Cold welding without direct contact

Cold welding without direct contact | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Cold welding without direct contact Lihua Wang, Yizhong Guo, Deping Guo, Cheng Qian, Zhanxin Wang, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5989110/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Welding is widely used in the fabrication of electronic devices and hierarchical systems with desired mechanical and physical properties. Conventional welding generally requires both high temperatures and significant compressive stress to ensure direct contact between the welded parts. Accordingly, traditional welding process may cause deformation of the atomic structure at the joint of the parts, thereby greatly reducing the performance of the device. In this study, the atomic-scale welding two separate platinum nanocrystals into a single crystal was observed in situ. Cold welding was achieved at a relatively low temperature without direct contact between the two platinum nanocrystals, which were separated by a distance of ~ 7.8 Å, more than three times the lattice spacing. The in situ atomic-scale observation revealed that cold welding occurred via forming monatomic chain between the separated nanocrystals by diffusion of atoms, then this monatomic chain grew layer-by-layer into diatomic and triatomic chains. Density functional theory calculations revealed that the adsorption energy of the atoms decreased with the reduction of the separation distance of the two parts, facilitating cold welding. This study demonstrates the feasibility of cold welding without direct contact, thereby facilitating the construction of high-performance nanodevices by atomic engineering. Physical sciences/Materials science/Structural materials/Mechanical properties Physical sciences/Materials science/Nanoscale materials/Structural properties Physical sciences/Materials science/Structural materials/Metals and alloys Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Welding techniques are fundamental for joining metallic parts and are widely used in constructing machines and connecting electronic devices, among other applications. These techniques have also been used in the construction of hierarchical structures from nanoobjects, enabling the electronic, optical, and magnetic properties of the integrated materials to be tailored to specific applications 1–15 . Traditional welding methods typically require high compressive stress between the parts, ensuring a sufficient direct contact area at the joint position 8,16–18 , along with elevated temperatures achieved via thermal 19 , laser 20 , and joule heating 21,22 . At the nanometre scale, two metal parts can be welded together at room temperature 1,4,5,9–11,23–30 . While compressive stress is generally applied between the two parts during the cold-welding process to ensure direct contact between the two welded metals 4,5,31 . This finding supports the widely held belief that direct contact is essential for metal welding: however, no direct evidence supports this. Despite numerous studies were carried out, direct experimental evidence of atomic-scale cold welding is lacking; thus, the mechanism of how cold welding between two parts is initiated remains unknown 11,22,32 . Additionally, as the size of those device down to nanosize, conventional welding techniques to connect electronic devices and metallic circuits presents significant challenges owing to the required high temperatures and compressive stresses, which may deform the materials at the joint 33–35 and thus adversely affect their conductivity and reliability. This problem is particularly significant in the construction of nanoscale electronic devices and circuits 36 , in which material stability and integrity are critical for device performance. The continued miniaturisation of electronic devices will necessitate the use of innovative welding techniques operable at room temperature with negligible residual stress to avoid structural deformation at the joint position. A technology that enables direct atomic-scale in-situ observations of the cold-welding process and welding nanomaterials with negligible stress, heat, and structural changes is highly desired. In this study, the cold welding of Pt nanocrystals were observed in situ using aberration-corrected transmission electron microscopy (Cs-TEM) 23,37–39 . Multiple cycles of atomic-scale cold welding and fracture were observed in situ at low temperature, revealing that two Pt nanocrystals within ~7.8 Å of each other can be cold welded together without direct contact. The cold-welding process was initiated via the formation of a monatomic chain between the two nanocrystals, which then grew to form diatomic and triatomic chains before finally restoring the nanocrystals layer-by-layer. Extensive testing revealed a critical distance of approximately 7.8 Å, above which cold welding does not occur. Density functional theory (DFT) calculations and atomic simulations revealed the atomic mechanism of cold welding and suggest that the adsorption energy decreases with the reduction of the separation distance between the crystals, thereby facilitating cold welding. Both practical experiments and DFT calculations indicate that the growth rate of the welding joint is inversely proportional to the distance between the nanocrystals. In this study, a Pt thin film (approximately 50 nm thick) was deposited on a single-crystal of NaCl via magnetron sputtering. The NaCl substrate was then dissolved in water to remove the thin film from the substrate and obtain free-standing thin films, which were then attached to an in situ TEM tensile device 40–42 and further milled using a Fischione 1040 NanoMill 43 to form numerous Pt nanocrystals in the sample. The sample was subjected to multiple cycles of tensile fracture and cold-welding under TEM observation using the in-situ TEM tensile device, which allows the displacement to be slowly and gently controlled while retaining the double-tilt capability, such that the sample can be oriented appropriately to a low-index crystallographic zone orientation for atomic-scale imaging. This procedure allowed the tensile fracture and cold-welding of single-crystalline nanocrystals to be observed in situ at the atomic scale in real time. Cold-welding was performed below ~ 100 °C using an FEI-Titan TEM equipped with an aberration corrector operated at 300 kV. Our experiments involved cold welding and fracture tests of several Pt nanocrystals, which showed that fractured single-crystalline nanocrystals can be easily repaired via cold welding without direct contact. According to the Lennard–Jones model, the attractive interaction between two atoms separated by twice the equilibrium distance decreases to 3.13% of that of two atoms at the equilibrium distance and is therefore negligible (Supplementary Fig. 1). Two crystals with a separation distance greater than twice the largest atomic distance in the crystal can therefore be considered as having no contact. The interplanar spacing of the {111} plane of the face-centred cubic Pt crystal was 2.30 Å; thus, Pt nanocrystals with a separation distance larger than ~ 4.6 Å are not in contact. Figure 1 shows a representative Pt nanocrystal after multiple cycles of ‘head-to-head’ welding and fracture. Images captured along the zone axis clearly show the (111) planes. We first maintained the distance between the two fractured nanocrystals at more than 1 nm for ~ 180 s to ensure that welding did not occur at this distance. The nanocrystals were then brough closer for welding. Fig. 1a depicts “cycle 1”, wherein two Pt nanocrystals are welded into a perfect single crystal, and then fractured again with loading. Cold welding can result in an unusual phenomenon, in which two separate nanocrystals are welded into a single crystal. With sufficiently small distances between the front surfaces of the tip of the crystals, an atomic-scale chain was formed between the two separated nanocrystals (Fig. 1a). The width of this atomic-scale chain was increased to 7, 10, and then to16 layers, thereby bridging the separated nanocrystals without forming an interface or defects, resulting in a perfect single crystal via the welding of the two separated nanocrystals. This same nanocrystal underwent a second and third welding and fracture, denoted “cycle 2” and “cycle 3”, during which a molecular chain containing 7 layers was formed at this fracture via cold welding, and subsequently fractured with reloading (Fig. 1b). Cold welding led to fracture restoration, whereas reloading led to fracture formation. A comparison of the width of the chains with the distances between the two separated nanocrystals showed that the width of the chains depends on the initial distance between the two nanocrystals. An atomic-scale chain formed between two nanocrystals separated by ~ 4.6 Å, with no direct contact, thereby forming a defect-free single crystal (Fig. 2a). The width of this chain increased to 15 layers within 62.7 s, with average growth rate of 0.24 layers/s. Similarly, a chain with 7 layers was formed between two nanocrystals separated by 4.8 Å between the two tips within 40.3 s, with average growth rate of 0.17 layers/s (Fig. 2b). As distance between the two fracture tips increased to 5.8 Å, as shown in Fig. 2c, the width of the chain increased into 9 layers after 452.2 s (Fig. 2c), giving a corresponding average growth rate of ~ 0.02 layers/s, nearly 1 order of magnitude lower than that in the previous examples (Fig. 2a and 2b). These observations indicate that the welding rate of two nanocrystals is significantly affected by the distance between the crystals. Further experiments using various distances between the two separated nanocrystals confirmed the dependence of the welding rate on the distance between the crystals (also see Fig. 3j). Magnified in-situ TEM images captured along the zone axis show the atomic-scale welding of two separated nanocrystals into a single-crystal without direct contact (Fig. 3a-d). The crack tip with distance of ~ 6.6 Å (Fig. 3a) is about three times of the (111) plane. After 3s, a monatomic chain was formed between these tips (Fig.3b). At 5s, another atom-column was also inserted in-between the tip of the nanocrystals, resulting in the formation of a diatomic chain (Fig. 3c). A triatomic chain is formed in the same manner (Fig. 3d), indicating cold welding proceeds in a layer-by-layer mechanism, which also involves rearrangement of the atoms near the surface of nanocrystal to accommodate the welding. Fig. 3e-h show the intensity profiles corresponding to the red framed region of Fig. 3a-d, respectively. These intensity profiles corresponding the welded procedures from “0 layer” to “1 layer” and then to “2 layers” and finally to “3 layers”, which supply details that elucidate the mechanism of cold welding. The intensity profile corresponding to the red framed region of Fig. 3a shows only two peaks corresponding to the tips of the fractured nanocrystal before welding (Fig. 3e). After welding was initiated, a clear peak appeared in between these two peaks, as denoted by an arrow in Fig. 3f. This peak does not correspond to the original fractured nanocrystal and was therefore attributed to atomic diffusion from the nearby free surface. The intensity profile corresponding to Fig. 3c shows two atomic chains resulting from atomic diffusion (Fig. 3g). Similarly, Fig. 3h shows three such peaks, further confirming the occurrence of atomic diffusion during cold welding (Supplementary Fig. 2). Fig. 3i displays the statistical analysis showing that cold-welding initiation is dependent on the distances between the two fracture tips, where the x-axis represents the numbers of the fracture nanocrystals, the y-axis represents the measured distances between the two fracture tips. In Fig. 3i, the orange circle dots denoted that the welding can be initiated, while the blue circle dots denoted that welding can’t be initiated. From Fig. 3i, one can see the cold welding only occurs when the distance between the two tips is below ~ 7.8 Å (Supplementary Figs. 3, 4 and 5), which is more than double the lattice spacing of the (111) plane. Fig. 3j shows the statistical results of the width vs time of the welding nanocrystals, where the x-axis represents the welded times, the y-axis represents the measured width of the nanocrystals. As shown in Fig. 3j, the cold welding cannot be initiated when the distance of the two tips exceeded ~ 8 Å even after several minutes. We also found that the smaller the distance between the two tips, the higher the growth rate of the molecular chain. When the distance of the two tips was between 3 Å ~ 5 Å, the width of the molecular chain between the nanocrystals reached 10 atomic layers in ~15 s, whereas that of the molecular chain between nanocrystals separated by 7 Å ~ 8 Å reached only 6 layers in ~30 s. In situ atomic-scale observations show that cold welding can restore fractured nanocrystals via atomic diffusion and surface relaxation facilitated by the high density of steps and corners 44 on the nanocrystals. To explain our observations, three structural models were constructed and the welding of the surfaces (Fig. 4a) and edges was simulated using first-principles calculations (Figs. 4d and g). In the simplest surface-to-surface model (Fig. 4a), the adsorption energy of an atom on the surface between both crystals decreases significantly with reduced spacing (Fig. 4b), indicating that adsorption stability