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.
Hydroxyapatite (HA) coatings can be deposited using a hybrid process of plasma electrolysis and electrophoresis, called plasma-assisted electrophoretic deposition (PEPD). HA aqueous suspensions with various pH values ...
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The stacking sequence of several layers of self-assembled semiconducting CdSe nanoparticles has been investigated using transmission electron microscopy. FCC, HCP, saddle sites occupation and ring structures were foun...
The stacking sequence of several layers of self-assembled semiconducting CdSe nanoparticles has been investigated using transmission electron microscopy. FCC, HCP, saddle sites occupation and ring structures were found coexisting in the supercrystals formed by CdSe nanoparticles.
New low-temperature methods to produce GaN:Eu and Ga 2 O 3 :Eu (0 ≤ x ≤ 1) highly-luminescent powders are presented. These procedures yield finely divided powders through exothermic reactions between the precursors....
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New low-temperature methods to produce GaN:Eu and Ga 2 O 3 :Eu (0 ≤ x ≤ 1) highly-luminescent powders are presented. These procedures yield finely divided powders through exothermic reactions between the precursors. The preparation of Eu-doped Ga 2 O 3 powders was achieved using a new combustion synthesis technique (hydrazine/metal-nitrate method). The process starts with aqueous solutions of Eu(NO 3 ) 3 and Ga(NO 3 ) 3 as the precursors and hydrazine as (non-carbonaceous) fuel. A spontaneous combustion reaction occurs by increasing the temperature to between 150 and 200 °C in a closed vessel filled with argon, and produces (Eu x Ga 1— x ) 2 O 3 directly. The preparation of Eu-doped GaN uses the ammonium hexafluoro-metal method. The powders present strong luminescence associated with the dopant. A sharp and strong GaN luminescence is observed, indicative of high purity and crystallinity as determined by low-temperature cathodoluminescence. The composition and powder morphology have been studied using energy dispersive spectroscopy and scanning electron microscopy.
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