• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Tuning photoresponse of graphene-black phosphorus heterostructure by electrostatic gating and photo-induced doping

    2022-03-14 09:29:14YnpnLiuMinYnJunpnLuYinLiuHonwiLiuErwnZnWiFuJunyonWnZnlinHuJunYinGokiSijiWnJiboYiAjynVinuKinPinLo
    Chinese Chemical Letters 2022年1期

    Ynpn Liu,Min Yn,Junpn Lu,Yin Liu,Honwi Liu,Erwn Zn,Wi Fu,Junyon Wn,Znlin Hu,Jun Yin,Goki E,Siji Wn,Jibo Yi,Ajyn Vinu,Kin Pin Lo,?

    aKey Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education,State Key Laboratory of Mechanics and Control of Mechanical Structures,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China

    bDepartment of Applied Physics,The Hong Kong Polytechnic University,Hong Kong,China

    cSchool of Physics,Southeast University,Nanjing 211189,China

    dCollege of Jincheng,Nanjing University of Aeronautics and Astronautics,Nanjing 211156,China

    eSchool of Physics and Technology,Nanjing Normal University,Nanjing 210023,China

    fDepartment of Chemistry,National University of Singapore,Singapore 117543,Singapore

    gInstitute of Materials Research and Engineering,Agency for Science,Technology and Research(A?STAR),Innovis 138634,Singapore

    hGlobal Innovative Centre for Advanced Nanomaterials,College of Engineering,Science and Environment,The University of Newcastle,Newcastle NSW 2308,Australia

    1These authors contributed equally to this work.

    ABSTRACT Metal-semiconductor diodes constructed from two-dimensional(2D)van der Waals heterostructures show excellent gate electrostatics and a large built-in electric field at the tunnel junction,which can be exploited to make highly sensitive photodetector.Here we demonstrate a metal-semiconductor photodiode constructed by the monolayer graphene(Gr)on a few-layer black phosphorus(BP).Due to the presence of a built-in potential barrier(~0.09 ± 0.03 eV)at the Gr-BP interface,the photoresponsivity of the Gr-BP device is enhanced by a factor of 672%,and the external quantum efficiency(EQE)increases to 648% from 84% of the bare BP.Electrostatic gating allows the BP channel to be switched between p-type and n-type conduction.We further demonstrate that excitation laser power can be used to control the current polarity of the Gr-BP device due to photon-induced doping.The versatility of the Gr-BP junctions in terms of electrostatic bias-induced or light-induced switching of current polarity is potentially useful for making dynamically reconfigurable digital circuits.

    Keywords:Black phosphorous Graphene Heterostructure Gate-tunable Photodetector Photoinverter

    Black phosphorus(BP)has attracted strong interests beyond graphene due to its high carrier mobility and layer-dependent bandgap(~0.3 eV for bulk and~2.0 eV for monolayer)[1-3].Fewlayer BP has been considered as an excellent platform for phototransistors due to light-driven thermoelectric,photobolometric and photovoltaic processes[4].Previously,few-layer BP photodetectors have been demonstrated to exhibit fast and wide-spectrum responses with a photo-responsivity up to 4.8 mA/W[3,5].The shortcomings of using few-layer BP as a photodetector include the unintended p-doping of BP,which reduces the photocarrier mobility through electron-electron scattering[4].Moreover,the small bandgap of few-layer BP results in a high dark current[4,6,7].To improve the photoconductive response,the barrier height at the BP-metal interface needs to be tuned by doping BP and shifting its Fermi level[4].For instance,chemical doping and other surface modifications(photoresponsivity of 2.56 A/W after 8.0 nm MoO3coating and 1.88 A/W after 8.0 nm Cs2CO3doping,respectively)have been applied to enhance the photoresponsivity,although chemical modifications are typically disadvantaged by their chemical instability[8,9].Alternatively,electrostatic doping and photoinduced doping,which are continuously tunable,non-destructive and implementable in ambient atmosphere,may be more suitable to tune both the polarity and magnitude of the photocurrent in 2D materials[10,11].Theoretical simulation predicts that the electrical and optical properties of ultrathin BP can be effectively tuned by electrostatic doping.Arising from the puckered honeycomb structure of BP,its band edges are mainly contributed by localized P 3pzorbitals,which have a strong response to the external perpendicular electric field[12-14].

    Recently,van der Waals(vdW)heterostructures based on 2D materials have been used to fabricate optoelectronic devices owing to the abrupt tunneling junction and strong photon-matter interactions[15-19].A ladder-type band structure in such heterojunction can be exploited to separate photo-excited electrons and holes(e-h)pairs,thereby reducing the recombination probability.Moreover,due to the absence of Fermi pinning effect that is universally observed at the traditional metal-semiconductor interface[1,3,13],the weak screening effect[12]and the ultrathin nature of 2D heterostructures allow the reversible modulation of band alignmentviaapplying a perpendicular electric field,which opens a new avenue to tune the optoelectronic properties of 2D heterostructures[20-26].

    Herein,we studied the photoresponsivity of a bipolar phototransistor using a vdW-stacked monolayer graphene(Gr)on a fewlayer BP flake.The photoresponsivity of the Gr-BP phototransistor is improved by a factor of 672% and its corresponding EQE is increased from 84% to 648% compared to that of a device using a bare BP.In addition,both photoresponsivity and the polarities of photocurrent of the Gr-BP heterojunction could be tuned by electrostatic gating.We further demonstrate that n- or p-type dominated transport in the device can be manipulated by laser power through photo-induced doping,which is unreachable for neither the bare BP device nor heterostructure with all Gr above BP flake in the previous reports[2,3,6,8,10,14].Our results suggest that Gr-BP heterostructure shows great potentials as a platform for broadband photodetectors,photoinverters and reversing commutators[6,11,19,21,25].

