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The adsorption of terephthalic acid ͓C 6 H 4 ͑COOH͒ 2 , TPA͔ on a Pd͑111͒ surface has been investigated by means of scanning tunneling microscopy ͑STM͒, x-ray photoelectron spectroscopy, and near-edge x-ray absorption fine structure spectroscopy under ultrahigh vacuum conditions at room temperature. We find the coexistence of one-͑1D͒ and two-dimensional ͑2D͒ molecular ordering. Our analysis indicates that the 1D phase consists of intact TPA chains stabilized by a dimerization of the self-complementary carboxyl groups, whereas in the 2D phase, consisting of deprotonated entities, the molecules form lateral ionic hydrogen bonds. The supramolecular growth dynamics and the resulting structures are explained by a self-limiting deprotonation process mediated by the catalytic activity of the Pd surface. Our models for the molecular ordering are supported by molecular mechanics calculations and a simulation of high resolution STM images.

A new scanning tunneling microscope reactor used for high-pressure and high-temperature catalysis studies Review of Scientific Instruments 79, 084101 (2008) To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy.