烷硫醇在Ge(100)表面上的吸附及熱分解反應

Adsorption and Thermal Decomposition of Alkanethiols on Ge(100) surface

李威霖(Wei-Lin Li)

指導教授 ： 洪偉修

國立臺灣師範大學/理學院/化學系/碩士(2007年)

摘要

利用程溫脫附儀(TPD)及光電子能譜儀(XPS)來探測硫化氫(H2S)及烷硫醇(R–SH，R = CH3，C2H5及C4H9)在鍺晶體表面上的吸附及熱分解反應。TPD是用來偵測表面上經由熱分解而脫附的產物，而XPS是用來鑑定熱分解過程中的表面化學組態。
在100K時，硫化氫曝露到鍺表面即會斷硫氫鍵，形成表面硫氫基及表面氫。H2，H2S及GeS是硫化氫在鍺表面上的熱分解脫附產物。短鏈的烷硫醇較長鏈的烷硫醇反應性為高，較容易進行脫氫反應產生表面烷基硫。100K時，甲硫醇分子在表面上即會分解為甲基硫和氫原子，但乙硫醇及丁硫醇分子，除了會分解為烷基硫及氫原子外，亦會以分子的形式吸附在表面上，而分子吸附的烷硫醇至320K時即會完全分解成烷基硫。隨著升溫，所有的烷基硫會進行兩個競爭反應 – 一部分進行重結合反應形成烷硫醇分子脫附，一部分斷硫碳鍵形成表面烷基及硫原子。
甲基硫在570K左右會分解形成表面甲基及硫原子，此表面甲基，在725K時，大部分直接脫附，小部分和氫原子結合成甲烷脫附。乙基硫在650K時，以β-hydride elimination反應脫附出乙烯及氫分子。丁基硫一樣進行脫去β-hydride而脫附出丁烯。殘存在表面上的硫原子在695K時以GeS的形式脫附。

關鍵字

鍺 ； 烷硫醇

並列摘要

The adsorptions and thermal decompositions of hydrogen sulfide (H2S) and alkanethiols (R–SH , where R = CH3 , C2H5 , and C4H9) on the Ge(100) surface were investigated with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation. The TPD measurement was ulitized to monitor the desorption products of the thermal decompositions. The surface intermediate species formed on the surface were characterized with XPS.
Adsorption of H2S results in the formation of hydrogen and HS via dissociation of the sulfhydryl hydrogen (–SH) on the Ge surface at 100 K. H2, H2S, and GeS were the desorption products of thermal decomposition. The alkanethiol molecule with a shorter alkyl chain is more reactive to deprotonate and form a alkanethiolate on the Ge(100) surface. The chemisorbed CH3SH dissociates to yield CH3S and H, whereas C2H5SH and C4H9SH adsorb both molecularly and dissociatively on Ge(100) at 100K. All chemisorbed C2H5SH and C4H9SH molecules can deprotonate to form additional surface thiolates and hydrogen below 320K. Upon raising the temperature, all the thiolates species undergo two competitive reactions – recombinative desorption of alkanethiols and decomposition via the scission of the S?C bond to form surface alkyl group and sulfur.
The CH3S decomposes to form surface CH3 and S at 570 K. The resulting CH3 can either desorb directly or combine with surface hydrogen to evolve CH4 at 725 K. The surface C2H5 obtained from the decomposition of C2H5SH produces C2H4 and H2 through β-hydride elimination at 650 K. The surface C4H9 group resulting from C4H9SH undergoes an exclusive elimination of β-hydride to form C4H8. The deposited sulfur desorbs in the form of GeS when the surface is heated above 695K.

並列關鍵字

Ge ； alkanethiols

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