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[Akira Aiba](https://orcid.org/0009-0007-9294-4330), [Marius Buerkle](https://orcid.org/0000-0003-3464-2549), [Satoshi Kaneko](https://orcid.org/0000-0002-0351-6681), [Tohru Tsuruoka](https://orcid.org/0000-0002-4322-4309), Sekito Nishimuro, [Kazuya Terabe](https://orcid.org/0000-0003-3988-3456), [Tomoaki Nishino](https://orcid.org/0000-0002-6691-5831)

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[Redox‐Induced Atomic Switch as Platform for Molecular Electronics Devices](https://mdr.nims.go.jp/datasets/d5184308-a637-4798-a493-a405c05e7e44)

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Redox‐Induced Atomic Switch as Platform for Molecular Electronics DevicesRESEARCH ARTICLEwww.small-journal.comRedox-Induced Atomic Switch as Platform for MolecularElectronics DevicesAkira Aiba, Marius Buerkle,* Satoshi Kaneko,* Tohru Tsuruoka,* Sekito Nishimuro,Kazuya Terabe, and Tomoaki Nishino*Molecular electronics is attracting increasing attention due to its potentialapplication in post-silicon electronics. However, fabrication of molecularjunctions, the fundamental building block of molecular electronic devices,requires complicated procedures, which hamper the efficient development ofnovel devices. Here, a simple fabrication process by utilizing an atomic switchoperated by redox reaction and migration of metal atoms are proposed. TheTa2O5-based silver atomic switches are operated with a small operationvoltage (0.3 V) in an acetylene atmosphere under an ultra-high vacuum. Theconsecutive operation of the atomic switch shows novel conductive statesaround 0.1 G0 (G0 = 2e2/h). Inelastic electron tunneling spectra andfirst-principles calculations reveal that the observed conductive states areattributed to the acetylene molecular junctions on the silver filament. Theproposed method accelerates the development of devices through themarriage of molecular junctions with atomic conductive filaments.1. IntroductionMolecular electronics has been an active research area over thelast few decades,[1–5] and molecular junctions are regarded asa promising building block to create the molecular devices asextremely small post-silicon devices.[6–8] Extensive studies weredevoted to the development of molecular junctions with a va-riety of electric functions, e.g., rectifiers,[9,10] switches,[1,11–13]and memories.[14,15] A wealth of knowledge is gained in termsA. Aiba, S. Kaneko, S. Nishimuro, T. NishinoDepartment of Chemistry, School of ScienceInstitute of Science Tokyo2-12-1 Ookayama, Meguro-ku, Tokyo 152–8550, JapanE-mail: kaneko.s@mct.isct.ac.jp; tnishino@chem.titech.ac.jpM.BuerkleCD-FMatNational Institute of Advanced Industrial Science andTechnology (AIST)Central 2,Umezono1-1-1, Tsukuba, Ibaraki 305–8568, JapanE-mail: marius.buerkle@aist.go.jpThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/smll.202507653© 2025 The Author(s). Small published by Wiley-VCH GmbH. This is anopen access article under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivs License, which permits use anddistribution in any medium, provided the original work is properly cited,the use is non-commercial and no modifications or adaptations aremade.DOI: 10.1002/smll.202507653of the creation of the molecular junctionsas electric components. The next challengein molecular electronics is therefore to as-semble these components to make a func-tional device. The obstacle in achievingthis goal lies in the formation and oper-ation process of the molecular junctions.Presently, mainly break-junction (BJ) tech-niques are employed to reliably prepareand activate the molecular junctions.[2–5]The BJ method involves the deformationof the metal electrodes in the junctionand consequently necessitates a macro-scopicmechanical component, i.e., the elec-trodes themselves and a piezoelectric de-vice. The macroscopic elements cruciallyprohibit parallelization and integration ofmolecular junctions to realizemolecular de-vices with sophisticated functionalities. Toovercome these limitations, the use of an atomic switch (AS)[16–20]offers unique opportunities. The AS relies on the formation ofa metal atomic filament by ion migration and redox reactionsin solid electrolytes such as oxides,[21,22] organic polymers[23,24]or chalcogenides.[17,19] The atomic filament can be reversiblyformed and broken down solely by externally applied voltages.The atomic filaments of the AS devices can serve as atomicscale electrodes actuated without mechanical modulations forthe molecular junctions. Furthermore, it has been demonstratedT. Tsuruoka, K. TerabeResearch Center for Materials Nanoarchitectonics (MANA)National Institute for Materials Science (NIMS)1-1, Namiki, Tsukuba, Ibaraki 305-0044, JapanE-mail: TSURUOKA.Tohru@nims.go.jpA. AibaDepartment of Chemical Science andEngineering, School ofMaterials andChemical TechnologyInstitute of ScienceTokyo2-12-1Ookayama,Meguro-ku, Tokyo 152–8550, JapanS. Kaneko, S.NishimuroDepartment ofMaterials Science andEngineering, School ofMaterials andChemical TechnologyInstitute of ScienceTokyo2-12-1Ookayama,Meguro-ku, Tokyo 152–8550, JapanSmall 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (1 of 7)http://www.small-journal.commailto:kaneko.s@mct.isct.ac.jpmailto:tnishino@chem.titech.ac.jpmailto:marius.buerkle@aist.go.jphttps://doi.org/10.1002/smll.202507653http://creativecommons.org/licenses/by-nc-nd/4.0/http://creativecommons.org/licenses/by-nc-nd/4.0/mailto:TSURUOKA.Tohru@nims.go.jphttp://crossmark.crossref.org/dialog/?doi=10.1002%2Fsmll.202507653&domain=pdf&date_stamp=2025-10-25www.advancedsciencenews.com www.small-journal.comFigure 1. a) Schematic images of the experimental setup for controlling the filament structure with an atomic switch. A sample tube filled with acetyleneis connected to the vacuum chamber. b) Schematic illustrations of the formation of the acetylene molecular junction with the atomic switch. First,acetylene molecules percolated into the Ta2O5 layer (i). Second, a metal filament formed in the Ta2O5 layer when the bias voltage was swept towardthe positive direction (SET process) (ii), and then the bias voltage was swept toward the negative direction (RESET process). The acetylene is trappedbetween the filament residue immediately after the filament rupture, forming the molecular junction (iii). Finally, the molecular junction is ruptured (iv).c, e) I–V curves measured in the vacuum (c) and acetylene (e) atmosphere. In the SET process, the formation of the filament decreases the resistance ofthe sample. Therefore, the effective voltage decreases at the same time as the current increases. d, f) 2D histograms of I–V curves measured in vacuum(d) and acetylene (f) atmosphere. The intensity (Int.) was normalized by the maximum histogram count. The numbers of traces used to compile thehistograms are 78 (a) and 130 (b).that the architecture of the AS devices is well suited for mas-sively parallel operations.[16,25] This inherent integrability of theAS devices offers a promising way to integrate the junction tobuild up molecular computing architecture. Moreover, the coor-dinated amalgamation of molecular junction function[4,14] andAS device neuromorphic behavior[26,27] holds the promise for thewidespread implementation of neuromorphic devices. These ad-vantages render the AS device an ideal platform to improve theformation process of molecular junctions.In this study, we demonstrate for the first time the success-ful fabrication of molecular junctions based on AS devices. TheAS was operated to form and rupture Ag filaments in its insulat-ing layer containing acetylene, which offers a promising way towire the molecular electronics.[28] The current-voltage (I–V) re-sponse demonstrated the emergence of conducting states domi-nated by the acetylene junction. The conductance states were in-vestigated by supplementary analytical techniques, namely con-ventional statistical conductance analysis and inelastic electrontunneling spectroscopy (IETS), with a comparison to the simula-tion by density functional theory (DFT).[29–32] The measured con-ductance value agree well with the structure model assuming theacetylene single-molecule junction. In IETS, electron–vibrationinteractions induce abrupt changes in the conductance and al-low the detection of vibrational modes as a peak or dip in thederivative of differential conductance, which is caused by the for-ward and backward scattering of the electron. The IETS corrobo-rated by the DFT calculations characterizes the acetylene trappedbetween Ag filaments, revealing the immobilization of the acety-lene in the Ta2O5 layer.2. Results and DiscussionWe fabricated an acetylene molecular junction by the atomicswitch break junction (AS-BJ) method, which is implementedfor the fabrication of the molecular junction for the first timeto the best of our knowledge. The AS-BJ was performed withAg/Ta2O5/Pt gapless-type AS operated in a custom-made vac-uum chamber (Figure 1a,b, Method, and Sections S1 and S2,Supporting Information). Before examining the formation ofthe molecular junction, fundamental properties of AS operationwere confirmed by I–V measurements (Figure 1c). As the biasvoltage was swept in the positive direction from 0 V, the currentsuddenly increased to approximately 0.3 V. This behavior corre-sponds to the transition of the AS device from the high-resistance(OFF) state to a low-resistance (ON) state and arose from the for-mation of a Ag filament, referred to as SET process. The sub-sequent voltage sweep in the negative direction caused the cur-rent decrease at approximately −0.3 V by the rupture of the fil-ament (RESET process). The switching performance as shownin Figure 1c agrees with literature.[16,33,34] The point contactSmall 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (2 of 7) 16136829, 2025, 47, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202507653 by National Institute For, Wiley Online Library on [07/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 2. a, d) 2D histograms of conductance traces of the Ag/Ta2O5/Pt atomic switch after VRESET was applied in vacuum (a) and in acetylene atmo-sphere (d). The inset is the typical extracted trace of the RESET process. We set the point at 0.7 G0 as the origin for the disconnection of the filament anddisplayed the time course of conductance. The intensity is normalized by the largest counts. The bin size was 0.025 s×0.1 G0. The numbers of traces are78 (a) and 130 (b). b,e) Conductance histograms of the Ag/Ta2O5/Pt atomic switch in vacuum (b) and acetylene atmosphere e). The numbers of tracesare 2465 (b) and 8229 (e). c, f) Distribution of VSET and VRESET under each condition corresponding to (a) and (b).spectroscopy also support the formation of the Ag filament (Sec-tion S3, Supporting Information). Similar measurements wereperformed in the presence of acetylene (Figure 1e). The Ta2O5layer is considered to absorb acetylene (Section S4, SupportingInformation). The I–V response exhibited a plateau indicated bythe red arrow in Figure 1e, where the current stayed nearly con-stant despite the voltage sweep, during the RESET process, i.e.,the rupture of the Ag filament. The constant current signatureduring the breakdown of atomically thin metal wires has beencommonly observed in conventional BJ studies[3–5] and is indica-tive of the formation of a molecular junction. Thus, Figure 1esuggests the accommodation of an acetylenemolecule in the bro-ken Ag filaments. A possible scenario for the formation of anacetylene molecular junction during the operation of the AS isshown in Figure 1b: (i) percolation of acetylene molecules intothe Ta2O5 layer, (ii) formation of the Ag filament during the SETprocess,[18,35–37] (iii) formation of the acetylene molecular junc-tion immediately after the rupture of the metal filament dur-ing the RESET process, and (iv) breakdown of the molecularjunction.The I–V responses were statistically evaluated by two-dimensional (2D) histograms constructed by overlaying the I–V curves (Figure 1d,f). A prominent conducting distribution ap-peared at the RESET process due to the current plateaus presentonly in the histogram taken under the acetylene atmosphere (thedashed rectangle in Figure 1f). For the detailed analyses of theconducting states associated with the acetylene molecule, we as-sessed time evolution of the conductance after applying the volt-age to induce the RESET process. The 2D map shows the pro-nounced conducting states at 10−1 G0 (G0 stands for the conduc-tance quantum and equals to 2e2/h, where e and h denote theelementary charge and the Planck constant, respectively) with alifetime of approximately 0.3 s in the measurements under theacetylene atmosphere (Figure 2d), while no noticeable states werefound in the absence of acetylene (Figure 2a,b). The distribu-tion of conductance further investigating by 1D conductance his-togram in Figure 2e demonstrates that the conductance of theacetylene-induced states is in the order of 10−3-10−1 G0, consid-ering that the conductance of the atomic contact formed in theAg filament is equal to or larger than 1G0.[38] It is noticeable thatsome traces show the plateau with the integer multiple of 0.2G0,indicating the multiple molecules trapped in the nanogap (Sec-tion S2, Supporting Information). Besides, the voltages requiredto activate the SET and RESET processes (VSET and VRESET, re-spectively) were examined as summarized in the histograms inFigure 2c and f for the absence and presence of acetylene, respec-tively. The VSET and VRESET values were 0.28 V and -0.28 V in thevacuum and 0.30 V and −0.27 V in the acetylene atmosphere,respectively. Similar operating voltages in both atmospheres in-dicate that the formation and rupture of the Ag filament are notaffected by the presence of acetylene.[22]To prove the accommodation of the acetylene molecule in thebroken Ag filament, we performed IETS measurements. Thespectra were acquired by sweeping the DC bias voltage from -400 to +400 mV at 20 K after the AS-BJ reached a stable con-ducting state (approximately 10−3 G0). Due to AS requiring aSmall 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (3 of 7) 16136829, 2025, 47, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202507653 by National Institute For, Wiley Online Library on [07/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 3. a) Typical d2I/dV2 spectra of the acetylene-absorbed atomic switch measured at three different states with different conductance values at V =0. The conductance values were 0.21 G0 (upper), 0.61 G0 (middle), and 0.97 G0 (lower). The peaks (or dips) are defined as the signal with the positive(or negative) intensity of the automatically fitted Gauss function, as shown by the arrows. b) Vibration energy histograms of the acetylene adsorbedatomic switch with different conductance values. The intensity represent the histogram counts normalized by the number of the measured spectra.c) 2D histogram of the conductance and vibrational energy. The intensity of the vibration energy is normalized with respect to the highest intensity ofvibration energy below 100 meV. The conductance and energy bin size are 0.1 G0 and 10 meV, respectively. The gray circle represents the local maximumof the relevant region. The total number of the spectra was 10602. The number of each conductance state is 3467 spectra for the low state, 1472 spectrafor the medium, and 1930 spectra for the high state.higher operation voltage at 20 K (see Section S5, SupportingInformation), the atomic configuration of the Ag filament isnot affected by the IETS measurements. Utilization of the grad-ual changes in the junction conductance, which caused by theatomic motion of the Ag filament, allowed us to measure theIETS spectra of the junctions with a range of the conductance:low-conductance region, 0.030 – 0.30 G0, medium-conductanceregion, 0.52–0.73 G0, and high-conductance region, 0.88 – 1.1G0 (Section S6, Supporting Information). Since the IETS spec-trum could be different even for similar conducting states due tothe variation of metal-molecule interactions, we constructed thehistogram of the vibrational energy obtained in the IETS spectrain each region to evaluate the vibrational energy. To prepare thehistograms, an automated fitting procedure was initially appliedto the datasets to extract the peaks present in each IETS spectrum.The peaks (or dips) are defined as the signal with the positive (ornegative) intensity of the automatically fitted Gauss function, asshown by the arrows. Subsequently, the vibrational energy his-tograms were compiled based on the detected peaks. The vibra-tional energy was determined by the fitting using the Gauss func-tion. The determined vibrational energies were sufficiently dis-tinguished from each other. The histogram counts were normal-ized by the total number of detected peaks within the specifiedconductance range (low, medium, and high), thereby facilitat-ing the comparison of histograms across different conductanceranges. Figure 3a,b shows typical spectra and histograms of thedetected vibrational energy, respectively. The prominent peaksfound in Figure 3b were summarized in Section S7 (Support-ing Information). The peaks observed in the histogram representthe electron–vibrational interactions induced at the correspond-ing vibrational energy.[29–32] Vibrational modes with energies lessthan 100 meV dominated the spectra for the high-conductancestates. The low-energy vibrations are ascribed to phonons of Agand Ta2O5 in the AS-BJ devices based on the phonon energies(28 meV for Ag,[37] and 35, 63, and 84 meV for Ta ions[39]). Thehigh-conductance states are, therefore, associated with the Agfilament, being consistent with their conductance values near 1G0. In contrast, vibrational modes with energies in the range of100–400 meV appeared in the spectra for the medium- and low-conductance states. These vibrational modes correspond to theintramolecular vibration of the acetylenemolecule,[40] as corrobo-rated by the DFT calculations below. The observation of the acety-lene vibrational modes demonstrates the successful formation ofthe acetylene molecular junctions in the broken Ag filament andthat the electron transport in the medium- and low-conductanceregimes is governed by the acetylene molecule trapped in thejunction. An additional experimental observation is the depen-dence of the vibrational energies on the conductance of the acety-lene molecular junction. Figure 3c shows the 2D mapping ofthe vibrational energy against the junction conductance for themedium- and low-conductance states, where the vibrationmodesof the acetylene molecule dominate. It was found that the vibra-tion modes located around 320 meV lowered in energy, whilethose located around 150 meV became higher energy with anincrease of conductance. The behaviors of the vibrational ener-gies originate from electron–vibration interaction altered by theconductance states.[30,31,41]To elucidate the observed vibrationalmodes in the junction, weperformed DFT calculations for the considered molecular junc-tion. To approximately simulate the BJ experiment, we startedfrom a relaxed structure labeledΔ = 0.0 Å (Figure 4a, Section S8,Supporting Information), where themolecule is already capturedinside the junction and decrease/increase the electrode separa-tion by 0.4 Å fully relaxing the structure in each step, i.e., assum-ing an adiabatic junction formation. In the optimized structure,the acetylenemolecule connected to the electrode via a C─C bondis perpendicular to the bonding direction, which is reasonable,given the anisotropy of acetylene’s 𝜋 orbitals. Acetylene tends toSmall 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (4 of 7) 16136829, 2025, 47, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202507653 by National Institute For, Wiley Online Library on [07/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 4. a) Considered pushed/pulled contact geometries. b) Calculated transmission spectra. c) Calculated IET spectra and the observed signals areat energies of the vibrational modes displayed (for example, for Δ = 0.0 Å, the characteristics of the modes remain comparable to that of the other Δ)in the inset.absorb via the di─𝜎─𝜋 bond on the surface.[42–44] Since the bind-ing energy of acetylene on the Ag surface was estimated to beonly 40 meV,[45] the other conformation is thermodynamicallyunstable. The pushing/pulling steps displayed in Figure 4a arestructures where qualitative changes, as compared to the previ-ous step, occur in the IETS. The conductance (transmission atthe Fermi energy) changes for these structures decreases fromapproximately 0.8 G0 to 10−2 G0 with increasing electrode sep-aration (Figure 4b). When the acetylene forms bonds to the Agelectrodes (Δ0.0 Å), the broad peak attributed to the molecularorbital is observed at 2 eV. The broadened peak attributes to thestrong interaction between acetylene and electrodes. Conversely,the peak diminished, and the transmission spectrum exhibiteda resemblance to the Ag atomic contact at a distance of 1.6 Å(Figure S9, Supporting Information). To determine the charac-teristics of the measured vibrational modes (Figure 3a,b), wecalculated the corresponding IET spectra (Figure 4c). The twolow-energy modes at 71 meV (symmetric bend) and 203 meV(symmetric CC stretching) fit well with the experimentally ob-served signals at 78 meV and 206 meV, respectively. The higherenergy mode at 394 meV (antisymmetric CH stretching), 398meV (symmetric CH stretching) overestimates the experimen-tally observed signal 345 meV. The difference between the simu-lated and experimental values can be attributed to the vibrationalanharmonicity and/or the electrode-acetylene interaction at theatomic protrusion.[46,47] The anharmonicity is known to overes-timate the vibrational energy, the magnitude of which dependson the vibrational modes.[46] The interaction between the metalelectrode surface and themolecule also influences the vibrationalenergy.[47,48] The atomic protrusions on the electrode that accountfor these interaction cannot be accurately incorporated in the the-oretical model, leading to the deviation of the theoretical predic-tion from the experimental observations. Therefore, the disorderof the surface structure at the relevant junction might affect vi-brational energy. The calculated shift in the vibrational energyinduced by changing the electrode separation reproduces the ex-perimental observations. When the separation was increased inthe simulations, corresponding to the decrease in conductance inthe experiments, the vibrational energy of the symmetric bend-ing mode around 100 meV decreased, whereas the antisymmet-ric CH stretching around 350 meV increased. This tendencyagreed well with the previous one channel model.[41,48] The in-creased (decreased) separation leads to a weakening (strength-ening) of the interaction between the molecule and the elec-trodes, and it is a well-established fact that the longitudinal vi-brationalmode energy decreases with decreasingmetal-moleculeinteraction in IETS of H2 and CO2 junctions.[41,48] Thus, alsoin the present study, the decrease in the vibrational energyof the longitudinal modes is attributed to weakened molecule-metal interaction. On the other hand, the vibrational energy ofthe transversal modes increases due to the enhanced restoringforce.[41,48]The vibrational assignment allows for the interpretation of thesystematic change in vibrational energy depending on conduc-tance. As observed in Figure 3c, the vibrational energy of the100–200 meV (300-400 meV) vibrational mode exhibited an in-crease (decrease) with increasing conductance. The changes invibrational energies arise from the alteration of symmetry inthe vibrational mode with respect to the direction of the trans-ported electron.[41,48] It is a well-established fact that the longitu-dinal vibrational mode energy decreases with decreasing metal-molecule interaction in IETS of H2 and CO2 junctions. In con-trast, the vibrational energy of the transverse vibrational modeincreases with the reduction of metal-molecule interaction.[41] Inthe present case, based on the atomic configuration of the acety-lene junction shown in Figure 4, it can be suggested that the𝜋-orbital is orthogonal to the direction of electron transmission.The vibrational modes observed between 200 meV and 400 meVare orthogonal to the 𝜋-orbital of acetylene. The CC vibrationalmode observed between 100 meV and 200 meV also contains vi-brational modes that are mainly parallel to the electron transmis-sion direction, although their contribution to the vertical trans-mission is still effective.We discuss the presence of peaks or dips in the IETS that de-rive from the acetylene vibrational modes. As previously men-tioned, the peaks and dips in the conductance represent enhance-ments and reductions resulting from forward and backward scat-tering caused by interaction between the electrons and vibrations.Small 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (5 of 7) 16136829, 2025, 47, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202507653 by National Institute For, Wiley Online Library on [07/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 5. a) vibrational mode observed in 90 meV–200 meV. b) vibrational mode observed in 200 meV–400 meV.Figure 5 shows the peak/dip histogram of the vibrational modesat 90–200 meV and 200–400 meV. In the 90 to 200 meV region,the electron–vibration scattering is mainly induced by the CCstretching mode, while from 200 to 400 meV, it is mainly in-duced by symmetric or antisymmetric CH vibrational modes.For the CC stretching mode, the peaks were more frequentlyobserved in the entire conductance region, even above 0.5 G0,while for the CH vibrational mode, the contribution of the dipincreased. Peaks were observed in both vibrational energy re-gions. In a single-channel model, it is expected that the con-ductance will enhance due to electron–vibration coupling for thelongitudinal vibrational mode, leading to a peak in the d2I/dV2spectra. However, there are exceptions to the matching ofthe symmetry of the vibrational mode and multichannelcontributions.[31,41,49] The orientational change of acetylene orthe gap-size modulation gives rise to a variety of conductancestates,[30,50] inducing changes in the electron–vibration interac-tion. The preceding discussion provides sufficient evidence tosupport the idea that the observed spectrum is derived from thevibrational mode of acetylene and the existence of the acetylenemolecule in the low and medium conductance states. Thoughthe Ag-hydrocarbon interaction is relatively small and molecu-lar junction is difficult to fabricate using Ag electrodes,[45,51] ourmethod enables the formation of the acetylene molecular junc-tion with the wide conductance range. The Ta2O5 layer facilitatesthe formation of a molecule that exhibits high conductivity but isthermodynamically unstable. The 𝜋 conjugated molecule, whichhas a state near the Fermi energy, can be connected more sta-bly without anchoring groups, improving the conductivity of themolecular junctions.3. ConclusionWe demonstrated the use of ultrathin metal filaments of atomicswitches as electrodes for the formation of acetylene molecularjunctions. The repeated SET and RESET processes conducted inan acetylene atmosphere led to the formation of stable conduct-ing states at 10−1 G0. The IETS revealed the vibrational mode as-sociated with the acetylene molecule to demonstrate the forma-tion of the Ag/acetylene/Ag junction, which was rationalized byDFT calculations. The present technique eliminates the need foranymechanical displacements of themetal electrodes in formingmolecular junctions. This advantage significantly simplifies thedesign of molecular devices and, in turn, leads to the paralleliza-tion and integration of these devices.4. Experimental SectionDevice Fabrication: Ag/Ta2O5/Pt atomic switches were fabricated on aSiO2-coated Si substrate according to literature.[22,26,52] First, 5-nm-thickTi and 30-nm-thick Pt layers were formed as the adhesion layer and thebottom electrode, respectively, by electron beam (EB) deposition. Next,a Ta2O5 layer as the ion-conducting electrolyte was deposited by radio-frequency sputtering using a polycrystalline target with a 77% Ar and 23%O2 gas mixture (Section S2, Supporting Information). Finally, 30-nm-thickAg and Pt layers were deposited as the top electrode and the coat layer,respectively, by EB deposition. Each atomic switch on the substrate had across-wire structure with a junction area of 5 μm × 5 μm.Electrical Measurements: The I–Vmeasurements were performed in avacuum chamber (Vacuum&Optical Instruments, Tokyo, Japan) at a basepressure of 10−3 Pa. The acetylene molecule was introduced at 200 Pato the chamber via capillary. IETS measurements were carried out at theliquid helium temperature for the atomic switch with the conducting statesat approximately 10−1 G0. The details of the electrical circuit for the I–V and IETS measurements can be found in the Section S1 (SupportingInformation).Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.Small 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (6 of 7) 16136829, 2025, 47, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202507653 by National Institute For, Wiley Online Library on [07/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comAcknowledgementsThis work was partially supported by a Grant-in-Aid for Scientific Research(20K05445, 22H04974), JSPS A3 Foresight Program from MEXT, researchgranted from Murata Science and Education Foundation, the Tokyo Insti-tute of Technology Research fund (Challenging Research Award).Conflict of InterestThe authors declare no conflict of interest.Data Availability StatementThe data that support the findings of this study are available from thecorresponding authors on request.Keywordsacetylene, atomic switch, conductive filament, inelastic electron tunnelingspectroscopy, molecular electronic device, single-molecule junctionReceived: June 25, 2025Revised: September 22, 2025Published online: October 25, 2025[1] X. 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Valov, S. Tappertzhofen, J. van den Hurk, T. Hasegawa,R. Waser, M. Aono, Adv. Funct. Mater. 2015, 25, 6374.Small 2025, 21, e07653 © 2025 The Author(s). Small published by Wiley-VCH GmbHe07653 (7 of 7) 16136829, 2025, 47, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202507653 by National Institute For, Wiley Online Library on [07/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.com Redox-Induced Atomic Switch as Platform for Molecular Electronics Devices 1. Introduction 2. Results and Discussion 3. Conclusion 4. Experimental Section Supporting Information Acknowledgements Conflict of Interest Data Availability Statement Keywords