Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable 'fingerprint' for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3-15 nanometres, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.

R. Zhang;Y. Zhang;振超 董;S. Jiang;C. Zhang;L. G. Chen;L. Zhang;Y. Liao;J. Aizpurua;Y. Luo;金龙 杨;建国 侯

Nature

2013

The single-electron tunneling (SET) spectroscopy of C60 molecule in a double-barrier tunnel junction is investigated by combining the scanning tunneling spectroscopy experiment and the theoretical simulation using the modified orthodox theory. The interplay between the SET effect and the discrete energy levels of C60 molecule is studied. Three types of SET spectroscopies with different characters are obtained, corresponding to different tunneling processes and consistent with the previous theoretical prediction. Both the charging mode and resonance mode can arouse the current increase in the SET spectroscopy. The resonance mode is realized mainly by two mechanisms, including the resonance when the electron spans the second junction after already spanning the first junction. Some previous confused results have been clarified. Our results show that three types of SET spectroscopies can be together examined to quantitatively determine the frontier orbitals of the nanostructure by identifying the modes of various current increases.

Bin Li;长淦 曾;Jin Zhao;金龙 杨;建国 侯;清时 朱

Journal of Chemical Physics

2006

The structure and electronic property at the cleaved (001) surfaces of the newly discovered pnictide superconductors BaFe_2-x Co_x As₂ with x ranging from 0 to 0.32 are systematically investigated by scanning tunneling microscopy. A √2×√2 surface structure is revealed to dominate for all the compounds and is identified to be Ba layer with half Ba atoms lifted off by combination with theoretical simulation. Charge inhomogeneity is observed at this √2×√2 surface associated with an energy gap of about 30 meV for all the compounds.

Hui Zhang;Jun Dai;Yujing Zhang;Danru Qu;Huiwen Ji;G. Wu;X. F. Wang;X. H. Chen;Bing Wang;长淦 曾;金龙 杨;建国 侯

Physical Review B - Condensed Matter and Materials Physics

2010-3-18

Tin oxide (SnO ₂ ) nanowires have been synthesized in bulk quantities at lower temperature (680 °C) by thermal evaporation of SnO powder. These as-synthesized SnO ₂ nanowires are single crystals with [3 0 1] growth axis, with diameters ranging from 10 to 190 nm and lengths extending to tens of micrometers. The growth of SnO ₂ nanowires synthesized by lower-temperature evaporation is dominated by a self-catalytic vapor-liquid-solid (VLS) mechanism. The self-catalytic effect in VLS process has been described.

翌庆 陈;Xuefeng Cui;Kun Zhang;Dengyu Pan;Shuyuan Zhang;Bing Wang;建国 侯

Chemical Physics Letters

2003-2-7

A tungsten tip and an iron-coated tungsten tip were used to investigate cobalt phthalocyanine molecules absorbed on a Au(111) surface. Similar STM images but different STS curves were obtained above the central part of the molecules. Theoretical analysis points out that the delocalized orbital of ligands hybridized with the Au surface at 0.4 eV below Fermi level can be detected and enhanced with an iron-coated tungsten tip due to the extended spatial distribution of the frontier orbital in the tip. As the spatial distribution of the frontier orbital in the tungsten tip is localized, the hybrid state cannot be detected above the central part of the molecule. These results indicate that the appropriateness of selection and preparation of the STM tip can probe richer chemistry and physics on surfaces.

Zhenpeng Hu;Lan Chen;Aidi Zhao;Zhenyu Li;Bing Wang;金龙 杨;建国 侯

Journal of Physical Chemistry C

2008-10-9

Orientationally ordered structures of two-dimensional (2D) C₆₀ at low temperature have been investigated theoretically and experimentally. Using total energy optimization with a phenomenological potential, we find the ground state is a close packed hexagonal lattice in which all the molecules have the same orientation. Several local minima of the potential energy surface are found to be associated with other 1 x 1 lattices as well as 2 x 2 lattices. The energies of the orientational domain boundaries of the 1 x 1 lattices are also computed, and two kinds of which yield negative values. A majority of these theoretical findings are confirmed by our low-temperature scanning tunneling microscopy study of a 2D C₆₀ array supported on a self-assembled monolayer.

