Three-dimensional vertical ZnO transistors with suspended top electrodes fabricated by focused ion beam technology

Three-dimensional(3D)vertical architecture transistors represent an important technological pursuit,which have distinct advantages in device integration density,operation speed,and power consumption.However,the fabrication processes of such 3D devices are complex,especially in the interconnection of electrodes.In this paper,we present a novel method which combines suspended electrodes and focused ion beam(FIB)technology to greatly simplify the electrodes interconnection in 3D devices.Based on this method,we fabricate 3D vertical core-double shell structure transistors with ZnO channel and Al₂O₃ gate-oxide both grown by atomic layer deposition.Suspended top electrodes of vertical architecture could be directly connected to planar electrodes by FIB deposited Pt nanowires,which avoid cumbersome steps in the traditional 3D structure fabrication technology.Both single pillar and arrays devices show well behaved transfer characteristics with an Ion/Ioff current ratio greater than 106 and a low threshold voltage around 0 V.The ON-current of the 2×2 pillars vertical channel transistor was 1.2μA at the gate voltage of 3 V and drain voltage of 2 V,which can be also improved by increasing the number of pillars.Our method for fabricating vertical architecture transistors can be promising for device applications with high integration density and low power consumption.     

Electrical impedance spectroscopy of ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate (ECOENG™ 110)

Ionic liquid “ECOENG? 110”, a promising electrolyte for electrochemical devices, was investigated by impedance spectroscopy. Metallic electrodes (Pt, Cu, Ag, and Mo) as well as carbon were used for the electrochemical characterization. The dependences of the real and imaginary impedance, polarization resistance and electrochemical capacity of the double layer on the electrode potential were investigated using electrical equivalent circuits of R₁(QR₂) and R₁[Q(R₂W)] types.     

Cu2S nanocrystals incorporated highly efficient non-fullerene ternary organic solar cells

Here, we report Cu₂S nanocrystals based non-fullerene ternary polymer solar cells by incorporating Cu₂S in conjugated polymer (PBDB-T: poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl) benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))]) and small molecule non-fullerene compound (ITIC:3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene). The devices were fabricated in inverted configuration i.e. ITO/ZnO/PBDB-T: Cu₂S NCs: ITIC/MoO₃/Ag. Effect of concentration of Cu₂S nanocrystals on the performance parameters of PBDB-T: ITIC based organic solar cells is studied. An enhancement in the power conversion efficiency from 8.24% to 9.53% is achieved for the optimum concentration of Cu₂S nanocrystals in the organic photoactive blend. The cause of improvement in the performance parameters of the device is investigated by means of the light intensity dependent electrochemical impedance spectroscopy and atomic force microscopy. It is found that the devices with Cu₂S nanocrystals have less trap-assisted recombination.     

Boron-Doped Diamond-Film-Based Two-Dimensional Electrode of Electrophoresis Tank

Chemically robust conductive p-type boron-doped diamond(BDD) films are an important electrode material and have been widely applied in electrochemistry.In this study,BDD films are taken as a two-dimensional(2D)electrode in a electrophoresis tank system instead of the conventional one-dimensional platinum wire electrode.The theoretical simulations by finite element numerical analysis reveal that the 2D BDD electrodes have relatively high intensity and uniformity of electric field in the tank.Experimentally,the 2D BDD electrodes with smaller size show excellent properties for the separation of DNA fragments.The advantages of the 2D BDD electrodes with chemical inertness,sustainability,high intensity and uniformity electronic field,as well as reduced small size of electrophoresis tank would open a possibility for realizing new generation,high-performance biological devices.     