    The exfoliations of graphene and black phosphorus were carried out in a glovebox filled with argon gas(O2<0.5 ppm and H2O<0.5 ppm).Typically,thin BP flakes were directly mechanically exfoliated onto Si/SiO2(300 nm oxide layer)substrate from bulk BP crystal(HQ graphene)using blue “magic” tape.After that,the desired rectangle shape(length>30 μm,thickness~5–20 nm BP flakes were located under optical microscopy for further stacking.Monolayer graphene was exfoliated onto PDMS films and then partially transferred onto BP flake with a dry transfer methodviaa home-built transfer platform in an argon glovebox.The Gr-BP stacks were then annealing at 180 °C in the glovebox for 30 min to remove possible air bubbles and form good contact.After these processes,the Gr-BP heterostructure was spin-coated with a PMMA layer both as a protective layer and a photoresist layer for electrode fabrications.In this work,Cr/Au(2 nm/60 nm)was chosen as metal electrodes,respectively.

    The Gr-BP heterostructure(Fig.1a)was fabricated on a silicon wafer(with 300 nm SiO2).Monolayer Gr and few-layer BP flake were precisely stacked together using a dry-transfer method(see Experimental section in Supporting information)[11,25].To avoid oxidization of BP,all the exfoliation and transfer processes were conducted in a glovebox filled with argon gas.Fig.1b shows the atomic force microscopy(AFM)image of a completed Gr-BP device.From the topography,the BP flake is smooth,and the thicknesses of BP and Gr were determined to be~8.0 nm and~0.5 nm,respectively(see Fig.S1 Supporting information for height profile).To investigate the interfacial quality and charge transfer of Gr-BP heterostructure,spatially resolved Raman was employed[2].As shown in Fig.1c,the G peak(the high-frequencyE2gphonon atΓpoint)redshifts from 1580 cm?1to 1572 cm?1and the frequency of 2D peak(second-order Raman scattering by two optical phonons)blueshifts from 2677 cm?1to 2688 cm?1,a clear indication that graphene is n-doped by underlying BP flake[2,27].Fig.1d displays the integrated intensity of Ag1peak of few-layer BP flake after measurement.The Ag1signal is uniform throughout the entire BP flake,and its Ag1/Ag2intensity ratio>0.9 is typical for a pristine BP flake[28].It is worth noting that phosphorene oxides and suboxides(bandgap~4.6 eV from PBE method)typically give an Ag1/Ag2ratio<0.6(Fig.S2 in Supporting information),thus we can conclude that these oxides are absent in our studies[14,29].

    Fig.2a shows the schematic illustration of the Gr-BP device.For comparison,bare BP device with similar thickness was also tested.As shown in Fig.2a,the electrode attached with Gr was chosen as drain throughout the whole measurements unless otherwise specified.Fig.2b shows the plot of photo-induced current density(Iph)versusbias(Vds)of bare BP and Gr-BP devices under global irradiation(532 nm,1 mW/mm2).It is seen that Gr-BP devices show higher outputIphover aVdsrange from ?0.05 V to+0.05 V and fast on-off photoresponse(Vds=+0.05 V,Fig.2c).To assess the performance of our device,photoresponsivity(R)and external quantum efficiency(EQE),the figures of merit of photodetector devices,are calculated according to the following equations[3,8]:

    whereIphis the photocurrent induced by incident light,Pstands for the light intensity,Sis the effective area under illumination,λis the wavelength of the incident light,h,canderepresent the Plank constant,the velocity of light and the charge of the electron,respectively.Based on Eq.1,the photoresponsivity of Gr-BP heterojunction is significantly enhanced(~672%)over the bare BP device,increasing from 3.6 × 102mA/W to 2.8 × 103mA/W and the corresponding EQE increases dramatically up to 648% from 84%,which are higher than previously reported metrics of BP-based photodetectors(Table S1 in Supporting information)[3,8].

    In order to investigate if the Gr-BP interface contributes to enhanced photoresponse by charge separation or built-in potential,a scanning photocurrent microscope(SPCM)equipped with a focused laser beam was used to identify individual contribution(sketched in Fig.2d).Fig.2e shows theJ-V(whereJrepresents current density)curves with the laser-focused at five regions(as marked in the right insert).All five regions show photo-response but with different magnitudes(Fig.S4 in Supporting information).A weak rectifying behavior was observed with photocurrent increasing atVds>0 V but decreasing atVds<0 V,revealing the existence of a small potential barrier that modulates the polarity of current flow.Among the five regions,the Gr-BP junction shows the highest photocurrent of 3.4 × 105mA/cm2(Jdark~1.96 × 105mA/cm2,Vds=+0.05 V),thus it is responsible for the dramatic differences in photocurrent between bare BP and Gr-BP devices(as exhibited in Figs.2b and c).Notably,the output of the Gr-BP device presents photovoltaic characteristic.Fig.2f shows the short-circuit current(Isc)and open-circuit voltage(Voc)acquired under light illumination with a power of~1.2 mW.Among them,the Gr-BP heterojunction shows the highest photocurrent,especially at its edge region,might be due to energy band depletion at the edge that generates potential at the edge and contributes to the output current(Figs.S4 and S5 in Supporting information).The existence ofVoc(?0.013 V)andIsc(0.6 μA)proves that the photoresponse behavior of the Gr-BP device is dominated by the photovoltaic effect rather than thermal driven processes[4].

