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The structures of self-assembled physisorbed monolayers of alkyl carbamates were examined with atomic detail by scanning tunneling microscopy at the liquid−solid interface. Through systematic variation of molecular structure, the factors determining the two-dimensional crystal packing and dynamics of alkyl carbamate monolayers were isolated. Two different conformational pseudopolymorphs on the surface were observed and their order of stability was varied by changing the length of the alkyl groups. The relative size of the two alkyl groups in a molecule affected the frequency of orientational flipping within a column, which in turn, exerts an influence on the relative orientation of the two-dimensional crystalline domains. These phenomena were explained on the basis of the preferred hydrogen-bonding geometry of the carbamate functional group and the different degree of van der Waals interaction for each form.

A single-phase synthesis of thiolate monolayer-protected gold clusters (MPCs) is described. This method avoids the problem of persistent ionic contamination from residual phase-transfer catalyst while retaining the versatility associated with the commonly used two-phase Brust synthesis. MPCs having alkyl, diphenylacetylene, ether, amide, or ester functionalities were prepared by this single-phase synthesis and characterized via ¹H NMR, FT-IR, and UV−vis absorption spectroscopy, TGA, STM, and TEM. Comparisons of products synthesized by this method and by existing methods are made for a subset of MPCs. Results are considered in the context of using MPC thin films as chemically sensitive interface layers in chemiresistor vapor sensors.

The first examples of self-assembled physisorbed monolayers containing a carbamate functional group have been imaged with atomic resolution by scanning tunneling microscopy. Two different conformational pseudopolymorphs and a clear structural transition between these packing structures are observed. Each of these minima is characterized by a different degree of van der Waals and electrostatic interactions. In addition, one of these modifications shows a pseudoperiodic change of column direction resulting from disordering of the packing structure associated with orientational flipping of the molecules. The phase transition behavior can be understood in the context of Ostwald's rule of stages, a widely observed phenomenon in three-dimensional crystallizations.

An instrument for the measurement of pulsatile blood flow has been developed. The device uses a small probe suitable for intravascular insertion, and the method of measurement employs a combination of ultrasonic pulse techniques and phase detection.