Field-effect Configuration Research Articles

Influence of swift heavy ion irradiation on charge transport and conduction mechanisms across the interface of LaMnO3 and La0.7Ca0.3MnO3 manganites

Swift heavy ion (SHI) irradiated LaMnO3/La0.7Ca0.3MnO3 (LMO/LCMO) interfaces have been investigated to understand their charge transport and conduction mechanisms. Prominent effect of ion fluence has been discussed for the interface resistivity behaviors and metal to insulator phase transition for LMO/LCMO interfaces on the bases of lattice strain, crystalline granular state, crystalline imperfection, average grain size, grain boundary density and rms surface roughness. Field effect configuration (FEC) has been employed to study the interesting modifications in the irradiated LMO/LCMO interface resistivity under different applied electric fields to understand the depletion region, free charge carrier density, ferromagnetic phase fractions and crystal field based distortions. A Phenomenological percolation model has been employed to understand the role of phase separation in governing the charge conduction processes across LMO/LCMO interfaces.

Enormous electroresistance and field effect studies on LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 manganite – manganite composite structure

Field effect configuration (FEC) coupled field effect studies (FES) is one of the prime requisites for the development of spintronic based logic and memory devices having better sensitivities for external perturbations specifically while scaling down the technology. In this communication, LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 (LMO / LCMO / LAO) manganite – manganite composite structure was successfully fabricated using cost effective chemical solution deposition (CSD) method. FEC coupled FES have been performed across the electrically polarizable LMO layer and LCMO conducting channel. Enormous room temperature colossal electroresistance (CER) has been acquired ∼ 7000 % under 2 MV/cm forward biased control electric field and ∼ 8.5 × 105 % under 0.9 MV/cm reverse biased control electric field. Elegant modifications in the resistive behavior have been understood on the bases of charge carrier density alterations, interface modifications, phase separation, Mott–type phase transformation and formation–break down of depletion region across the manganite – manganite composite structure.

Temperature dependent transport characteristics of La0.9Sr0.1MnO3 / SrNb0.002Ti0.998O3 device

We report detailed investigations on device functioning capabilities of La0.9Sr0.1MnO3 (LSMO) manganite thin film fabricated on SrNb0.002Ti0.998O3 (SNTO) substrate. The LSMO / SNTO structure has been verified using XRD ϕ–scan measurement. We interpret the device capabilities by investigating the temperature dependent current–voltage (I–V) characteristics. To understand the linearity – nonlinearity nature and temperature effect, current ratio for specific voltages has been identified. Logarithmic scale variation in forward bias current with applied voltages has been studied at different temperatures. For the identification of backward diode behaviour possibility, I–V characteristics at typical temperatures have been studied for forward and reverse currents, simultaneously. The theoretical model fits supporting conduction mechanism in the device understudy has also been investigated for the typical I–V characteristics. The field effect configuration based variation in junction resistance of LSMO / SNTO structure with temperature under applied different junction electric fields and temperature dependent variation in electroresistance (ER) have been recorded to interpret the conduction processes undergoing in the device understudy.

Low resistance electrical contacts to few-layered MoS2 by local pressurization

The performance of electronic and optoelectronic devices is dominated by charge carrier injection through the metal–semiconductor contacts. Therefore, creating low-resistance electrical contacts is one of the most critical challenges in the development of devices based on new materials, particularly in the case of two-dimensional semiconductors. Herein, we report a strategy to reduce the contact resistance of MoS2 via local pressurization. We fabricated electrical contacts using an atomic force microscopy tip and applied variable pressure ranging from 0 to 25 GPa. By measuring the transverse electronic transport properties, we show that MoS2 undergoes a reversible semiconducting-metallic transition under pressure. Planar devices in field effect configuration with electrical contacts performed at pressures above ∼15 GPa show up to 30-fold reduced contact resistance and up to 25-fold improved field-effect mobility when compared to those measured at low pressure. Theoretical simulations show that this enhanced performance is due to improved charge injection to the MoS2 semiconductor channel through the metallic MoS2 phase obtained by pressurization. Our results suggest a novel strategy for realizing improved contacts to MoS2 devices by local pressurization and for exploring emergent phenomena under mechano-electric modulation.

