• <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.

    中文字幕av成人在线电影| 美女xxoo啪啪120秒动态图| 九草在线视频观看| 真实男女啪啪啪动态图| 欧美成人免费av一区二区三区| 丝袜美腿在线中文| 国产精品av视频在线免费观看| 国产三级在线视频| 免费av不卡在线播放| 中文字幕免费在线视频6| 国模一区二区三区四区视频| 七月丁香在线播放| 欧美三级亚洲精品| 人人妻人人澡人人爽人人夜夜 | 国产精品久久久久久久电影| 欧美潮喷喷水| 嘟嘟电影网在线观看| 狂野欧美白嫩少妇大欣赏| 美女cb高潮喷水在线观看| 男女视频在线观看网站免费| 国产精品三级大全| 亚洲伊人久久精品综合 | 国产不卡一卡二| 日本免费一区二区三区高清不卡| 看免费成人av毛片| 精品久久久久久久人妻蜜臀av| 精品人妻一区二区三区麻豆| 超碰97精品在线观看| 人妻系列 视频| 国产亚洲精品久久久com| 亚洲av电影在线观看一区二区三区 | 伦精品一区二区三区| 国产av一区在线观看免费| 人妻少妇偷人精品九色| 亚洲aⅴ乱码一区二区在线播放| 国产精品一区二区三区四区久久| 少妇丰满av| 国产三级中文精品| 亚洲色图av天堂| 一级爰片在线观看| 热99re8久久精品国产| 亚洲五月天丁香| 国产成人福利小说| 男人舔女人下体高潮全视频| 国产av码专区亚洲av| 国产午夜精品一二区理论片| 国产精品久久电影中文字幕| 国产美女午夜福利| 国产成人a∨麻豆精品| 91在线精品国自产拍蜜月| 能在线免费看毛片的网站| 在线观看美女被高潮喷水网站| 丰满人妻一区二区三区视频av| 日韩精品青青久久久久久| h日本视频在线播放| 三级男女做爰猛烈吃奶摸视频| 日日摸夜夜添夜夜添av毛片| 亚洲人成网站高清观看| 成人亚洲精品av一区二区| 久久99热6这里只有精品| 亚洲精品国产av成人精品| 91精品伊人久久大香线蕉| 美女xxoo啪啪120秒动态图| 成人特级av手机在线观看| 精品久久久久久久久av| 亚洲国产欧洲综合997久久,| 黑人高潮一二区| 国产av不卡久久| 国产男人的电影天堂91| 男女下面进入的视频免费午夜| 日本黄色视频三级网站网址| 成人高潮视频无遮挡免费网站| 久久久欧美国产精品| 国产av一区在线观看免费| 亚洲人成网站在线播| 国产人妻一区二区三区在| 日日干狠狠操夜夜爽| 久久久精品94久久精品| 成人特级av手机在线观看| 精品久久久久久久久av| 国产精品一区二区三区四区久久| 长腿黑丝高跟| 亚洲内射少妇av| 亚洲欧洲国产日韩| 亚洲成人精品中文字幕电影| 天天躁夜夜躁狠狠久久av| 2021天堂中文幕一二区在线观| 午夜福利网站1000一区二区三区| 色网站视频免费| 国产探花极品一区二区| 国产伦一二天堂av在线观看| 亚洲国产精品久久男人天堂| 午夜精品国产一区二区电影 | 又爽又黄a免费视频| 成人亚洲精品av一区二区| 韩国高清视频一区二区三区| 久久久国产成人免费| 国产精品熟女久久久久浪| 国语对白做爰xxxⅹ性视频网站| 少妇裸体淫交视频免费看高清| 国产一区二区在线av高清观看| 久久99热这里只有精品18| 波多野结衣高清无吗| 寂寞人妻少妇视频99o| 国产黄片美女视频| 一个人看视频在线观看www免费| 国产亚洲av片在线观看秒播厂 | 成人一区二区视频在线观看| 国产乱人偷精品视频| 色视频www国产| 最近的中文字幕免费完整| 亚洲va在线va天堂va国产| 一区二区三区四区激情视频| 九九热线精品视视频播放| 亚洲av.av天堂| av在线观看视频网站免费| 