Spatially Mapping the Spectral Density of a Single<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mn mathvariant="normal">60</mml:mn></mml:msub></mml:math>Molecule

Lu, Xinghua; Grobis, M.; Khoo, Khoong Hong; Louie, Steven G.; Crommie, Michael F.

doi:10.1103/physrevlett.90.096802

Cited by 205 publications

(166 citation statements)

References 37 publications

Supporting

Mentioning

151

Contrasting

Unclassified

Order By: Relevance

“…Bright rows correspond to C 60 molecules in a missing Cu row while dim rows correspond to molecules located at double missing rows. Figure 1 exhibits, similar to the case of C 60 on Ag(100) [15], four molecular orientations on Cu(100).…”

Section: Controlled Contact To Amentioning

confidence: 72%

Controlled Contact to aC60Molecule

et al. 2007

View full text Add to dashboard Cite

Section: Controlled Contact To Amentioning

confidence: 72%

Controlled Contact to aC60Molecule

et al. 2007

View full text Add to dashboard Cite

“…2d), however, C 60 molecules form a very simple hexagonal lattice (lattice constant a ~10.5 Å) with long-range orientational ordering. The tri-star-like topography of each molecule suggests that C 60 in the second layer is oriented with a hexagon pointing up 14 . The third layer topograph is the same as the second layer.…”

mentioning

confidence: 99%

Tuning fulleride electronic structure and molecular ordering via variable layer index

et al. 2008

View full text Add to dashboard Cite

The ability to tune competing interactions in the fullerides arises from advances in our ability to grow well-controlled heterogeneous molecular films. Here we describe measurements on potassium doped C 60 (K x C 60 ) ultra-thin films having variable thickness from one to three layers (layer index i = 1, 2, and 3) for three specific doping concentrations (x = 3, 4, and 5). Fig. 1a displays a scanning tunneling microscope (STM) topograph of a representative K x C 60 multilayer on Au(111), where the color scale highlights the plateau structure. Narrow slivers of C 60 -free voids containing only K atoms 3 (brown) exist between continuous patches of K x C 60 . Islands of second (blue) and third layer (red) K x C 60 can be seen residing on top of the first K x C 60 layer (green). The average layer thickness is ~9.9 Å, greater than the 8 Å spacing found in undoped C 60 films 11 .We begin by describing our results for a multilayer of the x = 3 metallic system.Layer-dependent electronic structure in K 3 C 60 can be seen in Fig. 2a, which shows spatially-averaged dI/dV spectra measured at three different layer levels. Within each layer the spectrum is highly uniform with no sign of spatial inhomogeneity such as that found in the surface of bulk fullerides 12 . The first layer dI/dV displays a wide peak at the Fermi energy (E F ), reflecting the large electronic density of states (DOS) of a metallic LUMO-derived band (LUMO = Lowest Unoccupied Molecular Level). In contrast, the second layer spectrum shows a sharp dip at E F , indicating the emergence of an energy gap that tends to split the band into two halves. A similar gap-like feature persists in the third layer. The width of the gap-like feature (measured between adjacent local maxima) is ~ 0.2 eV, a much larger value than the superconducting gap 2∆ sc ~ 6 meV found in bulk K 3 C 60 13.The spatial arrangement of C 60 molecules also changes dramatically with layer index. The first layer of K 3 C 60 (Fig. 2c) exhibits a complex 3 3 × superstructure of bright molecules having different orientation from their dimmed nearest neighbors 8 . In the second layer ( Fig. 2d), however, C 60 molecules form a very simple hexagonal lattice (lattice constant a ~10.5 Å) with long-range orientational ordering. The tri-star-like topography of each molecule suggests that C 60 in the second layer is oriented with a hexagon pointing up 14 . The third layer topograph is the same as the second layer. 4The insulating x = 4 multilayer system displays a similar trend. Fig. 3a shows dI/dV spectra measured on a K 4 C 60 plateau structure where the number of layers is varied from i = 1 to 3. First layer spectra (i = 1) exhibit an insulating energy gap ∆ ~ 0.2 eV that is induced by molecular Jahn-Teller (JT) distortion 8 . As the layer index increases from i = 1 to 3, the energy gap opens continuously (by layer 3 the gap has well-defined edges and a flat bottom). The gap amplitudes observed here are estimated to be ∆ ~ 0.6 eV and 0.8 eV for layer 2 and 3 respectively. As seen in the metallic x = 3 ...

