Limits...
Single-molecule identification via electric current noise.

Tsutsui M, Taniguchi M, Kawai T - Nat Commun (2010)

Bottom Line: Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms.We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling.This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

View Article: PubMed Central - PubMed

Affiliation: The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.

ABSTRACT
Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms. Molecular fluctuations are a source of noise that often hinders single-molecule identification by obscuring the fine details of molecular identity. In this study, we report molecular identification through direct observation of quantum-fluctuation-induced inelastic noise in single organic molecules. We investigated current fluctuations flowing through a single molecule that is chemically connected to two electrodes. We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling. This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

No MeSH data available.


Related in: MedlinePlus

Inelastic contributions to electrical conductance and current fluctuations in a single-atom quasi-ballistic chain at 4.2 K.(a) <I>–Vb characteristics of an Au single-atom contact at 4 K. The dotted lines are the elastic component. (b) Δ<I> plots derived from the <I>–Vb curve in a. (c) σ–Vb plots measured for an Au single-atom contact formed at 4.2 K. (d) Plots of (σ–σ1/f) with respect to Vb and (e) the corresponding noise spectrum. Arrows point to the characteristic peaks in the spectrum at the positive Vb range measured.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3105297&req=5

f4: Inelastic contributions to electrical conductance and current fluctuations in a single-atom quasi-ballistic chain at 4.2 K.(a) <I>–Vb characteristics of an Au single-atom contact at 4 K. The dotted lines are the elastic component. (b) Δ<I> plots derived from the <I>–Vb curve in a. (c) σ–Vb plots measured for an Au single-atom contact formed at 4.2 K. (d) Plots of (σ–σ1/f) with respect to Vb and (e) the corresponding noise spectrum. Arrows point to the characteristic peaks in the spectrum at the positive Vb range measured.

Mentions: It is interesting to note that the σ peak profile agrees with what appears in the inelastic electron tunnelling (IET) spectrum20 (Fig. 1b). Indeed, we can assign σ peaks to electron energy loss spectroscopy (EELS) and Raman-active vibrational modes21,22, as listed in Table 1. This implies that the high-field current fluctuations in single HDT molecules are of inelastic origin23,24,25. To verify the possible roles of inelastic excitations of vibration modes of single-molecule junctions on current fluctuations, we conducted σ measurements on Au single-atom chains. Forming 1 G0 states using the self-breaking method, with a stretching speed of 6 pm s−1 at 4 K, we exhibited 50-point current measurements in a bias range of −0.04 V≤Vb≤0.04 V. The relatively small bias window was used because Au single-atom contacts tend to become increasingly unstable at bias voltage above 0.05 V presumably because of the local heating and current-induced forces13. <I>–Vb plots in Figure 4a show linear characteristics reflecting the quasi-ballistic nature of electron transport through an Au single-atom contact26. We extract the inelastic component by examining linear fitting to Figure 4a in a bias range from −0.001 V to 0.001 V. In contrast to HDT molecules demonstrating increased transmission via active inelastic channels, Δ<I>–Vb plots in Figure 4b reveal negative contributions of electron–phonon interactions in an Au single-atom chain on the electrical conductance26. This discrepancy can be explained by considering the relative importance of the counteracting effects of elastic and inelastic processes in electron transmission through single-atom and molecule junctions; whereas the inelastic mechanism leads to enhanced transmission, elastic contribution involving virtual phonon excitations decreases transmission27,28,29. Theoretical studies have predicted a shift in the balance towards predominance of inelastic effects as transmission T becomes <0.5 and superior elastic effects for T becomes >0.5, the overall tendency of which agrees with the positive and negative Δ<I> acquired for HDT single-molecule junctions with T~10−3 and Au single-atom chains with T~1, respectively27,28,29. As for the high-field current fluctuations, σ shows a stepwise manner analogous to that found for single HDT molecules (Fig. 4c,d). The corresponding σ spectrum demonstrates peaks at Vp=8 and 22 mV (Fig. 4e). Significantly, we again find good accordance between these peak voltages and the characteristic vibration modes of single-atom wires at energies 10 and 18 meV reported in previous scanning tunnelling microscopy studies30,31 (Table 1). It is therefore corroborated that bias voltage-induced conductance fluctuations can serve as a unique molecular signature for single-molecule identifications.


