Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films
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Case Western Reserve University School of Graduate Studies / OhioLINK
1995
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=case1057953585 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-case10579535852021-08-03T05:31:04Z Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films Wang, Hong-Ying Gas sensing mechanism study crystal structure determination phthalocyanine Langmuir-Blodgett films In the present research we have investigated the use of phthalocyanine Langmuir-Blodgett films as gas sensors. The fabrication and testing of the gas sensors, the study and modeling of the gas sensing mechanism, and the crystal structure determination of gas sensing films and the study of the effect of film structure on the gas sensor performance are reported. The silicon-based gas sensor substrate consists of interdigitated electrodes which measure the conductivity change of the gas sensing film integrated with a heating element and a temperature sensing diode to control and monitor the temperature of the sensor. The gas sensing materials used are ((C6H13)3SiOSiPcOGePcOH) (Si-Ge Pc dimer) and ((C6H13)3SiO(SiPcO)<sub>2</sub>H) (Si-Si Pc dimer), both specially designed and prepared for the Langmuir-Blodgett film deposition. The gas sensors fabricated were tested in halogen gases at different temperature, film thickness and gas concentration. The sensors show high sensitivity and fast response to halogen gases. The gas sensing mechanism was studied by proposing a model considering the gas adsorption and desorption on the film surface as rate processes and Fickian diffusion through the film. The model fits the experimental data very well. The solution obtained from the model for sensor response has multiple time constants, depending on the sensing film thickness, temperature, and diffusion coefficient. The conductance change from the gas exposure is a function of gas exposure time, gas concentration, film thickness, and film temperature. The crystal structural analysis of the gas sensing films was carried out using electron diffraction and synchrotron X-ray radiation. The structure refinement was done using the linked-atom least-squares (LALS) method. The phthalocyanine Langmuir-Blodgett film structures resulting from the film deposition mechanism for both Si-Si and Si-Ge are very different from the Si-Si single crystal structure. The film crystal structure belongs to the monoclinic space group Pn, while the single crystal structure belongs to the triclinic space group P1. The calculated film density is 0.990 g/cm<sup>3</sup> for Si-Si and 1.015 g/cm<sup>3</sup> for Si-Ge, much lower than the calculated density (1.333 g/cm<sup>3</sup>) for the Si-Si single crystal. It is the trihexyl tail group in both molecules that breaks the symmetry of the system and gives rise to the low film density. The low film density helps explain the gas sensor performance and the diffusion model. It is the low film density that facilitates the gas diffusion through the film, which gives rise to the fast response of the gas sensor. 1995 English text Case Western Reserve University School of Graduate Studies / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=case1057953585 http://rave.ohiolink.edu/etdc/view?acc_num=case1057953585 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Gas sensing mechanism study crystal structure determination phthalocyanine Langmuir-Blodgett films |
| spellingShingle |
Gas sensing mechanism study crystal structure determination phthalocyanine Langmuir-Blodgett films Wang, Hong-Ying Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films |
| author |
Wang, Hong-Ying |
| author_facet |
Wang, Hong-Ying |
| author_sort |
Wang, Hong-Ying |
| title |
Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films |
| title_short |
Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films |
| title_full |
Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films |
| title_fullStr |
Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films |
| title_full_unstemmed |
Gas sensing mechanism study and crystal structure determination of phthalocyanine Langmuir-Blodgett films |
| title_sort |
gas sensing mechanism study and crystal structure determination of phthalocyanine langmuir-blodgett films |
| publisher |
Case Western Reserve University School of Graduate Studies / OhioLINK |
| publishDate |
1995 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=case1057953585 |
| work_keys_str_mv |
AT wanghongying gassensingmechanismstudyandcrystalstructuredeterminationofphthalocyaninelangmuirblodgettfilms |
| _version_ |
1719421212333965312 |