Structural transformations originating from diverse rearrangements of the hydrogen bonding in water create various phases. Although most phases have been well investigated down to the molecular ...level, the molecular structure of the nanomeniscus, a ubiquitous form of nanoscale water in nature, still remains unexplored. Here, we demonstrate that the water nanomeniscus exhibits the stable, ice-VII-like molecular structure in ambient condition. Surface-enhanced Raman spectroscopy on trace amounts of water, confined in inter-nanoparticle gaps, shows a narrowed tetrahedral peak at 3340 cm
in the OH-stretching band as well as a lattice-vibrational mode at 230 cm
. In particular, the ice-VII-like characteristics are evidenced by the spectral independence with respect to temperature variations and differing surface types including the material, size and shape of nanoparticles. Our results provide un unambiguous identification of the molecular structure of nanoconfined water, which is useful for understanding the molecular aspects of water in various nanoscale, including biological, environments.
Friction in an ambient condition involves highly nonlinear interactions of capillary force, induced by the capillary-condensed water nanobridges between contact or noncontact asperities of two ...sliding surfaces. Since the real contact area of sliding solids is much smaller than the apparent contact area, the nanobridges formed on the distant asperities can contribute significantly to the overall friction. Therefore, it is essential to understand how the water nanobridges mediate the 'noncontact' friction, which helps narrow the gap between our knowledge of friction on the microscopic and macroscopic scales. Here we show, by using noncontact dynamic force spectroscopy, the single capillary bridge generates noncontact friction via its shear interaction. The pinning-depinning dynamics of the nanobridge's contact line produces nonviscous damping, which occurs even without normal load and dominates the capillary-induced hydrodynamic damping. The novel nanofriction mechanism may provide a deeper microscopic view of macroscopic friction in air where numerous asperities exist.
Capillary condensation is the first-order vapor-to-liquid phase transition taking place in confined geometries. Such heterogeneous nucleation has been well described by thermodynamic laws such as the ...Kelvin equation, but the equation’s applicability at the nanoscale is still unresolved. Here, we show that the Kelvin equation is valid down to approximately 0.5 nm radius of curvature when the curvature dependence of surface tension is taken into account. By the shear-mode atomic force microscopy, we have measured directly and accurately the critical tip-surface distance (dc) at which the water meniscus is capillary condensed in ambient condition; e.g.,dc≈1.2nmat 10% relative humidity. In particular, we can determine the Tolman length, the unique characteristic of the curvature-dependent surface tension, as the single fitting parameter (δ=0.21±0.05nm). Our results that unify the validity of the Kelvin equation at molecular scale and the characterization of the curvature effect of surface tension may provide a better understanding of general nucleation phenomena in nature, including the role of nanometric aerosols in cloud formation.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
We report a phenomenological observation of electric-field-induced formation and manipulation of liquid ball on an outer wall of the pulled pipette by using the quartz tuning fork-based atomic force ...microscope (QTF-AFM). The dye molecule solution with excitation wavelength of 488 nm and detection efficiency of 95% is used to investigate the movement characteristics of liquid droplets when the electric field is applied. The ejected liquid solution forms a microscale liquid droplet at the apex of the pipette by the application of electric field, containing dye molecules, which climbs up along the negatively charged outer surface of the pipette due to the electro-osmosis effect. With positive or negative bias voltages, we manipulate a liquid ball to slide upward or downward, respectively. This field-induced transport of a liquid droplet may be useful to nano-biotechnology or droplet-based microfluidic technology, for example, noncontact delivery and manipulation of liquid solution in the form of separated droplets.
