Study On The Self-assembled Molecular Film Of Alkylthiol On Au(111) Surface

Alkanethiol self-assembled monolayers(SAMS)have been attracted highly attentions during last two decades due to its easy prepared and highly ordered 2D structure.It has great potential in the field of molecular devices and molecular sensors,which is a hot issue in the field of molecular surface structure.Using of scanning tunneling microscope(STM)can realize atomic resolution of molecular imaging,and more accurate information can be provided directly,such as the bonding mechanism of surface molecules.What's more,metal substrate provides an important physical and chemical environment in the process of molecular self-assembling,it has great value to analysis the molecular mechanism of the interface structure during the assembly processing.But so far,in the alkyl thiol molecules system,many fundamental issues are remaining unclear.For example,the structure transformation of different molecular chain length of alkyl mercaptan in the Au(111)surface,the connection between the phase structures of unsaturated adsorption formed strip structure,the adsorption position of molecular self-assembly structures and so on.The main research results were investigated by the Omicron ultra-high vacuum temperature scanning tunneling microscopy(STM),which is operate to obtain the surface structures of alkanethiol SAMs with different chain-length on the Au(111).Dimethyl disulfide(CH3-S-S-CH3)(ADM)and propyl disulfide CH3(CH2)2-S-Au-S-CH3(CH2)2.We make a point that the probe of scanning tunneling microscopy(STM)can manipulate the functional groups for molecular,the cis and Trans configuration of a single molecule on the surface can be constructed,and the molecular switch function can be realized.Gas phase method is used to form the mixed chain molecules film.Methane and propane alkyl mercaptan molecular are deposited on Au(111)surface and two-dimensional crystal structure on the surface of thin film under low coverage is characterized by scanning tunneling microscopy(STM).Through the analysis of the molecular surface structure and the periodic measurement,three strips of unsaturated adsorption phase structure were observed,P(9×(?))strip phase and the structure of the two different P(8.5×(?))strip phase,respectively.According to the study of our molecular arrangement and the periodic structure on the surface of thiol molecules,the thermal dynamic process during the phase changing between saturated adsorption phase and strip phase were understanded.Futhermore,the formation of the three different coverage of strip phase structure were analyzed.Thirdly,the methane and propane alkyl mercaptan molecular SAM was gradually annealed for a propose that to obtain a single thiol molecules thin film.After that,C60 molecules were in situ deposited on propane mercaptan monomolecular layer surface under the low temperature.The experimental data showed that C60 can only spread to the defect site on the surface of the monolayer.Only a single molecule layer can be inserted into Au(111)surface and directly connected with the Au(111)surface.At room temperature,C60 molecule can form the disorderly alkyl mercaptan molecular self-assembly island structure.This island structure is formed under the restriction of self-assembled monolayer,it will be nucleation growth along a certain direction.