Atomic layer deposition of quantum-confined ZnO nanostructures.
The modulation of optoelectronic properties, such as the bandgap of a pure-component semiconductor material, is a useful ability that can be achieved by few techniques. Atomic layer deposition (ALD) was used here to experimentally demonstrate the ability to deposit films that exhibit quantum confinement on three-dimensional surfaces. Polycrystalline ZnO films ranging from approximately 1.5 to 15 nm in thickness were deposited via ALD using diethylzinc and hydrogen peroxide at 100 degrees C. Conformal, pinhole-free films were deposited on Si wafers and on nanosized spherical SiO(2) particles using an augmented central composite design strategy. Powder x-ray diffraction was used to measure the crystallite size of the films and monitor size evolution on the basis of the number of ALD cycles and thermal annealing post-treatments. The absorbance of the ZnO films on Si wafers and SiO(2) particles was measured using spectroscopic ellipsometry and diffuse transmittance techniques, respectively. Post-deposition annealing steps increased the crystallite size of the films, independently of the coating thickness. The ZnO bandgap was increasingly blue-shifted for films of decreasing crystallite size, approaching +0.3 eV at dimensions of 2-3 nm. The nonlinear bandgap response correlated well with the Brus model. This work represents an experimental demonstration of quantum confinement using ALD on two- and three-dimensional substrates.
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424, USA.
David M
DM
King
Samantha I
SI
Johnson
Jianhua
J
Li
Xiaohua
X
Du
Xinhua
X
Liang
Alan W
AW
Weimer
D003460:Crystallization / Q000379:methods*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013499:Surface Properties; D015034:Zinc Oxide / Q000737:chemistry*
D046911:Macromolecular Substances; D015034:Zinc Oxide