Self-Assembly of TBrPP-Co Molecules on an Ag/Si（111） Surface Studied by Scanning Tunneling Microscopy

Self-assembly of TBrPP-Co molecules on a Si（111）-√3t×√3 Ag substrate is studied by low-temperature scanning tunneling microscopy. With the same adsorbed amount （0.07 ML）, the molecules deposited by low-temperature evaporation show three kinds of ordered structures whereas those deposited by high-temperature evaporation have size-dependent ordered structures. The distinct differences in the self-assembly structures and in the electron density of states inside the molecule near the Fermi energy demonstrate that the Br atoms of the molecule desorb at the higher evaporation temperature.     

Scanning tunnelling microscope studies of growth of RuO2（110） thin layer on Ru（0001）

This paper reports that the growth of RuO_x(110) thin layer growth on Ru(0001) has been investigated by means of scanning tunnelling microscope (STM). The STM images showed a domain structure with three rotational domains of RuO_x(110) rotated by an angle of 120℃. The as-grown RuO_x(110) thin layer is expanded from the bulk-truncated RuO_x(110) due to the large mismatch between RuO_x(110) and the Ru(0001) substrate. The results also indicate that growth of RuO_x(110) thin layer on the Ru(0001) substrate by oxidation tends first to formation of the Ru-O (oxygen) chains in the [001] direction of RuO_x(110).     

Investigation of the Elasticity of Polymer Nanoparticle by Vibrating Scanning Polarization Force Microscopy

The elasticity of an individual polymer nanoparticle may be greatly different from that of the bulk one. Understanding the properties of individual particles such as elasticity and deformation under external forces is of great importance in controlling the final structures and functions of bulk materials. We study the compression properties of single polyethylenimine （PEI） particles using vibrating scanning polarization force microscopy. By controllably imaging PEI particles at different vibration amplitude set-point values, it is demonstrated that we can compress the single PEI nanoparticle with an atomic force microscopy tip in different loads. Based on the force-height and force-strain curves obtained, Young＇s moduli of PEI （5-160 MPa） in three force regions are estimated according to the Hertz model The results indicate that PEI has excellent elasticity, which may contribute to its high efficiency as vectors in gene transfection.     

Scanning tunneling microscopy study of molecular growth structures of Gd@C82 on Cu（111）

The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail. Upon molecular deposition at low temperature, Gd@C82 molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage. Further annealing treatment leads some of the Gd@C82 molecules to assemble into bright and dim patches, which are correlated to the adsorption induced substrate reconstruction. Upon sufficient thermal activation, Gd@C82 molecules sink into the Cu(111) surface one-copper-layer-deep, forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns. By considering the commensurability between the Gd@C82 nearest-neighbor distance and the lattice of the underlying Cu(111), we clearly identified two kinds of in-plane molecular arrangements as (19(1/2)×19(1/2))R23.4°and (19(1/2)×19(1/2))R36.6°with respect to Cu(111). Within the assembled Gd@C82 molecular, island molecules with dim-bright contrast are spatially distributed, which may be modulated by the preexisted species on Cu(111).     

Growth of Cu Films on Si(111)-7×7 Surfaces at Low Temperature: A Scanning Tunnelling Microscopy Study

Morphologies of Cu(111) films on Si(111)-7×7 surfaces prepared at lowtemperature are investigated by scanning tunnelling microscopy (STM) andreflection high-energy electron diffraction (RHEED). At the initial growth stage, Cu films are flat due to the formation of silicide at the interface that decreases the mismatch between Cu films and the Si substrate. Different from the usual multilayer growth of Cu/Cu(111), on the silicide layer a layer-by-layer growth is observed. The two dimensional (2D) growth is explained by the enhanced high island density at low deposition temperature. Increasing deposition rateproduces films with different morphologies, which is the result of Ostwald ripening.     

Growth of Mn5Ge3 ultrathin film on Ge（111）

The growth of Mn5Ge3 ultrathin films with different thicknesses, prepared by solid phase epitaxy, is studied. The results of scanning tunnelling microscopy and low energy electron diffraction studies show that the film can be formed and it is terminated with a （√3 × √3） R30° surface reconstruction when the thickness of Mn exceeds 3 monolayers. The magnetic properties show that the Curie temperature is about 300 K and the T^2-dependent behaviour is observed to remain up to 220 K.     

