Mind the gap

Applied Science

Planarized nanophotonic sensor for real-time fluid sensing

A planarized on-chip nanophotonic sensor based on a photonic crystal cavity is realized in this work. The sensor was embedded in a solid protecting material (flowable oxide) with perfect filled holes: this eliminates problems of fouling in practical applications. The functional area of the sensor is created by carefully removing the protecting material only on the top surface of the cavity. A wavelength shift of 7.5 nm was observed in experiment which is very close to a simulation result of 9.0 nm for sensing water (n=1.33) and crude oil (n=1.45) samples. Swift and accurate sensing was verified by a real-time dynamic measurement with rapidly alternating analytes in a microfluid channel.Petroleum Engineerin

Sensitive All-Optical Channel-Drop Sensor in Photonic Crystals

We report the results of a study of an optical sensor based on a channel-drop technique with two cascaded cavities in photonic-crystal slabs. Quality factors and intensities of the resonant modes of the sensor were analyzed with three-dimensional simulations. With the introduction of a reflector in the bus-channel and by control of the coupling between the two cavities and the drop-channel, the drop efficiency can be remarkably increased. In addition to the simulation, the two cavity sensor is fabricated and tested for optical response to water and oil infiltration. Both direct visual imaging and quantitative analysis were applied in experiment. A difference of refractive index ?n = 0.12 between water and oil samples results in a wavelength shift of 18.3 nm, which greatly matches the simulation result of 20 nm and indicates a sensitivity of 153 nm RIU-1. Both resonant peaks for water and oil infiltration have good selectivity in their transmission spectrum. The contrast between the broadband output of the bus-channel and the highly wavelength-selective outputs of the drop-channel opens opportunities for the two cascaded-cavity system as a fundamental building block for a multiplex drop-channel array for all-optical sensing, which can be widely used for bio/chemical detection and environmental monitoring.BT/BiotechnologyApplied Science

Proximity effect in ion-beam-induced deposition of nanopillars

Ion-beam-induced deposition (IBID) is a powerful technique for prototyping three-dimensional nanostructures. To study its capability for this purpose, the authors investigate the proximity effect in IBID of nanopillars. In particular, the changes in shape and dimension of pillars are studied when a second pillar is grown near an existing pillar. On a semiconducting bulk Si and on an insulating Si3N4 membrane the first pillar gets broader, whereas on Si it starts to bend. They attribute the broadening and bending to the additional deposition induced by the particles scattered from the growing second pillar. On Si the second pillar is taller than the first one, while on Si3N4 it is shorter and rougher. This difference points to an important role of the substrate conductivity in the proximity effect. In a conductive environment the changes in the second pillar are mainly caused by a precursor coverage enhancement in the pillar surface. This enhancement is caused by precursor molecules, which are reflected or desorbed from the first pillar. In the case of an insulating environment, the changes in the second pillar are mainly caused by the reduction in the substrate surface charging due to the presence of the first pillar.QN/Quantum NanoscienceApplied Science

Evaluation of LED application in general lighting

Kavli Institute of NanoscienceApplied Science

Field-based scanning tunneling microscope manipulation of antimony dimers on Si(001)

The manipulation of antimony dimers, Sb2, on the silicon (001) surface by means of a scanning tunneling microscope (STM) has been experimentally investigated. Directed hopping of the Sb2 dimers due the STM tip can dominate over the thermal motion at temperatures between 300 and 500 K. Statistics on the enhanced hopping are reported and possible tip–adsorbate models are discussed focusing on a field-based interaction. The low yield of directed hopping is believed to be due to the low gradient in the interaction energy intrinsic to a field-based mechanism. Ultimate resolution and limiting factors of this manipulation technique are discussed

Photonic crystal Mach-Zehnder interferometer operating in the self-collimation mode of light

Kavli Institute of NanoscienceApplied Science

2D InP photonic crystal fabrication process development

We have developed a reliable process to fabricate high quality 2D air-hole and dielectric column InP photonic crystals with a high aspect ratio on a STS production tool using ICP N2+Cl2 plasma. The photonic crystals have a triangular lattice with lattice constant of 400 nm and air-hole and dielectric column radius of 120 nm. Large efforts have been devoted on developing a proper mask. We obtained a perfect, clean and vertical profiled SiNX mask. The next main effort is InP pattern transfer in Cl2+N2 plasma. Etching selectivity, smooth sidewall and etch profile are directly related to plasma process condition, besides the quality of SiNX mask. We have optimized the N2+Cl2 plasma condition to obtain high aspect ratio, vertical profile and smooth sidewall InP structures. Cylindrical holes (2 micron depth) and rodlike pillars (2.4 micron height) are uniformly fabricated. An aspect ratio of 18 for 100nm trench lines has been obtained. AFM measurement evidences that etched surfaces are smooth. The root mean square roughness of pillar and hole is 0.7 nm and 0.8 nm, respectively. The optical transmission characterization of ridge waveguides has been carried out. Transmission spectrum of 1 micron wide waveguide has been obtained.Kavli Institute of NanoscienceApplied Science

Electronic tuning of integrated blue-violet GaN tunable coupled-cavity laser

We demonstrate an integrated tunable coupled-cavity InGaN/GaN laser with the emission wavelength centered on 409 nm. The electronic tuning range was 1.6 nm and threshold currents were 650 mA per cavity for 8.7-?m-wide laser ridges. Multimode laser emission with an average full width at half maximum of 0.3 nm was observed. We estimate the refractive index change due to free-carrier injection and optical gain to explain the experimental tuning range.Quantum NanoscienceElectrical Engineering, Mathematics and Computer Scienc