Characterization of electric properties of nanomaterials usually involves fabricating field effect transistors （FET） and deriving materials properties from device performances. However, the quality of electrode cont...Characterization of electric properties of nanomaterials usually involves fabricating field effect transistors （FET） and deriving materials properties from device performances. However, the quality of electrode contacts in FET devices heavily influences the device performance, which makes it difficult to obtain the intrinsic electric properties of nanomaterials. Dielectric force microscopy （DFM）, a contactless method developed recently, can detect the low-frequency dielectric responses of nanomaterials without electric contact, which avoids the influence of electric contact and can be used to study the intrinsic conductivity of nanomaterials. Here we study the influences of surface adsorbates on the conductivity of ZnO nanowires （NWs） by using FET and DFM methods. The conductivity of ZnO NW is much larger in N2 atmosphere than that in ambient environment as measured by FET device, which is further proven by DFM measurement that the ZnO NW exhibits larger dielectric response in N2 environment, and the influence of electrode contacts on measurement can be ruled out. Based on these results, it can be concluded that the adsorbates on ZnO NW surface highly influence the conductivity of ZnO NW rather than the electrode contact. This work also verifies the capability of DFM in measuring electric properties of nanomaterials.展开更多
Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorpti...Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorptive positions in energy, and methanol molecule interacts with the Pt surface through oxygen atoms. Moreover, we also explored the possible dissociation pathways of methanol on the Pt surface, and suggested that the products of dissociation can be controlled by the external manipulation.展开更多
The potential energy surface for the migration of an extra Ga atom on the GaAs（001） β2（2×4） surfuce was mapped out by performing calculations at the level of analytical bond-order potential. Based on this ca...The potential energy surface for the migration of an extra Ga atom on the GaAs（001） β2（2×4） surfuce was mapped out by performing calculations at the level of analytical bond-order potential. Based on this calculations, we found some lower-energy sites for the adsorption of an extra Ga atom in the surface, which were in agreement with the experimental data. Moreover, many possible pathways for an extra Ga atom diffusing in this surface were revealed. According to the relative energies of the possible pathways, the individual Ga adatoms preferably keep their diffusion in two pathways parallel to the As dimers. This result can be understood using the strain caused by the diffusing Ga atom in the pathways. In addition, the simulated kinetic processes of the extra Ga atom diffusing in different pathways at finite temperatures support the prediction from our calculated potential energy surface.展开更多
The influence of the magnetism of transition metal oxide,nickel(II)oxide(NiO),on its surface reactivity and the dependence of surface reactivity on surface orientation and reactant magnetism were studied by density fu...The influence of the magnetism of transition metal oxide,nickel(II)oxide(NiO),on its surface reactivity and the dependence of surface reactivity on surface orientation and reactant magnetism were studied by density functional theory plus U calculations.We considered five different antiferromagnetically ordered structures and one ferromagnetically ordered structure,NiO(001)and Ni(011)surfaces,paramagnetic molecule NO,and nonparamagnetic molecule CO.The calculations showed that the dependence of surface energies on magnetism was modest,ranging from49to54meV/?2for NiO(001)and from162to172meV/?2for NiO(011).On NiO(001),both molecules preferred the top site of the Ni cation exclusively for all NiO magnetic structures considered,and calculated adsorption energies ranged from?0.33to?0.37eV for CO and from?0.42to?0.46eV for NO.On NiO(011),both molecules preferred the bridge site of two Ni cations irrespective of the NiO magnetism.It was found that rather than the long‐range magnetism of bulk NiO,the local magnetic order of two coordinated Ni cations binding to the adsorbed molecule had a pronounced influence on adsorption.The calculated NO adsorption energy at the(↑↓)bridge sites ranged from?0.99to?1.05eV,and become stronger at the(↑↑)bridge sites with values of?1.21to?1.30eV.For CO,although the calculated adsorption energies at the(↑↓)bridge sites(?0.73to?0.75eV)were very close to those at the(↑↑)bridge sites(?0.71to?0.72eV),their electron hybridizations were very different.The present work highlights the importance of the local magnetic order of transition metal oxides on molecular adsorption at multi‐fold sites.展开更多
