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The present study aims to investigate utilizing field-effect for inducing heterogeneous surface charge and consequently changing the fluid flow in a solid-state nanochannel with converging-diverging periodicity. It is shown that the combination of geometry and applied gate voltage (V_{G}) would generate heterogeneous surface charge at the channel walls which can be modulated by V_{G}, i.e. a moderate V_{G} (0.7-0.9 V) causes charge inversion in diverging sections of the channel while V_{G} > 0.9 enables charge inversion in the entire channel but it is still non-uniform in each section. The results show that zeta ({\zeta}) potential is a function of V_{G} which shows a linear to non-linear transition due to dilution of electrolyte in agreement with density functional theory and Monte Carlo simulations. In contrast, electrolyte symmetry has a minor effect on the variation of {\zeta} potential. It is also shown that the difference in {\zeta} potential across the channel ({\Delta}{\zeta}) increases by dilution of electrolyte and utilizing a more symmetric electrolyte with lower valances. For the first time, it is shown that {\Delta}{\zeta} presents a maximum with the V_{G}. The V_{G} corresponding to the maximum {\Delta}{\zeta} decreases with both dilution of electrolyte and higher anion valance. This is of practical importance to overcome leakage current problem of field-effect fluidic devices. It is also shown that the velocity field can be altered by changing both electrolyte concentration and symmetry. However, applying VG was found to be a more efficient way than electrolyte modifications. This includes generating circulation inside the channel which is of prime importance for applications such as mixing or separation/trapping., Comment: 8 pages, 6 figures. arXiv admin note: text overlap with arXiv:2002.07058

In this paper, an analytical predictive model of the negative capacitance (NC) effect in symmetric long channel double-gate junctionless transistor is proposed based on a charge-based model. In particular, we have investigated the effect of the thickness of the ferroelectric on the I-V characteristics. Importantly, for the first time, our model predicts that the negative capacitance minimizes short channel effects and enhances current overdrive, enabling both low power operation and more efficient transistor size scaling, while the effect on reducing subthreshold slope shows systematic improvement, with subthermionic subthreshold slope values at high current levels (0.1 {\textmu}A/{\textmu}m). Our predictive results in a long channel junctionless with NC show an improvement in ON current by a factor of 6 in comparison to junctionless FET. The set of equations can be used as a basis to explore how such a technology booster and its scaling will impact the main figures of merit of the device in terms of power performances and gives a clear understanding of the device physics. The validity of the analytical model is confirmed by extensive comparisons with numerical TCAD simulations in all regions of operation, from deep depletion to accumulation and from linear to saturation.

High contact resistance is one of the primary concerns for electronic device applications of two-dimensional (2D) layered semiconductors. Here, we explore the enhanced carrier transport through metal-semiconductor interfaces in WS2 field effect transistors (FETs) by introducing a typical transition metal, Cu, with two different doping strategies: (i) a "generalized" Cu doping by using randomly distributed Cu atoms along the channel and (ii) a "localized" Cu doping by adapting an ultrathin Cu layer at the metal-semiconductor interface. Compared to the pristine WS2 FETs, both the generalized Cu atomic dopant and localized Cu contact decoration can provide a Schottky-to-Ohmic contact transition owing to the reduced contact resistances by 1 - 3 orders of magnitude, and consequently elevate electron mobilities by 5 - 7 times higher. Our work demonstrates that the introduction of transition metal can be an efficient and reliable technique to enhance the carrier transport and device performance in 2D TMD FETs., Comment: Under review

The present study aims at utilizing field effect phenomenon to induce heterogeneous surface charge and consequently changing the fluid flow in a solid state nanochannel with converging-diverging periodicity. It is shown that the proposed geometry causes non-uniform radial field adjacent to channel walls which is stronger around the diverging section and weaker next to the converging part of the wall. The later generates heterogeneous surface charge at channel walls depending on the applied gate potential i.e. applying low gate potential enables effective modulation of surface charge with the same polarity of the intrinsic charge at channel walls, while moderate gate potential causes charge inversion in diverging sections of the channel and generates reverse flow and thus results in fluid flow circulation. The potential application of flow circulation for trapping and rejection of particles is also demonstrated., Comment: 6 pages, 8 figures