Nanomaterials for electrochemical energy storage

The development of nanotechnology in the past two decades has generated great capability of controlling materials at the nanometer scale and has enabled exciting opportunities to design materials with desirable electronic, ionic, photonic, and mechanical properties. This development has also contributed to tile advance in energy storage, which is a critical technology in this century. In this article, we will review how the rational design of nanostructured materials has addressed the challenges of batteries and electrochemical capacitors and led to high-performance electrochemical energy storage devices. Four specific material systems will be discussed： i） nanostructured alloy anodes for Li-batteries, ii） nanostructured sulfur cathodes for Li-batteries, iii） nanoporous open- framework battery electrodes, and iv） nanostructured electrodes for electrochemical capacitors.     

Negative Differential Resistance and Rectifying Effects of Diblock Co-Oligomer Molecule Devices Sandwiched between C_2N-h2D Electrodes

Based on nonequilibrium Green's function method in combination with density functional theory, we study the electronic transport properties of dipyrimidinyl-diphenyl molecules embedded in a carbon atomic chain sandwiched between zigzag graphene nanoribbon and different edge geometries C_2N-h2D electrodes. Compared with the graphene electrodes, the C_2N-h2D electrode can cause rectifying and negative differential resistance effects.For C_2N-h2D with zigzag edges, a more remarkable negative differential resistance phenomenon appears, whereas armchair-edged C_2N-h2D can give rise to much better rectifying behavior. These results suggest that this system can be potentially useful for designs of logic and memory devices.     

Silver nanocrystals modified microstructured polymer optical fibres for chemical and optical sensing

In-fibre chemical and optical sensors based on silver nanocrystals modified microstructured polymer optical fibres (MPOFs) were demonstrated. The silver nanocrystals modified MPOFs were formed by direct chemical reduction of silver ammonia complex ions on the templates of array holes in the microstructure polymer optical fibres. The nanotube-like and nanoisland-like Ag-modified MPOFs could be obtained by adjusting the conditions of Ag-formation in the air holes of MPOFs. SEM images showed that the higher concentration of the reaction solution (silver ammonia 0.5 mol/L, glucose 0.25 mol/L), gave rise to a tubular silver layer in MPOF, while the lower concentration (silver ammonia 0.1 M, glucose 0.05 M) produced an island-like Ag nanocrystal modified MPOF. The tubular Ag-MPOF composite fibre was conductive and could be directly used as array electrodes in electrochemical analyses. It displayed high electrochemical activity on sensing nitrate or nitrite ions. The enhanced fluorescence of dye molecules was observed when the island-like Ag-modified MPOF was inserted into a fluorescent dye solution.     

Massively parallel low-cost pick-and-place of optoelectronic devices by electrochemical fluidic processing

We describe a novel electrochemical technique for the nonlithographic, fluidic pick-and-place assembly of optoelectronic devices by electrical and optical addressing. An electrochemical cell was developed that consists of indium tin oxide (ITO) and n -type silicon substrates as the two electrode materials and deionized water (R = 18 MOmega) as the electrolytic medium between the two electrodes. 0.8-20-microm-diameter negatively charged polystyrene beads, 50-100-microm-diameter SiO(2) pucks, and 50-microm LED's were successfully integrated upon a patterned silicon substrate by electrical addressing. In addition, 0.8-microm-diameter beads were integrated upon a homogeneous silicon substrate by optical addressing. This method can be applied to massively parallel assembly (>1000 x 1000 arrays) of multiple types of devices (of a wide size range) with very fast (a few seconds) and accurate positioning.     

Colloidal nanocrystal ZnO- and TiO<Subscript>2</Subscript>-modified electrodes sensitized with chlorophyll a and carotenoids: a photoelectrochemical study

Heterostructures formed of films of organic-capped ZnO and TiO₂ nanocrystals (both with the size of ca. 6 nm) and photosynthetic pigments were prepared and characterized. The surface of optically transparent electrodes (Indium Tin Oxide) was modified with nanocrystals and prepared by colloidal synthetic routes. The nanostructured electrodes were sensitized by a mixture of chlorophyll a and carotenoids. The characterization of the hybrid structures, carried out by means of steady-state optical measurements, demonstrated such class of dyes able to extend the photoresponse of the large band-gap semiconductors. The charge-transfer processes between the components of the heterojunction were investigated, and photoelectrochemical measurements taken on the sensitized ZnO and TiO₂ nanocrystals electrodes elucidated the photoactivity of the heterojunctions as a function of the dyes and of the red–ox mediator used in solution. The effect of methyl viologen as different red–ox mediator was also evaluated in order to show its effect on the heterojunction photoactivity. The overall results contributed to describe the photoelectrochemical potential of the investigated heterojunctions, highlighting a higher response of the dye-sensitized ZnO nanocrystals, and then provided the TiO₂-modified counterparts.     

