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Tongyao Zhang, Hanwen Wang, Xiuxin Xia, Ning Yan, Xuanzhe Sha, Jinqiang Huang, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Mengjian Zhu, Lei Wang, Jiantou Gao, Xilong Liang, Chengbing Qin, Liantuan Xiao, Dongming Sun, Jing Zhang, Zheng Han, Xiaoxi Li

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[A monolithically sculpted van der Waals nano-opto-electro-mechanical coupler](https://mdr.nims.go.jp/datasets/1a35d2a8-07df-4800-a16d-2682633ceeca)

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A monolithically sculpted van der Waals nano-opto-electro-mechanical couplerZhang et al. Light: Science & Applications           (2022) 11:48 Official journal of the CIOMP 2047-7538https://doi.org/10.1038/s41377-022-00734-7 www.nature.com/lsaART ICLE Open Ac ce s sA monolithically sculpted van der Waalsnano-opto-electro-mechanical couplerTongyao Zhang1,2, Hanwen Wang3,4, Xiuxin Xia3,4, Ning Yan1,2, Xuanzhe Sha1,2, Jinqiang Huang3,4, Kenji Watanabe 5,Takashi Taniguchi 6, Mengjian Zhu7, Lei Wang8, Jiantou Gao8,9✉, Xilong Liang2,10, Chengbing Qin 2,10✉,Liantuan Xiao2,10, Dongming Sun 3,4, Jing Zhang1,2, Zheng Han1,2✉ and Xiaoxi Li1,2✉AbstractThe nano-opto-electro-mechanical systems (NOEMS) are a class of hybrid solid devices that hold promises in bothclassical and quantum manipulations of the interplay between one or more degrees of freedom in optical, electricaland mechanical modes. To date, studies of NOEMS using van der Waals (vdW) heterostructures are very limited,although vdW materials are known for emerging phenomena such as spin, valley, and topological physics. Here, wedevise a universal method to easily and robustly fabricate vdW heterostructures into an architecture that hosts opto-electro-mechanical couplings in one single device. We demonstrated several functionalities, including nano-mechanical resonator, vacuum channel diodes, and ultrafast thermo-radiator, using monolithically sculpted grapheneNOEMS as a platform. Optical readout of electric and magnetic field tuning of mechanical resonance in a CrOCl/graphene vdW NOEMS is further demonstrated. Our results suggest that the introduction of the vdW heterostructureinto the NOEMS family will be of particular potential for the development of novel lab-on-a-chip systems.IntroductionModern sensors are often designed to couple optical,electrical, and mechanical degrees of freedom in nano-scales in a single device; it thus helps in exploring manyemerging properties in both classical and quantumregimes1–5. Systems constructed for the above purposesare defined as nano-opto-electro-mechanical system(NOEMS), which offers tremendous opportunities tocontrol the photonic, acoustic, and electric behaviors innanodevices, sometimes operating at very low powerconsumption2, and may be expanded in quantum systemssuch as superconducting circuits1. Recently, other thanthe usually adopted bulk materials, van der Waals (vdW)materials have been increasingly attractive for investiga-tions in NOEMS. For example, a valley-mechanical cou-pling in a suspended monolayer MoS2 resonator wasprobed with circularly polarized lights6.Indeed, two-dimensional (2D) vdW materials are ofparticular interest for future nano-electronic applications,owing to their peculiar mechanical and electro-magneticperformances7–10. More importantly, vdW layers can bevertically interfaced into arbitrary heterostructures thatincorporate inter-layer coupling in themselves, giving riseto the reconstruction of band structures that are enrichedof quantum and topological physics both optically andelectrically11–17. In addition, in many circumstances, vdWfunctional monolayers require packaging with protecting/supporting layers such as hexagonal boron nitride (h-BN),in order to preserve their intrinsic optical properties fromenvironmental inhomogeneities. It is thus expected thatvdW heterostructures are inherently an ideal platform toserve as NOEMS. However, due to a lack of a reliablefabrication method, the NOEMS studies involving vdW© The Author(s) 2022OpenAccessThis article is licensedunder aCreativeCommonsAttribution 4.0 International License,whichpermits use, sharing, adaptation, distribution and reproductionin any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate ifchangesweremade. The images or other third partymaterial in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to thematerial. Ifmaterial