We demonstrate the directed control of charge carriers in graphene using the electric field that accompanies the propagation of surface acoustic waves (SAWs) on a piezoelectric surface. Graphene grown by chemical vapor deposition was transferred to the surface of lithium niobate, allowing its direct integration with interdigital transducers used for SAW generation and detection. Radio frequency (RF) signal applied to the transducers at their resonant frequency was found to generate a direct current flow by the transport of p-type charge carriers. The acoustically induced current scales linearly with the applied RF power and can be observed even in presence of a counter-flow current induced by an applied bias.

Graphene and related materials can lead to disruptive advances in next-generation photonics and optoelectronics. The challenge is to devise growth, transfer and fabrication protocols providing high (≥5000 cm² V^–1 s^–1) mobility devices with reliable performance at the wafer scale. Here, we present a flow for the integration of graphene in photonics circuits. This relies on chemical vapor deposition (CVD) of single layer graphene (SLG) matrices comprising up to ∼12000 individual single crystals, grown to match the geometrical configuration of the devices in the photonic circuit. This is followed by a transfer approach which guarantees coverage over ∼80% of the device area, and integrity for up to 150 mm wafers, with room temperature mobility ∼5000 cm² V^–1 s^–1. We use this process flow to demonstrate double SLG electro-absorption modulators with modulation efficiency ∼0.25, 0.45, 0.75, 1 dB V^–1 for device lengths ∼30, 60, 90, 120 μm. The data rate is up to 20 Gbps. Encapsulation with single-layer hexagonal boron nitride (hBN) is used to protect SLG during plasma-enhanced CVD of Si₃N₄, ensuring reproducible device performance. The processes are compatible with full automation. This paves the way for large scale production of graphene-based photonic devices.

Out of the different structural phases of molybdenum ditelluride (MoTe₂), the distorted octahedral 1T′ possesses great interest for fundamental physics and is a promising candidate for the implementation of innovative devices such as topological transistors. Indeed, 1T′-MoTe₂ is a semimetal with superconductivity, which has been predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. Large instability of monolayer 1T′-MoTe₂ in environmental conditions, however, has made its investigation extremely challenging so far. In this work, we demonstrate homogeneous growth of large single-crystal (up to 500 μm) monolayer 1T′-MoTe₂via chemical vapor deposition (CVD) and its stabilization in air with a scalable encapsulation approach. The encapsulant is obtained by electrochemically delaminating CVD hexagonal boron nitride (hBN) from copper foil, and it is applied on the freshly grown 1T′-MoTe₂via a top-down dry lamination step. The structural and electrical properties of encapsulated 1T′-MoTe₂ have been monitored over several months to assess the degree of degradation of the material. We find that when encapsulated with hBN, the lifetime of monolayer 1T′-MoTe₂ successfully increases from a few minutes to more than a month. Furthermore, the encapsulated monolayer can be subjected to transfer, device processing, and heating and cooling cycles without degradation of its properties. The potential of this scalable heterostack is confirmed by the observation of signatures of low-temperature phase transition in monolayer 1T′-MoTe₂ by both Raman spectroscopy and electrical measurements. The growth and encapsulation methods reported in this work can be employed for further fundamental studies of this enticing material as well as facilitate the technological development of monolayer 1T′-MoTe₂.