is achieved below a critical spacing of approximately 8 Å. This trend in the adsorption energy was correlated with variations in the diffusion barrier (Supplementary Fig. 6), which is consistent with the experimental observations of spacing-dependent growth rates (Fig. 3j). Welding of crystals with spacings between 5.3 Å and 8 Å via atomic adsorption (Fig. 4c) in between the nanocrystals effectively narrows the gap. The adsorbed atoms, along with surface atoms, subsequently undergo shuffling and relaxation to progressively join the two surfaces. At spacings below 5.3 Å, the gap is insufficient to accommodate two atomic layers; thus, welding is realized via the adsorption of individual atoms (Fig. 4c right and Supplementary Fig. 7). We also examine two edge-to-edge models. The symmetric model features equivalent edges comprising co-edged (111) and (100) crystal surfaces with parallel (111) and (100) surfaces. This model considered three initial adsorption sites (Fig. 4d); however, only the stability-distance relationship curve of the most stable site was plotted (Fig. 4e). The adsorption energy of an adsorbed atom remains essentially consistent at a gap width ( d ) of 5 Å or more (Fig. 4e, blue shadowed region). At this distance, a diffusing atom (Fig. 4f, middle inset) preferentially binds to the (100) surface (site B), expanding the (111) surface (Fig. 4f, right inset) owing to its lower surface energy. Because the two (111) surfaces are parallel, this expansion gradually narrows the gap width between the edges, thereby transforming the edge-to-edge model into a simpler surface-to-surface model. Below 5 Å, the adsorption energy abruptly decreases, initiating direct welding (Fig. 4f, left). A diffusing surface atom is first adsorbed at site A, promoting bidirectional lateral growth along the (111) crystal direction with additional diffusion of surface atoms occupying sites B and C (Figs. 4f, middle and right, and Supplementary Fig. 8). An asymmetric edge-to-edge model was constructed by replacing the upper edge of the symmetric model with an edge consisting of two co-edged (111) surfaces (Fig. 4g). Four initial adsorption sites were considered, and the stability-distance curve of the most stable site was plotted (Fig. 4h). The adsorption energy decreases at larger distances (up to 5.5 Å) as an adatom diffuses across the upper edge. At this distance, the preferrable adsorption position shifts from site B to site A at the smaller separations (Fig. 4h insets). Accordingly, welding occurs at larger gap distances than in the symmetric model. The diffusing atoms on the bottom (111)/(100) edge, favouring the C site, expand the (111) surface, causing unilateral growth and joining of the unparallel (100) and (111) surfaces (Fig. 4i). The diffusion barriers associated with these processes are typically less than 0.75 eV (Supplementary Fig. 9), which are easily overcome at ~100 ℃, facilitating atomic diffusion and cold welding 25,38,45 . DFT calculations also indicate that cold welding proceeds without mechanical manipulation or direct contact. This finding contrasts with those of previous studies, which suggest that pressure, or at least direct contact, and relatively high temperatures are necessary for cold welding 16,17 . In summary, the atomic-scale cold welding of fractured platinum nanocrystals was observed in situ with atomic resolution using TEM, providing direct evidence that cold welding occurs between two nanocrystals without direct contact. We identified a critical distance above which cold welding will not occur, and the probability of welding increases significantly if the distance between the head-to-head Pt nanowires is reduced. In situ atomic-scale observations indicated that cold welding was initiated by the formation of monatomic and diatomic chains between the two nanowire heads. Cold welding is facilitated by clean nanocrystal surfaces, surface atom shuffling, and rapid atom diffusion on the Pt nanowire surface. Our observations shed light on the intriguing process through which the critical distance can significantly affect cold welding, and provide significant insights toward understanding the cold-welding mechanism, which is expected to have potential applications in the future bottom-up assembly of one-dimensional metallic nanostructures and next-generation interconnects for extremely dense logic circuits. Methods DFT calculations Calculations were performed using the generalised gradient approximation in the Perdew-Burke-Ernzerhof (PBE) form 46 of the exchange-correlation potential, projector augmented wave method 47 , and plane-wave basis set implemented in the Vienna ab-initio simulation package 48 . Grimme’s D3 form van der Waals correction was considered with the PBE exchange functional (PBE-D3) 49 for all structural relaxations. The structures were fully relaxed until the residual force per atom was less than 0.02 eV/Å. A plane wave energy cutoff of 350 eV was adopted to calculate the structural relaxation. A Dual-Slab Model 50 was adopted, consisting of at least five layers of Pt atoms in each slab separated by a vacuum region. The first Brillouin zones in the surface-to-surface and edge-to-edge models were sampled using a 3 × 3 × 1 k-mesh and a 2×3×1 k-mesh, respectively. A vacuum layer ( >15 Å) was adopted to reduce the image interactions. The diffusion barrier was estimated using the nudged elastic band method 51 . Declarations Acknowledgements This work was supported by the National Key R & D Program of China (2021YFA1200201), the Natural Science Foundation of China (12174014, 51771004, 91860202, 11974422), the Beijing Nova Program (20230484437), and the ‘‘111’’ Project (DB18015). W.J gratefully acknowledges financial support the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grants No. 22XNKJ30). Calculations were performed at the Physics Lab of High-Performance Computing (PLHPC-RUC) and the Public Computing Cloud (PCC-RUC) of Renmin University of China. Y.L. acknowledges the funding support from Research Grants Council of the Hong Kong Special Administrative Region, China underRFS2021-1S05 and C7074-23G. Author contributions X.H. and L.W. initiated and supervised the research. Y.G. performed the in-situ TEM experiments and analysed the data by the supervision of L.W. and X.H. J.T. synthesized the thin films. D.G. and C.Q. conducted the DFT calculations and analysed the results under the guidance of W.J. and F.D. Y.G., L.W. and W.J. wrote the initial draft. L.W., Y.L. and X.H. finalized the paper. All authors contributed to the discussion of the results and commented on the paper. Competing interests The authors declare no competing interests. Data availability The data supporting the findings of this study are available from the corresponding authors upon request. 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Efficient methods for finding transition states in chemical reactions: comparison of improved dimer method and partitioned rational function optimization method. J. Chem. Phys. 123 , 224101 (2005). Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.docx Supplementary Information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5989110","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":418266183,"identity":"18fb1f8a-8af9-4314-9cec-c26f3ba37306","order_by":0,"name":"Lihua 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Beijing","correspondingAuthor":false,"prefix":"","firstName":"Jiao","middleName":"","lastName":"Teng","suffix":""},{"id":418266189,"identity":"110cd138-4c40-420a-968d-7bfce0518687","order_by":6,"name":"Haibo Long","email":"","orcid":"","institution":"Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China","correspondingAuthor":false,"prefix":"","firstName":"Haibo","middleName":"","lastName":"Long","suffix":""},{"id":418266190,"identity":"ea9a6bb7-eaa1-4df9-9b77-571ac8344cee","order_by":7,"name":"Shengcheng Mao","email":"","orcid":"https://orcid.org/0000-0002-1505-5165","institution":"Beijing University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Shengcheng","middleName":"","lastName":"Mao","suffix":""},{"id":418266191,"identity":"bde51002-81af-41b8-881a-93745de3642e","order_by":8,"name":"Ang Li","email":"","orcid":"https://orcid.org/0000-0002-9802-9359","institution":"Faculty of Materials and Manufacturing, Beijing Key Lab of Microstructure and Properties of Advanced Materials, Beijing University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Ang","middleName":"","lastName":"Li","suffix":""},{"id":418266192,"identity":"47262a77-7757-4300-8937-2533a4858425","order_by":9,"name":"Cong Wang","email":"","orcid":"https://orcid.org/0000-0002-5297-9586","institution":"Renmin University of China","correspondingAuthor":false,"prefix":"","firstName":"Cong","middleName":"","lastName":"Wang","suffix":""},{"id":418266193,"identity":"a6da9a44-e1a6-4655-a2a5-0daf42f17cf8","order_by":10,"name":"Ze Zhang","email":"","orcid":"https://orcid.org/0000-0002-1739-9033","institution":"Zhejiang University","correspondingAuthor":false,"prefix":"","firstName":"Ze","middleName":"","lastName":"Zhang","suffix":""},{"id":418266194,"identity":"ac43f810-8137-4205-8d19-c3cc9c07b65a","order_by":11,"name":"Feng Ding","email":"","orcid":"","institution":"Suzhou Laboratory","correspondingAuthor":false,"prefix":"","firstName":"Feng","middleName":"","lastName":"Ding","suffix":""},{"id":418266195,"identity":"e9861347-7b96-40ea-abb5-4b0429445803","order_by":12,"name":"Wei Ji","email":"","orcid":"https://orcid.org/0000-0001-5249-6624","institution":"Renmin University of China","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Ji","suffix":""},{"id":418266196,"identity":"feef2fc1-44ce-4f5b-845a-61cf3cbb4d69","order_by":13,"name":"Yang Lu","email":"","orcid":"https://orcid.org/0000-0002-9280-2718","institution":"The University of Hong Kong","correspondingAuthor":false,"prefix":"","firstName":"Yang","middleName":"","lastName":"Lu","suffix":""},{"id":418266197,"identity":"a3c3977d-8fa3-4d17-99ed-947378d0e322","order_by":14,"name":"Xiaodong Han","email":"","orcid":"https://orcid.org/0000-0002-3353-3802","institution":"Beijing Key Laboratory of Microstructure and Property of Advanced Materials, Beijing University of Technology.","correspondingAuthor":false,"prefix":"","firstName":"Xiaodong","middleName":"","lastName":"Han","suffix":""}],"badges":[],"createdAt":"2025-02-08 17:20:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5989110/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5989110/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":79060560,"identity":"a9de3175-b506-4a43-9f0c-23c535550494","added_by":"auto","created_at":"2025-03-24 02:05:42","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1226394,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eIn situ\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eHRTEM images showing multiple cycles of the non-contact cold welding process.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, In-situ cold welding and fracture of “Cycle 1”. The “0 layer” indicating the two separated nanocrystals before welding. When the two nanocrystals approach toward each other, welding was initiated by the formation of atomic chains between the nanocrystals. The thickness of the atomic chain increased from 7 atomic layers to 10 layers and then to 16 layers. The welded nanocrystal was then fractured by puling. \u003cstrong\u003eb\u003c/strong\u003e, The same nanocrystal underwent a second cycle of cold welding and fracture, denoted “Cycle 2”. \u003cstrong\u003ec\u003c/strong\u003e, The same nanocrystal underwent a third cycle of cold welding and fracture, denoted “Cycle 3”.\u003c/p\u003e","description":"","filename":"Fig.1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5989110/v1/28c50cb9bab9bc1215661f20.jpg"},{"id":79060965,"identity":"65e7f6a4-18d5-46ba-acd2-9754117e0ff3","added_by":"auto","created_at":"2025-03-24 02:13:42","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1017060,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eIn situ\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eobservation of the atomic-scale non-contact cold welding at different distances.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, The distance between the two nanocrystals is ~ 4.6 Å, the atomic-scale chain grows to a thickness of 4 atomic layers in 3.4 s, and to 15 atomic layers in 62.7 s. \u003cstrong\u003eb\u003c/strong\u003e, Another example of cold welding at a distance of ~4.8 Å: the atomic chain grows to a thickness of 7 atomic layers in 40.3 s. The width of atomic-chain increased from 4 to 7 atomic-layers in a layer-by-layer welding process. \u003cstrong\u003ec\u003c/strong\u003e, The atomic chain between two nanocrystals with a separation distance of ~5.8 Å grows to a thickness of 9 atomic layers in 452.2 s.\u003c/p\u003e","description":"","filename":"Fig.2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5989110/v1/a44c0b62331291e5ea469056.jpg"},{"id":79060561,"identity":"23702001-c415-4e46-b5c0-8af750427a41","added_by":"auto","created_at":"2025-03-24 02:05:42","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":606251,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAtomic diffusion and the distance dependence in non-contact cold welding.\u003c/strong\u003e \u003cstrong\u003ea,\u003c/strong\u003eThe two separated nanocrystals before the initiation of cold welding. \u003cstrong\u003eb\u003c/strong\u003e–\u003cstrong\u003ed,\u003c/strong\u003eCold welding was initiated via the formation of a monatomic chain between the nanocrystals, which then grew into a diatomic and triatomic chain, indicating a layer-by-layer welding process. \u003cstrong\u003ee\u003c/strong\u003e–\u003cstrong\u003eh\u003c/strong\u003e, Intensity profiles corresponding to (\u003cstrong\u003ea\u003c/strong\u003e–\u003cstrong\u003ed\u003c/strong\u003e). The peaks denoted by these arrows indicate the cold welding via atomic chains that bridge the nanocrystals. \u003cstrong\u003ei\u003c/strong\u003e, A diagram of the separation distances vs welding cycles. The estimated critical distance for welding initiation is ~ 7.8 Å. The orange/blue circles represent cases where cold welding was/was not observed, respectively. \u003cstrong\u003ej\u003c/strong\u003e, The growth of the atomic chain vs time for different cases.\u003c/p\u003e","description":"","filename":"Fig.3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5989110/v1/35c9b4692232b304dcd5ead7.jpg"},{"id":79060563,"identity":"08f7caf8-bf31-4603-b37f-439038f86b80","added_by":"auto","created_at":"2025-03-24 02:05:42","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":416361,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eModels and welding mechanisms from first principles calculations.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Model of surface (100) to surface (100). Blue balls represent diffusing atoms. \u003cstrong\u003eb\u003c/strong\u003e, The adsorption energy vs distance in the model shown in Fig. 4a. Orange and blue regions represent regions of rapid direct welding and welding via atomic diffusion, respectively. \u003cstrong\u003ec\u003c/strong\u003e, Welding of the (100) surface to (100) surface at various distances. The black dotted line represents growth front. \u003cstrong\u003ed\u003c/strong\u003e, Edge (100)/(111) to edge (100)/(111) model. Blue atoms represent different adsorption sites. \u003cstrong\u003ee\u003c/strong\u003e, The adsorption energy vs distance and \u003cstrong\u003ef\u003c/strong\u003e, schematic of atomic welding at 5 Å in the edge (100)/(111) to edge (100)(111) model. \u003cstrong\u003eg\u003c/strong\u003e, Edge (111)/(111) to edge (100)/(111) model. \u003cstrong\u003eh\u003c/strong\u003e, The adsorption energy vs distance and \u003cstrong\u003ei\u003c/strong\u003e, schematic of atomic welding at 5.5 Å in the edge (111)/(111) to edge(100)/(111) model. Only the most stable adsorption sites are plotted in Fig. 4e and 4h.\u003c/p\u003e","description":"","filename":"Fig.4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5989110/v1/bafefa3726079711c04db080.jpg"},{"id":79061096,"identity":"97142e53-24c1-4438-87ce-445413be6768","added_by":"auto","created_at":"2025-03-24 02:21:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3933858,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5989110/v1/15778efd-68ae-4ea1-92c9-5082a04867d5.pdf"},{"id":79060564,"identity":"ad9e0837-8f63-4691-a9c4-17f7a60c5469","added_by":"auto","created_at":"2025-03-24 02:05:42","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5836574,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-5989110/v1/f44e8a21ada863d6f0eb8213.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Cold welding without direct contact","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWelding techniques are fundamental for joining metallic parts and are widely used in constructing machines and connecting electronic devices, among other applications. These techniques have also been used in the construction of hierarchical structures from nanoobjects, enabling the electronic, optical, and magnetic properties of the integrated materials to be tailored to specific applications\u003csup\u003e1\u0026ndash;15\u003c/sup\u003e. Traditional welding methods typically require high compressive stress between the parts, ensuring a sufficient direct contact area at the joint position\u003csup\u003e8,16\u0026ndash;18\u003c/sup\u003e,\u0026nbsp;along with elevated temperatures achieved via thermal\u003csup\u003e19\u003c/sup\u003e, laser\u003csup\u003e20\u003c/sup\u003e, and joule heating\u003csup\u003e21,22\u003c/sup\u003e. At\u0026nbsp;the\u0026nbsp;nanometre scale, two metal parts can be welded together at room temperature\u003csup\u003e1,4,5,9\u0026ndash;11,23\u0026ndash;30\u003c/sup\u003e. While compressive stress\u0026nbsp;is generally applied between the two parts during the cold-welding process\u0026nbsp;to ensure direct contact between the two welded metals\u003csup\u003e4,5,31\u003c/sup\u003e. This finding supports the widely\u0026nbsp;held belief that direct contact is essential for metal welding: however, no direct evidence supports this.\u0026nbsp;Despite numerous studies were carried out, direct experimental evidence of atomic-scale cold welding is lacking; thus, the mechanism of how cold welding between two parts is initiated remains unknown\u003csup\u003e11,22,32\u003c/sup\u003e. Additionally, as the size of those device down to nanosize, conventional welding techniques to connect electronic devices and metallic circuits presents significant challenges owing to the required high temperatures and compressive stresses, which may deform the materials at the joint\u003csup\u003e33\u0026ndash;35\u003c/sup\u003e and thus adversely affect their conductivity and reliability. This problem is particularly significant in the construction of nanoscale electronic devices and circuits\u003csup\u003e36\u003c/sup\u003e, in which material stability and integrity are critical for device performance. The continued miniaturisation of electronic devices will necessitate the use of innovative welding techniques operable at room temperature with negligible residual stress to avoid structural deformation at the joint position. A technology that enables direct atomic-scale in-situ observations of the cold-welding process and welding nanomaterials with negligible stress, heat, and structural changes is highly desired.\u003c/p\u003e\n\u003cp\u003eIn this study, the cold welding of Pt nanocrystals were observed in situ using aberration-corrected transmission electron microscopy (Cs-TEM)\u003csup\u003e23,37\u0026ndash;39\u003c/sup\u003e. Multiple cycles of atomic-scale cold welding and fracture were observed in situ at low temperature, revealing that two Pt nanocrystals within ~7.8 \u0026Aring; of each other can be cold welded together without direct contact. The cold-welding process was initiated via the formation of a monatomic chain between the two nanocrystals, which then grew to form diatomic and triatomic chains before finally restoring the nanocrystals layer-by-layer. Extensive testing revealed a critical distance of approximately 7.8 \u0026Aring;, above which cold welding does not occur. Density functional theory (DFT) calculations and atomic simulations revealed the atomic mechanism of cold welding and suggest that the adsorption energy decreases with the reduction of the separation distance between the crystals, thereby facilitating cold welding. Both practical experiments and DFT calculations indicate that the growth rate of the welding joint is inversely proportional to\u0026nbsp;the\u0026nbsp;distance between the nanocrystals.\u003c/p\u003e\n\u003cp\u003eIn this study, a Pt thin film (approximately 50 nm thick) was deposited on a single-crystal of NaCl via magnetron sputtering. The NaCl substrate was then dissolved in water to remove the thin film from the substrate and obtain free-standing thin films, which were then attached to an in situ TEM tensile device\u003csup\u003e40\u0026ndash;42\u003c/sup\u003e and further milled using a Fischione 1040 NanoMill\u003csup\u003e43\u003c/sup\u003e to form numerous Pt nanocrystals in the sample. The sample was subjected to multiple cycles of tensile fracture and cold-welding under TEM observation using the in-situ TEM tensile device, which allows the displacement to be slowly and gently controlled while retaining the double-tilt capability, such that the sample can be oriented appropriately to a low-index crystallographic zone orientation for\u0026nbsp;atomic-scale imaging. This procedure allowed the tensile fracture\u0026nbsp;and cold-welding of single-crystalline nanocrystals\u0026nbsp;to be observed\u0026nbsp;in situ\u0026nbsp;at\u0026nbsp;the atomic scale in real time.\u0026nbsp;Cold-welding was performed below ~ 100 \u0026deg;C\u0026nbsp;using an\u0026nbsp;FEI-Titan TEM equipped with an aberration\u0026nbsp;corrector operated at 300 kV.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur experiments involved cold welding and fracture tests of several Pt nanocrystals, which showed that fractured single-crystalline nanocrystals can be easily repaired via cold welding without direct contact. According to the Lennard\u0026ndash;Jones model, the attractive interaction between two atoms separated by twice the equilibrium distance decreases to 3.13% of that of two atoms at the equilibrium distance and is therefore negligible (Supplementary Fig. 1).\u0026nbsp;Two crystals with a separation distance greater than twice the largest atomic distance in the crystal can therefore be considered as having no contact. The interplanar spacing of the {111} plane of the face-centred cubic Pt crystal was 2.30 \u0026Aring;; thus, Pt nanocrystals with a separation distance larger than ~ 4.6 \u0026Aring; are not in contact. Figure 1\u0026nbsp;shows a representative Pt nanocrystal after multiple cycles of \u0026lsquo;head-to-head\u0026rsquo; welding and fracture. Images captured along the \u0026lt;110\u0026gt; zone axis clearly show the (111) planes. We first maintained the distance between the two fractured nanocrystals at more than 1 nm for ~ 180 s to ensure that welding did not occur at this distance. The nanocrystals were then brough closer for welding. Fig. 1a depicts \u0026ldquo;cycle 1\u0026rdquo;, wherein two Pt nanocrystals are welded into a perfect single crystal, and then fractured again with loading. Cold welding can result in an unusual phenomenon, in which two separate nanocrystals are welded into a single crystal. With sufficiently small distances between the front surfaces of the tip of the crystals, an atomic-scale chain was formed between the two separated nanocrystals (Fig. 1a). The width of this atomic-scale chain was increased to 7, 10, and then to16 layers, thereby bridging the separated nanocrystals without forming an interface or defects, resulting in a perfect single crystal via the welding of the two separated nanocrystals. This same nanocrystal underwent a second and third welding and fracture, denoted \u0026ldquo;cycle 2\u0026rdquo; and \u0026ldquo;cycle 3\u0026rdquo;, during which a molecular chain containing 7 layers was formed at this fracture via cold welding, and subsequently fractured with reloading (Fig. 1b). Cold welding led to fracture restoration, whereas reloading led to fracture formation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA comparison of the width of the chains with the distances between the two separated nanocrystals showed that the width of the chains depends on the initial distance between the two nanocrystals. An atomic-scale chain formed between two nanocrystals separated by ~ 4.6 \u0026Aring;, with no direct contact, thereby forming a defect-free single crystal (Fig. 2a). The width of this chain increased to 15 layers within 62.7 s, with average growth rate of 0.24 layers/s. Similarly, a chain with 7 layers was formed between two nanocrystals separated by 4.8 \u0026Aring; between the two tips within 40.3 s, with average growth rate of 0.17 layers/s (Fig. 2b). As distance between the two fracture tips increased to 5.8 \u0026Aring;, as shown in\u0026nbsp;Fig. 2c,\u0026nbsp;the\u0026nbsp;width of the chain increased into 9 layers after 452.2 s (Fig. 2c), giving a corresponding average growth rate of ~ 0.02 layers/s, nearly 1 order of magnitude lower than that in the previous examples (Fig. 2a and 2b). These observations indicate that the\u0026nbsp;welding rate of two\u0026nbsp;nanocrystals is significantly affected by the distance between the crystals. Further experiments using various distances between the two separated nanocrystals confirmed the dependence of the welding rate on the distance between the crystals (also see Fig. 3j).\u003c/p\u003e\n\u003cp\u003eMagnified in-situ TEM images captured along the \u0026lt;110\u0026gt; zone axis show the atomic-scale welding of two separated nanocrystals into a single-crystal without direct contact (Fig. 3a-d). The crack tip with distance of ~ 6.6 \u0026Aring; (Fig. 3a) is about\u0026nbsp;three times of the (111) plane. After 3s, a monatomic chain was formed between these tips (Fig.3b). At 5s, another atom-column was also inserted in-between the tip of the nanocrystals, resulting in the formation of a diatomic chain (Fig. 3c). A triatomic chain is formed in the same manner (Fig. 3d), indicating cold welding proceeds in a layer-by-layer mechanism, which also involves rearrangement of the atoms near the surface of nanocrystal to accommodate the welding. Fig. 3e-h show the intensity profiles corresponding to the red framed region of Fig. 3a-d, respectively. These intensity profiles corresponding the welded procedures from \u0026ldquo;0 layer\u0026rdquo; to \u0026ldquo;1 layer\u0026rdquo; and then to \u0026ldquo;2 layers\u0026rdquo; and finally to \u0026ldquo;3 layers\u0026rdquo;, which supply details that elucidate the mechanism of cold welding. The intensity profile corresponding to the red framed region of Fig. 3a shows only two peaks corresponding to the tips of the fractured nanocrystal before welding (Fig. 3e). After welding was initiated, a clear peak appeared in between these two peaks, as denoted by an arrow in Fig. 3f. This peak does not correspond to the original fractured nanocrystal and was therefore attributed to atomic diffusion from the nearby free surface. The intensity profile corresponding to Fig. 3c shows two atomic chains resulting from atomic diffusion (Fig. 3g). Similarly, Fig. 3h shows three such peaks, further confirming the occurrence of atomic diffusion during cold welding (Supplementary Fig. 2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig. 3i\u0026nbsp;displays the statistical analysis showing that cold-welding initiation is dependent on the distances between the two fracture tips, where the x-axis represents the numbers of the fracture nanocrystals, the y-axis represents the measured distances between the two fracture tips. In Fig. 3i, the orange circle dots denoted that the welding can be initiated, while the blue circle dots denoted that welding can\u0026rsquo;t be initiated. From Fig. 3i, one can see the cold welding only occurs when the distance between the two tips is below ~ 7.8 \u0026Aring; (Supplementary\u0026nbsp;Figs. 3, 4 and 5), which is more than double the lattice spacing\u0026nbsp;of the (111) plane.\u0026nbsp;Fig. 3j\u0026nbsp;shows the statistical results of the width vs\u0026nbsp;time\u0026nbsp;of the welding nanocrystals, where the x-axis represents the welded times, the y-axis represents the measured width of the nanocrystals. As shown in Fig. 3j, the cold welding cannot be initiated when the distance of the two tips exceeded ~ 8\u0026nbsp;\u0026Aring;\u0026nbsp;even after several minutes. We also found that the smaller the distance between the two tips, the higher the growth rate of the molecular chain.\u0026nbsp;When the distance of the two tips was between 3 \u0026Aring; ~ 5 \u0026Aring;, the width of the molecular chain between the nanocrystals reached 10 atomic layers in ~15 s, whereas that of the molecular chain between nanocrystals separated by 7 \u0026Aring; ~ 8 \u0026Aring; reached only 6 layers in ~30 s.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn situ atomic-scale observations show that cold welding can restore fractured nanocrystals via atomic diffusion and surface relaxation facilitated by the high density of steps and corners\u003csup\u003e44\u003c/sup\u003e on the nanocrystals. To explain our observations, three structural models were constructed and the welding of the surfaces (Fig. 4a) and edges was simulated using first-principles calculations (Figs. 4d and g). In the simplest surface-to-surface model (Fig. 4a), the adsorption energy of an atom on the surface between both crystals decreases significantly with reduced spacing (Fig. 4b), indicating that adsorption stability is achieved below a critical spacing of approximately 8 \u0026Aring;. This trend in the adsorption energy was correlated with variations in the diffusion barrier (Supplementary Fig. 6), which is consistent with the experimental observations of spacing-dependent growth rates (Fig. 3j). Welding of crystals with spacings between 5.3 \u0026Aring; and 8 \u0026Aring; via atomic adsorption (Fig. 4c) in between the nanocrystals effectively narrows the gap. The adsorbed atoms, along with surface atoms, subsequently undergo shuffling and relaxation to progressively join the two surfaces. At spacings below 5.3 \u0026Aring;, the gap is insufficient to accommodate two atomic layers; thus, welding is realized via the adsorption of individual atoms (Fig. 4c right and Supplementary Fig. 7).\u003c/p\u003e\n\u003cp\u003eWe also examine two edge-to-edge models. The symmetric model features equivalent edges comprising co-edged (111) and (100) crystal surfaces with parallel (111) and (100) surfaces. This model considered three initial adsorption sites (Fig. 4d); however, only the stability-distance relationship curve of the most stable site was plotted (Fig. 4e). The adsorption energy of an adsorbed atom remains essentially consistent at a gap width (\u003cem\u003ed\u003c/em\u003e) of 5 \u0026Aring; or more (Fig. 4e, blue shadowed region). At this distance, a diffusing atom (Fig. 4f, middle inset) preferentially binds to the (100) surface (site B), expanding the (111) surface (Fig. 4f, right inset) owing to its lower surface energy. Because the two (111) surfaces are parallel, this expansion gradually narrows the gap width between the edges, thereby transforming the edge-to-edge model into a simpler surface-to-surface model. Below 5 \u0026Aring;, the adsorption energy abruptly decreases, initiating direct welding (Fig. 4f, left). A diffusing surface atom is first adsorbed at site A, promoting bidirectional lateral growth along the (111) crystal direction with additional diffusion of surface atoms occupying sites B and C (Figs. 4f, middle and right, and Supplementary Fig. 8).\u003c/p\u003e\n\u003cp\u003eAn asymmetric edge-to-edge model was constructed by replacing the upper edge of the symmetric model with an edge consisting of two co-edged (111) surfaces (Fig. 4g). Four initial adsorption sites were considered, and the stability-distance curve of the most stable site was plotted (Fig. 4h). The adsorption energy decreases at larger distances (up to 5.5 \u0026Aring;) as an adatom diffuses across the upper edge. At this distance, the preferrable adsorption position shifts from site B to site A at the smaller separations (Fig. 4h\u0026nbsp;insets). Accordingly, welding occurs at larger gap distances than in the symmetric model. The diffusing atoms on the bottom (111)/(100) edge, favouring the C site, expand the (111) surface, causing unilateral growth and joining of the unparallel (100) and (111) surfaces (Fig. 4i). The diffusion barriers associated with these processes are typically less than 0.75 eV (Supplementary Fig. 9), which are easily overcome at ~100 ℃, facilitating atomic diffusion and cold welding\u003csup\u003e25,38,45\u003c/sup\u003e. DFT calculations also indicate that cold welding proceeds without mechanical manipulation or direct contact. This finding contrasts with those of previous studies, which suggest that pressure, or at least direct contact, and relatively high temperatures are necessary for cold welding\u003csup\u003e16,17\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eIn summary, the atomic-scale cold welding of fractured platinum nanocrystals was observed in situ with atomic resolution using TEM, providing direct evidence that cold welding occurs between two nanocrystals without direct contact. We identified a critical distance above which cold welding will not occur, and the probability of welding increases significantly if the distance between the head-to-head Pt nanowires is reduced. In situ atomic-scale observations indicated that cold welding was initiated by the formation of monatomic and diatomic chains between the two nanowire heads. Cold welding is facilitated by clean nanocrystal surfaces, surface atom shuffling, and rapid atom diffusion on the Pt nanowire surface. Our observations shed light on the intriguing process through which the critical distance can significantly affect cold welding, and provide significant insights toward understanding the cold-welding mechanism, which is expected to have potential applications in the future bottom-up assembly of one-dimensional metallic nanostructures and next-generation interconnects for extremely dense logic circuits.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eDFT calculations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCalculations were performed using the generalised gradient approximation in the Perdew-Burke-Ernzerhof (PBE) form\u003csup\u003e46\u003c/sup\u003e of the exchange-correlation potential, projector augmented wave method\u003csup\u003e47\u003c/sup\u003e, and plane-wave basis set implemented in the Vienna ab-initio simulation package\u003csup\u003e48\u003c/sup\u003e. Grimme\u0026rsquo;s D3 form van der Waals correction was considered with the PBE exchange functional (PBE-D3)\u003csup\u003e49\u003c/sup\u003e for all structural relaxations. The structures were fully relaxed until the residual force per atom was less than 0.02 eV/\u0026Aring;. A plane wave energy cutoff of 350 eV was adopted to calculate the structural relaxation. A Dual-Slab Model\u003csup\u003e50\u003c/sup\u003e was adopted, consisting of at least five layers of Pt atoms in each slab separated by a vacuum region.\u0026nbsp;The first Brillouin zones in the surface-to-surface and edge-to-edge models were sampled using a\u0026nbsp;3 \u0026times; 3 \u0026times; 1 k-mesh and\u0026nbsp;a 2\u0026times;3\u0026times;1 k-mesh, respectively. A vacuum layer ( \u0026gt;15 \u0026Aring;) was adopted to reduce the image interactions. The diffusion barrier was estimated using the nudged elastic band method\u003csup\u003e51\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Key R \u0026amp; D Program of China (2021YFA1200201), the Natural Science Foundation of China (12174014, 51771004, 91860202, 11974422), the Beijing Nova Program (20230484437), and the \u0026lsquo;\u0026lsquo;111\u0026rsquo;\u0026rsquo; Project (DB18015). W.J gratefully acknowledges financial support the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grants No. 22XNKJ30). Calculations were performed at the Physics Lab of High-Performance Computing (PLHPC-RUC) and the Public Computing Cloud (PCC-RUC) of Renmin University of China. Y.L. acknowledges the funding support from Research Grants Council of the Hong Kong Special Administrative Region, China underRFS2021-1S05 and C7074-23G.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX.H. and L.W. initiated and supervised the research. Y.G. performed the in-situ TEM experiments and analysed the data by the supervision of L.W. and X.H. J.T. synthesized the thin films. D.G. and C.Q. conducted the DFT calculations and analysed the results under the guidance of W.J. and F.D. Y.G., L.W. and W.J. wrote the initial draft. L.W., Y.L. and X.H. finalized the paper. All authors contributed to the discussion of the results and commented on the paper.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data supporting the findings of this study are available from the corresponding authors upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials \u0026amp; Correspondence\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence and requests for materials\u003c/strong\u003e should be addressed to Lihua Wang or Xiaodong Han.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eLu, Y., Huang, J. Y., Wang, C., Sun, S. \u0026amp; Lou, J. Cold welding of ultrathin gold nanowires. \u003cem\u003eNat. 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Phys.\u003c/em\u003e \u003cstrong\u003e123\u003c/strong\u003e, 224101 (2005).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5989110/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5989110/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Welding is widely used in the fabrication of electronic devices and hierarchical systems with desired mechanical and physical properties. Conventional welding generally requires both high temperatures and significant compressive stress to ensure direct contact between the welded parts. Accordingly, traditional welding process may cause deformation of the atomic structure at the joint of the parts, thereby greatly reducing the performance of the device. In this study, the atomic-scale welding two separate platinum nanocrystals into a single crystal was observed in situ. Cold welding was achieved at a relatively low temperature without direct contact between the two platinum nanocrystals, which were separated by a distance of ~ 7.8 Å, more than three times the lattice spacing. The in situ atomic-scale observation revealed that cold welding occurred via forming monatomic chain between the separated nanocrystals by diffusion of atoms, then this monatomic chain grew layer-by-layer into diatomic and triatomic chains. Density functional theory calculations revealed that the adsorption energy of the atoms decreased with the reduction of the separation distance of the two parts, facilitating cold welding. This study demonstrates the feasibility of cold welding without direct contact, thereby facilitating the construction of high-performance nanodevices by atomic engineering.","manuscriptTitle":"Cold welding without direct contact","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-24 02:05:37","doi":"10.21203/rs.3.rs-5989110/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-materials","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nmat","sideBox":"Learn more about [Nature Materials](http://www.nature.com/nmat/)","snPcode":"","submissionUrl":"","title":"Nature Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6872e4a4-2c13-4336-bb39-a38aa8a50ebe","owner":[],"postedDate":"March 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":44597758,"name":"Physical sciences/Materials science/Structural materials/Mechanical properties"},{"id":44597759,"name":"Physical sciences/Materials science/Nanoscale materials/Structural properties"},{"id":44597760,"name":"Physical sciences/Materials science/Structural materials/Metals and alloys"}],"tags":[],"updatedAt":"2025-03-24T02:05:37+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-24 02:05:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5989110","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5989110","identity":"rs-5989110","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}