is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtainpermission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Correspondence: Jiantou Gao (gaojiantou@ime.ac.cn) orChengbing Qin (chbqin@sxu.edu.cn) or Zheng Han (vitto.han@gmail.com) orXiaoxi Li (xiaoxili1987@gmail.com)1State Key Laboratory of Quantum Optics and Quantum Optics Devices,Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China2Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan030006, ChinaFull list of author information is available at the end of the articleThese authors contributed equally: Tongyao Zhang, Hanwen Wang, Xiuxin Xia,Ning Yan1234567890():,;1234567890():,;1234567890():,;1234567890():,;www.nature.com/lsahttp://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-6822-5113http://orcid.org/0000-0002-6822-5113http://orcid.org/0000-0002-6822-5113http://orcid.org/0000-0002-6822-5113http://orcid.org/0000-0002-6822-5113http://orcid.org/0000-0003-1552-7940http://orcid.org/0000-0003-1552-7940http://orcid.org/0000-0003-1552-7940http://orcid.org/0000-0003-1552-7940http://orcid.org/0000-0003-1552-7940http://creativecommons.org/licenses/by/4.0/mailto:gaojiantou@ime.ac.cnmailto:chbqin@sxu.edu.cnmailto:vitto.han@gmail.commailto:xiaoxili1987@gmail.comheterostructures are so far very limited. Recently, a cavity-modulated photon luminescence emission behavior wasreported in suspended h-BN/MoSe2/h-BN hetero-structures18.In this work, we utilize the vdW vertical assembly as aplatform to devise a monolithically sculpted nano-opto-electro-mechanical coupler. By adopting the dry-transfermethod19, we present a new fabrication process for sus-pending arrays of two-terminal or multi-terminal vdWheterostructures, which does not require such as criticalpoint drier or hot acetone method to obtain suspended2D material in conventional methods. Instead, with a one-step etching process, one can define a suspended vdWheterolayer with multifunctional potentials, which has notbeen achieved before. Hence, complicated vdW hetero-structures with multifunctional applications could befabricated using our new method with high sample yields.Taking the h-BN/graphene heterostructure, for example,several functionalities, including nano-mechanical reso-nator, vacuum channel diodes, and ultrafast thermo-radiator are realized in one single NOEMS device. Qualityfactors of mechanical resonances in them are found toexceed 103 at room temperature. Nanovacuum channelthermionic emission diodes with on-off ratios of 105 wereachieved in the same nanostructure. In the meantime, theh-BN/graphene NOEMS can serve as an ultrafastthermal-radiator modulated via electrical Joule heating.The principle-of-work of the proposed monolithicallysculpted nano-opto-electro-mechanical coupler can beexpanded to a wide variety of 2D materials and theirheterostructures, which sheds light on future lab-on-a-chip electronic systems based on vdW NOEMS.ResultsMonolithically sculpted vdW heterostructure mechanicalresonatorThe advantages of the NOEMS made of suspended vdWheterostructures in this work are that vdW materialsexhibit enriched spin, valley, and topological properties,with usually ~102MHz resonance frequency that can befurther coupled to an energy scale of such as Landaulevels20. Furthermore, the conduction channel of gra-phene allows us to utilize the suspended nanostructure asa filament to demonstrate ultrafast electron emitter,which is of stronger mechanical strength and can bepatterned into multi-terminal configuration, which wasnot achievable in those devices constructed out of a singleatomic layer studied before21–23. Moreover, vdW baseddevices are believed to be resistant under radiationenvironment, as will be discussed in the next sections.Now we introduce the example of application ofmechanical resonator realized using the method in thiswork. Holey h-BN with thicknesses of about 100–300 nmwere first prepared with plasma etching, as shown inFig. 1a. Multi-layered vdW heterostructures are thendeposited onto the holey h-BN (Fig. 1b), forming vdWfilms sealed cavities shown in Fig. 1c. Micrometer-sizedsuspended vdW multi-layered beams can thus be fab-ricated by a sole final step of dry etching. As shown inFig. 