Interface based field effect configuration and charge conduction mechanisms for manganite thin film heterostructures

Control over the movements of free charge carriers across any manganite based interface can functionalize the device for spintronic applications.

Magnetoresistive nature assisted field effect configuration for LaMnO3 / La0·7Ca0·3MnO3 interface

In this communication, LaMnO3/La0·7Ca0·3MnO3/LaAlO3 (LMO/LCMO/LAO) structure was prepared by low cost sol–gel based chemical solution deposition (CSD) method. Field effect configuration (FEC) based LMO/LCMO interface resistive nature has been investigated for the LMO/LCMO/LAO structure. Temperature dependent interface resistivity modulation factor has been understood using forward and reverse bias modes. Temperature dependent LMO/LCMO interface resistivity has been discussed in detail under different applied magnetic fields, different applied interface electric fields and different magnetic field directions to identify simultaneous possible existence of magnetoresistance (MR), electroresistance (ER) and anisotropic magnetoresistance (AMR) effects across the same LMO/LCMO interface. Zener double exchange (ZDE) polynomial law has been fitted theoretically to the obtained interface resistive nature to understand the possible spin fluctuations across the LMO/LCMO interface.

Electric Field Effects on Charge Conduction for LaMnO3 Controlled La0.7Ca0.3MnO3 Manganite

Control over the different electronic states in mixed valent manganites advances the development of oxide based electronic devices. In this context, carrier density is one of the key aspects that controls the electronic ground states of manganites in a sparkling way since it does not create any impurity within the manganite lattice, unlike chemical doping process. LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 (LMO / LCMO / LAO) manganite based heterostructure was fabricated by low cost chemical solution deposition (CSD) method where thickness of LMO ∼ 50 nm and LCMO ∼ 100 nm were grown on (100) single crystalline substrate. Structural quality and epitaxial nature of heterostructure was verified by performing X–ray diffraction (XRD) ϕ–scan measurement on grown La0.7Ca0.3MnO3 / LaAlO3 (LCMO / LAO) 100 nm thin film and LMO / LCMO / LAO heterostructure. Understanding of few other structural, morphological and chemical aspects of presently studied LMO / LCMO interface and LMO / LCMO / LAO heterostructure has been presented through grazing incidence X–ray diffraction (GIXRD), Rocking curve XRD, cross sectional scanning electron microscopy (SEM), atomic force microscopy (AFM) and X–ray photoelectron spectroscopy (XPS) measurements. Electric field modulated charge conduction for LCMO manganite channel has been understood in the context of field effect configuration (FEC) based transport measurements where temperature dependent LCMO channel resistance was recorded under different control electric fields applied across LMO / LCMO interface in LMO / LCMO / LAO heterostructure. Thermal hysteretic resistance measurements for LCMO manganite channel under zero control electric field exhibit metal to insulator phase transition at TP with finite width of the hysteretic resistance behaviours between two thermal cycles, i.e. cooling and heating. This has been understood on the basis of phase separation scenario, freezing effect and non–reversible electronic phase transformation. Applied control electric field induced improvement in resistance of LCMO manganite channel and reduction in value of TP have been understood on the basis of charge injection process, strain induced disorder dependent charge conduction, phase separation based movements of metal–insulator interface and negligibly small Joule heating effect. Realization of insulating phase fraction, arrested during thermal cycles, has been discussed for the explanation of reduced width of the hysteretic resistance behaviours of LCMO channel upon increase in control electric field applied across LMO / LCMO interface. Possible charge conduction mechanisms have been understood on the basis of Zener double exchange (ZDE) polynomial law for obtained metallic state of LCMO channel. Variation in electroresistance (ER) of LCMO manganite channel with temperature under different control electric fields (applied across LMO / LCMO interface) has been discussed on the basis of charge injection process with an effective role of phase separation scenario of LCMO channel in LMO / LCMO / LAO heterostructure.

