The device preconditioning dependent hysteresis and the consequential performance degradation hinder the actual performance and stability of the perovskite solar cells. Ion migration and charge trapping in the perovsk...The device preconditioning dependent hysteresis and the consequential performance degradation hinder the actual performance and stability of the perovskite solar cells. Ion migration and charge trapping in the perovskite with large contribution from grain boundaries are the most common interpretations for the hysteresis. Yet, the high performing devices often include intermediate hole and electron transporting layers, which can further complicate the dynamical process in the device. Here, by using Kelvin Probe Force Microscopy and Confocal Photoluminescence Microscopy, we elucidate the impact of chargetransporting layers and excess MAI on the spatial and temporal variations of the photovoltage on the MAPbI3-based solar cells. By studying the devices layer by layer, we found that the light-induced ion migration occurs predominantly in the presence of an imbalanced charge extraction in the solar cells, and the charge transporting layers play crucial role in suppressing it. Careful selection and processing of the electron and hole-transporting materials are thus essential for making perovskite solar cells free from the ion migration effect.展开更多
We investigated the surface potential dynamics of a ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIMNT) single crystal using Kelvin probe force microscopy (KPFM). The initial surface potential is a function...We investigated the surface potential dynamics of a ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIMNT) single crystal using Kelvin probe force microscopy (KPFM). The initial surface potential is a function of the applied bias since it reflects the interplay between the polarisation and screen charges. It is suggested that the different rates of tip injected charges are responsible for the asymmetric behaviour of the initial surface potential dependent on the sign of the applied bias. The polarisation, screen and tip injected charges are considered to explain the difference in surface potential dynamics.展开更多
The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate ...The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate the friction and wear properties of the MoS_(2)bilayer at the nanoscale by applying a normal load ranging from 200 to 1,000 nN.Scratch resistance is measured using the scratch mode in FFM based on a linearly increasing load from 100 to 1,000 nN.Kelvin probe force microscopy(KPFM)is performed to locally measure the surface potential in the tested surface to qualitatively measure the wear/removal of Mos,layers and identify critical loads associated with the individual failures of the top and bottom layers.The analysis of the contact potential difference values as well as that of KPFM,friction,and height images show that the wear/removal of the top and bottom layers in the MoS_(2)bilayer system occurred consecutively.The FFM and KPFM results show that the top MoS_(2)layer begins to degrade at the end of the low friction stage,followed by the bottom layer,thereby resulting in a transitional friction stage owing to the direct contact between the diamond tip and SiO_(2)substrate.In the stable third stage,the transfer of lubricious MoS_(2)debris to the tip apex results in contact between the MoS_(2)-transferred tip and SiO_(2).Nanoscratch test results show two ranges of critical loads,which correspond to the sequential removal of the top and bottom layers.展开更多
A surface plasmon(SP)is a fundamental excitation state that exists in metal nanostructures.Over the past several years,the performance of optoelectronic devices has been improved greatly via the SP enhancement effect....A surface plasmon(SP)is a fundamental excitation state that exists in metal nanostructures.Over the past several years,the performance of optoelectronic devices has been improved greatly via the SP enhancement effect.In our previous work,the responsivity of GaN ultraviolet detectors was increased by over 30 times when using Ag nanoparticles.However,the physics of the SP enhancement effect has not been established definitely because of the lack of experimental evidence.To reveal the physical origin of this enhancement,Kelvin probe force microscopy(KPFM)was used to observe the SP-induced surface potential reduction in the vicinity of Ag nanoparticles on a GaN epilayer.Under ultraviolet illumination,the localized field enhancement induced by the SP forces the photogenerated electrons to drift close to the Ag nanoparticles,leading to a reduction of the surface potential around the Ag nanoparticles on the GaN epilayer.For an isolated Ag nanoparticle with a diameter of~200 nm,the distribution of the SP localized field is located within 60 nm of the boundary of the Ag nanoparticle.For a dimer of Ag nanoparticles,the localized field enhancement between the nanoparticles was the strongest.The results presented here provide direct experimental proof of the localized field enhancement.These results not only explain the high performance of GaN detectors observed with the use of Ag nanoparticles but also reveal the physical mechanism of SP enhancement in optoelectronic devices,which will help us further understand and improve the performance of SP-based optoelectronic devices in the future.展开更多