日本免费一区二区三区高清不卡| 在线天堂最新版资源| 久久鲁丝午夜福利片| 天堂av国产一区二区熟女人妻| 亚洲不卡免费看| 一卡2卡三卡四卡精品乱码亚洲| 少妇熟女欧美另类| 国产69精品久久久久777片| 精品无人区乱码1区二区| 欧美色视频一区免费| 成人av在线播放网站| 亚洲最大成人手机在线| 能在线免费看毛片的网站| 亚洲高清免费不卡视频| 91精品伊人久久大香线蕉| 美女内射精品一级片tv| 亚洲av熟女| 观看美女的网站| 国产黄色小视频在线观看| 少妇裸体淫交视频免费看高清| 国产精品精品国产色婷婷| 最近视频中文字幕2019在线8| 久久久精品94久久精品| 看片在线看免费视频| 秋霞在线观看毛片| av卡一久久| 久久韩国三级中文字幕| 美女内射精品一级片tv| 亚洲精品影视一区二区三区av| 美女高潮的动态| 国产色爽女视频免费观看| 国产av一区在线观看免费| 国产综合懂色| 久久这里有精品视频免费| 亚洲性久久影院| 国语自产精品视频在线第100页| 午夜福利在线观看免费完整高清在| 久久热精品热| 日韩av在线免费看完整版不卡| 色噜噜av男人的天堂激情| 七月丁香在线播放| 色综合站精品国产| 一夜夜www| 欧美日韩国产亚洲二区| 麻豆成人av视频| 插逼视频在线观看| 精品人妻偷拍中文字幕| 亚洲精品成人久久久久久| 爱豆传媒免费全集在线观看| 久久久久久久午夜电影| 听说在线观看完整版免费高清| 搡老妇女老女人老熟妇| 欧美成人一区二区免费高清观看| 久久久色成人| 99久国产av精品国产电影| 热99re8久久精品国产| 国产视频内射| 别揉我奶头 嗯啊视频| 精品久久久久久久久久久久久| 久久久精品大字幕| 国产探花在线观看一区二区| 日日摸夜夜添夜夜添av毛片| 欧美+日韩+精品| 老司机影院毛片| 男女啪啪激烈高潮av片| 国产一区二区三区av在线| 亚洲精品色激情综合| 欧美一区二区亚洲| 麻豆成人午夜福利视频| 晚上一个人看的免费电影| 夜夜爽夜夜爽视频| 国产成人一区二区在线| 少妇熟女aⅴ在线视频| 亚洲国产高清在线一区二区三| 国产爱豆传媒在线观看| 亚洲精品,欧美精品| 美女黄网站色视频| 日韩强制内射视频| 岛国在线免费视频观看| 99久久精品国产国产毛片| 国产黄色视频一区二区在线观看 | 色网站视频免费| 国产一区二区在线观看日韩| 爱豆传媒免费全集在线观看| 欧美性感艳星| av女优亚洲男人天堂| 别揉我奶头 嗯啊视频| 看片在线看免费视频| 黄色配什么色好看| 寂寞人妻少妇视频99o| 中文欧美无线码| 日韩欧美三级三区| 男女国产视频网站| 免费观看性生交大片5| 国产精品久久久久久av不卡| 午夜免费激情av| 韩国av在线不卡| 99久久人妻综合| 久久久久久久久中文| 亚洲欧美日韩东京热| 午夜福利高清视频| 国产伦精品一区二区三区视频9| 精品久久国产蜜桃| 91久久精品国产一区二区成人| 大香蕉97超碰在线| 少妇人妻精品综合一区二区| 极品教师在线视频| 老师上课跳d突然被开到最大视频| 99热这里只有是精品50| 美女被艹到高潮喷水动态| 国产免费男女视频| 国产av码专区亚洲av| 男女啪啪激烈高潮av片| www日本黄色视频网| 免费av毛片视频| 国产国拍精品亚洲av在线观看| av在线天堂中文字幕| 91久久精品国产一区二区成人| 毛片女人毛片| 亚洲av电影不卡..