Transition Of Transport Mechanism Research Articles

2D Short‐Channel Tunneling Transistor Relying on Dual‐Gate Modulation for Integrated Circuits Application

AbstractWith continuous size scaling, the surface dangling bonds and short‐channel effects will degrade silicon based transistor performance. Thus, it is of great importance to seek new channel materials and transistor architectures to further continue Moore's law. Herein, a new ultra‐thin short‐channel tunneling transistor is developed comprising all 2D‐ components. Distinct from usual 2D planar transistor, this device is configured with vertical MoS2/WSe2 junction and in‐plane WSe2 channel, the switch states are realized by the gate‐regulated barrier height of heterojunction, enabling the transition of transport mechanism between thermionic‐emission and tunneling. Under dual‐gate configuration, the transistor exhibits high performance with drive current of 4.58 µA, on/off ratio of 4 × 107, subthreshold swing (SS) of 97 mV decade−1 and drain‐induced barrier lowering (DIBL) of 12 mV V−1, that can meet the requirement of logical applications in integrated circuits (IC). Taking advantage of the high‐speed tunneling current and unique short‐channel architecture, the device overcomes the issues of voltage spikes and long reverse recovery time that exist in usual electric components, and thus gains an access to the IC interface. This work provides a proof‐of‐concept transistor architecture relying on dual‐gate modulation, opening up a promising perspective for next generation low‐power, high‐density, and large‐scale IC technologies.

P.672 Serum nerve growth factor levels in children with specific learning disorder

To comprehensively investigate the correlation between free volume properties (size and distribution) in the interior of polyamide (PA) active layer and mass transport mechanism, six polyamide thin film composite (TFC) membranes were characterized using positron annihilation lifetime spectroscopy (PALS). In case of pressurized filtration conditions, the rejection rate of boron across all PA membranes was found to be inversely proportional to the free volume size. The more boron transport occurred at the membrane containing larger free volume. In addition, the transition of the neutral boron transport mechanism from convection to diffusion was found to occur at a membrane free volume radius around 0.275 nm within the applied pressure range (2 and 10 bar), as verified by PALS and the dimensionless Peclet number. We believe that mass transport mechanism transition from convection to diffusion is caused by the compression of polyamide active layer due to applied hydraulic pressure (10 bar), resulting in lowering the convective mass transport pathway inside polyamide active layer. These membrane free volume size criteria and experimental filtration results may subsequently be used as new design guidelines for the development of high boron rejection polyamide TFC membranes having a low energy consumption.

Systematic Modulation of Charge Transport in Molecular Devices through Facile Control of Molecule-Electrode Coupling Using a Double Self-Assembled Monolayer Nanowire Junction.

We report a novel solid-state molecular device structure based on double self-assembled monolayers (D-SAM) incorporated into the suspended nanowire architecture to form a "Au|SAM-1||SAM-2|Au" junction. Using commercially available thiol molecules that are devoid of synthetic difficulty, we constructed a "Au|S-(CH2)6-ferrocene||SAM-2|Au" junction with various lengths and chemical structures of SAM-2 to tune the coupling between the ferrocene conductive molecular orbital and electrode of the junction. Combining low noise and a wide temperature range measurement, we demonstrated systematically modulated conduction depending on the length and chemical nature of SAM-2. Meanwhile, the transport mechanism transition from tunneling to hopping and the intermediate state accompanied by the current fluctuation due to the coexistence of the hopping and tunneling transport channels were observed. Considering the versatility of this solid-state D-SAM in modulating the electrode-molecule interface and electroactive groups, this strategy thus provides a novel facile strategy for tailorable nanoscale charge transport studies and functional molecular devices.