Electronic properties of semiconductor quantum dots for Coulomb blockade applications

This paper deals with the electronic properties of Si and Ge nanocrystals (NCs) with a view to studying their potentialities for single electron devices. The 3D Poisson–Schrödinger equations are self-consistently solved for a single NC embedded in SiO₂. A 1D spherical approximation is compared to the full 3D approach. For various shapes and sizes of NC the energy levels and the density are calculated as a function of the applied voltage and the number of electrons stored in the NC. The potential properties of such nanostructures for Coulomb blockade operation are deduced.     

Coulomb blockade sensors based on nanostructured mesoporous silicon

Mesoporous silicon (mesoPS) is a nanosponge where Si nanocrystals are interconnected forming a disordered 3D array. The electronic characteristics of this material are particularly interesting, due to some intriguing effects, such as a huge increase of conductivity, reversible insulator-to-metal transition and n- or p-type doping of the nanocrystals, exhibited in presence of donor or acceptor molecules like NH₃ and NO₂. Here we report on the observation of a sharp conductance gap, which can be ascribed to Coulomb blockade phenomena. Moreover, we show that the width of the gap can be tuned by NO₂ molecules, so that the fabrication of highly sensitive threshold sensors is possible. Our results suggest that electrochemical etching of heavily doped Si can be used as a simple self-assembly technique for the production of Si nanocrystal arrays and for the fabrication of sensitive nanosensors.     

Binder-free composite electrodes using carbon nanotube networks as a host matrix for activated carbon microparticles

In this research, networks of single-walled carbon nanotubes (SWNTs) were used to host activated carbon (aC) microparticles to fabricate freestanding composite electrodes without the use of polymer binders. The aC-SWNT composite electrodes with up to 50 wt. % aC showed specific surface areas approaching 1000 m²/g and electrical conductivities >36 S/cm. The composite electrodes possessed the properties of both pure SWNT electrodes (e.g. low ohmic drop and rapid ion diffusion) and activated carbon particles (e.g. high specific capacitance). With an interconnected mesoporous microstructure and high electrical conductivity, the CNT networks provide an attractive alternative to polymer binders for forming freestanding electrodes for electrical energy storage devices. Here we show that micron-sized particles can be supported in this framework to utilize the performance enhancement and robustness provided by CNTs. Symmetric electrochemical capacitors fabricated with the electrodes in 6 M potassium hydroxide (KOH) aqueous electrolyte maintained specific capacitances of more than 45 F/g after 30,000 constant-current charge–discharge cycles with a current of 3.6 mA/cm².     

MEH-PPV/CdSe纳米复合器件的光电导特性的研究

以CdO和Se粉作为前驱物,在TOPO/TOP有机体系中制备了CdSe纳米晶,将其与聚合物MEH-PPV复合制备了复合光电导器件,研究了它的光电导特性,并将其与单层MEH-PPV光电导器件的特性进行了比较。结果发现纳米复合光电导器件的光电流响应光谱的2个峰的位置基本上与MEH-PPV和CdSe纳米晶的吸收峰的位置相对应,这说明CdSe纳米晶和聚合物MEH-PPV的吸收对光电流都有贡献,主要是由于CdSe纳米晶和MEH-PPV界面处的激子离化和电荷转移造成的。而且复合器件的光电流较单层有所增强,且MEH-PPV器件光谱的响应范围更宽。     