Current-voltage(I-V)characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory(ReRAM).It has been observed that the atmospheri...Current-voltage(I-V)characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory(ReRAM).It has been observed that the atmospheric environment can affect the resistive switching performance,but the origin of this effect is still under debate.Conductive Atomic Force Microscopy(c-AFM)is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory devices.This study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO_(2)thin film by performing c-AFM measurements in ambient air,synthetic air,and argon gas.It is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching,and it can also reduce the resistance at the low resistance state(LRS).Where the moisture in the environment can increase the set and reset voltages,and increase the resistance at LRS.These effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes,which have been further confirmed by Kelvin Probe Force Microscopy(KPFM)measurements.In addition,it is found that the local ionic dynamics of TiO_(2)during the resistive switching are strongly dependent of the environments by performing the FORC-IV(First Order Reversal Curve-Current-Voltage)measurements in the three gas environments.Results in this work can provide a new perspective on the effect of environments on the resistive switching of materials,that is,the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip.展开更多
Vanadium dioxide(VO_(2))undergoes an insulator to metal transition(MIT)and an accompanied phase transition from a monoclinic(M)structure to rutile(R)structure near room temperature,forming the basis for many VO_(2)-ba...Vanadium dioxide(VO_(2))undergoes an insulator to metal transition(MIT)and an accompanied phase transition from a monoclinic(M)structure to rutile(R)structure near room temperature,forming the basis for many VO_(2)-based functional devices.The MIT transition of VO_(2)and the functionality of VO_(2)-based devices can be controlled by a variety of chemical and physical stimuli.With these external stimuli,defects,such as oxygen vacancies,are often inevitably introduced.However,due to the VeO systeminduced challenge to synthesize stable VO_(2)with different oxygen vacancy concentrations,the impact of oxygen vacancies on the resistance and transition of the VO_(2)is not fully understood.Oxygen vacancy,as one of the typical defects in VO_(2),is expected to concentrate at grain boundaries,and hence a concentration gradient of oxygen vacancies may exist between the grains interior and the boundaries,and this suggests a possibility to study the effects of oxygen vacancies on the transition of VO_(2)by probing local phenomena at the grain boundaries.For investigating local phenomena at the grain boundaries,Scanning Probe Microscopy(SPM)techniques are effective,which allows probing the structure and various properties at the nanoscale.In this work,a series of SPM techniques,including Atomic Force Microscopy(AFM),conductive-AFM(c-AFM),Electrochemical Strain Microscopy(ESM),and Kelvin Probe Force Microscopy(KPFM),are employed to measure variations of the surface structure,the resistance,the oxygen vacancy concentration,and the work function between the grain interior and the grain boundary.It has been demonstrated that,for most cases,both the resistance and the work function are lower at the grain boundaries as a result of the accumulation of oxygen vacancies at those positions.In addition,the resistance change induced by the electric field has been observed in the deposited VO_(2)thin films,which may be associated with the generation/annihilation of the oxygen vacancies,rather than charge injection.This work has demonstrated the effects of oxygen vacancies in the transition of VO_(2)by probing the local phenomena at grain boundaries,also provided a new insight into the resistance change of VO_(2)under an electric field.展开更多
We report on an electrostatically formed nanowire （EFN）-based sensor with tunable diameters in the range of 16 nm to 46 nm and demonstrate an EFN- based field-effect transistor as a highly sensitive and robust room ...We report on an electrostatically formed nanowire （EFN）-based sensor with tunable diameters in the range of 16 nm to 46 nm and demonstrate an EFN- based field-effect transistor as a highly sensitive and robust room temperature gas sensor. The device was carefully designed and fabricated using standard integrated processing to achieve the 16 nm EFN that can be used for sensing without any need for surface modification. The effective diameter for the EFN was determined using Kelvin probe force microscopy accompanied by three- dimensional electrostatic simulations. We show that the EFN transistor is capable of detecting 100 parts per million of ethanol gas with bare SiO2.展开更多
By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrop...By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.展开更多
Interfacial reaction is a critical factor of lithium ion battery, but is also complicated and difficult to characterize. Scanning probe microscope(SPM) is one of the most effective tools to reveal the interface recons...Interfacial reaction is a critical factor of lithium ion battery, but is also complicated and difficult to characterize. Scanning probe microscope(SPM) is one of the most effective tools to reveal the interface reconstruction and interfacial properties(including the morphologies, mechanical properties and electricity properties) of energy material at nanoscale and at real time. In this paper, we briefly summarized the principles of AFM, conductive AFM(C-AFM) and Kelvin probe force microscope(KPFM), as well as their application to investigate the interface reconstruction of lithium-ion battery electrode material.展开更多