Abstract Goethite widely exists among ocean sediments; it plays an important role in fixing heavy metals and adsorbing organic contaminants. So the understanding of the adsorbing process of water molecule on its surfa...Abstract Goethite widely exists among ocean sediments; it plays an important role in fixing heavy metals and adsorbing organic contaminants. So the understanding of the adsorbing process of water molecule on its surface will be very helpful to further reveal such environmental friendly processes. The configuration, electronic properties and interaction energy of water molecules adsorbed on pnma goethite （010） surface were investigated in detail by using density functional theory on 6-31G （d,p） basis set and projec- tor-augment wave （PAW） method. The mechanism of the interaction between goethite surface and H20 was proposed. Despite the differences in total energy, there are four possible types of water molecule adsorption configurations on goethite （010） surface （Aa, Ab, Ba, Bb）, forming coordination bond with surface Fe atom. Results of theoretical modeling indicate that the dissociation process of adsorbed water is an endothermic reaction with high activation energy. The dissociation of adsorbed water molecule is a proton transportation process between water＇s O atoms and surface. PDOS results indicate that the bonding between 1-120 and （010） surface is due to the overlapping of water＇s 2p orbitals and Fe＇s 3d orbitals. These results clarify the mechanism on how adsorbed water is dissociated on the surface of goethite and potentially provide useful information of the surface chemistry of goethite.展开更多
The interface between a two-dimensional(2D)atomic crystal and a metal surface can be regarded as a nanoreactor, in which molecule adsorption and catalytic reactions may occur. In this work, we demonstrate that oxygen ...The interface between a two-dimensional(2D)atomic crystal and a metal surface can be regarded as a nanoreactor, in which molecule adsorption and catalytic reactions may occur. In this work, we demonstrate that oxygen intercalation and desorption occur at the interface between hexagonal boron nitride(h-BN) overlayer and Pt(111) surface by using near-ambient pressure X-ray photoelectron spectroscopy(NAP-XPS), photoemission electron microscopy, and low-energy electron microscopy.Furthermore, CO oxidation under the h-BN cover was also observed by NAP-XPS. The present results indicate that the nanospace under the 2D cover can be used for surface reactions, in which novel surface chemistry may be induced by the nanoconfinement effect.展开更多
The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica...The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica surface, with the hydrophobic alkyl groups pointing outward from the surface. Remarkably, such ethanol bilayer is laterally well-ordered with patterned adsorption sites. Each ethanol molecule in the first layer donates one hydrogen bond to the surface basal oxygen atoms and accepts one hydrogen bond from that in the second layer. The ethanol molecules within the bilayer exhibit constrained lateral mobility and delayed dynamics as compared with bulk ethanol, whereas those on top of the bilayer have bulk-like characteristics.展开更多
The surface geometry, electronic structure, and magnetism of Eu@C60 monolayer absorbed on Ag(111) have been investigated within the framework of density functional theory. The Eu@C60 monolayer has been constructed on ...The surface geometry, electronic structure, and magnetism of Eu@C60 monolayer absorbed on Ag(111) have been investigated within the framework of density functional theory. The Eu@C60 monolayer has been constructed on Ag(111) substrate by one of the hexagon faces of C60 downward and its mirror plane face parallel to Ag(111). The Eu@C60 monolayer induces a recon- struction of the Ag(111) substrate and the perpendicular distance between the Eu@C60 and Ag(111) surface is 2.06 A, being shorter than that between C60 and Ag(lll) surface by 0.05A. There is no chemical bond formed between the Eu@C60 and Ag(111), and only 0.55e transferred from Ag(111) to Eu@C60. A large magnetic moment about 6.80/μB per unit cell is found for Eu@C60/Ag(111) system.展开更多
文摘Characterization of electric properties of nanomaterials usually involves fabricating field effect transistors （FET） and deriving materials properties from device performances. However, the quality of electrode contacts in FET devices heavily influences the device performance, which makes it difficult to obtain the intrinsic electric properties of nanomaterials. Dielectric force microscopy （DFM）, a contactless method developed recently, can detect the low-frequency dielectric responses of nanomaterials without electric contact, which avoids the influence of electric contact and can be used to study the intrinsic conductivity of nanomaterials. Here we study the influences of surface adsorbates on the conductivity of ZnO nanowires （NWs） by using FET and DFM methods. The conductivity of ZnO NW is much larger in N2 atmosphere than that in ambient environment as measured by FET device, which is further proven by DFM measurement that the ZnO NW exhibits larger dielectric response in N2 environment, and the influence of electrode contacts on measurement can be ruled out. Based on these results, it can be concluded that the adsorbates on ZnO NW surface highly influence the conductivity of ZnO NW rather than the electrode contact. This work also verifies the capability of DFM in measuring electric properties of nanomaterials.
