Scanning tunneling spectroscopy

About: Scanning tunneling spectroscopy is a research topic. Over the lifetime, 7886 publications have been published within this topic receiving 213828 citations.

Site dependence of the apparent shape of a molecule in scanning tunneling micoscope images: Benzene on Pt{111}

Abstract: We present scanning tunneling microscope images of benzene adsorbed on the Pt{111} surface. We find three distinct types of images for isolated benzene molecules, depending upon the benzene adsorption site. This site dependence is in agreement with recent theoretical calculations, and may limit the usefulness of the scanning tunneling microscope in elucidating the structures of adsorpted molecules.

Vibrationally resolved fluorescence from organic molecules near metal surfaces in a scanning tunneling microscope.

Abstract: Intrinsic molecular fluorescence from porphyrin molecules on Au(100) has been realized by using a nanoscale multimonolayer decoupling approach with nanoprobe excitation in the tunneling regime. The molecular origin of luminescence is established by the observed well-defined vibrationally resolved fluorescence spectra. The molecules fluoresce at low ``turn-on'' voltages for both bias polarities, suggesting an excitation mechanism via hot electron injection from either tip or substrate. The excited molecules decay radiatively through Franck-Condon ${\ensuremath{\pi}}^{*}\mathrm{\text{\ensuremath{-}}}\ensuremath{\pi}$ transitions.

Negative differential resistance in the scanning-tunneling spectroscopy of organic molecules

Abstract: In the interpretation of scanning-tunneling spectroscopy data on molecular nanostructures the tunneling conductance is often assumed to be proportional to the local density of states of the molecule. This precludes the possibility of observing negative differential resistance (NDR). We report here the observation of NDR in the current-voltage $(I\ensuremath{-}V)$ characteristics of a self-assembled monolayer of $4\ensuremath{-}p\ensuremath{-}\mathrm{terphenylthiol}$ molecules on the Au(111) surface measured using a platinum tip. We argue that the NDR arises from narrow features in the local density of states of the tip apex atom and show that depending on the electrostatic potential profile across the system, NDR could be observed in one or both bias directions.

Direct Observation of Lanthanide(III)-Phthalocyanine Molecules on Au(111) by Using Scanning Tunneling Microscopy and Scanning Tunneling Spectroscopy and Thin-Film Field-Effect Transistor Properties of Tb(III)- and Dy(III)-Phthalocyanine Molecules

Abstract: The crystal structures of double-decker single molecule magnets (SMM) LnPc(2) (Ln = Tb(III) and Dy(III); Pc = phthalocyanine) and non-SMM YPc(2) were determined by using X-ray diffraction analysis. The compounds are isomorphous to each other. The compounds have metal centers (M = Tb(3+), Dy(3+), and Y(3+)) sandwiched by two Pc ligands via eight isoindole-nitrogen atoms in a square-antiprism fashion. The twist angle between the two Pc ligands is 41.4 degrees. Scanning tunneling microscopy was used to investigate the compounds adsorbed on a Au(111) surface, deposited by using the thermal evaporation in ultrahigh vacuum. Both MPc(2) with eight lobes and MPc with four lobes, which has lost one Pc ligand, were observed. In the scanning tunneling spectroscopy images of TbPc molecules at 4.8 K, a Kondo peak with a Kondo temperature (T(K)) of approximately 250 K was observed near the Fermi level (V = 0 V). On the other hand, DyPc, YPc, and MPc(2) exhibited no Kondo peak. To understand the observed Kondo effect, the energy splitting of sublevels in a crystal field should be taken into consideration. As the next step in our studies on the SMM/Kondo effect in Tb-Pc derivatives, we investigated the electronic transport properties of Ln-Pc molecules as the active layer in top- and bottom-contact thin-film organic field effect transistor devices. Tb-Pc molecule devices exhibit p-type semiconducting properties with a hole mobility (mu(H)) of approximately 10(-4) cm(2) V(-1) s(-1). Interestingly, the Dy-Pc based devices exhibited ambipolar semiconducting properties with an electron mobility (mu(e)) of approximately 10(-5) and a mu(H) of approximately 10(-4) cm(2) V(-1) s(-1). This behavior has important implications for the electronic structure of the molecules.