Ultrahigh Electron Research Articles

Ambipolar Conjugated Polymers with Ultrahigh Balanced Hole and Electron Mobility for Printed Organic Complementary Logic via a Two-Step CH Activation Strategy.

High mobility ambipolar conjugated polymers are seriously absent regardless their great potential for flexible and printed plastic devices and circuits. Here, ambipolar polymers with ultrahigh balanced hole and electron mobility are developed via a two-step CH activation strategy. Diketopyrrolopyrrole-benzothiadiazole-diketopyrrolopyrrole (DBD) and its copolymers with thiophene/selenophene units (short as PDBD-T and PDBD-Se) are used as examples. PDBD-Se exhibits highly efficient ambipolar transport with hole and electron mobility up to 8.90 and 7.71 cm2 V-1 s-1 in flexible organic field-effect transistors, presenting a milestone for ambipolar copolymer screening. Based on this performance metrics and good solubility, PDBD-Se is investigated as inkjet-printable semiconductor ink for organic complementary logic circuits. Under ambient processing, maximum hole and electron mobilities reach 6.70 and 4.30 cm2 V-1 s-1 , respectively. Printed complementary inverter and NAND gates with transition voltages near VDD /2 are fabricated, providing an easy-handling, general material for printed electronics and logic.

Copper(i) sulfide: a two-dimensional semiconductor with superior oxidation resistance and high carrier mobility.

Two-dimensional (2D) semiconductors with suitable direct band gaps, high carrier mobility, and excellent open-air stability are especially desirable for material applications. Herein, we show theoretical evidence of a new phase of a copper(i) sulfide (Cu2S) monolayer, denoted δ-Cu2S, with both novel electronic properties and superior oxidation resistance. We find that both monolayer and bilayer δ-Cu2S have much lower formation energy than the known β-Cu2S phase. Given that β-Cu2S sheets have been recently synthesized in the laboratory (Adv. Mater.2016, 28, 8271), the higher stability of δ-Cu2S than that of β-Cu2S sheets suggests a high possibility of experimental realization of δ-Cu2S. Stability analysis indicates that δ-Cu2S is dynamically and thermally stable. Notably, δ-Cu2S exhibits superior oxidation resistance, due to the high activation energy of 1.98 eV for the chemisorption of O2 on δ-Cu2S. On its electronic properties, δ-Cu2S is a semiconductor with a modest direct band gap (1.26 eV) and an ultrahigh electron mobility of up to 6880 cm2 V-1 s-1, about 27 times that (246 cm2 V-1 s-1) of the β-Cu2S bilayer. The marked difference between the electron and hole mobilities of δ-Cu2S suggests easy separation of electrons and holes for solar energy conversion. Combination of these novel properties makes δ-Cu2S a promising 2D material for future applications in electronics and optoelectronics with high thermal and chemical stability.

Ultrahigh electron mobility induced by strain engineering in direct semiconductor monolayer Bi2TeSe2.

The successful commercial applications as thermoelectric devices and, due to their exotic electronic properties, as topological insulators of bismuth telluride (Bi2Te3) and bismuth selenide (Bi2Se3) have stimulated research interest on Bi2Se3/Bi2Te3-based chemical compounds. Based on the first-principles calculations, we investigate the electronic, optical, vibrational and transport properties of new monolayer Bi2TeSe2 obtained by transmuting one Se atom into its neighboring Te atom in the same group from Bi2Se3. We find that the monolayer Bi2TeSe2 maintains a stable hexagonal structure up to 700 K. Monolayer Bi2TeSe2 possesses a direct bandgap of 0.29 eV due to the strong spin-orbit coupling effects, and it remains a direct semiconductor for strains in a moderate range. The optical absorption covers a wide range from the green region to the ultraviolet region, which may lead to applications in optoelectronic devices like saturable absorbers. An extremely high electron mobility of 20 678 cm2 V-1 s-1 along the zigzag direction can be achieved by strain engineering with -6% compressive strain, which is nearly ten times larger than the intrinsic mobility. These indicate that monolayer Bi2TeSe2 is a promising candidate for future high-speed (opto)electronic devices.

