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Chia‐Hung Wu, Chih‐Jen Ku, Min‐Wen Yu, Jhen‐Hong Yang, Pei‐Yuan Wu, Chen‐Bin Huang, Tien‐Chang Lu, Jer‐Shing Huang, [Satoshi Ishii](https://orcid.org/0000-0003-0731-8428), Kuo‐Ping Chen

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[Near‐Field Photodetection in Direction Tunable Surface Plasmon Polaritons Waveguides Embedded with Graphene](https://mdr.nims.go.jp/datasets/39452097-6bef-47f6-abaf-c1f781ce2816)

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Near‐Field Photodetection in Direction Tunable Surface Plasmon Polaritons Waveguides Embedded with GrapheneRESEARCH ARTICLEwww.advancedscience.comNear-Field Photodetection in Direction Tunable SurfacePlasmon Polaritons Waveguides Embedded with GrapheneChia-Hung Wu, Chih-Jen Ku, Min-Wen Yu, Jhen-Hong Yang, Pei-Yuan Wu,Chen-Bin Huang, Tien-Chang Lu, Jer-Shing Huang, Satoshi Ishii, and Kuo-Ping Chen*2D materials have manifested themselves as key components towardcompact integrated circuits. Because of their capability to circumvent thediffraction limit, light manipulation using surface plasmon polaritons (SPPs)is highly-valued. In this study, plasmonic photodetection using graphene as a2D material is investigated. Non-scattering near-field detection of SPPs isimplemented via monolayer graphene stacked under an SPP waveguide with asymmetric antenna. Energy conversion between radiation power and electricalsignals is utilized for the photovoltaic and photoconductive processes of thegold-graphene interface and biased electrodes, measuring a maximumphotoresponsivity of 29.2 mA W−1. The generated photocurrent is alteredunder the polarization state of the input light, producing a 400% contrastbetween the maximum and minimum signals. This result is universallyapplicable to all on-chip optoelectronic circuits.1. IntroductionThe unique properties of light, along with rapid advancementsin quantum technology and next-generation semiconductors, hasdriven researchers to explore innovative approaches for light ma-nipulation and signal modulation. Specified by the photon en-ergy, light has properties such as the primitive and orbital formsC.-H. Wu, M.-W. Yu, J.-H. YangCollege of PhotonicsNational Yang Ming Chiao Tung University301 Gaofa 3rd Road, Tainan 71150, TaiwanC.-J. Ku, K.-P. ChenInstitute of Imaging and Biomedical PhotonicsCollege of PhotonicsNational Yang Ming Chiao Tung University301 Gaofa 3rd Road, Tainan 71150, TaiwanE-mail: kpchen@ee.nthu.edu.twP.-Y. Wu, C.-B. Huang, K.-P. ChenInstitute of Photonics TechnologiesNational Tsing Hua UniversityHsinchu 300, TaiwanThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/advs.202302707© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.This is an open access article under the terms of the Creative CommonsAttribution License, which permits use, distribution and reproduction inany medium, provided the original work is properly cited.DOI: 10.1002/advs.202302707of angular momentum.[1] Due to theirintriguing interactions with matter atnanoscale, the spins and orbitals of pho-tons have gained considerable attention.[1,2]Optical communication technologies havebeen developed for global data traffic,cloud and data-center optical intercon-nects, high-performance computing, 5Gand B6G, military applications, astronomysystems, and chip-scale integrated circuits.Researchers have actively studied siliconphotonics to comply with Moore’s law. Asystem with optical interconnections be-tween or within devices actualizes a broaderbandwidth and faster data transfer.[3]However, on-chip silicon waveguidesscale up to tens of micrometers, which isnot sufficiently small compared to elec-tronic components. Plasmonics uses thecapability of metals to trap electromagnetic fields at deep-subwavelength scale, allowing considerable scaling down of de-vices. This reduction in size aids in welding optical and elec-tronic elements of the same size, introducing optoelectronic in-tegrated circuits. SPP is the delocalized oscillation of electrons atthe metal–dielectric interface when light couples with plasmonT.-C. LuDepartment of PhotonicsCollege of Electrical and Computer EngineeringNational Yang Ming Chiao Tung UniversityHsinchu 30010, TaiwanJ.-S. HuangLeibniz Institute of Photonic TechnologyAlbert-Einstein Straße 9, 07745 Jena, GermanyJ.-S. HuangInstitute of Physical Chemistry and Abbe Center of PhotonicsFriedrich-Schiller-Universität JenaHelmholtzweg 4, D-07743 Jena, GermanyJ.