http://dx.doi.org/10.1063/1.371334 (7 pages) | Cited 4 times

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A swept frequency absorbance plasma diagnostic technique for measurement of self-resonance frequency, intrinsic plasma-tool distributed capacitance, radiative energy loss, and effective plasma capacitance is described. The ex situ probe measures the plasma properties independently of all contributions from the plasma-tool and transmission line connection to the rf supply. The technique employs a swept frequency source and a balanced equal ratio arm bridge to measure the frequency response of the plasma tool after the plasma has been extinguished under plasma conjugate matching conditions. The resonant frequency of the combination of capacitances due to plasma-tool geometry (intrinsic capacitance, Ci) and the matching network (Cm) exhibits a shift from the excitation frequency (13.56 MHz) that is dependent on the effective plasma capacitance. Resonance frequency shift data are given for He, Ne, Ar, O2, N2, and N2O as a function of both pressure (0.02–0.8 mbar) and incident power (50 and 100 W). This technique allows the differentiation between dissociation and ionization processes within the plasma through a simple noninvasive rf measurement. © 1999 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

High-frequency modulation of an electron beam produced by a plasma cathode

A. Dunaevsky, Ya. E. Krasik, J. Felsteiner, and A. Rosenberg

J. Appl. Phys. 86, 4107 (1999); http://dx.doi.org/10.1063/1.371335 (11 pages) | Cited 6 times

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We present a detailed study of the recently discovered modulation at frequencies of hundreds of MHz of an electron beam produced by a plasma cathode. The plasma cathode consists of a ferroelectric disk sample [BaTiO3 or Pb(Zr, Ti)O3] that is placed in a cylindrical metal box having an output window covered by a grid. The plasma is prepared by an incomplete discharge that was ignited by a few kV driving pulse applied across the ferroelectric disk. It was shown that the current modulation appears only when the driving pulse is applied to the front gridded electrode of the ferroelectric sample and the solid rear electrode is grounded. The modulation spectrum is quite narrow (⩽3%), with harmonics at frequencies up to a few GHz. The basic frequency of modulation was found to be dependent on the length of the feed cable to the sample. Investigation of the plasma and the beam modulation properties and their dependence on the experimental parameters is presented. The results indicate the formation of a plasma at the vicinity of the front electrode of the ferroelectric sample during the modulation. The results are discussed within the frame of electrons oscillating in the potential well created by the positively charged plasma having feedback coupling with the input cable. © 1999 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Bx Electron sources
52.75.-d Plasma devices
41.75.Fr Electron and positron beams

Charge distribution function of plasma dust particles with secondary electron emission

B. F. Gordiets and C. M. Ferreira

J. Appl. Phys. 86, 4118 (1999); http://dx.doi.org/10.1063/1.371336 (6 pages) | Cited 8 times

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The charge distribution function (CDF) of dust particles in low temperature plasmas is obtained as a function of both negative and positive discrete charges Z = ∓1,∓2;,…, and various plasma parameters. Positively charged grains can be formed when secondary electron emission, that is, ionization of the grains by electron impact, is sufficiently important to change their charge. An expression for the CDF is derived from steady-state master equations for the densities of monodispersed, negatively or positively charged dust particles, with Z = ∓1,∓2,… discrete elementary charges and radius R, taking into account single and double elementary charge changes in collisions of the particle with plasma electrons or ions. © 1999 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Vy Impurities in plasmas

Role of Ar2+ and Ar2+ ions in a direct current argon glow discharge: A numerical description