Large-Area Self-Assembly of Rubrene on Au（111） Surface

Large-area self-assembly of rubrene has been fabricated on Au（111） surface and studied by scanning tunnelling microscopy. The rubrene monolayer on A u（111） surface is characterized by well-ordered row-like structures similar to the a-b plane of rubrene single crystal. However, the directions of the neighboured molecular rows are opposite to each other. In a two-layer film of rubrene on Au（111） surface, the arrangements of the top molecular rows are determined by the underneath rows, suggesting an orthorhombic crystal structure with a = 1.26 nm, b = 4.36 nm, c = 0.17nm for multilayer ofrubrene on Au（111）.     

Atomic-Scale Study of Ge-Induced Incommensurate Phases on Si（111）

Two Ge-induced incommensurate phases, γ and β, on Si（111） are observed and studied by {／it in situ} scanning tunneling microscopy. The γ phase consists of aligned triangular domains whose stacking sequence is faulted with respect to the Si（111）-1×1 surface. The β phase consists of two kinds of triangular domains whose stacking sequences are faulted and unfaulted with respect to the Si（111）-1×1 surface, respectively. In the β phase, two types of domain walls, zigzag＇＇ and face-to-face＇＇, form to release the strain. The triangular domains all exhibit a quasi-1×1 hexagonal close-packed structure. By studying the structural evolution from magic clusters to incommensurate structures, the structure models for γ and β phases are proposed.     

The structural formation of methylthiolate SAMs on Au(1 1 1) for short deposition times from solution

Scanning tunnelling microscopy was used to investigate the structural formation of methylthiolate self-assembled monolayers on Au(1 1 1). SAMs were prepared by exposing the gold crystal to an ethanol-dimethyldisulfide solution for immersion times of 12 min, 12 h, and 24 h. After preparation the formation of a () rect. striped phase was found. For this phase, the immersion time is the key parameter determining the size and number of ordered domains. Annealing induced a phase transition leading to large domains in a (3×4) structure. The annealing temperature determines whether a mixed phase of both structures or only the (3×4) structure are formed. We find no influence of the immersion time on the formation of the second structure. A structure model is presented for both phases on the basis on the same building block containing two methylthiolate molecules and a gold ad-atom.     

Fabrication and scanning tunneling microscopy studies of the Si(1 1 1)-(√31 × √31)-In surface

We report on the fabrication of single phase of the Si(1 1 1)-(√31 × √31)-In reconstruction surface, observed by scanning tunneling microscopy (STM) at room temperature. By depositing specific amounts of indium atoms while heating the Si(1 1 1)-(7 × 7) substrate at a critical temperature, the single phase of Si(1 1 1)-(√31 × √31)-In surfaces could be routinely obtained over the whole surface with large domains. This procedure is certified by our high-resolution STM images in the range of 5-700 nm. Besides, the high resolution STM images of the Si(1 1 1)-(√31 × √31)-In surface were also presented.     

Two-Step Oxidation of Pb（111） Surfaces

We report on a two-step method for oxidation of Pb（111） surfaces, which consists of low temperature （90K） adsorption of 02 and subsequent annealing to room temperature. In situ scanning tunnelling microscopy observation reveals that oxidation of Pb（111） can occur effectively by this method, while direct room temperature adsorption results in no oxidation. Temperature-dependent adsorption behaviour suggests the existence of a precursor state for 02 adsorption on Pb（111） surfaces and can explain the oxidation-resistance of clean Pb（111） surface at room temperature.     

Adsorption of cobalt phthalocyanine on a Si(1 0 0) surface with Bi-line structures as evaluated by scanning tunneling microscopy

We report the reaction dynamics of cobalt phthalocyanine (CoPc) molecules with Bi-line structures (BLSs) on a Si(1 0 0) surface, investigated using scanning tunneling microscopy (STM). When CoPc molecules were deposited on a Si(1 0 0) surface with BLSs at room temperature, single-spot protrusions were observed in the STM image instead of four-spot images corresponding to CoPcs flat molecular structure. Moreover, domains with a c(4 × 4) periodicity appeared on the terraces of the Si(1 0 0) surface. This indicates that CoPc molecules may have decomposed on the surface by catalytic reaction with Bi atoms.     

Indium-induced superstructures formed on Si(1 1 0) surfaces

Si(1 1 0) surfaces covered with small amounts of In deposit and then annealed at high temperature were investigated by RHEED, and two kinds of superstructures with A = 3a and B = −a + 4b, and A = 3a − 2b and B = −2a + 4b as primitive translational vectors are reported to form on the surfaces.     