-S. HuangResearch Center for Applied SciencesAcademia Sinica128 Academia Road, Sec. 2, Nankang District, Taipei 11529, TaiwanJ.-S. HuangDepartment of ElectrophysicsNational Yang Ming Chiao Tung UniversityNo. 1001 Daxue Rd, East District, Hsinchu 30010, TaiwanS. IshiiResearch Center for Materials Nanoarchitectonics (MANA)National Institute for Materials Science (NIMS)1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanAdv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (1 of 7)http://crossmark.crossref.org/dialog/?doi=10.1002%2Fadvs.202302707&domain=pdf&date_stamp=2023-09-03www.advancedsciencenews.com www.advancedscience.comfrequency under required conditions.[4] Light propagating in thisform has significant field confinement. Owing to their abilityto circumvent the diffraction limit, plasmonic nanostructureshave attracted much interest, and a wide variety of designshave been reported in recent years. Plasmonic devices such asnanowaveguides,[5–7] plasmonic nanolasers,[6,8,9] circulators,[10]and nanoantennas have been developed to advance further plas-monic circuitry technology.[11–14] The conventional approach todetect SPPs is to break the homogeneity of the propagation routesuch that the waves couple out of the surface and collect thescattered light in the far field.[15] Multiple optical elements andbulky systems are required to observe the SPPs radiation. There-fore, the compact and on-chip SPP detection system is highly de-manded.Semiconductor-based photodetectors, including silicon,[16,17]germanium,[2,16] perovskite,[18–20] and III-V materials have pro-gressed remarkably due to their capability to bridge the gap be-tween optical and electrical signals.[21] However, the conventionalsemiconductor photodetectors are with the thickness in μm scale.Furthermore, the band gaps of these semiconductors facilitate anarrow range of practical applications. Graphene is a one-atom-thick carbon sheet packed in a hexagonal lattice and is knownfor its excellent optical, mechanical and electrical properties.[22]Because of its transparency and flexibility, it has been applied inwearable sensors.[23] Graphene has a gapless band structure thatallows the absorption of light from 300 to 2500 nm and an acces-sible interband transition. The high carrier mobility in grapheneguarantees an ultrafast response of these photogenerated carri-ers, which is promising for photodetector applications and inte-grated photonics.[7,24–29]This study investigates a direction-tunable SPP graphene pho-todetector. Pioneering the use of graphene for detecting po-larization steered SPP propagation integrated with a subwave-length nanoantenna and plasmonic waveguide, creates a newparadigm in reconfigurable plasmonic photodetection systems.Previous studies have demonstrated that asymmetric nanostruc-tures can realize directional launching of SPPs.[15,30] However,this design has limitations in its application spectrum becausethe propagation direction is fixed upon fabrication. Alternatively,SPP steering can be realized using symmetric nanostructuresunder different excitation conditions.[1,2,10,14] This approach en-ables multiport signal transfer and is presumably applicable toall plasmonic-integrated circuits. The proposed SPP waveguidewas fabricated on a single-crystalline gold flake to minimize un-necessary propagation loss due to the inhomogeneous latticeorientation and surface roughness of the evaporated films. Agraphene sheet was placed under the waveguide to collect excitedSPPs and convert them into electrical signals. The mechanismof converting photoenergy into electrical signals in graphene canbe broadly classified into two categories, namely, carrier gener-ation and thermal effects. The former involves carrier genera-tion, including the photovoltaic effect (PV),[31–34] photoconduc-tive effect (PC)[31,35] and photogating effect (PG).[36,37] The lat-ter include the photothermoelectric effect (PTE)[38,39] and bolo-metric effect (BOL).[40,41] The PV effect entails the generation ofphoto-induced carriers in the graphene channel. Once photonsare absorbed by the graphene sheet, electron-hole pairs (EHPs)separate to form free carriers that diffuse by introducing a us-able electromotive force (EMF), usually proportional to the ir-radiance power. The diffusion force originates from the diver-gence of the material band structure, also known as the p-n junc-tion in semiconductors. Graphene can be modified as p- or n-type by applying a gate voltage or placing materials with differ-ent work functions underneath the sheet. However, the recom-bination length based on the internal electric field of the freecarriers barely exceeds 200 nm.