We use Raman spectroscopy to study the size, shape and crystallographic orientation of silicon nanocrystals formed by solid phase crystallization of amorphous Si/SiO2 superlattices (SLs) grown by radio-frequency sputt...
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We use Raman spectroscopy to study the size, shape and crystallographic orientation of silicon nanocrystals formed by solid phase crystallization of amorphous Si/SiO2 superlattices (SLs) grown by radio-frequency sputtering. The first and second Raman peaks broadening, their relative positions and intensities indicate the presence of nanoscale Si objects with a degree of disorder (grain boundaries) and strain (Si/SiO2 interfaces). Shapes of Si nanocrystals sandwiched between SiO2 layers strongly influence the Si/SiO2 interface roughness, which is inferred from the intensities of folded acoustic phonon scattering. The averaged crystallographic orientation of Si nanocrystals is determined by polarized Raman analysis. The laterally elongated nanocrystals exhibit 〈111〉 preferred crystallographic orientation along the SL axis due to orientation-dependent crystallization rates. These results demonstrate that control over Si nanocrystals structural parameters has been achieved and that solid phase crystallization of nanometer-thick amorphous Si films remains one of the most promising techniques for Si-based nanoelectronic device fabrication.
Solute-drag creep controls deformation at elevated temperatures and relatively slow strain rates in a variety of technologically important materials. Solute-drag creep gives rise to two beneficial behaviors which are ...
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Solute-drag creep controls deformation at elevated temperatures and relatively slow strain rates in a variety of technologically important materials. Solute-drag creep gives rise to two beneficial behaviors which are taken advantage of in engineering alloys. First, solute-drag creep increases creep strength by making dislocation glide more difficult than dislocation climb. Second, solute-drag creep increases tensile ductility by increasing the strain-rate sensitivity to a value near 1/3. The original model of Weertman for solute-drag creep is one of the most successful of creep theories. Recent work has aimed at extending this basic framework to better predict the behavior of complex engineering alloys. The results of modeling efforts for ternary alloys are discussed. Model predictions are compared to experimental data.
作者：
R. S. LakesDepartment of Engineering Physics
Engineering Mechanics Program Materials Science Program University of Wisconsin 147 ERB 1500 Engineering Drive Madison Wisconsin 53705
Composites with negative stiffness inclusions in a viscoelastic matrix are shown to have higher stiffness and mechanical damping tanδ than that of either constituent and exceeding conventional bounds. The causal mech...
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Composites with negative stiffness inclusions in a viscoelastic matrix are shown to have higher stiffness and mechanical damping tanδ than that of either constituent and exceeding conventional bounds. The causal mechanism is a greater deformation in and near the inclusions than the composite as a whole. Though a block of negative stiffness is unstable, negative stiffness inclusions in a composite can be stabilized by the surrounding matrix. Such inclusions may be made from single domains of ferroelastic material below its phase transition temperature or from prebuckled lumped elements.
Recently, physical properties of single crystals of quasi-one-dimensional sulfide KCu7−xS4 have been studied. These measurements show several anomalies, in which the “transition” temperatures and physical properties...
Recently, physical properties of single crystals of quasi-one-dimensional sulfide KCu7−xS4 have been studied. These measurements show several anomalies, in which the “transition” temperatures and physical properties depend strongly on x. It was suggested that these transitions are most likely due to vacancy ordering involving Cu+−ion diffusion along the Cu(2)-Cu(2) zigzag chains. In this paper we propose a long-range mean-field method to study vacancy ordering in a one-dimensional chain with 1/r Coulomb interactions. Our results indicate that phase transitions exist in a one-dimensional lattice gas system in which vacancy ordering is involved. The system has complex thermodynamic properties which are extremely sensitive to the occupancy. Each simple rational occupancy has a unique phase diagram.
A micro-mechanical switch has been designed and fabricated in which the bounce after contact closure has been reduced by using mechanical momentum transfer and magnetic damping, while maintaining high contact forces. ...
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ISBN:
(纸本)0780359984
A micro-mechanical switch has been designed and fabricated in which the bounce after contact closure has been reduced by using mechanical momentum transfer and magnetic damping, while maintaining high contact forces. The period of chatter has been reduced from 1.5 milliseconds to less than 0.3 milliseconds, while the switching speed is 5 millisecond. The switch has been fabricated using Permalloy (78% Ni and 22% Fe) and copper. The LIGA process was used in the fabrication of the switch. An improved copper process allowed the fabrication of high aspect ratio (20:1) structures which were subsequently freed and assembled.
Brushite (CaHPO 4 · 2H 2 O) is a precursor to hydroxyapatite [HA, Ca 5 (PO 4 ) 3 OH]. It has been shown that a modified form of brushite, with potassium substituting for calcium at specific sites, demonstrated ac...
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Because stick-slip or other flow disturbances inside the die land have been suggested as a possible mechanism of the sharkskin, our effort was to observe any relevant periodic changes inside the die land during the sh...
Because stick-slip or other flow disturbances inside the die land have been suggested as a possible mechanism of the sharkskin, our effort was to observe any relevant periodic changes inside the die land during the sharkskin condition. We used particle tracking and time-resolved birefringence and two-dimensional light scattering in conjunction with a slit die attached to an extruder and a tubular glass die attached to a pressurized reservoir. Both dies could be observed up to the exit; both could also be directly observed downstream of the exit. While periodicities were easily seen in the slip-stick regime, none of the methods revealed any periodicity in the sharkskin regime. Direct observation of the sharkskin formation outside the die suggests a tearing and rolling mechanism as the origin of the sharkskin ridges found on polybutadiene extrudates.
Ionic aggregates in a series of Zn-neutralized poly(styrene- co -styrene sulfonate) (SPS) random ionomers have been imaged using scanning transmission electron microscopy. The Zn-rich aggregates were found to have two...
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Nanoindentation is the penetration of a surface to nanometre depths using an indenting device. It can be simulated using the Bragg bubble-raft model1, in which a close-packed array of soap bubbles corresponds to the e...
Nanoindentation is the penetration of a surface to nanometre depths using an indenting device. It can be simulated using the Bragg bubble-raft model1, in which a close-packed array of soap bubbles corresponds to the equilibrium positions of atoms in a crystalline solid. Here we show that homogeneous defect nucleation occurs within a crystal when its surface roughness is comparable to the radius of the indenter tip, and that the depth of the nucleation site below the surface is proportional to the half-width of the contact. Our results may explain the unusually high local stress required for defect nucleation in nano-indented face-centred cubic crystals.
Recoil implantation was performed to create ultra shallow Sb doped layers in an Si (001) substrate. The technique consists of the initial deposition of thin (40 to 140 nm) Sb layers followed by high energy Ar+ ion irr...
Recoil implantation was performed to create ultra shallow Sb doped layers in an Si (001) substrate. The technique consists of the initial deposition of thin (40 to 140 nm) Sb layers followed by high energy Ar+ ion irradiation and final chemical stripping of the residual Sb film. The resulting Sb atoms are recoil implanted into the underlying Si substrate. The results show a linear dependence of Sb concentration with Ar+ ion dose. High resolution Medium Energy Ion Scattering (MEIS) measurements have shown the projected range to be 3.0 nm with a doped layer width of 2.8 nm. The deposited Sb layer thickness is also shown to be a weakly dependent parameter in determining the Sb concentration for a given ion energy and dose.
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