Yin Yuen

Spectral analysis of strongly enhanced visible light transmission through single C-shaped nanoapertures

We designed, fabricated, and characterized single C-shaped apertures in an Au film, resonant in the visible regime. Our C-shaped apertures showed transmission enhancement of 13–22 times over a square aperture of the same area and suggest as high as 106 enhancement over square apertures that are designed to produce the same near-field spot size. Spectra from individual apertures demonstrate the ability to tune this resonance over 70nm by scaling the dimensions of the apertures. This shows the C aperture to be a versatile tool for gaining high-resolution, enhanced transmission through single subwavelength apertures at optical wavelengths.

C-shaped nanoaperture-enhanced germanium photodetector

We present a C-shaped nanoaperture-enhanced Ge photodetector that shows 2-5 times the photocurrent enhancement over that from a square aperture of the same area at 1310 nm wavelength. We demonstrate the polarization dependence of the C-aperture photodetector over a wide wavelength range. Our experimental observation agrees well with finite-difference time-domain simulation results.

Ultra-high resolution resonant C-shaped aperture nano-tip.

We report a new optical near-field transducer comprised of a metallic nano-antenna extending from the ridge of a C-shaped metallic nano-aperture. Finite-difference time domain simulations predict that the C-aperture nano-tip (CAN-Tip) provides high intensity (650x), high optical resolution (~λ/60), and background-free near-field illumination at a wavelength of 980 nm. The CAN-Tip has an aperture resonance and tip antenna resonance which may be tuned independently, so the structure can be made resonant at ultraviolet wavelengths without being unduly small. This near-field optical resolution of 16.1 nm has been experimentally confirmed by employing the CAN-Tip as an NSOM probe.

8.1: Experimental verification of a λ/50 optical spot size of a C-aperture nano antenna tip for photo-electron emitter applications

We propose a photo-electron emitter structure whose electron beam size is 20nm using CsBr photo-emission layer and a novel nano-optical antenna structure. The optical spot size of 20nm has been experimentally demonstrated.

Fluorescence enhancement and focal volume reduction observed in c-shaped nano-apertures

We evaluate the potential ability of c-shaped apertures milled in aluminum thin films to reduce the effective measurement volume and to enhance the fluorescence signal for fluorescence correlation spectroscopy of ATTO655 dye dissolved in a HEPES buffer solution. Previous studies have shown that by morphing a square aperture into a rectangular aperture while holding the cross-sectional area constant will yield strong polarization dependence in the reduction of the effective volume and about a factor of 2-3 enhancement in the fluorescence count rate per molecule. By morphing the rectangular aperture into a c-shaped aperture we gain further reduction in focal volume while maintaining the count rate enhancements. In particular, we compare c-shaped apertures to squares with the same cross-sectional area and show that one can achieve one molecule per focal volume at ~3µM (about a 1000 times reduction in effective volume compared to confocal FCS) while maintaining a fluorescence count rate per molecule of about an order of magnitude higher than for bulk diffusing dyes. Two orthogonal polarizations for the incident field have been studied to explore the effects on the focal volume reduction and fluorescence count rate enhancements.

Single Molecule Pulsed Interleaved Excitation Fluorescence Resonance Energy Transfer (PIE-FRET) inside Nanometer-scale Apertures at Biologically Relevant Concentration

PIE-FRET offers significant advantages over conventional single molecule FRET techniques, but it still requires the dilution of samples to biologically low concentrations. Here, we present FRET measurements inside nm-sized apertures at -1000 times higher concentration.

Direct-write e-beam sub-micron domain engineering in liquid phase epitaxy LiNbO3 thin films

By using a direct-write e-beam technique with liquid phase epitaxy LiNbO3 thin films, we have successfully produced sub-micron domain structures for achieving dynamically switchable filters in a periodically poled lithium niobate (PPLN) waveguide. Sub-micron domain (~200 nm) structures with a period ~1.2 um are realized in liquid phase epitaxy LiNbO3 films on congruent LiNbO3 substrates by using the direct-write e-beam domain engineering method. In comparison with single crystal congruent LiNbO3 (CLN) and stoichiometric LiNbO3 (SLN), we show that LPE LiNbO3 is the most promising material for producing superior domain regularities and finer domain sizes than single crystals. A physical model is presented to qualitatively explain the observed differences in structure and regularity of the induced periodic domains among the three different materials we studied. We postulate that the higher Li/Nb ratio in LPE LN than in CLN enhances domain inversion initiation. Also, we believe that the vanadium incorporation and distortion due to the lattice mismatch between films and substrates enhance electron localization, domain wall pinning and domain nucleation in LPE materials, giving rise to better structures.

Ultra-high density optical data storage

Results on the use of C-shaped nano-apertures for optical data storage are reported. This type of aperture have a highly concentrated nanometer sized spot with a power throughput 1,000,000 times higher than for a square or round aperture producing the same spot size. Optical recording using contact media and conventional optical read-write media in DVD technology is also described.

Spectral study of enhanced transmission through single C-shaped nano-apertures

C-shaped apertures in a metal film, were made to be resonant at visible wavelengths. They showed transmission enhancement of 22 times over a square aperture of the same area. This resonance was tuned over 70 nm

Direct-Write E-beam Submicron Domain Engineering in LiNbO 3 Thin Films Grown by Liquid Phase Epitaxy

We demonstrate submicron ferroelectric domain engineering in liquid phase epitaxy (LPE) LiNbO 3 thin films grown on LiNbO 3 and LiTaO 3 substrates using a direct-write electron beam poling for waveguide applications. LiNbO 3 thin films of several-micron thickness were grown using a flux melt of 20 mol% LiNbO 3 -80 mol% LiVO 3 . To engineer domain structures in Z - oriented LPE LiNbO 3 films, a direct-write electron beam poling was implemented. It is shown that we can engineer the domain structure of LPE LiNbO 3 films by using direct e-beam poling, even though the domain orientations of the film and the substrate are opposite. We also compared e-beam poling behavior in a congruent LiNbO 3 single crystal and a LPE LiNbO 3 film. Using the same e-beam scan parameters, a much enhanced domain structure is obtained in LPE films. Defect structure and composition effects are also discussed.