    Fig.1.Schematic drawing and characterizations of Gr-BP heterostructure device.(a)Schematic diagram of Gr-BP heterostructure.Exfoliated graphene and BP flakes are partially overlapped in order to study the origin of photoresponsive enhancement.(b)AFM image of Gr-BP device.The graphene flake is marked in a white dashed line,while BP is enclosed in a green dash line.The white spots in graphene-covered region represent air-trapped bubbles/wrinkles.The scale bar is 5 μm.(c)Corresponding Raman spectra from three selected regions marked in(b)for comparison.For visualization,the signal of Gr(on BP flake)is enlarged by a factor of 10 to cancel the intensity loss from varied interference phenomena.The bottom BP and Gr symbols represent the intrinsic signals of BP(pink region)and Gr(purple region),respectively.For clarification,the peak at~520 cm?1 origins from the underlying silicon substrate.(d)Raman spatial mappings of representative Ag1 of black phosphorus.

    To determine the band alignment between Gr and BP,ultraviolet photoelectron spectroscopy secondary electron cut-off energies of bare BP flake,bare graphene films,and Gr-BP heterostructure(Fig.2g).Accordingly,their work functions are measured to beФBP=4.47 eV,ФGr=4.50 eV andФGr-BP=4.37 eV(see Experimental section in Supporting information for calculation details),respectively,which are in good agreement with the previous reports[30-32].Based on the above values,we can conclude that graphene is n-doped(~0.13 eV),and BP flake becomes highlypdoped withEF~0.02 eV above the valence band maximum(EVBM).With this information,the energy band diagrams are constructed as shown in Fig.2h.For Gr-BP device,due to the initial p-doping of BP(possibly originating from impurities and defect,Figs.S6 and S7 in Supporting information for XPS and STM data),downward band bending occurs at the interface to create a built-in potential(Фbi)proportional toФGr-EVBM(~0.09 ± 0.03 eV).Due to the built-in potential,Gr-BP heterojunction shows a rectifying behavior(Fig.2i).Upon photo-excitation,e-hpairs are generated in BP;after exciton dissociation,electrons are injected into a more conductive graphene layer,while the Schottky barrier at the interface blocks hole transport to graphene[32-34].

    Next,the photoresponse of Gr-BP heterojunction is electrostatically modulated using a back gate.Fig.3a shows theIds-Vgdata of the Gr-BP device with and without~1.4 mW laser illumination(Vds=+0.1 mV).In the dark,the Gr-BP device shows ambipolar and hole-dominant characteristics with hole mobility~1320 cm?2V ?1 s ?1 and electron mobility~745 cm?2V ?1 s?1.These values are two times larger than those of the bare BP device with the similar thickness(see Fig.S9 in Supporting information for bare BP device).Upon photo-irradiation,the photocurrent monotonically decreases withVgranging from ?50 V to around +27.5 V;this is followed by a sharp decline,and then the photocurrent becomes negative whenVg>~36.3 V.Fig.3b shows the gatetunability of outputI-Vcharacteristics from the same device(see the dark and illuminated current comparison in Fig.S10 in Supporting information).Fig.3c shows that the polarities of photocurrents(Iph,hereVds=+0.05 V)are opposite at negative and positive gate regimes;there is a higher current at negative gate voltage compared to positive gate voltage,which allows the types and heights of Schottky barrier across the Gr-BP junction to be determined.WhenVg<0(Fig.3d),the accumulation of holes at BP increases the downward band bending.Therefore,the wider depletion region(W)and larger potential barrier height(Фbi)prevent the tunneling or thermal injection of holes from BP into graphene.In this regime,the photocurrent increases monotonically with the magnitude of the negative gate voltage.In contrast,a positive gate voltage(0

    Fig.2.Photoresponse behavior and Gr-BP heterostructure.(a)Sketches of G-BP heterostructure under global illuminations.For the Gr-BP device,single-layer graphene was used as a source electrode.(b) Iph-Vds characteristics of bare BP and Gr-BP device under global laser irradiation with the same laser intensity.(c)Photoresponse behavior comparison between bare BP and Gr-BP devices.(d)Schematic diagram of Gr-BP heterostructure.(e) J-V curves of Gr-BP device with laser focusing on different regions.Inset shows the optical image of the device marked with different color spots for clarification.(f) VOC and ISC of the Gr-BP device with various parts exposed to laser illumination.(g)UPS data of bare Gr,bare BP and Gr-BP heterostructure.(h)Thermal equilibrium energy band alignment of the separated integral parts with Vds=0 V.(i)Power-dependent photoelectric behavior of Gr-BP heterostructure.