Efficacious Electrochemical Oxygen Evolution from a Novel Co(II) Porphyrin/Pyrene-Based Conjugated Microporous Polymer.

Oxygen evolution reaction (OER) is energetically challenging from the platform of making many photovoltaic devices such as metal-air batteries and water splitting systems because of its poor kinetics even when precious metals are used. Herein, a Co(II)-porphyrin/pyrene-comprised conjugated microporous polymer Co-MPPy-1 has been developed which shows efficient OER in alkaline medium. The material was characterized by Fourier transform infrared, solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance, N2 volumetric adsorption/desorption analysis, scanning electron microscopy, ultra high resolution-transmission electron microscopy, X-ray photoelectron spectroscopy, and other physical studies. Co-MPPy-1 showed Brunauer-Emmett-Teller surface area of ∼501 m2 g-1. Co-MPPy-1 achieved a current density of 1 and 10 mA/cm-2 at 340 and 420 mV, respectively. The turnover frequency calculated for the OER is 0.43 s-1. The heterogeneity of this electrocatalyst was tested by chronoamperometric measurement and 1000 cycle recyclability test with retainment of the excellent electrochemical catalytic activity. This can be attributed to the presence of high density of Co(II) porphyrin unit and efficient charge transport in the π-conductive conjugated polymeric backbone.

P3Cl2: A Unique Post-Phosphorene 2D Material with Superior Properties against Oxidation.

Herein, a unique class of post-phosphorene materials, namely, phosphorene halogenides (e.g., α-P3Cl2) with superior oxidation resistance and desirable bandgap characteristics, are proposed. Our first-principles computations show that monolayer α-P3Cl2 is a direct semiconductor with a wide bandgap of 2.41 eV (HSE06) or 4.02 eV (G0W0), while the bandgap exhibits only slight reduction with increasing number of layers. The monolayer α-P3Cl2 also possesses highly anisotropic carrier mobility, with both ultrahigh electron mobility (56 890 cm2 V-1 s-1) and hole mobility (26 450 cm2 V-1 s-1). Meanwhile, the outstanding optical properties and favorable band alignment of 2D P3Cl2 suggest its potential as a photocatalyst for visible-light water splitting. 2D α-P3X2 (X = F, Br, I) also exhibit good oxidation resistance and possess wide direct bandgaps ranging from 2.16 to 2.43 eV (HSE06). These unique electronic and optical properties render 2D phosphorene halogenide as promising functional materials for broad applications in electronic and optoelectronic devices.

Tunable Electronic Structures of Hydrogenated Zigzag and Armchair Dumbbell Silicene Nanosheets: A Computational Study

Very recently, zigzag and armchair dumbbell silicene (zd-Si and ad-Si) nanosheets have been identified as the most stable structures of two-dimensional silicon systems. Here, utilizing the first-principle calculations, we have investigated the fully hydrogenated forms of these dumbbell silicene (H-zd-Si and H-ad-Si). It is found that the hydrogenation is an energetically favorable process on the dumbbell silicene, for which the formed structures possess robust mechanical, dynamical, and thermal stabilities. Semiconducting behaviors are well preserved in these H-zd-Si and H-ad-Si nanosheets, which are indirect- and direct-gap semiconductors with larger band gaps than the pristine cases. The gap sizes and band features can be significantly modulated by uniaxial strains, and an indirect-to-direct (direct-to-indirect) band gap transition occurs in the H-zd-Si (H-ad-Si) nanosheet under a small y-axial tensile strain. More interestingly, a ultra high electron mobility is present in the H-ad-Si nanosheet, which ...

Changes in the Crystal Lattice Parameters of Montmorillonite during Its Modification by Cobalt and Aluminum Cations

The effect the modification (pillarization) of montmorillonite clays from different locations has on the crystallographic lattice parameters of montmorillonite is determined. It is revealed through ultrahigh resolution transmission electron microscopy and analyzing microdiffraction patterns that pillarization raises the distance between montmorillonite structural units to 2.2 nm, while the intracrystal distance between the atoms grows by 0.4 nm. The catalytic activity of specimens in the oxidation reaction between organic dyes and hydrogen peroxide is enhanced 2–3 times.