Annemie Bogaerts and Renaat Gijbels

J. Appl. Phys. 86, 4124 (1999); http://dx.doi.org/10.1063/1.371337 (10 pages) | Cited 32 times

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A two-dimensional model has been developed for calculating the behavior of Ar2+ and Ar2+ ions in a direct current argon glow discharge, by the use of balance equations describing the various production and loss processes for these species, as well as their transport by diffusion and migration. These balance equations are coupled to the equations for the Ar+ ions and electrons and solved simultaneously with Poisson’s equation, to obtain a self-consistent description of the charged particles behavior and the electrical characteristics in the glow discharge. Moreover, this model is combined with the other models that we have developed previously for the Ar atoms in various excited levels and the Cu atomic and ionic species, to obtain an overall description of the direct current argon glow discharge. The model is applied to typical conditions used for glow discharge mass spectrometry (pressure of 50–100 Pa, voltage of 600–1400 V, and current of 0.4–15 mA). Typical calculation results include the densities and fluxes of these ionic species, as well as the relative contributions of their production and loss processes. The Ar2+ ions are almost exclusively formed by two-electron ionization from Ar0 atoms, and they become primarily lost by diffusion and subsequent recombination at the cell walls. The Ar2+ ions are mainly created by Hornbeck–Molnar and metastable-metastable associative ionization, whereas atom to molecule conversion seems to play only a minor role at the discharge conditions under study. Loss of these Ar2+ ions is caused primarily by diffusion and recombination at the cell walls, but dissociative recombination in the plasma plays also a significant role. We found that the ratios of Ar2+/Ar+ and Ar2+/Ar+ ion densities and fluxes were in the order of 1%–10%, which is in good agreement with experimental observations. © 1999 American Institute of Physics.
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52.65.-y Plasma simulation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Hc Glow; corona
52.20.-j Elementary processes in plasmas
52.25.Fi Transport properties
52.25.-b Plasma properties
52.40.Hf Plasma-material interactions; boundary layer effects
34.80.Lx Recombination, attachment, and positronium formation

Experimental investigation of deviations from local thermodynamic equilibrium in high-pressure mercury discharges

Hatem Elloumi, Eckhard Kindel, Conrad Schimke, and Georges Zissis

J. Appl. Phys. 86, 4134 (1999); http://dx.doi.org/10.1063/1.371338 (8 pages) | Cited 9 times

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The determination of the radial profile of the ground state density without assuming local thermodynamic equilibrium (LTE) conditions in around atmospheric pressure (0.01 MPa<p<0.3 MPa) discharges used as light sources is a worthy investigation subject. This work deals with the high-pressure mercury discharge which could be considered as a “test case.” Particularly useful for the diagnostics of these plasmas is the self-reversed resonance mercury line 253.7 nm. In this article, two independent experimental methods were used: emission spectroscopy, called the “ΔλR method,” and interference shift measurements “hook method.” Using the Hg-253.7 nm resonance line, both experimental methods indicate similar deviations from LTE in particular for the lower pressure discharges (p<0.04 MPa). In those cases, the experimental errors for both methods are significantly lower than the detected deviations. Furthermore, the measured deviations are in good agreement with predicted values from a two-temperature, two-dimensional fluid model developed elsewhere. © 1999 American Institute of Physics.
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52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Internal sheaths in electronegative discharges

I. G. Kouznetsov, A. J. Lichtenberg, and M. A. Lieberman

J. Appl. Phys. 86, 4142 (1999); http://dx.doi.org/10.1063/1.371339 (12 pages) | Cited 43 times

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In three component electronegative discharges a parameter regime can be found in which the positive ions reach the local ion sound velocity at a position where the negative ion density may be significant compared to the electron density. For this regime a quasineutral electronegative core breaks down and a space charge region forms. Solutions in the space charge region are obtained in collisionless and collisional cases, neglecting ionization and positive-negative ion recombination. The structure of the non-neutral region is shown to vary significantly with the ratio of the negative ion and electron densities at the core edge, the ratio of ion and electron temperatures, and the ratio of the electron Debye length to the ion mean free path. If the first ratio is not too large the non-neutral region displays potential oscillations on the electron Debye length spatial scale, which damp away on the scale of the ion–neutral mean free path. The non-neutral region then terminates within the plasma. The change in electric potential across this region is several times the negative ion temperature, which is sufficient to confine the negative ions to the core. The non-neutral region merges with a quasineutral halo containing essentially only positive ions and electrons. If the negative ion density is sufficiently high compared to the electron density the electropositive halo disappears and the non-neutral region extends from the ion sound velocity threshold to the wall. For intermediate values of the negative ion density, a space charge double layer forms between the electronegative and electropositive regions. © 1999 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges
52.40.Hf Plasma-material interactions; boundary layer effects
52.65.Rr Particle-in-cell method
52.25.Fi Transport properties

