E. V. Demidov

Atomic-force microscopy of bismuth films

The surface structure of bismuth films is investigated using atomic-force microscopy. The films are prepared through vacuum thermal evaporation on mica substrates, followed by annealing. It is established that the films have a block structure with the preferred orientation of the C3 axis perpendicular to the substrate plane. The C2 axes of the neighboring blocks predominantly have mutually opposite orientations. Upon annealing, the sizes of blocks with the C3 axis perpendicular to the substrate plane increase at the expense of a virtually complete disappearance of blocks with random orientations of the C3 axis and the coalescence of blocks with the same orientation. The size and configuration of the blocks are most clearly revealed upon preliminary treatment of the films in a diluted solution of the etchant. The results obtained are of interest for the interpretation of the data on the transport phenomena occurring in bismuth films.

Optimization of the Conditions for Vacuum Thermal Deposition of Bismuth Films with Control of Their Imperfection by Atomic Force Microscopy

The structure and defects of bismuth films prepared through vacuum thermal deposition on mica substrates under different conditions (deposition rates, substrate temperatures, temperatures and times of annealing) have been investigated using atomic force microscopy. The conditions are determined under which recrystallization occurs with increasing crystallite size during annealing, which provides a decrease in the degree of imperfection of the films and an increase in the mobility of charge carriers.

Atomic-force microscopy of bismuth film defects decorated by oxidation

A method has been developed for revealing intercrystalline boundaries and mutual orientation of crystallites in bismuth films with the use of natural oxidation in combination with atomic-force microscopy. For bismuth films prepared through vacuum thermal evaporation on mica substrates, the block boundaries have been revealed, the sizes of blocks have been determined, and their mutual crystallographic orientation has been established. The results obtained have been used to determine thermal evaporation conditions that ensure a higher perfection of the film structure.

Mobility restriction of charge carriers in bismuth films due to film block structure

Electric properties of bismuth thin films on mica substrates depending on their structure and concentration of defects have been studied by atomic force microscopy. The obtained results allow optimization of the production of bismuth films with a structure close to single-crystal by thermal evaporation in vacuum.

Measurement of the thickness of block-structured bismuth films by atomic-force microscopy combined with selective chemical etching

A method for measuring the thickness of block-structured films by atomic-force microscopy and selective chemical etching is proposed. The method is tested for thin bismuth films formed on mica by thermal evaporation in vacuum.

Size effect in galvanomagnetic phenomena in bismuth films doped with tellurium

The results of experimental investigation of galvanomagnetic phenomena in single-crystalline and block films of tellurium-doped bismuth in the temperature range of 77–300 K and in the film-thickness range of 0.1–1 μm are presented. It is shown that the charge-carrier concentration in the investigated films is independent of thickness, the charge carriers are scattered at phonons, the film surface, structural defects, and crystallite boundaries. The values and ratio of the listed contributions to the restriction of charge-carrier mobility depend on the tellurium content, film thickness, and also their single-crystalline or block state.

Structure of bismuth films obtained using an array of identically oriented single-crystal bismuth islands preliminarily grown on a substrate

An array of identically oriented single-crystal bismuth islands formed on mica plates is used as a substrate to improve the structure of bismuth thin films grown by vacuum thermal evaporation. The array of islands is formed by the chemical etching of a single-crystal bismuth film 1 μm thick grown by floating-zone recrystallization under a coating. The structure of the obtained films is studied by X-ray diffraction, atomicforce microscopy, and electron backscatter diffraction scanning electron microscopy.

Galvanomagnetic Properties of Bi 95 Sb 5 Thin Films on Substrates with Different Thermal Expansions

Results of an investigation of galvanomagnetic properties of Bi95Sb5 block thin films on substrates with different coefficients of thermal expansion covered with polyimide are presented. The difference between thermal expansions of the film material and the substrate was found to have a strong effect on the films’ galvanomagnetic properties. Analysis of the properties of the films using the two-band model showed that the concentration and mobility of the charge carriers in the Bi95Sb5 films are related to the coefficient of thermal expansion of the substrate material.

Topological Insulator State in Thin Bismuth Films Subjected to Plane Tensile Strain

The results of experimental examination of galvanomagnetic properties of thin bismuth films subjected to plane tensile strain resulting from the difference in thermal expansion coefficients of the substrate material and bismuth are presented. The resistivity, the magnetoresistance, and the Hall coefficient were studied at temperatures ranging from 5 to 300 K in magnetic fields as strong as 0.65 T. Carrier densities were calculated. A considerable increase in carrier density in films thinner than 30 nm was observed. This suggests that surface states are more prominent in thin bismuth films on mica substrates, while the films themselves may exhibit the properties of a topological insulator.

Dependence of the surface morphology of ultrathin bismuth films on mica substrates on the film thickness

The results of studying the surface of 15- to 100-nm-thick bismuth films by atomic-force microscopy are reported. The near-linear character of the dependences of the average surface roughness and the average height of growth patterns on the film thickness is established. It is found that the average crystallite size increases, as the film thickness is increased. A slight dependence of the crystallite size on the film thickness is observed at thicknesses in the range of 27–70 nm.