Transport properties and electroresistance of manganite based heterostructure

In the present communication, ZnO/La0.7Sr0.3MnO3/Al2O3 (ZnO/LSMO/Al2O3) heterostructure was grown using chemical solution deposition (CSD) technique. X–ray diffraction (XRD) measurement confirms the (100) crystallographic oriented growth of LSMO manganite and polycrystalline hexagonal growth of ZnO layer. Temperature dependent resistivity behavior under different applied magnetic fields, performed for two different geometries [current in plane (CIP) and current perpendicular to plane (CPP)], suggests the modifications in metal to insulator transition temperature TP and alterations in resistivity with applied magnetic field and measurement geometry. This also implies the better charge conduction across the ZnO/LSMO interface (CPP) as compared to LSMO film layer (CIP). Various charge conduction mechanisms have been employed to understand the charge transport for observed low temperature resistivity minimum, metallic behavior, insulating state and magnetoresistance (MR) of LSMO film and ZnO/LSMO interface. Electroresistance (ER) and field effect configuration (FEC) have been investigated across the ZnO/LSMO interface by recording the LSMO channel resistance, at room temperature, that suggest the tuning of signature and value of ER by considering forward and reverse bias modes across the interface. FEC studies show the large ER ∼ +750% and −85% across the LSMO channel with its tunability under different interface biases.

Molecular screening effects on exciton-carrier interactions in suspended carbon nanotubes

Photoluminescence spectroscopy measurements are performed on suspended carbon nanotubes in a field-effect configuration, and the gate voltage dependence of photoluminescence spectra are compared for the pristine and the molecularly adsorbed states of the nanotubes. We quantify the molecular screening effect on the trion binding energies by determining the energy separation between the bright exciton and the trion emission energies for the two states. The voltage dependence shows narrower voltage regions of constant photoluminescence intensity for the adsorbed states, consistent with a reduction in the electronic bandgap due to screening effects. The charge neutrality points are found to shift after molecular adsorption, which suggests changes in the nanotube chemical potential or the contact metal work function.

Density functional perturbation theory for gated two-dimensional heterostructures: Theoretical developments and application to flexural phonons in graphene

The ability to perform first-principles calculations of electronic and vibrational properties of two-dimensional heterostructures in a field-effect setup is crucial for the understanding and design of next-generation devices. We present here an implementation of density functional perturbation theories tailored for the case of two-dimensional heterostructures in field-effect configuration. Key ingredients are the inclusion of a truncated Coulomb interaction in the direction perpendicular to the slab and the possibility of simulating charging of the slab via field-effects. With this implementation we can access total energies, force and stress tensors, the vibrational properties and the electron-phonon interaction. We demonstrate the relevance of the method by studying flexural acoustic phonons and their coupling to electrons in graphene doped by field-effect. In particular, we show that while the electron-phonon coupling to those phonons can be significant in neutral graphene, it is strongly screened and negligible in doped graphene, in disagreement with other recent first-principles reports. Consequently, the gate-induced coupling with flexural acoustic modes would not be detectable in transport measurements on doped graphene.

Electrical characterization of flame-soot nanoparticle thin films

Carbon nanoparticles, with diameter d ∼10nm, were produced in a premixed ethylene-air flame and used to grow self-assembled thin films by thermophoretic deposition on Si++/SiO2/Gold multilayer substrates inserted in flame.The particles’ size was measured by a Scanning Mobility Particle Sizer. UV–vis light absorption, Raman spectroscopy and Atomic Force Microscopy were used for the chemico-physical and morphological investigation of the carbon nanoparticle thin films. The electrical characterization was then performed in different environmental conditions with the basic aim to assess the potentiality of these films to be employed as electrically-active components in electronic and sensing applications.The films are composed by the aggregation of nanoscale grains whose size increases with the deposition time and are consequently highly porous with the electrical conduction properties showing a dependence on thickness suggesting a percolation-like behavior. Raman spectrum indicates that the chemical/structural composition of the film does not change with deposition time and consists in small graphitic crystallites with constant size.The electrical measurements show also the ohmic behavior of the IV curves. Moreover, an ambipolar response of the CNPs channels, when investigated in the field-effect configuration, was observed and, in parallel with conductivity, charge carrier mobility values were found to increase with thickness.

