A Review of 2D and 3D Plasmonic Nanostructure Array Patterns: Fabrication, Light Management and Sensing Applications

Abstract: This review article discusses progress in surface plasmon resonance (SPR) of two-dimensional (2D) and three-dimensional (3D) chip-based nanostructure array patterns. Recent advancements in fabrication techniques for nano-arrays have endowed researchers with tools to explore a material’s plasmonic optical properties. In this review, fabrication techniques including electron-beam lithography, focused-ion lithography, dip-pen lithography, laser interference lithography, nanosphere lithography, nanoimprint lithography, and anodic aluminum oxide (AAO) template-based lithography are introduced and discussed. Nano-arrays have gained increased attention because of their optical property dependency (lightmatter interactions) on size, shape, and periodicity. In particular, nano-array architectures can be tailored to produce and tune plasmonic modes such as localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), extraordinary transmission, surface lattice resonance (SLR), Fano resonance, plasmonic whisperinggallery modes (WGMs), and plasmonic gap mode. Thus, light management (absorption, scattering, transmission, and guided wave propagation), as well as electromagnetic (EM) field enhancement, can be controlled by rational design and fabrication of plasmonic nano-arrays. Because of their optical properties, these plasmonic modes can be utilized for designing plasmonic sensors and surfaceenhanced Raman scattering (SERS) sensors

Molecular hot spots in surface-enhanced Raman scattering

The chemical and electromagnetic (EM) enhancements both contribute to surface-enhanced Raman scattering (SERS). It is well-known that the EM enhancement is induced by the intense local field of surface plasmon resonance (SPR). This report shows that the polarizability of the molecules adsorbed on the metal surface can lead to another channel for the EM field enhancement. When aromatic molecules are covalently bonded to the Au surface, they strongly interact with the plasmon, leading to a modification of the absorption spectrum and a strong SERS signal. The effect is seen in both 3 nm-Au nanoparticles with a weak SPR and 15 nm-Au nanoparticles with a strong SPR, suggesting that the coupling is through both EM field and chemical means. Linear-chain molecules on the 3 nm-Au nanoparticles do not have a SERS signal. However, when the aromatic and linear molecules are co-adsorbed, the strong SPR/molecular polarizability interaction spatially extends the local EM field, leading to a strong SERS signal from the linear-chain molecules. The results show that aromatic molecules immobilized on Au can create “hot spots” just like plasmonic nanostructures

Plasmon-induced photonic and energy-transfer enhancement of solar water splitting by a hematite nanorod arra

Plasmonic metal nanostructures offer a promising route to improve the solar energy conversion efficiency of semiconductors. Here we show that incorporation of a hematite nanorod array into a plasmonic gold nanohole array pattern significantly improves the photoelectrochemical water splitting performance, leading to an approximately tenfold increase in the photocurrent at a bias of 0.23 V versus Ag|AgCl under simulated solar radiation. Plasmon-induced resonant energy transfer is responsible for enhancement at the energies below the band edge, whereas above the absorption band edge of hematite, the surface plasmon polariton launches a guided wave mode inside the nanorods, with the nanorods acting as miniature optic fibres, enhancing the light absorption. In addition, the intense local plasmonic field can suppress the charge recombination in the hematite nanorod photoanode in a photoelectrochemical cell. Our results may provide a general approach to overcome the low optical absorption and spectral utilization of thin semiconductor nanostructures, while further reducing charge recombination losses

Plasmon-Induced Photonic And Energy-Transfer Enhancement Of Solar Water Splitting By A Hematite Nanorod Array