1d, the heterostructure suspended beams on pre-patterned cavities can then serve as nano-mechanicalresonators with 2D materials functional layers ready tobe coupled for optical and electrical measurements. It isfound that with a cavity depth of about 200 nm, thesuccess rate of suspension is 100% when the lateral sizesare less than 3 μm (Fig. 1e, f), which is quite robust andfacile as compared to the conventional monolayeredsuspension of 2D materials, while the latter usuallyadopts dedicated process using critical point drier or ahot acetone technique24. More details of the workflow ofthe fabrication process can be found in SupplementaryFig. S1.Figure 2a illustrates typical devices of two-terminal vdWheterostructure (h-BN/graphene as an example wasdemonstrated here) resonators fabricated using themethod in Fig. 1. To determine the mechanical resonanceof the vdW NOEMS, the suspended h-BN/graphenebeams were modulated by an AC voltage capacitivelycoupled with the out-of-plane motion. As shown inFig. 2b, an optical interferometry setup was established tosensitively monitor the displacement of the emitters and afast photodiode was used to detect the interferometricstrength of the reflected laser. A vector network analyzer(VNA) was applied as an AC excitation to actuate theresonators and to read the mechanical resonance. DCback gate voltage was provided by a separate voltagesource. By testing the h-BN/graphene suspended hetero-structure, we obtained typical gate-tunable resonanceamplitude versus AC-driven frequency and DC gate vol-tage at room temperature, with resonance frequency f0 of115–116MHz, as shown in Fig. 2c. A line cut at Vg=−30 V is illustrated in Fig. 2d, in which the resonancepeak is fitted using a single Lorentzian, yielding a qualityfactor Q of 697.3. Figure 2e shows the extracted Q factorsas a function of gate voltage in the same device. Mea-surements of resonance at lower temperature and controlsamples are shown in Supplementary Fig. S2.vdW vertical vacuum channel thermionic emission diodesIn the following, we demonstrate that the fabricatedvdW NOEMS can be functioning as vertical vacuumchannel thermionic emission diodes. Optical image ofsuch solid device of vacuum channeled diodes and an artview of the finish of the device architecture are shown inFig. 3a, b, respectively. In this configuration, the holeyh-BN is used as a supporting dielectric with the deepholes serving as vacuum channels. In consequence, whenexerted with a large enough current in the emitterZhang et al. Light: Science & Applications           (2022) 11:48 Page 2 of 10(suspended graphene channel that is supported by a toph-BN beam), graphene will become a filament that shinesa bright light. And thermionic electron emission can takeplace when a certain positive collector (both Au andgraphite can be used as the collector, as shown inSupplementary Fig. S3) voltage is applied.For monolayer graphene vdW vertical thermionicemission diode, it is rather vulnerable to the thermionicelectron emission tests. Many of them cannot survivemore than two cycles of emission, with the emitterchannels collapsing easily, as shown in SupplementaryFigs. S4 and S5. In the following, we will mainly focus onfew-layered graphene emitters. Typical rectifying curvescan be seen in the vertical configuration with few-layeredgraphene emitters, shown in the linear and log scale inFig. 3c and its inset, respectively. And the thermionicemission onset voltage is about 3–4 V, with the maximumemission current (before the emitter channel is burntdown) at the order of 10 nA. Subthreshold swing (SS) isextracted to be at the order of 200 mV/decade, compar-able with the values obtained in previously reportednanosized vacuum tubes25,26. For thermionic emissiondiodes, we define the ratio of maximum emission currentto minimum emission current versus collector voltage at acertain Vds as an on-off ratio. According to the insetshown in Fig. 3c, the on-off ratios can reach a level up to105, in the condition of Vds= 4.4 V.A simplified Richardson–Dushman model depicts thatthe electrons emitted during the process of thermionicemission depend upon the surface area of the metalsurface and the temperature of the surface, written asIEmission ¼ AT2expð�WK�1T�1Þ27. Here, A is a constantSourceDraina b cdMonolithic patterningof vdW NOEMsPlasma etch1Top-BN2D functional materialsHoley–BN microcavitiesAu electrodeDry transfer2Etching+Metallization34e10080604020)%(tearSuscess300200120100h-BN cavity depth (nm)fgΦ2 μm1×2 μmSuspendedCollapsedVgCavity2×2 μm Φ3 μm1×2 μm2×2 μmΦ3 μ m1×3 μm1×3 μ m1×3 μ m2×2 μ m1×4 μm2×4 μmFig. 