Photoelectric Properties Of Amine Self-assembled Monolayer Based On Conducting Atomic Force Microscopy

It is one of the most fundamental scientific issue to explore charge transport across molecules.Self-assembled monolayers(SAM)are ordered molecular assemblies formed by adsorption of specific head group functional groups on the surface.They are spontaneously formed,simple to prepare,which have been widely used to study microscale charge transport.To explore SAM charge transport mechanism,it is necessary to build metal-molecular-metal junction.Conductive probe atomic force microscopy(CP-AFM)is a relatively simple and convenient method for building metal-molecular-metal junction.We mainly grow self-assembled monolayer on the gold surface by the interaction of amino and gold to explore their photoelectric properties.The first is to study the hopping transport in sub-1 nm molecular junction base on monolayer with amine as anchoring group.Anthracene-2,6-diamine(AND)and naphthalene-2,6-diamine(NTD)self-assembled monolayers on gold surface,whose length is about?1 nm,were measured by conductive probe atomic force microscope(CP-AFM).The precise temperature dependent measurement of AND SAM reveaed a exponential dependence of the conductance,indicating hopping is the dominant charge transport mechanism.Theoretical model base on single level tunneling and hopping was also used to analyze the I-V character and confirm the hopping transport as well.The control experiments of anthracene-2,6-dithiol(Anth(SH)₂)and anthracen-2-amine(ANA)show that the transport mechanism is tunneling.Therefore,there is may be another effect at the interface between the diamine molecule and the electrode in actual experiments.Using reflection-absorption infrared spectroscopy,we found a single layer of water molecules on the surface of the diamine SAM under very low humidity conditions which probably serves as a stairway to hopping transport.Then,the electrical properties of the diamine DPA self-assembled monolayer were studied by conductive probe atomic force microscope.The I-V characteristics are well fitted by hopping theoretical model,indicating that the charge transport mechanism of the diamine DPA self-assembled monolayer is hopping transport.At a scanning bias of±0.1 V,the current increased by 10 times after illumination,indicating that the diamine DPA is a very good photoresponsive material.Therefore,it is expected to make a major breakthrough in photoresponsive molecular devices.