Co-reporter:Arthur Yu, Shaowei Li, Gregory Czap, and W. Ho
Nano Letters 2016 Volume 16(Issue 9) pp:5433-5436
Publication Date(Web):August 16, 2016
DOI:10.1021/acs.nanolett.6b01824
The coupling of tunneling electrons with the tip-nanocluster-substrate junction plasmon was investigated by monitoring light emission in a scanning tunneling microscope (STM). Gold atoms were evaporated onto the ∼5 Å thick Al2O3 thin film grown on the NiAl (110) surface where they formed nanoclusters 3–7 nm wide. Scanning tunneling spectroscopy (STS) of these nanoclusters revealed quantum-confined electronic states. Spatially resolved photon imaging showed localized emission hot spots. Size dependent study and light emission from nanocluster dimers further support the viewpoint that coupling of tunneling electrons to the junction plasmon is the main radiative mechanism. These results showed the potential of the STM to reveal the electronic and optical properties of nanoscale metallic systems in the confined geometry of the tunnel junction.Keywords: nanoclusters; plasmons; scanning tunneling microscope; tunneling-electron-induced light emission;
Co-reporter:Zhumin Han, Xinyuan Wei, Chen Xu, Chi-lun Chiang, Yanxing Zhang, Ruqian Wu, and W. Ho
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 24) pp:5205-5211
Publication Date(Web):December 2, 2016
DOI:10.1021/acs.jpclett.6b02749
The van der Waals interactions are responsible for a large diversity of structures and functions in chemistry, biology, and materials. Discussion of van der Waals interactions has focused on the attractive potential energy that varies as the inverse power of the distance between the two interacting partners. The origin of the attractive force is widely discussed as being due to the correlated fluctuations of electron charges that lead to instantaneous dipole-induced dipole attractions. Here, we use the inelastic tunneling probe to image the potential energy surface associated with the van der Waals interactions of xenon atoms.
Co-reporter:T. M. Wallis, N. Nilius, and W. Ho
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 22) pp:4683-4688
Publication Date(Web):November 1, 2016
DOI:10.1021/acs.jpclett.6b02149
The vibrational properties of single CO molecules adsorbed on nanosized Ag, Au, and Pd islands on a NiAl(110) surface were studied with a scanning tunneling microscope. The sensitivity of single molecule vibrational spectroscopy to aspects of the local environment is demonstrated by comparative studies of CO-metal bond vibrations at island terrace and island edge sites. Vibrational spectra of single CO molecules adsorbed on Ag, Au, and Pd island terraces showed peaks at 27, 32, and 44 meV, respectively, which are assigned to the hindered rotational mode. CO molecules on Au and Pd island edges, on the other hand, showed blue-shifted hindered rotational modes at 34 and 46 meV, respectively. On Au islands, CO molecules showed a strong preference for adsorption on edges, while no such preference was observed on Pd.
Co-reporter:Arthur Yu, Shaowei Li, Bharat Dhital, H. Peter Lu, and W. Ho
The Journal of Physical Chemistry C 2016 Volume 120(Issue 37) pp:21099-21103
Publication Date(Web):June 29, 2016
DOI:10.1021/acs.jpcc.6b04087
The charging and tunneling electron induced light emission from single Panhematin (hemin) molecules were studied with the scanning tunneling microscope (STM). Hemin molecules were dosed onto Al2O3 thin film grown on NiAl (110) surface. Scanning tunneling spectroscopy (STS) revealed LUMO state at 1.3 V, which formed the SOMO (−0.8 V) and SUMO (2.3 V) states when an electron was injected from the tip into the molecule. Vibronic states were resolved in the light emission spectrum for the charged hemin ion. Analysis of tunneling electron induced light emission spectrum suggests the possibility of hemin to form a doubly charged transient state that facilitates radiative decay into the substrate.