    We performed density functional theory(DFT)calculation to investigate gate-modulated electronic properties of Gr-BP heterostructure to gain more insight.The interlayer distance between graphene and bi-layer BP(Fig.3g)is calculated to be 3.45 ?A.This vdW gap confirms the weak nature of the interfacial interaction,in good agreement with previous studies[35-37].Fig.3h shows the electronic band structure of Gr-BP heterostructure,from which it is clear that both the projected band structures of graphene and BP maintain the characteristics of the isolated counterparts upon their contact.The VBM of BP is close to the Fermi level of graphene and a p-type semiconductor/metal Schottky barrier is present.Due to the weak screening effect of BP and Gr,the contact barrier at the BP-Gr interface can be surmounted effectively by applying an external perpendicular electric field(Eext)[35].By considering Gr as the metal contact and few-layer BP as the semiconductor channel,the Schottky barrier height(SBH)could be estimated following Schottky-Mott rule,Eg=qФp+qФn,whereФpandФnrepresent the barriers against the hole and electron flow between Gr and BP,respectively[38].Fig.3i depicts the evolution of the contact barriers as a function of the applied electric field strength(see Fig.S11 in Supporting information for the evolution of band structure as a function ofEext).Subjected to a negative electric field(Eext<0 V),the Dirac cone of graphene shifts towards the VB of the BP,rendering the contact ohmic.In contrast,for increasing positiveVg,the Dirac cone gradually moves towards the CB of BP.When the electric field is larger than 2 eV/nm,the contact barrierФpbecomes smaller thanФn,turning the contact into n-type.These theoretical findings agree well with our experimental observation.We would like to point out that the layer-dependent bandstructure of BP,initial p-doping level and the approximation of exchange-correlation functionals render it highly challenging to calculate the exact barrier height,but the trend of the charge transfer and barrier variation with applied electric field is valid and consistent with the experimental observation.

    In Gr-BN[34],BP-ZnO[39]and BP-TiOx[40]system,a tunable photo-induced electron transfer has been reported at the interface.Spatial segregation of holes and electrons occurs at different layers,which rearranges the band alignment between two components.Similarly,we found that the Gr-BP heterostructure is capable of showing photo-induced electron transfer.Since absorbents and moisture easily contaminate graphene,all measurements were conducted in a vacuum cell,and thermal annealing was carried out to remove any impurities.Figs.4a and b illustrate the origins of the photo-doping induced inversion.In the dark state(Fig.4a),when BP is positively biased,the direction of the current is from BP to graphene.Upon laser illumination(Fig.4b),electrons are photo-excited from donor-like defects in BP to the conduction band;some of these electrons compensate the holes in BP,while excess electrons created by higher laser photoexcitation migrate to graphene and gives rise to a reverse current.In addition,this migration lifts theEFof graphene while lowering theEFof BP,as a result,band realignment occurs.A direct proof of the photoinduced doping effect is the shifting of Dirac point of graphene in Gr-BP FET device(all graphene placed on top of BP flake,Fig.S13 in Supporting information)upon illumination,where the charge neutral point of graphene shifts to higher negative gate voltage(Δ~6 × 1011cm?2),illustrating graphene becoming n-doped and the occurrence of photo-induced charge transfer.Fig.4c shows the power-dependentJ-Tcurves of Gr-BP heterojunction(edge region)underVds=?0.01 V.In the dark,a current flow from BP to Gr with the value of 9.0 × 104mA/cm2is initially observed when the BP side is positively biased;this current gradually decreases with increasing laser irradiation power and becomes closed at 2.0 mW laser exposure.Most interestingly,the direction of photocurrent reverses at higher laser power(P≥2.0 mW).When the laser moves into the center region of Gr-BP heterostructure,~3.0 mW laser power or larger is required to invert the current flow direction(see Fig.S14 in Supporting information forJ-Tcurves)[41].Moreover,this trend could be extended to a larger negative bias.For instance,underVds=?0.05 V,an excitation laser with a power larger than~12 mW(Fig.4d)is required to reverse the polarity of current flow.The ability to control the polarity of the current by adjusting the power of the laser is a unique feature of the Gr/BP junction,which is not shared by monolayer graphene or BP flake(Fig.S13d).For bare BP,although the photocurrent is proportional to the intensity of irradiation due to thermal driven effects,the polarity of current remains the same with the initial current flow for all laser intensity range.

    Fig.3.Gate-dependent photoelectric behavior of Gr-BP heterostructure.(a) R(Vg)data in Gr-BP device with and without light illuminations. Vds=+0.1 mV.Inserted is the plot of conductance vs gate curve of Gr-BP device in dark.FET mobility is given by where L and W are the length and width of the channel,respectively. C denotes the capacitance.(b) Ids-Vds curves measured in the dark and under light illuminations at various gate voltages.(c)Plots of Voc and Iph as a function of gate voltages.for Iph, Vds=+0.05 V.(d-f)Band alignment of BP and Gr under different gate voltages.(g,h)Lattice and electronic band structure of Gr-BP heterostructure.(i)Evolution of the band edges as a function of the electric field with respect to the Dirac point of graphene.

    There are several reasons why the Gr/BP interface is unique in terms of its gate tunability.The small band gap(~0.3 eV)and absence of interfacial pinning effect allow multilayer BP to be switched readily between the hole and electron-dominated transport under a moderate electric field,thus giving rise to ambipolar transport.In accordance with nonlinear Thomas-Fermi theory[12,13],the electrostatic screening behavior of multilayer BP(thickness ≤10 nm)is intermediate,thereby allowing the electric field from the back gate penetrating BP multilayer to influence the properties of graphene in Gr-BP heterostructure.In addition to maintain similar response time(Fig.S15 in Supporting information),the encapsulation of BP flake by the graphene layer not only overcomes the air instability of BP but also increases the photoresponsivity of BPviathe formation of a Schottky barrier[42].

    We have demonstrated that Gr-BP heterostructures can be used as photodetectors and photoinverters.Comparing with bare BP device,the photoresponsivity increases to 672%(R~2.8 × 103mA/W)due to the presence of a Schottky barrier at the interface of ptype BP and graphene.The height of the Schottky barrier can be modulated by either electrostatic doping or photo-induced doping,allowing the initial p-type conducting channel to be converted to n-type.The highly tunable nature of the Gr-BP interface suggests its potential application in future optoelectronic and logic applications.