文摘Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorptive positions in energy, and methanol molecule interacts with the Pt surface through oxygen atoms. Moreover, we also explored the possible dissociation pathways of methanol on the Pt surface, and suggested that the products of dissociation can be controlled by the external manipulation.
基金ACKNOWLEDGMENTS This work was supported by the Fund of University of Science and Technology of China, the Fund of Chinese Academy of Science, and the National Natural Science Foundation of China （No.50121202 and No.60176024）.
文摘The potential energy surface for the migration of an extra Ga atom on the GaAs（001） β2（2×4） surfuce was mapped out by performing calculations at the level of analytical bond-order potential. Based on this calculations, we found some lower-energy sites for the adsorption of an extra Ga atom in the surface, which were in agreement with the experimental data. Moreover, many possible pathways for an extra Ga atom diffusing in this surface were revealed. According to the relative energies of the possible pathways, the individual Ga adatoms preferably keep their diffusion in two pathways parallel to the As dimers. This result can be understood using the strain caused by the diffusing Ga atom in the pathways. In addition, the simulated kinetic processes of the extra Ga atom diffusing in different pathways at finite temperatures support the prediction from our calculated potential energy surface.
基金supported by the National Natural Science Foundation of China(91645202)the National Key R&D Program of China(2017YFB602205)+1 种基金the National Basic Research Program of China(2013CB834603)the Frontier Science Key Project of Chinese Academy of Sciences(QYZDJ-SSW-SLH054)~~
文摘The influence of the magnetism of transition metal oxide,nickel(II)oxide(NiO),on its surface reactivity and the dependence of surface reactivity on surface orientation and reactant magnetism were studied by density functional theory plus U calculations.We considered five different antiferromagnetically ordered structures and one ferromagnetically ordered structure,NiO(001)and Ni(011)surfaces,paramagnetic molecule NO,and nonparamagnetic molecule CO.The calculations showed that the dependence of surface energies on magnetism was modest,ranging from49to54meV/?2for NiO(001)and from162to172meV/?2for NiO(011).On NiO(001),both molecules preferred the top site of the Ni cation exclusively for all NiO magnetic structures considered,and calculated adsorption energies ranged from?0.33to?0.37eV for CO and from?0.42to?0.46eV for NO.On NiO(011),both molecules preferred the bridge site of two Ni cations irrespective of the NiO magnetism.It was found that rather than the long‐range magnetism of bulk NiO,the local magnetic order of two coordinated Ni cations binding to the adsorbed molecule had a pronounced influence on adsorption.The calculated NO adsorption energy at the(↑↓)bridge sites ranged from?0.99to?1.05eV,and become stronger at the(↑↑)bridge sites with values of?1.21to?1.30eV.For CO,although the calculated adsorption energies at the(↑↓)bridge sites(?0.73to?0.75eV)were very close to those at the(↑↑)bridge sites(?0.71to?0.72eV),their electron hybridizations were very different.The present work highlights the importance of the local magnetic order of transition metal oxides on molecular adsorption at multi‐fold sites.
