In this paper we propose two transistor concepts based on lateral heterostructures of monolayer MoS2, composed of adjacent regions of 1T (metallic) and 2H (semiconducting) phases, inspired by recent research showing the possibility to obtain such heterostructures by electron beam irradiation. The first concept, the lateral heterostructure field-effect transistor, exhibits potential of better performance with respect to the foreseen evolution of CMOS technology, both for high performance and low power applications. Performance potential has been evaluated by means of detailed multi-scale materials and device simulations. The second concept, the planar barristor, also exhibits potential competitive performance with CMOS, and an improvement of orders of magnitude in terms of the main figures of merit with respect to the recently proposed vertical barristor.

In this work, a novel one-dimensional geometry for metal-insulator-graphene (1D-MIG) diode with low capacitance is demonstrated. The junction of the 1D-MIG diode is formed at the 1D edge of Al 2 O 3 -encapsulated graphene with TiO 2 that acts as barrier material. The diodes demonstrate ultra-high current density since the transport in the graphene and through the barrier is in plane. The geometry delivers very low capacitive coupling between the cathode and anode of the diode, which shows frequency response up to 100 GHz and ensures potential high frequency performance up to 2.4 THz. The 1D-MIG diodes are demonstrated to function uniformly and stable under bending conditions down to 6.4 mm bending radius on flexible substrate.

A systematic investigation of graphene edge contacts is provided. Intentionally patterning monolayer graphene at the contact region creates well-defined edge contacts that lead to a 67% enhancement in current injection from a gold contact. Specific contact resistivity is reduced from 1372 Ωµm for a device with surface contacts to 456 Ωµm when contacts are patterned with holes. Electrostatic doping of the graphene further reduces contact resistivity from 519 Ωµm to 45 Ωµm, a substantial decrease of 91%. The experimental results are supported and understood via a multi-scale numerical model, based on density-functional-theory calculations and transport simulations. The data is analyzed with regards to the edge perimeter and hole-to-graphene ratio, which provides insights into optimized contact geometries. The current work thus indicates a reliable and reproducible approach for fabricating low resistance contacts in graphene devices.We provide a simple guideline for contact design that can be exploited to guide graphene and 2D material contact engineering.The extraordinary electronic, optoelectronic and mechanical properties of graphene make it a promising candidate as a technology booster for micro-and nanoelectronics applications.Examples include radio frequency electronics, 1,2 integrated photodetectors, 3-5 and nanoelectromechanical systems. 6,7 One of the major bottlenecks limiting the performance of graphene-based devices is the large and varying value of specific contact resistivity (R C ) between metal contact electrodes and graphene. [8][9][10][11] When a metal is brought into contact with graphene, a junction with high contact resistivity is created, typically attributed to the low density of states (DOS) in graphene in particular when the Fermi level is near the Dirac point. 11 Although abinitio calculations provide deeper insights into the contact problem, they also highlight the importance of the metal. 12-14 Experimentally, various methods have been reported to reduce R C : one of the most common approaches is post-metallization annealing. [15][16][17] Other methods aim to modify the graphene prior to metallization in a random manner, such as low power oxygen plasma etch (with or without post-metallization annealing), 18 ozone pre-treatment, 19 intentional doping of graphene below the contact metal, 20 and ion beam irradiation. 21,22 A more deterministic approach is the formation of "edge"-contacts, where the graphene under the contact is partially removed by lithographic methods to enable the formation of covalent bonds between graphene and metal. This idea was proposed by means of an ingenious contact geometry by Wang 23 . Subsequently, the partial removal of the graphene under the contact by lithography, plasma or ion bombardment allowed a more versatile contact design. In particular, Smith et al. 24 investigated edge patterning of graphene with rectangular cuts under palladium (Pd) and copper (Cu) contacts with the transfer length method (TLM). The conclusion of this study was extended by Park et a...

Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial aspects towards the development of voltage-controlled spintronic devices with low power dissipation. Members of the 2D transition metal dichalcogenides (TMDCs) have been recently predicted and experimentally reported as a new class of 2D TI materials, but in most cases edge conduction seems fragile and limited to the monolayer phase fabricated on specified substrates. Here, we realize the controlled patterning of the 1T'-phase embedded into the 2H-phase of thin semiconducting molybdenum-disulfide (MoS2) by laser beam irradiation. Integer fractions of the quantum of resistance, the dependence on laser-irradiation conditions, magnetic field, and temperature, as well as the bulk gap observation by scanning tunneling spectroscopy and theoretical calculations indicate the presence of the quantum spin Hall phase in our patterned 1T' phases.Two-dimensional (2D) topological insulting (TI) states have been mainly investigated in HgTe/CdTe or InAs/GaSb quantum well systems (1-3). In the 2D TI state the quantum spin Hall (QSH) effect emerges thanks to the simultaneous presence of a bulk energy gap and gapless helical edge states protected by time-reversal symmetry, namely, opposite and counter-propagating spin states forming a Kramers doublet. Interestingly, 2D TI states were first theoretically predicted for graphene (4-6), but experimentally reported in only few related systems (7-9) such as low-coverage Bi2Te3 nanoparticle-decorated graphene (8). Moreover, control of the QSH phase in graphene-based systems remains a challenge.Recently, a family of atom-thin transition metal dichalcogenides (TMDCs) materials has also been predicted to exhibit the QSHE (10-12), having its origin in the natural band inversion of the 1T' phase (one of the phases of TMDC; see Supplementary Material (SM) 1) and the spin-orbit coupling (SOC)induced band-gap opening. Moreover, the TI state has been experimentally verified in the case of WTe 2 (13-15) thanks to the stability and high-quality of WTe 2 monolayers carefully formed on bilayer graphene/atom-thin hBN. Various signatures of the TI state have been demonstrated in this 2 material (13,15), including the latest observation of a half-integer quantum value of resistance (RQ/2 = h/2e 2 = 12.9 k, where h is Planck's constant and e is the charge on the electron) (14).However, the TI phenomenon in WTe2 is rather sensitive to the substrates, synthesis process, and the chemical environment, making its controlled use in practical applications challenging. Moreover, although the (metastable) 1T' phase can be found or induced in other TMDCs (23,25), nobody has demonstrated the existence of the QSHE in these other TMDCs. The conditions under which helical edge states can exist at the 1T'-2H interfaces is a crucial problem which should be mastered for both TI physics and its applications. Here, we pattern a metallic 1T'-phase (SM 1) embedded into the nontopological and semiconducting 2H p...

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