Real space imaging of co-adsorbed CO and benzene molecules on Rh(111)

High-Resolution Scanning Tunneling Microscopy Images of Molecular Overlayers Prepared by a New Molecular Beam Deposition Apparatus with Spray-Jet Technique

We developed a new molecular beam deposition apparatus using a spray-jet technique for high-quality thin film preparation of nonsublimable molecules. The apparatus was used to deposit chloro[tri-tert-butyl-subphthalocyaninato]boron(III) (TBSubPc) molecules on an Au(111) surface for analysis by low-temperature scanning tunneling microscopy (STM). Highly resolved images, in which tert-butyl groups in a TBSubPc molecule were clearly identifiable, were obtained. The image quality and the resolution of these images compared favorably well to STM images taken on reference samples which were sublimed onto Au (111) from a heated crucible.

Molecular Shapes, Orientation, and Packing of Polyoxometalate Arrays Imaged by Scanning Tunneling Microscopy

Reported here are both STM images and spatially resolved tunneling spectra of four different polyoxometalate (POM) structural class members: Keggin structure, H(3)[PW(12)O(40)] (spherical); Finke-Droege (FD) structure, Na(16)[Cu(4)(H(2)O)(2)(P(2)W(15)O(56))(2)] (prolate spheroidal); Wells-Dawson (WD) structure, H(7)[P(2)Mo(17)VO(62)] (prolate spheroidal); and Pope-Jeannin-Preyssler (PJP) structure, K(12.5)Na(1.5)[NaP(5)W(30)O(110)] and (NH(4))(14) [NaP(5)W(30)O(110)] (oblate spheroidal). In all four cases, the results demonstrate the formation of well-ordered 2-D inorganic POM anion arrays (composed of catalytically active molecular constituents) on graphite. Importantly, the image shapes and lattice spacings accurately reflect the POM anisotropies, permitting the determination of anion orientation with respect to the surface plane.

Atomic-Scale Dynamics of a Two-Dimensional Gas-Solid Interface

The interface between a two-dimensional (2D) molecular gas and a 2D molecular solid has been imaged with a low-temperature, ultrahigh-vacuum scanning tunneling microscope. The solid consists of benzene molecules strongly bound to step edges on a Cu{111} surface. Benzene molecules on the Cu{111} terraces move freely as a 2D gas at 77 kelvin. Benzene molecules transiently occupy well-defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and exchange between the two phases at the interface are observed. On raised terraces of the copper surface, the 2D gas is held in a cage of the solid as in a 2D nanometer-scale gas bulb.

Molecules at interfaces: STM in materials and life sciences

The scanning tunneling microscope (STM) enables us, for the first time, to directly observe individual molecules both at surfaces under ultrahigh-vacuum conditions as well as at interfaces with fluids or soft solids. In suitable systems, structure and dynamics of single molecules or monomolecular layers can be investigated at a resolution down to the atomic length scale and the time scale of milliseconds. The structure of individual biopolymers and biological membranes on solid supports can be studied on the nanometer scale. Furthermore, the STM may be viewed as a tool to address individual molecules, e.g., for molecular electronics studies or the manipulation of individual molecular structures. The paper reviews selected STM results on organic conductors, as well as small organic molecules and large biopolymers, which have been chemi- or physisorbed to conducting substrates. Finally, some prospects for future work are discussed.

Scanning tunneling microscopy of planar biomembranes

We combined planar membrane monolayer techniques with scanning tunneling microscopy (STM) to measure the thickness of metal-coated purple membrane (PM) isolated from Halobacterium halobium. Although the metal coating precluded obtaining high-resolution lateral information, it facilitated obtaining high-resolution vertical information. For example, the apparent mean thickness of planar PM and variations in thickness of enzyme-treated PM could be detected and quantified at sub-nanometer resolution.