Lan Feng Yuan;金龙 杨;Haiqian Wang;长淦 曾;群祥 李;Bing Wang;建国 侯;清时 朱;东敏 陈

Journal of the American Chemical Society

2003-1-8

A knowledge of adsorption behaviors of oxygen on the model system of the reduced rutile TiO₂(110)-1×1 surface is of great importance for an atomistic understanding of many chemical processes. We present a scanning tunneling microcopy (STM) study on the adsorption of molecular oxygen either at the bridge-bonded oxygen vacancies (BBO_V) or at the hydroxyls (OH) on the TiO₂(110)-1×1 surface. Using an in situ O₂ dosing method, we are able to directly verify the exact adsorption sites and the dynamic behaviors of molecular O₂. Our experiments provide direct evidence that an O₂ molecule can intrinsically adsorb at both the BBO_V and the OH sites. It has been identified that, at a low coverage of O₂, the singly adsorbed molecular O₂ at BBO _V can be dissociated through an intermediate state as driven by the STM tip. However, singly adsorbed molecular O₂ at OH can survive from such a tip-induced effect, which implies that the singly adsorbed O₂ at OH is more stable than that at BBO_V. It is interesting to observe that when the BBO_Vs are fully filled with excess O₂ dosing, the adsorbed O₂ molecules at BBO_V tend to be nondissociative even under a higher bias voltage of 2.2 V. Such a nondissociative behavior is most likely attributed to the presence of two or more O₂ molecules simultaneously adsorbed at a BBO_V with a more stable configuration than singly adsorbed molecular O₂ at a BBO_V.

Shijing Tan;Yongfei Ji;Yan Zhao;Aidi Zhao;Bing Wang;金龙 杨;建国 侯

Journal of the American Chemical Society

2011-2-16

The in situ direct-current conductance behaviors of Cu/C₆₀ nano-scale granular films have been investigated experimentally. The results show that the incorporation of Cu into C₆₀ greatly increases the conductance of the film. The orientational phase transition that exists in pure C₆₀ single crystals still retains in the Cu/C₆₀ coevaporated films, while the transition temperature range is significantly widened. The interactions between the nano-scale Cu clusters and C₆₀ grains are discussed.

Xiang Li;Hai Qian Wang;建国 侯

Chinese Physics Letters

2000

We present a joint experimental and theoretical study on the geometric and electronic states and the initial oxidation of the (2×3) -Sr/Si (100) surface. With scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS) measurements combined with ab initio calculations, the atomic geometry and the electronic states of the (2×3) -Sr/Si (100) surface are identified. The dimerization of the Si atoms in the single atom row based on a (1×3) Si substrate model plays a critical role in stabilization of the surface structure and in determining the electronic properties. At the very initial oxidation of the surface, four features corresponding to the primary adsorption and oxidation sites are determined. Three of them are corresponding to the most favored oxidation sites with single oxygen molecules, whose local density of states gives semiconducting behavior. One is corresponding to the oxidation site with two oxygen molecules, whose local density of states gives metallic behavior. These features all exhibit dark spots with different shapes in the occupied state images but display either dark spots or bright protrusions depending on the different oxidation sites in the empty state images. Compared with the theoretical calculations, the plausible adsorption and oxidation models are proposed.

Wenhan Du;Bing Wang;Lei Xu;Zhenpeng Hu;Xuefeng Cui;必才 潘;金龙 杨;建国 侯

Journal of Chemical Physics

2008

Cs2 Ag F4 forms a layered perovskite structure and contains 4 d9 metal ions, similar to the 3 d9 Cu cuprates. However, the cuprates are antiferromagnetic, while Cs2 Ag F4 is ferromagnetic. Here we investigate the electronic and magnetic properties of Cs2 Ag F4 using density functional theory (DFT) to clarify the origin of its ferromagnetism. The ground state is found to be ferromagnetic and nearly semimetallic. Because of Jahn-Teller distortions in the [Ag F6] 4- octahedron, the ground state has a staggered order of z2 - x2 and z2 - y2 orbitals. The superexchange interaction through the Ag (z2 - x2) -F-Ag (z2 - y2) bridge stabilizes the ferromagnetism. In order to take into account the on-site Coulomb interaction, we also perform DFT+U calculations. The insulating state becomes the ground state, while the ferromagnetism and orbital order of z2 - x2 and z2 - y2 are still preserved.

Er Jun Kan;Lan Feng Yuan;金龙 杨;建国 侯

Physical Review B - Condensed Matter and Materials Physics

2007-7-13