Mo Chen

Linearly polarized light emission from quantum dots with plasmonic nanoantenna arrays.

Polarizers provide convenience in generating polarized light, meanwhile their adoption raises problems of extra weight, cost, and energy loss. Aiming to realize polarizer-free polarized light sources, herein, we present a plasmonic approach to achieve direct generation of linearly polarized optical waves at the nanometer scale. Periodic slot nanoantenna arrays are fabricated, which are driven by the transition dipole moments of luminescent semiconductor quantum dots. By harnessing interactions between quantum dots and scattered fields from the nanoantennas, spontaneous emission with a high degree of linear polarization is achieved from such hybrid antenna system with polarization perpendicular to antenna slot. We also demonstrate that the polarization is engineerable in aspects of both spectrum and magnitude by tailoring plasmonic resonance of the antenna arrays. Our findings will establish a basis for the development of innovative polarized light-emitting devices, which are useful in optical displays, spectroscopic techniques, optical telecommunications, and so forth.

Enhanced optical output power of blue light-emitting diodes with quasi-aligned gold nanoparticles

The output power of the light from GaN-based light-emitting diodes (LEDs) was enhanced by fabricating gold (Au) nanoparticles on the surface of p-GaN. Quasi-aligned Au nanoparticle arrays were prepared by depositing Au thin film on an aligned suspended carbon nanotube thin film surface and then putting the Au-CNT system on the surface of p-GaN and thermally annealing the sample. The size and position of the Au nanoparticles were confined by the carbon nanotube framework, and no other additional residual Au was distributed on the surface of the p-GaN substrate. The output power of the light from the LEDs with Au nanoparticles was enhanced by 55.3% for an injected current of 100xa0mA with the electrical property unchanged compared with the conventional planar LEDs. The enhancement may originate from the surface plasmon effect and scattering effect of the Au nanoparticles.

UV-based nanoimprinting lithography with a fluorinated flexible stamp

A custom-made copolymer of a perfluoropolyether (PFPE) and a hyperbranched polymer (HP) was employed to prepare an UV-based nanoimprinting lithographic (NIL) flexible HPFPE stamp. The properties of the HP afforded the resultant HPFPE resist with low viscosity, suitable surface energy, high Young’s modulus, and enhanced stability. The HPFPE resist also presented excellent properties of antisticking, and durability, no deformation, or distortion after long time usage; therefore, demonstrating an improvement in the NIL pattern transfer fidelity and resolution. By optimizing the UV-based NIL process with this flexible HPFPE stamp, the imprinting results showed near zero residues at the bottom of the resist grooves, and no sticking over a large area. The structure of the HPFPE flexible stamp was transferred intact onto a soft substrate indium tin oxide/polyethylene terephthalate film with good resolution, achieving a 50 nm linewidth and a 200 nm period.

Study of Carbon Nanotubes as Etching Masks and Related Applications in the Surface Modification of GaAs-based Light-Emitting Diodes

The surface modification of LEDs based on GaAs is realized by super-aligned multiwalled carbon nanotube (SACNT) networks as etching masks. The surface morphology of SACNT networks is transferred to the GaAs. It is found that the light output power of LEDs based on GaAs with a nanostructured surface morphology is greatly enhanced with the electrical power unchanged.

Highly Sensitive, Uniform, and Reproducible Surface-Enhanced Raman Spectroscopy Substrate with Nanometer-Scale Quasi-periodic Nanostructures

We introduce a simple and cost-effective approach for fabrication of effective surface-enhanced Raman spectroscopy (SERS) substrates. It is shown that the as-fabricated substrates show excellent SERS effects in various probe molecules with high sensitivity, that is, picomolar level detection, and also good reliability. With a SERS enhancement factor beyond 108 and excellent reproducibility (deviation less than 5%) of signal intensity, the fabrication of the SERS substrate is realized on a four-inch wafer and proven to be effective in pesticide residue detection. The SERS substrate is realized first through the fabrication of quasi-periodic nanostructured silicon with dimension features in tens of nanometers using superaligned carbon nanotubes networks as an etching mask, after which a large amount of hot spots with nanometer gaps are formed through deposition of a gold film. With rigorous nanostructure design, the enhanced performance of electromagnetic field distribution for nanostructures is optimized. With the advantage of cost-effective large-area preparation, it is believed that the as-fabricated SERS substrate could be used in a wide variety of actual applications where detection of trace amounts is necessary.

Graphene as discharge layer for electron beam lithography on insulating substrate

Charging of insulating substrates is a common problem during Electron Beam lithography (EBL), which deflects the beam and distorts the pattern. A homogeneous, electrically conductive, and transparent graphene layer is used as a discharge layer for EBL processes on insulating substrates. The EBL resolution is improved compared with the metal discharge layer. Dense arrays of holes with diameters of 50u2009nm and gratings with line/space of 50/30u2009nm are obtained on quartz substrate. The pattern placement errors and proximity effect are suppressed over a large area and high quality complex nanostructures are fabricated using graphene as a conductive layer.

Dielectric-Like Behavior of Graphene in Au Plasmon Resonator

Graphene has proven to be a promising conductive layer in fabricating optical plasmon resonators on insulator substrate using electron beam lithography and has the potential to construct electrically controlled active plasmon resonators. In this study, we investigate the effect of graphene on plasmon resonance using graphene and Au plasmon resonator system as a model at visible and near-infrared wavelength. Our experiment data show that the presence of graphene does not weaken and annihilate the plasmon resonance peaks, instead it predominantly makes the peaks redshift, which is similar to the behavior of depositing SiO2 film on Au plasmon resonators. This fact indicates that graphene predominantly exhibits dielectric-like behavior at visible and near-infrared wavelength, which can be attributed to the low carrier density in graphene compared with metals.

Stressed carbon nanotube devices for high tunability, high quality factor, single mode GHz resonators

The emerging applications of nanoelectromechanical systems (NEMS) in ground-state cooling, quantum manipulation, communication devices, etc., call for a nanoresonator with high frequency, quality factor, and tunability, as well as easy integration. Here we show that such a nanoresonator can be achieved by using a unique assembly technique that transfers the stressed inner shell of carbon nanotubes (CNTs) to a self-aligned device geometry. The as-fabricated nanoresonator shows excellent comprehensive performance, i.e., high frequency (2–3 GHz), high tunability (80–110 MHz/V), high quality factor (3 × 104), and single mode operation. The defect-free nature of the inner shell of the CNT gives rise to a high quality factor, and the preloaded tension improves the resonant frequency and tunability. This resonator with excellent performance also enables the integration of homogeneous devices and will play a key role in the emerging applications of NEMS.

The exposure process study of 100KV JBX-6300LS electron-beam nanolithograph system

We report on a series results of the performance of a Jeol model JBX-6300LS electron-beam nanolithography system operating at 100 KV. The exposure conditions are optimized to fabricate dense lines with 1:1 L/S and with the line-widths down to 30 nm for resist ZEP520A and PMMA. The lines show a very good uniformity within an area as large as 2 mmtimes2 mm. We obtained isolated metal lines with 22 nm widths through lift-off process based on 170 nm thick PMMA. Exposure studies were also performed for double layer resists to get a good under-cut cross section profile.