Thermal Evaporation Method

Skell and Owen have studied the reactions of Si atoms with methylsilanes by heating solid silicon, resistively, to 1400°C in vacuo followed by co-condensation with the substrates on the liquid-nitrogen-cooled walls. The silicon vapor thus obtained may contain some Si2 and Si3 species, but the monoatomic Si atoms should be predominant at low pressures.  

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Solid materials vaporize when heated to sufficiently high temperatures this process may proceed through the liquid phase. A thin film is obtained by the condensation of the vapor onto a colder substrate [4]. This thermal evaporation method is applied to deposit films of inorganic materials, such as metals and their alloys. However, the technique is being used increasingly for the formation of layers of low molecular weight organic compounds. 

Thermal evaporation of PANI has been also developed to fabricate PANI thin film by vacuum deposition of PANI powder on the reference electrode [310]. The chemically synthesized PANI powder was formed in pellet type and the pelletized PANI was evaporated on glass substrates at a pressure of 10 mm Hg to form PANI thin film. The pre-cleaned glass substrate was covered uniformly with PANI thin film and this thin film was utihzed as a carbon monoxide sensor. Thus, thermal evaporation method could be used for thin film formation of conducting polymer nanomaterials [311-313]. 

In the thermal evaporation method, the organic material used should be of low molecular weight. It can be deposited under high vacuum without decomposition. One advantage of thermal evaporation is that multiple layers of organic thin films can be deposited uniformly over a large area. As a result, device characteristics can be controlled by changing the materials and thickness. 

Shaalan NM, Yamazaki T, Kikuta T (2011) Influence of morphology and structure geometry on NO gassensing characteristics of Sn02 nanostructures synthesized via a thermal evaporation method. Sens Actuators B 153 11-16... 

Fabrication of low dimensional SnOz, that is, nanorods/wires and nanotubes, is one such approach to circumvent this problem. SnOz NWs can be prepared on a Si substrate via thermal evaporation method combined with self-catalyzed procedure, the as-prepared... 

Yadav BC, Pandey NK, Srivastava A, Sharma P (2007) Optictil humidity sensors based on titania films fabricated by sol-gel and thermal evaporation methods. Meas Sd Technol 18 260-264 Yajima T, Iwahara H, Uchida H, Koide K (1990) Relation between proton conduction and concentration of oxide ion vacancy in SrCe03 based sintered oxides. SoUd State Ionics 40-41 914-917 Yajima T, Iwahara H, Koide K, Yamamoto K (1991) CaZrOj-type hydrogen and steam sensors trial fabrication and their characteristics. Sens Actuators B 5 145-147... 

Reflective electrodes are readily obtained by the evaporation of metals—for example, aluminum or chromium. Other coatings such as layers of insulating dielectrics are also used to obtain specular surfaces. These can be deposited by both electron-beam and thermal-evaporation methods. ... 

Synthesis and Growth Mechanism of SiC/Si02 Core-Shell Nanowires by Thermal Evaporation Method... 

SiCNWs can be fabricated by several methods for example, chemical vapor deposition (CVD), carbon nanotubes templates, laser ablation and thermal evaporation. Most of these methods need special apparatuses and complicated operation, and some of them need catalyst which reduces the purity and quality of SiCNWs. Thermal evaporation method is a low cost and un-complex way to fabricate SiCNWs using pre-oxidized silicon powder and methane gas as precursors without any metal catalyst. High yield of products are obtained per one synthesis. 

Many SiCNWs formation mechanisms such as vapor-solid mechanism (VS), vapor-liquid-solid mechanism (VLS) and oxide-assist growth (OAG) have been proposed. It is needed to clarify the formation mechanism of SiCNWs synthesized by thermal evaporation method for improvement of the product quantity, which leads to the sufficient amount of SiCNWs for the application researches. Various chemical reactions have been discussed but there are no experimental results about exhaust gas from the SiCNWs production system and no direct observation of the formation of SiCNWs. 

After synthesis process, a white-blue wool-like SiCNWs product was obtained inside the mullite boat between silicon powder and alumina fiber net. SiCNW synthesized by the thermal evaporation method had a wire shape up to 1 mm long and very smooth surface as shown in Fig. 2. From XRD, TEM and FT-IR characterizations in our previous work [5], it was confirmed the SiCNWs produced by this process show P-SiC phase without any impurity peaks in XRD and had a single crystal P-SiC core ranging from 20 to 80 nm in diameter and low-crystalline Si02 shell about 10-20 nm thick. 

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