[34] Therefore, incorporating anexternal electric field could facilitate carrier collection efficiencyat the source-drain terminals. The photoconductive effect occurswhen the radiation energy is adequately high to excite the elec-trons in graphene from the valence band to the conduction band.This interband transition enables the free movement of elec-trons, thereby enhancing the conductivity of the sheet.[35] Thephotogating process occurs when a particular type of charged car-riers are trapped in graphene, providing an ultrahigh gain in re-sponsivity. This trap occurs in gated field effect transistors (FETs)and graphene heterostructures.[36,37] The photo-thermoelectricprocess depends on the temperature gradient of the graphenechannel induced by light illumination. The majority type of car-riers (n-type or p-type) are driven from the hot side toward thecold side of the channel, and the net carrier migration leads to adetectable photocurrent response.[39] In highly doped graphenephotodetectors, the bolometric process dominates the detectionresponse. The resistivity of the graphene channel is modulatedby the thermal disruption of local carriers caused by the incidentlight.[42] This retards the charged-carrier mobility characterizedby the bolometric coefficient 𝛽 = d𝜎dT, contributing to a bolomet-ric photocurrent response that is opposite in polarity to the givenbias current (IDS).+− Regarding multiple mechanisms, our pro-posed polarization-dependent photodetector was based on a fu-sion of the PV and PC effects, which introduced a device withlow power consumption and fast response. The PTE effect canbe neglected owing to the large channel length and outstandingthermal conductivity of graphene. The conditions for the BOL ef-fect are investigated further in this manuscript. It is difficult todecouple these effects; however, with careful design, engineeringthese mechanisms constitutes a crucial step in the optoelectronicindustry.2. Results and Discussions2.1. Graphene Photodetector DeviceA schematic diagram of the proposed photodetector (Device A)is shown in Figure 1a. 300 nm of SiO2 was deposited on a siliconsubstrate. To form the graphene channel, graphene was preparedby chemical vapor deposition (CVD), transferred to the substrate,and etched by oxygen plasma for 40 s. A shadow mask was de-posited by thermal evaporation on 200 nm gold electrodes. Fi-nally, a single-crystal gold flake was grown on a silicon substrateand patterned via focused ion beam (FIB). The flake with theplasmonic structure was flipped upside down and partially trans-ferred onto the channel, as shown in the inset of Figure 1a. (Referto the Methods section for a clearer step-by-step explanation ofthe fabrication process). The plasmonic waveguide contains anetched-through antenna and groove waveguide, which avoid di-rect laser illumination on graphene and may generate unwantedsignals larger than the SPP’s contributed photocurrents.Adv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (2 of 7) 21983844, 2023, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202302707 by Cochrane Japan, Wiley Online Library on [27/10/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comFigure 1. a) A schematic of SPP waveguide graphene photodetector. Inset: Transparent illustration of the patterned gold flake. Note that the antennaswere not in contact with the graphene boundary to refrain direct illumination. b) Simulated electric field profiles of the designed dimer antenna showingthe symmetric and anti-symmetric modes, excited by the 0° and 90° polarizations respectively; the scale bar is 0.2 μm. c) The SEM image of the fabricateddual channel SPP waveguide; the scale bar is 2 μm. d) Magnified image of the dimer antenna to aid the eyes; the scale bar is 0.5 μm. e) Magnified imageof the waveguide channel to aid the eyes; the scale bar is 0.5 μm.The dimer antenna shown in Figure 1b generates SPPs thatare altered by the change in incident polarization. With incidentpolarization states of 0° and 90° (depicted by the arrows), thedimer antenna generated symmetric and anti-symmetric modes,respectively, as shown in Figure 1b. The dimer antenna demon-strated an identical charge arrangement when subjected to an ex-citation polarization of 0°, whereas the resulting charge polaritywas distributed oppositely at an incident angle of 90°. Direction-tunable SPPs based on the modes mentioned above[10] were en-gineered through superposition.