Synthesis,characterization and performance enhancement of dry polyaniline-coated neuroelectrodes for electroencephalography measurement

Originating from a combination of neuroscience and biomedical engineering strategies, neuroprosthetics are developed as substitutes for sensory or cognitive modality damages caused by an injury or a disease. Dry electrodes are essential devices for monitoring of the biopotential such as electroencephalography (EEG) and electrocardiography (ECG). In this paper, polyaniline (PANI) coated stainless steel (SS) electrodes have been fabricated using in-situ electrochemical polymerization on the SS surface. The SEM images showed the formation of a nanoporous PANI-coating on the SS electrodes. EIS measurements on a skin model demonstrated a significantly lower contact impedance for the PANI-coated electrodes compared to bare SS electrodes. Furthermore, increasing the thickness of the nanoporous coating resulted in a higher contact impedance reduction. The comparison of the EEG measurements for the manufactured electrodes with conventional wet Ag/AgCl electrodes showed that the electrodes could successfully monitor alpha rhythms and muscle artifacts, as well. The prepared electrode can be used in various applications such as biopotential monitoring.     

Si-based solid blue emitters from 3C-SiC nanocrystals

A procedure for preparing 3C-SiC/SiO₂ composite nanocrystals embedded in Si matrix that emit blue light is reported. Through electrochemical etching of polycrystalline 3C-SiC wafers followed by ultrasonic treatment in water bath, we fabricated luminescent colloidal 3C-SiC nanocrystals. Porous Si samples that have been naturally oxidized in air for 12 h were immersed in agitated aqueous suspension of 3C-SiC nanocrystals for 10 min and then dried in air, followed by annealing in argon atmosphere to form core-shell structured 3C-SiC/SiO₂ nanocrystals embedded in Si matrix. Our result shows that the luminescence of 3C-SiC/SiO₂ composite nanocrystals is very stable over time or under high temperature. As robust and stable Si-based solid blue-emitters, they have important implications for engineering photonic components in optoelectronics and photonics. PACS 78.67.Bf; 78.55.Hx; 78.66.Sq     

温控/光控片上纳米裂结

由于分子尺寸小、可化学合成、与生物组织兼容等显著优点,以有机小分子为核心的单分子器件引起了人们的广泛关注,单分子器件有望成为硅基电子器件的一个重要的互补发展方向。已报道构筑单分子电子回路的大部分方法程序繁琐,且无法在平面基底上实时调控电极间的间距。这项工作采用机械切割结合电化学腐蚀的方法来制作纳米电极,通过控制施加在阴极和阳极之间的电压,并实时监测通过被腐蚀的金线的电流的大小,可以获得针尖状与分子大小匹配的纳米电极。进一步利用热胀冷缩的原理,采用比金的热膨胀系数小很多的材料作为基底,实现了环境温度对电极间距离的调控,即通过改变环境温度实现了可重复操作的电极间的连接及断开。在此温控基础之上,进一步实现了利用光强更为地精密调控电极间的距离,调控的精度可以达到原子级别。实验结果表明,我们制作的温控/光控片上纳米电极无需借助高精尖仪器,就可以实现对电极之间的距离的精密控制,其平面基底构型,为单分子电子器件的研究提供了有助于片上器件集成的新方法。     

Fabrication of ZnO and its enhancement of charge injection and transport in hybrid organic/inorganic light emitting devices

ZnO nanocrystals were synthesized by hydrolysis in methanol. X-ray diffraction and photoluminescence spectra confirm that good crystallized ZnO nanoparticles were formed. Utilizing those ZnO nanoparticles and poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), light emitting devices with indium tin oxide (ITO)/poly(3,4-oxyethyleneoxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS)/ZnO:MDMO-PPV/Al and ITO/PEDOT:PSS/MDMO-PPV/Al structures were fabricated. Electroluminescence (EL) spectra reveal that EL yield of hybrid MDMO-PPV and ZnO nanocrystals devices increased greatly as compared with pristine MDMO-PPV devices. The current-voltage characteristics indicate that addition of ZnO nanocrystals can facilitate electrical injection and charge transport. The decreased energy barrier to electron injection is responsible for the increased efficiency of electron injection.     