1 Monolithically sculpted vdW heterostructure NOEMS. a–d Art view of the workflow for patterning suspended vdW heterostructure beamson h-BN cavities, with 2D functional materials involved, thus forming a NOEMS structure. e–f A typical test on the suspension of vdW heterostructureon pre-patterned h-BN holes, with a global top vdW layer (f) deposited onto (e). g A statistic on the success rate of suspension (at step 3 in Fig. 1) ofh-BN/graphene heterostructure on h-BN cavities with different h-BN cavity depths. The different colors denote lateral sizes of the suspended areas.Ten samples were fabricated for each size for the statistic in (g)Zhang et al. Light: Science & Applications           (2022) 11:48 Page 3 of 10that is proportional to the emitter surface and beingmaterials-dependent, while W and T are work functionand temperature of the emitter material, respectively. Byassuming that the thermionic emission follows the law ofthe blackbody radiation, we measured the spectra at roomtemperature in a homemade vacuum chamber with thesetup illustrated in Supplementary Figs. S6 and S7. Thecorresponding temperature can be determined by thePlanck formula (Supplementary Figs. S8–S12). By plottingthe value of IEmission as a function of T2exp(−WK−1T−1)with the work function of 4.5 eV, we yield an A~14.8 Acm−2K−2, qualitative agreement with the experi-mental observations in other metallic materials28. How-ever, more dedicated modeling may be needed toquantitatively understand the exact behaviors in the stu-died devices, as the Richardson model may not be suffi-cient when it comes to low dimensional systems29.We also performed the total ionizing dose (TID) effectexperiment in the vdW NOEMS, which is important forour device to be used in radiation environments. InLaser source a  (a.u.) Amplitude118116114 Frequency (MHz)T = 294 K V  = – 30 VQ = 697.312001000800600400factor Q–40 0 40d eDataFitV   (V)g–40 –20Frequency (MHz)11311411511611711820 400T = 294 K0 1 Ampl. (a. u.)V   (V)gbBN/Gr cCryostat DCGate Bias tee  VNAOut In Fast photodiode BS Lens S DSubstrate 2-TerminalgFig. 2 Nano-mechanical resonances in vdW heterostructure NOEMS. a False colored SEM image of a typical resonator using vdW bilayer h-BN/graphene as the suspension channel. b Schematic of the setup for optical probe of the mechanical resonance. c Color map of the resonancefrequency as a function of gate voltage measured in a typical vdW NOEMS. The amplitude data with positive and negative values are mappedto a renormalized range of [0,1]. d Line profile of the resonance peak at Vg= –30 V, with a Lorentzian fit in the red solid curve. e Q factors obtainedfrom (c)Zhang et al. Light: Science & Applications           (2022) 11:48 Page 4 of 10general, TID effect is treated as a long-term cumulativeradiation effect. The ionized charges induced by high-energy rays and particles are trapped at either the insu-lators interfaces or in the bulk region that can cause turn-on voltage shift and leakage current increase. The TIDirradiation experiments were performed in a 60Co gammarays source with a dose rate of 50 rad(Si)s–1. During theirradiation, the vdW vertical thermionic emission diodeswere established in a float state. As shown in Fig. 3d, thethermionic electron emission behaviors before and aftera bBottom collectorcJn oissimE)m/A01×(V    (V)dsCollector voltage (V) 4.40 4.35 4.30 4.20 4.10 4.00 3.50 3.00 2.00 0.0114121086420–40 –20 0 20 401.51.00.50.0–40 –20 0 20 40Collector voltage (V)3 Mrad(Si) TID radiation After Before–10410210–2100Jnoiss imE)m/A (2Collector voltage (V)40 –20 0 20 40deeeeTop BNBottom BNVcCollectorGraphene emitterSource DrainI ds32Jno iss imE)A/m×10(32Fig. 3 Thermionic emission diode behavior in h-BN/graphene NOEMS. a Optical micrograph image of the arrays of nanosized vdW NOEMS.Scale bar= 5 μm. b Art view of the architecture of the “vintage” vacuum diode made of vdW heterostructure. c Thermionic emission current densityJEmission–VCollector curves in a VCollector range of ±40 V recorded in a typical device. The same data are plotted in a log scale in the inset. Traces andretraces are recorded. Data were obtained at 300 K in a vacuum chamber of about 10−2 mbar. d TID radiation effects characterization of the emissioncurrent in a typical vdW thermionic emission diode device shown in (a)Zhang et al. Light: Science & Applications           (2022) 11:48 Page 5 of 10the radiation with a TID dose of 3Mrad(Si) are almost thesame, exhibiting great stabilities in terms of TID effectsimilar to other nanosized vacuum channel transistors30.We also compare the characteristics of our vdW ther-mionic emission diodes with other nanosized thermionicemission devices. As shown in Supplementary Table S1,characteristic