Optical emission study of ablation plasma plume in the preparation of diamond-like carbon films by KrF excimer laser

Y. Yamagata, A. Sharma, J. Narayan, R. M. Mayo, J. W. Newman, and K. Ebihara

J. Appl. Phys. 86, 4154 (1999); http://dx.doi.org/10.1063/1.371340 (6 pages) | Cited 31 times

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Optical emission study of the laser ablation plasma plume during the preparation of diamond-like carbon (DLC) films using KrF excimer (248 nm) pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum (1×10−7 Torr), the emission lines from carbon ions of C+, C2+, and C3+ are observed in addition to atomic carbon emission lines, while no emission from the diatomic carbon molecule (C2) is observed. With increasing background nitrogen pressure up to 500 mTorr, the emission intensities of the C2 Swan band and the carbon nitride (CN) violet band increase. The diamond-like character of deposited DLC film degrades with background nitrogen pressure. The vibrational temperature of C2 and CN molecules decreases with the increasing of nitrogen pressure. The CN vibrational temperature for the first 2 μs after the laser pulse is very high and in agreement with the kinetic energy of monatomic carbon ions. The C2 vibrational temperature is as low as 0.6 eV and is consistent with the electron temperature of about 0.8–3.0 eV. It is conjectured that CN molecules are formed directly in reactions involving energetic ionic monatomic carbon, and that the formation of excited C2 molecules is the result of molecular recombinations of C atoms and ions. From the emission intensity measurements and the estimation of the vibrational temperature, it is suggested that the C2 molecule in the ablated plasma plume is not important, but energetic species, such as C+, are very important for producing high quality DLC films using PLD. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
81.05.ub Fullerenes and related materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
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Cavities in helium implanted and annealed silicon characterized by spectroscopic ellipsometry

W. Fukarek and J. R. Kaschny

J. Appl. Phys. 86, 4160 (1999); http://dx.doi.org/10.1063/1.371341 (6 pages) | Cited 14 times

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The formation of helium induced cavities in silicon during short-time annealing is analyzed by spectroscopic ellipsometry. Specimens implanted with 40 keV He+ ions to a dose of 5×1016 cm−2 are heat treated at 800 °C for times of 1–1200 s by rapid thermal annealing. Spectroscopic ellipsometry is employed to obtain quantitative information on the cavity volume depth profiles. A newly developed formula is used to model the optical multilayer depth profiles. The cavity volume is found to increase during annealing for about 300 s and to decrease for longer annealing times. Over this characteristic time a marked change in the He loss occurs, which has been reported only recently. Swelling of the helium implanted and annealed silicon is analyzed using an atomic force microscope. Step heights are consistent with the cavity volume per unit area obtained from spectroscopic ellipsometry data analysis. The number density of cavities after annealing for 600 s is calculated to be ≈ 1.16±0.27×1017 cm−3 and is found to be largely independent of depth in the central part of the cavity layer. © 1999 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
61.72.S- Impurities in crystals
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Occasional “long-range” nonequilibrium body-centered-cubic structures in NiFe/Cu spin valves