show abstract

“…These spectra exhibit several common features: a shoulder in the filled density of states (V<0) and two peaks in the empty density of states (V>0) that arise from tunneling into the C 60 highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital LUMO, and LUMO+1, respectively [11]. In the monolayer (bilayer) spectra, the features are centered at -1.4V (-2.0V), 0.75V (1.45V) and 2.05V (2.8V), respectively.…”

mentioning

confidence: 99%

“…The C 60 monolayer has an increased interaction with the Au(111) substrate, which adds a constant metallic density of states background to the monolayer electronic structure. Increased substrate interaction also broadens the C 60 molecular resonance widths [11,15,16]. The combination of these factors suppresses NDR from emerging in C 60 monolayer tunneling.…”

mentioning

confidence: 99%

Tuning negative differential resistance in a molecular film

Grobis

Wachowiak

Yamachika

et al. 2005

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

We have observed variable negative differential resistance (NDR) in scanning tunneling spectroscopy measurements of a double layer of C 60 molecules on a metallic surface.Minimum to maximum current ratios in the NDR region are tuned by changing the tunneling barrier width. The multi-layer geometry is critical, as NDR is not observed when tunneling into a C 60 monolayer. Using a simple model we show that the observed NDR behavior is explained by voltage-dependent changes in the tunneling barrier height. 2Negative differential resistance (NDR) is a crucial property of several important electronic components [1,2]. Originally observed in highly doped tunneling diodes [3], NDR has been seen in a variety of systems and caused by several different mechanisms [4,5,6,7,8]. Here we present a scanning tunneling spectroscopy (STS) study showing the appearance of NDR in the tunneling signature of thin molecular C 60 films deposited on Au(111). NDR is completely absent for tunneling into a single C 60 monolayer, but emerges when tunneling into second and higher layers of C 60 . In previous STS studies of molecular systems NDR has been commonly attributed to the convolution of energetically localized tip states with the molecular density of states [7]. The NDR observed in our study is inconsistent with this interpretation, but instead stems from the voltage dependence of the tunneling barrier height [4]. We further find that the relative decrease in current, induced by the NDR, increases with increasing tunneling barrier width, allowing for tunability of the NDR behavior. This behavior is explained by using a simple tunneling model. Our experiments were conducted using a homebuilt ultrahigh vacuum (UHV) STM with a PtIr tip. The single-crystal Au(111) substrate was cleaned in UHV and dosed with C 60 using a calibrated Knudsen cell evaporator before being cooled to 7K in the STM stage. dI/dV spectra and images were measured through lock-in detection of the ac tunneling current driven by a 451Hz, 10mV (rms) signal added to the junction bias under open-loop conditions (bias voltage here is defined as the sample potential referenced to the tip). All data were acquired at 7K.Figure 1(a) shows the topographic structure of a single layer of C 60 (monolayer), a second layer of C 60 (bilayer), and a third layer of C 60 (trilayer). Each layer is well ordered 3 and has a topographic structure consistent with previous measurements performed on similar monolayer and layered C 60 systems [9,10]. The step height of each C 60 layer is ~8.0Å.Step edges in the underlying Au(111) substrate lead to 2Å steps that run through the C 60 layers. dI/dV spectra performed on the C 60 monolayer and bilayer are shown in Fig. 1 (b).These spectra exhibit several common features: a shoulder in the filled density of states (V<0) and two peaks in the empty density of states (V>0) that arise from tunneling into the C 60 highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital LUMO, and LUMO+1, respectively [11]. In the monolayer (bilayer) s...

show abstract

Spatially Mapping the Spectral Density of a SingleC60Molecule

Cited by 205 publications

References 37 publications

Controlled Contact to aC60Molecule

Controlled Contact to aC60Molecule

Tuning fulleride electronic structure and molecular ordering via variable layer index

Tuning negative differential resistance in a molecular film

Contact Info

Product

Resources

About