Molecular Self-Assembly at Bare Semiconductor Surfaces: Preparation and Characterization of Highly Organized Octadecanethiolate Monolayers on GaAs(001)
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- 作者：Christine L. McGuiness ; Andrey Shaporenko ; Carole K. Mars ; Sundararajan Uppili ; Michael Zharnikov ; and David L. Allara
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：April 19, 2006
- 年：2006
- 卷：128
- 期：15
- 页码：5231 - 5243
- 全文大小：446K
- 年卷期：v.128,no.15(April 19, 2006)
- ISSN：1520-5126
文摘
Through rigorous control of preparation conditions, organized monolayers with a highlyreproducible structure can be formed by solution self-assembly of octadecanethiol on GaAs (001) at ambienttemperature. A combination of characterization probes reveal a structure with conformationally orderedalkyl chains tilted on average at 14 ± 1
from the surface normal with a 43 ± 5 twist, a highly oleophobicand hydrophobic ambient surface, and direct S-GaAs attachment. Analysis of the tilt angle and film thicknessdata shows a significant mismatch of the average adsorbate molecule spacings with the spacings of anintrinsic GaAs(001) surface lattice. The monolayers are stable up to ~100 C and exhibit an overall thermalstability which is lower than that of the same monolayers on Au{111} surfaces. A two-step solution assemblyprocess is observed: rapid adsorption of molecules over the first several hours to form disordered structureswith molecules lying close to the substrate surface, followed by a slow densification and asymptotic approachto final ordering. This process, while similar to the assembly of alkanethiols on Au{111}, is nearly 2 ordersof magnitude slower. Finally, despite differences in assembly rates and the thermal stability, exchangeexperiments with isotopically tagged molecules show that the octadecanethiol on GaAs(001) monolayersundergo exchange with solute thiol molecules at roughly the same rate as the corresponding exchangesof the same monolayers on Au{111}.
from the surface normal with a 43 ± 5 twist, a highly oleophobicand hydrophobic ambient surface, and direct S-GaAs attachment. Analysis of the tilt angle and film thicknessdata shows a significant mismatch of the average adsorbate molecule spacings with the spacings of anintrinsic GaAs(001) surface lattice. The monolayers are stable up to ~100 C and exhibit an overall thermalstability which is lower than that of the same monolayers on Au{111} surfaces. A two-step solution assemblyprocess is observed: rapid adsorption of molecules over the first several hours to form disordered structureswith molecules lying close to the substrate surface, followed by a slow densification and asymptotic approachto final ordering. This process, while similar to the assembly of alkanethiols on Au{111}, is nearly 2 ordersof magnitude slower. Finally, despite differences in assembly rates and the thermal stability, exchangeexperiments with isotopically tagged molecules show that the octadecanethiol on GaAs(001) monolayersundergo exchange with solute thiol molecules at roughly the same rate as the corresponding exchangesof the same monolayers on Au{111}.