在线观看| 成人一区二区视频在线观看| 久久久久国产网址| 天堂中文最新版在线下载 | 久久亚洲精品不卡| 国产精品三级大全| 日日摸夜夜添夜夜爱| 三级国产精品欧美在线观看| 三级男女做爰猛烈吃奶摸视频| 国产av码专区亚洲av| 国产av在哪里看| 黑人高潮一二区| 亚洲欧美日韩卡通动漫| 好男人在线观看高清免费视频| 超碰97精品在线观看| 一个人看视频在线观看www免费| 国产爱豆传媒在线观看| 久久久久精品久久久久真实原创| 久久精品综合一区二区三区| 日日摸夜夜添夜夜爱| 最近手机中文字幕大全| 啦啦啦啦在线视频资源| 99久久成人亚洲精品观看| 国产又色又爽无遮挡免| 免费无遮挡裸体视频| 麻豆久久精品国产亚洲av| 五月伊人婷婷丁香| 久久精品影院6| 日韩精品青青久久久久久| 欧美日韩精品成人综合77777| 中文精品一卡2卡3卡4更新| 91在线精品国自产拍蜜月| 午夜精品在线福利| 女的被弄到高潮叫床怎么办| 天堂网av新在线| 国产免费男女视频| 我的老师免费观看完整版| 亚洲国产精品sss在线观看| www.色视频.com| 亚洲av电影在线观看一区二区三区 | 国产精品久久久久久av不卡| 日韩一区二区三区影片| 男女那种视频在线观看| 国产白丝娇喘喷水9色精品| 日产精品乱码卡一卡2卡三| 精品午夜福利在线看| 久久6这里有精品| 午夜激情欧美在线| 日韩视频在线欧美| 天堂中文最新版在线下载 | 国产精品久久久久久精品电影小说 | 最近视频中文字幕2019在线8| 国模一区二区三区四区视频| 蜜桃亚洲精品一区二区三区| 中文字幕av在线有码专区| ponron亚洲| 国产精品国产三级国产av玫瑰| 91精品伊人久久大香线蕉| 亚洲人与动物交配视频| av线在线观看网站| 久久精品国产亚洲av涩爱| 日本五十路高清| 有码 亚洲区| 少妇熟女欧美另类| 亚洲av成人精品一区久久| 国内少妇人妻偷人精品xxx网站| 久久综合国产亚洲精品| 中文字幕制服av| 国产精品乱码一区二三区的特点| 男女下面进入的视频免费午夜| 乱人视频在线观看| 男插女下体视频免费在线播放| 国产精品一区www在线观看| 精品久久久久久久久久久久久| 精品熟女少妇av免费看| 男女下面进入的视频免费午夜| 国产免费视频播放在线视频 | 最近的中文字幕免费完整| 中文在线观看免费www的网站| 美女脱内裤让男人舔精品视频| 亚洲一级一片aⅴ在线观看| av在线天堂中文字幕| 欧美zozozo另类| 久久久国产成人免费| 女人被狂操c到高潮| 级片在线观看| 国产熟女欧美一区二区| 久久久久久久久大av| 亚洲最大成人av| 亚洲aⅴ乱码一区二区在线播放| 久久国内精品自在自线图片| 特大巨黑吊av在线直播| 欧美一级a爱片免费观看看| 欧美+日韩+精品| 国产av码专区亚洲av| 91aial.com中文字幕在线观看| 久久亚洲精品不卡| 69人妻影院| 亚洲va在线va天堂va国产| 久久久久久久国产电影| 欧美潮喷喷水| 亚洲精品aⅴ在线观看| 日韩欧美精品v在线| 国产精品一区二区三区四区久久| 性色avwww在线观看| 一级黄片播放器| 亚洲天堂国产精品一区在线| 亚洲av中文字字幕乱码综合| 久久久久国产网址| 亚洲自拍偷在线| 97超视频在线观看视频| 99九九线精品视频在线观看视频| 国产精品熟女久久久久浪| 久久精品国产99精品国产亚洲性色| 亚洲天堂国产精品一区在线| 国产精品精品国产色婷婷| 亚洲四区av| 亚洲国产成人一精品久久久| 51国产日韩欧美| 国产在线一区二区三区精 | 欧美一区二区亚洲| 永久免费av网站大全| 精华霜和精华液先用哪个| 最近视频中文字幕2019在线8| 一级毛片久久久久久久久女| 午夜精品在线福利| 精品久久久久久成人av| 国产v大片淫在线免费观看| 天堂网av新在线| 亚洲成av人片在线播放无| 真实男女啪啪啪动态图| 