Search Results - (Author, Cooperation:M. J. Aziz)

2015-09-26

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2014-01-10

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

The solidification of Si-As alloys induced by pulsed-laser melting was studied at regrowth velocities where the partition coefficient is close to unity. The congruent melting temperatures T0 of Si-As alloys were determined using a temperature measurement technique developed for this work, and was confirmed with T0 measurements using three other methods. The time-resolved temperature measurement uses a thin-film platinum thermistor, below and electrically isolated from the Si-As alloy layer, to directly measure the temperature during solidification. The other techniques compared the results of heat flow simulations with the fluence dependence of the peak melt depth obtained by transient conductance, the fluence dependence of the melt duration determined from time-resolved reflectivity and transient conductance, and the fluence threshold for the initiation of melting. This combination of measurements in conjunction with Rutherford backscattering spectrometry permitted the determination of the solid-liquid interface temperature, velocity and partition coefficient, the latent heat of fusion and T0 for Si-4.5 at. % As and Si-9 at. % As alloys. The values of T0 determined by all four independent methods were consistent, indicating overall agreement between the direct experimental measurements and the analyses based on heat flow simulations. T0 was determined to be 1565±25 K for 4.5 at. % As and 1425±25 K for 9 at. % As. In addition, the enthalpy of fusion was determined to be independent of composition for the range studied. The values obtained in this work are compared with previous measurements.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

A number of theories have been developed for the kinetics of steady-state interface motion during a phase transformation. One requirement of such theories is that they satisfy Onsager's reciprocity relations for coupled irreversible processes. We show how to apply Onsager's relations to a phase transformation at a moving planar interface in a two-component system. The appropriate pairs of thermodynamic forces and conjugate fluxes are determined and used to test two proposed theories for interface motion during solidification of binary alloys. It is shown that the continuous growth model "with solute drag'' of Aziz and Kaplan is inconsistent with Onsager's relations, but the continuous growth model "without solute drag'' is consistent with Onsager's relations.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Onsager's reciprocity relations have been applied to the motion of a planar interface in a phase transformation in a two-component system, in order to provide a test of kinetic models of alloy solidification. Although applicable to such models in general, Onsager's relations yield no information for a subclass of models in which the thermodynamic driving forces are linearly dependent to first order, as is the case for several models of alloy solidification including the continuous growth model (CGM) of Aziz and Kaplan. As a consequence, experimental tests will likely be required to distinguish between these models. If the CGM is generalized to include diffusion in the growing phase, Onsager's relations are applicable under some circumstances.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have investigated depth of melting as a function of pulse energy density in amorphous and crystalline silicon layers. The melting threshold for KrF laser pulses (λ=0.249 μm, τ=24×10−9 s) in amorphous (7660-A(ring)-thick) and crystalline silicon layers were determined to be 0.16±0.02 and 0.75±0.05 J cm−2, respectively. The formation of fine- and large-polycrystalline regions was clearly identified in the amorphous silicon layers for energy densities below that needed for complete annealing. The role of explosive recrystallization in the formation of the fine polycrystalline region is discussed.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The silicon liquid self-diffusivity was determined by pulsed laser melting of 30Si ion implanted silicon-on-insulator thin films. Secondary ion mass spectrometry was employed to measure the 30Si+ concentration-depth profile before and after melting and solidification. Melt depth versus time and total melt duration were monitored by time-resolved lateral electrical conductance and optical reflectance measurements. One-dimensional diffusion simulations were utilized to match the final 30Si+ experimental concentration spatial profile given the initial concentration profile and the temporal melt-depth profile. The silicon liquid self-diffusivity at the melting point is (4.0±0.5)×10−4 cm2/s. Calculations of buoyancy and Marangoni convection indicate that convective contamination is unlikely. © 1999 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

In this article, we describe a technique using NiSi and Pt thin film metal thermometers to provide accurate temperature information on a nanosecond time scale during pulsed laser processing of materials. A surface layer of interest is deposited onto the thermometer layer, and temperatures are determined from temperature dependent changes in the metal film's resistance. Details concerning the design and fabrication of the device structure and experimental considerations in making nanosecond resolved resistance measurements are discussed. Simple analytical estimates are presented to extract quantities such as incident laser energy stored in the sample. Finally, transient temperature data in the thermometer film, in combination with heat flow calculations, allow temperature determination as a function of time and depth into the sample and, additionally, can provide information about material properties of the surface layer.