Single-molecule identification via electric current noise.

Tsutsui M, Taniguchi M, Kawai T - Nat Commun (2010)

Inelastic contributions to electrical conductance and current fluctuations in a single-atom quasi-ballistic chain at 4.2 K.(a) <I>–Vb characteristics of an Au single-atom contact at 4 K. The dotted lines are the elastic component. (b) Δ<I> plots derived from the <I>–Vb curve in a. (c) σ–Vb plots measured for an Au single-atom contact formed at 4.2 K. (d) Plots of (σ–σ1/f) with respect to Vb and (e) the corresponding noise spectrum. Arrows point to the characteristic peaks in the spectrum at the positive Vb range measured.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105297&req=5

f4: Inelastic contributions to electrical conductance and current fluctuations in a single-atom quasi-ballistic chain at 4.2 K.(a) <I>–Vb characteristics of an Au single-atom contact at 4 K. The dotted lines are the elastic component. (b) Δ<I> plots derived from the <I>–Vb curve in a. (c) σ–Vb plots measured for an Au single-atom contact formed at 4.2 K. (d) Plots of (σ–σ1/f) with respect to Vb and (e) the corresponding noise spectrum. Arrows point to the characteristic peaks in the spectrum at the positive Vb range measured.
Mentions: It is interesting to note that the σ peak profile agrees with what appears in the inelastic electron tunnelling (IET) spectrum20 (Fig. 1b). Indeed, we can assign σ peaks to electron energy loss spectroscopy (EELS) and Raman-active vibrational modes21,22, as listed in Table 1. This implies that the high-field current fluctuations in single HDT molecules are of inelastic origin23,24,25. To verify the possible roles of inelastic excitations of vibration modes of single-molecule junctions on current fluctuations, we conducted σ measurements on Au single-atom chains. Forming 1 G0 states using the self-breaking method, with a stretching speed of 6 pm s−1 at 4 K, we exhibited 50-point current measurements in a bias range of −0.04 V≤Vb≤0.04 V. The relatively small bias window was used because Au single-atom contacts tend to become increasingly unstable at bias voltage above 0.05 V presumably because of the local heating and current-induced forces13. <I>–Vb plots in Figure 4a show linear characteristics reflecting the quasi-ballistic nature of electron transport through an Au single-atom contact26. We extract the inelastic component by examining linear fitting to Figure 4a in a bias range from −0.001 V to 0.001 V. In contrast to HDT molecules demonstrating increased transmission via active inelastic channels, Δ<I>–Vb plots in Figure 4b reveal negative contributions of electron–phonon interactions in an Au single-atom chain on the electrical conductance26. This discrepancy can be explained by considering the relative importance of the counteracting effects of elastic and inelastic processes in electron transmission through single-atom and molecule junctions; whereas the inelastic mechanism leads to enhanced transmission, elastic contribution involving virtual phonon excitations decreases transmission27,28,29. Theoretical studies have predicted a shift in the balance towards predominance of inelastic effects as transmission T becomes <0.5 and superior elastic effects for T becomes >0.5, the overall tendency of which agrees with the positive and negative Δ<I> acquired for HDT single-molecule junctions with T~10−3 and Au single-atom chains with T~1, respectively27,28,29. As for the high-field current fluctuations, σ shows a stepwise manner analogous to that found for single HDT molecules (Fig. 4c,d). The corresponding σ spectrum demonstrates peaks at Vp=8 and 22 mV (Fig. 4e). Significantly, we again find good accordance between these peak voltages and the characteristic vibration modes of single-atom wires at energies 10 and 18 meV reported in previous scanning tunnelling microscopy studies30,31 (Table 1). It is therefore corroborated that bias voltage-induced conductance fluctuations can serve as a unique molecular signature for single-molecule identifications.

Bottom Line: Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms.We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling.This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

View Article: PubMed Central - PubMed

Affiliation: The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.

ABSTRACT
Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms. Molecular fluctuations are a source of noise that often hinders single-molecule identification by obscuring the fine details of molecular identity. In this study, we report molecular identification through direct observation of quantum-fluctuation-induced inelastic noise in single organic molecules. We investigated current fluctuations flowing through a single molecule that is chemically connected to two electrodes. We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling. This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

No MeSH data available.


Related in: MedlinePlus