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15 Dec 1999

Volume 86, Issue 12, pp. 6627-7200

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Influence of neodymium concentration on the cw laser properties of Nd doped Ca3Ga2Ge3O12 laser garnet crystal

D. Jaque, U. Caldiño, J. J. Romero, and J. García Solé

J. Appl. Phys. 86, 6627 (1999); http://dx.doi.org/10.1063/1.371735 (7 pages) | Cited 15 times

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Spectral and laser properties of Nd3+ doped Ca3Ga2Ge3O12 have been investigated for different Nd concentrations ranging from 0.1 to 16 at %. The 4F3/2→4I11/2 emission spectrum is dominated by two main peaks at 1060 and 1065 nm whose stimulated emission cross sections change with Nd concentration. For concentrations above 0.5% luminescence quenching begins. Then, continuous wave laser gain experiments have been used to investigate the influence of these effects on the laser properties. The different factors (crystal losses and saturation intensity factor) contributing to the increase observed in the laser pump threshold with Nd concentration are discussed. Analysis of the laser spectra shows a double laser oscillation around 1060 and 1065 nm, which tends to disappear for high Nd concentrations. © 1999 American Institute of Physics.  
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.45.+h Stimulated emission
78.55.Hx Other solid inorganic materials
42.55.Xi Diode-pumped lasers

Secondary ion mass spectrometry study of space-charge formation in thermally poled fused silica

Thomas G. Alley, S. R. J. Brueck, and Michael Wiedenbeck

J. Appl. Phys. 86, 6634 (1999); http://dx.doi.org/10.1063/1.371736 (7 pages) | Cited 36 times

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Applying a dc electric field across a fused silica sample at elevated temperatures followed by cooling the sample with the field applied (thermal poling) leads to a second-order nonlinearity that has been linked to the formation of a space-charge region in bulk glass. The first microscopic information on the extent of the space-charge region and its behavior with poling time is reported using secondary ion mass spectrometry to monitor the distribution of charged impurities. Lithium and sodium ions are observed to form depletion regions. Potassium and sodium ions as well as a hydrogenated species appear to be injected from the surface. The extent of the space-charge region evolves approximately logarithmically with poling time well after the nonlinearity as measured by second-harmonic generation has been established. The evolution of the space charge region can be qualitatively understood by an ion-exchange model that allows interaction of two ionic carriers with vastly different mobilities. © 1999 American Institute of Physics.
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77.22.Jp Dielectric breakdown and space-charge effects
61.43.Fs Glasses
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
77.22.Ej Polarization and depolarization
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz

A quantitative analysis of single pulse ultraviolet dry laser cleaning

D. R. Halfpenny and D. M. Kane

J. Appl. Phys. 86, 6641 (1999); http://dx.doi.org/10.1063/1.371737 (6 pages) | Cited 18 times

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Particles as small as 0.3 μm in diameter have been successfully removed from a glass surface using a single ultraviolet pulse from a frequency doubled copper vapor laser (255.3 nm). Quantitative analysis of the particle density before and after laser irradiation shows that laser cleaning occurs after a fluence threshold is reached. The cleaning efficiency after threshold follows a nonlinear trend with respect to fluence. A model is presented which reveals that the cleaning efficiency is a function of the irradiance distribution of the beam used. Results of modeling thermal expansion of the substrate and particles, and particle adhesion do not confirm a thermal expansion mechanism for laser cleaning in this study, in contrast with other recent reports. © 1999 American Institute of Physics.
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81.05.Kf Glasses (including metallic glasses)
81.65.Cf Surface cleaning, etching, patterning

Operating conditions of continuous wave simultaneous dual wavelength laser in neodymium host crystals

H. Y. Shen and H. Su

J. Appl. Phys. 86, 6647 (1999); http://dx.doi.org/10.1063/1.371738 (5 pages) | Cited 10 times

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In consideration of the hole-burning effects, based on the single longitudinal mode rate equation, the operating condition of continuous wave simultaneous dual wavelength laser (SDWL) in neodymium host crystals is studied. The relationship between the operating threshold of SDWL and thresholds of the single wavelength laser for both wavelengths is ascertained. The effect of multilongitudinal modes on the operation result has been discussed qualitatively. Taking Nd:YAlO3 crystal as an example, the experimental results agree well with our theoretical analysis. © 1999 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Dynamic studies of polymerization in liquid crystal-polymer mixtures