H. Geng, J. W. Heckman, W. P. Pratt, J. Bass, F. J. Espinosa, S. D. Conradson, D. Lederman, and M. A. Crimp

J. Appl. Phys. 86, 4166 (1999); http://dx.doi.org/10.1063/1.371342 (10 pages) | Cited 7 times

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We describe conventional and high-resolution transmission electron microscopy (HRTEM) characterization of the microstructure of sputtered NiFe/Cu giant magnetoresistance spin valves (Cu/FeMn/NiFe/Cu/NiFe) sandwiched between thick Nb contact layers. Six spin valves, sputtered at different temperatures, three with thin (3 nm) and three with thick (24 and 30 nm) NiFe layers, were studied. All of the spin-valve layers were smooth and continuous, consisting of columnar grains generally 20–90 nm wide. In most cases, the grains had grown epitaxially from the bottom contact, through the entire multilayer, to the top contact layer. The columnar grains grew on the closest-packed planes (i.e., {110} planes for bcc Nb and {111} planes for fcc Cu, FeMn, and NiFe spin-valve components). This epitaxial growth yields an apparent Kurdjumov–Sachs {111}fcc∥{110}bcc; 〈110〉fcc∥〈111〉bcc orientation relationship. However, HRTEM imaging supported by fast Fourier transform analysis reveals that in some of the columnar grains the Cu, FeMn, and NiFe layers take up a nonequilibrium bcc structure. In these cases, the bcc Cu, FeMn, and NiFe layers grow on {110} planes and are epitaxial with the Nb contacts for the individual grain columns. While bcc Cu has been observed elsewhere, the length scale of the nonequilibrium bcc phases reported here is an order of magnitude greater than previously observed. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

The influence of boron ion implantation on hydrogen blister formation in n-type silicon

T. Höchbauer, K. C. Walter, R. B. Schwarz, M. Nastasi, R. W. Bower, and W. Ensinger

J. Appl. Phys. 86, 4176 (1999); http://dx.doi.org/10.1063/1.371343 (8 pages) | Cited 16 times

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We have studied the formation of surface blisters in 〈100〉 n-type silicon following co-implantation with boron and hydrogen. The silicon substrates had four different n-type dopant levels, ranging from 1014 to 1019 cm−3. These substrates were implanted with 240 keV B+ ions to a dose of 1015 cm−2, followed by a rapid thermal anneal at 900 °C for 30–60 s to force the boron atoms into substitutional lattice positions (activation). The samples were then implanted with 40 keV H+ to a dose of 5×1016 cm−2. The implanted H+ distribution peaks at a depth of about 475 nm, whereas the distribution in the implanted B+ is broader and peaks at about 705 nm. To evaluate the role of the B+ implantation, control samples were prepared by implanting with H+ only. Following the H+ implantation, all the samples were vacuum annealed at 390 °C for 10 min. Blisters resulting from subsurface cracking at depths of about 400 nm, were observed in most of the B+ implanted samples, but not in the samples implanted with H+ only. This study indicates that the blistering results from the coalescence of implanted H into bubbles. The doping with B facilitates the short-range migration of the H interstitials and the formation of bubbles. A comparison of the observed crack depth with the depth of the damage peak resulting from the H+ implantation (evaluated by the computer code TRIM) suggests that the nucleation of H bubbles occurs at the regions of maximum radiation damage, and not at the regions of maximum H concentration. For given values of B+ and H+ doping, the blister density was found to decrease with increasing n-type doping, when the boron is activated. Blister formation was also observed in B+ implanted samples which had not been activated. In this case, the blister density was found to increase with increasing value of n-type doping. © 1999 American Institute of Physics.
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61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
68.35.Gy Mechanical properties; surface strains

Strain and SiC particle formation in silicon implanted with carbon ions of medium fluence studied by synchrotron x-ray diffraction

F. Eichhorn, N. Schell, W. Matz, and R. Kögler

J. Appl. Phys. 86, 4184 (1999); http://dx.doi.org/10.1063/1.371344 (4 pages) | Cited 4 times

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Implantation of C ions with an energy of 195 keV into Si wafers heated up to 800 °C results in an elastic distortion of the Si host lattice and in the formation of crystalline SiC particles or their prestages depending on implantation dose and temperature. Synchrotron x-ray diffraction at the Rossendorf beamline in Grenoble was used to reveal phase formation and the correlated lattice strain changes. Only a Si lattice deformation without growth of SiC was observed if the fluence did not exceed 5×1015 C ions/ cm2. After implantation of C ions up to 4×1017 cm−2 at a temperature of 500 °C, agglomerations of Si–C and an altered state of Si lattice deformation are found. By implantation of 4×1017 ions/cm2 at 800 °C, particles of the 3C–SiC (β-SiC) phase grow, which are aligned with the Si matrix. They are aligned in such a way with the Si matrix that the cubic crystallographic axes of matrix and particles coincide with an accuracy of 3°. © 1999 American Institute of Physics.
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61.72.uf Ge and Si
66.30.Ny Chemical interdiffusion; diffusion barriers
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Effects of stress relaxation of epitaxial SrRuO3 thin film on microstructures

