Electrical characteristics of schottky barriers on 4H-SiC: The effects of barrier height nonuniformity

Electrical properties, including current-voltage (I-V) and capacitance-voltage (C-V) characteristics, have been measured on a large number of Ti, Ni, and Pt-based Schottky barrier diodes on 4H-SiC epilayers. Various nonideal behaviors are frequently observed, including ideality factors greater than one, anomalously low I-V barrier heights, and excess leakage currents at low forward bias and in reverse bias. The nonidealities are highly nonuniform across individual wafers and from wafer to wafer. We find a pronounced linear correlation between I-V barrier height and ideality factor for each metal, while C-V barrier heights remain constant. Electron beam induced current (EBIC) imaging strongly suggests that the nonidealities result from localized low barrier height patches. These patches are related to discrete crystal defects, which become visible as recombination centers in the EBIC images. Alternative explanations involving generation-recombination current, uniform interfacial layers, and effects related to the periphery are ruled out.     

Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1?xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

Properties of high-voltage stress generated traps in thin siliconoxide

It has previously been shown that trap generation inside thin oxides during high voltage stressing can be coupled to time-dependent-dielectric-breakdown distributions through the statistics linking wearout to breakdown. Since the stress-generated traps play a crucial role in the wearout/breakdown process, it is important to understand the properties of these traps. The properties of the traps in oxides with thicknesses between 2.5 nm and 22 nm have been studied, with emphasis on oxides in the 8.5-nm to 13-nm thickness range. The Coulombic scattering cross section of the traps responsible for the reduction in the tunneling current, an estimate of the spatial and energy distribution of the traps, and the charging/discharging properties of the traps have been measured. It will be shown that the measured properties of the high-voltage, stress-generated traps can be adequately described by the tunneling of electrons into and out of traps     

Laterally Coupled DFB Lasers for One-Step Growth Photonic Integrated Circuits in InP

Design and characterization of a transmitter building block for one-step growth photonic integration, featuring a 1310 - nm laterally coupled distributed-feedback laser with a front-side passive optical waveguide and a back-side optical power monitor, are presented. Formed on a semi-insulating Fe : InP substrate and processed by means of a stepper optical lithography, the device perfectly suits the multiguide vertical integration-a newly developed one-step growth photonic integrated technique in InP.     

Bright Aggregation‐Induced Emission Dots for Dynamic Tracking and Grading of Patient‐Derived Xenografts in Zebrafish

Cancer prognosis will benefit from a scoring system that could grade malignant traits of patient‐derived cells by assessing their growth and metastasis in a living system. Specific tracking of patient‐derived cells requires labeling by contrast agents with good signal‐to‐noise ratio and no specific stain of host tissues. Towards this aim, aggregation‐induced emission (AIE) dots are developed for in vivo cancer tracking with emphasis on reproducible optimized formulation and specific fluorescent labeling of cells that enable enhanced spatial temporal resolution in vivo. The importance of energy‐dependent AIE dots uptake for patient‐derived cell labeling is emphasized to reveal their specific uptake by viable cancer cells. Using optically transparent zebrafish embryo, the ability is demonstrated to follow the engraftment of transplanted AIE dot labeled cells in zebrafish brains over one week. Cells detected outside the brain after 7 d are quantified as metastatic cells. Results from seven clinical samples demonstrate the utility of this methodology to differentiate low engraftment level of benign neoplasms from higher engraftment level and metastasis detected in malignant ovarian cancer specimens. Achieving clinically validated results supports the use of AIE dot labeled patient derived cells in zebrafish xenografts for future cancer prognosis.     

Bounds on bearing and symbol estimation with side information

We develop Cramer-Rao bounds (CRBs) for bearing, symbol, and channel estimation of communications signals in flat-fading channels. We do this using the constrained CRB formulation of German and Hero (1990), and Stoica and Ng (see IEEE Signal Processing Lett., vol.5, p.177-79, 1998), with the unknown parameters treated as deterministic constants. The equality constraints may be combined arbitrarily, e.g., we may develop CRBs for bearing estimation of constant modulus (CM) signals where a subset of the symbols are known (semi-blind, CM case). The results establish the value of side information in a large variety of communications scenarios. We focus on the CM and semi-blind properties and develop closed-form CRBs for these cases. Examples are presented indicating the relative value of the training and CIM property. These show the significant amount of signal processing information provided under these two conditions. In addition, we consider the performance of the maximum-likelihood beamformer for the semi-blind case, assuming the bearings are known. This semi-blind beamformer achieves the appropriate (constrained) CRB with finite data at finite SNR. Analysis also reveals that in a semi-blind scenario with two closely spaced sources, ten or more training symbols are sufficient to achieve the asymptotic training regime. Together with previous results on angle estimation for known sources, these results indicate that relatively few training samples enable both angle estimation and closely spaced co-channel source separation that approaches the CRB with finite data and finite SNR     

