Charge Transfer Dynamics in Single-Wall Carbon Nanotubes Mat: In Situ Raman Spectroscopy
- PDF / 1,006,104 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 80 Downloads / 231 Views
D9.3.1
Charge Transfer Dynamics in Single-Wall Carbon Nanotubes Mat: In Situ Raman Spectroscopy S. Gupta1,∗, M. Hughes2, A.H. Windle2, and J. Robertson1 1 Engineering Department, University of Cambridge, Cambridge CB2 1PZ, UK 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK ABSTRACT Carbon nanotubes-based actuator has been investigated using in situ Raman spectroscopy in order to understand the actuation mechanism and to determine associated parameters. We built an actuator from a sheet of single-wall carbon nanotubes (SWNT mat) and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. Since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ~190 cm-1 varies inversely with the nanotube diameter and the G band at ~1590 cm-1 varies with the axial bond length, the variation of bonding was monitored with potential. In addition, the intensities of both the modes vary with either emptying/depleting or filling of the bonding and antibonding states due to electrochemical charge injection. We discuss the variation of intensity/frequency providing valuable information on the dynamics of charge transfer on the SWNT mat surface. We found the in-plane microscopic strain (~ -0.25%) and the charge transfer per carbon atom (fc ~ -0.005) as an upper bound for the electrolytes used. It is demonstrated that though the present analyses does comply with the proposition made earlier, but the quantitative estimates of the associated parameters are significantly lower if compared with those of reported values for carbon nanotubes. Moreover, the extent of variation (i.e. coupled electro-chemo-mechanical response) does depend upon the type of counter-ion used. The cyclic voltammetry (CV) is also described briefly. INTRODUCTION Single-wall carbon nanotubes (SWNTs) are currently the focus of intense multidisciplinary research because of their unique physical (optical, mechanical, and electronic) and chemical properties. As a consequence of which a wide range of technological applications have been emerged [1]. Besides mechanical properties, there has been particular interest in the electronic properties of SWNTs as well, which are predicted to exist uniquely either in conducting or semiconducting forms depending upon their chirality [2]. Since SWNTs possess outstanding electrical and mechanical properties, therefore it is not surprising that their electromechanical properties are unusual. One of the key applications of nanotubes based-on electrochemical double-layer - separates charges on an electrode from the ionic charges in solution - is electromechanical actuator proposed recently and is in the growing list of existing actuating materials [3]. A sheet of single-wall carbon nanotubes is dipped into an electrolyte and it expands or contracts if a voltage is applied between them and a counter electrode. Though it has been predicted that actuation is due primarily to changes in orbital occupation and band structure (quantum mechani
Data Loading...
