Unraveling the dynamics of conductive filaments in MoS-based memristors by operando transmission electron microscopy.

Advanced operando transmission electron microscopy (TEM) techniques enable the observation of nanoscale phenomena in electronic devices during operation. Here, we investigated lateral memristive devices composed of two dimensional layered MoS with Pd and Ag electrodes. Under external bias voltage, we visualized the formation and migration of Ag conductive filaments (CFs) between the two electrodes, and their complete dissolution upon reversing the biasing polarity.

Volatile and Nonvolatile Resistive Switching in Lateral 2D Molybdenum Disulfide-Based Memristive Devices.

Developing electronic devices capable of emulating biological functions is essential for advancing brain-inspired computation paradigms such as neuromorphic computing. In recent years, two-dimensional materials have emerged as promising candidates for neuromorphic electronic devices. This work addresses the coexistence of volatile and nonvolatile resistive switching in lateral memristors based on molybdenum disulfide with silver as the active electrode.

Volatile MoS Memristors with Lateral Silver Ion Migration for Artificial Neuron Applications.

Layered 2D semiconductors have shown enhanced ion migration capabilities along their van der Waals (vdW) gaps and on their surfaces. This effect can be employed for resistive switching (RS) in devices for emerging memories, selectors, and neuromorphic computing. To date, all lateral molybdenum disulfide (MoS)-based volatile RS devices with silver (Ag) ion migration have been demonstrated using exfoliated, single-crystal MoS flakes requiring a forming step to enable RS.

Contact Resistance Optimization in MoS Field-Effect Transistors through Reverse Sputtering-Induced Structural Modifications.

Two-dimensional material (2DM)-based field-effect transistors (FETs), such as molybdenum disulfide (MoS)-FETs, have gained significant attention for their potential for ultrashort channels, thereby extending Moore's law. However, MoS-FETs are prone to the formation of Schottky barriers at the metal-MoS interface, resulting in high contact resistance () and, consequently, reduced transistor currents in the ON-state. Our study explores the modification of MoS to induce the formation of conductive 1T-MoS at the metal-MoS interface via reverse sputtering.

Piezoresistive Platinum Diselenide Pressure Sensors with Reliable High Sensitivity and Their Integration into Complementary Metal-Oxide-Semiconductor Circuits.

Membrane-based sensors are an important market for microelectromechanical systems (MEMS). Two-dimensional (2D) materials, with their low mass, are excellent candidates for suspended membranes to provide high sensitivity, small footprint sensors. The present work demonstrates pressure sensors employing large-scale-synthesized 2D platinum diselenide (PtSe) films as piezoresistive membranes supported only by a thin polymer layer.

Unconventional Photovoltaic Effect in a Perovskite-Coated Metal-Insulator-Graphene Photodiode.

The photovoltaic effect offers a simple way for converting light into an electrical signal. Here, we report on the observation of a zero-bias photocurrent in the forward direction of a perovskite-covered metal-insulator-graphene diode (MIG-diode), which is the opposite current direction compared to conventional photovoltaic cells and photodiodes. Photocurrent mapping has been performed to gain insights into the precise position of photocurrent generation, demonstrating that the zero-bias photocurrent is primarily generated at the edges of the active device area.

in situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation.

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies ( ). Notwithstanding its significance, behaviors of the defective structure and in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (CeGdO) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massive rearrangement are stimulated and visualized in situ with sub-Å resolution.

High-Yield Large-Scale Suspended Graphene Membranes over Closed Cavities for Sensor Applications.

Suspended membranes of monatomic graphene exhibit great potential for applications in electronic and nanoelectromechanical devices. In this work, a "hot and dry" transfer process is demonstrated to address the fabrication and patterning challenges of large-area graphene membranes on top of closed, sealed cavities. Here, "hot" refers to the use of high temperature during transfer, promoting the adhesion.

Graphene Thermal Infrared Emitters Integrated into Silicon Photonic Waveguides.

Cost-efficient and easily integrable broadband mid-infrared (mid-IR) sources would significantly enhance the application space of photonic integrated circuits (PICs). Thermal incandescent sources are superior to other common mid-IR emitters based on semiconductor materials in terms of PIC compatibility, manufacturing costs, and bandwidth. Ideal thermal emitters would radiate directly into the desired modes of the PIC waveguides via near-field coupling and would be stable at very high temperatures.

Theoretical and Experimental Analysis of Single-Arm Bimodal Plasmo-Photonic Refractive Index Sensors.

In this paper, we study both theoretically and experimentally the sensitivity of bimodal interferometric sensors where interference occurs between two plasmonic modes with different properties propagating in the same physical waveguide. In contrast to the well-known Mach-Zehnder interferometric (MZI) sensor, we show for the first time that the sensitivity of the bimodal sensor is independent of the sensing area length. This is validated by applying the theory to an integrated plasmo-photonic bimodal sensor that comprises an aluminum (Al) plasmonic stripe waveguide co-integrated between two accessible SU-8 photonic waveguides.

Button shear testing for adhesion measurements of 2D materials.

Two-dimensional (2D) materials are considered for numerous applications in microelectronics, although several challenges remain when integrating them into functional devices. Weak adhesion is one of them, caused by their chemical inertness. Quantifying the adhesion of 2D materials on three-dimensional surfaces is, therefore, an essential step toward reliable 2D device integration.

Towards graphene-based asymmetric diodes: a density functional tight-binding study.

