Systematic Doping Control of CVD Graphene Transistors with Functionalized Aromatic Self‐Assembled Monolayers

Recent reports have shown that self‐assembled monolayers (SAMs) can induce doping effects in graphene transistors. However, a lack of understanding persists surrounding the quantitative relationship between SAM molecular design and its effects on graphene. In order to facilitate the fabrication of next‐generation graphene‐based devices it is important to reliably and predictably control the properties of graphene without negatively impacting its intrinsic high performance. In this study, SAMs with varying dipole magnitudes/directions are utilized and these values are directly correlated to changes in performance seen in graphene transistors. It is found that, by knowing the z‐component of the SAM dipole, one can reliably predict the shift in graphene charge neutrality point after taking into account the influence of the metal electrodes (which also play a role in doping graphene). This relationship is verified through density functional theory and comprehensive device studies utilizing atomic force microscopy, X‐ray photoelectron spectroscopy, Raman spectroscopy, and electrical characterization of graphene transistors. It is shown that properties of graphene transistors can be predictably controlled with SAMs when considering the total doping environment. Additionally, it is found that methylthio‐terminated SAMs strongly interact with graphene allowing for a cleaner graphene transfer and enhanced charge mobility.     

Stability of nc-Si:H TFTs With Silicon Nitride Gate Dielectric

We report the fabrication and characterization of bottom-gate and top-gate nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs) with amorphous-silicon nitride (a-SiN_x:H) as the gate dielectric. The devices were fabricated using standard 13.56-MHz plasma-enhanced chemical vapor deposition at 240 degC. Here, the same 80-nm nc-Si:H channel, 300-nm a-SiN_x:H gate dielectric, and 60-nm n⁺ nc-Si:H ohmic contact layers were used in both TFT structures. We analyzed the effects of gate configuration on TFT performance and, in particular, the electrical stability. The stability tests were carried out at a gate bias stress in the range from 20 to 40 V. The nc-Si:H TFTs demonstrated much better threshold-voltage (V_T ) stability compared with the amorphous-silicon (a-Si:H) counterparts, offering great promise for applications in active-matrix organic light-emitting diode (AMOLED) displays     

Effect of NiTe Nanoinclusions on Thermoelectric Properties of Bi2Te3

Metal nanoinclusions in bulk thermoelectric matrix create metal?Csemiconductor interfaces, which can result in improvement in the thermoelectric power factor due to low-energy electron filtering and a simultaneous reduction in lattice thermal conductivity due to increased phonon scattering at grain boundaries. The combined effect results in enhancement of the thermoelectric figure of merit. We report the effect of NiTe nanoinclusions in a Bi₂Te₃ matrix. The Bi₂Te₃/NiTe nanocomposite was synthesized by planetary ball milling. Different volume fractions of NiTe nanoinclusions were incorporated into the bulk (Bi₂Te₃) matrix and uniaxially hot pressed at 100?MPa and 500°C. The presence of nanoinclusions was confirmed by x-ray diffraction and transmission electron microscopy. The Seebeck coefficient, electrical conductivity, and thermal diffusivity were measured from room temperature to 150°C. The carrier concentration of the matrix (Bi₂Te₃) and the nanocomposites (NiTe/Bi₂Te₃) at room temperature were deduced from Hall-effect measurements. Addition of NiTe decreased the carrier concentration, and the power factor increased in the 1?vol.% NiTe/Bi₂Te₃ compared with inclusion-free Bi₂Te₃ matrix due to an increase in mobility.     

Recyclable,Flexible, Low‐Power Oxide Electronics

The ability to process and dimensionally scale field‐effect transistors with and on paper and to integrate them as a core component for low‐power‐consumption analog and digital circuits is demonstrated. Low‐temperature‐processed p‐ and n‐channel integrated oxide thin‐film transistors in the complementary metal oxide semiconductor (CMOS) inverter architecture are seamlessly layered on mechanically flexible, low‐cost, recyclable paper substrates. The possibility of building these circuits using low‐temperature processes opens the door to new applications ranging from smart labels and sensors on clothing and packaging to electronic displays printed on paper pages for use in newspapers, magazines, books, signs, and advertising billboards. Because the CMOS circuits reported constitute fundamental building blocks for analog and digital electronics, this development creates the potential to have flexible form factor computers seamlessly layered onto paper. The holistic approach of merging low‐power circuitry with a recyclable substrate is an important step towards greener electronics.     