    Fig.4.Photo-inverter behavior of Gr-BP heterostructure.(a)Band alignment of BP and Gr device with a negative source-drain bias in dark.The current flow is from BP to graphene.(b)Band re-alignment of BP and Gr heterostructure due to photo-induced doping effect.Under intense light irradiation,a reverse current flow occurs from graphene to BP.(c)Photogenerated current of Gr-BP device under different laser power density at Vds=?0.01 V.(d)Photogenerated currents of Gr-BP device with Vds=?0.05 V under 3,6 and 12 mW laser exposure.

    Declaration of competing interest

    The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

    Acknowledgments

    The authors wish to acknowledge the financial support provided by the Fundamental Research Funds for the Central Universities(Nos.NS2020008,NC2018001,NJ2020003,NZ2020001),the Program for Innovative Talents and Entrepreneur in Jiangsu,Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Nos.MCMS-I-0419G02,MCMS-I-0421K01),National Key Research and Development Program of China(No.2019YFA0705400),and Australian Research Council Future Fellowship(No.FT160100205),DECRA Fellowship(No.DE200101622).

    Supplementary materials

    Supplementary material associated with this article can be found,in the online version,at doi:10.1016/j.cclet.2021.06.079.

    大型黄色视频在线免费观看| 精品午夜福利视频在线观看一区| 人人妻人人看人人澡| 国产一区二区三区视频了| 草草在线视频免费看| 国产黄色小视频在线观看| bbb黄色大片| av在线老鸭窝| 成人高潮视频无遮挡免费网站| 国产乱人视频| 中文字幕熟女人妻在线| 国模一区二区三区四区视频| 天堂影院成人在线观看| 又紧又爽又黄一区二区| 国产精品一及| www.www免费av| 久久伊人香网站| 伊人久久精品亚洲午夜| av中文乱码字幕在线| 欧美黑人欧美精品刺激| 真人一进一出gif抽搐免费| 十八禁国产超污无遮挡网站| 国产精品1区2区在线观看.| www日本黄色视频网| 国内毛片毛片毛片毛片毛片| 国产69精品久久久久777片| 18+在线观看网站| 在线观看av片永久免费下载| 成年女人永久免费观看视频| 国产成人av教育| 美女被艹到高潮喷水动态| 人妻夜夜爽99麻豆av| 亚州av有码| 一本久久中文字幕| 又黄又爽又刺激的免费视频.| 国产白丝娇喘喷水9色精品| 国产精品一区二区性色av| 精品乱码久久久久久99久播| 午夜福利视频1000在线观看| 欧美一级a爱片免费观看看| 成人特级黄色片久久久久久久| 久久99热这里只有精品18| 亚洲黑人精品在线| 级片在线观看| 国产午夜福利久久久久久| 国产精品一及| 成年人黄色毛片网站| 亚洲在线自拍视频| 身体一侧抽搐| 国产精品日韩av在线免费观看| 成人性生交大片免费视频hd| 国产在线男女| 精品人妻1区二区| 舔av片在线| 国产真实乱freesex| 国产成人a区在线观看| 日本黄色视频三级网站网址| 亚州av有码| 亚洲av免费高清在线观看| 午夜久久久久精精品| 国产精品亚洲一级av第二区| 日本精品一区二区三区蜜桃| 无人区码免费观看不卡| 免费看光身美女| 3wmmmm亚洲av在线观看| 精品久久久久久久末码| 老师上课跳d突然被开到最大视频 久久午夜综合久久蜜桃 | 少妇的逼好多水| 麻豆国产av国片精品| 亚洲欧美日韩高清在线视频| 悠悠久久av| 成年女人永久免费观看视频| 成人国产综合亚洲| 