parameters such as On/Off emission ratio,collector voltage, and SS are summarized. It is seen thatthe vdW thermionic emission diodes investigated in thiswork show maximum On/Off emission ratio of about 105,and a SS reaching 200mV/decade. Furthermore, thedevices reported in our work are integratable using thevdW stacking technique, which is fully compatible withthe solid-state device fabrication process.Ultrafast thermal-radiator realized in vdW NOEMSWe now take the h-BN/graphene NOEMS as anexample to illustrate the functionality as an ultrafastthermal-radiator. A rectangular waveform of AC currentwas exerted into the suspended h-BN/graphene channel,with a width of the peak of about 10 ns and a DC biased totune periodically the Joule heating. Hence pulses ofblackbody radiation can be detected via a time-resolvedsingle-photon detector.Figure 4a shows typical ultrafast blackbody radiationexcited by square electrical pulse sequences with a fixedrepetition rate of 100 kHz (T= 10 μs) but various elec-trical pulse duration ΔTE= 10, 15, 30, 40, 50, and 60 ns,respectively. The input voltage signals (electrical voltagepulses of the excitation trace in ns time scale recorded byan oscilloscope) on the tested devices are presented in theinset in Fig. 4a. And ultrafast blackbody radiation inresponse to AC electrical current injection at differentrepetition frequencies is shown in Supplementary Fig.S13. It is noticed that, during the test, a bias voltage ofVdc= 0.8 V plus an AC voltage of around 2.1 V is applied.Electrical pulse width ΔTE versus the corresponding fullwidth at half maximum ΔTPhoton of the light-emissionpulse were extracted from Fig. 4a. As shown in Fig. 4b, aquasi-linear relationship with a slope of the unity betweenΔTPhoton and ΔTE is found for ΔTE > 30 ns. An interceptof ~14 ns on the ΔTE axis can be seen, which is attributedto a sum of the rise time Trise plus the fall time Tfall.Moreover, in the range of ΔTE < 20 ns, ΔTPhoton levels offat ~13 ns (black dashed line). This value is in agreementwith that of Trise+ Tfall. Assuming the Trise and Tfall arethe same; therefore, a cooling time of ~7 ns of thenanovacuum channel thermionic emission diode can beestimated in the condition of a sufficient long repetitionperiod (~10 μs). The above dynamic analysis thus pro-vides insights into such nanosized suspended thermionicemission systems.Figure 4c, d show the static Joule heating regime ofthe h-BN/graphene NOEMS. Static thermionicemission current IEmission as well as emitter channelcurrent Ids are recorded, in Fig. 4d. It is seen that the I–V curve of the emitter channel (green circles in Fig. 4d)exhibits a saturation behavior in Ids above Vds ~3.5 V. Itis noteworthy that, after the saturation regime of Ids(3 V < Vds < 3.7 V), a clear drop of Ids is seen when theVds is further increased. We define this point as theonset of detectable thermionic emission current, asindicated by the black arrow in Fig. 4d. At Vds= 4.0 V,emission current (red squared in Fig. 4d) can be cap-tured from the collector electrode, which rockets into10 nA at Vds = 4.2 V, and breaks down at 4.3 V. Similarbehavior is seen in multiple samples. In this setup, aKeithley 2400 multi-meter was used to detect emissioncurrent, and the sub-1 nA emission may be overlooked.Corresponding visible light emissions are also given inFig. 4c for each stage of Vds.DiscussionTo this stage, we have demonstrated a multifunctionalNOEMS fabricated by monolithically sculpting a vdWheterostructure. Taking h-BN/graphene bilayer systemas an example, optically, it can serve as an ultrafastthermal-radiator with cavity resonant peak tunable bythe depth of the cavity (Supplementary Fig. S9). Elec-trically, the system can be regarded as a nano-version ofthe “vintage” thermionic emission diode with a verticalvacuum channel and solid-state device structure. Inaddition, mechanically the fabricated system can wellplay the role of a mechanical resonator with Q factorsreaching 103 at room temperature. The observed multi-functionalities in a single solid device well define aprototype of NOEMS using vdW heterostructure as aplatform.Despite the demonstrated versatility of the vdWNOEMS in this work, there are yet rooms in them toimprove the performances such as thermionic emissionefficiency (i.e., to decrease the total power consumption)and the emission currents, as compared to those Si-basednanosized vacuum channel vacuum electron cold emit-ters21,22,30–37. For example, to enhance the thermionicelectron