Low-voltage Field Research Articles

An efficient novel low voltage field electron emitter with cathode consisting of template synthesized copper microarrays

Synthesis of copper microstructures was done using the electrochemical template technique using the NTF (Nuclear Track Filter). The NTF was fabricated using the polycarbonate SSNTD (Solid State Nuclear Track Detector) which was created by irradiation of Uranium ions. The synthesized copper microstructures were further used to fabricate a novel low voltage field electron emitter. As compared to traditional technique of lithography-based nano/micro fabrication, template synthesis is a simple technique, where pores of NTFs are used as templates and by using a suitable electrochemical cell design, any type of nano/microstructures can be fabricated. The present paper envisages the production of nuclear track filters and fabrication of copper microstructures through galvanic replication. The studies also reports first time, a excellent low voltage field electron emitter fabricated by using copper microstructures in comparison to the earlier work. This low voltage field electron emitter being a novel cold cathode emitter can be a potential candidate for an energy saving devices.

Imaging with low-voltage scanning transmission electron microscopy: A quantitative analysis

A dedicated specimen holder has been designed to perform low-voltage scanning transmission electron microscopy in dark field mode. Different test samples, namely InGaAs/GaAs quantum wells, InGaAs nanowires and thick InGaAs layers, have been analysed to test the reliability of the model based on the proportionality to the specimen mass-thickness, generally used for image intensity interpretation of scattering contrast processes. We found that size of the probe, absorption and channelling must be taken into account to give a quantitative interpretation of image intensity. We develop a simple procedure to evaluate the probe-size effect and to obtain a quantitative indication of the absorption coefficient. Possible artefacts induced by channelling are pointed out. With the developed procedure, the low voltage approach can be successfully applied for quantitative compositional analysis. The method is then applied to the estimation of the In content in the core of InGaAs/GaAs core-shell nanowires.

Low-voltage cathodoluminescence properties of green-emitting ZnAl 2O 4:Mn 2+ nanophosphors for field emission display

A low-cost ZnAl 2O 4:Mn 2+ green nanophosphor for field emission display (FED) was successfully synthesized by the coprecipitation method and a two-step firing, firstly calcining at 1200 °C for 2 h in air and then annealing at 900 °C for 3 h in flowing NH 3 gas. The effects of the preparation process and the Mn 2+ concentration on optical properties of ZnAl 2O 4:Mn 2+ were investigated. The phase composition, particle morphology, photoluminescence (PL) spectra of the ZnAl 2O 4:Mn 2+ phosphor as well as low-voltage field emission properties of the FED device prepared by using the synthesized ZnAl 2O 4:Mn 2+ phosphor were examined. Similar to ZnGa 2O 4:Mn 2+, Mn 2+-doped ZnAl 2O 4 showed two green emission bands centered at 508 and 517 nm, respectively, which originate from 4T 1( 4G)→ 6A 1( 6S) transitions of Mn 2+ on T d and O h sites. The PL intensity reached the maximum at 0.5 at.% Mn 2+. Under the low-voltage excitation, the FED device exhibited bright green emission, high voltage brightness saturation, and high color purity.

Ultralow-voltage field-ionization discharge on whiskered silicon nanowires for gas-sensing applications

Several hundred million volts per centimetre of electric-field strength are required to field-ionize gas species. Such fields are produced on sharp metallic tips under a bias of a few kilovolts. Here, we show that field ionization is possible at dramatically lower fields on semiconductor nanomaterials containing surface states, particularly with metal-catalysed whiskers grown on silicon nanowires. The low-voltage field-ionization phenomena observed here cannot be explained solely on the basis of the large field-amplification effect of suspended gold nanoparticles present on the whisker tips. We postulate that field penetration causes upward band-bending at the surface of exposed silicon containing surface states in the vicinity of the catalyst. Band-bending enables the valence electron to tunnel into the surface states at reduced fields. This work provides a basis for development of low-voltage ionization sensors. Although demonstrated on silicon, low-voltage field ionization can be detected on any sharp semiconductor tip containing proper surface states.

Atrial defibrillation voltage: Falling to a new low

Atrial defibrillation voltage: Falling to a new low

A novel 0.7 V high sensitivity complementary differential MAGFET sensor for contactless mechatronic applications

