Adsorption position of oxygen on the Pt(111) surface

The adsorption position of oxygen on the clean Pt(111) surface has been determined by means of the transmission channeling technique. Oxygen adsorbs in a well ordered p(2 × 2) overlayer structure at temperatures 200 T 350 K. From an analysis of the angular scans along the [111], [110] and [100] axial directions it is concluded that the O atoms are adsorbed in the fcc three-fold hollow site exclusively at a height of 0.85 ± 0.06 Å above the Pt surface layer. From a narrowing of the [111] angular O scan, the O RMS displacement parallel to the surface is found to be 0.16 ±0.03 Å.     

Structure of rutile TiO2 (110)-(1 x 2): formation of Ti2O3 quasi-1D metallic chains

Combining STM, LEED, and density functional theory, we determine the atomic surface structure of rutile TiO2 (110)-(1 x 2): nonstoichiometric Ti2O3 stripes along the [001] direction. LEED patterns are sharp and free of streaks, while STM images show monatomic steps, wide terraces, and no cross-links. At room temperature, atoms in the Ti2O3 group have large amplitudes of vibration. The long quasi-1D chains display metallic character, show no interaction between them, and cannot couple to bulk or surface states in the gap region, forming good atomic wires.     

Hydrogen bonding in mixed OH+H2O overlayers on Pt(111)

The stability of OH on Pt(111) has been investigated to determine the role of hydrogen bonding in stabilizing the overlayer. We find that the optimal structure is a mixed (OH+H2O) phase, confirming recent density-functional theory predictions. The reaction O+3H(2)O forms a hexagonal (sqrt[3]xsqrt[3])R30 degrees -(OH+H2O) lattice with a weak (3x3) superstructure, caused by ordering of the hydrogen bonds. The mixed overlayer can accommodate a range of H(2)O/OH compositions but becomes less stable as the H2O content is reduced, causing defects in the hydrogen-bonding network that lift the (3 x 3) superstructure and destabilize the overlayer.     

Long-range surface reconstruction: Si(110)-(16 x 2)

A variety of reconstruction models is studied for the Si(110)-(16 x 2) surface using first-principles calculations. Assuming appropriate rebonding of edge atoms and surface chains buckled in antiphase, we show that steps along the [112] direction yielding a trench indeed lower the surface energy. We explain the long-range surface reconstruction and develop a geometry model based on steps, adatoms, tetramers, and interstitials. The model is able to explain the stripes of paired pentagons seen obviously in empty-state scanning tunneling microscopy images.     

Thermally activated stripe reconstruction induced by O on Nb (011)

We report scanning tunneling microscopy and low energy electron microscopy (LEEM) observations for thin films of Nb (011) of stripe-phase behavior by two variants of an O-induced reconstruction. Stripes occur for thin films but not bulk crystals. At low temperatures the less-favored variant is thermally activated as single stripes on surface heterogeneities. Near T0 = 1505 K, where the reconstruction is lifted, the stripes crowd to form a periodic array with a temperature dependent spacing. LEEM permits quantitative insight into stripe behavior and reveals novel details of stripes interacting with topographic features such as steps, facets, and dislocations.     

Oxygen atom-induced D2 and D2O desorption on D/Si(1 1 1) surfaces

We studied reaction of oxygen atoms with D-terminated Si(1 1 1) surfaces from a desorption point of view. As the D (1 ML)/Si(1 1 1) surface was exposed to O atoms D₂ and D₂O molecules were found to desorb from the surface. The desorption kinetics of D₂ and D₂O molecules exhibited a feature characterized with a quick rate jump at the very beginning of O exposure, which was followed by a gradual increase with a delayed maximum and then by an exponential decrease. The O-induced D₂ desorption spectra as a function of T_s appeared to be very similar to the H-induced D₂ desorption spectrum from the D/Si(1 1 1) surfaces. Possible mechanisms for the O-induced desorption reactions were discussed.     

AES and TDS studies of electrochemically oxidized Pt(100)

Anodic films formed on Pt(100) in 0.3M HF using a quasi thin-layer electrochemical cell within a vacuum envelope were transferred to ultra-high vacuum for study by AES and TDS. Films generated at potentials above 1.1 V (RHE) survived emersion and pumpdown in a hydrated state. As the emersion potential increased, the integrated H₂O and O₂ thermal desorption signals increased in parallel, indicating a constant stoichiometry consistent with the formation of a platinum hydroxide layer. The oxygen TDS and AES signals after holding the electrode at constant potentials above 1.9 V (RHE) for several minutes saturated with formation of a surface phase containing 2.3 O/Pt (desorbing as O₂) and 2 H₂O/Pt. Much thicker films could be grown by AC polarization. XPS analysis combined with TDS indicated the most likely chemical state of the saturation layer to be Pt(OH)₄. Water evolved from all films at 400 K and higher, temperatures much higher than that reported for surface adsorbed hydroxyl groups produced by low-temperature gas-phase coadsorption of O₂ and h₂O [G.B. Fisher and B.A. Sexton, Phys. Rev. Letters 44 (1980) 683]. The higher temperature desorption is ascribed to the incorporation of hydroxyls into a surface phase involving place-exchange between Pt and OH.     