Predicting charge transport in the presence of polarons: The beyond-quasiparticle regime inSrTiO3

In materials with strong electron-phonon ($e$-ph) interactions, the electrons carry a phonon cloud during their motion, forming quasiparticles known as polarons. Predicting charge transport and its temperature dependence in the polaron regime remains an open challenge. Here, we present first-principles calculations of charge transport in a prototypical material with large polarons, SrTiO$_{3}$. Using a cumulant diagram-resummation technique that can capture the strong $e$-ph interactions, our calculations can accurately predict the experimental electron mobility in SrTiO$_{3}$ between 150$-$300 K. They further reveal that for increasing temperature the charge transport mechanism transitions from band-like conduction, in which the scattering of renormalized quasiparticles is dominant, to a beyond-quasiparticle transport regime governed by incoherent contributions due to the interactions between the electrons and their phonon cloud. Our work reveals long-sought microscopic details of charge transport in SrTiO$_{3}$, and provides a broadly applicable method for predicting charge transport in materials with strong $e$-ph interactions and polarons.

Tuning the charge transport and photo-physical behavior in hybrid poly(3-hexylthiophene) and silver sulfide quantum dot based nanocomposite devices

Abstract The charge transport properties are studied in hybrid thin films composed of poly (3-hexylthiophene) polymer (P3HT) and silver sulfide (Ag2S) quantum dots (QDs) by temperature and photo-dependent current-voltage (J–V) characteristics. A complete reversal in J-V characteristics is observed in ITO/Nanocomposite/Au devices as the QDs’ concentration in the polymer matrix reaches to 50 wt percentage (wt. %). A detailed study of charge injection through ITO exhibits a transition in transport mechanism from direct tunnelling to thermionic emission with increasing QDs up to 20 wt % and further governed by space charge limited conduction for 50 and 80 wt % devices. Charge injection through Au shows the transition from Poole-Frenkel to thermionic emission as the QDs surpasses 10 wt % in polymer matrix. The effect of injection barrier and charge transfer phenomena on the transport properties are discussed in details by photoluminescence and photocurrent measurements.

Gas concentration polarization and transport mechanism transition near thin polymeric membranes

Advanced material engineering gave rise to cutting-edge characteristics of sustainable separation by fabrication of high permeable and gas selective membranes. A developed fabrication process of ultrathin polymers with controlled microporosity helps understanding pore size dependent transport and performance of thin membranes with constant pore number from continuum to free-molecular to solution-diffusion regimes. Fabrication of polymer layers with controlled pore size was realized by stage-wise physical vapor deposition of dimethylsiloxane oligomers onto porous alumina support. Single process step forms high permeable porous films of 13 nm in thickness. Further deposition allows fabrication of up to 120 nm nanopore-free uniform layers with defined gas selectivity. Permeances as high as 1300 GPU through gas-selective, uniform dense films results in gas concentration polarization and apparent selectivity loss, so far only observed for porous materials. Our fabrication process enabled observation of two unseen separation regimes in the transport physics transition from (nano) channel flow to solution diffusion supported by mathematical model derived for transport through ultra-thin membranes.

Temperature-dependent electronic charge transport characteristics at MoS2/p-type Ge heterojunctions

Significant effort has been devoted to constructing two-dimensional transition metal dichalcogenides-based hybrid heterojunctions with enhanced performance or unique functionalities for versatile device applications in emerging electronics and optoelectronics. In this study, we report the temperature-dependent electronic charge transport characteristics in MoS2/p-type Ge heterojunction diodes. From the current-voltage (I-V) characteristics of the heterojunction device, it is observed that different transport phenomena can occur depending upon the temperature and bias voltage. The charge transport is dominated by thermionic emission in the high-temperature regime above 300 K, whereas in low-temperature regime below 300 K, the charge transport mechanism transitions from the thermionic emission to the tunneling mechanism associated with trap sites. In particular, the I-V characteristics in the low-temperature regime show a transition from the direct tunneling at a low bias to the Fowler-Nordheim tunneling mechanism at a high bias. This could be well described by the electrical analyses on temperature-dependent I-V behavior and corresponding energy band diagrams.

