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Applied Physics Letters

Issue 23 • Date Jun 1996

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Displaying Results 1 - 25 of 50
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Metalorganic molecular beam epitaxy of 1.3 μm wavelength tensile‐strained InGaAsP multi‐quantum‐well lasers

    Page(s): 3213 - 3215
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    We have studied metalorganic molecular beam epitaxy growth on strain‐compensated multi‐quantum‐wells (MQWs) in which well layer tensile strain ranges from 0.5 to 1.45%. Double‐crystal x‐ray and cross‐sectional transmission electron microscopy study reveal that each layer in the six‐well, 1.3% strained MQWs has well‐defined flat interfaces. The photoluminescence intensities of the MQWs are comparable to those of lattice‐matched MQWs and remain unchanged after 620 °C annealing. The threshold current density (Jths) of six‐well MQW lasers emitting at 1.3 μm wavelength decreases when increasing the tensile strain from 0.5 to 1.3%. The Jth and the threshold current of the 1.3% strained MQW lasers with a 300 μm cavity length are 0.6 kA/cm2 and 9 mA, respectively. © 1996 American Institute of Physics. View full abstract»

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  • Large non‐biased all‐optical bistability in an electroabsorption modulator using p‐i‐n‐i‐p diode and asymmetric Fabry–Perot cavity structure

    Page(s): 3216 - 3217
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    We have constructed a non‐biased all‐optical bistable device using electroabsorption in multiple quantum wells (MQWs). The device is made of a serial connection of two identical double p‐i‐n (p‐i‐n‐i‐p) diode structures within asymmetric Fabry–Perot (AFP) cavity. This scheme ensures both large internal electric field swing and full exploitation of the light intensity. From the measurement of the diode properties, the non‐biased bistability parameters—reflection change of 19%, contrast ratio of 17:1, and bistable loop width of 70%—were obtained. © 1996 American Institute of Physics. View full abstract»

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  • Efficient, fast response light‐emitting electrochemical cells: Electroluminescent and solid electrolyte polymers with interpenetrating network morphology

    Page(s): 3218 - 3220
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    The device performance of light‐emitting electrochemical cells is improved by adding a bifunctional liquid additive into the light‐emitting layer. Because of the surfactant‐like character of the additive, the light‐emitting layer exhibits a high surface area bicontinuous three‐dimensional network morphology. The semiconducting polymer forms a continuous network phase enabling electronic transport of injected electron and holes: the electrolyte forms a continuous network phase enabling fast ion transport; the nm length scale of the phase separated network enables rapid, effective transport of the ions into the conducting polymer during electrochemical doping. © 1996 American Institute of Physics. View full abstract»

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  • Time‐resolved photoluminescence study on AlxGa1-xAs spontaneous vertical quantum well structures

    Page(s): 3221 - 3223
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    We report on time‐resolved photoluminescence study of AlxGa1-xAs spontaneous vertical quantum well (SVQW) structures on GaAs V‐grooved substrates. Four distinct photoluminescence peaks are observed originating from the spatial nonuniformity of the alloy compositions spontaneously formed during metalorganic vapor phase epitaxial growth. The decay time of the (111)A sidewall AlGaAs decreased with increasing temperature, while that of the SVQW increased. The rise time of the SVQW was found to be longer than the typical value of the exciton formation and increases with increasing temperature, indicating that the exciton formation is not limiting factor of the rise time. These results are explained in terms of the exciton diffusion toward the SVQW from the outer AlGaAs layers with less Ga compositions. In addition, two dimensionality of the SVQW was evidenced by temperature dependence of the radiative lifetime. © 1996 American Institute of Physics. View full abstract»

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  • Dynamic range of an electro‐optic field sensor and its imaging applications

    Page(s): 3224 - 3226
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    We report the measurement of the dynamics of free‐space electro‐optic field sensors for pulsed electromagnetic wave radiation. With an optical probe power spanning six decades of linearity and excellent signal‐to‐noise ratio (SNR), it is feasible to convert a far‐infrared 2D image into an optical 2D image. A simple estimation indicates that 100 mW of optical probe power can achieve an image of 256×256 pixels with a 50 pA signal current per pixel and a SNR ≳200. We also present a comparison measurement of an ultrafast photoconductive antenna and an electro‐optic sensor crystal. © 1996 American Institute of Physics. View full abstract»

