Chaoguang Wang

Simple, fast, and cost-effective fabrication of wafer-scale nanohole arrays on silicon for antireflection

A simple, fast, and cost-effective method was developed in this paper for the high-throughput fabrication of nanohole arrays on silicon (Si), which is utilized for antireflection. Wafer-scale polystyrene (PS) monolayer colloidal crystal was developed as templates by spin-coating method. Metallic shadow mask was prepared by lifting off the oxygen etched PS beads from the deposited chromium film. Nanohole arrays were fabricated by Si dry etching. A series of nanohole arrays were fabricated with the similar diameter but with different depth. It is found that the maximum depth of the Si-hole was determined by the diameter of the Cr-mask. The antireflection ability of these Si-hole arrays was investigated. The results show that the reflection decreases with the depth of the Si-hole. The deepest Si-hole arrays show the best antireflection ability (reflection 600 nm), which was about 28 percent of the nonpatterned silicon wafers reflection. The proposed method has the potential for high-throughput fabrication of patterned Si wafer, and the low reflectivity allows the application of these wafers in crystalline silicon solar cells.

Performance Improving Method of Aligned Silver Nanorod by Grafting Au@Ag Core–Shell Nanoparticles for Surface-Enhanced Raman Scattering

A simple method for improving surface-enhanced Raman scattering (SERS) performance of aligned silver nanorod (Ag NR) array was investigated. This method was to construct a kind of hybrid substrate by grafting Au@Ag core–shell nanoparticles (NPs) into Ag NR array using poly(2-vinylphridine) (P2VPy) as a bridging agent. The hybrid substrate yielded excellent SERS performance as its detection limit improved from 10−6 M to 10−8 M using trans-1,2-bis(4-pyridyl)ethylene (BPE) as probe molecule, which was increased by two orders of magnitude compared with Ag NR array substrate. The significant improvement of SERS performance of Ag NR arrays was attributed to the addition of Au@Ag core–shell NPs. As a result of surface plasmon resonance generated by the interaction of electromagnetic (EM) (IAEM) filed between NP and NR structures, increasing hotspots were found at the connections of NPs and NRs, the gaps of adjacent rods, and the gaps of two particles consequently. These results were validated by the finite difference time domain (FDTD) calculation. Besides, hybrid substrate shows good performance in stability and reproducibility. The proposed method was simple and robust, which promoted SERS performance of Ag NR array effectively, showing great potential in the application of SERS substrate fabrication and SERS-based bio-chemical sensing.

Antireflection characteristics of inverted nanopyramid arrays fabricated by low-cost nanosphere lithography technology

A simple and effective process based on nanosphere lithography for the fabrication of periodic inverted nanopyramid structure is presented in this article. The prepared nanostructure has almost a drop of 40% in the average reflectance at normal incidence, when compared with its corresponding bare silicon surface. Moreover, we obtained the reflection spectra for bare silicon substrate and prepared nanostructure through experiments and numerical calculations, and the results agreed well with each other, respectively. Therefore, we can combine the simulation method and fabrication method together to optimize the nanostructured antireflection coatings for better antireflection characteristics, and this methodology is robust and promising for the development of crystalline silicon solar cells. We further discussed the influences of pyramid size and the lattice constant of the nanopyramid array on the antireflection effect by numerical calculation, and we got a conclusion that the antireflection effect is positively correlated with the area-ratio defined as the ratio of the sum of the area of the nanopyramid holes in a unit cell to the area of a unit cell. Finally, we provide some direction and help for other researchers about the antireflection application of inverted nanopyramid arrays.