Sonochemical synthesis and anchoring of zinc oxide on hemin-mediated multiwalled carbon nanotubes-cellulose nanocomposite for ultra-sensitive biosensing of H2O2

In this work, the metal oxide and biopolymer nanocomposites on multiwalled carbon nanotubes (MWCNT) were prepared using a simple sonochemical method. The hexagonal nanorods of zinc oxide (ZnO NR) were synthesized by probe sonication (frequency = 20 kHz, amplitude = 50) method and were integrated on ultrasonically functionalized MWCNT-cellulose nanocrystals (MWCNT-CNC) for the first time. The stable hemin bio-composites also were prepared using the bath sonication (37 kHz of frequency, 150 W of power) method, and was used for the selective and ultrasensitive electrochemical detection of H₂O₂. The UV–Vis spectroscopy studies confirmed the presence of native hemin on MWCNT-CNC/ZnO NR nanocomposite. Cyclic voltammetry studies revealed that an enhanced redox electrochemical behaviour of hemin was observed on hemin immobilised MWCNT-CNC/ZnO NR nanocomposite than that of other hemin modified electrodes. Also, the MWCNT-CNC/ZnO NR/hemin modified SPCE showed 2.3 folds higher electrocatalytic activity with a lower reduction potential (−0.2 V) towards H₂O₂ than that of other investigated hemin modified electrodes including hemin/MWCNT and hemin/CNC-ZnO. The fabricated biosensor displayed a stable amperometric response (-0.2 V vs Ag/AgCl) in the linear concentration of H₂O₂ ranging up to 4183.3 µM with a lower detection limit of 4.0 nM.     

Hydrogen bubble-assisted growth of Pt3Te4 for electrochemical catalysts

Novel materials and structures with abundant active sites have been in continuous demand for electrochemical catalytic applications. In this study, we synthesized platinum telluride (Pt₃Te₄) nanocrystals on two-dimensional metallic molybdenum ditelluride (MoTe₂) using a dynamic hydrogen bubble template method in the hydrogen evolution reaction (HER). The local crystal structure and chemical state of the Pt₃Te₄ nanocrystals were investigated using X-ray nano-diffraction and X-ray nano-absorption spectroscopy. In our electrochemical deposition method, the morphology, and HER performance of the Pt₃Te₄ nanocrystals could be manipulated through the hydrogen bubble generation rate. Thus, the nanorod-shaped Pt₃Te₄ nanocrystals, fabricated by a high rate of hydrogen bubble generation, exhibited outstanding HER performance, which is in contrast with the HER performance of hemisphere-shaped Pt₃Te₄. Our study provides a facile and systematic way of synthesizing high-performance electrochemical catalysts using the hydrogen bubble-assisted growth method.     

Two‐Dimensional Au Nanocrystals: Shape/Size Controlling Synthesis,Morphologies, and Applications

The fascinating roles of two‐dimensional (2D) nanomaterials in natural super‐strong bio‐composites (i.e. aragonite platelets in nacre and apatite platelets in bone) have aroused great interest in scientific communities to synthesize their artificial counterparts with controllable geometric and physical properties. The quantum 2D confinement of electrons recently revealed in graphene nanosheets further inspires to explore 2D metal nanocrystals with intrinsic anisotropic properties and quantum size effect. Among them, 2D Au nanocrystals stand out not only due to their unique structure‐ and environmental‐dependent properties, but also due to their rapid development in synthesis approaches and emerging applications in electronics, optics, sensing and biomedicines. In this Review the aim is to rationalize numerous newly published studies on 2D Au nanocrystals and to gain insight into their shape/size controlling synthesis, diverse morphologies, properties, and applications, potentially serving a handy guide to achieve on‐demand 2D Au nanocrystals.