本文選題：SiC　切入點：吸附　出處：《西安科技大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：有害、危險環(huán)境下稀薄氣體的探測一直以來都是微納米器件研究領(lǐng)域的熱門課題。近年來氣體敏感材料切片在氣體吸附脫附過程中表現(xiàn)出來的優(yōu)異特性,特別是良好的介電特性,使得采用氣敏法來檢測瓦斯氣體的濃度成為研究的焦點。氣敏法檢測瓦斯氣體濃度中氣敏材料的選取對氣體濃度探測精度至關(guān)重要,而作為新型氣敏材料的SiC對氣體有良好的吸附特性,在敏感元件領(lǐng)域具有非常高的研究價值。本文中以3種不同比例摻雜Ni原子的SiC(001)切面為氣體敏感吸附基底,使用Material Studio軟件構(gòu)建(3×3)的超晶胞,利用基于第一性原理的密度泛函理論方法模擬計算了CO和CH_4分子在摻雜材料表面的吸附性能。優(yōu)化模型后分別從吸附系統(tǒng)結(jié)構(gòu)變化、吸附能、電荷密度差以及態(tài)密度等幾個方面,對比分析氣體分子在摻雜材料表面4個不同經(jīng)典吸附位置(Top、Bridge、Hcp、Fcc)的吸附特性。在對CO分子進行化學(xué)吸附時得出,在1/9摻雜時Fcc位為最佳吸附位置;1/3摻雜時Bridge位為最佳吸附位置;2/3摻雜時Hcp位為最佳吸附位置;通過不同比例摻雜的對比,得出2/3摻雜比例時對SiC(001)切面的影響最大,不僅在吸附CO分子后系統(tǒng)更加穩(wěn)定,而且吸附過程中電子轉(zhuǎn)移速度加快,作為敏感吸附材料時,電阻率將發(fā)生明顯的變化。在對CH_4分子進行Top位物理吸附時得出,無論是從結(jié)構(gòu)的變化還是從作用過程中態(tài)密度的變化都表明1/9摻雜時的SiC(001)對CH_4的物理吸附更穩(wěn)定。在采集電路的設(shè)計上,耦合儀表放大器與差動放大器采集氣體敏感器件輸出的微弱電壓信號并進行邏輯放大,采用內(nèi)含模數(shù)轉(zhuǎn)換功能的微控制器STM32進行電壓采集,將采集到的電壓信號輸出顯示在4位一體數(shù)碼管上,當(dāng)采集到的電壓值超過報警閾值時進行聲光報警。在Keil軟件中編寫相應(yīng)的電壓采集和顯示輸出程序,利用基于STM32的最小系統(tǒng)、電位器以及4位一體數(shù)碼管搭建實物系統(tǒng)對軟件程序進行測試,結(jié)果表明該系統(tǒng)可實現(xiàn)對稀薄瓦斯氣體的探測和報警。本研究成果可應(yīng)用于礦業(yè)生產(chǎn)生活中,特別是煤礦開發(fā)方面可以減少有害氣體的積累和爆炸的可能性,使得開采環(huán)境更加安全。
[Abstract]:The detection of rarefied gases in hazardous and harmful environments has always been a hot topic in the field of micro and nano devices. In recent years, the slice of gas sensitive materials has shown excellent characteristics in the process of gas adsorption and desorption. Especially because of its good dielectric properties, it is very important to select gas sensitive materials for detecting gas concentration by using gas sensing method to detect the concentration of gas gas. As a new gas sensing material, SiC has good adsorption properties for gas and has a high value in the field of sensitive elements. In this paper, the gas sensitive adsorption substrate is three different proportions doped with Ni atoms. The supercell of 3 脳 3) was constructed by using Material Studio software. The adsorption properties of CO and CH_4 molecules on the surface of doped materials were simulated by density functional theory (DFT) method based on the first principle. After optimizing the model, the adsorption energy and the structure of the adsorption system were changed, respectively. The adsorption characteristics of gas molecules on four different classical adsorption sites on the surface of doped materials such as charge density difference and density of state are compared and analyzed. When the Fcc site is the best adsorption site at 1/9 doping, the Bridge site is the best adsorption site when the Bridge site is the best adsorption site, and the Hcp site is the best adsorption position when the Bridge site is doped with 2 / 3. By the comparison of different doping ratios, it is concluded that the influence of 2/3 doping ratio on the cutting plane of sic _ (1 / 1) is the greatest. Not only is the system more stable after the adsorption of CO molecules, but also the electron transfer rate is accelerated during the adsorption process. As a sensitive adsorption material, the resistivity will change obviously. When the CH_4 molecule is physically adsorbed at Top site, Both the change of structure and the change of density of states in the process of action indicate that the physical adsorption of CH_4 is more stable by 1/9 doped sic _ (001). In the design of the acquisition circuit, The coupling instrument amplifier and differential amplifier collect the weak voltage signal from the gas sensing device and amplify it logically. The voltage is collected by the microcontroller STM32, which contains the function of analog-to-digital conversion. The output of the collected voltage signal is displayed on the 4-bit integrated digital tube. The acousto-optic alarm is carried out when the collected voltage value exceeds the alarm threshold. The corresponding program of voltage acquisition and display output is written in Keil software. The software program is tested by using the minimum system based on STM32, potentiometer and 4-bit digital tube. The results show that the system can detect and alarm rarefied gas. The research results can be used in mining production and life, especially in coal mine development can reduce the accumulation of harmful gas and the possibility of explosion. Make the mining environment safer.
【學(xué)位授予單位】：西安科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TD712.55

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