动漫黄色视频在线观看| 麻豆国产97在线/欧美| 51国产日韩欧美| 人人妻人人看人人澡| 国产av在哪里看| 欧美性猛交╳xxx乱大交人| 三级毛片av免费| 午夜日韩欧美国产| 久久国产乱子免费精品| 嫩草影院入口| 乱码一卡2卡4卡精品| 变态另类成人亚洲欧美熟女| 久久这里只有精品中国| 亚洲精华国产精华精| 天堂影院成人在线观看| 日韩人妻高清精品专区| 岛国在线免费视频观看| 色尼玛亚洲综合影院| 婷婷精品国产亚洲av| 丰满的人妻完整版| 久久久色成人| 国产伦精品一区二区三区四那| 亚洲成人久久性| 国产免费av片在线观看野外av| 日韩欧美 国产精品| 99久久精品一区二区三区| 国内精品一区二区在线观看| 国产极品精品免费视频能看的| 亚洲精品亚洲一区二区| avwww免费| 久久天躁狠狠躁夜夜2o2o| 丰满人妻熟妇乱又伦精品不卡| 国产亚洲精品久久久久久毛片| 亚洲,欧美精品.| 国产精品嫩草影院av在线观看 | 色尼玛亚洲综合影院| 一区二区三区激情视频| 久久精品综合一区二区三区| 特大巨黑吊av在线直播| 欧美三级亚洲精品| 中文字幕熟女人妻在线| 丰满人妻熟妇乱又伦精品不卡| 动漫黄色视频在线观看| 在线观看美女被高潮喷水网站 | 99国产极品粉嫩在线观看| 少妇裸体淫交视频免费看高清| 婷婷丁香在线五月| 精品一区二区三区人妻视频| 少妇裸体淫交视频免费看高清| 成人亚洲精品av一区二区| 婷婷精品国产亚洲av| 日本精品一区二区三区蜜桃| 久久精品国产99精品国产亚洲性色| 欧美不卡视频在线免费观看| 九色成人免费人妻av| 日本撒尿小便嘘嘘汇集6| 日本熟妇午夜| 久久精品影院6| 一级黄片播放器| 日韩国内少妇激情av| 国产主播在线观看一区二区| 无人区码免费观看不卡| 在线观看免费视频日本深夜| 九九热线精品视视频播放| 国产单亲对白刺激| 色哟哟哟哟哟哟| 久久久精品欧美日韩精品| 国产v大片淫在线免费观看| 欧美最新免费一区二区三区 | 国内久久婷婷六月综合欲色啪| 成年女人看的毛片在线观看| 观看美女的网站| 美女高潮的动态| 熟妇人妻久久中文字幕3abv| 国产成年人精品一区二区| 狂野欧美白嫩少妇大欣赏| 国产精品人妻久久久久久| 搡老岳熟女国产| 十八禁人妻一区二区| 99久久精品一区二区三区| 无遮挡黄片免费观看| 久久午夜福利片| 看免费av毛片| 最新中文字幕久久久久| 少妇人妻精品综合一区二区 | 国产精品女同一区二区软件 | 亚洲电影在线观看av| 亚洲国产欧美人成| 丰满人妻熟妇乱又伦精品不卡| 1000部很黄的大片| 国产精品久久久久久人妻精品电影| 乱码一卡2卡4卡精品| 亚洲精品亚洲一区二区| 嫁个100分男人电影在线观看| 国产激情偷乱视频一区二区| 婷婷六月久久综合丁香| 一级黄片播放器| 国产白丝娇喘喷水9色精品| 一二三四社区在线视频社区8| 亚洲人成伊人成综合网2020| 欧美最新免费一区二区三区 | 日本一本二区三区精品| 欧美又色又爽又黄视频| 午夜福利视频1000在线观看| 亚洲国产精品合色在线| 高清日韩中文字幕在线| xxxwww97欧美| 日本黄大片高清| 免费大片18禁| 亚洲三级黄色毛片| 久久亚洲精品不卡| 美女 人体艺术 gogo| 少妇熟女aⅴ在线视频| 国产精品免费一区二区三区在线| 成人鲁丝片一二三区免费| 女同久久另类99精品国产91| 观看美女的网站| 国产 一区 欧美 日韩| 97碰自拍视频| 国产精品久久久久久人妻精品电影| 脱女人内裤的视频| 国产免费av片在线观看野外av| 一进一出抽搐动态| 少妇高潮的动态图| 嫩草影院精品99| 直男gayav资源| 男人舔奶头视频| 最近最新免费中文字幕在线| 国产精品亚洲美女久久久| 久久久久久久久大av| 在线免费观看不下载黄p国产 | 久久中文看片网| 两人在一起打扑克的视频| 女同久久另类99精品国产91| 偷拍熟女少妇极品色| 国产色爽女视频免费观看| 国产野战对白在线观看| 成人av在线播放网站| 国产精品国产高清国产av| 久久精品影院6| 婷婷丁香在线五月| 国产乱人视频| 久久午夜亚洲精品久久| 免费av不卡在线播放| 综合色av麻豆| 怎么达到女性高潮| 国产精品一及| 免费黄网站久久成人精品 | 国产精品久久久久久久久免 | 十八禁人妻一区二区| 国产午夜精品论理片| 日韩欧美三级三区| 亚洲不卡免费看| 日韩欧美国产一区二区入口| 男人和女人高潮做爰伦理| 搞女人的毛片| 露出奶头的视频| 日韩欧美国产在线观看| 亚洲精品一区av在线观看| 桃红色精品国产亚洲av| 国产乱人伦免费视频| www.999成人在线观看| 午夜福利在线观看吧| 又爽又黄无遮挡网站| 麻豆一二三区av精品| 国内精品一区二区在线观看| 国产老妇女一区| 欧美在线黄色| 久久午夜福利片| 韩国av一区二区三区四区| 亚洲激情在线av| 国产单亲对白刺激| av在线观看视频网站免费| 国产亚洲av嫩草精品影院| 欧美激情国产日韩精品一区| 九九热线精品视视频播放| 国产综合懂色| 久久国产乱子伦精品免费另类| 一本一本综合久久| 日本成人三级电影网站| 免费大片18禁| 国产亚洲精品av在线| 波多野结衣高清作品| 