Co-reporter:Dingwang Yuan; Zhumin Han; Gregory Czap; Chi-lun Chiang; Chen Xu; W. Ho;Ruqian Wu
The Journal of Physical Chemistry Letters 2016 Volume 7(Issue 12) pp:2228-2233
Publication Date(Web):May 27, 2016
DOI:10.1021/acs.jpclett.6b00894
The combination of a sub-Kelvin scanning tunneling microscope and density functional calculations incorporating van der Waals (vdW) corrections has been used successfully to probe the adsorption structure and low-frequency vibrational modes of single benzene molecules on Ag(110). The inclusion of optimized vdW functionals and improved C6-based vdW dispersion schemes in density functional theory is crucial for obtaining the correct adsorption structure and low-energy vibrational modes. These results demonstrate the emerging capability to quantitatively probe the van der Waals interactions between a physisorbed molecule and an inert substrate.
Co-reporter:Hui Wang; Shaowei Li; Haiyan He; Arthur Yu; Freddy Toledo; Zhumin Han; W. Ho;Ruqian Wu
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 17) pp:3453-3457
Publication Date(Web):August 16, 2015
DOI:10.1021/acs.jpclett.5b01501
Using inelastic electron tunneling spectroscopy with the scanning tunneling microscope (STM-IETS) and density functional theory calculations (DFT), we investigated properties of a single H2 molecule trapped in nanocavities with controlled shape and separation between the STM tip and the Au (110) surface. The STM tip not only serves for the purpose of characterization, but also is directly involved in modification of chemical environment of molecule. The bond length of H2 expands in the atop cavity, with a tendency of dissociation when the gap closes, whereas it remains unchanged in the trough cavity. The availability of two substantially different cavities in the same setup allows understanding of H2 adsorption on noble metal surfaces and sets a path for manipulating a single chemical bond by design.
Co-reporter:Arthur Yu
The Journal of Physical Chemistry C 2015 Volume 119(Issue 26) pp:14737-14741
Publication Date(Web):March 5, 2015
DOI:10.1021/acs.jpcc.5b00494
A new method of imaging with the scanning tunneling microscope (STM) is used to study magnesium porphyrin (MgP) molecules adsorbed on Au(110) surface. Hydrogen molecules are deposited onto the surface and diffuse freely until temporarily trapped in the tunnel junction. The vibrational and rotational modes of the H2 are monitored with inelastic electron tunneling spectroscopy with the STM. The MgP presents the H2 with a highly localized position-dependent adsorption potential, which causes variations in the energies of both vibrational and rotational modes of the trapped H2 molecule. Imaging at the vibrational and rotational energies of H2 reveals salient features in the chemical structure of the MgP molecule, in particular, the positions of the nitrogen atoms. The electrostatic interaction between H2 and MgP plays a crucial role in determining the imaged features, which provide a visualization of the interaction potential within the MgP molecule.
Co-reporter:N. Nilius ; T. M. Wallis ; M. Persson ;W. Ho
The Journal of Physical Chemistry C 2014 Volume 118(Issue 50) pp:29001-29006
Publication Date(Web):April 14, 2014
DOI:10.1021/jp502036q
Monatomic Au chains with 2.89 and 4.08 Å interatomic spacing were constructed on a NiAl(110) surface, using atom manipulation techniques with a scanning tunneling microscope. Differential conductance spectra taken on the two chains revealed a series of unoccupied quantum well states that exhibit the parabolic dispersion of a free-electron-like band. The effective electron mass of the band, a measure of the coupling strength between the Au atomic orbitals, was found to be two times smaller in the compact (0.5 me) than that in the loosely packed chain (0.94 me). Moreover, the band onset shifted toward the Fermi level (1.5 versus 0.75 eV) with decreasing distance between the Au atoms. The interrelation between geometric and electronic properties of the two chains was analyzed with density functional theory calculations and tight binding modeling. In the compact chain, the large orbital overlap results in a relatively steep parabolic electron band with strong Au 6sp character. The band flattens out as the interatomic distance increases in the more open Au chain. In both cases, the NiAl support leads to a renormalization of the band properties that arises from a hybridization between the Au 6sp atomic states and the NiAl bulk bands.