Screening for Lactobacillus plantarum Strains That Possess Organophosphorus Pesticide-Degrading Activity and Metabolomic Analysis of Phorate Degradation.

This work performed a large scale assessment for organophosphorus pesticides (OPPs) degradation activity of 121 Lactobacillus (L.) plantarum strains. Six L. plantarum strains (P9, IMAU80110, IMAU40100, IMAU10585, IMAU10209, and IMAU80070) were found to possess high capacity of degrading three commonly used OPPs, namely dimethoate, phorate, and omethoate; and they were selected for more detailed characterization. Moreover, the three OPPs were mainly detected in the culture supernatants but not in the cell extracts, further confirming that the OPPs were degraded rather than absorbed by the cells. Among the six selected strains, P9 was most tolerant to gastrointestinal juices and bile. We thus used ultra-high performance liquid chromatography electron spray ionization coupled with time-of-flight mass spectrometry (UPLC/ESI-Q-TOF/MS) to generate the metabolomic profiles of the strain P9 growing in MRS medium with and without containing phorate. By using orthogonal partial least squares discriminant analysis, we identified some potential phorate-derived degradative products. This work has identified novel lactic acid bacteria resources for application in pesticide degradation. Our results also shed light on the phorate degradation mechanism by L. plantarum P9.

Distorted Janus Transition Metal Dichalcogenides: Stable Two-Dimensional Materials with Sizable Band Gap and Ultrahigh Carrier Mobility

Transition metal dichalcogenides (TMDs) are ideal layered materials to fabricate field effect transistors (FETs) due to their sizable band gaps and high stability, however, the low carrier mobility limits the response speeds. Here, based on recent experimental progress, we employed first principle calculations to reveal a distorted phase of the Janus TMD, 1T′ MoSSe, which is highly stable, exhibiting a moderate band gap and ultrahigh carrier mobility. We show that 1T′ MoSSe can be obtained via structural transition from the synthesized 2H phase after overcoming an energy barrier of 1.10 eV, which can be significantly reduced with alkali metal adsorption, thus proposing a feasible approach for experimental fabrications. 1T′ MoSSe is predicted to be a semiconductor with a trivial band gap of 0.1 eV (based on Heyd–Scuseria–Ernzerhof calculations), which can be closed to form Dirac nodes and then reopened under strain deformation. Due to the almost linear dispersion of the band states, an ultrahigh electron (...

High Efficiency Light-Emitting Transistor with Vertical Metal-Oxide Heterostructure.

The monolithic integration of light-emission with a standard logic transistor is a much-desired multifunctionality. Here, a high-efficiency light-emitting transistor (LET) employing an inorganic quantum dots (QDs) emitter and a laser-annealed vertical metal-oxide heterostructure is reported. The experimental results show that the peak efficiency and luminance of this QDs LET (QLET) are 11% and 8000 cdm-2 , respectively at a monochromatic emitting light wavelength of 585 nm. As far as it is known, these are among the highest values ever achieved for LETs. More importantly, the QLET exhibits an ultrahigh electron mobility of up to 25 cm2 V-1 S-1 , a lower efficiency roll-off (7% at high 3000 cdm-2 ), and excellent stability with long-duration gate stress switching cycles. Additionally, this approach is compatible with those used in conventional large-area silicon electronic manufacturing and can enable a scalable and cost-effective procedure for future integrated versatile displays and lighting applications.

Ultra-high brightness electron beams from very-high field cryogenic radiofrequency photocathode sources

Recent investigations of RF copper structures operated at cryogenic temperatures performed by a SLAC-UCLA collaboration have shown a dramatic increase in the maximum surface electric field, to 500 MV/m. We examine use of these fields to enable very high field cryogenic photoinjectors that can attain over an order of magnitude increase in peak electron beam brightness. We present beam dynamics studies relevant to X-ray FEL injectors, using start-to-end simulations that show the high brightness and low emittance of this source enables operation of a compact FEL reaching a photon energy of 80 keV. The preservation of beam brightness in compression, exploiting micro-bunching techniques is discussed. While the gain in brightness at high field is due to increase of the emission current density, further increases in brightness due to lowering of the intrinsic cathode emittance in cryogenic operation are also enabled. While the original proposal for this type of cryogenic, ultra-high field photoinjector has emphasized S-band designs, there are numerous potential advantages that may be conferred by operation in C-band. We examine issues related to experimental implementation in C-band, and expected performance of this type of device in a future hard X-ray FEL such as MaRIE.

