银(110)表面苝有序薄膜电子态的研究

运用紫外光电子能谱(UPS)和低能电子衍射(LEED)技术,对银(110)表面上有机分子苝（perylene）的生长进行了研究.有机分子价带的4个特征峰分别位于费米能级以下3.5、4.8、6.4和8.5 eV处.当有机薄膜约为单分子层(厚度为0.3 nm)时, 苝在银(110)表面上形成C(6×2)的有序结构.角分辨紫外光电子能谱(ARUSP)的测量显示:在界面处的苝分子平面平行于衬底.苝在银(110)表面稳定性很高,随着对衬底加热，有机材料发生脱附,在140 ℃以下没有观察到分解现象.     

The initial growth behavior of perylene on Cu(100)

Using scanning tunneling microscopy (STM) together with density functional theory (DFT) the growth behavior of perylene on the Cu(100) substrate has been investigated. As revealed by STM images, perylene molecules prefer to adopt lying configuration with their molecular plane parallel to the substrate, and two symmetrically equivalent ordered domains were observed. DFT calculations show that perylene molecule prefers to adsorb on the top site of substrate Cu atoms with its long molecular axis aligning along the [011] or [01-1] azimuth of the substrate which is the most stable adsorption geometry according to its highest binding energy. Consequently, two adsorption structures of c(8×4) and c(8×6), each containing two perylene molecules per unit cell, are proposed based on our STM images. The growth mechanism for ordered perylene domains on Cu(100) can be attributed to the balance between weak adsorbate-adsorbate interaction and comparable adsorbate-substrate interaction.     

氯原子在Ag低指数面上的吸附位和吸附态

应用原子和表面簇合物相互作用的5参数Morse势方法(简称5-MP)对Cl-Ag低指数表面体系进行了研究, 并获得了全部的临界点特性, 如吸附位、吸附几何、结合能、正则振动等. 计算结果表明: 在Ag(100)面上, Cl原子吸附在四重洞位; 在Ag(111)面上, Cl吸附在三重洞位; 尽管第一与第二周期原子在(110)面上的稳定吸附态大都为赝式三重位和长桥位, 但在Ag(110)面上, 四重洞位是氯原子的稳定吸附态. 理论分析结果和实验推测结果符合得很好. 理论结果给出Cl原子在Ag表面的吸附结合能和表面簇合物的粗糙度有关, 结合能从小到大的顺序为(111)＜(100)＜(110).     

Metal organic frameworks showing hydrocarbon adsorption properties commensurate with their pore structure

Commensurate adsorption occurs when the number of molecules adsorbed per unit cell relates to the symmetry of the framework and its topology. While rare in zeolite materials, commensurate adsorption has been observed in several MOF materials. In some MOF materials, several molecules having dimensions within a limited size range show this effect. This paper describes the commensurate adsorption properties of three MOF materials and also two MOFs showing unusual combined structure-composition adsorption features.     

Morphology selected molecular architecture: acridine carboxylic acid monolayers on Ag (111)

The molecular architecture of acridine-9-carboxylic acid (ACA) grown on Ag (111) by physical vapor deposition was characterized by using UHV-STM and XPS. At lower coverage, ACA molecules exist in a 2-d gas phase on the surface at room temperature. With increased coverage (>0.4 ML), ACA molecules self-organize into distinctive adlayer structures that are correlated with underlying substrate morphology. On step-free Ag (111) regions, ACA molecules form large islands in coexistence with the 2-d ACA gas. These islands are commensurate with the Ag (111) substrate, indexed as (4 0, 2 4) in matrix notation, and can exceed 100 nm in size. There are two nonequivalent ACA molecules in each unit cell. XPS core level measurements reveal a hydrogen-bonding interaction between ACA molecules, with the ring nitrogen acting as the H-bond acceptor and the carboxyl proton acting as the H-bond donor. A structural model for this phase consists of chains of ACA molecules linked by head-to-tail hydrogen bonds along the substrate [10] direction. Alternating ACA tilting angles account for the two nonequivalent ACA molecules and the observed high packing density. Completely different molecular arrangements are observed on Ag (111) surface regions roughened by a higher density of crystallographic steps (terrace widths < or = 6 nm). Pairs of ACA molecules arrange in a zigzag pattern in a (12 2, 6 5) overlayer structure with a diluted packing density. The structural model for this lower density phase consists of carboxyl-carboxyl linked ACA dimers in a flat-lying molecular orientation.     

