We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment individual layer crystal axes. illustrate approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers monolayer flakes. The Raman spectra this artificial possess wide 2D band, which is best fit four Lorentzians, consistent Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on graphene, and spectroscopy as function gate voltage constant...

According to electronic structure theory, bilayer graphene is expected have anomalous properties when it has long-period moir\'e patterns produced by small misalignments between its individual layer honeycomb lattices. We realized crystals with accurately controlled twist angles smaller than 1 degree and studied their using scanning probe microscopy electron transport. observe conductivity minima at charge neutrality, satellite gaps that appear carrier densities for degree, tunneling...

Resistive-switching memory (RRAM) based on transition metal oxides is a potential candidate for replacing Flash and dynamic random access in future generation nodes. Although very promising from the standpoints of scalability technology, RRAM still has severe drawbacks terms understanding modeling resistive-switching mechanism. This paper addresses resistive switching bipolar metal-oxide RRAMs. Reset set processes are described voltage-driven ion migration within conductive filament...

We report the fabrication of back-gated field-effect transistors (FETs) using ultra-thin, mechanically exfoliated MoSe2 flakes. The FETs are n-type and possess a high gate modulation, with On/Off ratios larger than 106. devices show asymmetric characteristics upon swapping source drain, finding explained by presence Schottky barriers at metal contact/MoSe2 interface. Using four-point, we measure intrinsic conductivity mobility as function bias, temperature. Samples room temperature ~50...

To reduce Schottky-barrier-induced contact and access resistance, the impact of charged impurity phonon scattering on mobility in devices based 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques dielectric engineering using $high-\kappa$ oxides, respectively. The goal this work is to demonstrate a that serves as an effective n-type charge transfer dopant monolayer (ML) molybdenum disulfide ($MoS_{2}$). Utilizing amorphous...

Resistive-switching random access memory (RRAM) based on the formation and dissolution of a conductive filament (CF) through insulating materials, e.g., transition metal oxides, may find applications as novel logic devices. Understanding resistive-switching mechanism is essential for predicting controlling scaling reliability performances RRAM. This paper addresses set/reset characteristics RRAM devices <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML"...

We demonstrate gate-tunable resonant tunneling and negative differential resistance in the interlayer current–voltage characteristics of rotationally aligned double bilayer graphene heterostructures separated by hexagonal boron nitride (hBN) dielectric. An analysis heterostructure band alignment using individual layer densities, along with experimentally determined chemical potentials indicates that resonance occurs when energy bands two are aligned. discuss dependence on hBN thickness, as...

Multilevel operation in resistive switching memory (RRAM) based on HfOx is demonstrated through variable sizes and orientations of the conductive filament. Memory states with same resistance, but opposite orientation defects, display a different response to an applied read voltage, therefore allowing improvement information stored each physical cell. The multilevel scheme allows 50% increase (from 2 3 bits) information. As service our authors readers, this journal provides supporting...

We study the magnetotransport properties of high-mobility holes in monolayer and bilayer WSe_{2}, which display well defined Shubnikov-de Haas (SdH) oscillations, quantum Hall states high magnetic fields. In both mono- SdH oscillations occur predominantly at even filling factors, evincing a twofold Landau level degeneracy. The Fourier transform analysis WSe_{2} reveals presence two subbands localized top or bottom layer, as negative compressibility. From temperature dependence we determine...

Using different types of WSe2 and graphene-based heterostructures, we experimentally determine the offset between graphene neutrality point conduction valence band edges, as well dielectric constant along c-axis. In a first heterostructure, consisting WSe2-on-graphene, use layer top in dual-gated field-effect transistors to capacitance function thickness, second heterostructure graphene-on-WSe2, lateral electron transport shows ambipolar behavior characteristic combined with conductivity...

We use electron transport to characterize monolayer graphene-multilayer MoS2 heterostructures. Our samples show ambipolar characteristics and conductivity saturation on the branch that signals onset of conduction band population. Surprisingly, carrier density in graphene decreases with gate bias once is populated, demonstrating negative compressibility MoS2. are able interpret our measurements quantitatively by accounting for disorder using random phase approximation (RPA) exchange...

Transition metal dichalcogenides are of interest for next generation switches, but the lack low resistance electron and hole contacts in same material has hindered development complementary field-effect transistors circuits. We demonstrate an air-stable, reconfigurable, monolayer MoTe2 transistor encapsulated hexagonal boron nitride, using electrostatically doped contacts. The introduction a multigate design with prepatterned bottom allows us to independently achieve contact threshold...