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  • Measurement of large electro‐optic coefficients in thin films of strontium barium niobate (Sr0.6Ba0.4Nb2O6)

    Page(s): 3227 - 3229
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    A reflection‐grating measurement technique is reported for measurement of the electro‐optic coefficient in crystalline strontium barium niobate thin films grown using pulsed laser deposition. The measurement yields a value of about 350 pm/V for the r33 coefficient of the Sr0.6Ba0.4Nb2O6(SBN:60) film. The measurement technique is based on a modulated diffraction pattern measurement using coplanar electrodes and can be extended to a range of cases where it is not possible to deposit electrodes on both sides of a film. © 1996 American Institute of Physics. View full abstract»

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  • Reciprocal‐space analysis of photoluminescence and photoluminescence excitation spectra

    Page(s): 3230 - 3232
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    We show that energy positions of features in photoluminescence and photoluminescence excitation (PLE) spectra can be obtained more accurately by Fourier transforming segments of these spectra and analyzing the resulting coefficients in reciprocal space than by using conventional real‐space analysis. Fourier transform analysis is particularly advantageous where base line effects are significant, as in PLE. © 1996 American Institute of Physics. View full abstract»

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  • Photonic band gap quantum well and quantum box structures: A high‐Q resonant cavity

    Page(s): 3233 - 3235
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    We have tested a series of high‐Q photonic band gap (PBG) resonant cavities in the mm‐wave regime and achieved a cavity‐Q of 2.3×104, the highest value reported among all two‐ and three‐dimensional PBG cavities. We have also systematically varied the size and reflectivity of such cavities to study their effect on cavity properties such as cavity modal frequency, linewidth, and cavity Q value. We show that the resonant frequencies can be tuned throughout the PBG regime and that linewidths (or equivalently Q value) can be varied over two orders of magnitude (i.e., a Q value from ∼2.7×102 to 2.3×104). © 1996 American Institute of Physics. View full abstract»

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  • Time resolved four‐wave mixing technique to measure the ultrafast coherent dynamics in semiconductor optical amplifiers

    Page(s): 3236 - 3238
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    A femtosecond four‐wave mixing technique is used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers. A heterodyne detection scheme enables us to measure a background‐free quasi‐degenerate four‐wave mixing signal even without spatial separation of the pump and probe beam. First results indicate that the polarization dephasing time close to the transparency point is on the order of 100 fs. © 1996 American Institute of Physics. View full abstract»

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  • Computed light scattering cross sections of oxide particles in silicon

    Page(s): 3239 - 3241
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    We have used the discrete‐dipole approximation (DDA) method, implemented as a modified version of the DDSCAT program of Draine and Flatau, to calculate 3D light scattering intensity diagrams for individual oxide particles present in Czochralski silicon wafers. The particles were either octahedra or plates with normalized sizes x=0.01–5. The signals that would be measured for light scattered through 90° or 180° were determined from the diagrams, these angles corresponding to the cases of light scattering tomography (LST) and reflection confocal (RC) scanning infrared microscopy (SIRM), respectively. The results show that as x increases, the signal (particle image contrast) increases ∝x6 for x≪∼1, but increased more slowly and in an irregular manner for x≳∼1. The signal also depends markedly on the particle shape and orientation. These findings demonstrate the difficulty of deducing quantitative data, e.g., individual particle sizes, from SIRM image contrasts. However, they also indicate the type of measurements that need to be made and provide a basis for the quantitative interpretation of the experimental results. © 1996 American Institute of Physics. View full abstract»

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  • CaF2:Er3+ molecular beam epitaxial layers as optical waveguides

