Wang Wechung Maria, Stoltenberg Randall M, Liu Shuhong, Bao Zhenan
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
ACS Nano. 2008 Oct 28;2(10):2135-42. doi: 10.1021/nn8005416.
Various methods for the patterned assembly of metal nanoparticles have been developed in order to harness their unique electrical and optical properties for device applications. This paper discusses a method for direct writing of Au nanoparticles at nanoscale resolution using dip-pen nanolithography. First, a procedure was developed for increasing the loading of Au nanoparticles onto AFM tips to prolong patterning life. AFM tips were subsequently imaged by scanning electron microscopy to determine ink coverage and to gain insight into the deposition process. Next, surface interactions, relative humidity, and writing speed were controlled to determine an optimal range of conditions for deposition. Various ink-substrate combinations were studied to elucidate the dependence of deposition on interactions between Au nanoparticles and the substrate surface; inks consisted of positively and negatively charged particles, and substrates were SiO(2) surfaces modified as hydrophilic or hydrophobic and interacted electrostatically or covalently with Au nanoparticles. Results indicate that a highly hydrophilic surface is required for Au nanoparticle deposition, unless covalent binding can occur between the Au and substrate surface. The optimal range of relative humidity for patterning was found to be 40-60%, and Au nanoparticle deposition was not sensitive to writing speeds ranging from 0.01 to 2 microm/s.
为了将金属纳米颗粒独特的电学和光学特性应用于器件，人们开发了各种用于其图案化组装的方法。本文讨论了一种使用蘸笔纳米光刻技术以纳米级分辨率直接写入金纳米颗粒的方法。首先，开发了一种增加金纳米颗粒在原子力显微镜（AFM）针尖上的负载量以延长图案化寿命的程序。随后通过扫描电子显微镜对AFM针尖进行成像，以确定墨水覆盖率并深入了解沉积过程。接下来，控制表面相互作用、相对湿度和写入速度，以确定沉积的最佳条件范围。研究了各种墨水 - 基底组合，以阐明沉积对金纳米颗粒与基底表面之间相互作用的依赖性；墨水由带正电和带负电的颗粒组成，基底是修饰为亲水或疏水的SiO₂表面，并与金纳米颗粒发生静电或共价相互作用。结果表明，除非金与基底表面之间能发生共价结合，否则金纳米颗粒沉积需要高度亲水的表面。发现图案化的最佳相对湿度范围为40 - 60%，并且金纳米颗粒沉积对0.01至2微米/秒的写入速度不敏感。