[14] In this work, a 650 nm con-tinuous wave (CW) laser was used because of its accessibility.The main purpose of this study was to demonstrate the near-field detection of SPPs through graphene. Therefore, the plas-monic structure could also be replaced by other designs withdirectional launching capability. The directional launching ofSPPs has been reported and adequately studied.[10,15,43,44] Theparameters of this plasmonic waveguide designated by finite-difference time-domain (FDTD) simulation are briefly intro-duced in Figure 1c. Larm, the length of the waveguide arm, wasset to 4 μm. It is not a deciding factor for the wavelength or prop-agation mode but essential for keeping the confined electric fieldsin plane with the graphene sheet and preventing scattering loss.With the optimal design of the dimer antenna (Ls = 720 nm, Ld= 290 nm, and Wd = 240 nm), SPPs can be launched at the tar-get wavelength effectively. The upper, lower, and grooves (Wup =135 nm, Wlo = 145 nm, and Wsc = 80 nm) of the waveguide pre-served the targeted wavelengths and granted propagation in thewaveguide. The waveguide radius was optimized to R = 3 μm byFDTD simulation, which was mainly determined by the propa-gation length and bending loss of the SPP wave. The gap (Wgap =110 nm) between the two SPP channels provides the spatial phasedistribution required to interfere with the field profiles generatedby the dimer antennas.2.2. SPP Waveguide CharacterizationBefore fabricating the proposed photodetector, its ability to steerSPPs with linearly polarized light was tested. Device B was fab-ricated using the designed SPP waveguide structure shown inFigure 2a,c. To minimize propagation loss in the waveguide, asingle-crystalline gold flake with a thickness of 200 nm (hsc) wasgrown and transferred via poly (methyl methacrylate) (PMMA)onto a 100-nm gold film evaporated on a glass substrate.[45] Thegold stack with a total thickness of 300 nm was patterned withthe designed plasmonic waveguide using FIB. The waveguidegroove depth (d = 120 nm) was designated by simulation, andfurther analysis of additional etching depths is provided in theFigure S1 (Supporting Information). Gaussian beams of 650 nmwavelength with different polarization states (0°, 45°, 90°, and– 45°) were illuminated from the backside of the sample as il-lustrated in Figure 2b, and the simulated electric field profile isshown in Figure 2d–g. (Detailed information on the simulationenvironment is provided in Figure S2a–d (Supporting Informa-Adv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (3 of 7) 21983844, 2023, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202302707 by Cochrane Japan, Wiley Online Library on [27/10/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comFigure 2. a) Schematic of the optical sample (device B). b) Cross section of the optical sample, the arrow gradient colored represents the incident beam.c) Optical microscope image obtained with the camera; the scale bar is 10 μm. The simulated electric field profiles under d) 0°, e) 45°, f) 90° and g)−45° excitations, respectively.tion). From the results, it is clear that the SPPs were steered due tothe superposition of the modes described in Figure 1b, as all thelinear polarizations could be disassembled into different weightsof the horizontal and vertical vectors.Figure 3f shows the optical measurement system configura-tion. A commercial halogen lamp with a 630 nm long pass filterwas used as the light source. The light then passes through apolarizer to control the polarization and focuses on a higherpower density with a condenser lens. The scattering of theexcitations was collected using an objective lens, followed by theoptical elements inside a commercial microscope, and finally, thecamera and spectrometer. The experimental results of steeringSPPs are shown in Figure 3a,b. Figure 3a shows the steering andscattering images when the input polarization is set to 45°. Thecontours in the figure have been added to aid the eyes. The ex-perimental data are in good agreement with the near-field profileand far-field projection FDTD simulations shown in Figure 