This paper discusses the design of a novel low-voltage complementary differential magnetic field effect transistor (CDMAGFET) with enhanced magnetic field sensing capability compared to previously reported NMOS only MAGFET or the single-ended cross-coupled MAGFET (CCMAGFET). It uses split-drain concave NMOS and PMOS devices which are cross-connected and operated differentially to provide an enhanced sense voltage. Simulations using the IBM 130 nm CMOS process technology indicate that it has almost double the sensed voltaic output ( V SENSE) for the same magnetic field intensity ( B Z ) applied in quadrature to the MAGFET plane. Short channel devices are used for this design and comparison. The NMOS MAGFET had a sensing channel area of 2 × 0.13 μm × 30 μm while the PMOS MAGFET had a sensing channel area of 2 × 0.13 μm × 150 μm. Depending on the operating bandwidth the sensing channel area can be linearly increased in order to increase the mTESLA vs. channel area sensitivity of the MAGFET (usually by using longer channel length). Careful CDMAGFET layout techniques are discussed to eliminate DC offsets in the presence of a DC magnetic field. Also, in order to minimize the transversal thermal noise current in an AC magnetic field a very low CDMAGFET bias current is used. Experimental verification of the nanometric CDMAGFET operation in the presence of orthogonal DC and AC magnetic field is also reported. The measured relative DC and AC voltaic sensitivity for the experimental CDMAGFET was, respectively, 0.564 and 1.65 mV/(V mTESLA) (the peak AC sensitivity @ 250 kHz).

Cathodoluminescence degradation of PLD thin films

The cathodoluminescence (CL) intensities of Y2SiO5:Ce3+, Gd2O2S:Tb3+ and SrAl2O4:Eu2+,Dy3+ phosphor thin films that were grown by pulsed laser deposition (PLD) were investigated for possible application in low voltage field emission displays (FEDs) and other infrastructure applications. Several process parameters (background gas, laser fluence, base pressure, substrate temperature, etc.) were changed during the deposition of the thin films. Atomic force microscopy (AFM) was used to determine the surface roughness and particle size of the different films. The layers consist of agglomerated nanoparticle structures. Samples with good light emission were selected for the electron degradation studies. Auger electron spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the thin films. AES and CL spectroscopy were done with 2 keV energy electrons. Measurements were done at 1×10−6 Torr oxygen pressure. The formation of different oxide layers during electron bombardment was confirmed with X-ray photoelectron spectroscopy (XPS). New non-luminescent layers that formed during electron bombardment were responsible for the degradation in light intensity. The adventitious C was removed from the surface in all three cases as volatile gas species, which is consistent with the electron stimulated surface chemical reaction (ESSCR) model. For Y2SiO5:Ce3+ a luminescent SiO2 layer formed during the electron bombardment. Gd2O3 and SrO thin films formed on the surfaces of Gd2O2S:Tb3+ and SrAl2O4:Eu2+,Dy3+, respectively, due to ESSCRs.

100 W Operation of a Cold Cathode TWT

Recent demonstration of low-voltage high-transconductance field emitter array operation holds promise for the successful development of reliable cold cathode vacuum electronics device technologies. This paper reports on the experimental studies of implementation of such field emitter arrays as the electron source for a moderate power traveling wave tube (TWT) operating in the C-band frequency regime. The cold cathode TWT has operated for over 150 h at duty factors up to 10%, beam currents up to 121 mA, and RF powers up to 100 W at 5 GHz. High cathode current densities of 15.4 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were achieved concurrent with excellent beam control, resulting in 99.4% beam transmission under zero-RF-drive operating conditions and 97.3% transmission at maximum RF output power. The cathode is shown to operate with a 72% reduction in the operating voltage from the previous generation of emitters fabricated by SRI International, bringing the operating voltage for full current operation well below 100 V. Extensive device characterization and life testing has been performed, and interesting variation in cathode performance was observed during the high-duty high-current portion of the testing program. The results presented here represent the highest current, highest power, and highest duty factor ever reported for an RF vacuum device employing a field emission cold cathode electron source.

Vibro-electrostatic separation of binary ABS/PS granular mixtures

This paper presents the results of experimental studies of the performance of avibro-electrostatic plastic separator, which essentially consists of two plate electrodes undergoing translational harmonic vibrations along the horizontal plane. The principle behind the separation technique for such a separator is based on the difference between Coulomb forces acting on plastic particles after triboelectric charging. The separator has the advantages of a low-voltage field and a small structure over free-fall triboelectric separators. Separation tests were performed on binary mixtures. The effects of the feed composition of the mixtures and operating parameters, such as electric field strength, applied voltage polarity and triboelectric charging time, on separation efficiency were examined. This study was conducted to understand the effects of various parameters on separation efficiency, in order to obtain the optimum operating conditions for separators.

Low-voltage organic ferroelectric field effect transistors using Langmuir–Schaefer films of poly(vinylidene fluoride-trifluororethylene)

Langmuir–Schaefer transfer was used to fabricate ultrathin films of ferroelectric copolymer, poly(vinylidene fluoride-trifluoroethylene) (70–30 mol%), for non-volatile memory application at low operating voltage. Increasing the number of transferred monolayers up to 10 led to improved film crystallinity in the “in-plane” direction, which reduced surface roughness of the semicrystalline film. Treatment of the substrate surface by plasma results in different film coverage which was subsequently found to be governed by interaction of the deposited film and surface condition. Localized ferroelectric switching was substantially attained using piezo-force tip at 10 V on 10-monolayer films. Integrating this film as a dielectric layer into organic capacitor and field effect transistor yields a reasonably good leakage current (<10 −7 A/cm 2) with hysteresis in capacitance and drain current with ON/OFF ratio of 10 3 for organic ferroelectric memory application at significantly reduced operating voltage of |15| V.

