Scanning tunneling microscopy of charge density wave structure in 1T-TaS[sub 2]

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1991

OSTI ID:7114803

Thomson, R E

A scanning tunneling microscope (STM) was used to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS[sub 2]) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9[degrees] relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS[sub 2] exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10[degrees] and 12.5[degrees] relative in the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase. In the T phase, STM images clearly show discommensurations and domains of the CDW which are verified by the satellite spots in the Fourier transform. The shape and size of these domains do not agree with those of the stretched honeycomb model proposed by Nakanishi and Shiba, but do agree with the striped model developed by B. Burk from his new x-ray diffraction results. STM studies are reported of two other CDW materials, blue bronze and o-TaS[sub 3]. With blue bronze STM images are obtained of the atomic structure but the CDW are not observed. With o-TaS[sub 3] 1-D CDW fluctuations are observed above the critical temperature.

• Research Organization: California Univ., Berkeley, CA (United States)
• OSTI ID: 7114803
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360204 -- Ceramics
Cermets
& Refractories-- Physical Properties
CHALCOGENIDES
CHARGE DENSITY
CRYSTAL LATTICES
CRYSTAL STRUCTURE
MICROSCOPY
REFRACTORY METAL COMPOUNDS
SULFIDES
SULFUR COMPOUNDS
TANTALUM COMPOUNDS
TANTALUM SULFIDES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
TRANSITION ELEMENT COMPOUNDS
TUNNEL EFFECT