The kesterite-structured semiconductor Cu_2 Zn Sn(S,Se)_4(CZTSSe) is prepared by spin coating a non-hydrazine precursor and annealing at Se atmosphere. Local electrical and optoelectronic properties of the CZTSSe thin...The kesterite-structured semiconductor Cu_2 Zn Sn(S,Se)_4(CZTSSe) is prepared by spin coating a non-hydrazine precursor and annealing at Se atmosphere. Local electrical and optoelectronic properties of the CZTSSe thin-film are explored by Kelvin probe force microscopy and conductive atomic force microscopy. Before and after irradiation, no marked potential bending and very low current flow are observed at GBs, suggesting that GBs behave as a charge recombination site and an obstacle for charge transport. Furthermore, Cd S nano-islands are synthesized via successive ionic layer adsorption and reaction(SILAR) method on the surface of CZTSSe. By comparing the work function and current flow change of CZTSSe and Cd S in dark and under illumination, we demonstrate photo-induced electrons and holes are separated at the interface of p-n junction and transferred in Cd S and CZTSSe, respectively.展开更多
Atomic force microscopy(AFM)and scanning probe lithography can be used for the mechanical treatment of various surfaces,including polymers,metals,and semiconductors.The technique of nanoshaving,in which materials are ...Atomic force microscopy(AFM)and scanning probe lithography can be used for the mechanical treatment of various surfaces,including polymers,metals,and semiconductors.The technique of nanoshaving,in which materials are removed using the AFM tip,is employed in this work to produce nanopatterns of self-assembled monolayers(SAMs)on two-dimensional(2D)materials.The materials used are monolayers of transition metal dichalcogenides(TMDs),namely,MoS_(2)and WS_(2),which are noncovalently functionalized with perylene diimide(PDI),a perylene derivative.The approach involves rastering an AFM probe across the surface at a controlled increased load in ambient conditions.As a result of the strong bond between PDI SAM and TMD,loads in excess of 1|1N are required to pattern the monolayer.Various predefined patterns,including a grating pattern with feature sizes below 250 nm,are demonstrated.Results indicate the high precision of nanoshaving as an accurate and nondestructive lithographic technique for 2D materials.The work functions of shaved heterostructures are also examined using Kelvin probe force microscopy.展开更多
基金supported by the MEYS project, Czech Republic [No.CZ.02.1.01/0.0/0.0/15_003/0000464 (CAP)]the ’Severo Ochoa’ program for Centers of Excellence in R&D [MINECO, Grant SEV2016-0686]+3 种基金the Natural Science Foundation of Jiangsu Province, China [BK20180601]the Fundamental Research Funds for the Central Universities [JUSRP11834, JUSRP11834B]the Jiangsu Postdoctoral Science Foundation [2018K112C, 2018K113C]funding from the Lab and Equipment Management of Jiangnan University (JDSYS201906)。
文摘The device preconditioning dependent hysteresis and the consequential performance degradation hinder the actual performance and stability of the perovskite solar cells. Ion migration and charge trapping in the perovskite with large contribution from grain boundaries are the most common interpretations for the hysteresis. Yet, the high performing devices often include intermediate hole and electron transporting layers, which can further complicate the dynamical process in the device. Here, by using Kelvin Probe Force Microscopy and Confocal Photoluminescence Microscopy, we elucidate the impact of chargetransporting layers and excess MAI on the spatial and temporal variations of the photovoltage on the MAPbI3-based solar cells. By studying the devices layer by layer, we found that the light-induced ion migration occurs predominantly in the presence of an imbalanced charge extraction in the solar cells, and the charge transporting layers play crucial role in suppressing it. Careful selection and processing of the electron and hole-transporting materials are thus essential for making perovskite solar cells free from the ion migration effect.
文摘We investigated the surface potential dynamics of a ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIMNT) single crystal using Kelvin probe force microscopy (KPFM). The initial surface potential is a function of the applied bias since it reflects the interplay between the polarisation and screen charges. It is suggested that the different rates of tip injected charges are responsible for the asymmetric behaviour of the initial surface potential dependent on the sign of the applied bias. The polarisation, screen and tip injected charges are considered to explain the difference in surface potential dynamics.
基金This study was supported by the Research Program funded by the SeoulTech(Seoul National University of Science and Technology,Republic of Korea).
文摘The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate the friction and wear properties of the MoS_(2)bilayer at the nanoscale by applying a normal load ranging from 200 to 1,000 nN.Scratch resistance is measured using the scratch mode in FFM based on a linearly increasing load from 100 to 1,000 nN.Kelvin probe force microscopy(KPFM)is performed to locally measure the surface potential in the tested surface to qualitatively measure the wear/removal of Mos,layers and identify critical loads associated with the individual failures of the top and bottom layers.The analysis of the contact potential difference values as well as that of KPFM,friction,and height images show that the wear/removal of the top and bottom layers in the MoS_(2)bilayer system occurred consecutively.The FFM and KPFM results show that the top MoS_(2)layer begins to degrade at the end of the low friction stage,followed by the bottom layer,thereby resulting in a transitional friction stage owing to the direct contact between the diamond tip and SiO_(2)substrate.In the stable third stage,the transfer of lubricious MoS_(2)debris to the tip apex results in contact between the MoS_(2)-transferred tip and SiO_(2).Nanoscratch test results show two ranges of critical loads,which correspond to the sequential removal of the top and bottom layers.
