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The self-assembly of nanoparticle strips is stimulated and inhibited by contact angle. (a) and (b) Self-assembly occurs at larger contact angle. (c) The contact line is detached from the assembled nanoparticle strip accompanied by the decrease in contact angle when the blade is elevated. (d) Another nanoparticle strip is created after the blade moves closer to the substrate.
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The reliability and sensitivity of a strain gauge made from a nanoparticle monolayer intrinsically depend on electron tunneling between the adjacent nanoparticles, so that creating nanoscale interstitials with uniform distribution and tuning the interparticle separation reversibly during cyclic mechanical stress are two vital issues for performance...
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... able to tailor contact angle in a reliable manner is a key requirement to investigate the dependency of convective assembly on contact angle. Figure 3 illustrates the operating principle of nanoparticle assembly that can be triggered by contact angle. Solvent evaporation stimulates self-assembly of gold nanoparticles near the contact line as shown in Fig. 3(b) when the contact angle is appropriate. ...
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... to tailor contact angle in a reliable manner is a key requirement to investigate the dependency of convective assembly on contact angle. Figure 3 illustrates the operating principle of nanoparticle assembly that can be triggered by contact angle. Solvent evaporation stimulates self-assembly of gold nanoparticles near the contact line as shown in Fig. 3(b) when the contact angle is appropriate. When raising the blade upwards, the contact line abruptly detaches from the assembled nanoparticles. When the contact angle becomes smaller than what is shown in Fig. 3(b), the contact line continues to slip onto the glass substrate, and nanoparticle self-assembly switches off; this scenario is ...
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... can be triggered by contact angle. Solvent evaporation stimulates self-assembly of gold nanoparticles near the contact line as shown in Fig. 3(b) when the contact angle is appropriate. When raising the blade upwards, the contact line abruptly detaches from the assembled nanoparticles. When the contact angle becomes smaller than what is shown in Fig. 3(b), the contact line continues to slip onto the glass substrate, and nanoparticle self-assembly switches off; this scenario is illustrated in Fig. 3(c). The assembly process will not switch on again until the contact angle resumes a larger value (5°) after adjusting the blade [see Fig. 3(d)]. ...
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... the contact angle is appropriate. When raising the blade upwards, the contact line abruptly detaches from the assembled nanoparticles. When the contact angle becomes smaller than what is shown in Fig. 3(b), the contact line continues to slip onto the glass substrate, and nanoparticle self-assembly switches off; this scenario is illustrated in Fig. 3(c). The assembly process will not switch on again until the contact angle resumes a larger value (5°) after adjusting the blade [see Fig. 3(d)]. ...
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... the contact angle becomes smaller than what is shown in Fig. 3(b), the contact line continues to slip onto the glass substrate, and nanoparticle self-assembly switches off; this scenario is illustrated in Fig. 3(c). The assembly process will not switch on again until the contact angle resumes a larger value (5°) after adjusting the blade [see Fig. 3(d)]. ...
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... larger than the threshold value, strip width cannot increase infinitely. In theory, the threshold contact angle of ~4.2° needed to stimulate convective assembly corresponds to a nanoparticle monolayer with a maximum width of ~1.5 m, and this value is in good agreement with the statistical analysis of the strip width observed in this work (see Fig. S3 in the ...
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... For example, colloidal metal calchogenide quantum dots, metal and magnetic particles, inorganic particles of different materials (e.g. ZnO, TiO 2 , Nb 2 O 5 ), Janus particles, microgel particles, metal/hydrogel core/shell particles or objects of different shapes such as nanocubes, nanorods, carbon nanotubes, nanoplates, graphene and graphene oxide nanosheets have been assembled using drop coating and evaporation in a cell [133,293,294,[592][593][594][595][596], vertical deposition [346], drag coating [366,597], electric field based self-assembly [229], spin coating [245,598], interfacial self-assembly [244,246,521,522,529,541,552,553,567,585,[599][600][601][602][603][604][605][606][607][608][609]. It is noteworthy to observe how interfacial self-assembly is playing a rising role in self-assembly of very diverse materials. ...
Self-assembly of quasi-spherical colloidal particles in two-dimensional (2D) arrangements is essential for a wide range of applications from optoelectronics to surface engineering, from chemical and biological sensing to light harvesting and environmental remediation. Several self-assembly approaches have flourished throughout the years, with specific features in terms of complexity of the implementation, sensitivity to process parameters, characteristics of the final colloidal assembly. Selecting the proper method for a given application amidst the vast literature in this field can be a challenging task. In this review, we present an extensive classification and comparison of the different techniques adopted for 2D self-assembly in order to provide useful guidelines for scientists approaching this field. After an overview of the main applications of 2D colloidal assemblies, we describe the main mechanisms underlying their formation and introduce the mathematical tools commonly used to analyse their final morphology. Subsequently, we examine in detail each class of self-assembly techniques, with an explanation of the physical processes intervening in crystallization and a thorough investigation of the technical peculiarities of the different practical implementations. We point out the specific characteristics of the set-ups and apparatuses developed for self-assembly in terms of complexity, requirements, reproducibility, robustness, sensitivity to process parameters and morphology of the final colloidal pattern. Such an analysis will help the reader to individuate more easily the approach more suitable for a given application and will draw the attention towards the importance of the details of each implementation for the final results.