Silicon-ion-implanted PMMA with nanostructured ultrathin layers for plastic electronics

Being of interest for plastic electronics, ion-beam produced nanostructure, namely silicon ion (Si+) implanted polymethyl-methacrylate (PMMA) with ultrathin nanostructured dielectric (NSD) top layer and nanocomposite (NC) buried layer, is examined by electric measurements. In the proposed field-effect organic nanomaterial structure produced within the PMMA network by ion implantation with low energy (50 keV) Si+ at the fluence of 3.2 × 1016 cm−2 the gate NSD is ion-nanotracks-modified low-conductive surface layer, and the channel NC consists of carbon nanoclusters. In the studied ion-modified PMMA field-effect configuration, the gate NSD and the buried NC are formed as planar layers both with a thickness of about 80 nm. The NC channel of nano-clustered amorphous carbon (that is an organic semiconductor) provides a huge increase in the electrical conduction of the material in the subsurface region, but also modulates the electric field distribution in the drift region. The field effect via the gate NSD is analyzed. The most important performance parameters, such as the charge carrier field-effect mobility and amplification of this particular type of PMMA- based transconductance device with NC n-type channel and gate NSD top layer, are determined.

Ambipolar molybdenum diselenide field-effect transistors: field-effect and Hall mobilities.

We report a room temperature study on the electrical response of field-effect transistors (FETs) based on few-layered MoSe2, grown by a chemical vapor transport technique, mechanically exfoliated onto SiO2. In contrast to previous reports on MoSe2 FETs electrically contacted with Ni, MoSe2 FETs electrically contacted with Ti display ambipolar behavior with current on to off ratios up to 10(6) for both hole and electron channels when applying a small excitation voltage. A rather small hysteresis is observed when sweeping the back-gate voltage between positive and negative values, indicating the near absence of charge "puddles". For both channels the Hall effect indicates Hall mobilities μH ≃ 250 cm(2)/(V s), which are comparable to the corresponding field-effect mobilities, i.e., μFE ∼ 150 to 200 cm(2)/(V s) evaluated through the conventional two-terminal field-effect configuration. Therefore, our results suggest that MoSe2 could be a good candidate for p-n junctions composed of a single atomic layer and for low-power, complementary logic applications.

Electrochemical doping of few-layer ZrNCl from first principles: Electronic and structural properties in field-effect configuration

We develop a first-principles theoretical approach to doping in field-effect devices. The method allows for calculation of the electronic structure as well as complete structural relaxation in field-effect configuration using density-functional theory. We apply our approach to ionic-liquid-based field-effect doping of monolayer, bilayer, and trilayer ZrNCl and analyze in detail the structural changes induced by the electric field. We show that, contrary to what is assumed in previous experimental works, only one ZrNCl layer is electrochemically doped and that this induces large structural changes within the layer. Surprisingly, despite these structural and electronic changes, the density of states at the Fermi energy is independent of the doping. Our findings imply a substantial revision of the phase diagram of electrochemically doped ZrNCl and elucidate crucial differences with superconductivity in Li intercalated bulk ZrNCl.

Room Temperature Electrostatic Across the Interface in Nanostructured ZnO/La $_{0.7}$Sr$_{0.3}$ MnO$_{3}$/SNTO Heterostructure

PLD grown ZnO/La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /SrTi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.998</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.002</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanostructured heterostructure has been studied for its nanoelectronic properties at room temperature under zero applied field. XRD φ-scan reveals the epitaxial growth of La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LSMO) film, while the transport of 10-nm LSMO manganite layer can be tuned with applied electric field using various field effect configurations. 10-nm LSMO layer shows a large change in resistance with the application of voltage, i.e., exhibiting colossal electroresistance (CER) ~100% (negative) and large positive electroresistance (ER) ~2683% under 4.5 V at room temperature. The variation scenario in 10-nm LSMO transport has been discussed on the basis of electric-field-induced modifications in the charge carrier density and electronic states.