Performance evaluation of polyamide TFC membranes: Effects of free volume properties on boron transport

To comprehensively investigate the correlation between free volume properties (size and distribution) in the interior of polyamide (PA) active layer and mass transport mechanism, six polyamide thin film composite (TFC) membranes were characterized using positron annihilation lifetime spectroscopy (PALS). In case of pressurized filtration conditions, the rejection rate of boron across all PA membranes was found to be inversely proportional to the free volume size. The more boron transport occurred at the membrane containing larger free volume. In addition, the transition of the neutral boron transport mechanism from convection to diffusion was found to occur at a membrane free volume radius around 0.275nm within the applied pressure range (2 and 10bar), as verified by PALS and the dimensionless Peclet number. We believe that mass transport mechanism transition from convection to diffusion is caused by the compression of polyamide active layer due to applied hydraulic pressure (10bar), resulting in lowering the convective mass transport pathway inside polyamide active layer. These membrane free volume size criteria and experimental filtration results may subsequently be used as new design guidelines for the development of high boron rejection polyamide TFC membranes having a low energy consumption.

Thermal and transport properties of La2−xNdxMo2O9

Single-phase La2−xNdxMo2O9 (0≤x≤1.8) compounds were prepared using solid-state reaction technique. Their structural and thermal properties were characterized by room and high temperatures X-ray diffraction (XRD), thermo gravimetric analysis-differential scanning calorimetry (TG-DSC), and high temperature Raman spectra. The transport properties were investigated using D.C. four-probe technique and Hebb-Wagner polarization method. The substitution limit of Nb3+ in La2−xNdxMo2O9 was determined to be in the range of 1.8<x<1.9, and the cubic lattice parameter of La2−xNdxMo2O9 decreased linearly with the increasing of x. When the Nb3+ substitution content x was larger than 0.6, the α/β phase transition could be depressed to such a great degree that the phase transition thermal enthalpy was not detected by DSC. The temperature dependence of electrical conductivities for La1.4Nd0.6Mo2O9 below 873 K and that for LaNdMo2O9 below 923 K obeyed the Arrhenius law, while above 873 and 923 K Vogel-Tammann-Fulcher (VTF) model could describe the conduction behaviors satisfactorily. The transition of transport mechanism from Arrhenius to VTF was caused by the change of structure, which was supported by the high temperature XRD and Raman results. The ionic transport number of La1.4Nd0.6Mo2O9 in air was larger than 0.99 at 1073 K, and with the increasing of temperature it was close to 0.98 at 1173 K. In view of the phase transition, thermal expansion and conductivity properties, La1.4Nd0.6Mo2O9 should be a promising electrolyte material in La2−xNdxMo2O9 series.

Singular Temperatures Connected to Charge Transport Mechanism Transitions in Perylene Bisimides from Steady-State Photocurrent Measurements

Perylene bisimides (PBIs) are n-type semiconducting and photogenerating materials widely used in a variety of optoelectronic devices. Particularly interesting are PBIs that are simultaneously water-soluble and liquid-crystalline (PBI-W+LC) and, thus, attractive for the development of high-performing easily processable applications in biology and “green” organic electronics. In this work, singular temperatures connected to charge transport mechanism transitions in a PBI-W+LC derivative are determined with high accuracy by means of temperature-dependent photocurrent studies. These singular temperatures include not only the ones observed at 60 and 110 °C, corresponding to phase transition temperatures from crystalline to liquid-crystalline (LC) and from LC to the isotropic phase, respectively, as confirmed by differential scanning calorimetry (DSC), but also a transition at 45 °C, not observed by DSC. By analyzing the photocurrent dependence simultaneously on temperature and on light intensity, this transition is interpreted as a change from monomolecular to bimolecular recombination. These results might be useful for other semiconducting photogenerating materials, not necessarily PBIs or even organic semiconductors, which also show transport behavior changes at singular temperatures not connected with structural or phase transitions.

Scaling of Trigate nanowire (NW) MOSFETs to sub-7 nm width: 300 K transition to Single Electron Transistor

In this paper we show that on scaling nanowire width from 20nm down to sub-7nm regime, together with achieving excellent short channel effect control (DIBL=12mV/V for LG=20nm), we hit a dramatic transition in transport mechanism from monotonously increasing ID–VG of a FET to oscillating ID–VG of a Single Electron Transistor. This transition in transport mechanism is brought about by process induced channel potential variability. It poses a challenge to further scaling of nanowire MOSFETs. However, we show that it provides an exciting opportunity to cointegrate Single Electron Transistors with high-k/metal gate operating at room temperature (at VD=±0.9V) with the state-of-the-art nanowire MOSFETs enabling large scale manufacturing of Beyond Moore devices.

