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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 film (blue line) and solvent molecules (black line) on HOPG substrate (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min). Both spectra are smoothened by averaging the 10 nearest points of the raw data.
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Figure 2: STM-LE spectra of PTCDI-C7 thin film (blue line) and solvent molecules (black line) on HOPG substrate (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min). Both spectra are smoothened by averaging the 10 nearest points of the raw data.

Mentions: Figure 2 shows the STM-LE spectrum obtained from the PTCDI-C7 thin film (blue line) on the HOPG substrate. The spectrum shown in black represents the result of a 1-tetradecene (solvent) thin film without PTCDI-C7 molecules on the HOPG substrate. In both the spectra, the sample bias voltage, tunneling current, and accumulation time were fixed at +2.2 V, 20 nA, and 15 min, respectively. Both the spectra were acquired with the tip scanning 50 × 50 nm2 of the surface. No emission was observed from the 1-tetradecene thin film; in contrast, sufficient emission was observed from the PTCDI-C7 thin film on the HOPG substrate. To the best of our knowledge, there are only a few STM-LE studies of the HOPG substrate, since there is no surface plasmon mode on the HOPG surface in the visible light wavelength region and plasmon enhancement cannot be effectively used to obtain meaningful STM-LE intensities from adsorbed molecules. We considered that the sufficient intensity of the STM-LE from the PTCDI-C7 thin film on the HOPG substrate is caused by a high quantum yield of the radiative decay of PTCDI-C7 (93% [19]). Uehara and Ushioda [20] reported the STM-LE of a single molecule of rhodamine 6G adsorbed on the HOPG surface. In their study, the quantum yield of light emission via the transition of an electron from the lowest unoccupied molecular orbital to the highest occupied molecular orbital was also high (95% [21]). Note that we obtained no light emission from the PTCDI-C7 thin film fabricated by deposition in vacuum on the HOPG surface, suggesting that the morphology of molecular thin films affected by fabrication processes affects the emission efficiency in STM-LE. A strong visible light is radiated by TIP on the metal substrates such as Au, Ag, and Cu. TIP emission is superimposed on the emission from the adsorbed molecules, so that it is difficult to extract the true spectra of target molecules on metal surfaces. Thus, the STM-LE spectra of adsorbed molecules on an HOPG substrate with no plasmon resonance in the visible spectral range can be used to analyze the intrinsic molecular emission without any disturbance of TIP emission, although the interaction of the molecules with the HOPG surface must be taken into account.


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 film (blue line) and solvent molecules (black line) on HOPG substrate (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min). Both spectra are smoothened by averaging the 10 nearest points of the raw data.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: STM-LE spectra of PTCDI-C7 thin film (blue line) and solvent molecules (black line) on HOPG substrate (Vs = +2.2 V, It = 20 nA, acquisition time = 15 min). Both spectra are smoothened by averaging the 10 nearest points of the raw data.
Mentions: Figure 2 shows the STM-LE spectrum obtained from the PTCDI-C7 thin film (blue line) on the HOPG substrate. The spectrum shown in black represents the result of a 1-tetradecene (solvent) thin film without PTCDI-C7 molecules on the HOPG substrate. In both the spectra, the sample bias voltage, tunneling current, and accumulation time were fixed at +2.2 V, 20 nA, and 15 min, respectively. Both the spectra were acquired with the tip scanning 50 × 50 nm2 of the surface. No emission was observed from the 1-tetradecene thin film; in contrast, sufficient emission was observed from the PTCDI-C7 thin film on the HOPG substrate. To the best of our knowledge, there are only a few STM-LE studies of the HOPG substrate, since there is no surface plasmon mode on the HOPG surface in the visible light wavelength region and plasmon enhancement cannot be effectively used to obtain meaningful STM-LE intensities from adsorbed molecules. We considered that the sufficient intensity of the STM-LE from the PTCDI-C7 thin film on the HOPG substrate is caused by a high quantum yield of the radiative decay of PTCDI-C7 (93% [19]). Uehara and Ushioda [20] reported the STM-LE of a single molecule of rhodamine 6G adsorbed on the HOPG surface. In their study, the quantum yield of light emission via the transition of an electron from the lowest unoccupied molecular orbital to the highest occupied molecular orbital was also high (95% [21]). Note that we obtained no light emission from the PTCDI-C7 thin film fabricated by deposition in vacuum on the HOPG surface, suggesting that the morphology of molecular thin films affected by fabrication processes affects the emission efficiency in STM-LE. A strong visible light is radiated by TIP on the metal substrates such as Au, Ag, and Cu. TIP emission is superimposed on the emission from the adsorbed molecules, so that it is difficult to extract the true spectra of target molecules on metal surfaces. Thus, the STM-LE spectra of adsorbed molecules on an HOPG substrate with no plasmon resonance in the visible spectral range can be used to analyze the intrinsic molecular emission without any disturbance of TIP emission, although the interaction of the molecules with the HOPG surface must be taken into account.

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