... With these unique characteristics, the assembled metallic thin films can be used for catalysis [13,14], surface-enhanced Raman scattering substrate [15,16], and mirror [17]. Recently, NP monolayer film, assembled at the liquid-gas interface within the confined space at micron scale, has been constructed as strain gauge, which shows superior sensitivity and dynamic response to the externally acoustic vibration [18]. Therefore, interfacial self-assembly is also a powerful bottom-up strategy to make functional unit of the nanoscale devices from NPs [19]. ...
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Material used in flexible devices may experience anisotropic strain with identical magnitude, outputting coherent signals that tend to have a serious impact on device reliability. In this work, the surface topography of the nanoparticles (NPs) is proposed to be a parameter to control the performance of strain gauge based on tunneling behavior. In contrast to anisotropic tunneling in a monolayer of spherical NPs, electron tunneling in a monolayer of urchin-like NPs actually exhibits a nearly isotropic response to strain with different loading orientations. Isotropic tunneling of the urchin-like NPs is caused by the interlocked pikes of these urchin-like NPs in a random manner during external mechanical stimulus. Topography-dependent isotropic tunneling in two dimensions reported here opens a new opportunity to create highly reliable electronics with superior performance.
... The stacking layer of each strip is correlated with the groove's diameter; thus an NP monolayer with a tiny gap is fabricated within the tiny grooves [49]. Recently, it was demonstrated that self-assembly of an NP monolayer consisting of parallel strips can be switched on and off by precisely tailoring the contact angle of gold colloids on substrates across a critical value of 4.2 • [50]. Whether and where the NP strips are created within a confined space on the micron scale depends on the magnitude of the contact angle, which can be quantitatively characterized by light interference (See Fig. 3) [50,51]. ...
... Recently, it was demonstrated that self-assembly of an NP monolayer consisting of parallel strips can be switched on and off by precisely tailoring the contact angle of gold colloids on substrates across a critical value of 4.2 • [50]. Whether and where the NP strips are created within a confined space on the micron scale depends on the magnitude of the contact angle, which can be quantitatively characterized by light interference (See Fig. 3) [50,51]. ...
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We demonstrate an ultrasensitive strain gauge based on a discontinuous metal film with a record detection limit as low as 8.3 × 10–6. Constructed by well-tunable crevices on the nanometer scale within the film, this gauge exhibits an ultrafast dynamic response to vibrations with a frequency range of 1 Hz to 10 kHz. More importantly, the temperature coefficient of resistivity (TCR) of the metal film is tunable owing to the cancellation effect caused by the possibility of tunneling across the nanoscale crevices (showing a negative temperature dependence) and the electron conduction within the metal islands (showing a positive temperature dependence). Consequently, a nullified TCR is achievable when the crevice size can be precisely controlled. Thus, a fabrication strategy to precisely control the nanoscale crevices was developed in this study through the real-time tracking of the electrical conductivity during thermal evaporation. The ultrasensitive strain gauge with a tunable thermal drift introduces numerous opportunities for precision devices and wearable electronics with superior reliability.[Figure not available: see fulltext.] © 2016 Tsinghua University Press and Springer-Verlag Berlin Heidelberg
... The electrical resistivity controlled by tunneling is exponentially dependent on the interparticle distance, hence, it is extremely sensitive to any external stress as demonstrated by Mueggenburg et al. [9]. Indeed, colloidal nanoparticles provide promising alternative to conventional resistive strain gauges based on metallic thin films and semiconductor piezoelectric resistive strain gauges [10,11]. It has been shown that a gauge factor (the ratio between the relative resistivity change and the applied stress) of the nanoparticle strain gauges can outperform that of the conventional ones by up to two orders of magnitude [4,6,[12][13][14]. ...
... The simulated models include Au/SiO 2 SHIN aggregates with dimer, trimer, heptamer, and nonamer structures situated onto a gold film, as illustrated in Figure 1a, which present the most typical multiparticle systems and can be fabricated by DNA assemble method, 2,8,28 nanoimprint lithography, 29 or con- vective assembly at the confined volume. 30 The diameter of the Au core, thickness of the SiO 2 shell and interparticle distance are set to 80, 1, and 1 nm, respectively. Taking the actual experimental conditions into account, the normal incident plane wave with polarization along the horizontal axis is adopted as the light source in the calculation model, as shown in Figure 1b. ...
The precise control over the locations of hot spots in a nanostructured ensemble is of great importance in plasmon-enhanced spectroscopy, chemical sensing and super resolution optical imaging. However, for multiparticle configurations over metal films that involve various localized and propagating surface plasmon modes, the locations of hot spots are difficult to predict due to complex plasmon competition and synergistic effects. In this work, theoretical simulations based on multiparticle-film configurations predict that the locations of hot spots can be efficiently controlled in the particle-particle gaps, the particle-film junctions, or in both, by suppressing or promoting specific plasmonic coupling effects in specific wavelength ranges. These findings offer an avenue to obtain strong Raman signals from molecules situated on single crystal surfaces, and simultaneously avoid signal interference from particle-particle gaps.
... The electrical resistivit y controlled by tunneling is exponentiall y dependent on the interparticle distance , hence, it is extremel y sensitive to any external stress as demonstrated by Mueggenburg et al. [8]. Indeed, colloidal nanoparticles provide promising alternative to conventio nal resistive strain gauges based on metallic thin films and semiconductor piezoelectric resistive strain gauges [9,10]. It has been shown that a gauge factor (the ratio between the relative resistivit y change and the applied stress) of the nanoparticle strain gauges can outperform that of the conventional ones by up to two orders of magnitude [4,6,11]. ...
SAXS, nanoparticle monolayer, strain sensor