2eand Figure S2e (Supporting Information). The SPPs were guidedtoward the right channel, followed by scattering, to free space asthe surface waves collided with the vertical scattering grooves, asshown in Figure 3e. Note that the scattering grooves were addedonly for the optical setup (Device B) and excluded from theelectrical setup (Device A) to avoid scattering loss and enhancethe in-plane field absorption of graphene. With the input set to –45°, the SPPs can be launched into the left waveguide, as shownin Figure 3b. The generated electric field confinement must bestudied to analyze the largest possible photocurrent contrast.An easy way to obtain preliminary results is to calculate theextinction ratio between the energies confined in the channelsof the proposed waveguide. The spectra of the right (SCR) andFigure 3. Experimental results of the SPP waveguide. Optical image of the far field measurement under a) 45° and b) −45° excitations, respectively. Thescale bar is 3 μm. c) and d) are the experimental and simulated extinction ratio of scattered SPPs signals. e) SEM image of the fabricated SPP waveguideon the optical device. The scale bar is 0.2 μm. f) Schematic of the optical measurement setup.Adv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (4 of 7) 21983844, 2023, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202302707 by Cochrane Japan, Wiley Online Library on [27/10/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comFigure 4. Photocurrent response and simulated SPP flux under a) full-azimuthal polarization excitation and b) different incident laser powers of the SPPwaveguide photodetector.left (SCL) scattering ports were obtained under an excitation of45° using a spectrometer. Figure 3c,d show the experimentaland simulated extinction ratio (ER) at an excitation of 45°, whereER = SCR/SCL.2.3. Photocurrent Alternation and MechanismsAfter the proposed plasmonic waveguide exhibited positive re-sults in the optical far-field characterization, a near-field pho-todetector device was fabricated. The result in Figure 4a showsthe photocurrent alternation under different excitation polariza-tions, indicating promising properties for integration in inte-grated circuits. The simulation settings and field profiles are pro-vided in Figure S3 (Supporting Information). The excitation in-strument was a commercial 650 nm CW laser with its power setto 1.15 mW. When the polarization angle was set to 150°, the pho-tocurrent exhibited the largest response of ≈IPC = 9 nA. SPPsunder this scenario were launched toward and confined in thewaveguide, where the graphene channel was positioned. The lo-cal EHPs in the graphene channel is separated owing to the ther-mal effects caused by the SPPs in the waveguide. At an excitationangle of 60°, the SPPs would propagate along the opposite chan-nel lacking graphene; therefore, it could be inferred that small orno photocurrent could be generated. As illustrated in Figure 4b,there is a linear relationship between the photocurrent responseand the incident beam, indicating that the device operates by em-ploying photovoltaic (PV) and photoconductive (PC) effects.[46]The excitation energies are proportional to the number of pho-tons responsible for the SPP generation intensity. In contrast,SPPs generate hot carriers that excite free electrons and holesdriven by externally applied electric fields (VDS =−0.3 V), therebycontributing to the photocurrent.To further study the effects of photocurrent in graphene, a bias-dependent experiment was conducted. The measured photocur-rent exhibited a polarity equivalent to the externally applied cur-rent when |VDS| < 2 V. In Figure 5a, the photocurrent response iszero at bias currents -2 and 2 V, indicating a switch in the domi-nant photocurrent effects. Note that the PV, PC, BOL, and PTE ef-fects may occur simultaneously. However, by carefully designingthe photodetector setup, it is possible to engineer the dominatingeffect. Interestingly, the photocurrent response with polarization-dependent properties, as depicted in Figure 4a, emerged onlyin the PV and PC regions. The photocurrent response becomesindependent of the polarization alternation in the BOL region,as shown in Figure S4 (Supporting Information). To the bestof our knowledge, few studies have investigated this issue. Inthis state, the photocurrent obtained is due to the heat distur-bance introduced by the incident beam