男的添女的下面高潮视频| 色哟哟·www| 久久久久九九精品影院| 国产探花在线观看一区二区| 一区二区三区高清视频在线| 国产欧美另类精品又又久久亚洲欧美| 免费观看的影片在线观看| 高清在线视频一区二区三区 | 日韩成人伦理影院| 亚洲中文字幕日韩| 久久久久久久久大av| 亚洲高清免费不卡视频| 亚洲精品一区蜜桃| h日本视频在线播放| 精品久久久久久久久亚洲| 日韩强制内射视频| 日韩亚洲欧美综合| 日本三级黄在线观看| 亚洲在久久综合| 国产亚洲5aaaaa淫片| 变态另类丝袜制服| 少妇人妻精品综合一区二区| 日本一本二区三区精品| 精品不卡国产一区二区三区| 热99在线观看视频| 亚洲av电影在线观看一区二区三区 | 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 日产精品乱码卡一卡2卡三| 97超视频在线观看视频| 久久6这里有精品| a级毛色黄片| 午夜免费男女啪啪视频观看| 一级黄色大片毛片| 村上凉子中文字幕在线| 日韩强制内射视频| 一级黄片播放器| 看片在线看免费视频| 成人毛片a级毛片在线播放| 男女边吃奶边做爰视频| 99久国产av精品| 亚洲成色77777| 在线观看一区二区三区| 有码 亚洲区| 久久人人爽人人片av| 久久久久久久亚洲中文字幕| 欧美最新免费一区二区三区| 亚洲av日韩在线播放| 久久久成人免费电影| 久久韩国三级中文字幕| 女的被弄到高潮叫床怎么办| 成人高潮视频无遮挡免费网站| 一区二区三区高清视频在线| 国产av不卡久久| 成人漫画全彩无遮挡| 蜜桃亚洲精品一区二区三区| .国产精品久久| 国产精品久久久久久精品电影| 日韩av在线大香蕉| 一卡2卡三卡四卡精品乱码亚洲| 久久久久免费精品人妻一区二区| 午夜日本视频在线| 日韩三级伦理在线观看| 国产淫片久久久久久久久| 国产精品一二三区在线看| 国产激情偷乱视频一区二区| 网址你懂的国产日韩在线| 亚洲国产欧洲综合997久久,| 在线免费十八禁| 色5月婷婷丁香| 菩萨蛮人人尽说江南好唐韦庄 | 日本爱情动作片www.在线观看| 国产成人精品一,二区| 一个人看的www免费观看视频| 久久精品国产自在天天线| 一级毛片我不卡| 亚洲在线观看片| 欧美又色又爽又黄视频| 精品久久久久久久久av| 久久国内精品自在自线图片| 天堂av国产一区二区熟女人妻| 边亲边吃奶的免费视频| 亚洲国产欧洲综合997久久,| 色播亚洲综合网| 99热这里只有精品一区| 成人高潮视频无遮挡免费网站| 国产精品无大码| 18禁裸乳无遮挡免费网站照片| 在线免费十八禁| 简卡轻食公司| 久久久久久久久久成人| 亚洲精品,欧美精品| 视频中文字幕在线观看| 久久草成人影院| 蜜臀久久99精品久久宅男| 男女视频在线观看网站免费| 国产在线一区二区三区精 | 亚洲av中文字字幕乱码综合| 久久国产乱子免费精品| 一夜夜www| 欧美成人免费av一区二区三区| 国产白丝娇喘喷水9色精品| 国产欧美另类精品又又久久亚洲欧美| 精品欧美国产一区二区三| 免费观看精品视频网站| 我的老师免费观看完整版| 高清av免费在线| 日韩 亚洲 欧美在线| 蜜桃久久精品国产亚洲av| 国产精品1区2区在线观看.