Resistive-switching random access memory (RRAM) devices utilizing a crossbar architecture represent promising alternative for Flash replacement in high-density data storage applications. However, RRAM arrays require the adoption of diodelike select with high on-off -current ratio and sufficient endurance. To avoid use devices, one should develop passive where nonlinear characteristic device itself provides self-selection during read write. This paper discusses complementary switching (CS)...

We study the magnetotransport of high-mobility electrons in monolayer and bilayer ${\mathrm{MoSe}}_{2}$, which show Shubnikov--de Haas (SdH) oscillations quantum Hall states high magnetic fields. An electron effective mass $0.8{m}_{e}$ is extracted from SdH oscillations' temperature dependence; ${m}_{e}$ bare mass. At a fixed density longitudinal resistance shows minima at filling factors (FFs) that are either predominantly odd, or even, with parity changes as tuned. The insensitive to an...

We report a study of the quantum Hall states (QHS) holes in mono- and bilayer ${\mathrm{WSe}}_{2}$. The QHS sequence transitions between predominantly even odd filling factors as hole density is tuned range $1.6--12\ifmmode\times\else\texttimes\fi{}1{0}^{12}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$. Measurements tilted magnetic fields reveal an insensitivity to in-plane field, evincing that spin locked perpendicular ${\mathrm{WSe}}_{2}$ plane. Furthermore, insensitive applied electric...

A major challenge in achieving high density crossbar arrays based on resistive-switching memory (RRAM) is the identification of a select device (e.g. diode) with suitable supply current and on-off swing. Recently, complementary resistance switch (CRS) concept 2-RRAM stack was proposed to solve sneak-path problem [1]. This work demonstrates switching (CS) single-stack nonpolar-RRAM devices. After describing CS characteristics by simulations, we show operation under DC/pulsed regime discuss...

Using an ab initio density functional theory based electronic structure method, we study the effects of adatoms on properties monolayer transition metal dichalcogenide Molybdenum-disulfide (MoS2). We consider 1st (Li, Na, K) and 7th (F, Cl, Br) column atoms metals (Sc, Ti, Ta, Mo, Pd, Pt, Ag, Au). Three high symmetry sites for adatom surface MoS2 are examined as starting points to search most energetically stable configuration each adatom-monolayer system, well type associated bonding. For...

We investigate interlayer tunneling in heterostructures consisting of two tungsten diselenide (WSe2) monolayers with controlled rotational alignment, and separated by hexagonal boron nitride. In samples where the WSe2 are rotationally aligned we observe resonant tunneling, manifested a large conductance negative differential resistance vicinity zero bias, which stem from energy- momentum-conserving tunneling. Because spin-orbit coupling leads to coupled spin-valley degrees freedom, twist...

The electronic properties of two-dimensional materials such as graphene are extremely sensitive to their environment, especially the underlying substrate. Planar van der Waals bonded substrates hexagonal boron nitride (hBN) have been shown greatly improve electrical performance devices by reducing topographic variations and charge fluctuations compared amorphous insulating substrates}. Semiconducting transition metal dichalchogenides (TMDs) another family that recently received interest...

We present a combined experimental and theoretical study of valley populations in the valence bands trilayer WSe_{2}. Shubnikov-de Haas oscillations show that holes populate two distinct subbands associated with K Γ valleys, effective masses 0.5m_{e} 1.2m_{e}, respectively; m_{e} is bare electron mass. At fixed total hole density, an applied transverse electric field transfers from orbitals to orbitals. are able explain this behavior terms larger layer polarizability orbital subband.

The resistive switching memory (RRAM) may offer a scalable solution for 3D high-density non-volatile storage. For physics-based prediction of RRAM scalability, however, accurate models must be developed. This work presents numerical model bipolar switching, capable describing set/reset processes and reliability issues, such as program/read disturbs retention. is based on field- temperature-activated ion migration accounts characteristics different compliance currents timescales (10 ns - 100...

Bipolar resistive switching memory (RRAM) relies on ion migration effects taking place at a conductive filament (CF). Understanding the evolution of CF during set and reset transitions is essential for predicting RRAM scalability developing new methods storage computation. This work describes bipolar through numerical simulations drift/diffusion. The defect distribution profile increasing current after transition voltage are shown. Finally, asymmetric shape evidenced polarity-dependent...

Resistive switching random access memory (RRAM) offers fast switching, high endurance and CMOS-compatible integration. Although functional devices below 10 nm have been already demonstrated, assessing the ultimate scaling of RRAM requires a detailed understanding modeling reliability processes. This work discusses bipolar in RRAM. An analytical model is first introduced to describe temperature- field-accelerated growth conductive filament (CF) induced by ion migration. The accounts for...