We investigated the orientations of interface dipole moments of individual non-planar titanyl phthalocyanine(TiOPc)molecules on Cu(111)and Cu(100)substrates using scanning tunneling microscope(STM)and noncontact atomic force microscope(NC-AFM).The dipole moment orientations corresponding to two different configurations of individual TiOPc molecules were determined unambiguously.The correlation between the actual molecular structures and the corresponding STM topographies is proposed based on the sub-molecular resolution imaging and local contact potential difference(LCPD)measurements.Comparing with the pristine substrate,the LCPD shift due to the adsorption of non-planar molecule is dependent on the permanent molecular dipole,the charge transfer between the surface and the molecule,and the molecular configurations.This work would shed light on tailoring interfacial electronic properties and controlling local physical properties via polar molecule adsorption.
Individual titanyl phthalocyanine(TiOPc)molecules on ultrathin sodium chloride striped films grown on Cu(110)exhibit two different topographies with 8-lobes and 6-lobes when imaged by scanning tunneling microscopy(STM).Direct images of the molecular orbitals of the molecules with 8-lobes are obtained,indicating that the electronic structure of the TiOPc molecule are decoupled from the metallic substrate.For the TiOPc molecule with 6-lobes,the STM images at negative and positive bias polarities show the same structures as 2-fold symmetry except for the 90°rotation with respect to each other.This phenomenon may be attributed to the splitting of the two former degenerate lowest unoccupied molecular orbitals due to the negative charging of the molecule.The identification of the molecular orbital splitting on the ultrathin insulating layer could deepen the understanding of the intrinsic properties of semi-conducting molecules.
It has been demonstrated that intermolecular interaction,crucial in a plenty of chemical and physical processes,may vary in the presence of metal surface.However,such modification is yet to be quantitatively revealed.Here,we present a systematical density functional theory study on adsorbed bis（para-pyridyl）acetylene（BPPA） tetramer on Au（111） surface.We observed unusually high electron density between two head-to-head N atoms,an intermolecular ＂non-bonded＂ region,in adsorbed BPPA tetramer.This exceptional electron density originates from the wavefunction hybridization of the two compressed N lone-electron-pair states of two BPPA,as squeezed by a newly revealed N-Au-N threecenter bonding.This bond,together with the minor contribution from N...H-C intermolecular hydrogen bonding,shortens the N-N distance from over 4 A to 3.30 A and offers an attractive lateral interacting energy of 0.60 eV,effectively to a surface-confined in-plane pressure.The overlapped non-bonding vvavefunction hybridization arising from the effective pressure induced by the N-Au-N three-center bonding,as not been fully recognized in earlier studies,was manifested in non-contact Atomic Force Microscopy.
In an indentation test,the effective Young's modulus of a film/substrate bilayer heterostructure varies with the indentation depth,a phenomenon known as the substrate effect.In previous studies investigating this,only the Young's modulus of the film was unknown.Once the effective Young's modulus of a film/substrate structure is determined at a given contact depth,the Young's modulus of the film can be uniquely determined,i.e.,there is a one-to-one relation between the Young's modulus of the film and the film/substrate effective Young's modulus.However,at times it is extremely challenging or even impossible to measure the film thickness.Furthermore,the precise definition of the layer/film thickness for a two-dimensional material can be problematic.In the current study,therefore,the thickness of the film and its Young's modulus are treated as two unknowns that must be determined.Unlike the case with one unknown,there are infinite combinations of film thickness and Young's modulus which can yield the same effective Young's modulus for the film/substrate.An inverse problem is formulated and solved to extract the Young's modulus and thickness of the film from the indentation depth-load curve.The accuracy and robustness of the inverse problem-solving method are also demonstrated.
微波是整个电磁频谱非常重要的组成部分,可以与物质发生丰富的相互作用;而原子力显微术(Atomic Force Microscopy,AFM)有超高的空间分辨率,是纳米研究的核心工具。将微波技术与AFM结合将实现一种全新的扫描微波显微术(Scanning Microwave Microscopy,SMM)。该技术可以探测各种样品(包括导体、半导体、绝缘体及其它新型材料)在微纳米尺度的多种电学性质,如载流子类型、介电常数、电导率和导磁系数等;以及实现微纳米尺度下微波探测技术,如NMR、ESR等,具有非常广阔的应用前景。文中综述了SMM的基本原理,仪器组成,并介绍了其在电学性质探测、各种新型材料、生物等方面的前沿应用实例。最后,文章展望了扫描微波显微术的进一步技术发展和应用研究。