中文字幕免费在线视频6| 欧美+亚洲+日韩+国产| 高清毛片免费观看视频网站| 一个人看的www免费观看视频| 我要看日韩黄色一级片| 亚洲三级黄色毛片| 亚洲精品色激情综合| 亚洲欧美精品综合久久99| 精品人妻偷拍中文字幕| 久久午夜亚洲精品久久| 久久精品91蜜桃| 久久6这里有精品| 中文字幕高清在线视频| 天堂√8在线中文| 在线播放国产精品三级| av欧美777| 国产69精品久久久久777片| 99久久久亚洲精品蜜臀av| 18美女黄网站色大片免费观看| 国产熟女xx| 99在线人妻在线中文字幕| 日本三级黄在线观看| 久久人人精品亚洲av| 日本一二三区视频观看| 国产精品人妻久久久久久| 国产三级在线视频| 亚洲av熟女| 久久精品国产亚洲av天美| 日本五十路高清| 麻豆国产av国片精品| 精品不卡国产一区二区三区| 日本 欧美在线| 欧美+日韩+精品| 国产亚洲欧美在线一区二区| 亚洲av成人精品一区久久| 热99在线观看视频| 老司机午夜福利在线观看视频| 亚洲av成人不卡在线观看播放网| 亚洲人成电影免费在线| 免费在线观看影片大全网站| 欧美一区二区亚洲| 日本在线视频免费播放| 日日摸夜夜添夜夜添av毛片 | 欧美色欧美亚洲另类二区| 欧美日韩国产亚洲二区| 国产精品一区二区三区四区久久| 成年免费大片在线观看| 欧美区成人在线视频| 九色成人免费人妻av| 婷婷丁香在线五月| 色哟哟哟哟哟哟| 女人十人毛片免费观看3o分钟| 天堂网av新在线| 亚洲国产精品sss在线观看| 欧美乱妇无乱码| 老熟妇乱子伦视频在线观看| 淫秽高清视频在线观看| 级片在线观看| 此物有八面人人有两片| 一个人观看的视频www高清免费观看| 中文字幕av成人在线电影| 国产高清有码在线观看视频| 亚洲三级黄色毛片| 久久精品国产自在天天线| 国内精品久久久久久久电影| 波野结衣二区三区在线| 欧美性猛交黑人性爽| 久久伊人香网站| 男人舔奶头视频| 啪啪无遮挡十八禁网站| 欧美最黄视频在线播放免费| 精品国产三级普通话版| 一级毛片久久久久久久久女| 久久国产精品人妻蜜桃| av在线蜜桃| 观看美女的网站| 日本一本二区三区精品| 一进一出抽搐gif免费好疼| 嫩草影院新地址| 国产aⅴ精品一区二区三区波| 久久人人精品亚洲av| 欧美成人a在线观看| 小蜜桃在线观看免费完整版高清| 国产精品av视频在线免费观看| 午夜精品在线福利| 国产精品不卡视频一区二区 | 精品午夜福利视频在线观看一区| 亚洲专区中文字幕在线| 性色avwww在线观看| a级一级毛片免费在线观看| 男女做爰动态图高潮gif福利片| 国产视频内射| 动漫黄色视频在线观看| 一个人免费在线观看电影| av专区在线播放| 国产欧美日韩一区二区三| 亚洲人成伊人成综合网2020| 熟女电影av网| 国产高清有码在线观看视频| av专区在线播放| www.色视频.com| 最新在线观看一区二区三区| 午夜两性在线视频| 欧美性猛交黑人性爽| 又爽又黄a免费视频| 日韩欧美精品v在线| 久久久久国内视频| 人妻制服诱惑在线中文字幕| 综合色av麻豆| 人妻丰满熟妇av一区二区三区| 亚洲成人中文字幕在线播放| 毛片女人毛片| 欧美+日韩+精品| 变态另类丝袜制服| 亚洲欧美精品综合久久99| 欧美一区二区精品小视频在线| 夜夜爽天天搞| 亚洲中文日韩欧美视频| 一a级毛片在线观看| 热99re8久久精品国产| 老熟妇乱子伦视频在线观看| 免费大片18禁| 精品国内亚洲2022精品成人| 3wmmmm亚洲av在线观看| 99热6这里只有精品| 亚洲国产高清在线一区二区三| 69人妻影院| 欧美一级a爱片免费观看看| 亚洲美女视频黄频| 免费在线观看成人毛片| 日本成人三级电影网站| 一个人免费在线观看电影| 日日摸夜夜添夜夜添小说| 日韩中字成人| 国产精品美女特级片免费视频播放器| 在线观看66精品国产| 美女xxoo啪啪120秒动态图 | www.色视频.com| 久久久国产成人精品二区| 一区二区三区高清视频在线| 免费大片18禁| 国产精品久久久久久久久免 | 精品乱码久久久久久99久播| 免费在线观看亚洲国产| 国产一级毛片七仙女欲春2| 精品免费久久久久久久清纯| 淫妇啪啪啪对白视频| 国产三级在线视频| 欧美成狂野欧美在线观看| 亚洲中文日韩欧美视频| 国产av不卡久久| 又爽又黄a免费视频| 精华霜和精华液先用哪个| bbb黄色大片| 午夜福利在线观看免费完整高清在 | 最近视频中文字幕2019在线8| 观看免费一级毛片| 欧美bdsm另类| 国产69精品久久久久777片| 国内少妇人妻偷人精品xxx网站| 一边摸一边抽搐一进一小说| 日本熟妇午夜| 国产精品自产拍在线观看55亚洲| 成人一区二区视频在线观看| 黄片小视频在线播放| 亚洲美女搞黄在线观看 | 两人在一起打扑克的视频| 国产伦精品一区二区三区四那| 国产精品综合久久久久久久免费| 1024手机看黄色片| 在线观看66精品国产| 国产高清有码在线观看视频| 在线十欧美十亚洲十日本专区| 久久久精品欧美日韩精品| 亚洲中文日韩欧美视频| 亚洲内射少妇av| 窝窝影院91人妻| 久久人人爽人人爽人人片va | 