High-precision THz Dielectric Spectroscopy of Tris-HCl Buffer

Tris-HCl buffer solution is extensively used in biochemistry and molecular biology to maintain a stablepH for biomolecules such as nucleic acids and proteins. Here we report on the high-precision THz dielectricspectroscopy of a 10 mM Tris-HCl buffer. Using a double Debye model, including conductivity of ionicspecies, we measured the complex dielectric functions of Tris-HCl buffer. The fast relaxation time of watermolecules in Tris-HCl buffer is ~20% longer than that in pure water while the slow relaxation time changeslittle. This means that the reorientation dynamics of Tris-HCl buffer with such a low Tris concentrationis quite different from that of pure water.1111Ysciescopuskc

THz Spectroscopy for Nano-Bio Photonics

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Subsurface nanoimaging by THz pulse near-field microscopy

Combined with THz time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, we experimentally demonstrate a broadband THz pulse near-field microscope that provides subsurface nanoimaging with a nearly frequency-independent lateral resolution of 90 nm, corresponding to -X/3300 at 1 THz.1

Inertial force-driven synthesis of near-infrared plasmonic nanosphere composites

Near-infrared (NIR) responsive nanoparticles (NPs) like gold nanorods (GNRs) are important in biomedical fields because of their transparency for biological tissues. Although GNRs are sought after as contrast agents for theranostics in cancer studies, capping ligands like cetyl trimethyl ammonium bromide (CTAB) used for the GNR synthesis are toxic for biological tissues. This work aimed to develop a physical method as an alternative to toxic GNR chemical process. The synthesis process, using colloidal citrate capped gold as model NP, was simple, cost-effective, and did not require the use of a toxic chemical like CTAB. The inertial (g-) force-driven synthesis of nanosphere composites (NSCs) resulted in composites of two NPs combined together with little or no gaps between them. The formed NSCs showed rod-like characteristics, which are typified by the evolution of absorption spectra from the transverse to longitudinal mode, similar to GNRs. The new nanomaterials by the g-force-driven technique showed high potential to be an effective alternative to many existing toxic NPs, particularly GNRs.1

THz Near-Field Microscopy

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THz Biomolecular Spectroscopy

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Integrable semiconductor ring lasers and two-dimensional rectangular lattice distributed feedback lasers

Two types of integrable semiconductor lasers are investigated in this thesis. Semiconductor ring lasers with circular and square ring resonators are analyzed, and their fabrications and laser results are described. Two-dimensional rectangular lattice distributed feedback lasers are proposed and analyzed by a coupled mode theory.Strained-layer InGaAs-AlGaAs-GaAs circular ring lasers with a single Y-junction output coupler are fabricated by SiCl\sb4 reactive ion etching. The bending loss calculated by a Wentzel-Kramers-Brilloin (WKB) analysis and the measured threshold currents suggest that the loss of the small radius lasers is mainly due to the nonradiative recombination and scattering at the deeply etched sidewall. A comparison between the estimated and measured longitudinal mode spacings indicates that the small radius ($<$76 $\mu$m) ring lasers operate in relatively low order whispering gallery modes.Strained-layer InGaAs-AlGaAs-GaAs square ring lasers with total internal reflection (TIR) mirrors and narrow gap output couplers are described. The modal reflectivity of TIR mirrors is calculated by a plane wave expansion method. A new fabrication technique requiring a single SiO\sb2 mask layer is developed. The square ring lasers operate in a single longitudinal mode with a side mode suppression ratio of $\sim$20 dB. An asymmetry in the emission spectra indicates the traveling wave operation of the square ring lasers. A new self-aligned etch process is developed for TIR mirrors without additional lift-off and dielectric depositions, and is demonstrated to produce high quality TIR mirrors with a reflectivity of $\sim$0.93.Two-dimensional rectangular lattice distributed feedback lasers are described by a coupled-mode analysis of the scalar wave equation derived from a TE vector field. Threshold conditions are presented with the optimum design conditions for minimum threshold gains. For a given area and periods of the grating, there is an optimum structural angle of the grating. If the normal incidence coupling constants of the two orthogonal gratings are the same, the optimum structural angle should be the same as the incidence angle which is determined by the Bragg condition. For the different normal incidence coupling constants, the optimum structural angles are obtained numerically.U of I OnlyETDs are only available to UIUC Users without author permissio

High Performance Triboelectric Nanogenerators for Self-Powered Electronics

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Holographic nanolithography techniques for the fabrication of microcavity arrays

Two-dimensional (2D) photonic quasicrystals (PQCs) were fabricated by a holographic nanolithography technique. Using two laser beams with different angles incident on the sample, microcavities with 2D internal nanostructures are patterned with a few micrometer periods11Nsciescopu

Ultra-compact terahertz 50:50 power splitter designed by a perceptron based algorithm

We designed and simulated an ultra-compact 1 × 2 power splitter operating in the terahertz region. A machine learning approach was implemented to design the photonic device. The designed power splitter has a footprint of 500 µm × 500 µm. We calculated the insertion loss using a three-dimensional finite difference time domain method. The calculated insertion loss was less than 4 dB over the operating wavelength range of 275–325 µm. The machine learning algorithm implemented in this work can be applied to the inverse design of various photonic devices.11