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We report on the photoluminescence (PL) spectra of ZnO nanorod (NR) films prepared by using the room-temperature solution-process method. Without any post-annealing process, the PL spectra of ZnO NR films exhibit a strong near-band-edge peak in UV region even at room temperature while the deep-level (DL) peak in the visible region is almost suppressed. The temperaturedependent PL measurement shows that the donor-bound exciton peaks are strongly observed at the lowest temperatures. The red-shift of the DL peak with decreasing temperature indicates that the origin of the DL emission might be related with the oxygen vacancy.

We demonstrate that photocurrent spectroscopy can be used to study optical absorption in the active layer of InGaN-based light-emitting diodes. The temperature dependence of the photocurrent spectrum was compared with that of the photoluminescence, clearly showing the effect of carrier localizations at low temperatures below 70 K. The photocurrent spectrum investigated by applying reverse biases revealed that type-II optical transitions between the InGaN quantum well and the GaN barrier were considerable at high reverse voltages.

We develop a theory for generation and detection of coherent phonons in graphene and carbon nanotubes. Coherent phonons are generated via phonon interactions with photogenerated carriers. Electronic states are treated in an extended tight binding model while phonon modes are treated using valence force field models. The amplitude for each coherent phonon mode satisfies a driven oscillator equation with a driving function that depends on the photoexcited carrier distributions.

Time‐resolved spectroscopy was performed with tunable probe pulses for single and multilayer graphene. The induced absorption was observed for multilayer graphene only near probe energy of 0.6 eV, which was explained by the intersubband carrier transitions from states near Dirac point to upper subband states.

Coherent G‐mode optical phonons were generated and detected in multi‐layer graphene by using pump‐probe technique with ultrashort pulse laser. The anharmonic properties of coherent G‐mode oscillations were studied by analyzing temperature dependent phonon frequency and dephasing time changes.

ZnO based nanostructures have recently attracted much attention due to their potential applications in spintronic and ultraviolet (UV) to violet light‐emitting and other optoelectronic device. We investigated the photoluminescence (PL) spectra of solution‐based synthesized ZnO nanorods in various gas atmospheres such as N2, O2, Ar, H2, CO, and H2O. The ZnO nanorods were fabricated by using a simple sonochemical method. The typical feature in PL spectra is a strong and sharp peak near 375 nm (NBE peak) and a broad structure near 550 nm (deep level). In the N2 atmosphere, the NBE peak is dramatically enhanced, but the deep level emission is significantly suppressed. These behaviors are observed similarly in Ar, H2 and CO gas atmospheres. In contrast, this behavior is reversed in the O2 atmosphere. Our finding is discussed in relation to the surface states formed in ZnO nanorods.

With performing time‐resolved transmission measurements in InGaN based laser diode structure, we find that the negative transient transmission is closely related with defect states, showing correlated behaviors with device performance. Our probing method may be used to noninvasively characterize defect density and expected device performance of InGaN materials.

We study coherent phonon oscillations in GaAs/AlxGa1−xAs MQW’s with varying x and fixed well and barrier widths of 100A. We have observed large plasmon-phonon coupling in x=0.2 MQW, although it is generally believed that the 2D nature of plasmon makes the plasmon-phonon coupling very difficult. One possible explanation for this phenomenon is the bulk-like, growth direction plasmon oscillations mediated by the anomalously large well-to-well coupling for small x (x

To compare management strategies for pediatric diabetic ketoacidosis (DKA) among physicians with different specialty training.We conducted a mail survey of 1000 randomly selected physicians, including 200 pediatric endocrinologists, 200 general emergency physicians, 200 pediatric emergency physicians, 200 pediatric intensivists, and 200 pediatric chief residents. We posed questions regarding a hypothetical 10-year-old patient with new onset of diabetes mellitus who is approximately 10% dehydrated but alert, with venous pH of 7.1 and serum glucose concentration of 34.7 mmol/L (625 mg/dL). Questions involved the rate of rehydration, content of intravenous fluids, insulin therapy, potassium replacement, use of sodium bicarbonate, and adjustments in therapy for decreasing serum glucose concentration. We compared responses of physicians in each specialty and used multiple regression analysis to adjust for potential confounding variables, including number of years in practice, number of children with DKA seen per month, and practice setting.Five hundred eighty-one physicians (58.1%) completed the survey, with responses demonstrating significant, consistent differences between specialties. Extremes of responses included the following: (1) 59% of endocrinologists vs 11% of general emergency physicians would give an initial fluid bolus of less than 20 mL/kg (odds ratio [OR], 11.7; 95% confidence interval [CI], 5.0-27.7) (P.001); (2) 83.5% of general emergency physicians vs 42.5% of pediatric intensivists would administer an initial insulin bolus (OR, 4.1; 95% CI, 2.0-8.7) (P.001); (3) 58.2% of pediatric intensivists vs 9% of general emergency physicians would replace fluids over a period of greater than 24 hours (OR, 14.1; 95% CI, 5.5-37.5) (P.001); and (4) 54.3% of general emergency physicians vs 7.3% of pediatric intensivists would use potassium chloride alone for potassium replacement (OR, 10.8; 95% CI, 5.0-23.8) (P.001). All of these differences persisted after adjusting for the potential confounding variables.Substantial differences exist in the management of pediatric DKA among physicians of different specialties, presumably due to differences in specialty training. These differences obscure our ability to evaluate the treatment of DKA and highlight the necessity for further studies comparing the outcomes of different treatment strategies.

Control of acoustic phonon generation with external bias is demonstrated for an InGaN light-emitting diode by performing femtosecond pump–probe measurements. The evolution of both the carrier dynamics and the acoustic phonon strength with an external bias reveals that the acoustic wave is generated during the carrier sweeping process of the depletion field, where electric field screening accompanies stress of the lattice for a piezoelectric material.

The gain and phase dynamics of a high quality quantum dot semiconductor optical amplifier were measured at various wavelengths. In the ground state (GS), the amplitude of the slow component was negligible and the fast dominant gain recovery time was 0.7 ps. In the excited state (ES), the slow component was not negligible although small. The time required to recover from 90% to 10% was 2.0 ps in the GS but gradually increased to 31 ps in the ES. This finding predicts no pattern effects in the GS, but finite pattern effects in the ES.

We present a time-resolved optical study of the dynamics of carriers and phonons in Ga_{1-x}Mn_{x}As layers for a series of Mn and hole concentrations. While band filling is the dominant effect in transient optical absorption in low-temperature-grown (LT) GaAs, band gap renormalization effects become important with increasing Mn concentration in Ga_{1-x}Mn_{x}As, as inferred from the sign of the absorption change. We also report direct observation on lattice vibrations in Ga1-xMnxAs layers via reflective electro-optic sampling technique. The data show increasingly fast dephasing of LO phonon oscillations for samples with increasing Mn and hole concentration, which can be understood in term of phonon scattering by the holes., Comment: 13 pages, 3 figures replaced Fig.1 after finding a mistake in previous version