emission current, surface coating of oxides onthe graphene emitter to further lower its work functionmay be our future studies38.As shown in Supplementary Fig. S14a, thanks to theenriched library of 2D materials, the current studiedsystem can thus be expanded into those of electronic andoptical properties that involve such as spin and valleydegrees of freedom (Supplementary Fig. S14b, c). More-over, it is noticed that the unique fabrication process ofthe vdW NOEMS also allows the realizations of such asmultiple-terminal suspended vdW conduction channels,shown in Supplementary Fig. S14d, which is of potentialfor opto-electro-mechanical studies especially in theZhang et al. Light: Science & Applications           (2022) 11:48 Page 6 of 10quantum Hall regime, which was considered technicallyextremely difficult before20,39.To further demonstrate the interplay of optical, elec-trical, and mechanical degrees of freedom in one singleNOEMS using our technique, we now discuss a platformfor optical readout of electric and magnetic field tuningof mechanical resonance in a CrOCl/graphene vdWNOEMS. Recently, the temperature dependence ofcd4.54.03.53.02.52.01.51.0)Am(  1614121086Detectableelectron emissionBurnt down10density current EmissionI dsV   (V)ds= 4.2 VV   ds= 3.8 VV   ds= 3.4 VV   ds= 3.3 VV   ds= 3.0 VV   dsa(a.u.) counts dector photon Single 806040200–20 Time (ns) 10 ns 15 ns 30 ns 40 ns 50 ns 60 nsΔTEΔTE (ns)4030201006050403020100ΔTPhoton(ns)b~14 ns ~13 nsΔTPhoton ΔTE=        – 14 ns  Data)  m/A(24103 Voltage (a.u.) 80400 Time (ns)Fig. 4 Dynamics of the vdW NOEMS functioning as ultrafast thermo-radiators. a Typical ultrafast blackbody radiation excited by squareelectrical pulse sequences with a fixed repetition rate of 100 kHz (T= 10 μs) but various electrical pulse duration ΔTE= 10, 15, 30, 40, 50, and 60 ns,respectively. Inset presents the input voltage signals (electrical voltage pulses of the excitation trace in ns time scale recorded by an oscilloscope) onthe tested devices. b Electrical pulse width ΔTE versus the corresponding light-emission pulse width ΔTPhoton extracted from (a). Dashed lines arelinear fits. c Optical image captured in the CCD camera at fixed Vds, showing the status of light emission of the vertical vdW thermionic emissiondiode. White dashed lines illustrate the top view profile of the emitter. Scale bar= 5 μm. Data were obtained at 300 K and under a vacuum conditionof about 10−2 mbar. A collector voltage of +40 V was maintained throughout the measurements. d Profiles of thermionic electron emission IEmission(red squares) and Ids (green circles) as a function of Vds. Error bars represent the fluctuation of currents recorded during measurementsZhang et al. Light: Science & Applications           (2022) 11:48 Page 7 of 10mechanical resonance in magnetic semiconductors,such as XPS3 (X= Fe, Mn, Ni)40 and Cr2Ge2Te641, areinvestigated. Meanwhile, magnetic field-driven redshift ofmechanical resonance in the anti-ferromagnetic (AF)vdW insulators from AF to ferromagnetic transitionin CrI342. Here, we adopt an AF insulator CrOCl,which is known to exhibit enriched magnetic phasetransitions43,44.As shown in the SEM and AFM images in Fig. 5a, usingthe fabrication technique described in Fig. 1, the CrOCl/graphene heterostructure are fabricated into arrays ofdrum-like resonators, with the monolayer graphene actingas the capacitive coupling layer to the AC and DC gatevoltages, and the 10 nm CrOCl layer is the AF layer in thisNOEMS. A schematic picture of the coupling betweenoptical probe, mechanical resonance, and electrical tuningis given in Fig. 5b. At the base temperature of 5 K in oursetup, the resonant frequency f0 at the ground state ismeasured by the optical interferometer to be ~55MHz,and at about 4 T, a shift of ~0.8MHz is observed, an orderof magnitude higher than those reported in other AF vdWresonators42. Gate tuning of f0, and more details of thetemperature dependences can be found in SupplementaryFigs. S15–S18. Notice that the blueshift of f0 correspondsto an increase of strain in the membrane, which is causedby the magnetostriction effect in the few-layered CrOCl.adbμ  H (T)–5f (MHz)5454.55555.55656.5c50HHResonanceOptical probeVg Electrical tuningCrOClGraphene012345Amplitude (a. u.)400–500z (nm)h-BNAu/Ti56.055.855.655.455.255.054.8)zHM( f86420Hμ  H (T)00123Sweeping HT = 5 KFig. 5 Demonstration of a CrOCl/graphene vdW NOEMS using our technique. a Bird view of SEM image of the CrOCl/graphene NOEMS