Characterization of Mechanisms of Glutathione Conjugation with Halobenzoquinones in Solution and HepG2 Cells.

Halobenzoquinones (HBQs) are a class of emerging disinfection byproducts. Chronic exposure to chlorinated drinking water is potentially associated with an increased risk of human bladder cancer. HBQ-induced cytotoxicity involves depletion of cellular glutathione (GSH), but the underlying mechanism remains unclear. Here we used ultrahigh performance liquid chromatography-high resolution mass spectrometry and electron paramagnetic resonance spectroscopy to study interactions between HBQs and GSH and found that HBQs can directly react with GSH, forming various glutathionyl conjugates (HBQ-SG) in both aqueous solution and HepG2 cells. We found that the formation of HBQ-SG varies with the initial molar ratio of GSH to HBQ in reaction mixtures. Higher molar ratios of GSH to HBQ facilitate the conjugation of more GSH molecules to an HBQ molecule. We deduced the reaction mechanism between GSH and HBQs, which involves redox cycling-induced formation of halosemiquinone (HSQ) free radicals and glutathione disulfide, Michael addition, as well as nucleophilic substitution. The proposed reaction rates are in the following order: formation of HSQ radicals > substitution of bromine by GSH > Michael addition of GSH on the benzoquinone ring > substitution of chlorine by GSH > substitution of the methyl group by GSH. The conjugates identified in HBQ-treated HepG2 cells were the same as those found in aqueous solution containing a 5:1 ratio of GSH:HBQs.

Development of an ultrahigh vacuum low temperature transmission electron microscope for in-situ observation of ices

これまでの透過型電子顕微鏡を使った氷の研究では，鏡体内の残留水蒸気分圧が高く，氷の生成を制御した実験は困難であった．そこで，本研究では超高真空鏡体内の極低温に冷却した薄膜上に氷を作り，それに種々のプロセスを与え，構造・組織変化のその場観察を可能にする超高真空極低温透過型電子顕微鏡を開発した．この装置の概要を紹介し，さらに，この装置を用いておこなった研究の一例を紹介する．ひとつは，マトリックス昇華法と命名した新しい方法による高密度アモルファス氷の生成である．10KでCO：H2O=50：1の混合ガスを蒸着し，その後温度を上昇させると40K前後でCOが昇華し，高密度のアモルファス氷が残る．この氷はH2Oガスのみを蒸着させて作ったアモルファス氷より高密度で，高圧法で作ったアモルファス氷の密度に匹敵する．もうひとつは，10Kでアモルファス氷に紫外線を照射し，その後温度を上昇させると，50K前後で高粘性の液体的状態へ変化することを発見したことである．この液体的状態は50-140Kで観察された．水のガラス転移温度が136Kであることを考慮すると，これは驚くべき発見であり，惑星科学的にも重要な意義がある．

Graphene-based label-free electrochemical aptasensor for rapid and sensitive detection of foodborne pathogen.

Reduced graphene oxide (rGO) has emerged as a promising nanomaterial for reliable detection of pathogenic bacteria due to its exceptional properties such as ultrahigh electron transfer ability, large surface to volume ratio, biocompatibility, and its unique interactions with DNA bases of the aptamer. In this study, rGO-azophloxine (AP) nanocomposite aptasensor was developed for a sensitive, rapid, and robust detection of foodborne pathogens. Besides providing an excellent conductive and soluble rGO nanocomposite, the AP dye also acts as an electroactive indicator for redox reactions. The interaction of the label-free single-stranded deoxyribonucleic acid (ssDNA) aptamer with the test organism, Salmonella enterica serovar Typhimurium (S. Typhimurium), was monitored by differential pulse voltammetry analysis, and this aptasensor showed high sensitivity and selectivity for whole-cell bacteria detection. Under optimum conditions, this aptasensor exhibited a linear range of detection from 108 to 101cfumL-1 with good linearity (R 2=0.98) and a detection limit of 101cfumL-1. Furthermore, the developed aptasensor was evaluated with non-Salmonella bacteria and artificially spiked chicken food sample with S. Typhimurium. The results demonstrated that the rGO-AP aptasensor possesses high potential to be adapted for the effective and rapid detection of a specific foodborne pathogen by an electrochemical approach. Graphical abstract Fabrication of graphene-based nanocomposite aptasensor for detection of foodborne pathogen.