Andy Y.-G. Fuh, M.-S. Tsai, Y.-H. Fan, C.-R. Lee, and K.-Y. Lo

J. Appl. Phys. 86, 6652 (1999); http://dx.doi.org/10.1063/1.371739 (5 pages) | Cited 1 time

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This work studied the dynamic behavior of polymerization in films of liquid crystal (LC)-polymer mixtures by using the pump-probe technique. Chopped Ar+ laser pulses were used as pump beams, and probed by a cw He—Ne laser. The experimental results indicated that the transmission of the probe beam was modulated in response to the chopping frequency of the pump beam. The modulation was such that transmission during the on-time of the pump beam was initially smaller than, then equal to, and finally larger than that in the off-time. Analyzing the transparency difference between the films with and without the Ar+ laser pulse allows us to recognize the three stages of polymerization process, initiation, propagation, and termination. Moreover, both the LC content in the sample and the chopping on/off ratio of the pump beam significantly affected the turning point occurred and the modulation amplitude of the probe beam. A model is proposed to explain these observed results. © 1999 American Institute of Physics.
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82.35.-x Polymers: properties; reactions; polymerization
61.30.-v Liquid crystals
78.66.Qn Polymers; organic compounds

A perturbation model to predict thermal sensitivity of transverse waves on thin quartz plates

J. B. Briot, S. Ballandras, and G. Martin

J. Appl. Phys. 86, 6657 (1999); http://dx.doi.org/10.1063/1.371740 (8 pages)

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The development of new acoustic wave devices has received increasing interest for various applications, particularly for sensors, but also in the telecommunication domain. The need to increase operating frequencies together with the efficiency of such devices pushes new principles to produce high-quality acoustic wave resonators and filters. Previous work has been done to experimentally measure the thermal sensitivity of transverse waves trapped by metal strip gratings deposited on thin quartz plates. Temperature compensation was found for AT-cut devices in an extended range of frequency, with the turnover temperature varying from 30 to 0 °C. Moreover, thermal compensation was found for higher-order modes in the Z cut, although the first mode exhibited a very high sensitivity to temperature. A theoretical model has been developed to explain these results. It is based on the Sinha–Tiersten perturbation approach combined with a model of unperturbed propagation, taking piezoelectricity into account. Comparison between the theoretical results provided by this model and experimental data is presented. A very good agreement is found for Z and AT-cut devices, even if second-order effects appear to be predominant in the latter case. © 1999 American Institute of Physics.
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77.65.Fs Electromechanical resonance; quartz resonators
43.38.-p Transduction; acoustical devices for the generation and reproduction of sound
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
43.60.-c Acoustic signal processing
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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Modeling of the field reversal in a capacitively coupled high frequency sheath

H.-B. Valentini

J. Appl. Phys. 86, 6665 (1999); http://dx.doi.org/10.1063/1.371741 (8 pages) | Cited 3 times

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Dealing with the collisionless plane sheath of a capacitively coupled high frequency (hf) discharge a two-point boundary value problem of the standard form is elaborated for a set of ordinary differential equations. The numerical solution yields that the direction of the electric field is reversed in a short interval of the period if the hf amplitude exceeds a threshold. The sheath model hitherto often used is extended to include the effect of the field reversal in a relatively simple way. At the electrode various boundary conditions are taken into account. It is shown that the different screening of the time-averaged component and of the high frequent components of the electric field near the electrode and in the interior of the sheath is the physical reason for the occurrence of the field reversal. In front of the electrode, the field reversal decreases the electron density and the electron current and causes an additional step in the displacement current. Apparently, recent experiments known from the references confirm the theoretical results. © 1999 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.80.Pi High-frequency and RF discharges
52.65.-y Plasma simulation
02.30.Hq Ordinary differential equations
02.60.Lj Ordinary and partial differential equations; boundary value problems
52.25.-b Plasma properties

Lifetime and switching characteristics of a high-current multichannel pseudospark