X. Q. Pan, J. C. Jiang, W. Tian, Q. Gan, R. A. Rao, and C. B. Eom

J. Appl. Phys. 86, 4188 (1999); http://dx.doi.org/10.1063/1.371345 (4 pages) | Cited 9 times

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We report the effect of lattice stress relaxation on the microstructures of epitaxial thin films by domain structure studies of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates. X-ray diffraction analysis revealed that the as-grown films are single domain and have a strained lattice due to the lattice mismatch with the substrate. In contrast, plan-view transmission electron microscopy (TEM) images obtained from the same films showed the coexistence of domains with three different crystallographic orientations. The discrepancy is attributed to the lattice stress relaxation occurring on the TEM specimens as the substrate material is eliminated by ion milling or etching, resulting in the formation of elastic domains with different crystallographic orientations. These studies directly reveal a crucial effect of the lattice strain relaxation on the microstructures and properties of epitaxial thin films when the substrate material is removed. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
68.55.-a Thin film structure and morphology

Sensitivity of near-edge x-ray absorption fine structure spectroscopy to ion beam damage in diamond films

A. Laikhtman, I. Gouzman, A. Hoffman, G. Comtet, L. Hellner, and G. Dujardin

J. Appl. Phys. 86, 4192 (1999); http://dx.doi.org/10.1063/1.371346 (7 pages) | Cited 28 times

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In the present work, we study the sensitivity of the near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to ion induced defects in polycrystalline diamond films. The ion bombardment of hydrogenated films is performed using 30 keV Xe+ ions at room temperature for doses ranging from 2×1013 ions/cm2, producing local point defects, to 2×1015 ions/cm2, which results in almost complete amorphization of the diamond surface. Auger electron spectroscopy measurements are not sensitive to the modifications induced by the lowest implantation dose. Whereas partial electron yield (PEY) NEXAFS measurements, applied in surface and bulk-sensitive modes, using 35, 15, and 8 eV secondary electrons, respectively, reveals the formation of a defective structure and gradual deterioration of diamond in the near-surface region. From PEY NEXAFS spectra measured using 15 eV secondary electrons, the position of C(1s) binding energy is measured. The x-ray photoelectron spectra of the samples were measured using an incident photon energy of 450 eV. It is found that the C(1s) binding energy in the implanted samples has a positive shift of 0.6–1 eV, which is indicative of transformation of diamond to disordered carbon. The high sensitivity of NEXAFS spectroscopy to point defects induced by the low dose ion implantation was reflected by a sharp reduction in the intensity of the diamond core exciton peak and by the appearance of a new spectral feature in the pre-edge region, below the C(1s)−π∗ transition. Analysis of the NEXAFS spectra of ion implanted films is performed on the basis of the electronic structure of diamond. © 1999 American Institute of Physics.
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81.05.ub Fullerenes and related materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.80.Jh Ion radiation effects
78.70.Dm X-ray absorption spectra
81.05.Cy Elemental semiconductors
61.82.Fk Semiconductors
61.72.J- Point defects and defect clusters
79.60.Dp Adsorbed layers and thin films

Nematic polar anchoring strength measured by electric field techniques

Yu. A. Nastishin, R. D. Polak, S. V. Shiyanovskii, V. H. Bodnar, and O. D. Lavrentovich

