Surface chemistry and surface electronic properties of ZnO single crystals and nanorods

Abstract

The surface chemistry of ZnO single crystals of (0001) and (101¯0) orientations and ZnO nanorods was studied using x-ray and ultraviolet photoelectron spectroscopies. Air drying and UV-ozone preparations were studied in particular as chemical treatments that could be applied to poly(3-hexylthiophene) (P3HT)-ZnO solar cells to enhance performance. The UV-ozone treatment showed negligible effect by photoelectron spectroscopy on the ZnO single crystal surfaces, but brought about electronic shifts consistent with increased upward band bending by ∼0.25eV on the ZnO nanorod surface. Modest interface dipoles of ∼0.15 and ∼0.25eV were measured between P3HT and the (101¯0) and (0001) single crystal orientations, respectively, with the dipole moment pointing from ZnO to the P3HT layer. The sol-gel films showed evidence of forming a small interface dipole in the opposite direction, which illustrates the difference in surface chemistry between the solution-grown ZnO and the ZnO single crystals.

Morphological Features and Band Bending at Nonpolar Surfaces of ZnO

“…ZnO band alignment based on the ionization potential. The horizontal lines represent the experimental reported values: 7.82 eV for I b and 3.44 eV for the bulk band gap; , for the (101̅0) and (112̅0) a I s value of 8.00 eV , and 7.82 eV, respectively. “(D)” has the same meaning as in Table .…”

“…This property is defined as the energy needed to take an electron from the Fermi level, which like I s , is very sensitive to the sample history, surface preparation procedure, the method of measurement and the facet involved. , For example, for the (101̅0) face, different work function values have been reported by experiment and theory: ca. 4.6 eV, ,,,− ca. 4.3 eV. ,,− Kuo et al reported a work function value of 3.74, 3.95, and 4.21 eV for as-deposited ZnO films, after Ar sputter cleaning and after exposure to oxygen plasma .…”

“…We calculated the ZnO bulk ionization potential (with a recently developed method) 50 and then studied the effect of different surface features (including point defects in the form of dimer vacancies and a line of four vacancies along the [001] direction, grooves and steps) on the ionization potential. and 3.44 eV for the bulk band gap; 80,81 for the (101̅ 0) and (112̅ 0) a I s value of 8.00 eV 54,67 and 7.82 eV, 52 respectively. "(D)" 50 has the same meaning as in Table 6.…”

Ultrathin Metal Hydroxide/Oxide Nanowires: Crystal Growth, Self-Assembly, and Fabrication for Optoelectronic Applications

“…It is an n-type semiconductor with a direct wide bandgap of 3.3 eV [40]. The electronic properties have been widely studied for CuO and ZnO nanostructures [41][42][43]. By fabricating smoother surfaces with minimum defects of metal oxide dielectrics can utilize their good electrical insulation without compensating its high k [44].…”

Improving the performance of inorganic-organic hybrid photovoltaic devices by uniform ordering of ZnO nanorods and near-atmospheric pressure nitrogen plasma treatment

“…[1][2][3][4][5][6][7][8] HPV devices promise advantages of both organic and inorganic materials. Organic materials offer high light absorption coefficients, flexibility, ease of processing, and structural diversity.…”