Self-consistent charge density functional tight-binding (DFTB) calculations have been performed to investigate the electrical properties and transport behavior of asymmetric graphene devices (AGDs). Three different nanodevices constructed of different necks of 8 nm, 6 nm and 4 nm, named Graphene-N8, Graphene-N6 and Graphene-N4, respectively, have been proposed. All devices have been tested under two conditions of zero gate voltage and an applied gate voltage of +20 V using a dielectric medium of 3.

Combined Structural and Plasmonic Enhancement of Nanometer-Thin Film Photocatalysis for Solar-Driven Wastewater Treatment.

Titanium dioxide (TiO) thin films are commonly used as photocatalytic materials. Here, we enhance the photocatalytic activity of devices based on titanium dioxide (TiO) by combining nanostructured glass substrates with metallic plasmonic nanostructures. We achieve a three-fold increase of the catalyst's surface area through nanoscale, three-dimensional patterning of periodic, conical grids, which creates a broadband optical absorber.

Unbiased Plasmonic-Assisted Integrated Graphene Photodetectors.

Photonic integrated circuits (PICs) for next-generation optical communication interconnects and all-optical signal processing require efficient (∼A/W) and fast (≥25 Gbs) light detection at low ( View Article and Find Full Text PDF

Stacking Polymorphism in PtSe Drastically Affects Its Electromechanical Properties.

PtSe is one of the most promising materials for the next generation of piezoresistive sensors. However, the large-scale synthesis of homogeneous thin films with reproducible electromechanical properties is challenging due to polycrystallinity. It is shown that stacking phases other than the 1T phase become thermodynamically available at elevated temperatures that are common during synthesis.

2D materials for future heterogeneous electronics.

Graphene and two-dimensional materials (2DM) remain an active field of research in science and engineering over 15 years after the first reports of 2DM. The vast amount of available data and the high performance of device demonstrators leave little doubt about the potential of 2DM for applications in electronics, photonics and sensing. So where are the integrated chips and enabled products? We try to answer this by summarizing the main challenges and opportunities that have thus far prevented 2DM applications.

Evidence for Local Spots of Viscous Electron Flow in Graphene at Moderate Mobility.

Dominating electron-electron scattering enables viscous electron flow exhibiting hydrodynamic current density patterns, such as Poiseuille profiles or vortices. The viscous regime has recently been observed in graphene by nonlocal transport experiments and mapping of the Poiseuille profile. Herein, we probe the current-induced surface potential maps of graphene field-effect transistors with moderate mobility using scanning probe microscopy at room temperature.

Novel Methodologies for Multiaxial Strain Measurements with Piezoresistive Films based on Graphene Nanoplatelets.

Many recent investigations in the context of graphene nanoplatelets (GNPs) coatings report surface strain measurements by using piezoresistive sensing capabilities. An often underestimated problem is that the strain field is unknown and the principal strain components as well as their orientations must be determined. Herein, GNP films subjected to multiaxial strain are examined.

Large-area integration of two-dimensional materials and their heterostructures by wafer bonding.

Integrating two-dimensional (2D) materials into semiconductor manufacturing lines is essential to exploit their material properties in a wide range of application areas. However, current approaches are not compatible with high-volume manufacturing on wafer level. Here, we report a generic methodology for large-area integration of 2D materials by adhesive wafer bonding.

Graphene-Quantum Dot Hybrid Photodetectors with Low Dark-Current Readout.

Graphene-based photodetectors have shown responsivities up to 10 A/W and photoconductive gains up to 10 electrons per photon. These photodetectors rely on a highly absorbing layer in close proximity to graphene, which induces a shift of the graphene chemical potential upon absorption, hence modifying its channel resistance. However, due to the semimetallic nature of graphene, the readout requires dark currents of hundreds of microamperes up to milliamperes, leading to high power consumption needed for the device operation.

Nanoelectromechanical Sensors Based on Suspended 2D Materials.

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles.

Does carrier velocity saturation help to enhance in graphene field-effect transistors?

It has been argued that current saturation in graphene field-effect transistors (GFETs) is needed to get optimal maximum oscillation frequency ( ). This paper investigates whether velocity saturation can help to get better current saturation and if that correlates with enhanced . We have fabricated 500 nm GFETs with high extrinsic (37 GHz), and later simulated with a drift-diffusion model augmented with the relevant factors that influence carrier velocity, namely: short-channel electrostatics, saturation velocity effect, graphene/dielectric interface traps, and self-heating effects.

Insulators for 2D nanoelectronics: the gap to bridge.

Nanoelectronic devices based on 2D materials are far from delivering their full theoretical performance potential due to the lack of scalable insulators. Amorphous oxides that work well in silicon technology have ill-defined interfaces with 2D materials and numerous defects, while 2D hexagonal boron nitride does not meet required dielectric specifications. The list of suitable alternative insulators is currently very limited.

Manufacture and characterization of graphene membranes with suspended silicon proof masses for MEMS and NEMS applications.

Graphene's unparalleled strength, chemical stability, ultimate surface-to-volume ratio and excellent electronic properties make it an ideal candidate as a material for membranes in micro- and nanoelectromechanical systems (MEMS and NEMS). However, the integration of graphene into MEMS or NEMS devices and suspended structures such as proof masses on graphene membranes raises several technological challenges, including collapse and rupture of the graphene. We have developed a robust route for realizing membranes made of double-layer CVD graphene and suspending large silicon proof masses on membranes with high yields.