Valence electronic properties of n-channel organic materials based on fluorinated derivatives of perylene diimides

The valence electronic states of three kinds of fluorinated derivatives of perylene diimides, D2MFPP, D3MFPP, and D4MFPP, on Cu(110) and SiO(2)Si surface were studied by photoemission and density functional calculations. When these organic molecules were deposited on the Cu(110) and thermally oxidized SiO(2) surfaces, five well-resolved photoemission features originating from the molecules were observed. On Cu(110) surface, two emission features with pi-like character increased their binding energy with increasing the coverage of organic molecule, indicating a strong interaction between the organic molecules and Cu substrate. The density functional calculations suggest flat-lying adsorption geometry for D3MFPP and D4MFPP on Cu(110) surface.     

Adsorption geometry of 4-picoline chemisorbed on the Cu(110) surface: a study of forces controlling molecular self-assembly

The adsorption of 4-picoline (4-methylpyridine) on the Cu(110) surface has been studied with time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD) and other methods. Using deuterium labeling in the methyl group and hydrogen labeling on the aromatic ring, it has been possible to separately monitor by TOF-ESDIAD the C-D bond directions and the C-H bond directions in the adsorbed molecule. These triangulation measurements have led to a detailed understanding of the conformation of the adsorbed molecule relative to the Cu(110) crystal lattice, allowing one to witness changes in the molecular conformation as adsorbate-adsorbate interactional effects take place for increasing coverages. At low coverages, the molecule adsorbs by the N atom at an atop Cu site with the aromatic ring parallel to the <001> azimuth and with the molecular axis inclined 33 (+/- 5) degrees along the <001> azimuth. As rows of 4-picoline molecules form long range ordered chain structures oriented along the <112> azimuth, the aromatic ring twists 29 degrees about the inclined molecular axis as a result of forces between the adsorbate molecules. The initial tilting of the molecular axis at low coverage is likely due to the interaction of the positive-outward dipole with its image in the substrate. The ring twist may result from dipoleminus signdipole forces between the adsorbate molecules in the rows formed tending to form nested parallel pyridine rings. These studies are the first to apply the TOF-ESDIAD method for the measurement of the direction of chemical bonds at more than one molecular location within an adsorbed molecule and the new method is named electron stimulated desorption-molecular triangulation (ESD-MT). The results obtained give information of importance in understanding the factors which control conformational effects during the molecular self-assembly of complex adsorbed molecules on surfaces.     

Scanning tunneling microscopy investigation of the structure of methanethiolate on Ag(111)

Scanning tunneling microscopy (STM) has been used to investigate the structure of the ordered methanethiolate overlayer formed on Ag(111) by reaction at room temperature with dimethyl disulfide. High-resolution images show an ordered structure with three inequivalent atomic-scale protrusions within each ( radical7 x radical7)R19 degrees surface unit mesh which can be reconciled with methanethiolate species on a regular lateral submesh, similar to that proposed in the multilayer ( radical7 x radical7)R19 degrees -S sulfide phase previously reported. STM imaging during dynamic dosing also provides evidence for a significant change in the outermost layer Ag atom density, consistent with a reconstructed surface model. Possible models for this reconstruction are presented and discussed in the light of available information.     

Behavior of molecular hydrogen on the platinum crystal surface: Quantum-chemical modeling

The interaction of molecular hydrogen with the (111), (110), and (100) surfaces of the platinum crystal has been modeled by the density functional theory method within the generalized gradient approximation (GGA). The (100) surface is the least energetically favorable one, while the (111) and (110) surfaces are close in energy. The hydrogen molecule is attached to all three types of surfaces without a barrier. The largest decrease in energy is realized for the (100) surface. The bidentate coordination of hydrogen atoms is typical of the (100) and (110) surfaces, and the tridentate coordination is characteristic of the (111) surface. The H atoms can migrate over the crystal surface, overcoming moderate potential barriers of ??0.1?C0.2 eV; however, over the (110) surface, migration is possible only along the ridges. The maximal number of attached atoms per surface atom is close to unity for the (111) or (110) surface and to 1.67 for the (100) surface.     

Adsorption of pentacene on filled d-band metal surfaces: long-range ordering and adsorption energy

The growth of pentacene on suitable metallic templates is studied by means of low-energy electron diffraction and ultraviolet photoelectron spectroscopy. Highly ordered pentacene single layers can be prepared by deposition on filled d-band metal templates kept at 370 K. The presence of the steps for the Cu(119) vicinal surface and of the Au troughs for the Au(110)-(1 x 2) surface allows the formation of commensurate long-range ordered structures with (3 x 7) and (3 x 6) periodicities, respectively. A detailed analysis of the molecular induced electronic states evolution is performed for different growth morphologies. The adsorption energy of the ordered molecular single layers on the Au(110) surface is lower (1.90 eV) than on the Cu vicinal surface (2.36 eV), where the steps enhance the molecule adsorption energy.     