arrayusing the method described in Fig. 1, with the boxed region scanned by AFM. It is seen that the drum-like cavities (dashed circles in the AFM image)are invisible under AFM. Scale bar= 5 μm. b A cartoon illustration of the as-prepared of CrOCl/graphene NOEMS. c Color map showing theresonance frequency of the CrOCl/graphene NOEMS in the parameter space of frequency and magnetic fields at a temperature of 5 K. d Line profileof the resonance frequency f0 extracted from (c), as a function of magnetic field. Data were obtained in trace and retrace, with a magnetic phasetransition from H1 to H3, with f0 blueshifts of about 0.8 MHzZhang et al. Light: Science & Applications           (2022) 11:48 Page 8 of 10By examining the trace and retrace of f0-μ0H curve in Fig.5d, one can see that the system undergoes three magneticphase transitions (at H1, H2, and H3, respectively), whichis in agreement with the report elsewhere43,44. The CrOClcrystal has a monoclinic phase below the Néel tempera-ture, and exhibits a so-called stripy AF-↑↑↓↓ magneticground state due to magnetoelastic coupling44. It thenreaches a ferrimagnetic phase ↑↑↑↓↓ above H3. It is thusinferred that the few-layered CrOCl may have a structuralphase transition above H3, with the lattice constantshrunk and hence a stiffness enhancement in the mem-brane. Our technique thus provides a NOEMS platformfor opto-mechanical detection of complex electro-magneto responses in vdW heterostructures.To conclude, we devised a monolithically sculptednano-opto-electro-mechanical coupler with high sampleyields. Multi-functionalities, including mechanical, opti-cal, and electrical operations, are integrated into onesingle vdW NOEMS device made of h-BN/graphene. Forexample, it can serve as an ultrafast thermal-radiator, anano-version of the “vintage” thermionic emission diode,and a mechanical resonator. In principle, the proposedmonolithically sculpted nano-opto-electro-mechanicalvdW heterostructure system can be expanded to a widevariety of 2D materials, and can also be shaped into multi-terminal NOEMS. Optical readout of electric and mag-netic field tuning of mechanical resonance in a CrOCl/graphene vdW NOEMS is further demonstrated. Ourfindings suggest that, as shown in Supplementary Fig. S14,the monolithically sculpted suspended vdW assembliesproposed here opens up opportunities for future NOEMSstudies with both classical and quantum degrees of free-dom, including spin- and valley-tronics, as well asmechanical coupling to possible quantum opto-electronicstates.Materials and methodsThe BN-encapsulated graphene was fabricated in anambient condition, using the dry-transfer method. ABruker Dimension Icon AFM was used for thicknessesand morphology tests. Electron beam lithography wasdone using a Zeiss Sigma 300 SEM with an Raith ElphyQuantum graphic writer. The high precision of currentmeasurements of the devices was measured using aLakeShore vacuum probe station at room temperature,with an Agilent B1500A Semiconductor Device ParameterAnalyzer.A homemade vacuum chamber (4 cm × 5 cm × 2 cm insize) is used for monitoring the electrical and opticalperformances of the vdW heterostructure NOEMSsimultaneously under a vacuum of about 10−2 mbar(Supplementary Figs. S6 and S7). The vacuum testchamber was inversely mounted on an X–Y scanningstage on top of a microscope for optical measurements,while the electrical wiring is connected from a standardchip carrier via a vacuum feed-through. To locate thegraphene emitter, we first find the sample by opticalmicroscope. Then a mild voltage of Vds ~3 V (correspondsto an Ids of ~10mA) is applied onto the emitter channel,in which condition no observable light emission can beseen by the CCD camera. However, at such currentdensity, a very faint blackbody radiation starts to occur,which can be captured by the single-photon detector. Onecan thus carry out spatial mapping and precisely locatethe center position of the emitter (Supplementary Fig. S8).For optical interferometric detection, the beam of atemperature-controlled semiconductor laser (λ= 780 nm)was focused on vdW NOEMS samples with a spot radiusof ~2 μm and its power density was kept in a range from 4to 8 μWμm−2. The samples were mounted in a helium-free cryostat under a vacuum below 10−2 mbar. Thereflected laser was detected by a fast photoreceiver with a–3 dB bandwidth at 650MHz. The actuation AC voltage(lower than ~4mV) between the graphene emitter and theback gate was supplied by a VNA to modulate thereflection