A. Naweed, J. Kiefer, M. Röhner, and W. Neff

J. Appl. Phys. 86, 6673 (1999); http://dx.doi.org/10.1063/1.371742 (4 pages) | Cited 3 times

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A radial multichannel pseudospark switch is integrated into a plasma focus system designed to generate soft x rays to determine switch durability in a long-term test. The operating parameters correspond to a repetition rate of up to 2 Hz, stand-off voltages of 10 kV and peak currents of 200 kA. Only minimal electrode erosion is witnessed after a serial test of 180 000 shots where the electrode surfaces are inspected after every 25 000 shots. The good condition of electrode surfaces suggests the possibility of an additional 200 000 shots, implying that for the given parameter range the lifetime of the multichannel pseudospark is at least four times longer than that of traditional high-current switches such as spark gaps. In a comparative test the performance of the multichannel pseudospark switch is evaluated against a multichannel spark gap. The results of these investigations show that the low-erosive pseudospark is well suited to substitute for spark gaps in high-current applications. © 1999 American Institute of Physics.
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52.75.Kq Plasma switches (e.g., spark gaps)
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.55.Ez Theta pinch
06.60.Mr Testing and inspecting procedures
52.70.La X-ray and γ-ray measurements
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Characterization of defect-related optical absorption in ZnGeP2

S. D. Setzler, P. G. Schunemann, T. M. Pollak, M. C. Ohmer, J. T. Goldstein, F. K. Hopkins, K. T. Stevens, L. E. Halliburton, and N. C. Giles

J. Appl. Phys. 86, 6677 (1999); http://dx.doi.org/10.1063/1.371743 (5 pages) | Cited 17 times

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A broad optical absorption band with a peak near 1 μm is present in most single crystals of ZnGeP2. These same crystals have an electron paramagnetic resonance (EPR) signal which has been assigned to singly ionized zinc vacancies. A direct correlation between the intensity of the optical absorption at 1 μm and the intensity of the EPR signal has been established using a set of ZnGeP2 crystals where this absorption varied widely. These results suggest that the singly ionized zinc vacancy acceptor plays a direct role in the electronic transition(s) responsible for the 1 μm optical absorption. In separate experiments, it was found that illuminating the ZnGeP2 crystals with a He–Ne laser (632.8 nm) while at temperatures near 25 K produces an increase in the absorption at 1 μm and an increase in the zinc vacancy EPR spectrum. These latter results provide further evidence that the absorption at 1 μm is associated with the singly ionized zinc vacancy acceptor. © 1999 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
76.30.Mi Color centers and other defects
61.72.J- Point defects and defect clusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
71.55.Ht Other nonmetals

Quantification of the surface- and bulk-order parameters of a homogeneously aligned nematic liquid crystal using fully leaky guided modes

B. T. Hallam, C. V. Brown, and J. R. Sambles

J. Appl. Phys. 86, 6682 (1999); http://dx.doi.org/10.1063/1.371744 (8 pages) | Cited 10 times

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An optical waveguide technique, involving the excitation of fully leaky guided modes, has been used to quantify the director distortions induced by the application of weak in-plane electric fields to a homogeneously aligned nematic liquid crystal, E7. The twist profile of the nematic is determined by fitting angle-dependent reflectivity and transmission data to multilayer optical theory. By considering the Frank–Oseen free energy in the bulk, with Rapini–Papoular-type anchoring at the surfaces, we have determined accurate values for both the azimuthal anchoring strength Wa and the twist elastic constant k22 as a function of temperature. Values for the temperature-dependent surface and bulk average-order parameters have also been deduced by allowing for a spatially varying nematic-order parameter. © 1999 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.70.Df Liquid crystals
42.79.Gn Optical waveguides and couplers
65.20.-w Thermal properties of liquids
65.40.gd Entropy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.10.+s Mechanical properties of liquids

Preparation of highly overstoichiometric LaNi5+x (1 ⩽ x ⩽ 4) single-phase films by ion beam sputtering

F. Cuevas, M. Hirscher, B. Ludescher, and H. Kronmüller

J. Appl. Phys. 86, 6690 (1999); http://dx.doi.org/10.1063/1.371745 (7 pages) | Cited 4 times

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Single-phase LaNi6.1 and LaNi9.2 films with hexagonal TbCu7 structure have been successfully obtained. Films in the micron scale range were deposited by ion beam sputtering on sapphire and glass substrates heated at 600 K. A two-material La–Ni mosaic target was used for this purpose. X-ray diffraction and transmission electron microscopy investigations show that the lattice parameters of the hexagonal structure follow a linear dependence for Ni concentration. This result relates to a random substitution of La atoms for Ni dumbbell pairs in the ordered CaCu5 structure. The films exhibit a strong preferential orientation, with the c axis parallel to the substrate plane, which seems to be favored by the presence of Ni dumbbell pairs. The expected impact of this phase on the preparation of new hydrogen storage materials is discussed. © 1999 American Institute of Physics.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys

Implant dose dependence in doping Si atoms from a-Si:H films into S+-implanted GaAs

Katsuhiro Yokota, Kazuhiro Nakamura, Tomoyuki Ishizu, Masanori Sakaguchi, Hiromichi Takano, and Masao Kumagai

J. Appl. Phys. 86, 6697 (1999); http://dx.doi.org/10.1063/1.371746 (4 pages)

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Sulfur (S+) ions were implanted into gallium arsenide (GaAs) at 50 keV at various doses. Hydrogenated amorphous silicon (a-Si:H) films were deposited on the surface of the S+-implanted GaAs using a radio-frequency glow discharge system. The samples were annealed in an Ar atmosphere at 1000 °C for 10 min. During annealing, Si atoms were diffused from the a-Si:H films into the S+-implanted GaAs. The concentration [Si] of the Si atoms increased with the dose [S] of the implanted S+ ions as [Si]=1.6×10−6 [S]1.45. © 1999 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
61.80.Jh Ion radiation effects
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Carbon-coated Fe–Co(C) nanocapsules prepared by arc discharge in methane

X. L. Dong, Z. D. Zhang, S. R. Jin, and B. K. Kim

J. Appl. Phys. 86, 6701 (1999); http://dx.doi.org/10.1063/1.371747 (6 pages) | Cited 48 times

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Characterization and magnetic properties of Fe–Co(C) nanocapsules were investigated systematically by means of x-ray diffraction, Mössbauer spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive spectroscopy analysis, chemical analysis, oxygen determination, and magnetization measurement. The effects of elemental carbon, decomposed from a methane atmosphere in carbon arc process, on the phase structures, magnetic states and surface characterization were studied. Carbon atoms favor forming a new core/shell type structure, consisting of a carbon coating and a core containing a carbon solution. The mechanism of formation of the nanocapsules as well as origin of ferromagnetism and paramagnetism are discussed. © 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
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Rs Spray coating techniques
76.80.+y Mössbauer effect; other γ-ray spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
79.60.Jv Interfaces; heterostructures; nanostructures

Shear strength measurements in a tungsten alloy during shock loading

J. C. F. Millett, N. K. Bourne, Z. Rosenberg, and J. E. Field

J. Appl. Phys. 86, 6707 (1999); http://dx.doi.org/10.1063/1.371748 (3 pages) | Cited 33 times

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Lateral stress measurements in a tungsten alloy, in combination with known Hugoniot data, have been used to find the shear strength of this material, and its variation with longitudinal shock stress, up to 14 GPa. Results show that the shear strength increases significantly with increasing stress. Prior to this work, there has been disagreement in the literature on the effect of shock stress on the shear strength of tungsten and its alloys. The present work agrees with the data obtained by Zhou and Clifton [J. Appl. Mech. 64, 487 (1997)] who used pressure shear. However, the range of stresses studied has been greatly extended. © 1999 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Yield properties, phase transition, and equation of state of aluminum nitride (AlN) under shock compression up to 150 GPa

Tsutomu Mashimo, Masakazu Uchino, Akira Nakamura, Takamichi Kobayashi, Eiichi Takasawa, Toshimori Sekine, Yuichi Noguchi, Hideaki Hikosaka, Kiyoto Fukuoka, and Yasuhiko Syono