| 婷婷六月久久综合丁香| 亚洲欧美清纯卡通| 久久精品国产鲁丝片午夜精品| 女人久久www免费人成看片 | 91久久精品国产一区二区成人| av线在线观看网站| av天堂中文字幕网| 亚洲av免费在线观看| 一级毛片我不卡| 免费人成在线观看视频色| 日本免费一区二区三区高清不卡| 国产av不卡久久| 精品无人区乱码1区二区| 两性午夜刺激爽爽歪歪视频在线观看| 3wmmmm亚洲av在线观看| 色播亚洲综合网| 国产 一区 欧美 日韩| 国产免费福利视频在线观看| 亚洲国产欧美在线一区| 国语对白做爰xxxⅹ性视频网站| 精品人妻一区二区三区麻豆| 99视频精品全部免费 在线| 国产一区亚洲一区在线观看| videossex国产| 男女那种视频在线观看| 两个人的视频大全免费| 丰满乱子伦码专区| 成人鲁丝片一二三区免费| 一个人看视频在线观看www免费| 欧美日韩精品成人综合77777| 最近中文字幕高清免费大全6| 精品99又大又爽又粗少妇毛片| 国产精品国产高清国产av| 色综合亚洲欧美另类图片| 最近手机中文字幕大全| 国产高清三级在线| 亚洲精品日韩av片在线观看| 久久国内精品自在自线图片| 亚洲欧美成人精品一区二区| 免费播放大片免费观看视频在线观看 | 免费人成在线观看视频色| 自拍偷自拍亚洲精品老妇| 久久久久九九精品影院| 夜夜爽夜夜爽视频| 日韩中字成人| 成人av在线播放网站| 免费av观看视频| 美女国产视频在线观看| 禁无遮挡网站| 国产午夜精品论理片| 久久久成人免费电影| 午夜爱爱视频在线播放| 国产伦一二天堂av在线观看| 午夜a级毛片| 最近手机中文字幕大全| 午夜精品一区二区三区免费看| 欧美精品一区二区大全| 91久久精品国产一区二区三区| 欧美极品一区二区三区四区| 一级黄色大片毛片| 日本猛色少妇xxxxx猛交久久| 久久久久久久国产电影| 国产成人精品久久久久久| 嫩草影院入口| 亚洲国产精品国产精品| av在线观看视频网站免费| 精品久久久久久久末码| 亚洲人成网站高清观看| 国产av在哪里看| 性插视频无遮挡在线免费观看| 成人二区视频| 老司机影院毛片| 淫秽高清视频在线观看| 日本三级黄在线观看| 国产不卡一卡二| 亚洲国产色片| 成人毛片60女人毛片免费| 一边摸一边抽搐一进一小说| 啦啦啦韩国在线观看视频| 亚洲av中文av极速乱| 国产老妇伦熟女老妇高清| 亚洲最大成人中文| 听说在线观看完整版免费高清| 亚洲国产精品国产精品| 在线观看av片永久免费下载| 99久久精品国产国产毛片| 欧美日韩国产亚洲二区| 七月丁香在线播放| av线在线观看网站| 男女啪啪激烈高潮av片| 精品免费久久久久久久清纯| 国产在视频线在精品| 久久久久精品久久久久真实原创| 国产精品熟女久久久久浪| 国产白丝娇喘喷水9色精品| 精品免费久久久久久久清纯| 男女那种视频在线观看| 少妇被粗大猛烈的视频| 久热久热在线精品观看| 国产av码专区亚洲av| 激情 狠狠 欧美| 老女人水多毛片| 汤姆久久久久久久影院中文字幕 | 国产精品电影一区二区三区| 国产三级在线视频| 丰满少妇做爰视频| 久久久欧美国产精品| 欧美bdsm另类| 免费黄色在线免费观看| 亚洲成色77777| 国产精品精品国产色婷婷| 欧美日韩国产亚洲二区| 五月玫瑰六月丁香| 99久国产av精品| 国产极品精品免费视频能看的| 久久综合国产亚洲精品| 男女边吃奶边做爰视频| 日韩一区二区三区影片| 国产熟女欧美一区二区| 我要搜黄色片| 亚洲丝袜综合中文字幕| 国产高清视频在线观看网站| 国产一区有黄有色的免费视频 | 亚洲av成人精品一区久久| 国产欧美另类精品又又久久亚洲欧美| 国产久久久一区二区三区| av在线观看视频网站免费| 国产真实乱freesex| av福利片在线观看| 久久6这里有精品| 看免费成人av毛片| 激情 狠狠 欧美| 成人欧美大片| 精品午夜福利在线看| 亚洲三级黄色毛片| 最新中文字幕久久久久| 国产精品永久免费网站| 黄片无遮挡物在线观看| 热99re8久久精品国产| 精品人妻视频免费看|