The sharpness of tips used in scanning tunneling microscopy (STM) is one factor which affects the resolution of the STM image. In this paper, we report on a direct-current (dc) drop-off electrochemical etching procedure used to sharpen tips for STM. The shape of the tip is dependent on the meniscus which surrounds the wire at the air–electrolyte interface. The sharpness of the tip is related to the tensile strength of the wire and how quickly the electrochemical reaction can be stopped once the wire breaks. We have found that the cutoff time of the etch circuit has a significant effect on the radius of curvature and cone angle of the etched tip; i.e., the faster the cutoff time, the sharper the tip. We have constructed an etching circuit with a minimum cut-off time of 500 ns which uses two fast metal–oxide semiconductor field effect transistors (MOSFET) and a high-speed comparator. The radius of curvature of the tips can be varied from approximately 20 to greater than 300 nm by increasing the cutoff time of the circuit.

XANES spectra of nickel K-edge and x-ray diffraction patterns of several nickel oxycompounds were measured. The shift in energy of the Ni K-absorption edge toward higher values correlates well with the increase in the oxidation state of nickel from +2 to +4 in the compounds studied. The inflection point energy of the Ni pre-edge structure shifts approximately 1 eV per unit change in valency. Our results provide evidence which supports the assignment that the valency of Ni in ~-NiOOH is +3; Ni302(OH)4 and commercial nickel peroxide (NiO2) likewise contain trivalent nickel. The edge shift for quadrivalent nickel in KNiiO6 is reported for the first time.

The local atomic structure of Co, Fe, and Ce in aluminum-rich amorphous alloys of Al&00 2"Co"Ce" (x=8, 9, and 10) and Ce in A180FeloCelo has been investigated by x-ray-absorption fine structure (XAFS) spectroscopy. The materials, 1and 3-p,m-thick films, were prepared by vapor quenching using the dc magnetron sputtering method. %'e show that the composition of the glass-forming region of these magnetron-sputtered alloys strictly follows the theoretical limit calculated on the basis of the atomic size criterion. From analyses of the XAFS data at the E edges of Co and Fe and the L3 edge of Ce, the following conclusions with regard to local structure are made. The first coordination sphere of Co in Alloo 2"Co"Ce"(x=8, 9, and 10) consists of 5.8 to 6.4 Al atoms at a distance of 2.44 A. The local coor-0 dination sphere for Fe in A180FeloCelo consists of 6.4 Al atoms at a distance of 2.47 A. Ce in both sys-0 tems appears to be coordinated with roughly 5 and 9 Al atoms at distances of 2.95 and 3.15 A, respectively. These results are discussed in light of the dense random packing (DRP) of hard spheres model. Both Co-Al and Fe-Al bond lengths are anomalously short (9 and 8%%uo contraction, respectively) with also anomalously low coordination numbers (45% reduction) from values based on the DRP model using the metallic state radii. These anomalous changes indicate a strong interaction between Co or Fe atoms and the Al atoms which perhaps may be a result of a covalently bonded environment. The Ce-Al dis-0 tance in both the Al-Co-Ce and Al-Fe-Ce systems, on the other hand is smaller by only 0.17 A (a contraction of only 5%) and the coordination number is reduced by only 13% from expected values based on the DRP model. The contraction in the distance and reduction in the coordination number for Ce are much smaller than those values of the Co or Fe and, hence, the local bonding for Ce is likely to be metallic in character. Ihf+RODUtmrONAluminum-based metallic glasses with remarkably high Al content are relatively new materials that were discovered independently by He, Poon, and Shiflet, ' and Tsai, Inoue, and Masumoto. Typical composition is Al-TM-R where TM is a late transition element such as iron, cobalt, or nickel and 8 is yttrium or a rare-earth element such as gadolinium or cerium. These amorphous alloys can be prepared with extremely high aluminum content either by vapor quenching using the dc magnetronsputtering method3 or rapid solidification from the liquid phase using the melt-spinning method. ' The amorphous phase is formed with an Al content as high as 84 at. %%u o forsample sprepare db y th emagnetron-sputtering process and as high as 90 at. %%u o forsample sprepare dby the melt-spinning process. These materials are truly noncrystalline alloys which combine the properties of a metal with the short-range order of a glass. They are very homogeneous and lack the defects such as grain boundaries and dislocations typical of a crystalline material. The homogeneity and the lack of grain boundaries have led to a number o...

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We report x-ray photoemission spectra of the surface of iron (III) oxyhydroxide (α-FeOOH) particles. Research grade purity (99.0%) α-FeOOH sample was commercially obtained from Alfa/AESAR. The XPS spectra were measured with the Physical Electronics Model 5400 X-ray Photoelectron Spectrometer using unmonochromated Mg Kα x-rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C 1s, O 1s and 2s, Fe 2p and 3p photoemission lines, valence band region as well as the Fe L3VV Auger line were measured at an analyzer energy resolution of 0.54 eV. The XPS spectra indicate that the surface of α-FeOOH powdered material consists mainly of its bulk chemistry with small quantities of oxidized carbon and hydrocarbon as contaminants.