Articles you may be interested inModular ultrahigh vacuum-compatible gas-injection system with an adjustable gas flow for focused particle beam-induced depositionThe authors have deposited Pt from Pt͑PF 3 ͒ 4 using a focused 10 keV electron beam ͑scanning electron microscopy͒ in an FEI 620 dual beam system and measured the resistivity and composition of the deposits. To measure resistivity, lines of Pt were deposited across four gold fingers and the cross-sectional area of the lines was measured by focused ion beam sectioning. The resistivity varies between about 30 and 650 ⍀ cm and is orders of magnitude lower than the resistivity achieved by e-beam-induced deposition using the usual organometallic precursor, ͑methylcyclopentadienyl͒ trimethyl platinum. In general, the higher the beam current the lower the resistivity. They have used wavelength dispersive x-ray analysis to measure the composition of rectangles deposited with various beam currents. Typical at.% values of ͑Pt:P:F͒ are 81:17:2 and 58:32:10. Minimum linewidth that they have deposited is 80 nm, and with a stationary beam of 2.8 nA they have deposited a pillar of 135 nm in diameter. They have also deposited Pt structures on freestanding carbon nanotubes and have used the deposits to contact nanofibers. Electron-beam-induced deposition of a "good" metal is particularly useful in geometries where standard lithography is awkward, such as making contacts to fibers or nanotubes randomly dispersed on a surface or freestanding.
In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024 ϫ 1024 focal plane arrays (FPAs) using Rockwell Scientific's double-layer planar heterostructure (DLPH) architecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, Ͼ5E6 cm Ϫ2 ), and these dislocations act as conductive pathways for tunneling currents that reduce the R o A and increase the dark current of the diodes. To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used. Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe.
MgSe has been studied using energy dispersive x-ray diffraction to 202 GPa and local density approximation and ultrasoft pseudopotentials to 500 GPa. MgSe undergoes a "continuous" phase transformation from the rocksalt to FeSi (B28) beginning at around 99 6 8 GPa and approaching sevenfold coordination at 202 GPa. Theoretical computation finds the B28 transition beginning at 58 GPa followed by a transition to an orthorhombic distortion of the B2 structure at 429 GPa.[S0031-9007(98)
Single crystals of the isotypic hydrides Ba 2 H 3 X (X = Cl or Br) were obtained by solid-state reactions of Ba, NaCl, NaNH 2 and metallic Na, or Ba, NH 4 Br and Na, respectively, in sealed, silicajacketed stainless-steel ampoules. The crystal structures of the new compounds were determined by means of single crystal X-ray diffraction. Ba 2 H 3 Cl and Ba 2 H 3 Br crystallize in a stuffed anti CdI 2 structure and adopt the space group P3m1 (No. 164) with the lattice parameters a = 443.00(6), c = 723.00(14) pm and a = 444.92(4), c = 754.48(14) pm, respectively. The hydride positions are derived by crystallographic reasoning and with the help of EUTAX calculations. The results are compared with known data for binary and ternary alkaline earth metal hydrides.
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