CARBON NANOTUBES' ARRAYS BASED SURFACE ACOUSTIC WAVE CHEMICAL SENSOR ELEMENT V. V. Barkaline * Belarussian National Technical University * Slobodski proiezd 4-52 Minsk 220025 Belarus e-mail: barkaline@yahoo.com , tel.: +375(017)2399185, fax: +375(017)2313051 Abstract: Prospects of carbon nanotubes’ oriented arrays in chemical sensorics are studied from the viewpoint of acoustic pickup of 100-1000 MHz frequency range. Nanotube arrays are understood as nanostructured dispersion medium bonded by inter-tube molecular interactions modulated by external molecules penetrating into the areas between nanotubes and changing elastic properties of the array. Sensitivity coefficients of such systems are estimated. Keywords: carbon nanotube, surface acoustic wave, chemical sensor. The development of the processes of creation of ordered arrays of carbon nanotubes on various substrates [1,2] seems to be one of the most promising achievements of current nanotechnology. Such arrays may consist of single or multiple wall nanotubes with diameters from dozens to hundreds of Å and lengths up to several mm. Here we discus the prospects of such arrays as chemical sensor elements with surface acoustic wave (SAW) based pickup. SAW chemical sensors are based on the effects of adsorbed molecules on geometrical, elastic and electric properties of gas-sensing layer and corresponding mass-loading of the working surface of substrate carrying SAW (Fig.1). z y x Acoustic channel Electric channel External medium influence ZnO SAW Si Array Fig. 1. SAW chemical sensor with carbon nanotube array sensing element and acoustic and electric output signal These effects lead to SAW phase velocity local changes determining sensor output signal. For SAW propagating along x axis, the relationship between SAW phase velocity V relative changes and changes of layer acoustic properties is shown to be      +   l    L  D + D r = D 11 11 11 2 C C h h A C V kh V V -     ü   l    L  D + D +   l    L  D + D + 55 55 55 66 66 66 C C h h C C C C h h B C ( ) + D + + r - m C B A k ( ) ( ) . h y C C y h C C V 2 D 66 12 66 12 2   ü    D ¶ - ¶ + ¶ ¶ - D r + (1) Here h, C 11 , С 12 , С 55 , С 66 - thickness and elastic modules of layer, m – mass of layer per unit square, r - density of substrate, A, B, C, D – parameters characterizing SAW energy distribution across the substrate thickness, k – SAW wave number. A, B, C, D values for various silicon substrates are presented in Table 1. For all cases one has A<B<C. Table 1. Substrate factors in SAW phase velocity sensitivity for various crystallographic orientations of substrate Euler angles, deg. m 100 A 100 C 100 B 100 D 45 90 90 11.3 16.5 0 0 45 90 35 5.1 13.7 0.3 0 45 90 0 4.1 12.2 0 0 45 54.74 0 3.1 9.3 1.6 -2.2 0 0 45 10.2 18.5 0 0 0 0 0 11.6 17.4 0 0 At present paper we study the behavior of sensing layer composed from ordered array of carbon nanotubes. Volume part of nanotubes in sensing layer will be denoted as x. Surface mass density of layer can be represented as x  + x -  = tube ad m ) 1 ( m m , (2) where m ad and m tube are squared mass densities of adsorbate and nanotubes, respectively. Effective elastic modules of layer are defined as: x  + x -  = tube IJ er int IJ IJ C ) 1 ( C С , (3) PDF created with FinePrint pdfFactory Pro trial version www.pdffactory.com