Oxidation of Pt(110)

Using scanning tunneling microscopy and temperature programmed desorption we investigate the Pt(110) surface under strongly oxidizing conditions involving either high-pressure O2 or atomic oxygen exposure. At low temperatures, only disordered Pt oxide structures are observed. After annealing ordered surface oxide islands are observed to coexist with a highly stable reconstructed (12x2)-O chemisorption structure. From density functional theory calculations a model for the surface oxide phase is revealed. The phase is found to be metastable, and its presence is explained in terms of stabilizing defects in the chemisorption layer and reduced Pt mobility.     

反式二氯二L-苯丙氨酸乙酯合铂分子结构和晶体结构

反式二氯二L-苯丙氨酸乙酯合铂[Pt(C₁₁H₁₅NO₂)₂Cl₂]属单斜晶系,空间群为P2₁,α=13.555(6)?,b=6.487(3)?,c=15.588(5)?,β=109.42(3)°,Z=2。该化合物晶体结构由重原子法求解,用块矩阵最小二乘方法修正,R=0.0617,R_w=0.0575。Pt—N 2.065(14)?,2.084(14)?;Pt—Cl 2.285(7)?,2.312(8)?。结构由以N—H……O氢键联结的分子层交错堆积组成。 关键词：     

Optical absorption spectrum of gold atoms deposited on SiO(2) from cavity ringdown spectroscopy

The optical properties of gold atoms supported on amorphous silica (alpha-SiO2) were studied experimentally and theoretically in the visible range. Samples were prepared in situ by depositing Au atoms at low coverages (5 x 10(12) cm(-2)) in UHV, and the optical absorption spectra were recorded by cavity ringdown spectroscopy. The atomic absorption bands can be attributed to gold atoms trapped at [triple bond] Si-O(.-) and [triple bond]Si-O(-) defect sites. The absence of optical transitions typical for Au(2) shows that the atoms are efficiently anchored at these defect sites, preventing diffusion and aggregation. Furthermore, these experimental results reveal that it is now possible to study optical properties of well-defined nanostructures at surface coverages as low as 5 x 10(11) cm(-2).     

若干具有[（PO4）4Mo6^VO15]^12^-簇骼的化合物的光谱研究

Five novel organic-molybdenum phosphates with [(PO4)4Mo6(V)O15]12- cluster, Na x (H4TETA)3 x (H3O)5 x {Zn[(HPO4)2(PO4)2Mo6O15]2} (2), (H2en)7 x (H3O)4 x {Cu[(HPO4)2(PO4)2Mo6O15]2} x H2O (3), (H3DETA)2 x (H3O)3 x {Co0.5[(HPO4)2(PO4)2Mo6O15]} x H2O (4), [Co(H3TETA)]2{Co0.5[(HPO4)(PO4)3Mo6O15] x 3.5H2O (5) and (H3DETA) x (H3O)4 x {Co1.5 [(HPO4)2(PO4)2Mo6O15]} x 0.5H2O (6), have been synthesized. The relationship between their properties and structures was studied by using FTIR, NIR FT-Raman, UV-Vis DRS and fluorescence etc. In these compounds, every two [(PO4)4Mo6O15] clusters are coordinated by a metal atom to form a {M[(PO4)4Mo6O15]2} dimer. In compound 2, 3 and 4, {M[(PO4)4Mo6O15]2} dimers are hydrogen-bonded by the organic molecules and water molecules to form a three-dimensional expended framework, respectively. In compound 5 and 6, {Co[(PO4)4Mo6O15]2} dimers are coordinated by [Co(H3TETA)] groups and [CoO4] tetrahedra to form a network, respectively. These characteristic vibrational frequencies of the molybdenum phosphates are related to the structure of these compounds. Three characteristic bands in UV-Vis DRS spectra of these compounds have to be attributed to the absorptions of O(d) --> Mo, O(mu) --> Mo and O --> M charge transfer, respectively. These compounds exhibit strong fluorescence emission bands at about 410 nm when excited by 240 nm, which are caused by O(mu) --> Mo charge transfer.     