Epitaxial growth of pentacene films on Cu110

The molecular structure of thin pentacene (C(22)H(14)) films grown on a Cu(110) surface has been studied by means of He atom scattering, low energy electron diffraction, thermal desorption spectroscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. Depending on the actual film thickness three different crystalline phases have been identified which reveal a characteristic reorientation of the molecular plane relative to the substrate surface. In the monolayer regime the molecules form a highly ordered commensurate (6.5x2) structure with a planar adsorption geometry. For thin multilayers (thickness <2 nm) a second phase is observed which is characterized by a lateral ((-0.65 5.69) ( 1.90 1.37)) structure and a tilting of the molecular plane of about 28 degrees around their long axis which remains parallel to the surface. Finally, when exceeding a thickness of about 2 nm subsequent growth proceeds with an upright molecular orientation and leads to the formation of crystalline films which are epitaxially oriented with respect to the substrate. The present study thus demonstrates that also on metal substrates highly ordered pentacene films with an upright orientation of the molecular planes can be grown. Photoelectron spectroscopy data indicate further that thick films do not grow in a layer-by-layer mode but reveal a significant degree of roughness.     

Helium atom scattering study of the interaction of water with the BaF2(111) surface

The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (1 x 1) translational symmetry already after an exposure of 3 L (1 L=10(-6) Torr s) at temperatures below 150 K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 46+/-2 kJ mol(-1), corresponding to a desorption temperature of 165 K. The desorption of multilayers was observed at 150 K, consistent with a binding energy of 42+/-2 kJ mol(-1). Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (square root of 3 x square root of 3)R30 degrees lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200 K, consistent with an unexpectedly strong bonding of the molecules to the substrate.     

Phase diagram of pentacene growth on Au(110)

We studied the growth of pentacene (C22H14) on the Au(110) surface by means of He atom scattering and Synchrotron X-ray photoemission. We found that two-dimensional commensurate growth only occurs in the monolayer range for a substrate temperature, T(s), higher than approximately 370 K. Larger amounts of deposited molecules forms three-dimensional uncorrelated clusters on the wetting layer. The desorption of second layer molecules occurs at T(s) > or = 420 K. The highest coverage ordered phase displays a (6 x 8) symmetry and corresponds to the saturation coverage at T(s) = 420 K. The (3 x 6) symmetry phase, recently reported for a multilayer planar film [Ph. Guaino, et al. Appl. Phys. Lett. 2004, 85, 2777], is only found at a coverage slightly lower than the (6 x 8) one. The (3 x 6) phase corresponds to the saturation coverage of the first layer at T(s) = 470 K.     

苯并-12-冠-4分子的晶体结构和电子结构

冠醚类化合物对金属离子有特殊的络合能力,并已在分析、萃取、催化和高分子化学等方面得到广泛应用,因此有关共结构和性质的基础研究具有理论和实际意义。大量研究结果表明,冠醚分子的环孔穴大小无疑是决定其络合能力的一个重要因素。在已详细研究过的冠醚中,12-冠-4分子的孔穴最小,但它仍然能同一些金属离子形成稳定的配合物。我们在实验工作中发现,苯并-12-冠-4分子络合能力较差,为较深入地揭示其原因,测定了它的晶体结构并对共电子结构进行了量子化学近似计算。     

Nondissociative chemisorption of methanethiol on Ag(110): a critical result for self-assembled monolayers

Three definitive experiments have been performed to investigate the possibility of dissociative adsorption of methanethiol (CH3SH) on clean Ag(110). On the clean Ag(110) surface, the adsorption in the first layer occurs to 0.5 ML, producing a (2 x 1) low-energy electron diffraction (LEED) structure. The undissociated molecule desorbs starting at approximately 140 K, and only tiny quantities of other gaseous products are desorbed, and only tiny quantities of S-containing species remain. Using a 50:50% mixture of CH3SD and CD3SH, we find no evidence of S-H or S-D bond scission between these molecules upon desorption. And finally, when the CH3SH molecule is incident on the clean Ag(110) surface in the temperature range of 230-400 K, less than 1% of the incident molecules dissociate to produce adsorbed sulfur-containing species. The results influence our thinking about the surface bonding of alkanethiol-based self-assembled monolayers (SAMs) on noble metals.     

