Neville V. Richardson

Fabrication of surface-supported low-dimensional polyimide networks.

Interest in thermal and chemical stability of surface-supported organic networks has stimulated recent attempts to covalently interlink adsorbed molecular species into extended nanostructures. We show, using low-temperature scanning tunneling microscopy, that imidization of anhydrides and amines adsorbed on Au(111) can be thermally initiated under controlled ultrahigh vacuum conditions. Using two types of amine-functionalized polyphenyl molecules together with the organic semiconductor PTCDA, monolayer thick linear polymeric strands and a porous polymeric network with nanoscale dimensions are obtained.

Chemisorption induced chirality: glycine on Cu{110}

The adsorption induced surface chirality has been examined with high resolution STM observation of ordered glycine on Cu{1 1 0} surface. Two domains with different internal molecular arrangement have been identified. The homochiral domain shows a pseudo-centered structure while the heterochiral domain presents a clear glide plane symmetry. The lateral relationship between these two domains has also been analysed, which gives the details of the assignment of individual features in the STM images.

Symmetry analysis of angle-resolved photoemission: Polarization dependence and lateral interactions in chemisorbed benzene

Abstract Using an oriented free-molecule model, exact selection rules are used to determine which bands are allowed in both normal and off-normal emission as a function of polarization direction. An approximate angular analysis of the final states is then applied to give a qualitative account of the emission angle dependence. The consequences of both inter- and intra-ad sorbate unit cell lateral interactions are considered, with effects which are new to adsorbate photoemission. When applied to benzene-on-Pd(100) angle-resolved spectra these concepts are shown to give a very adequate description of the results. Previous assignments are confirmed with the exception that the second π-orbital is now located on the leading edge of the C-band, thus implying that both π-orbitals are subject to similar adsorbate-substrate binding shifts. In conjunction with LEED data a specific adsorbate geometry is proposed.

Hydrogenation of but-2-enal over supported Au/ZnO catalysts

The hydrogenation of but-2-enal over supported Au catalysts is discussed, together with a detailed characterisation study using X-ray diffraction, infrared spectroscopy and transmission electron microscopy. Au/ZnO catalysts are found to be selective for the formation of the unsaturated alcohol, but-2-en-1-ol rather than the saturated aldehyde, butanal. In general, the addition of thiophene is found to enhance the yield of the unsaturated alcohol. Detailed transmission electron microscopy and infrared spectroscopy studies show that thiophene modification of Au/ZnO catalysts does not affect the Au-particle size or morphology; rather, thiophene undergoes irreversible dissociative adsorption giving a surface in which the Au sites are electronically promoted by sulfur. It is observed that thiophene modification does not give any marked effect on catalyst performance for the catalysts that contain large Au-particles (10 nm) and, hence, it is considered that the sulfur promotion observed is associated with smaller Au nanoparticles. The highest but-2-en-1-ol selectivities (∽80%) are observed for 5 wt.% Au/ZnO catalysts reduced at 400°C prior to reaction. It is proposed that the origin of high selectivity is associated with large Au particles (10–20 nm in diameter) that are present in this catalyst.

A vibrational study of the adsorption of glycine on clean and Na modified Si(100)-2×1 surfaces

The chemisorption of glycine and its fully deuterated analogue, d5-glycine, deposited on the clean and Na modified Sið 100 Þ-2 � 1 surfaces, has been studied by high-resolution electron energy loss spectroscopy (HREELS) and ab initio methods. HREELS indicates that chemisorption of glycine and d5-glycine on Na/Sið 100 Þ-2 � 1 occurs through cleavage of the OH and OD bonds in the carboxylic groups. The adsorbed species are bonded through the formation of an ionic bond between the deprotonated carboxylate group and the adsorbed Na atom, leading to species in a bidentate coordination. In contrast, we observe monodentate glycinate and d5-glycinate species following the exposure of Sið 100 Þ-2 � 1 to glycine and deuterated glycine. The thermal stability of glycine on clean Sið 100 Þ-2 � 1 and on the Na modified surface has been studied by heating the substrate to various temperatures. 2002 Elsevier Science B.V. All rights reserved.

He-I photoelectron spectra of some d 0 transition metal compounds

Photoelectron spectra excited in the gas phase with He-I radiation are reported for the tetroxides, RuO4 and OsO4, and for the oxychloride species VOCl3, CrO2Cl2 and MoO2Cl2. The X-ray photoelectron spectrum of OsO4 has also been measured. The nature of the metal-oxygen bonding in these molecules, as inferred from the spectrometric data, is discussed.

Spectroscopic and kinetic studies of formic acid adsorption on Cu(110)

The adsorption of formic acid on Cu(110) has been studied using Fourier-transform reflection/absorption IR spectroscopy (FTRAIRS) and molecular beam measurements. The adsorption is inefficient at 300 K, having an initial sticking coefficient (S0) of ca. 0.1. Experiments with sub-ambient crystal temperatures show much more efficient adsorption with S0 being 0.9 at 180 K. The absorption appears to be of the precursor type. FTRAIRS indicates that the species adsorbed at 200 K is very different from that at 300 K. The latter is the usually reported bidentate formate with a simple IR spectrum and symmetrically equivalent oxygens. At 200 K we propose that formate is produced in the monodentate form, that is strongly anchored to the surface through one oxygen, with the other in the form of a carbonyl group. However, the carbonyl group may also be bonding to the surface weakly. The monodentate species converts to bidentate upon heating. If the bidentate formate is cooled to 200 K, formic acid can be adsorbed from the gas phase and this converts all the formate on the surface back to the monodentate form.

Tailoring Low-Dimensional Organic Semiconductor Nanostructures

The quest for miniaturization of organic nanostructures is fueled by their possible applications in future nanoscale electronic devices. Here we show how a range of nanostructures of reduced dimensionality of the organic semiconductor PTCDA can be realized on Au(111) by intermixing the latter with hydrogen bonding spacer molecules. The purpose of the spacers is to separate nanounits of pure PTCDA, using hydrogen bonds between the anhydride end of PTCDA and amine groups of the spacers. A highly regular array of potential quantum dots can be realized by this approach.

9 Physical studies of chiral surfaces

Driven by the demand for heterogeneous asymmetry catalysis, studies of chiral surfaces have become important aspects of modern surface science. With the maturity of surface science techniques, this has enriched the success in the study of low-symmetry chiral surfaces at the molecular level. In this review we summarise the methods to create chiral surfaces and the symmetry properties of chiral surfaces. Physical methods that have been used to recognise and understand the structure and properties of chiral surfaces are discussed in detail.

Scanning tunnelling microscopy of tetracene on Si(100)-2 × 1

Scanning tunnelling microscopy (STM) has been used to follow the adsorption of tetracene molecules on the Si(100)-2 × 1 surface. Two distinct types of adsorption are indicated by filled state images but three types may be distinguished in empty state images. Molecules aligned both along and perpendicular to the silicon dimer rows can be observed. The calculated charge densities associated with occupied and unoccupied orbitals near the Fermi level are compared with the STM images. Possible bonding arrangements and their correlation with the STM images are postulated.