Novel Chemical Sensor Concept for Neutral Radical Detection in Gas Phase
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Novel Chemical Sensor Concept for Neutral Radical Detection in Gas Phase Vladislav V. Styrov, Alex Y. Kabansky1, Victor P. Grankin, Stanislav Kh. Shigalugov2, and Yuri I. Tyurin3 Physics Department, Azov Sea State Technical University, Mariupol 87500, UKRAINE 1 R&D Department, Cypress Semiconductor, San Jose, CA 95134, U.S.A 2 Physics Department, Noril’sk Industrial Institute, Noril’sk 663310, RUSSIAN FEDERATION 3 Physics Department, Tomsk Polytechnic University, Tomsk 634050, RUSSIAN FEDERATION ABSTRACT A novel concept of solid-state chemical sensors for neutral radical detection in gas-phase and related technique are proposed based on chemiluminescence of sensing materials excited by heterogeneous chemical reactions of radicals on sensor surface. The radical species of interest include H, O, N, O2, CO, SO, NO and others. Surface activated phosphors, nano-phosphors and semiconductor films are good candidates for sensors. The advantages of these sensors are the enhanced sensitivity (~105 at/cm-3 or better), real-time response, reliability, proximate analysis, ability to be fabricated in combination with up-to-date nanotechnologies. INTRODUCTION The energy transferred to the crystal from the heterogeneous chemical reactions may be as high as 3 or more electron-volts per chemical event, which is sufficient to provide excitations of electrons in the crystal (sensor). The related phenomena have been discovered and intensively studied in semiconductors and dielectrics (see [1] and references therein). The assumption of similar electron excitations in metals during gas-surface interactions were made in [2]. Recently, this phenomenon was experimentally discovered by means of Schottky metal-semiconductor contacts [3-5]. Heterogeneous chemiluminescence (HCL) of semiconductors (dielectrics) is the lightemitting relaxation of surface luminescent centers in crystal electronically excited in chemical events on the surface (adsorption, recombination of radicals and/or more complicated reactions) due to direct chemical energy transfer to these centers. The HCL excited in the reactions of adsorption of atomic or molecular radicals is called adsorboluminescence (AL). In case of atomic or radical recombination reactions, HCL is named radical-recombination luminescence - RRL. Both AL and RRL are proved as new sensitive means of radical detection in gas phase [6, 7]. Nanoporous phosphors, other nanostructural luminescent materials with high surface-to-volume ratio become attractive for HCL chemical sensors due to surface mechanism of HCL phenomena. This paper presents a concept of novel chemical sensors based on HCL phenomena and a related technique for measurement of the concentration or flux of gaseous atoms (radicals). THEORETICAL BACKGROUND Two different mechanisms are known to describe recombination reactions of free atoms (radicals) on surfaces. One of them, Rideal-Eley (RE) mechanism, involves a direct collision of an atom impinging on the surface from the gas phase with an atom previously adsorbed. In another one, the
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