Molecular and atomic oxygen adsorption on the kinked Pt(321) surface

Oxygen adsorption and desorption were characterized on the kinked Pt(321) surface using high resolution electron energy loss spectroscopy, thermal desorption spectroscopy and Auger electron spectroscopy. Some dissociation of molecular oxygen occurs even at 100 K on the (321) surface indicating that the activation barrier for dissociation is smaller on the Pt(321) surface than on the Pt(111) surface. Molecular oxygen can be adsorbed at 100 K but only in the presence of some adsorbed atomic oxygen. The dominance of the v(OO) molecular oxygen stretching mode in the 810 to 880 cm^?1 range indicates that the molecular oxygen adsorbs as a peroxo-like species with the OO axis parallel or nearly parallel to the surface, as observed previously on the Pt(111) surface [Gland et al., Surface Sci. 95 (1980) 587]. The existence of at least two types of peroxo-like molecular oxygen is suggested by both the unusual breadth of the v(OO) stretching mode and breadth of the molecular oxygen desorption peak. Atomic oxygen is adsorbed more strongly on the rough step sites than on the smooth (111) terraces, as indicated by the increased thermal stability of atomic oxygen adsorbed along the rough step sites. The two forms of adsorbed atomic oxygen can be easily distinguished by vibrational spectroscopy since oxygen adsorbed along the rough step sites causes a v(PtO) stretching mode at 560 cm^?1, while the v(PtO) stretching mode for atomic oxygen adsorbed on the (111) terraces appears at 490 cm^?1, a value typical of the (111) surface. Two desorption peaks are observed during atomic oxygen recombination and desorption from the Pt(321) surface. These desorption peaks do not correlate with the presence of the two types of adsorbed atomic oxygen. Rather, the first order low temperature peak is a result of the fact that about three times more atomic oxygen can be adsorbed on the Pt(321) surface than on the Pt(111) surface (where only a second order peak is observed). The heat of desorption for atomic oxygen decreases from about 290kJ/mol (70 kcal/mol) to about 196 kJ/mol (47 kcal/mol) with increasing coverage. Preliminary results concerning adsorption of molecular oxygen from the gas phase in an excited state are also briefly discussed.     

Role of long range interaction in oxygen superstructure formation on Cu(001) and Ni(001)

On the basis of electronic structure calculations, we show that the long range Coulomb interaction provides the driving mechanism for oxygen overlayer formation on Cu(001). We illustrate that this interaction in the precursor c(2 x 2) phase induces a missing row reconstruction of Cu(001), and leads to the (2sqrt[2] x sqrt[2])R45 degrees O structure, which has strong covalent pO-dCu coupling. For the c(2 x 2)O overlayer on Ni(001) and Cu(001), we show that pO-dNi bonding is larger than pO-dCu and serves to neutralize the perturbation of the Coulomb interaction induced by the O overlayer. Consequently, c(2 x 2)O/Ni(001)) is stable while c(2 x 2)O/Cu(001) exists only in limited environments.     

250 keV He+ 离子注入钽酸锂改性研究

室温下,将能量为250 keV He+ 离子注入z 切钽酸锂单晶,注量范围5.0x1014~5.0x1016 He+/cm2,应用三维轮廓仪、X射线衍射(XRD)、紫外可见(UV-Vis ) 光学吸收谱对未注入和注入样品进行了表征和分析。分析结果表明,在注量达到5.0x1016He+/cm2 时,样品表面出现大量凸起条纹,同时晶格沿着[001] 方向出现明显肿胀,吸收边则表现出明显的注量相关性。注入样品在空气中放置60 d后,最高注量的样品表面原来凸起的条纹变为细长的裂纹,晶格应变及光学吸收边均出现较大的恢复。讨论了样品表面形貌、晶格应变和光学吸收边与He 行为的关系。The effects of 250 keV He + implantation in the fluence from 5.0x1014 to 5.0x1016 He+/cm2 on lithium tantalate at room temperature were investigated by 3D surface profiler, XRD and UV-Vis optical absorption spectroscopies.The experimental results show that a large number of raised stripes appear on the surface of the sample and the significant lattice swelling occurs along the direction [ 001 ] at the fluence of 5.0x1016 He+/cm2. The dependence of changes absorption edge on the fluences was revealed. After the samples had been exposed to the air for 60 days, the raised stripes on the surface have evolved into narrow cracks. Furthermore, the lattice strain and the optical absorption edge has also recovered dramatically. The relationship between surface morphology, lattice strain, optical absorption edge and behaviorof He-ions was discussed.     

Novel nanostructuring of the O/Cu(110) surface by reaction to oxygen

We present a scanning tunneling microscopy (STM) study of the reactivity to oxygen of the O/Cu(110) surface nanostructured with alternating oxidized and clean Cu stripes leading to novel nanostructuring by troughs made of missing top-most Cu atoms. The copper atoms extracted from these troughs are participating to the added-row reconstruction of the surface. The oxidation of the nanostructured surface proceeds by enlargement of the oxidized stripes and by oxidation of the troughs until the surface is fully covered by oxygen. At saturation, the trough arrangement, templated by the oxygen-free stripes, led to a novel nanostructure of the O/Cu(110) surface made of the (2 × 1) phase only.A limited influence of the step density was found as the nanostructuration blocks almost all the primary sources of copper atoms at the step edges. In this case, the troughs became the spare source feeding the reconstruction. Careful analysis of the trough distribution in the vicinity of step edges and on terraces shows clear indication of an anisotropic diffusion of the copper adatoms at the surface.     

