A Dissertation Presented to the Faculty of the Graduate School of Cornell University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

Đăng ngày | Thể loại: | Lần tải: 0 | Lần xem: 0 | Page: 140 | FileSize: 8.24 M | File type: PDF
of x

A Dissertation Presented to the Faculty of the Graduate School of Cornell University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. In ME it is hard to distinguish between expenditure on research and development and the costs incurred for the current output. The reason is that in a process with a high share of made-to-measure products, some research and a lot of development may be undertaken in connection with special orders. That is especially the case for small and medium-sized firms. Thus it is true that the available figures for research and development in ME do not reflect all the efforts taken by firms to find new technical solutions and to optimize products as well as clients’ processes. However, all of.... Giống những giáo án bài giảng khác được bạn đọc giới thiệu hoặc do sưu tầm lại và giới thiệu lại cho các bạn với mục đích nghiên cứu , chúng tôi không thu tiền từ bạn đọc ,nếu phát hiện tài liệu phi phạm bản quyền hoặc vi phạm pháp luật xin thông báo cho website ,Ngoài thư viện tài liệu này, bạn có thể tải tiểu luận miễn phí phục vụ nghiên cứu Vài tài liệu tải về thiếu font chữ không xem được, có thể máy tính bạn không hỗ trợ font củ, bạn tải các font .vntime củ về cài sẽ xem được.


Nội dung

MECHANICAL AND ELECTRICAL PROPERTIES OF GRAPHENE SHEETS A Dissertation Presented to the Faculty of the Graduate School of Cornell University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Joseph Scott Bunch May 2008 © 2008 Joseph Scott Bunch MECHANICAL AND ELECTRICAL PROPERTIES OF GRAPHENE SHEETS Joseph Scott Bunch, Ph. D. Cornell University 2008 This thesis examines the electrical and mechanical properties of graphene sheets. We perform low temperature electrical transport measurements on gated, quasi-2D graphite quantum dots. In devices with low contact resistances, we use longitudinal and Hall resistances to extract a carrier density of 2-6 x 1011 holes per sheet and a mobility of 200-1900 cm2/V-s. In devices with high resistance contacts, we observe Coulomb blockade phenomena and infer the charging energies and capacitive couplings. These experiments demonstrate that electrons in mesoscopic graphite pieces are delocalized over nearly the whole graphite piece down to low temperatures. We also fabricate nanoelectromechanical systems (NEMS) from ultra thin graphite and graphene by mechanically exfoliating thin sheets over trenches in SiO2. Vibrations with fundamental resonant frequencies in the MHz range are actuated either optically or electrically and detected optically by interferometry. We demonstrate room temperature charge sensitivities down to 2x10-3 e/Hz½. The thinnest resonator consists of a single suspended layer of atoms and represents the ultimate limit of a two dimensional NEMS. In addition to work on doubly clamped beams and cantilevers, we also investigate the properties of resonating drumheads, which consist of graphene sealed microchambers containing a small volume of trapped gas. These experiments allow us to probe the membrane properties of single atomic layers of graphene. We show that these membranes are impermeable and can support pressure differences larger than one atmosphere. We use such pressure differences to tune the mechanical resonance frequency by ~100 MHz. This allows us to measure the mass and elastic constants of graphene membranes. We demonstrate that atomic layers of graphene have stiffness similar to bulk graphite (E ~ 1 TPa). These results show that single atomic sheets can be integrated with microfabricated structures to create a new class of atomic scale membrane-based devices. BIOGRAPHICAL SKETCH Joseph Scott Bunch was born on November 8, 1978 in Miami, Florida. He attended elementary, middle, and high school in Miami. After high school, he remained in Miami and enrolled at Florida International University (FIU) where he received his B.S. degree in physics in 2000. While at FIU, he was introduced to nanoscience research through an undergraduate research opportunity studying electrodeposition of metallic nanowires in Professor Nongjian Tao’s lab. He also spent one summer in a research program at the University of Tennessee, Knoxville working with a scanning tunneling microscope in Professor Ward Plummer’s lab. After graduation from FIU, Scott was awarded a graduate fellowship from Lucent Technologies, Bell Laboratories to continue his education. He spent the summer of 2000 at Bell Laboratories in Murray Hill, N.J. working with Nikolai Zhitenev on the electrodeposition of scanning single electron transistor tips. In August 2000, he enrolled in the physics department at Cornell University where he joined Paul McEuen’s group and continued nanoscience research. His research focused primarily on the electrical and mechanical properties of graphene. After finishing his Ph.D. in May 2008, Scott will do postdoctoral research on mass sensing with nanoelectromechanical systems in Professor Harold Craighead and Professor Jeevak Parpia’s lab at Cornell University before heading off to Colorado in August 2008 to become an Assistant Professor of Mechanical Engineering at the University of Colorado at Boulder. iii ... - tailieumienphi.vn 803760

Tài liệu liên quan

Xem thêm