    Page(s): 3242 - 3244
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    CaF2:Er thin films grown by molecular beam epitaxy on CaF2 substrates have been characterized as optical waveguides. The characterization has been carried out by measuring the synchronous angles in attenuated total reflection experiments. It has been found that the incorporation of Er3+ ions to the CaF2 crystal produces an increase of the refractive index of the material giving rise to the formation of a steplike planar optical waveguide. The refractive index increase shows a linear dependence with Er3+ concentration up to 35 mol %, at which point saturation is observed. The obtained results compared well with previously reported data on the lattice parameter of CaF2:Er3+ bulk crystals and fluorescence quenching from Er3+ ions in these layers. The results of this work show that the preparation of CaF2:Er3+ layers on CaF2 substrates by molecular beam epitaxy is an ideal method to produce monomode active optical waveguides useful for optoelectronic devices. © 1996 American Institute of Physics. View full abstract»

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  • Effects of laser‐ablation target damage on particulate production investigated by laser scattering with deposited thin film and target analysis

    Page(s): 3245 - 3247
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    Experiments have been carried out to correlate ablated particulate density and size to the number of KrF excimer laser (248 nm, 40 ns, ≪1.2 J) pulses incident on a single location of a pure solid aluminum target and to relate particulate production to target surface damage. An analysis of laser ablation deposited aluminum films on silicon substrates was used to determine the density of ablated particulate greater than 0.5 μm in diameter. For an undamaged target, the laser deposited particulate density was on the order of 8.6×105 cm-2 per 1000 shots. A damaged target (following 1000 laser pulses) produced a density on the order of 1.6×106 cm-2 per 1000 shots on the substrate. Dye laser optical scattering was also used to measure, in real time, the velocity of the particulate and the relative particulate density in the laser‐ablation plume versus target damage. Results indicated a rapid rise in the production of particulate as target damage was increased up to 3000 laser pulses; after this number of shots the density of particulate in the laser ablation plume saturated. A peak in the scattered light for each stage of target damage occurred 40 μs after the initial KrF laser pulse, translating to a velocity of about 100 m/s for the smaller particulate (≪1 μm diameter). The later scattered signal, around 160 μs, was apparently due to the larger particulate (5–15 μm), traveling at a velocity of approximately 25 m/s. Particulate production is related to the formation of laser ablation‐induced cones on the damaged targets. © 1996 American Institute of Physics. View full abstract»

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  • Growth and properties of scandium epitaxial films on GaN

    Page(s): 3248 - 3250
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    Epitaxial scandium films have been grown on c‐axis‐oriented wurtzite GaN. The films are highly ordered, adherent, and reflective. For substrate temperatures in the range 640–780 °C an interfacial reaction yields a ScN layer whose thickness increases with temperature, consistent with Sc diffusion as the rate limiting step. Electrical contacts fabricated from the Sc/ScN/GaN films exhibit a 1.0 eV barrier height on n‐type GaN. The Sc films, which represent a class of ductile materials, may constitute a compliant substrate for overgrowth of GaN. © 1996 American Institute of Physics View full abstract»

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  • Encapsulation of Ag films on SiO2 by Ti reactions using Ag–Ti alloy/bilayer structures and an NH3 ambient

    Page(s): 3251 - 3253
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    Thin encapsulated silver films have been prepared on oxidized silicon by nitridation of ∼200‐nm‐thick Ag–19 at. % Ti alloy films and Ag(120 nm)/Ti(22 nm) at 300–700 °C in an ammonia ambient. The encapsulation process has been studied in detail by Rutherford backscattering, and scanning Auger and secondary‐ion‐mass spectrometry, which showed that Ti‐nitride and Ti‐oxide‐silicide formation take place at the surface and the Ag–Ti/SiO2 interface, respectively. Four‐point‐probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼4 μΩ cm were measured in encapsulated Ag alloy films with initial low Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as‐deposited Ag (∼3 μΩ cm). © 1996 American Institute of Physics. View full abstract»

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  • Characterization of diamond deposition from chloromethane reactants by laser reflective interferometry