Plasmonic metal nanostructures offer a promising route to improve the solar energy conversion efficiency of semiconductors. Here we show that incorporation of a hematite nanorod array into a plasmonic gold nanohole array pattern significantly improves the photoelectrochemical water splitting performance, leading to an approximately tenfold increase in the photocurrent at a bias of 0.23 V versus Ag|AgCl under simulated solar radiation. Plasmon-induced resonant energy transfer is responsible for enhancement at the energies below the band edge, whereas above the absorption band edge of hematite, the surface plasmon polariton launches a guided wave mode inside the nanorods, with the nanorods acting as miniature optic fibres, enhancing the light absorption. In addition, the intense local plasmonic field can suppress the charge recombination in the hematite nanorod photoanode in a photoelectrochemical cell. Our results may provide a general approach to overcome the low optical absorption and spectral utilization of thin semiconductor nanostructures, while further reducing charge recombination losses

Plasmonic hot electrons for sensing, photodetection, and solar energy applications: A perspective

In plasmonic metals, surface plasmon resonance decays and generates hot electrons and hot holes through non-radiative Landau damping. These hot carriers are highly energetic, which can be modulated by the plasmonic material, size, shape, and surrounding dielectric medium. A plasmonic metal nanostructure, which can absorb incident light in an extended spectral range and transfer the absorbed light energy to adjacent molecules or semiconductors, functions as a “plasmonic photosensitizer.” This article deals with the generation, emission, transfer, and energetics of plasmonic hot carriers. It also describes the mechanisms of hot electron transfer from the plasmonic metal to the surface adsorbates or to the adjacent semiconductors. In addition, this article highlights the applications of plasmonic hot electrons in photodetectors, photocatalysts, photoelectrochemical cells, photovoltaics, biosensors, and chemical sensors. It discusses the applications and the design principles of plasmonic materials and devices

Prevalence of pulmonary tuberculosis in western China in 2010–11: a population-based, cross-sectional survey

Background Progress in tuberculosis control in China has been the slowest in western areas, which have the highest prevalence. We assessed the prevalence of pulmonary tuberculosis in the Xinjiang province, China, 10 years after introduction of a control programme based on directly observed treatment, short course. Methods In this population-based, cross-sectional survey, we used a multistage stratifi ed random cluster sample design to estimate the prevalence of smear-positive and bacteriologically confi rmed (either smear positive or culture positive, or both) pulmonary tuberculosis among adults (aged ≥15 years) in Xinjiang who had been resident in their household for the last 6 months. The screening strategy and diagnosis followed WHO guidelines. We estimated prevalence by combining inverse probability weighting and multiple imputation of missing data. We compared our prevalence survey estimates with the ones from the 2010 China national pulmonary tuberculosis survey and the ones from a provincial pulmonary survey done in Xinjiang in 2000. The new smear-positive pulmonary tuberculosis notifi cation rate in 2011 in Xinjiang was obtained to allow the calculation of patient diagnosis rate (PDR). Findings Between Sept 1, 2010, and July 31, 2011, 31 081 individuals were eligible, of whom 29 835 (96·0%) participated in the survey. We identifi ed 50 (0·2%) smear-positive and 101 (0·3%) bacteriologically confi rmed pulmonary tuberculosis cases. The weighted prevalence of smear-positive pulmonary tuberculosis was 170 (95% CI 103–233) per 100 000 people and of bacteriologically confi rmed pulmonary tuberculosis was 430 (249–611) per 100 000 people. Compared with 2000 Xinjiang survey estimates, the prevalence of smear-positive pulmonary tuberculosis has decreased by 26·4% (from 231 [95% CI 148–314] per 100 000 people), whereas the prevalence of bacteriologically confi rmed pulmonary tuberculosis has increased by 17·8% (from 365 [237–493] per 100 000 people). In each age group and sex, the pulmonary tuberculosis prevalence was higher in the 2010–11 Xinjiang survey than in the 2010 national survey. The PDR in 2011 was 0·34 (95% CI 0·25–0·44). Interpretation Despite progress in other parts of China, the prevalence of pulmonary tuberculosis in Xinjiang remains high. The very low PDR suggests poor access to diagnosis and care. Further studies are needed to understand the barriers to diagnosis and care of this population, and eff orts are urgently needed to enhance tuberculosis screening in this area