Kelvin probe force microscopy (KFM) was applied to two-dimensional profiling of silicon pn-structures covered with a 2 nm-thick oxide layer. The surface potential contrast between the p- and n-type regions depended on the hydrophobicity of the oxide surface when KFM imaging was conducted in air with a relative humidity of more than 50%. By decreasing the density of surface hydroxyl groups on the oxide layer through thermal annealing, the potential contrast between the p- and n-type regions increased. While there was no detectable contrast on samples covered with hydrophilic oxide with a water contact angle of almost 0°, contrast increased to greater than 50 mV on the samples covered with hydrophobic oxide with a water contact angle of about 80°. However, when KFM imaging was conducted in a dry nitrogen atmosphere with relative humidity less than 0.6%, a clear potential contrast of about 50 mV could be acquired even on samples covered with the hydrophilic oxide layer. Since samples with less adsorbed water on their surface showed greater potential contrast, contrast degradation is attributed to a shielding effect of the adsorbed water layer.
Micropatterning techniques using vacuum ultra-violet light at 172 nm in wavelength and an
ultra-violet laser at 244 nm were applied to organosilane self-assembled monolayers
(SAMs) formed on Si substrates covered with a 2 nm thick oxide layer. These
SAMs were prepared from precursors, that is, octadecyltrimethoxysilane (ODS) or
p-chloromethylphenyltrimethoxysilane (CMPhS). Polar functional groups such as COOH
were generated through photochemical oxidation of the SAMs. Furthermore, the SAMs
were simultaneously etched and finally removed from the photoirradiated area. Surface
potentials of the photoirradiated areas at various irradiation dose rates were measured by
Kelvin-probe force microscopy (KFM) using the unirradiated area on each of the
photopatterned samples as a reference. Changes in the surface chemical composition
of the SAMs could be clearly and sensitively measured by KFM through the
difference in surface potential between the irradiated and unirradiated SAMs.
Articles you may be interested inReversible work function changes induced by photoisomerization of asymmetric azobenzene dithiol selfassembled monolayers on gold Appl. Phys. Lett. 93, 083109 (2008); 10.1063/1.2969468 Micropatterning organosilane self-assembled monolayers with plasma etching and backfilling techniques J. Vac. Sci. Technol. B 23, 354 (2005); 10.1116/1.1861041Organosilane self-assembled monolayers directly linked to the diamond surfaces A photopatterning process of an alkylsilane self-assembled monolayer ͑SAM͒ using vacuum ultraviolet ͑VUV͒ light at 172 nm has been studied by characterizing the VUV-irradiated SAM surfaces through lateral force microscopy ͑LFM͒ and Kelvin-probe force microscopy ͑KFM͒. The SAM was formed from n-octadecyltrimethoxysilane on a Si substrate covered with a 2-nm thick oxide layer. Due to VUV irradiation in the presence of atmospheric oxygen, polar functional groups, e.g., COOH, were generated through photochemical oxidation of the SAM which was gradually etched. Finally, the SAM was completely removed from the VUV-irradiated region. Relative frictional forces and surface potentials of the VUV-irradiated regions at various irradiation dose rates were measured by LFM and KFM using the unirradiated regions on each sample as a reference. Changes in the surface chemical composition of the SAM could be measured by these scanning probe microscopic methods. The LFM contrast increased monotonically with the increase in the dose rate, while the surface potential contrast measured by KFM showed a characteristic feature. At a certain dose rate of 10-15 J/cm 2 , VUV-irradiated SAMs showed particularly lower surface potentials than the other SAM surfaces with different dose rates. This is most likely because COOH groups, which were considered negatively charged in part, had been accumulated on the surfaces. LFM and KFM measurements are promising in order to probe chemistries on organic thin films proceeding in small domains with a scale.
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