亚洲精品一卡2卡三卡4卡5卡| 极品教师在线免费播放| 精品久久久久久久人妻蜜臀av| 久久精品影院6| 一本精品99久久精品77| 免费av毛片视频| 欧洲精品卡2卡3卡4卡5卡区| 少妇被粗大猛烈的视频| 欧美中文日本在线观看视频| 99国产极品粉嫩在线观看| 老司机午夜十八禁免费视频| 欧美一区二区精品小视频在线| 久久久色成人| 国产高清视频在线播放一区| 午夜精品在线福利| 麻豆久久精品国产亚洲av| 好男人在线观看高清免费视频| 亚洲精品在线美女| 日韩欧美精品免费久久 | 在线观看午夜福利视频| 在线十欧美十亚洲十日本专区| 偷拍熟女少妇极品色| 亚洲国产日韩欧美精品在线观看| 色哟哟·www| 能在线免费观看的黄片| 欧美不卡视频在线免费观看| 久久精品综合一区二区三区| 成人无遮挡网站| 国产伦在线观看视频一区| 久久精品久久久久久噜噜老黄 | 长腿黑丝高跟| 女人被狂操c到高潮| 国产老妇女一区| 亚洲av日韩精品久久久久久密| 亚洲av电影不卡..在线观看| 麻豆成人av在线观看| 亚洲无线在线观看| 国产探花在线观看一区二区| 少妇的逼好多水| 国产探花在线观看一区二区| 美女高潮喷水抽搐中文字幕| 国产高清三级在线| 97超视频在线观看视频| 乱码一卡2卡4卡精品| 国产91精品成人一区二区三区| 色综合欧美亚洲国产小说| 成人国产一区最新在线观看| 亚洲五月婷婷丁香| 国产精品国产高清国产av| 综合色av麻豆| 国产色爽女视频免费观看| 最新中文字幕久久久久| x7x7x7水蜜桃| 我的老师免费观看完整版| 色播亚洲综合网| 久久久久免费精品人妻一区二区| 天堂动漫精品| 在线播放国产精品三级| 3wmmmm亚洲av在线观看| 国产成人aa在线观看| 亚洲中文字幕日韩| 国产精品女同一区二区软件 | 亚洲男人的天堂狠狠| 亚洲专区中文字幕在线| 欧美黑人巨大hd| netflix在线观看网站| 亚洲av日韩精品久久久久久密| 少妇的逼水好多| 久久久久久国产a免费观看| 中文字幕高清在线视频| 亚洲无线在线观看| 少妇的逼水好多| 国产91精品成人一区二区三区| 99热这里只有是精品在线观看 | 亚洲欧美日韩卡通动漫| 可以在线观看毛片的网站| 日本 av在线| 免费在线观看亚洲国产| 日韩中文字幕欧美一区二区| 免费大片18禁| 日韩大尺度精品在线看网址| 一a级毛片在线观看| 在线免费观看不下载黄p国产 | av欧美777| 级片在线观看| 精品午夜福利在线看| 啦啦啦观看免费观看视频高清| 有码 亚洲区| 亚洲av中文字字幕乱码综合| 18禁在线播放成人免费| 丁香六月欧美| 超碰av人人做人人爽久久| 国产精品电影一区二区三区| 一个人免费在线观看的高清视频| 亚洲,欧美,日韩| 啪啪无遮挡十八禁网站| 成人特级黄色片久久久久久久| 精品人妻熟女av久视频| 午夜福利18| 色综合欧美亚洲国产小说| 国产欧美日韩一区二区三| 看免费av毛片| 国产精品爽爽va在线观看网站| 99国产精品一区二区三区| 色播亚洲综合网| 亚洲电影在线观看av| 成人性生交大片免费视频hd| 久久久久亚洲av毛片大全| 国产69精品久久久久777片| 亚洲精品日韩av片在线观看| 成熟少妇高潮喷水视频| 美女黄网站色视频| 国产伦精品一区二区三区四那| 亚洲狠狠婷婷综合久久图片| 久久精品国产亚洲av涩爱 | 在线看三级毛片| 欧美在线黄色| 精品人妻一区二区三区麻豆 | 国产精品不卡视频一区二区 | 国产黄片美女视频| 给我免费播放毛片高清在线观看| 国产一级毛片七仙女欲春2| 99热6这里只有精品| 久久国产乱子免费精品| 丰满人妻熟妇乱又伦精品不卡| 亚洲18禁久久av| 免费av观看视频| 一夜夜www| 小说图片视频综合网站| 久久午夜亚洲精品久久| 久久久久亚洲av毛片大全| 久久久国产成人精品二区| 国内揄拍国产精品人妻在线| 又黄又爽又刺激的免费视频.| a级毛片免费高清观看在线播放| 内射极品少妇av片p| 久久亚洲真实| 不卡一级毛片| 精品无人区乱码1区二区| eeuss影院久久| 精品一区二区三区av网在线观看| or卡值多少钱| 亚洲色图av天堂| 99在线视频只有这里精品首页| 99国产极品粉嫩在线观看| 校园春色视频在线观看| 五月玫瑰六月丁香| 18+在线观看网站| 免费观看人在逋| 国产老妇女一区| 国产麻豆成人av免费视频| 日本五十路高清| 蜜桃久久精品国产亚洲av| 亚州av有码| 午夜免费男女啪啪视频观看 | 又紧又爽又黄一区二区| 在现免费观看毛片| 99国产极品粉嫩在线观看| 婷婷丁香在线五月| 97超视频在线观看视频| 午夜免费男女啪啪视频观看 | 动漫黄色视频在线观看| 日韩 亚洲 欧美在线| 日本与韩国留学比较| 亚洲男人的天堂狠狠| 亚洲精品色激情综合| 午夜免费男女啪啪视频观看 | 亚洲精品亚洲一区二区| 成年女人毛片免费观看观看9| 黄色女人牲交| 怎么达到女性高潮| 黄色视频,在线免费观看| 少妇熟女aⅴ在线视频| www.www免费av| 久久国产乱子伦精品免费另类| 丁香六月欧美| 一本久久中文字幕| 一a级毛片在线观看| 中文资源天堂在线| 最近在线观看免费完整版| 欧美日本亚洲视频在线播放|