of the optical cavity formed by the grapheneemitter and the collector. The out-of-plane displacementwas monitored by such optical interferometry and mea-sured as a function of driven frequency by the same VNA.Mechanical resonance data of different h-BN/graphenesamples at low temperatures are shown in SupplementaryFig. S2.AcknowledgementsThis work is supported by the National Key R&D Program of China(2019YFA0307800, 2017YFA0304203, and 2018YFA0306900) and the NationalNatural Science Foundation of China (NSFC) (Grants 12004389, 11974357,U1932151, and 12174444). L.W. acknowledges support from the Key ResearchProgram of Frontier Sciences, CAS (Grant ZDBS-LY-JSC015). X. Li acknowledgessupport from the Joint Research Fund of Liaoning-Shenyang NationalLaboratory for Materials Science with Grant No. 2019JH3/30100031. D.S.acknowledges the Strategic Priority Research Program of Chinese Academy ofSciences (XDB30000000), the Key Research Program of Frontier Sciences of theChinese Academy of Sciences (ZDBS-LY-JSC027, QYZDB-SSW-SLH031), andLiaoning Revitalization Talents Program (XLYC1807109).Author details1State Key Laboratory of Quantum Optics and Quantum Optics Devices,Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China.2Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan030006, China. 3Shenyang National Laboratory for Materials Science, Instituteof Metal Research, Chinese Academy of Sciences, Shenyang 110016, China.4School of Material Science and Engineering, University of Science andTechnology of China, Anhui 230026, China. 5Research Center for FunctionalMaterials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan. 6International Center for Materials Nanoarchitectonics, NationalInstitute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan. 7College ofAdvanced Interdisciplinary Studies, National University of Defense Technology,Changsha 410073, China. 8The Key Laboratory of Science and Technology onSilicon Devices, Institute of Microelectronics, Chinese Academy of Sciences,Beijing 100029, China. 9The University of Chinese Academy of Sciences, Beijing100029, China. 10State Key Laboratory of Quantum Optics and Quantum OpticsDevices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006,ChinaZhang et al. Light: Science & Applications           (2022) 11:48 Page 9 of 10Author contributionsZ.H. and X. Li conceived the experiment and supervised the overall project.X. Li, H.W., T.Z., N.Y., X.X. and J.H. fabricated the devices and carried outelectrical transport measurements; K.W. and T.T. provided high-quality h-BNbulk crystals. C.Q., Z.H., L.X., T.Z., X. Liang, and M.Z. carried out opticalmeasurement of the graphene vacuum emitter. T.Z., X. Li, and X. S. performedthe mechanical resonator-related experiments. T.Z., X. Li, and Z.H. analyzed thedata, with J.Z., D.S., and C.Q. participated in the data analysis. J.G. and L.W.performed TID radiation experiment. The manuscript was written by Z.H. andC.Q. with discussion and inputs from all authors.Data availabilityThe data that support the findings of this study are available at Zenodo,https://doi.org/10.5281/zenodo.4725515.Code availabilityThe computational codes that support the findings of this study are availablefrom the corresponding authors upon reasonable request.Conflict of interestThe authors declare no competing interests.Supplementary information The online version contains supplementarymaterial available at https://doi.org/10.1038/s41377-022-00734-7.Received: 7 October 2021 Revised: 25 January 2022 Accepted: 8 February2022References1. Singh, V. et al. Optomechanical coupling between a multilayer graphenemechanical resonator and a superconducting microwave cavity. Nat. Nano-technol. 9, 820–824 (2014).2. Qian, Z. Y. et al. Zero-power infrared digitizers based on plasmonicallyenhanced micromechanical photoswitches. Nat. Nanotechnol. 12, 969–973(2017).3. 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Light: Science & Applications           (2022) 11:48 Page 10 of 10https://doi.org/10.5281/zenodo.4725515https://doi.org/10.1038/s41377-022-00734-7https://doi.org/10.1021/acs.nanolett.1c04373https://doi.org/10.1021/acs.nanolett.1c04373 A monolithically sculpted van der Waals nano-�opto-electro-mechanical coupler Introduction Results Monolithically sculpted vdW heterostructure mechanical resonator vdW vertical vacuum channel thermionic emission diodes Ultrafast thermal-radiator realized in vdW NOEMS Discussion Materials and methods Acknowledgements Acknowledgements