基金financial supports from the National Natural Science Foundation of China (Nos.50673085,20677053)
文摘Abstract Goethite widely exists among ocean sediments; it plays an important role in fixing heavy metals and adsorbing organic contaminants. So the understanding of the adsorbing process of water molecule on its surface will be very helpful to further reveal such environmental friendly processes. The configuration, electronic properties and interaction energy of water molecules adsorbed on pnma goethite （010） surface were investigated in detail by using density functional theory on 6-31G （d,p） basis set and projec- tor-augment wave （PAW） method. The mechanism of the interaction between goethite surface and H20 was proposed. Despite the differences in total energy, there are four possible types of water molecule adsorption configurations on goethite （010） surface （Aa, Ab, Ba, Bb）, forming coordination bond with surface Fe atom. Results of theoretical modeling indicate that the dissociation process of adsorbed water is an endothermic reaction with high activation energy. The dissociation of adsorbed water molecule is a proton transportation process between water＇s O atoms and surface. PDOS results indicate that the bonding between 1-120 and （010） surface is due to the overlapping of water＇s 2p orbitals and Fe＇s 3d orbitals. These results clarify the mechanism on how adsorbed water is dissociated on the surface of goethite and potentially provide useful information of the surface chemistry of goethite.
基金supported by the National Natural Science Foundation of China(21222305,21373208,and21033009)the National Basic Research Program of China(2011CB932704,2013CB933100,and 2013CB834603)+1 种基金the Key Research Program of the Chinese Academy of Science(KGZD-EWT05)The Advanced Light Source and beamlines 11.0.2 and 9.3.1 are supported by the Director,Office of Energy Research,Office of Basic Energy Sciences,and Chemical Sciences Division of the US Department of Energy under contracts No.DE-AC02-05CH11231
文摘The interface between a two-dimensional(2D)atomic crystal and a metal surface can be regarded as a nanoreactor, in which molecule adsorption and catalytic reactions may occur. In this work, we demonstrate that oxygen intercalation and desorption occur at the interface between hexagonal boron nitride(h-BN) overlayer and Pt(111) surface by using near-ambient pressure X-ray photoelectron spectroscopy(NAP-XPS), photoemission electron microscopy, and low-energy electron microscopy.Furthermore, CO oxidation under the h-BN cover was also observed by NAP-XPS. The present results indicate that the nanospace under the 2D cover can be used for surface reactions, in which novel surface chemistry may be induced by the nanoconfinement effect.
基金Supported by Grants from Chinese Academy of Sciences,the National Natural Science Foundation of China under Grant No. 10825520National Basic Research Program of China under Grant No. 2007CB936000China Postdoctoral Science Foundation under Grant No. 20100480645
文摘The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica surface, with the hydrophobic alkyl groups pointing outward from the surface. Remarkably, such ethanol bilayer is laterally well-ordered with patterned adsorption sites. Each ethanol molecule in the first layer donates one hydrogen bond to the surface basal oxygen atoms and accepts one hydrogen bond from that in the second layer. The ethanol molecules within the bilayer exhibit constrained lateral mobility and delayed dynamics as compared with bulk ethanol, whereas those on top of the bilayer have bulk-like characteristics.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10874039 and 11147172)support from the National Basic Research Program of China (Grant No. 2011CB606401)
文摘The surface geometry, electronic structure, and magnetism of Eu@C60 monolayer absorbed on Ag(111) have been investigated within the framework of density functional theory. The Eu@C60 monolayer has been constructed on Ag(111) substrate by one of the hexagon faces of C60 downward and its mirror plane face parallel to Ag(111). The Eu@C60 monolayer induces a recon- struction of the Ag(111) substrate and the perpendicular distance between the Eu@C60 and Ag(111) surface is 2.06 A, being shorter than that between C60 and Ag(lll) surface by 0.05A. There is no chemical bond formed between the Eu@C60 and Ag(111), and only 0.55e transferred from Ag(111) to Eu@C60. A large magnetic moment about 6.80/μB per unit cell is found for Eu@C60/Ag(111) system.
