Zoval J V, Biernacki P R, Penner R M
Institute for Surface and Interface Science, Department of Chemistry, University of California, Irvine, California 92715-2025.
Anal Chem. 1996 May 1;68(9):1585-92. doi: 10.1021/ac951114+.
Highly oriented pyrolytic graphite (HOPG) surfaces, on which atomically well-defined roughness has been introduced via high-temperature gasification reactions, are investigated by noncontact mode atomic force microscopy (NC-AFM) and Raman spectroscopy both before and after the electrochemical deposition of silver nanocrystallites on these surfaces. Exposure of freshly cleaved HOPG surfaces to an O(2)-rich ambient at 650 °C for a few minutes caused the formation of 1-monolayer-deep, circular etch pits on the HOPG basal plane surface. Silver nanocrystallites were electrochemically deposited onto these etched surfaces at two coverages: 0.5 mC cm(-)(2) (or 5 nmol of Ag(0) cm(-)(2)) and 2.4 mC cm(-)(2) (25 nmol of Ag(0) cm(-)(2)). At the lower coverage, NC-AFM images revealed that silver decorated only the circumference of the circular etch pits, forming a uniform annular ring with an apparent diameter of 200-250 Å and a height of ∼15 Å. At the higher silver coverage, an increase in the height but not the diameter of this annulus was observed, and additional silver nanostructures [Formula: see text] having dimensions of 300-350 Å diameter and 15 Å height [Formula: see text] were observed on atomically smooth regions of the graphite basal plane. The Raman spectroscopy of these surfaces was investigated and compared with spectra for nanocrystallite-modified but unetched HOPG basal plane surfaces and thermally etched surfaces on which no silver was deposited. For for thermally etched HOPG surfaces at either silver coverage, SERS-augmented Raman spectra were obtained in which defect modes of the graphite surface [Formula: see text] derived from "finite" graphite domains at the surface [Formula: see text] were strongly and preferentially enhanced. In addition, an enhanced band near 2900 cm(-)(1) was assigned to ν(OH) from carboxylate moieties present at step edges based on the basis of the observed pH dependence of the enhancement.
通过高温气化反应引入了原子级清晰粗糙度的高度取向热解石墨（HOPG）表面，在这些表面上电沉积银纳米微晶之前和之后，均采用非接触模式原子力显微镜（NC-AFM）和拉曼光谱进行研究。将刚解理的HOPG表面在650℃下暴露于富氧环境中几分钟，导致在HOPG基面表面形成1单层深的圆形蚀刻坑。银纳米微晶以两种覆盖率电化学沉积在这些蚀刻表面上：0.5 mC cm⁻²（或5 nmol Ag(0) cm⁻²）和2.4 mC cm⁻²（25 nmol Ag(0) cm⁻²）。在较低覆盖率下，NC-AFM图像显示银仅装饰圆形蚀刻坑的周边，形成一个表观直径为200 - 250 Å、高度约为15 Å的均匀环形环。在较高银覆盖率下，观察到该环的高度增加但直径未增加，并且在石墨基面的原子级光滑区域观察到了尺寸为直径300 - 350 Å、高度15 Å的额外银纳米结构[公式：见原文]。对这些表面的拉曼光谱进行了研究，并与纳米微晶修饰但未蚀刻的HOPG基面表面以及未沉积银的热蚀刻表面的光谱进行了比较。对于两种银覆盖率下的热蚀刻HOPG表面，均获得了表面增强拉曼散射（SERS）增强的拉曼光谱，其中源自表面[公式：见原文]“有限”石墨域的石墨表面缺陷模式[公式：见原文]被强烈且优先增强。此外，基于观察到的增强的pH依赖性，将2900 cm⁻¹附近的增强带归属于台阶边缘处存在的羧酸盐部分的ν(OH)。
