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STM-induced light emission from thin films of perylene derivatives on the HOPG and Au substrates.

Fujiki A, Miyake Y, Oshikane Y, Akai-Kasaya M, Saito A, Kuwahara Y - Nanoscale Res Lett (2011)

Bottom Line: A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules.The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes.The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Precision Science & Technology, Graduate school of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan. fujiki@ss.prec.eng.osaka-u.ac.jp.

ABSTRACT
We have investigated the emission properties of N,N'-diheptyl-3,4,9,10-perylenetetracarboxylic diimide thin films by the tunneling-electron-induced light emission technique. A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules. The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes. The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained.

No MeSH data available.


Related in: MedlinePlus

STM-LE spectra of PTCDI-C7 thin films on Au (red line) and HOPG (blue line) substrates (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min).
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Figure 5: STM-LE spectra of PTCDI-C7 thin films on Au (red line) and HOPG (blue line) substrates (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min).

Mentions: Figure 5 shows the STM-LE spectra of the PTCDI-C7 thin films on the Au (red line) and HOPG (blue line) substrates. Two spectra were obtained under the same STM conditions (Vs = +2.2 V, It = 20 nA). The emission on the Au substrate originated from the PTCDI-C7 molecules because the peak positions for the Au substrate were consistent with those for the HOPG substrate. It should be noticed that the emission intensities of the peaks at 750 and 860 nm were significantly enhanced about fivefold, whereas the peak intensities at 625 and 680 nm were unchanged. Such a selective enhancement of the emission peaks can be explained by the resonance matching with the TIP mode on the Au substrate. In general, the wavelength of the emission by TIP strongly depends on both the material and shape of the metal tip/substrate. In our case, the resonance wavelength of TIP characterized by the Pt/Ir tip and Au substrate was located in the wavelength range of 700-1000 nm [26]. We clearly showed that TIP selectively enhances emission peaks related to vibronic transitions that are energy-matched to the resonance wavelength of TIP. Thus far, photoluminescence measurements of molecular thin films related to surface plasmon enhancement effects have been carried out. They have shown that molecular fluorescence/phosphorescence intensities are significantly enhanced on noble-metal surfaces [27,28]; however, it is difficult to control the selective enhancement on metal surfaces because the wavelength of surface plasmons varies over a wide band owing to the nanoscale and random roughness of actual metal surfaces. For the selective enhancement of molecular emission, the resonance energy for the fluorescence/phosphorescence of luminescent layers and their associated surface plasmon excitation mode should be adjusted using size- and shape-controlled metal nanoparticles [10,29]. Ino et al. [30] observed STM-LE luminescence from one of the perylene derivatives (i.e., 3,4,9,10-perylenetetracarboxylic dianhydride: PTCDA) deposited on a Ag(111) surface. They found that not only molecular emission but also plasmon-mediated emission is quenched in the case of 1 ML PTCDA adsorption owing to the hybridization of the surface electronic state and the modification of the dielectric constant of the STM gap. In the 2 ML PTCDA thin film, however, they observed one broad structureless peak of molecular fluorescence. The behavior of the STM-LE of PTCDI-C7 obtained in this study differed from their results, which might be due to the morphology of the thin films used.


STM-induced light emission from thin films of perylene derivatives on the HOPG and Au substrates.

Fujiki A, Miyake Y, Oshikane Y, Akai-Kasaya M, Saito A, Kuwahara Y - Nanoscale Res Lett (2011)

STM-LE spectra of PTCDI-C7 thin films on Au (red line) and HOPG (blue line) substrates (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211436&req=5

Figure 5: STM-LE spectra of PTCDI-C7 thin films on Au (red line) and HOPG (blue line) substrates (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min).
Mentions: Figure 5 shows the STM-LE spectra of the PTCDI-C7 thin films on the Au (red line) and HOPG (blue line) substrates. Two spectra were obtained under the same STM conditions (Vs = +2.2 V, It = 20 nA). The emission on the Au substrate originated from the PTCDI-C7 molecules because the peak positions for the Au substrate were consistent with those for the HOPG substrate. It should be noticed that the emission intensities of the peaks at 750 and 860 nm were significantly enhanced about fivefold, whereas the peak intensities at 625 and 680 nm were unchanged. Such a selective enhancement of the emission peaks can be explained by the resonance matching with the TIP mode on the Au substrate. In general, the wavelength of the emission by TIP strongly depends on both the material and shape of the metal tip/substrate. In our case, the resonance wavelength of TIP characterized by the Pt/Ir tip and Au substrate was located in the wavelength range of 700-1000 nm [26]. We clearly showed that TIP selectively enhances emission peaks related to vibronic transitions that are energy-matched to the resonance wavelength of TIP. Thus far, photoluminescence measurements of molecular thin films related to surface plasmon enhancement effects have been carried out. They have shown that molecular fluorescence/phosphorescence intensities are significantly enhanced on noble-metal surfaces [27,28]; however, it is difficult to control the selective enhancement on metal surfaces because the wavelength of surface plasmons varies over a wide band owing to the nanoscale and random roughness of actual metal surfaces. For the selective enhancement of molecular emission, the resonance energy for the fluorescence/phosphorescence of luminescent layers and their associated surface plasmon excitation mode should be adjusted using size- and shape-controlled metal nanoparticles [10,29]. Ino et al. [30] observed STM-LE luminescence from one of the perylene derivatives (i.e., 3,4,9,10-perylenetetracarboxylic dianhydride: PTCDA) deposited on a Ag(111) surface. They found that not only molecular emission but also plasmon-mediated emission is quenched in the case of 1 ML PTCDA adsorption owing to the hybridization of the surface electronic state and the modification of the dielectric constant of the STM gap. In the 2 ML PTCDA thin film, however, they observed one broad structureless peak of molecular fluorescence. The behavior of the STM-LE of PTCDI-C7 obtained in this study differed from their results, which might be due to the morphology of the thin films used.

Bottom Line: A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules.The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes.The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Precision Science & Technology, Graduate school of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan. fujiki@ss.prec.eng.osaka-u.ac.jp.

ABSTRACT
We have investigated the emission properties of N,N'-diheptyl-3,4,9,10-perylenetetracarboxylic diimide thin films by the tunneling-electron-induced light emission technique. A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules. The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes. The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained.

No MeSH data available.


Related in: MedlinePlus