performance. Here we demonstrate that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of TMDs 5,6 with a picosecond photoresponse comparable to that of graphene 7-9 , thereby optimizing both speed and efficiency in a single photodetector. We follow in time the extraction of photoexcited carriers in these devices using timeresolved photocurrent measurements and demonstrate a photoresponse time as short as 5.5 ps, which we tune by applying a bias and by varying the TMD layer thickness. Our study provides direct insight into the physical processes governing the detection speed and quantum efficiency of these van der Waals (vdW) heterostuctures, such as out-of-plane carrier drift and recombination.The observation and understanding of ultrafast and efficient photodetection demonstrate the potential of hybrid TMD-based heterostructures as a platform for future optoelectronic devices. 2The optoelectronic response of 2D crystals is currently the subject of intense investigation [1][2][3][5][6][7][8][9][10][11][12][13][14][15][16] prompted by the need for next-generation photodetectors with superior performance in terms of efficiency, detection speed, as well as flexibility and transparency 17 . High photon absorption 5,18 and large photoconducting gain 11,12,14 have been observed in devices based on semiconducting 2D crystals. Yet, the observed response time typically ranges from nanoseconds 16 to seconds 11,14 , with faster devices often displaying lower responsivity 11 . Therefore, the main challenge is to develop and assess photodetectors based on 2D semiconductor crystals that simultaneously possess a large active area, high internal efficiency, and fast response time.A promising approach to create such versatile devices is to sandwich a TMD layer between two graphene sheets serving as charge extraction contacts. In contrast to lateral photodetectors, such vertical van der Waals (vdW) heterostructures 4 have the advantage of possessing a large, scalable active area and an atomically short charge extraction channel, potentially enabling both efficient and fast photodetection. Whereas the quantum efficiency of these vdW devices 5,6,13 and the dynamics of photocarrier creation and relaxation in TMDs [19][20][21][22][23][24][25][26][27] have been addressed, the response time of TMD-based photodetectors, as well as the dynamic processes governing their quantum efficiency remain elusive.Here, we report on the intrinsic processes that limit the performance of photodetectors based on high-quality G/WSe2/G (with G representing graphene) vdW heterostructures encapsulated in hexagonal boron nitride (hBN) 28 . We perform time-resolved photocurrent measurements 7,29 on devices consisting of WSe2 flakes with a range of thicknesses (monolayer and multilayers from 2.2 to 40 nm). This technique, which combines electronic detection with subpicosecond optical excitation, allows probing of the extraction ( Figure 1a) and loss dynamics of the photoexcited charge carriers in the photoactive TMD layer. We ...

Suspended monolayer transition metal dichalcogenides (TMD) are membranes that combine ultralow mass and exceptional optical properties, making them intriguing materials for opto-mechanical applications. However, the low measured quality factor of TMD resonators has been a roadblock so far. Here, we report an ultrasensitive optical readout of monolayer TMD resonators that allows us to reveal their mechanical properties at cryogenic temperatures. We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 1.6 × 104 at liquid nitrogen temperature and 4.7 × 104 at liquid helium temperature. This surpasses the quality factor of monolayer graphene resonators with similar surface areas. Upon cooling the resonator, the resonant frequency increases significantly due to the thermal contraction of the WSe2 lattice. These measurements allow us to experimentally study the thermal expansion coefficient of WSe2 monolayers for the first time. High Q-factors are also found in resonators based on MoS2 and MoSe2 monolayers. The high quality-factor found in this work opens new possibilities for coupling mechanical vibrational states to two-dimensional excitons, valley pseudospins, and single quantum emitters and for quantum opto-mechanical experiments based on the Casimir interaction.