The effect of electron damage on silicon solar cells coated with diamond‐like carbon films

The unique properties of the diamond‐like carbon (a:DLC), such as high mechanical hardness and abrasive resistance, optical transparency in the visible and IR spectral regions and high thermal conductivity, provide this material with advantages over other types of protecting materials for solar cells. Furthermore, the a:DLC films are inert to corrosive gases and other corrosive agents. Resistance to radiation damage of the a:DLC films deposited on solar cells is very important for space application. In the study we investigate the effect of electron damage on silicon solar cells coated with a:DLC films. We measure the I – V characteristic and the spectral response and calculate the values of the seven parameters of the double exponential solar cell model (usually not investigated) as a function of electron fluence irradiation. In addition we obtain also the usual external parameters I_sc, V_oc, I_m, V_m, FF, and efficiency) of the solar cells. We investigate solar cells with and without anti‐reflecting coating coated with a:DLC films which were exposed to electron radiation. The main findings show that the solar cells with a:DLC films of thickness up to 500 nm degrade similarly to regular silicon cells exposed to electron irradiation. The degradation of the spectral response of the solar cell is mainly in the range of longer wavelengths and the irradiation affects the solar cell parameters (mainly the reverse saturation currents). Copyright © 2000 John Wiley & Sons, Ltd.     

Low operational voltage and high performance organic field effect memory transistor with solution processed graphene oxide charge storage media

Low voltage organic field effect memory transistors are demonstrated by adapting a hybrid gate dielectric and a solution processed graphene oxide charge trap layer. The hybrid gate dielectric is composed of aluminum oxide (AlO_x) and [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) plays an important role of both preventing leakage current from gate electrode and providing an appropriate surface energy to allow for uniform spin-casting of graphene oxide (GO). The hybrid gate dielectric has a breakdown voltage greater than 6 V and capacitance of 0.47 μF/cm². Graphene oxide charge trap layer is spin-cast on top of the hybrid dielectric and has a resulting thickness of approximately 9 nm. The final device structure is Au/Pentacene/PMMA/GO/PhO-19-PA/AlO_x/Al. The memory transistors clearly showed a large hysteresis with a memory window of around 2 V under an applied gate bias from 4 V to −5 V. The stored charge within the graphene oxide charge trap layer was measured to be 2.9 × 10¹² cm⁻². The low voltage memory transistor operated well under constant applied gate voltage and time with varying programming times (pulse duration) and voltage pulses (pulse amplitude). In addition, the drain current (I_ds) after programming and erasing remained in their pristine state after 10⁴ s and are expected to be retained for more than one year.     

Multichannel, Single Tral Event Related Potential Classification

We report on the effect of electrode placement and number of electrodes on the classification of single trial event related potentials (ERP's). The subjects read propositions relating fictitious people and their occupations while ERP's were recorded. The subjects decided if the proposition was correct or incorrect and responded as per instructions. The single trial, multichannel ERP data were classified using various methods, e. g., hold-out, leave-one-out, resubstitution. Several other factors were examined to determine their effect on ERP classification, including taking a majority vote among channels, using the single best channel, and averaging the data across channels for a single ERP. The results from other experiments are compared to those presented here.     

Inactivation of Shiga toxin-producing O157:H7 and non-O157:H7 Shiga toxin-producing Escherichia coli in brine-injected, gas-grilled steaks

We quantified translocation of Escherichia coli O157:H7 (ECOH) and non-O157:H7 verocytotoxigenic E. coli (STEC) into beef subprimals after brine injection and subsequently monitored their viability after cooking steaks cut therefrom. Beef subprimals were inoculated on the lean side with ca. 6.0 log CFU/g of a five-strain cocktail of rifampin-resistant ECOH or kanamycin-resistant STEC, and then passed once through an automatic brine-injector tenderizer, with the lean side facing upward. Brine solutions (9.9% ± 0.3% over fresh weight) consisted of 3.3% (wt/vol) of sodium tripolyphosphate and 3.3% (wt/vol) of sodium chloride, prepared both with (Lac(+), pH = 6.76) and without (Lac(-), pH = 8.02) a 25% (vol/vol) solution of a 60% potassium lactate-sodium diacetate syrup. For all samples injected with Lac(-) or Lac(+) brine, levels of ECOH or STEC recovered from the topmost 1 cm (i.e., segment 1) of a core sample obtained from tenderized subprimals ranged from ca. 4.7 to 6.3 log CFU/g; however, it was possible to recover ECOH or STEC from all six segments of all cores tested. Next, brine-injected steaks from tenderized subprimals were cooked on a commercial open-flame gas grill to internal endpoint temperatures of either 37.8 °C (100 °F), 48.8 °C (120 °F), 60 °C (140 °F), or 71.1 °C (160 °F). Regardless of brine formulation or temperature, cooking achieved reductions (expressed as log CFU per gram) of 0.3 to 4.1 of ECOH and 0.5 to 3.6 of STEC. However, fortuitous survivors were recovered even at 71.1 °C (160 °F) for ECOH and for STEC. Thus, ECOH and STEC behaved similarly, relative to translocation and thermal destruction: Tenderization via brine injection transferred both pathogens throughout subprimals and cooking highly contaminated, brine-injected steaks on a commercial gas grill at 71.1 °C (160 °F) did not kill all cells due, primarily, to nonuniform heating (i.e., cold spots) within the meat.