Crystalline surface structures induced by ion sputtering of Al-rich icosahedral quasicrystals

Low-energy electron diffraction patterns, produced from quasicrystal surfaces by ion sputtering and annealing to temperatures below ∼700 K, can be assigned to various terminations of the cubic CsCl structure. The assignments are based upon ratios of spot spacings, estimates of surface lattice constants, bulk phase diagrams vs surface compositions, and comparisons with previous work. The CsCl overlayers are deeper than about five atomic layers, because they obscure the diffraction spots from the underlying quasicrystalline substrate. These patterns transform irreversibly to quasicrystalline(like) patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically identical, but symmetrically inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. The model explains not only the symmetries of the cubic surface terminations, but also the number and orientation of domains

Multifunctional Devices and Logic Gates With Undoped Silicon Nanowires

We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be effective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid-helium temperature. By independently tuning the effective Schottky barrier heights, a variety of reconfigurable device functionalities could be obtained. In particular, the same nanowire device could be configured to work as a Schottky barrier transistor, a Schottky diode or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one.Comment: 6 pages, 5 figure

From colonial port to socialist metropolis: imperialist legacies and the making of ‘New Dalian’

This article explores the transformation of the city of Dalian from a colonial export port to an industrialized core city of the Japanese wartime empire and finally a model production city of the People's Republic of China. These shifts in the economic and political function of the city also resulted in complex identity issues for Dalian's urban residents. Dalian's rise reminds that there were trajectories of urban development and modernity in China which were different from that of Shanghai. Dalian provides an important, local view of the transition from empire to nation in this strategically important part of Manchuria

Monolithic thulium fiber laser with 567 W output power at 1970 nm

We report on a monolithic thulium fiber laser with 567 W output power at 1970 nm which, to the best of our knowledge, is the highest power reported so far directly from a thulium oscillator. This is achieved by optimization of the splice parameters for the active fiber (minimizing signal light in the fiber cladding) and direct water cooling. Dual transverse mode operation is visible from the optical spectrum and can be deduced from the measured beam quality of M2 = 2.6

Surface preparation and characterization of the icosahedral Al-Pd-Mn-Ga quasicrystal

Auger electron spectroscopy and low-energy electron diffraction (LEED) provide basic information about the structure and composition of the fivefold surface of the quaternary quasicrystal, icosahedral Al67Pd4Mn21Ga8. Surface preparation techniques established previously for two of the icosahedral ternary alloys, Al-Pd-Mn and Al-Cu-Fe, appear to be similarly effective for Al-Pd-Mn-Ga. After annealing in the range 600-950 K, the surface concentration of Ga is constant and low. After annealing in the range 900-950 K, a good LEED pattern is obtained. LEED indicates that Ga changes the surface structure significantly

Surface preparation and characterization of the icosahedral Al-Pd-Mn-Ga quasicrystal

Auger electron spectroscopy and low-energy electron diffraction (LEED) provide basic information about the structure and composition of the fivefold surface of the quaternary quasicrystal, icosahedral Al67Pd4Mn21Ga8. Surface preparation techniques established previously for two of the icosahedral ternary alloys, Al-Pd-Mn and Al-Cu-Fe, appear to be similarly effective for Al-Pd-Mn-Ga. After annealing in the range 600-950 K, the surface concentration of Ga is constant and low. After annealing in the range 900-950 K, a good LEED pattern is obtained. LEED indicates that Ga changes the surface structure significantly

TEM study of schottky junctions in reconfigurable silicon nanowire devices

The physical and electrical properties of a silicon nanowire reconfigurable field effect transistor (RFETs) are determined by the Schottky junction between the participating phases. TEM studies on such junctions require a careful FIB-based target preparation of thin lamellae with minimal ion-beam induced damage. In the current study, the nickel silicide phase forming the Schottky junction with silicon is identified using EDX in the TEM, considering a calibration based on the Fourier transforms of the HRTEM micrographs of known diffraction patterns of the nickel silicide phases. The TEM lamellae are prepared using the so-called lift-out technique and low voltage Ga+ ion polishing to minimize the near-surface amorphization. The structural and compositional data of the nickel silicide phase are needed for engineering the Schottky junction and corresponding theoretical modeling