SR-PES and STM observation of metastable chemisorption state of oxygen on Si(1 1 0)-16 × 2 surface

Initial adsorption of oxygen molecules on the Si(1 1 0)-16 × 2 surface and subsequent modification of the bonding states induced by mild (300 °C) annealing have been studied by synchrotron-radiation photoemission spectroscopy and scanning-tunneling microscopy. It has been shown that upon annealing, the intensity and the energy positions of the Si 2p suboxide components shift towards the values characteristic for the thermal oxide. This indicates the presence of a metastable chemisorption state of oxygen on the Si(1 1 0)-16 × 2 surface.     

Hydrogen-induced metallization on Ge(1 1 1) c(2 × 8)

We have studied hydrogen adsorption on the Ge(1 1 1) c(2 × 8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2 × 8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states.     

Bi- and Au-Induced Reconstructions on GaAs（001）-2 × 4 Surface

Submonolayer Bi and Au adsorptions on the GaAs（001）-2× 4 surface are investigated by scanning tunnelling microscopy, low energy electron diffraction and first-principles calculations. The 1 ×4 and 3 × 4 reconstructed surface induced by Bi and Au, respectively, are revealed and their structural models are proposed based on experiments and first-principles calculations. Moreover, the validity of the recently proposed generalized electron counting （GEC） model [Phys. Rev. Lett. 97 （2006） 126103] is examined in detail by using the two surfaces. The GEC model perfectly explains the structural features, such Bi-1 × 4 surface and the 3x arrangement of four-atom Au as the characteristic short double-line structure in the clusters.     

Surface treatments toward obtaining clean GaN(0 0 0 1) from commercial hydride vapor phase epitaxy and metal-organic chemical vapor deposition substrates in ultrahigh vacuum

We studied processes of cleaning GaN(0 0 0 1) surfaces on four different types of wafers: two types were hydride vapor phase epitaxy (HVPE) free-standing substrates and two types were metal-organic chemical vapor deposition (MOCVD) films grown on these HVPE substrates and prepared by annealing and/or Ar ion sputtering in ultra high vacuum. We observed the surfaces through treatments using in situ low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy, and also using ex situ temperature programmed desorption, X-ray photoelectron spectroscopy, X-ray diffraction, and secondary ion mass spectrometry. For HVPE samples, we obtained relatively clean surfaces under optimized three-step annealing conditions (200 °C for 12 h + 400 °C for 1 h + 500 °C for 5 min) without sputtering, after which the surface contamination of oxide and carbide was reduced to ∼20% of that before annealing. Clear GaN(0 0 0 1)1×1 patterns were obtained by LEED and RHEED. STM images showed flat terraces of ∼10 nm size and steps of ∼0.5 nm height. Upon annealing the HVPE-GaN samples at a much higher temperature (C), three-dimensional (3D) islands with facets were formed and the surface stoichiometry was broken down with the desorption of nitrogen in the form of ammonia, since the samples include hydrogen as an impurity. Ar⁺ sputtering was effective for removing surface contamination, however, postannealing could not recover the surface roughness but promoted the formation of 3D islands on the surface. For MOCVD/HVPE homoepitaxial samples, the surfaces are terminated by hydrogen and the as-introduced samples showed a clear 1×1 structure. Upon annealing at 500-600 °C, the surface hydrogen was removed and a 3×3 reconstruction structure partially appeared, although a 1×1 structure was dominant. We summarize the structure differences among the samples under the same treatment and clarify the effect of crystal quality, such as dislocations, the concentration of hydrogen impurities, and the residual reactant molecules in GaN films, on the surface structure.     

Adsorption of Al on the Si(0 0 1) surface

The first-principles calculations have been presented to study the adsorption of aluminum (Al) on the Si(0 0 1)(2×1) surface. We have investigated the optimized geometries and electronic structures of the adatom-substrate system. The adsorption energy of the system has been calculated. The most stable adsorption sites were consequently determined to be HH site and T3+T4. It is shown that the Si-Si dimer is asymmetric on the reconstructed bare surface and become symmetric upon Al adsorption. In addition, the bond length of Si-Si was found to be considerably elongated in the adsorption system. It is found that the work function change obtained in our work is different from other previous results on the adsorption of alkali metals on the Si(0 0 1) surface. In order to investigate the relative stability of phases at different coverages, the surface formation energy of the adsorption system was calculated. To shed light on the nature of the Al-Si bond and the character of silicon surface, the density of states (DOS) and difference charge density of the system were evaluated.