Techane Sirnegeda D, Gamble Lara J, Castner David G
National ESCA and Surface Analysis Center for Biomedical Problems, Departments of Chemical Engineering and Bioengineering, University of Washington Box 351750, Seattle, WA 98195-1750, USA.
J Phys Chem C Nanomater Interfaces. 2011 Apr 21;115(19):9432-9441. doi: 10.1021/jp201213g.
Gold nanoparticles (AuNPs) with 14, 25 and 40nm diameters were functionalized with different chain length (C6, C8, C11 and C16) carboxylic acid terminated alkanethiol self-assembled monolayers (COOH-SAMs). X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to examine the changes in surface chemistry as both AuNP diameter and SAM chain length were varied. COOH-SAMs on flat gold surfaces were also examined and compared to the COOH-SAM on AuNP results. For a given surface, as the COOH-SAM chain length increased the XPS C/Au atomic ratio increased due to an increased number of carbon atoms per molecule in the overlayer and an increased attenuation of the Au substrate signal. For the C16 COOH-SAMs, as the size of AuNPs decreased the XPS C/Au atomic ratio and the apparent SAM thickness increased due to the increased curvature of the smaller AuNPs. The C16 COOH-SAMs on the flat Au had the lowest XPS C/Au atomic ratio and apparent SAM thickness of any C16 COOH-SAM covered Au surface. The effective take-off angles of the COOH-SAMs were also calculated by comparing the apparent thickness of COOH-SAMs with literature values. The effective take-off angle for C16 COOH-SAM on 14nm, 25nm and 40nm diameter AuNPs and flat Au were found to be 57°, 53°, 51° and 39°, respectively, for data acquired in a mode that collects a wide range of photoelectron take-off angles. The effective take-off angle for C16 COOH-SAM on 14nm AuNP and flat Au decreased to 52° and 0°, respectively, for data acquired in a mode that collects a narrow range of photoelectron take-off angles. The ToF-SIMS results showed similar changes in surface chemistry with COOH-SAM chain length and AuNP size. For example, the ratio of the sum of the C(1-4)H(x)O(y) positive ion intensities to the sum of the Au-containing positive ions intensities increased with decreasing AuNP size and increasing COOH-SAM chain length. Fourier transform IR spectroscopy in the attenuated total reflectance mode (FTIR-ATR) was used to characterize the crystallinity of the COOH-SAMs. The CH(2) stretching frequencies decreased with increasing COOH-SAM chain length on flat Au. The C16 COOH-SAM on the 14nm AuNPs exhibited a crystalline-like CH(2) stretching frequency. The size, size distribution, shapes and solution stability of AuNPs were investigated with transmission electron microscopy (TEM) and UV/VIS spectroscopy. As the average diameter of the AuNPs decreased the size distribution became narrower and the shape became more spherical.
直径为14纳米、25纳米和40纳米的金纳米颗粒（AuNPs）用不同链长（C6、C8、C11和C16）的羧酸封端烷硫醇自组装单分子层（COOH - SAMs）进行功能化处理。随着AuNP直径和SAM链长的变化，使用X射线光电子能谱（XPS）和飞行时间二次离子质谱（ToF - SIMS）来检测表面化学的变化。还对平坦金表面上的COOH - SAMs进行了检测，并与AuNP上的COOH - SAM结果进行比较。对于给定的表面，随着COOH - SAM链长增加，XPS C/Au原子比增加，这是由于覆盖层中每个分子的碳原子数量增加以及Au基底信号的衰减增加。对于C16 COOH - SAMs，随着AuNPs尺寸减小，XPS C/Au原子比和表观SAM厚度增加，这是因为较小AuNPs的曲率增加。平坦Au上的C16 COOH - SAMs在所有被C16 COOH - SAM覆盖的Au表面中具有最低的XPS C/Au原子比和表观SAM厚度。还通过将COOH - SAMs的表观厚度与文献值进行比较来计算COOH - SAMs的有效出射角。对于在收集宽范围光电子出射角的模式下获取的数据，发现直径为14纳米、25纳米和40纳米的AuNPs以及平坦Au上C16 COOH - SAM的有效出射角分别为57°、53°、51°和39°。对于在收集窄范围光电子出射角的模式下获取的数据，14纳米AuNP和平坦Au上C16 COOH - SAM的有效出射角分别降至52°和0°。ToF - SIMS结果显示，随着COOH - SAM链长和AuNP尺寸的变化，表面化学也有类似变化。例如，C(1 - 4)H(x)O(y)正离子强度总和与含Au正离子强度总和的比值随着AuNP尺寸减小和COOH - SAM链长增加而增加。使用衰减全反射模式的傅里叶变换红外光谱（FTIR - ATR）来表征COOH - SAMs的结晶度。在平坦Au上，CH(2)伸缩频率随着COOH - SAM链长增加而降低。14纳米AuNPs上的C16 COOH - SAM表现出类似晶体的CH(2)伸缩频率。用透射电子显微镜（TEM）和紫外/可见光谱研究了AuNPs的尺寸、尺寸分布、形状和溶液稳定性。随着AuNPs平均直径减小，尺寸分布变窄，形状变得更接近球形。
