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Silica nanowires decorated with silver nanocrystals on quartz substrate were employed as SERS substrates. The substrates features reusablity, backside measurement, and wide measuring range from >0.1M to near single molecule detection, tested on Rhodamine 6G.

The optical properties of tetrodotoxin (TTX), a scarce toxin with anesthetic properties, were studied using nanoparticle arrays-assisted surface-enhanced Raman scattering (SERS). The nanoparticles arrays were fabricated using nanosphere lithography and a metallic lift-off process to control the particle size, shape, and spacing in the arrays. In the SERS experiment, we were able to measure the Raman spectrum with a TTX concentration as less as 0.9 ng/mL. This sensitivity is comparable to that from high performance liquid chromatography.

Nonlinear optical absorption of InN epitaxial films in the range of 720-790 nm were investigated by Z-scan measurements. The optical absorption cross-sections of the InN films were estimated, and the values are found in good agreement with band-filling model.

THz radiation from series of GaAs and InAlAs surface intrinsic-N + (SIN + ) structures with the built-in electric field as bias is studied. When the bias exceeds the so-called critical electric field, the amplitude of THz waves radiated is independent of the built-in electric field. However, the THz amplitude is proportional to the number of photo-excited free charged carriers and thus the thickness of the intrinsic layer of the SIN + structures. The critical electric field determined from the THz amplitude as a function of the electric field may be useful in estimating the Γ to L valley splitting in semiconductors. Lattice-matched GaAs and In0.52Al0.48As surface intrinsic-N + (SIN + ) structures with various thicknesses of intrinsic layers grown by conventional molecular beam epitaxy are used as the THz emitters in this study. The built-in electric field is used as the bias. The as-grown heterosturctures possess a common structure consisting of various thicknesses of undoped layers on top of 1 µm of a Si-doped, n-type buffer layer that have been grown previously on an Fe-doped semi-insulated (100) substrate. The doping concentration in the buffer layer is approximately 8.4×10 17 cm -3 . Samples with various undoped layer thicknesses are also obtained from as-grown samples by subsequent etches. The built-in electric field is determined as a function of the thickness of the intrinsic layers using modulation spectroscopy of photoreflectance (PR). Figure 1a) displays the THz waves radiated from SI (100) GaAs wafer, and GaAs and In0.52Al0.48As SIN + structures. Figure 1b) plots THz waves in the frequency domain obtained by applying the fast Fourier transform to the THz waves in the time domain. The amplitude of the THz wave from the In0.52Al0.48As SIN + structure with an intrinsic layer of 2000A is five times of that from the SI GaAs wafer. Figure 2 plots the amplitude of the THz radiation from In0.52Al0.48As and GaAs SIN + structures as a function of the thickness of the intrinsic layer. Figure 3 depicts the built-in electric field, determined from PR spectra in our previous studies, as a function of the thickness of the intrinsic layer. 5-7 The negative values of thickness represent the thickness of the buffer layer that has been etched away, therefore; the built-in electric field in these samples locates within the charge depletion layer. Figures 2 and 3, however, reveal that the amplitude of the THz radiation is independent of the built-in electric fields in the emitters but is proportional to the thickness of the intrinsic layer of the SIN + structure. This behavior is interpreted