Improvement of sensitivity of graphene photodetector by creating bandgap structure**Project supported by the National Natural Science Foundation of China (Grant No. 51271210), the Chongqing Municipal Research Program of Basic Research and Frontier Technology, China (Grant No. cstc2015jcyjBX0039), and the Foundation for the Creative Research Groups of Higher Education of Chongqing Municipality, China (Grant No. CXTDX201601016).

Graphene has aroused large interest in optoelectronic applications because of its broad band absorption and ultrahigh electron mobility. However, the low absorption of 2.3% seriously limits its photoresponsivity and restricts the relevant applications. In this paper, a method to enhance the sensitivity of graphene photodetector is demonstrated by introducing electron trapping centers and creating a bandgap structure in graphene. The carrier lifetime obviously increases, and more carriers are collected by the electrodes. Compared with intrinsic graphene detector, the defective graphene photodetector possesses high photocurrent and low-driving-voltage, which gives rise to great potential applications in photodetector area.

Optimization of monochromated TEM for ultimate resolution imaging and ultrahigh resolution electron energy loss spectroscopy

The performance of a monochromated transmission electron microscope with Wien type monochromator is optimized to achieve an extremely narrow energy spread of electron beam and an ultrahigh energy resolution with spectroscopy. The energy spread in the beam is improved by almost an order of magnitude as compared to specified values. The optimization involves both the monochromator and the electron energy loss detection system. We demonstrate boosted capability of optimized systems with respect to ultra-low loss EELS and sub-angstrom resolution imaging (in a combination with spherical aberration correction).

Surface plasmons in suspended graphene: launching with in-plane gold nanoantenna and propagation properties

Graphene physics and plasmonics are two fields which, once combined, promise a variety of exciting applications. One of those applications is the integration of active nano-optoelectronic devices in electronic systems, using the fact that plasmons in graphene are tunable, highly confined and weakly damped. A crucial challenge remains before achieving these active devices: finding a platform enabling a high propagation of Graphene Plasmons Polaritons (GPPs). Suspended graphene presenting ultrahigh electron mobility has given rise to increasing interest. We numerically studied the plasmonic properties of suspended graphene. We propose a hybrid configuration and a set of conditions to launch graphene plasmons via an in-plane gold nanoantenna, for micrometric propagation of surface plasmons in suspended graphene. Finally, we propose a realistic optoelectronic device based on the use of suspended graphene.