    Page(s): 3254 - 3256
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    Laser reflective interferometry (LRI) was employed to compare the nucleation and film growth characteristics of diamond deposition between methane and chloromethane reactants. LRI has the capability of in situ monitoring of the film‐forming stage and the film growth stage. During the film‐forming stage deposition behavior involves the nucleation and subsequent growth of discrete diamond crystallites. During the film growth stage, it involves the growth of a continuous film. In comparison to methane reactant, chloromethane was observed to enhance slightly the growth rate during the film growth stage by 7%, 16%, and 39% at substrate temperatures of 850, 750, and 650 °C, respectively. However, chloromethane reduced the time required for film formation and increased the nucleation densities significantly, particularly at low growth temperatures. The reason that chloromethane enhances the total growth rates at low temperature is mainly due to its ability to stabilize diamond nucleus precursor and thus enhance diamond nucleation. © 1996 American Institute of Physics. View full abstract»

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  • Atomic layer controlled deposition of silicon nitride with self‐limiting mechanism

    Page(s): 3257 - 3259
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    Thin (2–10 nm) silicon nitride films have been grown by repetitive plasma nitridation of Si using a NH3 remote plasma and deposition of Si by a SiH2Cl2 thermal reaction. The deposition rate is self‐limited at nearly half‐molecular layer (ML) per one deposition cycle. The process window for the half‐ML/cycle of growth has been investigated with respect to the NH3 plasma power, SiH2Cl2 exposure time, and substrate temperature. The thickness fluctuation of the film over a 2 in. wafer is within measurement accuracy of the ellipsometer (± 1.9%) for the atomic layer controlled film while it is ± 8.5% for all the remote‐plasma chemical vapor deposition film. © 1996 American Institute of Physics. View full abstract»

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  • Crystalline quality and phase stability of hexagonal GdSi1.7 layers formed by channeled ion‐beam synthesis

    Page(s): 3260 - 3262
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    Previous reports show that, among all rare‐earth silicides, GdSi1.7 is the most difficult one to grow epitaxially with a good crystalline quality on a Si substrate. However, this letter shows that by using channeled implantation, a continuous GdSi1.7 layer with good crystalline quality (χmin=10%) can be formed by implantation of 90 keV Gd ions in Si(111). Besides, the hexagonal phase of the GdSi1.7 layer is stable up to a temperature of 850 °C for 30 min, which is much more stable than previously reported. After annealing at temperatures ≥900 °C for 30 min, the hexagonal GdSi1.7 phase transforms into the orthorhombic GdSi2 phase. Rutherford backscattering/channeling, transmission electron microscopy, and x‐ray diffraction are used in this study. © 1996 American Institute of Physics. View full abstract»

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  • Influence of surface morphology on ordered GaInP structures

    Page(s): 3263 - 3265
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    Ga0.51In0.49P layers, grown by organometallic chemical vapor deposition on differently misoriented (001) GaAs substrates exhibit CuPtB‐type domains. The increase in structural homogeneity of the ordered domains, with increasing substrate misorientation, results in a very sharp distribution of the degree of ordering. The correlation between cathodoluminescence emission from ordered regions and changes in surface step distribution direction confirm the influence of the surface morphology on the distribution of ordered regions and their antiphase boundaries. © 1996 American Institute of Physics. View full abstract»

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  • Optical spectroscopic observation of spontaneous long range ordering in AlGaInP

    Page(s): 3266 - 3268
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    We report the unambiguous optical spectroscopic observation of spontaneous long‐range crystal ordering in AlGaInP epitaxial layers grown by metalorganic vapor phase epitaxy. Polarized spectroscopy demonstrates the existence of an in‐plane anisotropy for samples grown on substrates oriented close to (100). This anisotropy results from the order‐induced splitting of the normally degenerate zone‐center valence‐band states. Our measurements allow the size of the valence‐band splitting to be measured and also allow a determination of the order‐induced band‐gap reduction. Both of these quantities are found to decrease with increasing misorientation of the substrate away from (100), indicating that the degree of ordering also decreases with increasing misorientation. © 1996 American Institute of Physics. View full abstract»