Despite recent progress in nano-optomechanics, active control of optical fields at the nanoscale has not been achieved with an on-chip nano-electromechanical system (NEMS) thus far. Here we present a new type of hybrid system, consisting of an on-chip graphene NEMS suspended a few tens of nanometres above nitrogen-vacancy centres (NVCs), which are stable single-photon emitters embedded in nanodiamonds. Electromechanical control of the photons emitted by the NVC is provided by electrostatic tuning of the graphene NEMS position, which is transduced to a modulation of NVC emission intensity. The optomechanical coupling between the graphene displacement and the NVC emission is based on near-field dipole–dipole interaction. This class of optomechanical coupling increases strongly for smaller distances, making it suitable for nanoscale devices. These achievements hold promise for selective control of emitter arrays on-chip, optical spectroscopy of individual nano-objects, integrated optomechanical information processing and open new avenues towards quantum optomechanics.

Solid state quantum emitters are a mainstay of quantum nanophotonics as integrated single photon sources (SPS) and optical nanoprobes. Integrating such emitters with active nanophotonic elements is desirable in order to attain efficient control of their optical properties but typically degrades the photostability of the emitter itself. Here, we demonstrate a tuneable hybrid device that integrates lifetime-limited single emitters (linewidth ~ 40 MHz) and 2D materials at sub-wavelength separation without degradation of the emission properties. Our device's nanoscale dimensions enable ultra-broadband tuning (tuning range > 400 GHz) and fast modulation (frequency ~ 100 MHz) of the emission energy, which renders it an integrated, ultra-compact tuneable SPS. Conversely, this offers a novel approach to optical sensing of 2D material properties using a single emitter as a nanoprobe.Hybrid nanophotonic systems blend the strengths of distinct photonic elements to strongly enhance light-matter interactions 1 in integrated photonic circuits. In these systems, narrow-linewidth quantum light emitters play a key role as single photon sources (SPS) which interact with their nanoscale environment 2,3 . Controlling these interactions provides versatile SPS tuning 4 required for coupling quantum resources [5][6][7] . Integrating nanoscale light emitters with two-dimensional (2D) materials is motivated by the rich physics of near-field interactions 8 and new hybrid light-matter states 9,10 . This approach unites integrated solid-state SPS such as nitrogen vacancy centres 11 , quantum dots 12 and single molecules 13 with the diverse optoelectronic properties of 2D materials that facilitate emitting 14 , controlling [15][16][17] and detecting 18 light at the nanoscale. In such hybrid devices, quantum emitters can be integrated at sub-wavelength separation to the 2D interface to achieve efficient near-field coupling 8 , which modifies the emitter's radiative decay rate [19][20][21] or transition energy 22,23 . Recent experimental studies integrated 2D materials with ensembles of broadband emitters to demonstrate electrical 24-26 and electromechanical 27 tuning of the decay rate by controlling non-radiative energy transfer (nRET) or the energy flow to confined electromagnetic modes such as 2D polaritons 26,28 . Therefore, hybrids of 2D materials and SPS have the potential for in situ control of the conversion and channelling of single photons at the nanoscale. So far, these studies have been limited to ensembles and broad linewidth emitters. Integrating bright and narrow quantum emitters in such systems paves 2 the way towards a tuneable quantum light-matter interface, which is an essential ingredient for integrated quantum networks.Here, we demonstrate hybrid integration of 2D materials (semi-metallic graphene or semi-conducting MoS2) with single, lifetime-limited quantum emitters in nanocrystals to provide active emission control. Using the 2D materials as transparent electrodes, we show broadband Stark tuning of the emission energy o...

In this study we lay the groundwork for a graphene-based fundamental ruler at the nanoscale. It relies on the efficient energy-transfer mechanism between single quantum emitters and low-doped graphene monolayers. Our experiments, conducted with dibenzoterrylene (DBT) molecules, allow going beyond ensemble analysis due to the emitter photo-stability and brightness. A quantitative characterization of the fluorescence decayrate modification is presented and compared to a simple model, showing agreement with the − d 4 dependence, a genuine manifestation of a dipole interacting with a 2D material. With DBT molecules, we can estimate a potential uncertainty in position measurements as low as 5 nm in the range below 30 nm.