throughout the graphenechannel. The carrier mobility was suppressed, indicating an in-crease in channel resistance. Therefore, at high bias voltages, themeasured bolometric effect was pronounced, overwhelming theother graphene photocurrent effects. As the alternation of theincident beam polarization does not affect the power, the intro-duced heat disturbance was the same. Because the contributingFigure 5. a) Bias-dependent photocurrent response of the photodetector, presenting the conversion between operating effects. For clear observationsof photocurrent response in the PV & PC region, b) is added to aid the eyes.Adv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (5 of 7) 21983844, 2023, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202302707 by Cochrane Japan, Wiley Online Library on [27/10/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comphotocurrent scales of BOL and PV are significantly different,the polarization-dependent photocurrent response feature is de-prived of the device under the abovementioned conditions.3. ConclusionOptically integrated circuits have been developed to meet theever-growing demands of global communication technology.Photodetectors are the solutions to optical and electrical signalconversion. However, owing to size incompatibility, on-chip inte-gration remains an issue for conventional photodetectors. Minia-turized photodetectors have attracted significant interest in re-cent years.A polarization-dependent SPP near-field photodetector basedon graphene was developed in this work. By illuminating thebackside of the groove waveguide, the antenna served as ananoscale light source, exciting waves that propagated throughthe desired channel. Subsequently, the SPP waves are absorbeddirectly and converted into electrical signals in the near field, of-fering a promising near-optical field detector based on graphene.Different photocurrents were observed under alternating inci-dent polarization. The responsivities of the device under 150°and 60° excitation were 29.2 and 6.2 mA W−1, respectively, in-troducing a 400% electrical signal contrast for further applica-tions in integrated circuits. In addition, the photocurrent gen-eration mechanism of graphene in the device was investigated.The device was subjected to different VDS values to measurethe PV, PC, and BOL effects of graphene. The different effectsof photocurrent generation can be employed under careful de-sign and particular conditions to accommodate the vast appli-cations of the optoelectronic device industry. For future im-provement of the device performance, the integrated transition-metal dichalcogenides (TMDCs) 2D heterostructures,[47] hybridplasmonic waveguides (HPWGs),[48–50] and decreasing the drainto source channel length could be considered. Near-field SPPdetection, introduced by the fusion of photovoltaic and pho-toconductive effects, saves energy and avoids complicated andexpensive fabrication procedures. The proposed device can beused in nanolaser-integrated plasmonic circuits for ultracompactnanophotonic communication.4. Experimental SectionDevice Fabrication: The device was fabricated by depositing a 300 mminsulating layer of silicon dioxide on a silicon substrate using an elec-tron beam evaporation system (ULVAC VT1-10CE). The insulating layerrestricted any contact between the electrode and silicon layer. Therefore,the photocurrent contributed by silicon was not detected by the sourcemeter (B2901A). Graphene was transferred onto the sample using the wettransfer method, followed by oxygen plasma etching[51] using a reactiveion etching system to obtain a channel with uniform edges. Subsequently,the designed plasmonic waveguide was milled using an FIB on a single-crystal gold flake grown on a silicon substrate using a wet chemical syn-thesis method.[45] As structural deformities may affect SPP propagationin a lossy manner, the FIB working current was set to a low value (7 pA) toachieve effective results. To realize different milling depths in the waveg-uide and antenna, each was patterned separately using the bitmap func-tion of the FIB (FEI Helios NanoLab G3 CX, NCKU, Taiwan). The structuredflake was transferred upside down and aligned at the desired location.Graphene Wet Transfer: A monolayer graphene sheet grown on a cop-per foil by the chemical vapor deposition (CVD) method was transferredusing the wet chemical technique. Graphene was protected by spin coat-ing a thin layer of photoresist (PMMA-A4). The copper foil was removedby placing the stack in a Fe(NO3)3 solution (33 wt.