Micro- and nanomanipulation inside the SEM

Based on individual piezodriven nanomotoric units a nanomanipulation platform is integrated into a low voltage field emission SEM (Zeiss Gemnini). The instrumentation allows the controlled movement of individual particles (ca. 50 nm), the cutting of ultrathin polymer membranes or the deformation of hollow polymer spheres with an ultrathin elastic membrane (ca. 20 nm thickness). Interaction with the objects can be done under direct microscopic observation. Imaging up to 20000 x magnification without any detectable influences of external vibrations guarantees the precise manipulation. Under appropriate imaging conditions (e.g. using low energy electrons) specimen charging can be avoided and even uncoated glass tips can be used to manipulate samples.

A Novel Gas Sensor Based on Tunneling-Field-Ionization on Whisker-Covered Gold Nanowires

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Typical gas ionization sensors (GISs) work by fingerprinting the ionization breakdown voltages of the gases to be identified. In this work, we developed a GIS that operates by field-ionizing the unknown gas at exceptionally low voltages. The resultant field-ion current-voltage <formula formulatype="inline"> <tex>$(I-V)$</tex></formula> characteristic was then used to identify the gas. Freestanding gold nanowires (AuNW), terminated with nanoscale whisker-like features, were employed as field-amplifiers to reduce the field ionization threshold voltages. Synthesis of the AuNWs was carried out by the template-assisted technique accompanied by two alterations: 1) polystyrene (PS) microspheres were incorporated to reduce the compactness of the pores, thus prevent the nanostructures from collapse, and 2) the template was impregnated by <formula formulatype="inline"><tex>$\hbox{HAuCl}_{4}$</tex></formula> to form gold nanowhiskers during the electrochemical nucleation of AuNWs. The sensor was tested in three elemental gases: Ar, <formula formulatype="inline"><tex>$\hbox{N}_{2}$</tex> </formula> and He, in a pressure range of <formula formulatype="inline"><tex>$0.01≪P≪100$</tex> </formula> torr. Each gas demonstrated a distinctive <formula formulatype="inline"> <tex>$I-V$</tex></formula> curve, particularly in the field-limited regime. The threshold ionization voltages ranged from 1 to 10 V, almost three orders of magnitude lower than the voltages used in field-ion-microscopy. The low-voltage field ionization was attributed to the field-amplifying nanoscale whiskers on the AuNW tips, as well as the presence of residual amorphous alumina with semiconducting characteristics, due to incomplete removal of the porous anodized alumina (PAA) template. </para>

Fabrication of Carbon Nanofiber Emitters for Excitation of Organic Phosphor Thin Films

For applications to a novel low-voltage acceleration field emission display, carbon nanofiber (CNF) emitters were fabricated using a screen printing method. The two types of CNF of different lengths, normal-length CNFs, and cut CNFs were examined. A current density of 1.4 mA/cm2 was achieved at 10 V/µm in CNF emitters prepared from the paste composed of normal-length CNFs (1 wt %), glass paste (6 wt %), and gold nanometal ink (30 wt %). The field enhancement factor β in the Fowler–Nordheim equation was ca. 5800. CNF emitters without gold nanometal ink showed low performance. Emitter performance was determined on the basis of the results of scanning electron microscopy (SEM) and field emission characteristics.

Degradation of Y₂SiO₅ :Ce phosphor powders

The degradation of the cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y₂SiO₅:Ce) phosphor powders was investigated for possible application in low voltage field emission displays (FEDs).

Studies of luminescence properties of ZnO and ZnO:Zn nanorods prepared by solution growth technique

Pyramidal ZnO nanorods with hexagonal structure having c-axis preferred orientation are grown over large area silica substrates by a simple aqueous solution growth technique. The as-grown nanorods were studied using XRD, SEM and UV–vis photoluminescence (PL) spectroscopy for their structural, morphological and optical properties, respectively. Further, the samples have also been annealed under different atmospheric conditions (air, O 2, N 2 and Zn) to study the defect formation in nanorods. The PL spectra of the as-grown nanorods show narrow-band excitonic emission at 3.03 eV and a broad-band deep-level emission (DLE) related to the defect centers at 2.24 eV. After some mild air annealing at 200 °C, fine structures with peaks having energy separation of ∼100 meV were observed in the DLE band and the same have been attributed to the longitudinal optical (LO) phonon-assisted transitions. However, the annealing of the samples under mild reducing atmospheres of N 2 or zinc at 550 °C resulted in significant modifications in the DLE band wherein high intensity green emission with two closely spaced peaks with maxima at 2.5 and 2.7 eV were observed which have been attributed to the V O and Zn i defect centers, respectively. The V– I characteristic of the ZnO:Zn nanorods shows enhancement in n-type conductivity compared to other samples. The studies thus suggest that the green emitting ZnO:Zn nanorods can be used as low voltage field emission display (FED) phosphors with nanometer scale resolution.