In this paper, an analytical predictive model of interface charge traps in symmetric long channel double-gate junctionless transistors is proposed based on a charge-based model. Interface charge traps arising from the exposure to chemicals, high-energy ionizing radiation or aging mechanism could degrade the charge-voltage characteristics. The model is predictive in a range of temperature from 77K to 400K. The validity of the approach is confirmed by extensive comparisons with numerical TCAD simulations in all regions of operation from deep depletion to accumulation and linear to saturation.

We study the optical properties of MoS$_2$ nanotubes (NTs) with walls comprising dozens of monolayers. We reveal strong peaks in micro-photoluminescence ($\mu$-PL) spectra when detecting the light polarized along the NT axis. We develop a model describing the optical properties of the nanotubes acting as optical resonators which support the quantization of whispering gallery modes inside the NT wall. The experimental observation of the resonances in $\mu$-PL allows one to use them as a contactless method of the estimation of the wall width. Our findings open a way to use such NTs as polarization-sensitive components of nanophotonic devices., Comment: 7 pages, 4 figures

In this paper we study the device physics of a technique for realizing an n-p-n bipolar transistor action in the source side of a junctionless nanowire tunneling FET (BJN-TFET). In the on-state, tunneling of electrons from valence band of the source to conduction band of the channel enhances the hole concentration as well as the potential in the source region which drives a built-in BJT transistor by forward biasing the base-emitter junction, with the source acting as a p-type region. Owing to the sharp switching of the JN-TFET and high BJT current gain, the overall performance is improved, including favorable high on-state current (2.17*10-6 A/um), and sub 60 mV/dec subthreshold swing (~ 50 mV/dec) at low supply voltages. This approach modifies the current mechanism owning to the triggered BJT and makes the proposed structure more attractive for scaling requirements in future low power application., Comment: 24 pages, 11 figures, 1 table

Van der Waals (vdW) heterojunctions composed of 2-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibit novel physics phenomena that can power high performance electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature (RT) Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions, and widen the potential applications base of 2D layered materials., Comment: 27 pages, 11 figures

We report on the fabrication and characterization of synthesized multiwall MoS2 nanotube (NT) and nanoribbon (NR) field-effect transistors (FETs). The MoS2 NTs and NRs were grown by chemical transport, using iodine as a transport agent. Raman spectroscopy confirms the material as unambiguously MoS2 in NT, NR, and flake forms. Transmission electron microscopy was used to observe cross sections of the devices after electrical measurements and these were used in the interpretation of the electrical measurements allowing estimation of the current density. The NT and NR FETs demonstrate n-type behavior, with ON/OFF current ratios exceeding 10^3, and with current densities of 1.02 {\mu}A/{\mu}m, and 0.79 {\mu}A/{\mu}m at VDS = 0.3 V and VBG = 1 V, respectively. Photocurrent measurements conducted on a MoS2 NT FET, revealed short-circuit photocurrent of tens of nanoamps under an excitation optical power of 78 {\mu}W and 488 nm wavelength, which corresponds to a responsivity of 460 {\mu}A/W. A long channel transistor model was used to model the common-source characteristics of MoS2 NT and NR FETs and was shown to be consistent with the measured data.

The growth rate of laser-photoenhanced thermally grown native oxides of InP in a N2O ambient and its dependence on growth condition are presented. Increased laser power, substrate temperature, and N2O pressure are observed to increase the growth rate. The topography and the composition of these oxides have been studied using secondary electron microscopy and X-ray photoemission spectroscopy, respectively. The oxide layers contain In2O3 and a phosphate, probably InPO4. The enhanced growth appears to be caused by both excited oxidizing species and a photon-enhanced surface reaction.