Characterization and control of molecular ordering on adsorbate-induced reconstructed surfaces

Pai, Woei Wu; Hsu, Cheng‐Hsing; Lin, K. C.; Sin, L. Y. Mandy; Tang, Tong B.

doi:10.1016/j.apsusc.2004.09.089

Cited by 20 publications

(15 citation statements)

References 12 publications

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“…For larger height difference ͑ϳ0.5 Å or above͒, it indicates the presence or difference of interface reconstruction. 23 In addition, all observed height differences were nearly bias independent, supporting the C 60 contrast as of topographic origin. This suggests that the B-, D-, and F-C 60 have different adsorption interface structure but are identical in either the 2B1D or 1B1D phases.…”

supporting

confidence: 52%

Coverage-dependent adsorption superstructure transition ofC60/Cu(001)

Wong¹,

Pai²,

Chen³

et al. 2010

Phys. Rev. B

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We have investigated the growth and structure of a C 60 monolayer film on Cu͑001͒ with scanning tunneling microscopy at room temperature and 100 K. We discovered that the equilibrium adsorption structure of annealed C 60 films depends sensitively on the initial deposition coverage; for a coverage of 0.5 monolayer C 60 orders in an one-bright-and-one-dim ͑1B1D͒ row sequence along the ͓110͔ direction whereas for a coverage close to one monolayer C 60 orders in a two-bright-and-one-dim ͑2B1D͒ sequence. At the transition region of the bright and dim row segments, C 60 often appears "frizzy" at room temperature. This indicates that a C 60 rotates and adopts molecular orientations with inequivalent symmetry. Upon annealing, the C 60 film exhibits a high thermal stability before C 60 fragmentation and desorption occur at ϳ880-960 K, depending on its adsorption superstructure. The duality of equilibrium superstructure in C 60 / Cu͑001͒ is unique among studied C 60 monolayers on metals. We argue that different boundary energy of the 1B1D and 2B1D phases offers a plausible explanation on the observed tunability of superstructure versus coverage.

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supporting

confidence: 52%

Coverage-dependent adsorption superstructure transition ofC60/Cu(001)

Wong¹,

Pai²,

Chen³

et al. 2010

Phys. Rev. B

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“…C 60 fullerides are uniquely flexible molecular materials that exhibit a rich variety of behavior 1 , including superconductivity and magnetism in bulk compounds 2, 3 , novel electronic and orientational phases in thin films [4][5][6][7][8][9] , and quantum transport in a single-C 60 transistor 10 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).…”

mentioning

confidence: 99%

Tuning fulleride electronic structure and molecular ordering via variable layer index

et al. 2008

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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 ...

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“…After 25 min of evaporation, a clear change in the original LEED pattern is observed ( figure 1(c)). The symmetry (4×4) of the pattern reveals the formation of a commensurate ML of C 60 on the Cu(111) substrate [22,49], showing the LbL growth, at least up to the first ML in agreement with previous measurements using AES [8]. Increasing the film thickness, (50 min of evaporation) produces the loss of the LEED pattern ( figure 1(d)), indicating that the ordered structure is not preserved beyond the formation of the first layer.…”

Section: Growth On Cu(111) Leed Resultsmentioning

confidence: 99%

Growth, thermal desorption and low dose ion bombardment damage of C₆₀ films deposited on Cu(111)

et al. 2017

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Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and reflection electron energy loss spectrometry (REELS) were used to characterize the growth and thermal stability of C 60 films deposited on Cu(111). By means of LEED we found that while C 60 grows in an ordered fashion up to the first monolayer (ML) at room temperature (RT), it turns amorphous beyond that point. On the other hand, when the substrate temperature is kept at 450 K, films up to two ML with crystalline structure are obtained. For substrate temperatures beyond 570 K thick films (more than 1 ML) do not grow at all. By using AES, we found that a thick C 60 film starts to desorb at a temperature around 470 K but the first ML remains stable up to temperatures as high as 900 K. A ML with a better crystalline order is obtained after desorption than that growth with the substrate at RT or higher temperatures. When the substrate is heated at 970 K, the first ML is not fully removed but the C 60 molecular structure is altered or molecules break up into smaller pieces. The ion induced damage on C 60 on Cu(111) films was studied for typical ions, incoming energies and irradiation doses used in low energy ion scattering (LEIS) experiments. The D-value of C(KLL) Auger spectra, the π-plasmon of REELS and the evolution of the LEIS spectra, were monitored to characterize the damage caused to the film. We found that, at low doses (∼10 14 ions cm −2 ), damage is only detectable for massive ions like Ar, but not for H and He in the 2-8 keV range.

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Characterization and control of molecular ordering on adsorbate-induced reconstructed surfaces

Cited by 20 publications

References 12 publications

Coverage-dependent adsorption superstructure transition ofC60/Cu(001)

Coverage-dependent adsorption superstructure transition ofC60/Cu(001)

Tuning fulleride electronic structure and molecular ordering via variable layer index

Growth, thermal desorption and low dose ion bombardment damage of C₆₀ films deposited on Cu(111)

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Characterization and control of molecular ordering on adsorbate-induced reconstructed surfaces

Cited by 20 publications

References 12 publications

Coverage-dependent adsorption superstructure transition ofC60/Cu(001)

Coverage-dependent adsorption superstructure transition ofC60/Cu(001)

Tuning fulleride electronic structure and molecular ordering via variable layer index

Growth, thermal desorption and low dose ion bombardment damage of C60 films deposited on Cu(111)

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Growth, thermal desorption and low dose ion bombardment damage of C₆₀ films deposited on Cu(111)