Figure 2. Physical properties of ZnO microtubes. (A) Photoluminescence spectra .

1. Microwave Growth and Characterization of Zinc Oxide Single Crystal Microtubes for Optoelectronic Applications Jiping Cheng & Ruyan Guo, Pennsylvania State University (DMR-0505946) • Anovel microwave growth technique has been used for fabrication of high quality and high purity ZnO single crystal microtubes with unique crystalline structure and excellent opto-electronic properties. • The microwave grown ZnO microtubes are colorless, fully transparent, and of near-perfect crystallinity as shown in Fig. 1. The wall thickness of the ZnO microtubes is typically between 0.5-1 mm. By adjusting microwave growth parameters, the ZnO tubes can be fabricated into various cross-sectional dimensions ranging from 100 to 250 mm and different length up to 5 mm. • Some unique physical properties of ZnO single crystal microtubes shown in Fig. 2 indicate potential applications of ZnO microtubes in optoelectronic devices: (A) The photoluminescence Spectra at room-temperature shows strong near band-edge emission for light emission applications deep as deep blue LEDs and laser diodes. (B) ZnO microtubes demonstrated high ultraviolet (UV) photoresponse that can be used as UV detection devices. (C) The strong electric field emission properties of the ZnO microtube reveal a promising application in flat panel display devices. • P-type ZnO regions are formed successfully withverification of I-V characteristics. The significant results are thepotential increase of solubility limit by the microwave-assistedplasma processing to make p-n junction on ZnO crystals for the optoelectronic applications. Figure 1. SEM images of ZnO microtubes. Figure 2. Physical properties of ZnO microtubes. (A) Photoluminescence spectra. (B) Photoresponse spectra. (C) Electrical field emission properties.

2. Microwave Growth and Characterization of Zinc Oxide Single Crystal Microtubes for Optoelectronic Applications Jiping Cheng & Ruyan Guo, Pennsylvania State University (DMR-0505946) • Education and Outreach: • Paris Y. Liu, graduate student, passed her PhD candidacy exam andis making excellent progress inthis research project conducting fabrication and characterization of p-n junction on ZnO crystals. • Piezoelectric properties of ZnO microtubes are investigated using high precision optical interferometer method. Microtube ZnO is found to have larger d33 coefficient than bulk crystals. • EE412 Optical Engineering Lab - the interferometric measurement set uphas been adapted and added as an advancedoptical engineering lab for the undergraduate students of Dept. ofElectrical Engineering. • Technology Transfer: the project was represented at the Open House, Pennsylvania Center for Optical Technologies, 2005and 2006. • REU: Hosting Lab tour for undergraduate students participating in NSF EEREU program (Dr. Guo serves as PI in EEREU program). • Several talks on fabrication and characterization of ZnO microtubes and related crystal materials were presented at professional conferences. • Collaborative Research: Lehigh University and Penn State University have formed partnershipthrough Center for Optical Technologies (COT), funded by theCommonwealth of Pennsylvania. The early effort developing the ZnOmicrotubes was supported through COT seed grant and collaboration. Paris Y. Liu, a graduate student, is using the microwave plasma PVD system to fabricate p-n junction on ZnO single crystal materials. The PI, Dr. Cheng, gives a invited talk entitled “Advancements in microwave fabrication of ZnO crystal materials” at the 2005 International Workshop on Advanced Material held in Wuhan University of Technology, China.