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Research Interests

We are interested in molecule-substrate interface problems associated with molecular electronics, organic electronics and graphene-related devices, including:

1. Self-assembled functional molecular nanostructure arrays for their applications in molecular electronics, organic electronics, and solid state quantum computation

Molecular self-assembly on surfaces or surface nanotemplates via weak but selective noncovalent interactions, including electrostatic forces, hydrogen bonds, van-der-Waals forces, and metal-ligand interactions, offers a promising bottom-up approach to fabricate molecular nanostructure arrays with desired functionalities over macroscopic areas. The objectives of this sub-program are (i) to understand how the intermolecular interactions and molecule-substrate interfacial interactions determine the molecular self-assembly on surfaces, and (ii) to fabricate tunable and well-ordered 2D arrays of molecular nanostructures for device applications. The experiments will be carried out in a customer-designed low-temperature scanning tunneling microscopy (LT-STM, Omicron).

2. Molecular-level interface controlled organic thin films for organic photovoltaic devices

The aim of this sub-program is to investigate the interface properties of various molecular-level interface-controlled organic thin films or organic-organic heterojunctions, including electronic energy level alignment at the molecule-substrate interfaces, supramolecular packing and molecular orientation at the organic-organic heterojunctions, orientation dependent interface properties, and the charge and energy transfer at the organic-organic heterojunction interfaces. The experiments will be mainly carried out in a Singapore synchrotron light source (SSLS) using high-resolution photoemission spectroscopy (PES), near-edge x-ray absorption fine structure measurement (NEXAFS) and resonant photoemission spectroscopy (RPES).

3. Interface problems associated with graphene-related devices

Monocrystalline graphitic films with one or few-layer thickness have attracted much attention recently due to their exotic properties, such as the existence of massless Dirac fermions, quantum Hall effect, and gate control of transport (electron or hole) properties. In particular, it has been demonstrated that ultrathin graphene films epitaxially grown on commercial silicon carbide substrates by thermal decomposition in vacuum can be patterned using standard nanolithography methods, making it compatible with current semiconductor technology. The main aim of this project targets for the large scale (wafer-size) production of high-quality graphene films for their device application. The growth mechanism, surface transfer doping, electronics structures of graphene, and various surface modification schemes to manipulate the electronic properties of graphene will be also studied.

Publications

Low- Temperature Scanning Tunneling Microscopy Investigation of Epitaxial Growth of F16CuPc Thin Films on Ag(111)"
Huang H, Chen Wei*, Wee ATS*, J. Phys. Chem. C. 112, 14913-14918 (2008). Cover in issue 39 25th Sep.

“Self-Assembled Organic Donor/Acceptor Nanojunction Arrays”
Chen Wei*, Zhang HL, Huang H, Chen L, Wee ATS*, Appl. Phys. Lett.92, 193301 (2008) (cover image in the 12th May issue). Highlighted by Nature Nanotechnology 3, 375 (2008).

“2D Pentacene:PTCDA supramolecular chiral networks on Ag(111)”
Chen Wei*, Li H, Huang H, Fu YX, Zhang HL, Ma J*, Wee ATS*, J. Am. Chem. Soc. 130, 12285-12289 (2008).

“Molecular Orientation Transition of Organic Thin Films on Graphite: the Effect of Intermolecular Electrostatic and Interfacial Dispersion Forces”
Chen Wei*, Huang H, Wee ATS*, Chemical Communication 4276-4278 (2008).

“Orientationally ordered C60 on p-sexiphenyl nanostripes on Ag(111)”
Chen Wei*, Zhang HL, Huang H, Chen L, Wee ATS*, ACS Nano 2, 693 (2008).

“Preferential trapping of C60 in nanomesh voids” (communication)
Zhang HL, Chen Wei*, Huang H, Chen L, Wee ATS*, J. Am. Chem. Soc. 130, 2720 (2008).

“Tunable arrays of C60 molecular chains”
Chen L, Chen Wei*, Huang H, Zhang HL, Yuhara J, and Wee ATS*, Advanced Materials. 20, 484 (2008).

“Molecular Orientation Dependent Interfacial Dipole at the F16CuPc/CuPc Organic Heterojunction Interface”
Chen Wei*, Chen S, Huang H, Qi DC, Gao XY, Wee ATS*, Appl. Phys. Lett. 92, 063308 (2008).

“C60 molecular chain on α-sexithiophene nanostripes”
Zhang HL, Chen Wei*, Chen L, Huang H, Wang XS, Yuhara J, and Wee ATS*, Small 3, 2015 (2007).

“Molecular Orientation of PTCDA Thin Films at Organic Heterojunction Interfaces”
Chen Wei*, Huang H, Chen S, Chen L, Zhang HL, Gao XY, and Wee ATS*, Appl. Phys. Lett. 91, 114102 (2007).

“Surface transfer p-type doping of epitaxial graphene”
Chen Wei*, Chen S, Qi DC, Gao XY, and Wee ATS*, J. Am. Chem. Soc. 129,10418 (2007).

“Surface transfer doping of organic semiconductors using functionalized self-assembled monolayers”
Chen Wei, Gao XY, Qi DC, Chen S, Chen ZK, and Wee ATS*, Advanced Functional Materials, 17,1339 (2007).

“Effect of functional group (fluorine) of aromatic thiols on the electron transfer at the molecule-metal interface”
Chen Wei, Wang L, Huang C, Lin TT, Gao XY, Loh KP, Chen Zhi Kuan, and Wee ATS*, J. Am. Chem. Soc. 128, 935 (2006).

“Atomic structure of the 6H-SiC(0001) nanomesh”
Chen Wei, Xu H, Liu L, Gao XY, Qi DC, Peng GW, Tan SC, Feng YP, Loh KP, and Wee ATS*, Surf. Sci. 596, 176 (2005).Perspective article by Rosei F, Surf. Sci. 600, 1-5 (2006)