We propose and experimentally demonstrate a new plasmonic nonlinear light generation (NLG) structure, termed plasmonic-enhanced, charge-assisted second-harmonic generator (p-CASH), that not only achieves high second-harmonic generation (SHG) enhancement (76-fold), large SHG tunability by bias (8%/V), wide tuning range (280%), 7.8 × 10–9 conversion efficiency, and high stability but also exhibits a SHG tuning, that is bipolar rather than unipolar, not due to the third-order nonlinear polarization term, hence fundamentally different from the classic electric field induced SHG-tuning (EFISH). We propose a new SHG tuning mechanism: the second-order nonlinear polarization term enhanced by plasmonic effects, changed by charge injection and negative oxygen vacancies movement, and is nearly 3 orders of magnitude larger than EFISH. p-CASH is a bipolar parallel-plate capacitor with thin layers of plasmonic nanostructures, a TiOx (semiconductor and nonlinear) and a SiO2 (insulator) sandwiched between two electrodes. Fabrication of p-CASH used nanoimprint on 4″ wafer and is scalable to wallpaper-sized areas. The new structure, new properties, and new understanding should open up various new designs and applications of NLG in various fields.

We report the structure, performance and large-area fabrication of a thin plasmonic infrared absorber, termed “bar-shaped disk-coupled dots-on-pillar antenna-array” (bar-D2PA). The bar-D2PAs, which are simple to fabricate, demonstrate the following, experimentally: (i) a different light-absorption resonance for each polarization with the resonance peak tunable by the bar-to-backplane gap and the bar size; (ii) for the geometry tested, the reflection is nearly constant at ∼10%, but the transmission and absorption highly depend upon the bar size and the gap between the bar and the backplane (e.g., the absorption of 77% (30%), the transmission of 9% (62%), and the resonance peak at 3.12 μm (3.04 μm) for the polarization along 700 nm long (185 nm short) axis and a 20 nm gap); (iii) a smaller gap significantly enhances the normalized extraordinary transmission, and (iv) the extraordinary transmissions become larger as the polarized bar side is in deeper subwavelength. The bar-D2PAs were fabricated in large area using nanoimprint lithography, etching plus one metal deposition that forms all metal structures in one step with excellent self-alignment and self-assembly. The design and fabrication can be extended to broad plasmonic applications.Keywords: disk-coupled dots-on-pillar cavity antenna array (D2PA); enhanced absorption; extraordinary transmission; infrared biochemical sensing; nanobar absorber; nanoimprint lithography; plasmonic nanostructures

Protein detection is universal and vital in biological study and medical diagnosis (e.g., cancer detection). Fluorescent immunoassay is one of the most widely used and most sensitive methods in protein detection (Giljohann, D. A.; Mirkin, C. A. Nature2009, 462, 461–464; Yager, P.; et al. Nature2006, 442, 412–418). Improvements of such assays have many significant implications. Here, we report the use of a new plasmonic structure and a molecular spacer to enhance the average fluorescence of an immunoassay of Protein A and human immunoglobulin G (IgG) by over 7400-fold and the immunoassay’s detection sensitivity by 3 000 000-fold (the limit of detection is reduced from 0.9 × 10–9 to 0.3 × 10–15 molar (i.e., from 0.9 nM to 300 aM), compared to identical assays performed on glass plates). Furthermore, the average fluorescence enhancement has a dynamic range of 8 orders of magnitude and is uniform over the entire large sample area with a spatial variation ±9%. Additionally, we observed that, when a single molecule fluorophore is placed at a “hot spot” of the plasmonic structure, its fluorescence is enhanced by 4 × 106-fold, thus indicating the potential to further significantly increase the average fluorescence enhancement and the detection sensitivity. Together with good spatial uniformity, wide dynamic range, and ease to manufacture, the giant enhancement in immunoassay’s fluorescence and detection sensitivity (orders of magnitude higher than previously reported) should open up broad applications in biology study, medical diagnosis, and others.

We report a new approach, termed “growth by nanopatterned host-medicated catalyst” (NHC growth), to solve nonuniformities of Si nanowires (NWs) grown on amorphous substrates. Rather than pure metal catalyst, the NHC uses a mixture of metal catalyst with the material to be grown (i.e., Si), nanopatterns them into desired locations and anneals them. The Si host ensures one catalyst-dot per-growth-site, prevents catalyst-dot break-up, and crystallizes catalyst-dot (hence orientating NWs). The growth results straight silicon NWs on SiO2 with uniform length and diameter (4% deviation), predetermined locations, preferred orientation, one-wire per-growth-site, and high density; all are 10–100 times better than conventional growth.

We report fabrication and characterization of a novel real-time, label-free DNA detector, that uses a long nanofluidic channel to stretch a DNA strand and a nanogap detector (with a gap as small as 9 nm) inside the channel to measure the electrical conduction perpendicular to the DNA backbone as it moves through the gap. We have observed electrical signals caused by 1.1 kilobase-pair (kbp) double-stranded (ds)-DNA passing through the gap in the nanogap detectors with a gap equal to or less than 13 nm.

We report a new approach to adjust and improve nanostructures after their initial fabrication, which can reduce the trench width and hole diameter to sub-10 nm, while smoothing edge roughness and perfecting pattern shapes. In this method, termed pressed self-perfection by liquefaction (P-SPEL), a flat guiding plate is pressed on top of the structures (which are soften or molten transiently) on a substrate to reduce their height and guide the flow of the materials into the desired geometry before hardening. P-SPEL results in smaller spacing between two structures or smaller holes in a thin film.

We report a new method to fabricate self-enclosed optically transparent nanofluidic channel arrays with sub-10 nm channel width over large areas. Our method involves patterning nanoscale Si trenches using nanoimprint lithography (NIL), sealing the trenches into enclosed channels by ultrafast laser pulse melting and shrinking the channel sizes by self-limiting thermal oxidation. We demonstrate that 100 nm wide Si trenches can be sealed and shrunk to 9 nm wide and that λ-phage DNA molecules can be effectively stretched by the channels.