We report a phenomenological observation of electric-field-induced formation and manipulation of liquid ball (dye molecule solution) on an outer wall of the pulled pipette by using the quartz tuning fork-based atomic force microscope (QTF-AFM). Display omitted
•Phenomenological observation of field-induced formation and manipulation of liquid ball.•Precise control of the tip-surface distance via a QTF-AFM.•Liquid ejection through the mechanically pulled pipette.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
We introduce a nanopipette/quartz tuning fork (QTF)-atomic force microscope (AFM) for nanolithography and a nanorod/QTF-AFM for nanoscratching with in situ detection of shear dynamics during ...performance. Capillary-condensed nanoscale water meniscus-mediated and electric field-assisted small-volume liquid ejection and nanolithography in ambient conditions are performed at a low bias voltage (~10 V) via a nanopipette/QTF-AFM. We produce and analyze Au nanoparticle-aggregated nanowire by using nanomeniscus-based particle stacking via a nanopipette/QTF-AFM. In addition, we perform a nanoscratching technique using in situ detection of the mechanical interactions of shear dynamics via a nanorod/QTF-AFM with force sensor capability and high sensitivity.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We present a general analytical theory that enables one to determine accurately the unknown tip-sample interactions from the experimental measurement of the amplitude and phase of the oscillating tip ...in amplitude-modulation atomic force microscopy (AM-AFM). We apply the method to the known Lennard-Jones-type forces and find excellent agreement with the reconstructed results. AM-AFM, widely used in air and liquid, is now not only an imaging tool but also a quantitative force measurement tool.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A quartz tuning fork and its qPlus configuration show different characteristics in their dynamic features, including peak amplitude, resonance frequency, and quality factor. Here, we present an ...electromechanical model that comprehensively describes the dynamic responses of an electrically driven tuning fork and its qPlus configuration. Based on the model, we theoretically derive and experimentally validate how the peak amplitude, resonance frequency, quality factor, and normalized capacitance are changed when transforming a tuning fork to its qPlus configuration. Furthermore, we introduce two experimentally measurable parameters that are intrinsic for a given tuning fork and not changed by the qPlus configuration. The present model and analysis allow quantitative prediction of the dynamic characteristics in tuning fork and qPlus, and thus could be useful to optimize the sensors' performance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We demonstrate that the designed and fabricated tuning fork resonators have quality factors of about 10
3
–10
4
in the diverse frequency range from 50 Hz to 10 kHz in ambient condition. Metal and ...ceramic materials such as tantalum, steel, silicon nitride are used as resonator materials for high quality factors with minimal loss of mechanical energy. Resonators of various sizes with a tuning fork shape are realized by metal 3D printing method as well as metal machining process. We show that the increase in crystallinity of the 3D printed PLA tuning fork via annealing leads to an increase in quality factor, by which we confirm that the material to be used as a resonator should be with high crystallinity rather than an amorphous state. In addition, since the quality factor depends on the mass symmetry of both prongs for the case of a tuning fork-type resonator, we improve the quality factor by matching the position and mass of the displacement-sensing accelerometer and the displacement-inducing actuator. The quality factor differences between predicted quality factor and measured one indicate that there are specific defects inside the material used as a resonator, which will be useful when the various-frequency tuning forks are employed as a highly sensitive force sensing resonator in the dynamic force microscopy and spectroscopy.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
When the surface of water is curved at nanoscale as a bubble, droplet and meniscus, its surface tension is expected to be smaller than that of planar interface, which still awaits experimental ...studies. Here, we report static and dynamic force spectroscopy that measures the capillary force of a single nanoscale water meniscus at constant curvature condition. Based on the Young-Laplace equation, the results are used to obtain the effective surface tension (ST) of the meniscus, which decreases to less than 20% of the bulk value at the radius-of-curvature (ROC) below 25 nm, while indicating the bulk behaviour above ~130 nm ROC. Interestingly, such a possibility provides a qualitative resolution of the unsettled discrepancies between experiments and theories in the thermodynamic activation processes for the mentioned three types of nano-curvatured water. Our results may not only lead to development of microscopic theories of ST as well as further experimental investigations, but also help better understanding of the ST-induced nanoscale dynamics such as cluster growth or protein folding, and the ST-controlled design of nano-biomaterials using the nano-meniscus.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Q-control technique enables to actively change the quality factor of the probe oscillation in dynamic atomic force microscopy. The Q-control is realized by adding a self-feedback loop into the ...original actuation-detection system, in which a damping force with controllable damping coefficient in magnitude and sign is applied to the oscillating probe. While the applied force alters the total damping interaction and thus the overall ‘signal’ of the probe motion, the added feedback system changes the ‘noise’ of the motion as well. Here, we systematically investigate the signal, the noise, and the signal-to-noise ratio of the qPlus sensor under the active Q-control. We quantify the noise of the qPlus motion by measuring the noise spectral density, which is reproduced by a harmonic oscillator model including the thermal and the measurement noises. We show that the noise signal increases with the quality factor controlled, scaling as the square root of the quality factor. Because the overall signal is linearly proportional to the quality factor, the signal-to-noise ratio scales as the square root of the quality factor. The Q-controlled qPlus with a highly enhanced Q, up to 10,000 in air, leads to the minimum detectable force gradient of 0.001 N/m, which would enhance the capability of the qPlus sensor for atomic force microscopy and spectroscopy.
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