基金supported by the National Key R&D Program of China(2016YFB0400101,2016YFB0400900)the National Natural Science Foundation of China(Grant Nos.61574142,61322406 and 61274038)+3 种基金the Special Project for Inter-government Collaboration of the State Key Research and Development Program(2016YFE0118400)the Jilin Provincial Science&Technology Department(Grant No.20150519001JH)the CAS Interdisciplinary Innovation Team,and the Youth Innovation Promotion Association of CAS(Grant No.2015171),For MIS's workthe support was provided by grant No.DE-FG02-11ER46789 from the Materials Sciences and Engineering Division,Office of the Basic Energy Sciences,Office of Science,U.S.Department of Energy.
文摘A surface plasmon(SP)is a fundamental excitation state that exists in metal nanostructures.Over the past several years,the performance of optoelectronic devices has been improved greatly via the SP enhancement effect.In our previous work,the responsivity of GaN ultraviolet detectors was increased by over 30 times when using Ag nanoparticles.However,the physics of the SP enhancement effect has not been established definitely because of the lack of experimental evidence.To reveal the physical origin of this enhancement,Kelvin probe force microscopy(KPFM)was used to observe the SP-induced surface potential reduction in the vicinity of Ag nanoparticles on a GaN epilayer.Under ultraviolet illumination,the localized field enhancement induced by the SP forces the photogenerated electrons to drift close to the Ag nanoparticles,leading to a reduction of the surface potential around the Ag nanoparticles on the GaN epilayer.For an isolated Ag nanoparticle with a diameter of~200 nm,the distribution of the SP localized field is located within 60 nm of the boundary of the Ag nanoparticle.For a dimer of Ag nanoparticles,the localized field enhancement between the nanoparticles was the strongest.The results presented here provide direct experimental proof of the localized field enhancement.These results not only explain the high performance of GaN detectors observed with the use of Ag nanoparticles but also reveal the physical mechanism of SP enhancement in optoelectronic devices,which will help us further understand and improve the performance of SP-based optoelectronic devices in the future.
基金This work is supported by Ministry of Education(Singapore)through National University of Singapore under the Academic Research Grant(AcRF)R-265-000-406-112.One of the authors(WHL)would also like to thank the postgraduate scholarship from National University of Singapore.
文摘Current-voltage(I-V)characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory(ReRAM).It has been observed that the atmospheric environment can affect the resistive switching performance,but the origin of this effect is still under debate.Conductive Atomic Force Microscopy(c-AFM)is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory devices.This study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO_(2)thin film by performing c-AFM measurements in ambient air,synthetic air,and argon gas.It is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching,and it can also reduce the resistance at the low resistance state(LRS).Where the moisture in the environment can increase the set and reset voltages,and increase the resistance at LRS.These effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes,which have been further confirmed by Kelvin Probe Force Microscopy(KPFM)measurements.In addition,it is found that the local ionic dynamics of TiO_(2)during the resistive switching are strongly dependent of the environments by performing the FORC-IV(First Order Reversal Curve-Current-Voltage)measurements in the three gas environments.Results in this work can provide a new perspective on the effect of environments on the resistive switching of materials,that is,the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip.
基金the support from Ministry of Education,Singapore through National University of Singapore on the Academic Research Fund(AcRF)R-265-000-496-112,and R265-000-596-112.