Quantum Hall Effect and Semimetallic Behavior of Dual-Gated ABA-Stacked Trilayer Graphene

The electronic structure of multilayer graphenes depends strongly on the number of layers as well as the stacking order. Here we explore the electronic transport of purely ABA-stacked trilayer graphenes in a dual-gated field-effect device configuration. We find that both the zero-magnetic-field transport and the quantum Hall effect at high magnetic fields are distinctly different from the monolayer and bilayer graphenes, and that they show electron-hole asymmetries that are strongly suggestive of a semimetallic band overlap. When the ABA trilayers are subjected to an electric field perpendicular to the sheet, Landau level splittings due to a lifting of the valley degeneracy are clearly observed.

Characterization of Graphene Grown on Bulk and Thin Film Nickel

We report on graphene films grown by atmospheric pressure chemical vapor deposition on bulk and thin film nickel. Carbon precipitation on the polycrystalline grains is controlled by the methane concentration and substrate cooling rate. It is found that graphene grows over multiple grains, with edges terminating along the grain boundaries and with dimensions directly correlated to the size of the underlying grains. This greatly restricts the resulting graphene size (<10 μm) in the thin film growth, whereas monolayer graphene with linear dimensions of hundreds of micrometers takes up the great majority of the surface overlayers on the bulk nickel (>50%). In addition, the number of layers can be better controlled in the bulk growth. Characterizations of the graphene sheets using transmission electron microscopy, Raman spectroscopy, and transport measurements in the field-effect configuration are also discussed.

The investigation of reversible strain and polarization effect in (011)-La0.9Ba0.1MnO3 film using field effect configuration

We have investigated the influence of the electric bias field on the magnetic and transport properties of (011)-oriented La0.9Ba0.1MnO3 (LBMO) thin film epitaxially grown on (011)-0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) single crystal substrate. It was found that strain and polarization effects induced by electric bias coexist in the whole temperature range and both of them can modulate the transport properties of (011)-LBMO on PMN–PT. The relative change of resistance ΔR/R exhibits peak values of −22% and −32% for bias fields of +12 and −12 kV/cm, respectively, around metal-insulator transition temperature, TMI. However, the sign of ΔR/R shows polarity dependence at temperature far below TMI. Further careful analysis demonstrates that these two opposite behaviors can be ascribed to the different influence of strain and polarization effects on transport properties.

Ambipolar field-effect transistor based on α,ω-dihexylquaterthiophene and α,ω-diperfluoroquaterthiophene vertical heterojunction

Organic field-effect transistors (OFETs) are alternative emerging device structures for efficient light generation, that could provide a novel architecture to address open issues like exciton-contact and exciton-charge quenching, that still limit the OLEDs efficiency and brightness. Recently, it has been introduced by our research group the model of a tri-layer organic heterostructure implemented in a field-effect configuration, that allows preventing at one time the exciton-metal as well as the exciton-charge quenching in an organic electroluminescence generating device. The device active region is formed by a central optical layer sandwiched between an electron and a hole field-effect conducting film. In order to understand the complex phenomena that happens at the interfaces, with the target to fabricate the most balanced ambipolar structure with high morphological compatibility and high mobility in a vertical heterojunction geometry, we made a preliminary study of a single layer and bi-layer OFET structure composed by α,ω-dihexylquaterthiophene (DH4T) and α,ω-diperfluoroquaterthiophene (DHF4T). By means of this study we showed a new highly balanced ambipolar OFET made of these materials, a first step toward their implementation in a more complex structure as the tri-layer is.

Electroresistance and field effects in epitaxial thin films of Pr0.7Sr0.3MnO3

Highly epitaxial thin films of Pr0.7Sr0.3MnO3 were grown on (100) SrTiO3 single crystal substrates by laser ablation. Similar to other manganite compounds, these Pr0.7Sr0.3MnO3 films exhibited remarkable magnetoresistance. Application of electric currents could induce a remarkable reduction in resistivity, demonstrating a strong electroresistance effect. The ratio of the resistance variation, ER=[R(0)−R(I)]/R(I), is about 33% at metal-insulator transition temperature. Using a planar field effect configuration, significant field modulation of the metal-insulator transition was achieved. The observed field effects were discussed based on the strong interactions between carrier spins and localized spins in Mn ions, as well as the percolative mechanism of phase separation.