J. Appl. Phys. 86, 4199 (1999); http://dx.doi.org/10.1063/1.371347 (15 pages) | Cited 50 times

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We analyze the high-electric-field technique designed by Yokoyama and van Sprang [J. Appl. Phys. 57, 4520 (1985)] to determine the polar anchoring coefficient W of a nematic liquid crystal-solid substrate. The technique implies simultaneous measurement of the optical phase retardation and capacitance as functions of the applied voltage well above the threshold of the Frederiks transition. We develop a generalized model that allows for the determination of W for tilted director orientation. Furthermore, the model results in a new high-field technique, (referred to as the RV technique), based on the measurement of retardation versus applied voltage. W is determined from a simple linear fit over a well-specified voltage window. No capacitance measurements are needed to determine W when the dielectric constants of the liquid crystal are known. We analyze the validity of the Yokoyama–van Sprang (YvS) and RV techniques and show that experimental data in real cells often do not follow the theoretical curves. The reason is that the director distribution is inhomogeneous in the plane of the bounding plates, while the theory assumes that the director is not distorted in this plane. This discrepancy can greatly modify the fitted value of 1/W, and even change its sign, thus making the determination of W meaningless. We suggest a protocol that allows one to check if the cell can be used to measure W by the YvS or RV techniques. The protocol establishes new criteria that were absent in the original YvS procedure. The results are compared with other data on W, obtained by a threshold-field technique for the same nematic-substrate pair. © 1999 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.22.Ch Permittivity (dielectric function)

Gettering of Cu by microcavities in bonded/ion-cut silicon-on-insulator and separation by implantation of oxygen

Miao Zhang, Xuchu Zeng, Paul K. Chu, R. Scholz, and Chenglu Lin

J. Appl. Phys. 86, 4214 (1999); http://dx.doi.org/10.1063/1.371348 (6 pages) | Cited 1 time

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Microcavities formed by H+ and He+ implantation and subsequent annealing are effective gettering sites for transition metal impurities in silicon. However, gettering in silicon-on-insulator (SOI) materials is quite different from that in silicon. In this work, we investigate the gettering of Cu to these microcavities in silicon, separation by implantation of oxygen (SIMOX) and bonded/ion-cut SOI wafers. Our data indicate that He+ implantation in the high dose regime (0.2–1×1017 cm−2) creates a wide band of microcavities near the projected range without causing blistering on the sample surface. On the other hand, the implantation dose of H+ needed for stable microcavity formation is relatively narrow (3–4×1016 cm−2), and this value is related to the projected range. The different behavior of H and He in silicon is discussed and He implantation is more desirable with regard to impurity gettering. Cu is implanted into the surface region of the Si and SOI samples, followed by annealing at 700 and 1000 °C. Our results indicate that the microcavities can effectively getter a high dose of Cu (2.5×1015 cm−2) at 700 °C in bulk Si wafer, but higher temperature annealing is needed for the effective gettering in SIMOX. Gettering of Cu by the intrinsic defects at or beneath the buried oxide interface of the SIMOX is observed at 700 °C, but no trapped impurities are observed after 1000 °C annealing in the samples in the presence of microcavities. Almost all of the 1×1014 cm−2 Cu implanted into the Si overlayer of the bonded/ion-cut SOI diffuse through the thermally grown oxide layer and are captured by the cavities in the substrate after annealing at 1000 °C. © 1999 American Institute of Physics.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Yx Interaction between different crystal defects; gettering effect
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.82.Ms Insulators
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.up Other materials
61.72.uf Ge and Si
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Correlation between tip-apex shape and surface modification by scanning tunneling microscopy

Seiji Heike, Yasuo Wada, and Tomihiro Hashizume

J. Appl. Phys. 86, 4220 (1999); http://dx.doi.org/10.1063/1.371349 (5 pages) | Cited 3 times

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The correlation between the shape of a probe tip apex for scanning tunneling microscopy and the surface modification patterns on a Si(111)-7×7 surface is demonstrated by using an in situ tip evaluation technique. The tip apex is inversely imaged by using a very sharp nanoneedle fabricated on the sample surface by applying a high voltage between the tip and the surface. When a large current of 100–300 nA flows between the tip and the surface, silicon atoms on the surface are extracted and a trench pattern is formed. The trench pattern agrees well with the geometry of the tip apex. The correlation between the tip shape and the fabrication pattern is discussed in terms of the electric field under the tip. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Investigation of nanostructures in ordinary Portland cement through positron annihilation lifetime spectroscopy

