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There are two main approaches which are used to form hybrid materials: 1. Building block approach: A well-defined preformed matrix is applied to react with building blocks to form the final hybrid material. Regularly, the matrix consists of at least one functional group that allows an interaction with the building blocks. A representative example of this approach is the bonding of organic molecules to silicon surfaces. 2. In situ formation of the components: One or more structural units are formed from the precursors that are transformed into a novel network structure. In these cases well-defined discrete molecules are transformed to multidimensional structures, which often show totally different properties from the original precursors. Typical examples of this approach are polymer reactions and Sol-Gel techniques. We use the building block approach since it has a main advantage associated with the in situ formation in which the structural unit will remain well-defined and usually does not suffer from significant structural changes during the hybrid-matrix formation. Additionally, the building blocks or the matrix can be designed independently in such a way to give the best performance and to be designed to our desire. For example polar or non-polar molecules can be attached to the silicon matrix for sensing application or for FETs applications. 2.2. Chlorination/Alkylation process The organic building blocks were connected to SiNW surfaces following the building-block approach. We report on the functionalization of SiNWs with alkyl chains using a versatile two step chlorination/alkylation process [8]. The two step process found to be gentle in the sense that it did not break the matrix (i.e.) SiNWs or change their diameters. The SiNWs were terminated with alkyl chains using a two-step chlorination/alkylation route (see Figure 1). Before any chemical treatment, each sample was cleaned by N 2 flow. After being cleaned, H-terminated SiNWs were prepared by etching the amorphous SiO x coating by exposing the SiNWs to buffered HF solution (pH=5) for 60 s and then NH 4 F for 30 s. The samples were then rinsed in water for <10 s to limit oxidation, dried in flowing N 2 (g) for 10 s, and immersed into a saturated solution of PCl 5 in C 6 H 5 Cl (0.65 M) that contained a few grains of C 6 H 5 OOC 6 H 5 that act as a radical initiator. The reaction solution was heated to 90-100 °C for 5-7 min. Then the sample was removed from the reaction solution and rinsed in tetrahydrofuran (THF) followed by rinsing in methanol and then dried under a stream of N 2 (g). The Chlorine (Cl) terminated SiNWs were alkylated by immersion in 0.5 M alkyl Grignard, R-MgCl, in THF, with R= methyl (CH 3 ; hereinafter C1), ethyl (CH 3 CH 2 ; hereinafter C2), propyl (CH 3 (CH 2) 2 ; hereinafter C3), butyl (CH 3 (CH 2) 3 ; hereinafter C4), pentyl (CH 3 (CH 2) 4 ; hereinafter C5), or hexyl (CH 3 (CH 2) 5 ; hereinafter C6), or Octyl(CH 3 (CH 2) 7 ; hereinafter C8), or Nonyl(CH 3 (CH 2) 8 ; hereinafter C9), or Decyl(CH 3 (CH 2) 7 ; hereinafter C10). The ...
There are two main approaches which are used to form hybrid materials: 1. Building block approach: A well-defined preformed matrix is applied to react with building blocks to form the final hybrid material. Regularly, the matrix consists of at least one functional group that allows an interaction with the building blocks. A representative example of this approach is the bonding of organic molecules to silicon surfaces. 2. In situ formation of the components: One or more structural units are formed from the precursors that are transformed into a novel network structure. In these cases well-defined discrete molecules are transformed to multidimensional structures, which often show totally different properties from the original precursors. Typical examples of this approach are polymer reactions and Sol-Gel techniques. We use the building block approach since it has a main advantage associated with the in situ formation in which the structural unit will remain well-defined and usually does not suffer from significant structural changes during the hybrid-matrix formation. Additionally, the building blocks or the matrix can be designed independently in such a way to give the best performance and to be designed to our desire. For example polar or non-polar molecules can be attached to the silicon matrix for sensing application or for FETs applications. 2.2. Chlorination/Alkylation process The organic building blocks were connected to SiNW surfaces following the building-block approach. We report on the functionalization of SiNWs with alkyl chains using a versatile two step chlorination/alkylation process [8]. The two step process found to be gentle in the sense that it did not break the matrix (i.e.) SiNWs or change their diameters. The SiNWs were terminated with alkyl chains using a two-step chlorination/alkylation route (see Figure 1). Before any chemical treatment, each sample was cleaned by N 2 flow. After being cleaned, H-terminated SiNWs were prepared by etching the amorphous SiO x coating by exposing the SiNWs to buffered HF solution (pH=5) for 60 s and then NH 4 F for 30 s. The samples were then rinsed in water for <10 s to limit oxidation, dried in flowing N 2 (g) for 10 s, and immersed into a saturated solution of PCl 5 in C 6 H 5 Cl (0.65 M) that contained a few grains of C 6 H 5 OOC 6 H 5 that act as a radical initiator. The reaction solution was heated to 90-100 °C for 5-7 min. Then the sample was removed from the reaction solution and rinsed in tetrahydrofuran (THF) followed by rinsing in methanol and then dried under a stream of N 2 (g). The Chlorine (Cl) terminated SiNWs were alkylated by immersion in 0.5 M alkyl Grignard, R-MgCl, in THF, with R= methyl (CH 3 ; hereinafter C1), ethyl (CH 3 CH 2 ; hereinafter C2), propyl (CH 3 (CH 2) 2 ; hereinafter C3), butyl (CH 3 (CH 2) 3 ; hereinafter C4), pentyl (CH 3 (CH 2) 4 ; hereinafter C5), or hexyl (CH 3 (CH 2) 5 ; hereinafter C6), or Octyl(CH 3 (CH 2) 7 ; hereinafter C8), or Nonyl(CH 3 (CH 2) 8 ; hereinafter C9), or Decyl(CH 3 (CH 2) 7 ; hereinafter C10). The ...
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