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  • Characteristics of InGaN multi‐quantum‐well‐structure laser diodes

    Page(s): 3269 - 3271
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    InGaN multi‐quantum‐well (MQW)‐structure laser diodes fabricated from III–V nitride materials were grown by metalorganic chemical vapor deposition on (111) MgAl2O4 substrates. The laser consisted of a InGaN MQW, GaN optical guiding layers and AlGaN cladding layers. The observed stimulated emission was at a wavelength around 419 nm, with a threshold current of 320 mA (13 kA/cm2) and a threshold voltage of 28 V under pulsed current injection at room temperature. The stimulated emission also showed a strong transverse electric polarization. The beam full widths at half power for the parallel and perpendicular far‐field radiation patterns were 5° and 17°, respectively. © 1996 American Institute of Physics. View full abstract»

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  • Direct observation of vibrational modes in Hg1-xCdxTe

    Page(s): 3272 - 3274
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    The vibrational modes in Hg1-xCdxTe epitaxial films and HgTe/CdTe superlattices have been investigated by means of far‐infrared (FIR) transmittance spectra at temperatures from 4.2 to 300 K. The observations were put forward in the spectral range from 20 to 350 cm-1, emphasizing the wave‐number region at the low‐frequency side of the reststrahlen absorption band. A series of single‐phonon and two‐phonon modes as well as impurities‐ and defects‐induced vibrational modes are observed. FIR transmission seems to be a good probe for characterization of the perfection of Hg1-xCdxTe films. © 1996 American Institute of Physics. View full abstract»

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  • Electronic properties of defects introduced during low‐energy He‐ion bombardment of epitaxially grown n‐GaAs

    Page(s): 3275 - 3277
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    We have employed deep level transient spectroscopy to investigate the defects introduced by low‐energy (5 keV) He‐ion bombardment of epitaxially grown n‐GaAs. This introduced four electron traps, EHe1–EHe4, with discrete energy levels identical to those of the Eα1–Eα4 defects introduced during high‐energy (5.4 MeV) α‐particle irradiation of the same n‐GaAs, but in different relative concentrations. EHe3 with a level at Ec-0.35 eV exhibits the same metastability as Eα3. In addition, low‐energy ion bombardment introduced a band of defects close to the GaAs surface with a continuous energy distribution. © 1996 American Institute of Physics. View full abstract»

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  • Observation of boron doping induced surface roughening in silicon molecular beam epitaxy

    Page(s): 3278 - 3280
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    Boron doping induced surface roughening was observed in conventional silicon molecular beam epitaxy. Reflection high energy electron diffraction and cross‐sectional transmission electron microscopy revealed that as growth continued, the growth surface remained no longer planar but developed {113} facets. The facets evolved along with growth, and finally resulted in a severely roughened surface. The evolution of the roughening was found to remain the same in the boron doping concentration range of 1×1017–2×1020 cm-3 and the growth temperature range of 500–650 °C. This surface roughening effect is attributed to boron segregation behavior. © 1996 American Institute of Physics. View full abstract»

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  • Identification of Cr in p‐type silicon using the minority carrier lifetime measurement by the surface photovoltage method

    Page(s): 3281 - 3283
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    The effect of CrB pair dissociation on the minority carrier lifetime in p‐type silicon is studied using the surface photovoltage (SPV) and deep level transient spectroscopy (DLTS) methods. Experiments were conducted using Cr doped samples (0.5×1012–5×1012 cm-3) with resistivity ranging from 1 to 50 Ω cm. The minority carrier lifetime, increased after the dissociation of CrB by a factor ranging, depending upon resistivity, approximately from 2.0 to 10. This is in contrast to a tenfold reduction observed in the minority carrier lifetime following the dissociation of FeB pairs. The resistivity dependence of the minority carrier lifetime in Cr doped sample can be successfully predicted according to the Shockley–Reed–Hall (SRH) model. It is demonstrated that the defects with energy levels of Ev+0.27 eV and Ec -0.22 eV are the main recombination centers for CrB and Cri, respectively. © 1996 American Institute of Physics. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory