Remote‐Controllable Interfacial Electron Tunneling at Heterogeneous Molecular Junctions via Tip‐Induced Optoelectrical Engineering

Abstract Molecular electronics enables functional electronic behavior via single molecules or molecular self‐assembled monolayers, providing versatile opportunities for hybrid molecular‐scale electronic devices. Although various molecular junction structures are constructed to investigate charge transfer dynamics, significant challenges remain in terms of interfacial charging effects and far‐field background signals, which dominantly block the optoelectrical observation of interfacial charge transfer dynamics. Here, tip‐induced optoelectrical engineering is presented that synergistically correlates photo‐induced force microscopy and Kelvin probe force microscopy to remotely control and probe the interfacial charge transfer dynamics with sub‐10 nm spatial resolution. Based on this approach, the optoelectrical origin of metal–molecule interfaces is clearly revealed by the nanoscale heterogeneity of the tip‐sample interaction and optoelectrical reactivity, which theoretically aligned with density functional theory calculations. For a practical device‐scale demonstration of tip‐induced optoelectrical engineering, interfacial tunneling is remotely controlled at a 4‐inch wafer‐scale metal–insulator–metal capacitor, facilitating a 5.211‐fold current amplification with the tip‐induced electrical field. In conclusion, tip‐induced optoelectrical engineering provides a novel strategy to comprehensively understand interfacial charge transfer dynamics and a non‐destructive tunneling control platform that enables real‐time and real‐space investigation of ultrathin hybrid molecular systems.


Figure S1 .
Figure S1.Mechanism of PiFM-based IR-excitation switching at the molecule junction systems, which efficiently induce the interfacial electron tunneling.Schematic illustration of a) before IR-excitation, b) induced dipole-dipole interaction, and c) tip-enhanced thermal expansion (left), enabling localized thermal expansion at the tip-sample junction, compared to global thermal expansion.(right)

Figure S3 .
Figure S3.Experimental setup.a) FESEM image of KPFM ElectriMulti75-G tip (top) and PiFM NCHR tip (bottom) after all experiments.b) photography of KPFM sliver paste electrode (left) and attached Cu (111) wafer on the top of the sliver paste electrode (right), where interfacial charge transfer is the only possible.c) PiFM QCL laser intensity spatial map of initial focus positions.

Figure
Figure S4.a) Optical heterogeneity between self-assembled domain and bare Cu (111) domain.b) FT-IR spectra of heterocyclic compounds, exhibiting the intrinsic chemical bonding compositions.

Figure S5 .
Figure S5.XPS spectra of organic self-assembled monolayers.a) XPS full spectrum, b) High-resolution XPS spectra of O 1s peak, which indicates surface oxidation inhibition via self-assembly.

Figure S7 .
Figure S7.Surface roughness distribution of bottom electrode and SAMs.a) Surface roughness pixel distribution shift, b) 3D topography image, c) Z height profile of bottom Cu (111) electrode and each SAMs.

Figure S8 .
Figure S8.Adhesion force distribution between Cu (111) and SAMs domains, which indicates the larger adhesion force of the self-assembled domains compared to Cu (111).

Figure S10 .
Figure S10.Energy level diagram of metal (Cu)-molecule-dielectric barrier (air)-AFM tip (Pt) junction with polarization (right) and IR-excitation (left), which generate the localized electrical field and near field at tip-sample junction, thereby enabling the remote-controllable interfacial charge transfer dynamics.

Figure S11 .
Figure S11.Electrical potential shift within a) upward electrical field and b) downward electrical field, which clearly exhibits the nanoscale heterogeneity of the sample polarizability, charge transfer dynamics and tip-sample electrical potential difference.

Figure S12 .
Figure S12.Tip bias effects of electrical potential shift within a) upward electrical field and b) downward electrical field, which clearly exhibits the nanoscale heterogeneity of the sample polarizability, charge transfer dynamics and tip-sample electrical potential difference.

Figure S13 .
Figure S13.Statistical work function pixel distribution of (a) 2A5MT, (b) 3ATZ, and (c) PTT, which indicates the heterogeneous electron tunneling behavior between Cu-S bonding and Cu-N bonding.

Figure S14 .
Figure S14.Phase shift at a) PTT, which anchored with Cu-S and Cu-N bonding, and b) Cu2O, which clearly indicates the heterogeneous tip-sample electrostatic interaction.

Figure S15 .
Figure S15.Tip bias effects of phase shift at a) sulfur-anchored domain and b) nitrogenanchored domain, which clearly indicates the heterogeneous tip-sample electrostatic interaction.

Figure
Figure S16.a) PiFM spatio-spectral imaging with IR-excitation switching, which was spatially correlated with heterogeneous IR spectra intensity.Line profile b) IR spectra of PTT and Cu (111) wafer and c) XPS C 1s peak, exhibiting the nanoscale chemical characteristics of PTT.

Figure S17 .
Figure S17.Spatial resolution calculation of KPFM and PiFM imaging.a) 2A5MT PiFM image, b) Local 2A5MT PiFM image and c) line profile, which indicates the PiF heterogeneity, and d) 2A5MT KPFM image, e) Local 2A5MT work function image and f) line profile, which indicates the work function heterogeneity.

Figure S18 .
Figure S18.XPS N 1s spectra of a) 2A5MT monolayers and b) 2A5MT multilayers, which imply that the N-N bonding formation is presence in the multilayer-scale, whereas absence in the monolayer-scale.