Chih-n Hsu

Synthesis of diamond nanowires using atmospheric-pressure chemical vapor deposition.

We report diamond nanowires grown in an atmospheric pressure chemical vapor deposition process. These diamond nanowires are straight, thin and long, and uniform in diameter (60-90 nm) over tens of micrometers. Spectroscopic analysis, electron diffraction, and transmission electron microscopy provided confirmation that these nanowires are diamond with high crystallinity and high structural uniformity. They further revealed that these diamond nanowires are encased within multiwalled carbon nanotubes.

Quantum dot/carbon nanotube/silicon double heterojunctions for multi-band room temperature infrared detection

We report on the observation of room temperature multi-band photocurrent response from a novel structure formed by interior loading of PbS quantum dots into carbon nanotubes grown on silicon. In addition to a mid infrared photoresponse band at ∼ 0.22 eV due to the carbon nanotubes and one band at 1.1 eV corresponding to silicon, two bands in the mid/near infrared at 0.63 and 0.82 eV, corresponding to the first and second exciton bands of the PbS quantum dots, are observed in photocurrents measured at room temperature, in uncooled operation. We have also observed a red shift of the 0.63 and 0.82 eV bands with cooling that reflects a behavior typical for PbS and supports the hypothesis that these photoresponse bands are due to absorption in the PbS quantum dots.

Design and development of carbon nanostructure-based microbolometers for IR imagers and sensors

EO/IR Sensors and imagers using nanostructure based materials are being developed for a variety of Defense Applications. In this paper, we will discuss recent modeling effort and the experimental work under way for development of next generation carbon nanostructure based infrared detectors and arrays. We will discuss detector concepts that will provide next generation high performance, high frame rate, and uncooled nano-bolometer for MWIR and LWIR bands. The critical technologies being developed include carbon nanostructure growth, characterization, optical and electronic properties that show the feasibility for IR detection. Experimental results on CNT nanostructures will be presented. We will discuss the path forward to demonstrate enhanced IR sensitivity and larger arrays.

Directly Pumped Silicon Lasing

Enhanced photoluminescence and 1.28 mum laser emission from nano-engineered silicon originating respectively from phonon k-selection rule breaking and point defect-mediated phononless recombination in an array of emissive structural deformation zones in a SOI wafer are reported.

Nano-engineered crystalline silicon for enhanced photoluminesence and 1.28μm laser action: a study of mechanisms

1.278μm laser emission has been observed in a SOI structure which has been nanopatterned to contain an array of nanopores. The optical transition is known to be associated with phononless recombination mediated by the bistable, carbon-related G-center. A physical model is proposed to explain the enhanced optical activity of the G-centers in the presence of the nanopore array. The effects of the SOI, strain, dielectric modification and breaking of phonon k-selection rules on the optical properties of the nanopatterned silicon are addressed. Temperature limitations are discussed.

Directly-Pumped All-Silicon Laser

We report laser emission from novel nano-engineered all-silicon structures, originating from A-center mediated phononless (direct) recombination allowing the population inversion. TEM shows regions with high-density of structural defects, most likely responsible for the emission.