Engineering Papers⌕ Search

Engineering topics

Baldeschwieler, J. D.

Publications and source records attributed to Baldeschwieler, J. D..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Imaging graphite in air by scanning tunneling microscopy - Role of the tip

Atomically resolved images of highly oriented pyrolytic graphite (HOPG) in air at point contact have been obtained. Direct contact between tip and sample or contact through a contamination layer provides a conduction mechanism in addition to the exponential tunneling mechanism responsible for scanning tunneling microscopy (STM) imaging. Current-voltage (I-V) spectra were obtained while scanning in the current imaging mode with the feedback circuit interrupted in order to study the graphite imaging mechanism. Multiple tunneling tips are probably responsible for images without the expected hexagonal or trigonal symmetry. The observations indicate that the use of HOPG for testing and calibration of STM instrumentation may be misleading.

Colton, R. J.↗
NASA NTRS1987

'Oxide-free' tip for scanning tunneling microscopy

A new tip for scanning tunneling microscopy and a tip repair procedure that allows one to reproducibly obtain atomic images of highly oriented pyrolytic graphite with previously inoperable tips are reported. The tips are shown to be relatively oxide-free and highly resistant to oxidation. The tips are fabricated with graphite by two distinct methods.

Colton, R. J.↗
NASA NTRS1972

Fourier transform C-13 NMR analysis of some free and potassium-ion complexed antibiotics.

Fourier transforms of the noise-decoupled, natural abundance C-13 NMR free induction decays of the cyclic antibiotic valinomycin and its potassium-ion complex have been obtained at 25.2 MHz. Comparisons are made with C-13 NMR spectra taken at 22.6 MHz of the cyclic antibiotic nonactin and the synthetic polyether dicyclohexyl-18-crown-6 and their potassium complexes. The results obtained suggest that conformational rearrangements of the molecule as a whole can compete with direct interactions between carbons and the potassium ion in determining C-13 chemical shift differences between the free and complexed species.

Ohnishi, M.↗