A model for diffraction-limited high-power multimode fiberamplifiers using seeded stimulated Brillouin scattering phaseconjugation

Diffraction-limited polarized stimulated Brillouin scattering (SBS) Stokes output from a multimode fiber is possible when the Stokes beam is the phase conjugate of diffraction-limited polarized pump light from a narrow-band master oscillator. Net amplification can be obtained by interposing a gain medium, such as a fiber amplifier between the master oscillator and the region of SBS generation. This paper proposes and studies numerically a model which describes the space-time dynamics of SBS generation, including phase conjugation, attenuation, phonon decay, thermal noise, inhomogeneous broadening, and amplifier gain. Noise reduction and phase locking are obtained by seeding the low-power end of the fiber at the Stokes frequency. Simulations are described for the case of 1.064 μm light amplification in a dual-clad Yb-doped multimode fiber amplifier     

Highly Efficient,Solution‐Processed,Single‐Layer,Electrophosphorescent Diodes and the Effect of Molecular Dipole Moment

A new family of highly soluble electrophosphorescent dopants based on a series of tris‐cyclometalated iridium(III) complexes (1–4) of 2‐(carbazol‐3‐yl)‐4/5‐R‐pyridine ligands with varying molecular dipole strengths have been synthesized. Highly efficient, solution‐processed, single‐layer, electrophosphorescent diodes utilizing these complexes have been prepared and characterized. The high triplet energy poly(9‐vinylcarbazole) PVK is used as a host polymer doped with 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD) for electron transport. Devices with a current efficiency of 40 cd A^?1 corresponding to an EQE of 12% can thus be achieved. The effect of the type and position of the substituent (electron‐withdrawing group (CF₃) and electron‐donating group (OMe)) on the molecular dipole moment of the complexes has been investigated. A correlation between the absorption strength of the singlet metal‐to‐ligand charge‐transfer (¹MLCT) transition and the luminance spectral red shift as a function of solvent polarity is observed. The strength of the transition dipole moments for complexes 1–4 has also been obtained from TD‐DFT computations, and is found to be consistent with the observed molecular dipole moments of these complexes. The relatively long lifetime of the excitons of the phosphorescence (microseconds) compared to the charge‐carrier scattering time (less than nanoseconds), allows the transition dipole moment to be considered as a “quasi permanent dipole”. Therefore, the carrier mobility is sufficiently affected by the long‐lived transition dipole moments of the phosphorescent molecules, which are randomly oriented in the medium. The dopant dipoles cause positional and energetic disorder because of the locally modified polarization energy. Furthermore, the electron‐withdrawing group CF₃ induces strong carrier dispersion that enhances the electron mobility. Therefore, the strong transition dipole moment in complexes 3 and 4 perturbs both electron and hole mobilities, yielding a reduction in exciton formation and an increase in the device dark current, thereby decreasing the device efficiency.     

Prediction of total intake of dry matter and net energy in a lactation

Daily records on DM intake, net energy intake, and milk yield from 191 Holstein cows in six herds were used to study the differences in accuracy and precision among different methods of estimating total DM intake during a lactation. In using cumulative measures of intake from partial lactations to predict total intake, accuracy reached 85% at 100 d postpartum. Measurements of intake taken around midlactation gave better predictions of total intake than those taken during other periods of lactation. Methods were evaluated for estimating total feed intake during a lactation based on data collected intermittently and separated by either equal or unequal intervals throughout the lactation. The average percentage of bias across all sampling schemes was 6% or less of actual intake. Six of the seven sampling schemes using only 10 d of intake information throughout the lactation had correlations with actual intake of .97 or higher. For equally spaced methods, both accuracy and precision of estimation increased with increased frequency of sampling. For unequally spaced methods, accuracy increased with sampling frequency after 150 d in milk. Total milk production was used to predict feed intake during a lactation. Milk yield alone accounted for 37 and 33% of the variation of total intake using actual and estimated yields, respectively.     

Effect of tray liners on the drip loss of lamb chops during retail display

The amount of drip lost by lamb chops during display was affected by the type of tray liner used. In one study involving chilled and frozen/thawed meat, the use of an absorbent paper liner increased the drip loss and influenced whether or not the quantity of drip was affected by freezing/thawing. In another study, thawed chops held for 24 h on plastic coated trays without liner or on a plastic coated liner had less than 2% drip loss, whereas adjacent chops from the same loin processed and held in the same way but displayed on liners of absorbent paper or paper pouches of diatomaceous earth lost 4·3% and 5·6% drip, respectively. This effect of the material in contact with the meat should be considered when reporting drip loss data and when comparing results with those of other researchers.