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1089-7550

AIP Digital Archive

Physics

Pulsed laser melting experiments were performed on GexSi1−x alloys (x≤0.10) with regrowth velocities ranging from 0.25 to 3.9 m/s. Analysis of post-solidification Ge concentration profiles, along with time-resolved melt depth measurements, allowed determination of the liquid-phase diffusivity Dl for Ge in Si and the dependence of the Ge partition coefficient k on interface velocity v. A Dl of 2.5×10−4 cm2/s was measured. The k vs v data were analyzed using various models for partitioning, including both the dilute and nondilute Continuous Growth Models (CGM). Extrapolating to zero velocity using the partitioning models, an equilibrium partition coefficient of approximately 0.45 was obtained. Best fitting of partitioning data to the nondilute CGM yields a diffusive speed of 2.5 m/s. These measurements quantify previous indications of partitioning observed in other studies of pulsed laser processed GexSi1−x alloys. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have measured the pressure dependence of the solid phase epitaxial growth rate of self-implanted Si (100) by using the in situ time-resolved interferometric technique in a high-temperature and high-pressure diamond anvil cell. With fluid argon as the pressure transmission medium, a clean and perfectly hydrostatic pressure environment is achieved around the sample. The external heating geometry employed provides a uniform temperature across the sample. At temperatures in the range of 530–550 °C and pressures up to 3.2 GPa (32 kbar), the growth rate is enhanced by up to a factor of 5 over that at 1 atmosphere pressure. The results are characterized by a negative activation volume of approximately −3.3 cm3/mole (−28% of the atomic volume). These results show a significantly weaker pressure dependence than does the previous work of Nygren et al. [Appl. Phys. Lett. 47, 232 (1985)], who found an activation volume of −8.7 cm3/mole. The implication of this measurement for the nature of the defects responsible for crystal growth is discussed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have measured the effect of pressure on the solid phase epitaxial growth rate of Ge(100) into self-implanted amorphous Ge by using in situ time-resolved infrared interferometry in a high-temperature, high-pressure diamond anvil cell. In the temperature range 300–365 °C, a rate enhancement of more than a factor of 100 over that at ambient pressure has been observed due to hydrostatic pressures of up to 5.2 GPa (52 kbar). The pressure enhancement is characterized by a negative activation volume of −6.2±0.6 cm3/mol (−45% of the atomic volume), which is of the same sign but greater in magnitude than we found in Si. We conclude that the defects controlling the solid phase epitaxy of Ge cannot be vacancies in the crystal, that mechanisms based on other point defects migrating to the interface from either phase are unlikely, and that mechanisms based on point defects residing in the interface are plausible.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The interface response functions for alloy solidification were measured in the nondegenerate regime of partial solute trapping. We used a new technique to measure temperatures and velocities simultaneously during rapid solidification of Si-As alloys induced by pulsed laser melting. In addition, partition coefficients were determined using Rutherford backscattering. The results are in good agreement with predictions of the Continuous Growth Model without solute drag of M. J. Aziz and T. Kaplan [Acta Metall. 36, 1335 (1988)] and are inconsistent with all solute drag models.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Sequential implantation of Ga and As into silicon followed by thermal annealing has been used to synthesize GaAs buried inside silicon. The GaAs exists in the form of nanocrystals which are three-dimensionally oriented with respect to the silicon matrix. Thermodynamic criteria which are important in determining whether the desired compound will form are discussed. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Electronic Resource

1077-3118

AIP Digital Archive

Physics

In molecular-beam epitaxy a monolayer of Pb on the Si(111) surface induces single-crystal growth at temperatures well below those required for similar growth on a bare surface. We demonstrate that the suppression of dopant segregation at the lower temperatures attainable by Pb-mediated growth allows the incorporation of As donors at concentrations reaching a few atomic percent. When Pb and Si are deposited on an As-terminated Si(111) substrate at 350 °C, the Pb segregates to the surface without doping the Si film while the As is buried within nanometers of the substrate–film interface. The resulting concentration of electrically active As, 1.8×1021 cm−3, represents the highest concentration of As donors achieved by any delta-doping or thin-film deposition method. © 2001 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The effect of externally applied in-phase stresses on the solid-phase epitaxial growth rate of both intrinsic and B-doped Si has been measured using time-resolved reflectivity. The data are described phenomenologically by a product of a function of concentration, an Arrhenius function of temperature, and a Boltzmann factor in the product of the stress and the activation strain V*, with V11*=(+0.14±0.04) and (+0.17±0.02) times the atomic volume, in intrinsic and B-doped material, respectively. © 2001 American Institute of Physics.

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