J. Appl. Phys. 86, 6710 (1999); http://dx.doi.org/10.1063/1.371749 (7 pages) | Cited 24 times

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Inclined-mirror Hugoniot measurements were performed on pure AlN polycrystals in the pressure range up to 150 GPa to study the yield properties, phase transition, and equation of state. The Hugoniot-elastic limit (HEL) stress was approximately 9.4 GPa. Above the HEL, the Hugoniot data converged to a static compression curve despite the high thermal conductivity, which indicated that the thermal property is not an important factor in determining the shock yield property. The phase transformation from wurtzite-type (B4) to rock salt-type (B1) structure took place at approximately 19.4 GPa, and was completed by about 75 GPa. The corrected transition pressure at 298 K was 19.2 GPa. Shock velocity (Us) versus particle velocity (Up) relation of the final phase was given by Us = 3.27+1.81Up km/s. The Birch–Murnaghan fitting curve of the calculated isothermal compression curve of the B1-type phase roughly coincided with the recent static x-ray diffraction data up to over 100 GPa. The Grüneisen parameter, bulk moduli (K0), and the pressure derivative (K0′) at zero pressure of the B1-type phase were estimated to be 1.51±0.03, 304±4 GPa, and 3.9±0.2 (K0″ = −0.02), respectively. © 1999 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
81.05.Ea III-V semiconductors
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity
64.30.-t Equations of state of specific substances
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
62.20.D- Elasticity

An estimate of the linear strain rate dependence of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine

P. A. Conley and D. J. Benson

J. Appl. Phys. 86, 6717 (1999); http://dx.doi.org/10.1063/1.371722 (12 pages) | Cited 5 times

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It is the long term goal of our work to elucidate the microscale mechanisms involved in the initiation of porous energetic materials (EMs) through direct numerical simulation of EM microstructures subjected to dynamic loading. Through this effort it is hoped that we may suggest appropriate continuum level constitutive models (reactive and inert) for porous EMs. A major obstacle in this effort is the lack of reliable parameters for the constitutive models in current use in computation. In the current study, we examine the theoretical dependence of shock structure upon the viscous nature of the deformation. In particular, we attempt to demonstrate that a unique value of the viscous parameter exists for an elastoplastic strength model in concert with a simple Newtonian viscous shear rate dependence, which allows us to accurately simulate shock structures observed in experimental studies of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. In doing this, a reasonable estimate of the viscous parameter is suggested for use in future modeling efforts. © 1999 American Institute of Physics.  
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62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.43.Gt Powders, porous materials

Elasticity, shear strength, and equation of state of molybdenum and gold from x-ray diffraction under nonhydrostatic compression to 24 GPa

Thomas S. Duffy, Guoyin Shen, Jinfu Shu, Ho-Kwang Mao, Russell J. Hemley, and Anil K. Singh

J. Appl. Phys. 86, 6729 (1999); http://dx.doi.org/10.1063/1.371723 (8 pages) | Cited 64 times

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Lattice strains were measured as a function of the angle ψ between the diffracting plane normal and the stress axis of a diamond anvil cell in a layered sample of molybdenum and gold. The sample was compressed over the range 5–24 GPa and the lattice strains were measured using energy-dispersive x-ray diffraction. As ψ is varied from 0° to 90°, the mean lattice parameter of molybdenum increases by up to 1.2% and that of gold increases by up to 0.7%. A linear relationship between Q(hkl), which is related to the slope of the measured d spacing versus 1−3 cos2 ψ relation, and 3Γ(hkl), a function of the Miller indices of the diffracting plane, is observed for both materials as predicted by theory. The pressure dependence of the uniaxial stress t for gold from this and other recent studies is given by t = 0.06+0.015P, where P is the pressure in GPa. The uniaxial stress in molybdenum can be described by t = 0.46+0.13P. Using gold as an internal pressure standard, the equation of state of molybdenum depends strongly on ψ. The bulk modulus obtained from a Birch–Murnaghan fit varies from 210 to 348 GPa as ψ varies from 0° to 90°. However, an equation of state in good agreement with shock and ultrasonic isotherms is obtained for ψ = 54.7° where the deviatoric contribution to the lattice strain vanishes. Second-order elastic moduli for gold and molybdenum are obtained from the data. The results are generally consistent with an earlier x-ray study and with extrapolations of low-pressure ultrasonic data. The pressure dependence of the shear modulus C44 is smaller for the x-ray data than predicted by extrapolation of ultrasonic data. © 1999 American Institute of Physics.
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62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids

Mechanism maps for electromigration-induced failure of metal and alloy interconnects

Vaibhav K. Andleigh, V. T. Srikar, Young-Joon Park, and Carl V. Thompson

J. Appl. Phys. 86, 6737 (1999); http://dx.doi.org/10.1063/1.371750 (9 pages) | Cited 10 times

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Numerical simulation of electromigration-induced stress evolution provides a versatile technique for analyzing the reliability of interconnects under a wide range of conditions. We study the evolution of stress in confined, layered, stud-terminated, pure metal, and alloy interconnects. Failure times are estimated using different failure criteria associated with different failure modes for broad ranges of line lengths and current densities. The simulation results can be conveniently catalogued through construction of failure mechanism maps that display domains of dominance of different failure modes. Failure mechanism maps are constructed for several different failure criteria, illustrating regimes of line immortality, void-nucleation-limited failure, void-growth-limited failure, and compressive failure as a function of line length and current density. The effects of changes in failure criteria, geometry, and composition are studied for representative interconnect stacks at accelerated and service temperatures. Failure maps may be used to: (i) provide an overview of predicted reliability behavior, (ii) assess how data from accelerated tests can be accurately scaled to service conditions, and (iii) predict the effects of changes in interconnect and shunt-layer materials and dimensions on interconnect reliability. © 1999 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
02.60.-x Numerical approximation and analysis

Interfacial reaction and wetting behavior in eutectic SnPb solder on Ni/Ti thin films and Ni foils

P. G. Kim, J. W. Jang, T. Y. Lee, and K. N. Tu

J. Appl. Phys. 86, 6746 (1999); http://dx.doi.org/10.1063/1.371751 (6 pages) | Cited 69 times

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Ni-based under bump metallization (UBM) is of interest in low cost flip chip technology primarily due to a slower chemical reactions with high-Sn solders such as eutectic SnPb as compared to Cu-based UBM. We studied wetting behaviors and interfacial reactions of the eutectic 63Sn–37Pb on Ni foils and Ni/Ti thin films using transmission electron microscopy (TEM), scanning electron microscopy, and energy dispersion x-ray analysis. Wetting angle, morphology of solder surface, and the rate of consumption of Ni have been studies as a function of reflow time at the temperatures of 200, 220, and 240 °C. From the TEM analysis, we found that Ni forms a single layer of scallop-type Ni3Sn4 compound with the eutectic SnPb. During the isothermal annealing, we observed the spalling of Ni3Sn4 compound from the Ni/Ti thin films. The spalling phenomenon is similar to that of Cu6Sn5 from the Cu/Cr thin films, yet the rate is slower. The spalling of Ni–Sn compound eventually caused dewetting of the molten solder from the Ti surface. © 1999 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Experimental investigation of structures of interior interfaces in GaAs

Georg Bernatz, Siegfried Nau, Rasmus Rettig, Heinz Jänsch, and Wolfgang Stolz

J. Appl. Phys. 86, 6752 (1999); http://dx.doi.org/10.1063/1.371752 (6 pages) | Cited 9 times

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A method for the structural investigation of interior inverted GaAs/AlAs interfaces is presented which combines highly selective etching and subsequent atomic force microscopy. It provides three-dimensional mappings of interior GaAs interfaces on a lateral scale on the order of micrometers with angstrom z resolution. The perfection of this method is demonstrated, which allows the observation of the real interface monolayer island and terrace structure. Potential aluminum residues on the uncovered interfaces are below the detection limit of Auger electron spectroscopy, which is estimated to 16% of aluminum in a single monolayer on a GaAs crystal. The structure of an interior interface can differ significantly from that of a corresponding surface layer after cooling down from the growth temperature. The substantial restructuring of the interface morphology caused by growth interruptions is investigated in detail for metalorganic vapor phase epitaxy. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
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
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Molecular dynamics simulation of silicon surface smoothing by low-energy argon cluster impact

Chang-Koo Kim, Alison Kubota, and Demetre J. Economou

J. Appl. Phys. 86, 6758 (1999); http://dx.doi.org/10.1063/1.371753 (5 pages) | Cited 3 times

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The molecular dynamics simulation method was employed to study the mechanism of silicon (001) surface smoothing by impact of Ar16 or Ar40 clusters with energy at or below 20 eV per constituent atom. Smoothing of a pyramid on top of an otherwise “flat” silicon surface was used as a model system to elucidate the mechanism of cluster-substrate interaction. Surface smoothing is achieved by lateral displacement of substrate atoms during cluster impact. There exists an optimum energy of around 4–5 eV per constituent atom of the cluster for efficient surface smoothing; this implies that a proper energy is required for effective lateral displacement. Cluster size also affects surface smoothing because lateral displacement depends on the nonlinear effect of multiple collisions in the near surface region. As anticipated, damage in the substrate increases with cluster energy. © 1999 American Institute of Physics.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Grazing incidence small angle x-ray scattering from free-standing nanostructures

Markus Rauscher, Rogerio Paniago, Hartmut Metzger, Zoltan Kovats, Jan Domke, Johann Peisl, Hans-Dieter Pfannes, Jörg Schulze, and Ignaz Eisele

J. Appl. Phys. 86, 6763 (1999); http://dx.doi.org/10.1063/1.371724 (7 pages) | Cited 88 times

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We develop the theory for grazing incidence small-angle x-ray scattering (GISAXS) from nanometer-sized naked islands on a flat substrate in the framework of the distorted-wave Born approximation (DWBA). The scattered wave amplitude is composed of four terms, including all combinations of scattering from the islands and reflection from the substrate. We apply this theory to x-ray measurements on Ge islands grown on Si(111), and show that we can determine the full triangular symmetry of these islands. The results also show that the DWBA must be used for smooth substrates near the angle of total external reflection. We finally discuss the advantages of GISAXS as compared to transmission small angle x-ray scattering for determining the symmetry of nanostructures. © 1999 American Institute of Physics.
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78.70.Ck X-ray scattering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Correlation between microstructure and optical properties of Ge2Sb2Te5 thin films

Jin-Hong Kim

J. Appl. Phys. 86, 6770 (1999); http://dx.doi.org/10.1063/1.371725 (3 pages) | Cited 11 times

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The microstructure and optical properties of amorphous and crystalline Ge2Sb2Te5 thin films prepared under different sputtering conditions were investigated. The microstructure of amorphous films was modified by changing the sputtering Ar gas pressure during the deposition. The optical properties and the microstructure of the sample prepared at high Ar gas pressure were remarkably different from the samples prepared at low pressures. A strong correlation between the microstructure and optical properties of Ge2Sb2Te5 thin films was found. © 1999 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.40.Pg Disordered solids
78.40.Fy Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
78.66.Li Other semiconductors
68.55.-a Thin film structure and morphology

Nanoindentation on AlGaN thin films

D. Cáceres, I. Vergara, R. González, E. Monroy, F. Calle, E. Muñoz, and F. Omnès

J. Appl. Phys. 86, 6773 (1999); http://dx.doi.org/10.1063/1.371726 (6 pages) | Cited 28 times

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Hardness and Young’s modulus were measured in AlGaN thin films with different Al content, using a nanoindentation technique. Hardness slightly decreases with increasing Al content, ranging from 20.2 to 19.5 GPa for Al content from 0.09 to 0.27, respectively. No significant variations of Young’s modulus were observed. The resulting value of Young’s modulus is 375 GPa. Discontinuities in load–displacement curves were found, which are associated with dislocation nucleation. The threshold load for this discontinuity depends on the conditions of the nanoindentation test. Below the threshold load, the sample surface flexes elastically in response to the indenter contact and the displacements recover completely when the sample is unloaded. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
62.20.M- Structural failure of materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Raman studies on ferroelectric phase (phase III) of KNO3

Ramaswamy Murugan, Anil Ghule, and Hua Chang

J. Appl. Phys. 86, 6779 (1999); http://dx.doi.org/10.1063/1.371727 (10 pages) | Cited 10 times

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In order to understand the nature, stability, and existence temperature width of phase I, phase II, and phase III (ferroelectric phase) of KNO3, a detailed Raman investigation was carried out with various heating/cooling rates, repeated thermal cycles, and different preheating temperatures. The increase in the existence temperature width of the phase III of KNO3 was observed with the increase of heating/cooling rate but the repeated thermal cycling reduced it. The phase III to phase II transformation extended to a lower temperature in the cooling process when the sample was subjected to a higher preheating temperature. The phase III could be retained down to room temperature with higher cooling rate and higher preheating temperature. This could be important in its applications. The coexistence of phase III with phase II was observed with all the heating/cooling rates. In this work, special attention was also paid to study the behavior of the lattice modes of KNO3 during the successive phase transformations. © 1999 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
78.30.Hv Other nonmetallic inorganics
77.55.-g Dielectric thin films
78.66.Li Other semiconductors
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