Cary Allen

Self-limiting deposition of semiconducting ZnO by pulsed plasma-enhanced chemical vapor deposition

Self-limiting growth of zinc oxide was accomplished over a temperature range from 25to155°C by pulsed plasma-enhanced chemical vapor deposition using dimethyl zinc [Zn(CH3)2] as the metal precursor. The deposition rate was independent of plasma exposure (1–5s) but was found to increase from 1.4to6.0A∕cycle as a function of temperature. Over the narrow range explored, substrate temperature had a dramatic impact on the film structure and properties. Amorphous films were obtained at room temperature, while a polycrystalline morphology with a preferred (100) orientation developed as the temperature increased. The electrical resistivity decreased linearly with temperature from 45to∼2Ωcm. Spectroscopic characterization showed that films deposited at room temperature were contaminated by carbon and hydroxyl impurities; however, these defects were attenuated with temperature and were not detected in films deposited above 64°C. Room temperature photoluminescence was dominated by defect emission in most films; howe...

Comparison of Molecular Monolayer Interface Treatments in Organic-inorganic Photovoltaic Devices

In this study, we explore the effects of alkyl surface terminations on ZnO for inverted, planar ZnO/poly(3-hexylthiophene) (P3HT) solar cells using two different attachment chemistries. Octadecylthiol (ODT) and octadecyltriethoxysilane (OTES) molecules were used to create 18-carbon alkyl surface molecular layers on sol gel-derived ZnO surfaces. Molecular layer formation was confirmed and characterized using water contact angle measurements, infrared (IR) transmission measurements, and X-ray photoelectron spectroscopy (XPS). The performances of the ZnO/P3HT photovoltaic cells made from ODT- and OTES-functionalized ZnO were compared. The ODT-modified devices had higher efficiencies than OTES-modified devices, suggesting that differences in the attachment scheme affect the efficiency of charge transfer through the molecular layers at the treated ZnO surface.

Octadecyltriethoxysilane Surface Modification of Zinc Oxide

Zinc Oxide (ZnO) is actively investigated for hybrid organic inorganic device applications. The interface greatly influences the electronic properties of these devices. Molecular surface modification of ZnO is being investigated for its potential to control the alignment of energy levels, charge transfer, as well as, interfacial chemical characteristics that influence device fabrication. In this study, octadecyltriethoxysilane (OTES) treatments of thin film ZnO produced by sol-gel decomposition were explored. The ZnO films were hydroxylated and then modified using OTES in solution. The condensation reaction of the OTES at the surface was promoted by the addition of a protoamine catalyst. Contact angle and infrared spectroscopy studies confirmed the surface modification and indicated that the coverage of the OTES was submonolayer. The modified ZnO films were reproducible and stable for long periods. The effects of the modification on subsequently spin-cast poly[3-hexylthiophene](P3HT) and on hybrid ZnO/P3HT organic solar cell performance are discussed.

Method to compensate for fluctuations in optical power delivered to a near-field scanning optical microscope

Near-field scanning optical microscopy (NSOM) is a scanning probe technique that uses a tapered optical fiber to probe optical characteristics of a surface in registry with topography. Light can either be injected into the sample or collected from the sample via the subwavelength aperture formed at the tip of the probe. While operating in injection mode, variations in the optical power delivered to the probe, and consequently variations in the optical flux through the aperture, place limits on the imaging of spatial variations in optical properties. We present a novel method utilizing bend loss in an optical fiber to correct for variations in the optical flux of the aperture of a NSOM probe.