Molecular and continuum hydrodynamics in graphene nanopores

An ultrathin graphene membrane is a promising candidate for various applications such as gas separation, water purification, biosensors, etc. In this study, we investigate water transport mechanisms and hydrodynamic properties such as water flux, pressure variation, velocity, viscosity, slip length, etc. Due to the unique water structure, confined in the radial direction and layered in the axial direction of the pore, water viscosity and slip length increase with a decrease in the pore radius, in contrast to water confined in a carbon nanotube. As the diameter of the pore increases, the water transport mechanism transitions from collective diffusion to frictional flow described by the modified Hagen–Poiseuille equation. Graphene membrane is shown to be ultra-efficient by comparing the permeation coefficient of graphene membrane to that of a carbon nanotube and an ultrathin silicon membrane. We envision that the study presented here will help to understand and design various membrane separation processes using graphene membrane.

Low-field mobility and carrier transport mechanism transition in nanoscale MOSFETs

This paper extends the flux scattering method to study the carrier transport property in nanoscale MOSFETs with special emphasis on the low-field mobility and the transport mechanism transition. A unified analytical expression for the low-field mobility is proposed, which covers the entire regime from drift-diffusion transport to quasi-ballistic transport in 1-D, 2-D and 3-D MOSFETs. Two key parameters, namely the long-channel low-field mobility (μ0) and the low-field mean free path (λ0), are obtained from the experimental data, and the transport mechanism transition in MOSFETs is further discussed both experimentally and theoretically. Our work shows that λ0 is available to characterize the inherent transition of the carrier transport mechanism rather than the low-field mobility. The mobility reduces in the MOSFET with the shrinking of the channel length; however, λ0 is nearly a constant, and λ0 can be used as the “entry criterion" to determine whether the device begins to operate under quasi-ballistic transport to some extent.

Transition from direct tunneling to field emission in carbon nanotube intramolecular junctions

Transport measurements through metal-semiconductor carbon nanotube intramolecular junctions were carried out at high gate voltages in which regime the influence of Schottky barrier to charge transport is weak. The I-Vds curves exhibit an inflection point in the form of ln(I∕Vds2)−1∕Vds, showing a transition of transport mechanism from direct tunneling to field emission. The findings are interpreted in terms of quantum tunneling through a rectanglelike barrier at the junction, with a barrier width of ∼4nm, in good agreement with that observed on pentagon-heptagon defects at nanotube junctions via scanning tunneling spectroscopy.

The kinetics of lithium transport through Li 1− δCoO 2 by theoretical analysis of current transient

The kinetics of alkali atom transport through intercalation compounds was theoretically considered through numerical simulation of the current transient and concentration profile across the electrode with time. For the theoretical calculation of those two different points of view, the following were considered: that alkali ion diffusion is a rate-controlling step of alkali atom transport through the electrode subjected to ‘real potentiostatic’ constraint; and that cell-impedance purely governs alkali atom transport. We presented current transient and change in alkali atom content profile across the electrode with time, numerically simulated based upon the two approaches. As an example lithium transport through a carbon-dispersed Li 1− δ CoO 2 composite electrode was examined from the two points of view. From the comparison of experimentally obtained current transients with those numerically simulated, it is suggested that lithium transport during intercalation into and deintercalation from the Li 1− δ CoO 2 composite electrode in the single α phase region are purely governed by cell-impedance. However, the ‘cell-impedance-controlled’ lithium transport during intercalation into the Li 1− δ CoO 2 electrode in the coexistence of two phases α and β is converted into ‘diffusion-controlled’ lithium transport. This transition in transport mechanism can be accounted for in terms of the input flux at the subsurface toward the electrode between by chemical diffusion and by the quotient of potential drop divided by cell-impedance.