Showing papers by "Peter H. Beton published in 2007"

Honeycomb Networks and Chiral Superstructures Formed by Cyanuric Acid and Melamine on Au(111)

Abstract: Two distinct bimolecular cyanuric acid-melamine intermixed structures, a honeycomb network and a larger superstructure, have been observed on Au(111) using a scanning tunneling microscope under ultrahigh vacuum conditions. The superstructure is formed as a regular array of chiral hexagonal rings of melamine, linked by single molecules of cyanuric acid. These bimolecular networks show both key similarities and differences to related networks studied previously on surfaces and in bulk phases. We also compare our results with networks formed by related molecules on Au(111) and Ag-terminated silicon.

Hierarchical organisation on a two-dimensional supramolecular network.

Abstract: The spontaneous organisation of molecules into larger structures is pervasive in biological systems and has been identified as a key pathway towards the realisation of “bottom-up” strategies for controlled nanostructure formation. A common aspect of organisation in naturally occurring systems is the formation of structures that display hierarchies of order. Currently there are many examples of artificial self-assembled molecular nanostructures which display a single level of order. The extension of organisation in this class of materials to hierarchies of order provides a challenge which has recently attracted considerable interest. This is of particular relevance to spontaneous organisation on surfaces, a rapidly developing research field with great promise for applications such as biosensors and molecular electronics. Example of hierarchical organisation of molecular clusters was recently demonstrated by Bl4m et al. and Spillmann et al. In addition, several examples of systems which display multiple levels of organisation have been realised through an interplay of molecular self-assembly and a second physical ordering mechanism arising from, for example, surface reconstruction 26,27] or dewetting. Herein we show that hierarchies of organisation may be introduced intrinsically by a self-assembled two-dimensional network. Specifically, we show that a self-assembled template can be used, not only to stabilise size-specific molecular nanostructures, but also influence their relative placement. The system reported here is a new intermixed bi-molecular structure formed by perylene tetra-carboxylic di-imide (PTCDI) and melamine on Au ACHTUNGTRENNUNG(111) in which rows of pores are formed, each of which has the capacity to stabilise a C60 dimer. Importantly, we observe a non-random pore occupancy with an enhanced probability of filling for nearest neighbour sites along the rows. These results imply that the supramolecular network imposes a hierarchy of organisation. At the lowest level of order the network cavities provide size-controlled capture sites for highly specific cluster geometries, while on a larger scale a correlation of occupancy is promoted within the network. A Au ACHTUNGTRENNUNG(111) surface was prepared by loading a 5 mm>10 mm piece of gold on mica (purchased from Molecular Imaging Inc.) into a UHV system with a base pressure of 1>10 10 torr. The surface was cleaned using Ar ion sputtering (4>10 6 torr, 1 kV, 1–3 mA) followed by annealing at 150–450 8C for several hours. Images of the surface were acquired using a scanning tunnelling microscope (STM) housed within the UHV system operating in constant-current mode at room temperature and using electrochemically etched tungsten tips. Following the sputteranneal cycle, we observed the characteristic (22> p 3) herringbone reconstruction of the Au ACHTUNGTRENNUNG(111) surface. Both PTCDI and C60 were sublimed onto the surface with the substrate held at room temperature. Melamine was sublimed with the substrate held either at room temperature or at an elevated temperature of 80–90 8C. Sequential deposition of PTCDI and melamine (molecular structures are shown in Figures 1a and b) onto the Au ACHTUNGTRENNUNG(111) surface leads to the formation of an intermixed phase. Subsequent annealing in the range 60–80 8C results in the formation of hexagonal networks. The ordering of closely related molecules has also been reported by other groups recently. By annealing at higher temperature, ~90 8C, the hexagonal networks are converted into a parallelogram arrangement (see Figure 2). At the boundary between these two annealing con-

Electrospray deposition of fullerenes in ultra-high vacuum: in situ scanning tunneling microscopy and photoemission spectroscopy

Abstract: Electrospray deposition of fullerenes on gold has been successfully observed by in situ room temperature scanning tunneling microscopy and photoemission spectroscopy. Step-edge decoration and hexagonal close-packed islands with a periodicity of 1 nm are observed at low and multilayer coverages respectively, in agreement with thermal evaporation studies. Photoemission spectroscopy shows that fullerenes are being deposited in high purity and are coupling to the gold surface as for thermal evaporation. These results open a new route for the deposition of thermally labile molecules under ultra-high vacuum conditions for a range of high resolution surface science techniques.

Growth front nucleation of rubrene thin films for high mobility organic transistors

Abstract: We demonstrate a mode of thin film growth in which amorphous islands crystallize into highly oriented platelets. A cascade of crystallization is observed, in which platelets growing outward from a central nucleation point impinge on neighboring amorphous islands and provide a seed for further nucleation. Through control of growth parameters, it is possible to produce high quality thin films which are well suited to the formation of organic transistors. We demonstrate this through the fabrication of rubrene thin film transistors with high carrier mobility.

Coadsorbed NTCDI-melamine mixed phases on Ag-Si(111)

Abstract: Luis M. A. Perdigao,1 Giselle N. Fontes,1,2 Ben L. Rogers,1 Neil S. Oxtoby,3 Gudrun Goretzki,3 Neil R. Champness,3 and Peter H. Beton1,* 1School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom 2Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, Avenida Antonio Carlos, 6627-Belo Horizonte, Minas Gerais CEP 30123-970, Brazil 3School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom Received 25 April 2007; revised manuscript received 3 August 2007; published 5 December 2007