Electron field emission from semiconducting nanowires

In this paper we report on investigations of field emission (FE) properties of semiconducting (SiC, ZnO) one-dimensional (1D) nanostructures – nanowire/nanorod arrays, and fabrication of low-voltage field emission display (FED) devices based on these 1D nanomaterials. SiC nanowires were grown on Ni-coated Si substrates using a thermal metal-organic chemical vapor deposition (MOCVD) technique, and ZnO nanostructures were grown on gold-coated Si substrates by a thermal CVD method. Electron field emission properties of SiC and ZnO nanostructures were examined in plane geometry using a flat phosphor screen. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure and surface morphology of the produced 1D nanostructures was established. Diode-type FED devices (flat vacuum lamps) with SiC-nanowire-based cathodes were developed and fabricated. The FEDs are characterized by low threshold and operating electric fields – lower 2 V/μm and 5 V/μm, respectively, high current density and brightness, and stable performance of the nanowire-based cathodes.

Cathodoluminescence degradation of Y2SiO5:Ce thin films

Cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y2SiO5:Ce) phosphor thin films grown by pulsed laser deposition were investigated for possible application in low voltage field emission displays (FEDs). A thin layer of tin oxide (SnO2) was ablated on some of the films in order to investigate the effect of the coated layer on the degradation of the CL intensity. Auger electron spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the thin films. AES and CL spectroscopy were done with 2keV energy electrons and with beam current densities of 26 and 52mAcm−2. Measurements were done in high vacuum and in oxygen pressures of 1×10−8, 1×10−7, and 1×10−6Torr. Residual gas mass analysis showed that the adventitious carbon (C) was removed from the surface as volatile gas species, which is consistent with the electron stimulated surface chemical reaction model. The SnO2 coated thin films resulted in a lower but more stable CL intensity than the uncoated thin films. The degradation of the CL intensity was much less for the thin films after the same time period than for the Y2SiO5:Ce powders.

The application of single-walled carbon nanotubes in field emission display

Carbon nanotube field emission display has been regarded as one of the most promising flat panel displays due to its unique advantages. The morphology of the cathode material composed of the nanotubes will directly affect the field emission display properties. In this paper, we used single-walled carbon nanotubes synthesized by arc discharge method as the cathode material. This material was printed onto the conducting surface of the cathode plate using a screen-printing process. We studied the field emission properties of the cathode and the brightness of the green phosphor also screen printed on the anode. The display unit exhibited good field emission properties. The single-walled nanotube cathode was shown to have low turn-on voltage and high field emission current density.

The Grain Boundary Embrittlement and De-Embrittlement Mechanism in Age Hardenable Fe-Ni-Ti Steels

The strengthening and grain boundary embrittlement in an age hardenable Fe-20.4Ni-2.8Ti ternary alloy were investigated. The Vickers hardness and tensile properties were evaluated using a Vickers hardness and tensile tester and the precipitation behavior during aging treatment was observed by transmission electron microscopy (TEM). The fracture surface was observed using low voltage field emission scanning electron microscopy (FE-SEM). The alloy showed typical aging hardening curves with a single aging peak near 640 HV, but was found to undergo severe grain boundary embrittlement from the initial stages of aging treatment. Many fine particles were observed at the grain boundary fracture surface. These particles were identified as η-Ni3Ti precipitates nucleated at the prior austenite grain boundaries. When the aging time was extended, austenite nucleated at the interface of the matrix and η-Ni3Ti precipitate. With the formation of the austenite, the tensile ductility was recovered. It was concluded that the precipitation of the η-Ni3Ti intermetallic particles at the prior austenite grain boundaries and formation of the austenite are the main causes of embrittlement and subsequent de-embrittlement in aging of this alloy.

Characterization of Y2SiO5:Ce thin films

Uncoated and SnO2-coated Y2SiO5:Ce thin film phosphors grown on Si (100) substrates by a pulsed laser deposition technique were characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-Ray analysis (EDS) and X-Ray diffraction (XRD). Cathodoluminescence (CL) of both the uncoated and SnO2-coated thin film phosphors was investigated for possible application in low voltage field emission displays (FEDs). Blue emission with peak values at 440 and 500nm was from spherically shaped particles distributed unevenly on the surfaces of both the uncoated and coated thin film phosphors.