Graphene-based gas sensor

Graphene, a honeycomb structure with single layer sp2 hybridization carbon atom, has extraordinary mechanical and electrical properties, exhibiting great potential in sensing area. The ultrahigh electron mobility in room temperature as well as the ultrahigh specific surface area, endows graphene a promising candidate for ultrasensitive gas sensor. As a typical two dimensional material, every atom in graphene can be regarded as surface atom. Therefore, every atom will be able to interact with gas molecule, which provides an ultrahigh sensitivity and the ultralow detection limit (as low as for single molecule detection). The current researches for improvement of gas sensing mainly focus on two aspects: (1) Design of different working principle devices; (2) surface modification on graphene and composite with other materials (i.e . metal, metal oxide and organic polymer). The specific adsorption sites can be achieved, resulting the improvement of selectivity. This review will present and summarize recent achievements of graphene-based gas sensor in both aspects and also predict the potential research direction in the future. According to different working mechanism, graphene-based gas sensor can be classified as resistive type, field-effect-transistor (FET) type, mass sensitive type, and micro-electromechanical system (MEMS) type. Each kind has its advantages. Thanks to the simple manufacture process, resistive gas sensor is investigated broadly. Compared to passive resistive sensor, the active FET sensor exhibits better performance in sensitivity and stability generally. As for mass sensitive sensor, the unique mechanism can provide a new device structure different from the other three types. However, concerning the compatibility with integrated circuits (IC) manufacture, MEMS sensor can be a good choice. Materials with high specific surface area are able to provide more adsorption sites. Consequently, sensor performance can be improved sharply. Therefore, surface modification on graphene and composite with other materials attracts broad attention recently. By changing the density and the type of functional groups on graphene surface, specific adsorption sites can be achieved. Hence, the ability for selective gas detection is enhanced. Besides, graphene-based composite with other materials (i.e. metal, metal oxide and organic polymer) is another effective strategy to optimize sensor performance. In conclusion, lots of achievements and big breakthroughs for graphene-based gas sensor have been made in recent years. Especially the obvious enhancement for sensitivity (as low as for single molecule detection) and gas selective detection, graphene-based gas sensor exhibits great advantage compared with traditional sensors. However, the time-consuming process of gas adsorption and desorption hampers the real-time measurements due to the long response and recover time. Therefore, improvement in response and recover performance will be a potential research direction in the future. In addition, the integration of different kinds of gas sensors even other types of sensors will be a trend. Also, it will be a desirable fundamental research to give explanations for the sensing mechanism as well as to investigate the dynamic interaction between gas molecules and graphene. Recently, it is believed that with the help of special in - situ holder, researchers can launch experiments in transmission electron microscope (TEM) to explore this fundamental study.

Detection of Quinoline in G. boninense-Infected Plants Using Functionalized Multi-Walled Carbon Nanotubes: A Field Study.

Carbon nanotubes (CNTs) reinforced with gold nanoparticles (AuNPs) and chitosan nanoparticles (CTSNPs) were anchored on a screen-printed electrode to fabricate a multi-walled structure for the detection of quinoline. The surface morphology of the nanocomposites and the modified electrode was examined by an ultra-high resolution field emission scanning electron microscope (FESEM), and Fourier-transform infrared (FT-IR) spectroscopy was used to confirm the presence of specific functional groups on the multi-walled carbon nanotubes MWCNTs. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to monitor the layer-by-layer assembly of ultra-thin films of nanocomposites on the surface of the electrode and other electrochemical characterizations. Under optimized conditions, the novel sensor displayed outstanding electrochemical reactivity towards the electro-oxidation of quinoline. The linear range was fixed between 0.0004 and 1.0 μM, with a limit of detection (LOD) of 3.75 nM. The fabricated electrode exhibited high stability with excellent sensitivity and selectivity, specifically attributable to the salient characteristics of AuNPs, CTSNPs, and MWCNTs and the synergistic inter-relationship between them. The newly developed electrode was tested in the field. The Ipa increased with an increase in the amount of quinoline solution added, and the peak potential deviated minimally, depicting the real capability of the newly fabricated electrode.

Silver nanoparticles supported over Al2O3@Fe2O3 core-shell nanoparticles as an efficient catalyst for one-pot synthesis of 1,2,3-triazoles and acylation of benzyl alcohol

Metallic nanoparticles supported over core-shell metal oxide nanostructures have huge scope in heterogeneous catalysis due to the scope for fine dispersion of the reactive NPs on high surface area material. Silver nanoparticles are supported over Al2O3@Fe2O3 core-shell nanostructured material through aqueous phase reduction method. Ag-Al2O3@Fe2O3 core-shell nanoparticles has been characterized through powder X-ray diffraction, ultra high resolution transmission electron microscopy, scanning electron microscopy, N2 adsorption/desorption isotherm, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy and thermogravimetric analysis. The N2 adsorption/desorption isotherms of Ag-Al2O3@Fe2O3 material are classified as typical type IV isotherm with a large H2 type hysteresis loop for the mesopores. This core-shell mesoporous nanocatalyst showed high catalytic efficiency for the synthesis of 1,4-disubstituted 1,2,3-triazoles in water and acylation of benzyl alcohol under solvent-free conditions. The catalyst is heterogeneous in nature and can be easily recovered and reused without appreciable decrease in its catalytic activity.