%) at room tempera-ture (23–26°C) for ≈12 h. Consequently, the copper foil was fully etchedaway, leaving a photoresist/graphene stack. The stack was cleaned for 1 husing deionized (DI) water to remove etchant residue. To enhance surfaceenergy, the target substrate was treated with UV-ozone before the trans-fer, providing a location adjustable transfer process without damaging thegraphene. The stack with the substrate was left in an oven at room tem-perature to complete dehydration, then immersed in acetone to removethe photoresist and subsequently washed in isopropanol (IPA).Upside-Down Transfer of Patterned Single Crystalline Gold Flake: Few ap-plications require the upside-down transfer of nanostructures. In the pro-posed device, this technique plays a crucial role in creating a light sourceat the nanoscale and precludes direct illumination of the graphene sheet.First, the waveguide was patterned on a single crystalline gold flake, then2 μL of photoresist was applied on the target flake with a pipette and leftto dry on a hot plate for 2 min at 150°C. The resist/gold stack was peeledfrom the native substrate with tweezers, aided by a few drops of DI wateron the edge. The stack was placed on a thin PDMS stamp and immersedin acetone for 2 h to reveal the gold flakes. The PDMS, along with theflake, was mounted onto a micromanipulator and aligned with the deviceusing a microscope. The device and stamp stack were heated to 120°C toprovide better contact energy between the flakes and device. Finally, thePDMS stamp was slowly peeled off from the device, leaving the patternedflake at the desired location. For clear schematics, please refer to Figure S7(Supporting Information).Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsThis work was supported by the National Science and Technology Council(NSTC 109-2628-E-007-003 -MY3; 112-2923-E-007-004 -MY2; 112-2223-E-007-007-MY3; 112-2628-E-007-021; 112-2119-M-A49-008). Supports fromDFG via projects HU2626/5-1 (445415315), SFB-NOA-C1 (398816777)and IRTG-2675-C1 (437527638) are also gratefully acknowledged. Thefunding JST FOREST (JPMJFR2139) is also acknowledged.Conflict of InterestThe authors declare no conflict of interest.Author ContributionsC.-H. W., C.-J. K., and M.-W. Y. performed sample fabrication, simulation,and optical characterization. J.-H. Y., P.-Y. W., C.-B. H., T.-C. L., J.-S. H.,S. I. and K.-P. C. helped analyze the experimental data. C.-H. W., M.-W. Y.and K.-P.C. wrote the manuscript. All authors discussed the results andcommented on the manuscript.Data Availability StatementThe data that support the findings of this study are available from the cor-responding author upon reasonable request.Keywordsgraphene, photodetectors, surface plasmon polaritons, unidirectionalpropagation, waveguidesAdv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (6 of 7) 21983844, 2023, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202302707 by Cochrane Japan, Wiley Online Library on [27/10/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensewww.advancedsciencenews.com www.advancedscience.comReceived: April 28, 2023Revised: August 6, 2023Published online: September 3, 2023[1] M. Thomaschewski, Y. Yang, C. Wolff, A. S. Roberts, S. I. Bozhevolnyi,Nano Lett. 2019, 19, 1166.[2] E. Krauss, G. Razinskas, D. Köck, S. Grossmann, B. Hecht, Nano Lett.2019, 19, 3364.[3] Y. Su, Y. Zhang, C. Qiu, X. Guo, L. Sun, Adv. Mater. Technol. 2020, 5,1901153.[4] W. X. Tang, H. C. Zhang, H. F. Ma, W. X. Jiang, T. J. Cui, Adv. Opt.Mater. 2019, 7, 1800421.[5] T.-Y. Chen, J. Obermeier, T. Schumacher, F.-C. Lin, J.-S. Huang, M.Lippitz, C.-B. Huang, Nano Lett. 2019, 19, 6424.[6] J. Guo, J. Li, C. Liu, Y. Yin, W. Wang, Z. Ni, Z. Fu, H. Yu, Y. Xu, Y. Shi,Light: Sci. Appl. 2020, 9, 29.[7] J. E. Muench, A. Ruocco, M. A. Giambra, V. Miseikis, D. Zhang, J.Wang, H. F. Watson, G. C. Park, S. Akhavan, V. Sorianello, Nano Lett.2019, 19, 7632.[8] H. Li, Z. T. Huang, K. B. Hong, C. Y. Hsu, J. W. Chen, C. W. Cheng, K.P. Chen, T. R. Lin, S. J. Gwo, T. C. Lu, Adv. Sci. 2020, 7, 2001823.[9] Y.-H. Chou, B.-T. Chou, C.-K. Chiang, Y.-Y. Lai, C.-T. Yang, H. Li, T.-R.Lin, C.-C. Lin, H.-C. Kuo, S.-C. Wang, ACS Nano 2015, 9, 3978.[10] T.-Y. Chen, D. Tyagi, Y.-C. Chang, C.-B. Huang, Nano Lett. 2020, 20,7543.