Engineering Radial Deformations in Single-Walled

ARTICLE

Engineering Radial Deformations in Single-Walled Carbon and Boron Nitride Nanotubes Using Ultrathin NanomembranesMeng Zheng, Lian-feng Zou, Howard Wang, Cheol Park, ,§ and Changhong Ke ,* Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, New York 13902, United States, National Institute of Aerospace, 100 Exploration Way, Hampton, Virginia 23666, United States, and§Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904, United States adial deformations of one-dimensional tubular nanostructures, such as carbon nanotubes (CNTs) and boronnitride nanotubes (BNNTs), are of great importance to their respective electrical properties and electronics applications (e.g., eld e ect transistors (FETs),1 singleelectron transistors (SETs),2 and optoelectronic devices3). From the structural point of view, CNTs and BNNTs are made of alike hexagonal sp2 covalent CÀC and partially ionic BÀN bonding networks, respectively. Both tubes have extraordinary mechanical and thermal properties. For instance, they have comparable Young's moduli, with reported values of up to 1.2À1.3 TPa.4À10 Their thermal conductivities are reportedly to be above 3000 W 3 mÀ1 3 KÀ1.11,12 However, the electrical properties of these two types of tubes are of distinct di erence. Single-walled CNTs (SWCNTs) are either metallic or semiconductive depending on the tube chirality, while BNNTs are excellent insulators with band-gaps of about 5À6 eV and being largely independent of the tube chirality.13À15 Both experiments and theoretical modeling demonstrate that the radial deformation of SWCNTs can greatly in uence their electronic structures (e.g., band-gaps) and result in semiconductorto-metal or metal-to-semiconductor transitions in reportedly reversible fashions.16À21 In addition, studies show that radial deformation can reduce the band gap of BNNTs from insulator to semiconductor or even conductor. 18,22 Tuning the band-gaps of these tubular nanostructures through engineering their transverse deformations will greatly impact many of their novel electronics applications.ZHENG ET AL .

R

ABSTRACT Radial deformations of car-

bon and boron-nitride nanotubes are of great importance to their respective electronic properties and applications. In this paper, we present a simple and practical approach of engineering radial deformations in singlewalled carbon and boron-nitride nanotubes (SWCNTs and SW-BNNTs) through covering individual nanotubes lying on at substrates with subnanometer-thick monolayer graphene oxide (GO) nanomembranes. The GO membrane conforms to and transversely compresses the underlying nanotube as a result of its adhesion binding interaction with the substrate. Our atomic force microscopy (AFM) imaging measurements reveal that the engineered net radial deformations of both types of tubes increase with the tube diameter and are more f

or SWBNNTs compared with SWCNTs of the same tube diameter. Our results capture the net crosssection height reductions of up to 44.1% for SW-BNNTs and up to 29.7% for SWCNTs. Our work clearly demonstrates the e ectiveness of our proposed approach for engineering and controlling the radial deformation in one-dimensional tubular nanostructures and opens a promising route for mechanical tuning of their electronic properties for novel nanoelectronics applications.KEYWORDS: boron nitride nanotubes . carbon nanotubes . graphene-oxide nanosheets . radial deformation . atomic force microscopy

Prior studies show that noticeable tube deformation occurs along its transverse direction when a carbon nanotube is deposited on a at substrate, which is due to the van der Waal (vdw) interaction between the nanotube and the substrate.23À25 However, such radial deformation is only substantial for nanotubes of very large diameters (e.g., 4À5 nm). For SWCNTs of relatively small diameters, none-to-little radial deformation occurs. For instance, MD simulations show that vdw adhesion-induced radial deformation for a (20, 20) SWCNT (2.70 nm in diameter) is about 13% of its original tubeVOL. 6’

* Address correspondence to cke@binghamton.edu. Received for review December 13, 2011 and accepted January 20, 2012. Published online January 26, 2012 10.1021/nn2048813C 2012 American Chemical Society

NO. 2

’

1814– 1822

’

2012

1814

ARTICLE

diameter, while merely 2% for a (10,10) tube of 1.34 nm in diameter.23 It is noted that substantial radial deformations, as higher as 50% of the original tube diameter,18,19 are desired for inducing signi cant band gap and electrical conductance changes in nanotubes. Signi cant radial deformations on individual tubes can be engineered using nanomanipulation with sharp scanning probe microscopy (SPM) probes.2,21,26 However, this method is a slow and sequential approach, which is only useful for a very small quantity of nanotubes and is not feasible for large-scale processing. Introducing signi cant radial deformations in nanotubes with scalability for large-scale integration is still not available. In this paper, we propose a simple and practical approach for engineering radial deformations in individual nanotubes, and demonstrate its e ectiveness through engineering radial deformations in SWCNTs and single-walled BNNT (SW-BNNTs). Our proposed approach is to cover or partially cover individual nanotubes lying on at substrates with subnanometer-thick nanomembranes, as illustrated in Figure 1a. Figure 1b shows schematically the cross sections of a nanotube with a height of h0 (left) and the membrane-covered nanotube (right) staying on a at substrate, respectively. The cross-section height of the membranecovered nanotube, h, is measured as the height di erence of the membrane from the position right on top of the underlying nanotube …… 此处隐藏：41318字，全部文档内容请下载后查看。喜欢就下载吧 ……