Shanwei Hu

Growth and electronic structure of Sm on thin Al2O3/Ni3Al(111) films

The growth and electronic structure of vapor-deposited Sm on a well-ordered Al(2)O(3)/Ni(3)Al(111) ultrathin film under ultrahigh vacuum conditions at room temperature have been studied comprehensively using synchrotron radiation photoemission spectroscopy, X-ray photoelectron spectroscopy, work function measurements, scanning tunneling microscopy, and low-energy electron diffraction. Our results indicate that at room temperature Sm grows in a layer-by-layer fashion up to at least 1 ML, followed by three-dimensional growth. The interaction of Sm with Al(2)O(3) thin films leads to an initial oxidation of Sm, accompanied by a parallel reduction of the Al(2)O(3) substrate. Both the oxidation states of Sm(2+) and Sm(3+) are found at low coverage (<1 ML). The concentration of Sm(2+) saturates below 0.4 ML, while that of Sm(3+) keeps increasing until the metallic state of Sm appears at high coverages.

Chiral Kagome Lattices from On-surface Synthesized Molecules

Kagome lattices have attracted much attention owing to their potential applications in spin-frustrated magnetism and host-guest chemistry. Examples toward the fabrication of 2D Kagome lattices reported previously have in common that the precursor molecules were typically deposited on the surface structurally intact with no chemical reactions accompanied. Herein, by using a combination of synchrotron radiation photoelectron spectroscopy (SRPES) and scanning tunneling microscopy (STM), we demonstrated the fabrication of two types of chiral Kagome lattices from on-surface synthesized organometallic compounds, which are known as intermediates of Glaser coupling on silver single crystal surfaces. These Kagome lattices are stabilized by the interplay of various intermolecular interactions, including Br⋅⋅⋅Br bonds, C-Br⋅⋅⋅π bonds and π-π stacking. The chiral transference and host-guest supramolecular structure in the novel Kagome lattices were also studied. Our studies may pave a new way to engineer complex supramolecular networks through on-surface reactions.

Sm on CeO2(111): A Case for Ceria Modification via Strong Metal–Ceria Interaction

The growth, electronic structure and stability of Sm on ordered CeO2(111) thin films grown on Cu(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), low energy electron diffraction, and scanning tunneling microscopy (STM). Metallic samarium was deposited on the CeO2(111) surface by thermal evaporation under ultrahigh vacuum conditions at room temperature. The XPS data suggest that metallic Sm is oxidized to Sm3+ upon the deposition of Sm on CeO2, accompanied by the reduction of Ce4+ to Ce3+. With increasing the Sm coverage, the concentration of Ce3+ increases monotonically. After depositing 6 ML of Sm, only Ce3+ is observed within the detection depth of XPS. The STM results indicate that Sm exhibits a two-dimensional growth on the CeO2(111) surface at low coverages. Annealing to higher temperatures leads to the agglomeration of Sm particles and concurrent diffusion of Sm into the ceria film. These results illustrate that Sm can modify both the electronic and structural properties of ceria.

Electronic states of Ca/PC61BM: Mechanism of low work function metal as interfacial material

We have studied the electronic states at Ca/PC61BM interface using photoemission spectroscopy. It is found that the state of unoccupied molecular orbitals of the top molecular layer (TML) becomes occupied by the electrons transferred from the Ca atoms. The work function of the heavily doped TML of PC61BM film is smaller than that of metal Ca, and thus the contact between the TML and metal Ca is Ohmic. A transition layer (TL) of several molecular layers forms beneath the TML due to the diffusion of the Ca atoms. The TL is conductive and aligns its Fermi level with the negative integer charge transfer level of the interior PC61BM. The built-in electric field in the TL facilitates the electron transport from the interior of the PC61BM film to the TML.We have studied the electronic states at Ca/PC61BM interface using photoemission spectroscopy. It is found that the state of unoccupied molecular orbitals of the top molecular layer (TML) becomes occupied by the electrons transferred from the Ca atoms. The work function of the heavily doped TML of PC61BM film is smaller than that of metal Ca, and thus the contact between the TML and metal Ca is Ohmic. A transition layer (TL) of several molecular layers forms beneath the TML due to the diffusion of the Ca atoms. The TL is conductive and aligns its Fermi level with the negative integer charge transfer level of the interior PC61BM. The built-in electric field in the TL facilitates the electron transport from the interior of the PC61BM film to the TML.

Nickel Adatoms Induced Tautomeric Dehydrogenation of Thymine Molecules on Au(111)

Tautomerization of nucleobases may induce base mismatches resulting in the abnormal disturbance of gene replication and expression, which has therefore attracted widespread interests in many disciplines. Metal atoms participating in a variety of important biological processes are found to be able to affect the nucleobase tautomerization as evidenced by many theoretical and spectroscopic studies. To get the real-space evidence and to unravel the underlying mechanism for the metal-induced tautomerization, especially from the keto form to the enol one, the interplay of high-resolution scanning tunneling microscopy imaging/manipulation and density functional theory (DFT) calculations has been employed. We present a process showing the Ni adatom-induced keto-enol tautomeric dehydrogenation of thymine molecules on Au(111). The key to making such a process feasible is the Ni atoms which greatly lower the energy barrier for the tautomerization from keto to enol form, which is rationalized by extensive DFT-based transition-state search calculations.