[11] M. Abb, Y. Wang, C. De Groot, O. L. Muskens, Nat. Commun. 2014,5, 4869.[12] A. Shaltout, J. Liu, V. M. Shalaev, A. V. Kildishev, Nano Lett. 2014, 14,4426.[13] V. Giannini, A. I. Fernández-Domínguez, S. C. Heck, S. A. Maier,Chem. Rev. 2011, 111, 3888.[14] D. Tyagi, T. Y. Chen, C. B. Huang, Laser Photonics Rev. 2020, 14,2000076.[15] S. Huang, C.-Y. Wang, H.-Y. Chen, M.-H. Lin, Y.-J. Lu, S. Gwo, ACSPhotonics 2016, 3, 584.[16] J. Michel, J. Liu, L. C. Kimerling, Nat. Photonics 2010, 4, 527.[17] M. Ghioni, F. Zappa, V. P. Kesan, J. Warnock, IEEE Trans. Electron De-vices 1996, 43, 1054.[18] Z. Yang, Y. Deng, X. Zhang, S. Wang, H. Chen, S. Yang, J. Khurgin, N.X. Fang, X. Zhang, R. Ma, Adv. Mater. 2018, 30, 1704333.[19] H. Jing, R. Peng, R.-M. Ma, J. He, Y. Zhou, Z. Yang, C.-Y. Li, Y. Liu, X.Guo, Y. Zhu, Nano Lett. 2020, 20, 7144.[20] J. He, C.-Y. Li, D.-X. Qi, Q. Cai, Y. Liu, R.-H. Fan, J. Su, P. Huo, T. Xu,R. Peng, Nano Lett. 2022, 22, 6655.[21] A. Ren, L. Yuan, H. Xu, J. Wu, Z. Wang, J. Mater. Chem. C 2019, 7,14441.[22] K. S. Novoselov, L. Colombo, P. Gellert, M. Schwab, K. Kim, Nature2012, 490, 192.[23] E. Singh, M. Meyyappan, H. S. Nalwa, ACS Appl. Mater. Interfaces2017, 9, 34544.[24] F. Koppens, T. Mueller, P. Avouris, A. Ferrari, M. Vitiello, M. Polini,Nat. Nanotechnol. 2014, 9, 780.[25] C.-H. Liu, Y.-C. Chang, T. B. Norris, Z. Zhong, Nat. Nanotechnol. 2014,9, 273.[26] Y. Zhang, D. Meng, X. Li, H. Yu, J. Lai, Z. Fan, C. Chen, Opt. Express2018, 26, 30862.[27] C.-H. Wu, C.-J. Ku, M.-W. Yu, J.-H. Yang, T.-C. Lu, T.-R. Lin, C.-S. Yang,K.-P. Chen, ACS Appl. Mater. Interfaces 2022, 13, 693.[28] M. A. Giambra, V. Mis ̌eikis, S. Pezzini, S. Marconi, A. Montanaro,F. Fabbri, V. Sorianello, A. C. Ferrari, C. Coletti, M. Romagnoli, ACSNano 2021, 15, 3171.[29] V. Sorianello, A. Montanaro, M. A. Giambra, N. Ligato, W. Templ, P.Galli, M. Romagnoli, ACS Photonics 2023, 10, 1446.[30] L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D.E. Brown, C. W. Kimball, Nano Lett. 2005, 5, 1399.[31] F. Xia, T. Mueller, Y.-m. Lin, A. Valdes-Garcia, P. Avouris, Nat. Nan-otechnol. 2009, 4, 839.[32] X. Gan, R.-J. Shiue, Y. Gao, I. Meric, T. F. Heinz, K. Shepard, J. Hone,S. Assefa, D. Englund, Nat. Photonics 2013, 7, 883.[33] B. Y. Zhang, T. Liu, B. Meng, X. Li, G. Liang, X. Hu, Q. J. Wang, Nat.Commun. 2013, 4, 1811.[34] T. Mueller, F. Xia, P. Avouris, Nat. Photonics 2010, 4, 297.[35] M. H. Weik, Computer Science and Communications Dictionary,Springer US, Boston, MA 2001, 1266.[36] X. Guo, W. Wang, H. Nan, Y. Yu, J. Jiang, W. Zhao, J. Li, Z. Zafar, N.Xiang, Z. Ni, Optica 2016, 3, 1066.[37] H. Jiang, J. Wei, F. Sun, C. Nie, J. Fu, H. Shi, J. Sun, X. Wei, C.-W. Qiu,ACS Nano 2022, 16, 4458.[38] S. Schuler, D. Schall, D. Neumaier, L. Dobusch, O. Bethge, B.Schwarz, M. Krall, T. Mueller, Nano Lett. 2016, 16, 7107.[39] D. Wang, A. E. L. Allcca, T.-F. Chung, A. V. Kildishev, Y. P. Chen, A.Boltasseva, V. M. Shalaev, Light: Sci. Appl. 2020, 9, 126.[40] M. Freitag, T. Low, F. Xia, P. Avouris, Nat. Photonics 2013, 7, 53.[41] Y. Wang, W. Yin, Q. Han, X. Yang, H. Ye, Q. Lv, D. Yin, Chin. Phys. B2016, 25, 118103.[42] X. Wang, X. Gan, Chin. Phys. B 2017, 26, 034203.[43] J. Lin, J. B. Mueller, Q. Wang, G. Yuan, N. Antoniou, X.-C. Yuan, F.Capasso, Science 2013, 340, 331.[44] I. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Martín-Moreno, F. García-Vidal, A. Boltasseva, Opt. Express 2009, 17, 7228.[45] J.-S. Huang, V. Callegari, P. Geisler, C. Brüning, J. Kern, J. C.Prangsma, X. Wu, T. Feichtner, J. Ziegler, P. Weinmann, Nat. Com-mun. 2010, 1, 150.[46] H.-S. Ee, Y.-S. No, J. Kim, H.-G. Park, M.-K. Seo, Opt. Lett. 2018, 43,2889.[47] R. Xiao, C. Lan, Y. Li, C. Zeng, T. He, S. Wang, C. Li, Y. Yin, Y. Liu, Adv.Mater. Interfaces 2019, 6, 1901304.[48] Z. Ma, K. Kikunaga, H. Wang, S. Sun, R. Amin, R. Maiti, M. H.Tahersima, H. Dalir, M. Miscuglio, V. J. Sorger, ACS Photonics 2020,7, 932.[49] D. Ansell, I. Radko, Z. Han, F. Rodriguez, S. Bozhevolnyi, A.Grigorenko, Nat. Commun. 2015, 6, 8846.[50] P. Sharma, D. K. Vishwakarma, IEEE Trans. Nanotechnol. 2019, 18,940.[51] J. Bai, X. Zhong, S. Jiang, Y. Huang, X. Duan, Nat. Nanotechnol. 2010,5, 190.Adv. Sci. 2023, 10, 2302707 © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH2302707 (7 of 7) 21983844, 2023, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/advs.202302707 by Cochrane Japan, Wiley Online Library on [27/10/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License