Optimization of surface coating condition using vapor form of alkanethiol on Cu nano powders for the application of oxidation prevention

There has been a growing interest in metal nano powders recently, and researches on Copper (Cu) nano particles are actively pursued due to its good electrical conductivity and its low prices. However, its easiness to oxidation and corrosion has delayed its research progress in Cu nano particles to be applied in inkjet printed electronics and other related research area. To overcome these problems, new surface coating method on Cu nano particles has been developed using dry process instead of conventional wet coating method. Octanethiol was used as a dry coating material because it has sulfur at the end of monolayer to chemically bond to the surface of fresh non-oxidized Cu nano particles to prevent oxidation. Octanethiol does not bond to oxidized surface of Cu nano particles. Previously, bonding between octanethiol and Cu nano particles, more specifically bonding between Cu surface and Sulfur (S) was analyzed using X-ray Photoelectron Spectroscopy (XPS). As a result, S peak was detected on the coated Cu nano particles, indicating that octanethiol chain has been successfully coated on the surface of Cu nano particles.In this study, optimization of dry coating condition was studied by varying coating time and cycles. XPS was used to analyze the composition of coated material to monitor the change in amount of S and O peaks for each condition. It was found that as the amount of Sulfur increased, the amount of Oxygen decreased and vice versa. This finding indicates that dry coating has suppressed the formation of oxygen on the surface of Cu nano powders by surrounding Cu surface with Sulfur end of octanethiol chain. Based on these experiments, the optimum coating condition for suppressing Cu oxidation was found to be 5 min and 6 cycles. For future work, the lifetime of octanethiol layer on the surface of Cu surface needs to be studied.     

Tunneling Electron Induced Fluorescence from Single Porphyrin Molecules Decoupled by Striped-Phase Octanethiol Self-assembled Monolayer

We investigate tunneling electron induced luminescence from isolated single porphyrin molecules that are decoupled by striped-phase self-assembled monolayer of octanethiol from the underneath Au(111) substrate. Intrinsic single-molecule electroluminescence has been realized by such decoupling at both bias polarities. The photon emission intensity acquired from the molecular lobe is found stronger than that from the molecular center. These re-sults provide useful information on the understanding of electroluminescent behavior and mechanism in molecular tunnel junctions.     

隧道电子激发的辛硫醇条纹相自组装膜上卟啉单分子荧光

利用扫描隧道显微镜诱导发光技术,对单个卟啉分子的电致荧光现象进行了研究. 为了避免金属衬底对单个卟啉分子的荧光淬灭,利用条纹状辛硫醇自组装膜作为脱耦合层,实现了单个中性卟啉分子的电致荧光,并且发现分子荧光的产生呈现双极性特征. 另外,分子瓣上的荧光强度要强于分子中心的荧光强度.