Co-reporter:Chi-lun Chiang;Zhumin Han;Chen Xu;W. Ho
Science 2014 Volume 344(Issue 6186) pp:885-888
Publication Date(Web):23 May 2014
DOI:10.1126/science.1253405
Abstract
The arrangement of atoms and bonds in a molecule influences its physical and chemical properties. The scanning tunneling microscope can provide electronic and vibrational signatures of single molecules. However, these signatures do not relate simply to the molecular structure and bonding. We constructed an inelastic tunneling probe based on the scanning tunneling microscope to sense the local potential energy landscape of an adsorbed molecule with a carbon monoxide (CO)–terminated tip. The skeletal structure and bonding of the molecule are revealed from imaging the spatial variations of a CO vibration as the CO-terminated tip probes the core of the interactions between adjacent atoms. An application of the inelastic tunneling probe reveals the sharing of hydrogen atoms among multiple centers in intramolecular and extramolecular bonding.
Co-reporter:Ying Jiang;Y. N. Zhang;J. X. Cao;R. Q. Wu;W. Ho
Science 2011 Vol 333(6040) pp:324-328
Publication Date(Web):15 Jul 2011
DOI:10.1126/science.1205785
Rows of paramagnetic oxygen molecules adsorbed on a gold surface exhibit both deconfined and localized Kondo screening.
Co-reporter:Chi Chen;C. A. Bobisch;W. Ho
Science 2009 Volume 325(Issue 5943) pp:981-985
Publication Date(Web):21 Aug 2009
DOI:10.1126/science.1174592
Co-reporter:S. W. Wu;N. Ogawa;W. Ho
Science 2006 Vol 312(5778) pp:1362-1365
Publication Date(Web):02 Jun 2006
DOI:10.1126/science.1124881
Abstract
Spatial resolution at the atomic scale has been achieved in the coupling of light to single molecules adsorbed on a surface. Electron transfer to a single molecule induced by green to near-infrared light in the junction of a scanning tunneling microscope (STM) exhibited spatially varying probability that is confined within the molecule. The mechanism involves photo-induced resonant tunneling in which a photoexcited electron in the STM tip is transferred to the molecule. The coupling of photons to the tunneling process provides a pathway to explore molecular dynamics with the combined capabilities of lasers and the STM.
Co-reporter:G. V. Nazin;S. W. Wu;W. Ho
PNAS 2005 102 (25 ) pp:8832-8837
Publication Date(Web):2005-06-21
DOI:10.1073/pnas.0501171102
The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper
phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed.
The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy
shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to
the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction,
as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the
molecule. A simple, sequential tunneling model explains the observed trends.
Co-reporter:H. J. Lee Dr.;J. H. Lee;W. Ho
ChemPhysChem 2005 Volume 6(Issue 5) pp:
Publication Date(Web):22 APR 2005
DOI:10.1002/cphc.200400616
Structural and electronic properties of single zinc etioporphyrin molecules adsorbed on Al2O3/NiAl(110) were probed by a low-temperature scanning tunneling microscope (STM). Scanning tunneling spectroscopy (STS) revealed progressions of spectral features corresponding to the vibronic states of individual molecules that depend strongly on the molecular conformations. Vibronic features observed by STS were compared with the results from fluorescence induced by tunneling electrons (tunneling-induced fluorescence, TIF).