Synthesis,crystal structure,and reactivity of alkali and silver salts of sulfonated imidazoles

Both 2-methylimidazole and 2-ethyl-4-methylimidazole were monosulfonated with oleum in the five position. In crystals of the monohydrate of 2-methylimidazole-5-sulfonic acid, hydrogen bonds link the molecules into a 3-dimensional network, while in crystals of 2-ethyl-4-methylimidazole-5-sulfonic acid, corrugated 2-dimensional layers are present. The Li and Ag salts and the bis(trimethylsilyl) derivatives of 2-ethyl-4-methylimidazole-5-sulfonic acid were prepared, and there is evidence for doubly deprotonated imidazolesulfonate in aqueous solution. The monohydrate of the Li salt and the Ag salt also form a 3-dimensional, H-bonded network. Only in the Ag salt does the asymmetric unit consist of more than one basic formula unit. One Ag atom is 2-coordinate and links two nitrogen atoms, while the other Ag atom has distorted tetrahedral coordination and links the sulfonate groups into an infinite chain. Reactions of the silver salt with 1,4-dibromobutane in non-protic solvents such as 1-methyl-2-pyrrolidone were used to link two of the imidazolesulfonic acid units with a 4-carbon chain at the nitrogens.     

Structural evolution of perfluoro-pentacene films on Ag(111): transition from 2D to 3D growth

The structural evolution and thermal stability of perfluoro-pentacene (PF-PEN) thin films on Ag(111) have been studied by means of low-temperature scanning tunnelling microscopy (STM), low-energy electron diffraction (LEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). Well-defined monolayer films can be prepared by utilizing the different adsorption energy of mono- and multilayer films and selectively desorbing multilayers upon careful heating at 380 K, whereas at temperatures above 400 K, a dissociation occurs. In the first monolayer, the molecules adopt a planar adsorption geometry and form a well-ordered commensurate (6 × 3) superstructure where molecules are uniformly oriented with their long axis along the <110> azimuth. This molecular orientation is also maintained in the second layer, where molecules exhibit a staggered packing motif, whereas further deposition leads to the formation of isolated, tall islands. Moreover, on smooth silver surfaces with extended terraces, growth of PF-PEN onto beforehand prepared long-range ordered monolayer films at elevated temperature leads to needle-like islands that are uniformly aligned at substrate steps along <110> azimuth directions.     

Two solid phases of pyrimidin‐1‐ium hydrogen chloranilate monohydrate determined at 225 and 120 K

The crystal structures of two solid phases of the title compound, C₄H₅N₂⁺·C₆HCl₂O₄⁻·H₂O, have been determined at 225 and 120 K. In the high‐temperature phase, stable above 198 K, the transition temperature of which has been determined by ³⁵Cl nuclear quadrupole resonance and differential thermal analysis measurements, the three components are held together by O—H...O, N...H...O, C—H...O and C—H...Cl hydrogen bonds, forming a centrosymmetric 2+2+2 aggregate. In the N...H...O hydrogen bond formed between the pyrimidin‐1‐ium cation and the water molecule, the H atom is disordered over two positions, resulting in two states, viz. pyrimidin‐1‐ium–water and pyrimidine–oxonium. In the low‐temperature phase, the title compound crystallizes in the same monoclinic space group and has a similar molecular packing, but the 2+2+2 aggregate loses the centrosymmetry, resulting in a doubling of the unit cell and two crystallographically independent molecules for each component in the asymmetric unit. The H atom in one N...H...O hydrogen bond between the pyrimidin‐1‐ium cation and the water molecule is disordered, while the H atom in the other hydrogen bond is found to be ordered at the N‐atom site with a long N—H distance [1.10 (3) Å].     

Infrared spectroscopy of physisorbed and chemisorbed N2 in the Pt(111)(3x3)N2 structure

Using infrared spectroscopy and low electron energy diffraction, we have investigated the adsorption of N(2), at 30 K, on the Pt(111) and the Pt(111)(1x1)H surfaces. At monolayer coverage, N(2) orders in commensurate (3x3) structures on both surfaces, and we propose that the unit cells contain four molecules in each case. The infrared spectra reveal that N(2) exclusively physisorbs on the Pt(111)(1x1)H surface, while both physisorbed and chemisorbed N(2) is detected on the Pt(111) surface. Physisorbed N(2) is the majority species in the latter case, and the two adsorption states show an almost identical uptake behavior, which indicates that they are intrinsic constituents of the growing (3x3) N(2) islands. An analysis of the infrared absorbance data, based on a simple scaling concept suggested by density functional theory calculations, supports a model in which the (3x3) unit cell contains one chemisorbed molecule in end-on atop configuration and three physisorbed molecules. We note that a classic "pinwheel" structure on a hexagonal lattice, with the end-on chemisorbed N(2) molecules acting as "pins," is compatible with this composition.