Influence of strain in Ag on Al(111) and Al on Ag(100) thin film growth

We demonstrate the influence of interfacial strain on the growth modes of Ag films on Al(111), despite the small magnitude of the lattice misfit in this system. The strain is relieved by the formation of stacking fault domains bounded by Shockley partial dislocations. The growth mode and the step roughness appear to be strongly connected. Growth is three-dimensional (3D) as long as the steps are straight, but switches to 2D at higher coverage when the steps become rough. Anisotropic strain relaxation and straight steps seem to be related. We also report related observations for Al deposited on Ag(100)

Lattice expansion in islands stabilized by electron confinement: Ag on Si(111)-7×7

Ag on Si(111)-7×7 was one of the first systems where height selection of metal islands was attributed to electron confinement, i.e., stabilization of selected heights through a quantum size effect (QSE). However, it has been puzzling how the requisite electron standing waves can form, because the Fermi level EF (along the growth [111] direction) is within the gap for bulk Ag. With detailed experiments over a wide coverage and temperature range, we show that a large increase of 12% is present in the interlayer spacing within the bilayer islands. This can shift EF below the gap, allowing electron confinement to control height selection. This conclusion is also supported by the observation of a corrugation pattern of period 3 nm on top of the Ag islands, which is bias dependent and can only be the result of QSE-generated standing waves normal to the film

Tribological properties of a B2-type Al-Pd-Mn quasicrystal approximant

The tribological properties of a B2-type Al–Pd–Mn quasicrystal approximant were investigated and compared with those of an Al–Pd–Mn icosahedral quasicrystal. The approximant was of the _ phase, having a crystalline CsCl-type structure and nominal composition Al48Pd42Mn10. Friction coefficients measured in ultrahigh vacuum between a pair of Al48Pd42Mn10 samples having truly clean surfaces were found to be twice as high as those reported for the Al70Pd21Mn9 quasicrystal. When the surfaces were oxidized by exposure to O2 or H2O, the friction coefficients decreased by roughly a factor of two for both materials but the friction coefficient for the approximant remained roughly twice that of the quasicrystal. The rate of oxidation of the approximant was found to be one order of magnitude higher than that of the quasicrystal. This corroborates findings that suggest that quasicrystals exhibit an inherent resistance to oxidation and corrosion. Vickers hardness measurements show that the quasicrystal is roughly three times as hard as the approximant

Novel metal-film configuration: Rh on Ag(100)

We present the results of an investigation of Rh films on Ag(100). The films are studied using Auger-electron spectroscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, ion-scattering spectroscopy, and scanning Auger microscopy. Overlayer characteristics are examined at substrate temperatures of 300 and 600 K. We find that the equilibrium configuration is not predicted by any of the three traditional growth modes (Frank–Van der Merwe, Stranski-Krastanov, or Volmer-Weber). Rather, the equilibrium film structure is that of a Ag-Rh-Ag sandwich, most probably flat. Formation of the sandwich is thermodynamically driven by the difference in surface free energies between Ag and Rh, and is kinetically accessible because of the high mobility of the Ag atoms

Novel Self-Organized Structure of a Ag-S Complex on the Ag(111) Surface below Room Temperature

A well-ordered, self-organized dot-row structure appears after adsorption of S on Ag(111) at 200 K. This dot-row motif, which exhibits fixed spacing between dots within rows, is present over a wide range of coverage. The dots are probably Ag3S3 clusters with adsorbed S in the spaces between dots. Dynamic rearrangements are observed. Small domains of aligned dot-rows form during adsorption and grow quickly after adsorption ends. The domains also exhibit large equilibrium fluctuations after adsorption. The dot-row structure disappears reversibly upon heating above 200 K and transforms reversibly to an elongated island structure upon cooling below 200 K. DFT supports the assignment of the dots as Ag3S3 trimers and also lends insight into the possible origins of other structures observed in this complex system

Preface: Special Topic on Supramolecular Self-Assembly at Surfaces

Supramolecular self-assembly at surfaces is one of the most exciting and active fields in Surface Science today. Applications can take advantage of two key properties: (i) versatile pattern formation over a broad length scale and (ii) tunability of electronic structure and transport properties, as well as frontier orbital alignment. It provides a new frontier for Chemical Physics as it uniquely combines the versatility of Organic Synthesis and the Physics of Interfaces. The Journal of Chemical Physics is pleased to publish this Special Topic Issue, showcasing recent advances and new directions

Surface Studies of Oxidation of a Single-Grain Quasicrystal

We have used Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) to characterize the surface properties of a single-grain Al70Pd21Mn9 (APM) quasicrystal (QC) upon oxidation. When oxygen is adsorbed on this surface, a disordered layer is formed at low coverages. This chemisorbed oxygen destroys the five-fold quasiperiodicity completely. Further adsorption of oxygen leads to a thin layer (less than 20 A) of AI oxide which passivates the surface. At elevated temperatures (870 K), adsorption of oxygen induces an enrichment of AI on the surface. This is explained by the exothermicity of its oxide and the possibility of increased mobility of AI at higher temperatures. Al is the only element in this QC which can be oxidized. No evidence of oxidization for Pd and Mn is observed

Identification of reconstruction in Pt films deposited on Pd(110) at room temperature

We have studied the properties of Pt films on Pd(110), grown by deposition at 300 K and annealed up to 900 K, using low-energy electron diffraction and Auger-electron spectroscopy. We observe (1×2) and (1×3) superstructures, depending upon Pt coverage and annealing temperature. At one monolayer, the (1×1) periodicity is unperturbed. Between one and three monolayers, a broad and streaky (1×2) develops upon annealing, then fades to (1×1) as the film dissolves. At three monolayers and above, the broad and streaky (1×2) splits to a (1×3), then fades again to (1×1) at high temperature. Adsorption of CO causes (1×3)→(1×1) reversion at relatively low temperature, 430 K. Based upon the known behavior of Pt(110) reconstructions, this is strong evidence that the (1×3) structure of the Pt film is a surface reconstruction

Catalytic reaction between adsorbed oxygen and hydrogen on Rh(111)

Abstract unavailable

Influence of carrier density on the friction properties of silicon pn junctions

We present experimental results showing a significant dependence of the friction force on charge carrier concentration in a Si semiconductor sample containing p- andn-type regions. The carrier concentration was controlled through application of forward or reverse bias voltages in the p and n regions that caused surface band bending in opposite directions. Excess friction is observed only in the highly doped p regions when in strong accumulation. The excess friction increases with tip-sample voltage, contact strain, and velocity. The sample is an oxide-passivated Si (100) wafer patterned with arrays of 2-μm-wide highly doped p-type strips with a period of 30 μm in a nearly intrinsic n-type substrate. The countersurface is the tip of an atomic force microscope coated with conductive titanium nitride. The excess friction is not associated with wear or damage of the surface. The results demonstrate the possibility of electronically controlling friction in semiconductor devices, with potential applications in nanoscale machines containing moving parts