R. R. Schlittler

Observation of a chemical reaction using a micromechanical sensor

We describe a new form of calorimeter designed for use in gaseous and vacuum environments which can sense chemical reactions with an estimated sensitivity limit of approximate to 1 pJ. The device is based on a micromechanical Si lever coated with a thick layer of Al upon which a sample in the form of a thin layer is fixed or deposited. Heat fluxes are detected by measuring the cantilever deflection induced by the differential thermal expansion of the lever (bimetallic effect) using the optical position sensor from a force microscope. The limit of sensitivity to local temperature changes is approximate to 10(-5) K at 300 K. Using this technique the catalytic conversion of H-2 + O-2 to form H2O over a thin Pt overcoated layer is observed to exhibit self-sustained oscillations in the reaction rate on the macroscopic scale.

Controlled Room-Temperature Positioning of Individual Molecules: Molecular Flexure and Motion

Two-dimensional positioning of intact individual molecules was achieved at room temperature by a controlled lateral “pushing” action of the tip of a scanning tunneling microscope. To facilitate this process, four bulky hydrocarbon groups were attached to a rigid molecule. These groups maintained sufficiently strong interactions with the surface to prevent thermally activated diffusional motion, but nevertheless allowed controllable translation. Simulations demonstrated the crucial role of flexure during the positioning process. These results outline the key role of molecular mechanics in the engineering of predefined properties on a molecular scale.

Photon Emission at Molecular Resolution Induced by a Scanning Tunneling Microscope

The tip-surface region of a scanning tunneling microscope (STM) emits light when the energy of the tunneling electrons is sufficient to excite luminescent processes. These processes provide access to dynamic aspects of the local electronic structure that are not directly amenable to conventional STM experiments. From monolayer films of carbon-60 fullerenes on gold(110) surfaces, intense emission is observed when the STM tip is placed above an individual molecule. The diameter of this emission spot associated with carbon-60 is approximately 4 angstroms. These results demonstrate the highest spatial resolution of light emission to date with a scanning probe technique.

Room‐temperature repositioning of individual C60 molecules at Cu steps: Operation of a molecular counting device

C60 molecules absorbed on a monoatomic Cu step have been reversibly repositioned at room temperature with the tip of a scanning tunneling microscope by performing controlled displacements along the step direction. We demonstrate the feasibility of building an abacus on the nanometer scale using single molecules as ‘‘counters,’’ Cu monoatomic steps as ‘‘rods’’ that constrain the molecular motion to one dimension, and the scanning tunneling microscope as an ‘‘actuator’’ for counting operations.

Parallel nanodevice fabrication using a combination of shadow mask and scanning probe methods

We describe a resistless proximal probe-based lithography technique, which enables the direct patterning of complex and submicron-sized structures of various materials. The method is based on a combination of scanning probe microscopy and the shadow masking technique, whereby structures are locally deposited through pinhole-like apertures situated in the proximity of a cantilever tip. Predefined excursions of the sample lead to the direct fabrication of arbitrary structures on the surface. Complex patterns such as rings and intersecting lines with linewidths well below 0.1 μm are presented.

Scanning tunneling microscopy of individual molecules: beyond imaging

Abstract We discuss several concepts of handling molecule-adsorbent and hetero-molecular structures on an individual molecular basis. Molecular recognition using scanning tunneling microscopy underpins the fundamental progress made. “Beyond imaging” implies repositioning, patterning, and exploring the functionality of individual molecules. Using porphyrin- and fullerene-based systems, we discuss issues such as conformational analysis, supramolecular systems, patterning, and the fabrication of a molecular adding machine. These examples form the beginnings of a bottom-up approach to fabrication and “sciengineering” from a molecule-by-molecule perspective.

One-dimensional metal structures at decorated steps

It is shown how wire structures a few nanometers wide can be fabricated by decorating step edges at vicinal surfaces. Their growth modes and electronic states are studied using Scanning Tunneling Microscopy (STM) and inverse photoemission. The observed growth modes are two-dimensional analogs of Stranski-Krastanov growth and layer-by-layer growth in three dimensions, e.g., for Cu on stepped Mo(1 1 0) and W(1 1 0), respectively. Contrast between different metals is achieved in STM pictures by resonant tunneling via surface states and image states, with the latter providing a map of the work function. The limit of single atomic rows decorating step edges is studied by inverse photoemission, and an energy shift of 0.4 eV is found for electronic states of step atoms. We expect stripe structures to become useful for the study of two- vs one-dimensional magnetism, for magnetoresistive films, and in the design of anisotropic materials.

Low-temperature ultra-high-vacuum scanning tunneling microscope

Note: Part B Reference LPS-ARTICLE-1992-002doi:10.1016/0304-3991(92)90495-6 Record created on 2007-06-20, modified on 2016-08-08

Photon emission scanning tunneling microscope

The analysis of photons emitted from the tip–surface region of an STM has produced new information on local dissipative processes in tunneling. A key objective to extend our work to a general spectroscopic and microscopic method is to collect and detect photons as efficiently as possible and here we describe our experimental arrangements, one of which incorporates an ellipsoidal mirror and the other a lens system to collect the photons. The systems operate in UHV and have in situ sample and tip transfer facilities. Examples of a variety of photon spectroscopy modes including photon spectra, isochromat spectra, angular distributions, and photon mapping are presented.

Observation of a new Au ( 111 ) reconstruction at the interface of an adsorbed C60 overlayer

Abstract Scanning tunneling microscope studies of monolayer films of C 60 sublimed onto Au ( 111 ) facets reveal a new Au reconstruction at the C 60 -Au ( 111 ) interface after annealing to a temperature of 700 K. C 60 forms two well-ordered hexagonal phases upon which is superimposed a striped texturing with a long-range height modulation of ≈ 1 A. and a periodicity of 90–160 A. This texturing is shown to arise from a modification of the reconstruction of clean Au ( 111 ) present at the C 60 -Au interface. The observations indicate that the C 60 -Au interaction reduces energetic factors favoring compression of the first Au layer resulting in a substantial increase in the unit cell of the Au reconstruction along 〈110〉 directions. This decompression of the first Au layer also favors the formation of a commensurate C 60 layer.