文摘Vanadium dioxide(VO_(2))undergoes an insulator to metal transition(MIT)and an accompanied phase transition from a monoclinic(M)structure to rutile(R)structure near room temperature,forming the basis for many VO_(2)-based functional devices.The MIT transition of VO_(2)and the functionality of VO_(2)-based devices can be controlled by a variety of chemical and physical stimuli.With these external stimuli,defects,such as oxygen vacancies,are often inevitably introduced.However,due to the VeO systeminduced challenge to synthesize stable VO_(2)with different oxygen vacancy concentrations,the impact of oxygen vacancies on the resistance and transition of the VO_(2)is not fully understood.Oxygen vacancy,as one of the typical defects in VO_(2),is expected to concentrate at grain boundaries,and hence a concentration gradient of oxygen vacancies may exist between the grains interior and the boundaries,and this suggests a possibility to study the effects of oxygen vacancies on the transition of VO_(2)by probing local phenomena at the grain boundaries.For investigating local phenomena at the grain boundaries,Scanning Probe Microscopy(SPM)techniques are effective,which allows probing the structure and various properties at the nanoscale.In this work,a series of SPM techniques,including Atomic Force Microscopy(AFM),conductive-AFM(c-AFM),Electrochemical Strain Microscopy(ESM),and Kelvin Probe Force Microscopy(KPFM),are employed to measure variations of the surface structure,the resistance,the oxygen vacancy concentration,and the work function between the grain interior and the grain boundary.It has been demonstrated that,for most cases,both the resistance and the work function are lower at the grain boundaries as a result of the accumulation of oxygen vacancies at those positions.In addition,the resistance change induced by the electric field has been observed in the deposited VO_(2)thin films,which may be associated with the generation/annihilation of the oxygen vacancies,rather than charge injection.This work has demonstrated the effects of oxygen vacancies in the transition of VO_(2)by probing the local phenomena at grain boundaries,also provided a new insight into the resistance change of VO_(2)under an electric field.
文摘We report on an electrostatically formed nanowire （EFN）-based sensor with tunable diameters in the range of 16 nm to 46 nm and demonstrate an EFN- based field-effect transistor as a highly sensitive and robust room temperature gas sensor. The device was carefully designed and fabricated using standard integrated processing to achieve the 16 nm EFN that can be used for sensing without any need for surface modification. The effective diameter for the EFN was determined using Kelvin probe force microscopy accompanied by three- dimensional electrostatic simulations. We show that the EFN transistor is capable of detecting 100 parts per million of ethanol gas with bare SiO2.
文摘By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.
基金supported by the National Key R&D Program of China(2016YFB0700600)Soft Science Research Project of Guangdong Province(No.2017B030301013)Shenzhen Science and Technology Research Grant(ZDSYS201707281026184)。
文摘Interfacial reaction is a critical factor of lithium ion battery, but is also complicated and difficult to characterize. Scanning probe microscope(SPM) is one of the most effective tools to reveal the interface reconstruction and interfacial properties(including the morphologies, mechanical properties and electricity properties) of energy material at nanoscale and at real time. In this paper, we briefly summarized the principles of AFM, conductive AFM(C-AFM) and Kelvin probe force microscope(KPFM), as well as their application to investigate the interface reconstruction of lithium-ion battery electrode material.
基金supported by the National Basic Research Program of China(2011CB9323012011CB808704)+2 种基金the National Natural Science Foundation of China(2112790121373236)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB12020100)
文摘The kesterite-structured semiconductor Cu_2 Zn Sn(S,Se)_4(CZTSSe) is prepared by spin coating a non-hydrazine precursor and annealing at Se atmosphere. Local electrical and optoelectronic properties of the CZTSSe thin-film are explored by Kelvin probe force microscopy and conductive atomic force microscopy. Before and after irradiation, no marked potential bending and very low current flow are observed at GBs, suggesting that GBs behave as a charge recombination site and an obstacle for charge transport. Furthermore, Cd S nano-islands are synthesized via successive ionic layer adsorption and reaction(SILAR) method on the surface of CZTSSe. By comparing the work function and current flow change of CZTSSe and Cd S in dark and under illumination, we demonstrate photo-induced electrons and holes are separated at the interface of p-n junction and transferred in Cd S and CZTSSe, respectively.
基金Science Foundation Ireland,PI_15/IA/3131,Georg Stefan Duesberg。
文摘Atomic force microscopy(AFM)and scanning probe lithography can be used for the mechanical treatment of various surfaces,including polymers,metals,and semiconductors.The technique of nanoshaving,in which materials are removed using the AFM tip,is employed in this work to produce nanopatterns of self-assembled monolayers(SAMs)on two-dimensional(2D)materials.The materials used are monolayers of transition metal dichalcogenides(TMDs),namely,MoS_(2)and WS_(2),which are noncovalently functionalized with perylene diimide(PDI),a perylene derivative.The approach involves rastering an AFM probe across the surface at a controlled increased load in ambient conditions.As a result of the strong bond between PDI SAM and TMD,loads in excess of 1|1N are required to pattern the monolayer.Various predefined patterns,including a grating pattern with feature sizes below 250 nm,are demonstrated.Results indicate the high precision of nanoshaving as an accurate and nondestructive lithographic technique for 2D materials.The work functions of shaved heterostructures are also examined using Kelvin probe force microscopy.
