Flat Gold Substrates Research Articles

Molecular electronics of a single photosystem I reaction center: studies with scanning tunneling microscopy and spectroscopy.

Thylakoids and photosystem I (PSI) reaction centers were imaged by scanning tunneling microscopy. The thylakoids were isolated from spinach chloroplasts, and PSI reaction centers were extracted from thylakoid membranes. Because thylakoids are relatively thick nonconductors, they were sputter-coated with Pd/Au before imaging. PSI photosynthetic centers and chemically platinized PSI were investigated without sputter-coating. They were mounted on flat gold substrates that had been treated with mercaptoacetic acid to help bind the proteins. With tunneling spectroscopy, the PSI centers displayed a semiconductor-like response with a band gap of 1.8 eV. Lightly platinized (platinized for 1 hr) centers displayed diode-like conduction that resulted in dramatic contrast changes between images taken with opposite bias voltages. The electronic properties of this system were stable under long-term storage.

Scanning tunneling microscopy of silver and gold metal liquidlike films

Metal liquidlike films (MELLFs) are formed when an aqueous colloidal metal suspension is in contact with an immiscible organic liquid phase. That the major constituent of the films is metal is evident from their metallic luster and high reflectivity. They can easily flow, support hydrodynamic waves, and generally do not tear upon insertion of objects through them. They thus exhibit the rheological properties of liquids. They do not, however, conduct. These films have been lifted onto an atomically flat gold substrate and examined with a scanning tunneling microscope. The very high vertical resolution of this instrument provides a unique insight into the shape of the deposited metal particles. On silver MELLFs two types of features are consistently observed: long, slablike features with flat faces of width ∼500 Å, and spheroid features of similar lateral dimension, some of which also exhibit flat facets (smooth to within 10 Å). Only the latter type of feature has been observed on gold MELLFs, but the lateral dimensions are smaller, approximately 200 Å. The dimensions of the spheroidal particles are confirmed by both transmission electron microscopy and atomic force microscopy.

Writing nanometer-scale symbols in gold using the scanning tunneling microscope

The conditions required to electroetch nanometer-sized craters in flat gold substrates with a scanning tunneling microscope operating in air are identified. Reproducible nanometer-scale modifications of the substrate are possible. Letters and complex symbols with linewidths as small as 2 nm have been written. Experiments show that a good tunneling tip is not destroyed by the writing process.