Effects of oblique angle deposition on structural, electrical and wettability properties of Bi thin films grown by thermal evaporation

Oblique angle deposition is a promising technique for tuning the physical properties of thin films. Structural, surface morphology, electrical and wettability properties are strongly influenced by the angle of deposition. A comparison of these physical properties of normally and obliquely deposited Bi films is carried out in this study. X-ray diffraction studies show that films have highly oriented hexagonal crystal structure and crystallite size is smaller for obliquely deposited (70 nm) film as compared to that of normally deposited film (111 nm). Raman spectra of the films consist of peaks corresponding to E-g and A(1g) first-order Raman modes of bismuth. The atomic force and scanning electron microscopy studies show that the surface roughness of obliquely deposited film is higher as compared to that of normally deposited film. Contact angle measurements reveal that both films are strongly hydrophobic in nature with the contact angles of 105 +/- 1 degrees and 119 +/- 1 degrees for normally and obliquely deposited films respectively. Oblique angle deposition enhances the hydrophobicity of the film. The electrical conductivity of the film is significantly reduced by oblique angle deposition. The activation energies for electrical conduction were determined by four-probe measurements and are 0.0166 +/- 0.0003 eV and 0.0178 +/- 0.0003 eV for normally and obliquely deposited films respectively.