Co-reporter:G. V. Nazin;X. H. Qiu;W. Ho
Science 2003 Vol 302(5642) pp:77-81
Publication Date(Web):03 Oct 2003
DOI:10.1126/science.1088971
Abstract
Artificial nanostructures, each composed of a copper(II) phthalocyanine (CuPc) molecule bonded to two gold atomic chains with a controlled gap, were assembled on a NiAl(110) surface by manipulation of individual gold atoms and CuPc molecules with a scanning tunneling microscope. The electronic densities of states of these hybrid structures were measured by spatially resolved electronic spectroscopy and systematically tuned by varying the number of gold atoms in the chains one by one. The present approach provides structural images and electronic characterization of the metal-molecule-metal junction, thereby elucidating the nature of the contacts between the molecule and metal in this junction.
Co-reporter:T. Yamanaka, A. Hellman, Shiwu Gao, W. Ho
Surface Science 2002 Volume 514(1–3) pp:404-408
Publication Date(Web):10 August 2002
DOI:10.1016/S0039-6028(02)01659-X
State-resolved two-pulse correlation measurement is useful to study the time scale and mechanism of photo-induced desorption as well as electronic structures of admolecules before desorption. In photodesorption of nitric oxide molecules from Pt(1 1 1) at 250 K induced by 80 fs, 620 nm laser pulses, the yields and translational temperatures reached a maximum at zero delay time. In contrast, the rotational temperature of Ω=3/2 molecules reached a maximum at a delay time of ±1 ps, while that of Ω=1/2 molecules was enhanced at around zero delay. In addition, the ratio of total yields of Ω=1/2 molecules to that of Ω=3/2 molecules increased at short delay times. All of these results can be explained by the model of rotational heating, including spin–orbit (SO) coupling, where the difference in the correlation time was found to be due to the SO structure in the adsorbed phase.
Co-reporter:Jennifer Gaudioso
Angewandte Chemie 2001 Volume 113(Issue 21) pp:
Publication Date(Web):31 OCT 2001
DOI:10.1002/1521-3757(20011105)113:21<4204::AID-ANGE4204>3.0.CO;2-0
Ein negativer differentieller Widerstand (NDW), hervorgerufen durch Schwingungsanregung, hängt stark von Molekülstruktur und -dynamik ab, wie durch Rastertunnelmikroskopie-Untersuchungen an Cu(001)-gebundenem Pyrrolidin und N-Methylpyrrolidin bei 9 K gezeigt wurde. Tunnelnde Elektronen lassen Ersteres zwischen den Konformationen I und II hin- und herspringen (siehe schematische Darstellung), sodass ein NDW auftritt. Eine Methylgruppe am N-Atom reicht jedoch aus, um eine einzelne Konformation „einzufrieren“ (siehe Bild), sodass ein linearer Strom-Spannungs-Verlauf resultiert.
Co-reporter:Jennifer Gaudioso
Angewandte Chemie International Edition 2001 Volume 40(Issue 21) pp:
Publication Date(Web):31 OCT 2001
DOI:10.1002/1521-3773(20011105)40:21<4080::AID-ANIE4080>3.0.CO;2-4
Negative differential resistance (NDR), mediated by vibrational excitation, is strongly dependent on molecular structure and dynamics, according to scanning tunneling microscopy on Cu(001)-bound pyrrolidine and N-methylpyrrolidine at 9 K. Tunneling electrons cause the former to switch between conformations I and II (see picture), so that NDR is observed. The methyl group of of the latter compound restricts it to a single conformation (see picture), and a linear current–voltage characteristic results.
.jpg)
![Benzene, 1,1'-(1E)-1,2-ethenediylbis[4-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/64500/64496-23-7.png)
![Benzene, 1,1'-(1E)-1,2-ethenediylbis[4-[(1E)-2-phenylethenyl]-](http://img.cochemist.com/ccimg/64500/64496-23-7_b.png)
![Ethanethioic acid,S,S'-[1,4-phenylenebis[(1E)-2,1-ethenediyl-4,1-phenylene]] ester](/data/chemimg/113500/500530-78-9.png)
![Ethanethioic acid,S,S'-[1,4-phenylenebis[(1E)-2,1-ethenediyl-4,1-phenylene]] ester](/data/chemimg/113500/500530-78-9_b.png)