Growth of a single layer gold stripe and investigation of the preferable growth direction on reconstructed Au(1 1 1) surface using STM

We have investigated the growth of nanometer-scale gold stripes on reconstructed Au(1 1 1) surface using scanning tunneling microscopy (STM). The experiment was carried out under the conditions of ultrahigh vacuum and room temperature. The stripes were grown by the scanning motion of the STM tip over the area containing more than one step edge with the tunnel resistance less than several tens of mega ohms (MΩs). Unlike the previous reports [J.C. Heyraud, J.J. Metoris, Surf. Sci. 100 (1989) 519; V.M. Hallmark, S. Chiang, J.F. Rabolt, J.D. Swalen, R.J. Wilson, Phys. Rev. Lett. 59 (1987) 2879], we found, by directly comparing the direction of the stripes and the orientation of the underlying lattice, that the gold stripes grow preferentially along [1,−1,0] direction and its threefold symmetric directions at (1 1 1) surface of fcc structure. We also found that the scanning direction of the STM tip does not affect the direction of the stripe growth although the growth rate is suppressed remarkably when the scanning direction is close to [1,1,−2] direction of Au(1 1 1) surface.     

Contrasting bonding configurations of acetone on Pt(111) and Ru(001) surfaces.

The comparative chemistry of acetone adsorption on Pt(111) and Ru(001) has been studied by EELS. On the more easily oxidized Ru(001) surface, acetone bonded in a side-on, η²(O,C) configuration, whereas on the well-defined. close- packed regions of the Pt(111) surface acetone adopted a weak adduct-like, end-on, η¹(O) configuration. On Pt(111), some η²(O,C) was also observed and associated with adsorption at low coordination accidental step sites.     

Study of the e(g) orbitals in the bilayer manganite La(2--2x)Sr(1+2x)Mn(2)O(7) by using magnetic Compton-profile measurement.

From the magnetic Compton-profile (MCP) measurement, we have directly differentiated for the first time the populations in two e(g)-type orbitals ( x(2) - y(2) and 3z(2) - r(2)) in a manganite. The experimental MCP's along the [001] direction for La(2--2x)Sr(1+2x)Mn(2)O(7) at x = 0.35 and 0.42 are fitted by the theoretical profiles obtained from the (MnO(6))(8-) ab initio calculations. The calculation confirms that the MCP clearly detects the oxygen hybridization in the e(g) orbitals. The e(g) state is dominated by the x(2) - y(2)-type orbital with almost constant population, while the population in the 3z(2) - r(2)-type orbital decreases with increasing the hole concentration x.     

Adsorption and interaction of CO and NO on Pt(410): I. TPD studies

NO and CO adsorption and the NO/CO reaction on Pt(410) are studied by TPD. NO is found to dissociate on Pt(410) at 120 K, but it reacts to form N₂O at higher exposures. The N₂O desorbs in two peaks at 135 and 150 K. CO adsorbs molecularly, and desorbs in 5 peaks at 550, 500, 450, 380 and about 130 K. CO is also found to dissociate upon heating, leaving a carbon residue on the surface which changes the TPD spectra. The NO/CO reaction shows a surface explosion at 360 K. These results provide additional evidence that Pt(410) has unusual reactivity, as predicted by Banholzer, Park, Mak and Masel, Surface Sci. 128 (1983) 176.     

2,3-二羟基萘钼多酸有机衍生物的合成及1H NMR和IR谱学研究

本文对二种新合成的2，3－二羟基萘二钼和四钼多酸有机衍生物[n-Bu)4N]2[Mo2O5(OC10H6O)2](Ⅰ）和[n-Bu)4N]2[Mo4O10(OC10H6O)2(OCH3)2](Ⅱ)进行了红外光谱与核磁共振波谱研究，发现[Mo2O5]^2 中钼氧多桥键的红外振动频率较[Mo4O10(OCH3)2]^2 中钼氧多桥键的红外振动频率红移，而在配合物Ⅱ中2，3－二羟基中芳环的^1H化学位移较配合物Ⅰ中向低场移动。同时还发现含二钼配位中心[Mo2O5]^2 的[Mo2O5(OC10H6O)2]^2-与含四钼配位中心[Mo4O10(OCH3)2]^2 的[Mo4O10(OC10H6O)2(OCH3)2]^2-生成条件的差异仅仅只在反应体系的pH值的微小变化，说明钼多酸有机衍生物阴离子是对体系酸碱度极为敏感的物质。