G. Consolati, G. Dotelli, and F. Quasso

J. Appl. Phys. 86, 4225 (1999); http://dx.doi.org/10.1063/1.371350 (7 pages) | Cited 5 times

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Early hydration (up to four weeks) of five ordinary Portland cement pastes with different water-to-cement ratios (0.3, 0.4, 0.5, 0.6, and 1.0 wt) was investigated through positron annihilation lifetime spectroscopy. Measurements were performed at four different hydration times (1 day and 1, 2, and 4 weeks) and compared with results obtained from thermogravimetric analyses. Deconvolution of positron spectra allowed us to separate orthopositronium annihilations in the evacuated gel pores from those in the pores containing water, and therefore, to monitor the pores’ evolution with aging time. It is found that the concentration of gel pores increases with aging time, as well as by increasing the content of water in the paste; on the other hand, the typical sizes of the pores do not show significant variations, either with aging time or with the water-to-cement ratio.© 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
78.70.Bj Positron annihilation
81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis

Viscoelastic crack healing and adhesion

J. M. Baney and C.-Y. Hui

J. Appl. Phys. 86, 4232 (1999); http://dx.doi.org/10.1063/1.371351 (10 pages) | Cited 14 times

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Closing cracks in viscoelastic materials are analyzed using a cohesive zone model. The analysis is relevant to the bonding of surfaces of viscoelastic materials, and in particular to the Johnson–Kendall–Roberts (JKR) experiment. A crack bonding theory due to Schapery is extended to include the case of the standard linear solid material, and some consequences of this material’s finite long time compliance are illustrated. The stress field behind a steadily closing crack in a standard linear solid is also investigated in detail. Finally, a method for applying Schapery’s crack bonding theory to the analysis of a JKR-type experiment involving viscoelastic cylinders is given explicitly. © 1999 American Institute of Physics.
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46.50.+a Fracture mechanics, fatigue and cracks
62.20.M- Structural failure of materials
68.35.Gy Mechanical properties; surface strains
46.35.+z Viscoelasticity, plasticity, viscoplasticity

Measurements of laser driven spallation in tin and zinc using an optical recording velocity interferometer system

E. Moshe, S. Eliezer, E. Dekel, Z. Henis, A. Ludmirsky, I. B. Goldberg, and D. Eliezer

J. Appl. Phys. 86, 4242 (1999); http://dx.doi.org/10.1063/1.371352 (7 pages) | Cited 12 times

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Measurements of the dynamic strength, in tin and zinc, shocked by a high power pulsed laser to tens of kilobars pressures are reported. The strain rates in these experiments are of the order of 107 s−1, higher by two-to-three orders of magnitude than those reached with conventional shock generators like plane impacts or explosives. The free surface velocity time history, which is related to the spallation process, was measured with an optical recording velocity interferometer system. This diagnostic technique is noninterfering and provides a highly accurate continuous measurement in time. The spall strength estimated from the free surface velocity profile was compared with the theoretical upper limit for the spall strength, calculated from a wide range equation of state for metals. © 1999 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
62.50.-p High-pressure effects in solids and liquids
61.82.Bg Metals and alloys

Dislocation core reconstruction and its effect on dislocation mobility in silicon

João F. Justo, Vasily V. Bulatov, and Sidney Yip

J. Appl. Phys. 86, 4249 (1999); http://dx.doi.org/10.1063/1.371353 (9 pages) | Cited 15 times

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Through atomistic calculations of kink nucleation and migration in the core of partial dislocations in silicon we demonstrate that symmetry-breaking structural reconstructions will strongly affect dislocation mobility. Core reconstructions give rise to multiple kink species, and, relative to kinks in an unreconstructed dislocation, an increase in kink formation and migration energies. These factors provide additional resistance to dislocation motion which scales with the energy reconstruction. Our results indicate that the observed variations of dislocation mobility in going from elemental to IV–IV, and further to III–V and II–VI zinc-blende semiconductors, can be attributed in part to the weakening of core reconstruction across the series. © 1999 American Institute of Physics.
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61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations
66.30.Lw Diffusion of other defects
66.30.Dn Theory of diffusion and ionic conduction in solids
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