Water meniscus

Aimed 2D structures are completely artificially generated using appropriate tools. The favourite tool is, without doubt, the AFM tip. Mirkin et al. applied AFM tools to use it as a pen [53,54]. With the help of the water meniscus between tip and surface, which is always present at a room atmosphere, molecules from a reservoir on top of the tip are transported to a surface, which must have strong attraction to at least one end of the molecules. 

The high surface tension of a water meniscus explains why various small insects are able to skate across the surface of a pond. 

Figure 3.27. Schematic representation of the DPN technique. A water meniscus forms between the AFM tip coated with alkanethiols and the gold substrate. The size of the meniscus, which is controlled by relative humidity, affects the molecular transport rate, the effective tip-substrate contact area, and DPN resolution.

Figure 2.21 shows two spherical, hydrophilic solid particles held together by a water meniscus. If the upper particle is held fixed, calculate the minimum force (F) required to pull the lower particle away. Assume that water has a zero contact angle with the solid. 

A colloidal particle is held on to a solid surface by a water meniscus, as illustrated in Figure 2.22. Estimate the minimum force (F) required to detach the particle. (Ignore the mass of the colloid.)... 

Figure 2.21 Two spherical particles held together by a water meniscus.

Figure 2.22 Colloidal particle attached to a solid surface by a water meniscus.

In dip-pen lithography, molecules (such as thiols) are placed on the AFM tip and delivered to a substrate surface (such as gold) via a water meniscus. The tip is loaded either by dipping in a solution or by vapour deposition. In damp air, a water meniscus... 

This same apparatus permits estimates to be made of the so-called jacketed compressibility (the reciprocal of the effective bulk modulus) during early cure. This is accomplished by applying momentary pressure to the bed alone (ram pressure) and observing the corresponding bed volume change in the water meniscus. 

Five significant figures are justified on the basis of the one set of data given, but repeated measurements would show that you would be unable to reproducibly adjust the water meniscus with four-place accuracy, so a density value of 8.411 g/ml would be more reasonable. 

Figure 14.18 Dip-pen nanolithography.122 The thiol ink is transferred from the tip to the gold substrate through the water meniscus between the tip and the substrate according to the direction of scan.

Allow the sample to come to ambient temperature, then mark the water meniscus on the site of the 1-L sample bottle for determination of the exact sample volume. Add 1 mL of the acetone-diluted internal standard solution (see Section 5.12) to the sample bottle. Cap the bottle, and mix the sample by gently shaking for 30 seconds. Filter the sample through a 0.45 micron filter that has been rinsed with toluene. 

The so-called dip-pen nanolithography is one of these promising novel techniques. It has been developed by Ch. Mirkin etal. and is based on the use of Atomic Force Microscopy (AFM) tips to deposit functionalized molecules on appropriate surfaces. The molecules are first deposited in solid state on the tip. The transport to the surface happens by means of the water meniscus between the tip and the surface that is present in air of usual humidity. Gold surfaces are preferably used to deposit thiol molecules forming strong Au-S bonds. The places were thiol molecules are deposited simply depend on the software moving the AFM tip on the surface. Figure 13 explains in a simplified manner the process. 

One of the innovative applications of scanning probe microscopy for nanolithography is dip pen nanolithography (DPN). In this special technique the water meniscus formed between the tip and the substrate acts as a medium for molecular transport. The technique depends on the key phenomenon that the molecule to be deposited on the substrate (which is referred as the ink ) can be transported in a controlled way from the tip (which is initially coated with the ink) to the substrate. The molecule (the ink) to be deposited on the substrate should interact with the substrate to form a chemical bond, leading to a stable structure [82]. 

The core concept that the water meniscus at the tip-substrate contact can indeed be controlled and can be used as the molecular transport medium came from basic investigations of water meniscus on lateral force microscopy (LFM) [83]. It was... 

One of the significant problems in MEMS operation under humid conditions is the high stiction forces owing to adsorbed water molecules on the device surfaces. The thickness of the condensed water layer varies with the relative humidity and the surface chemistry (hydrophilicity, hydrophobility, organic contamination, etc.). As water has a very high surface tension (ywater = 72dyn/cm), the water meniscus formed between two... 

SO acts as a focus for stress concentration. During drying and in machine draws, local stresses are set up in the sheet. If the local friction between the filler particle and the fibre surface is large, then the fibre network locks until the drying stress exceeds the local failure stress. When local failure occurs the water meniscus between the fibres may be broken the fibre surfaces are then too far apart for hydrogen bonding to develop and reconsolidation of the bond is unlikely. 

There have been a number of attempts to revise and elaborate Brown s description of the film formation process [11,30]. For an overview of these approaches the reader is refmed to Mazur s review [25]. Perhaps the most important insight is that in a strict thermodynamic sense, there is no distinction betweai the osmostic pressure, II, and the mean capillaiy pressure, pc, which develops when the meniscus intercepts the surface of the particles. As the system becomes more concentrated, there will be some contribution of capillary forces to 11 before the particles come into contact and before the particle-water meniscus develops. Ultimately, n must converge to pc once the particles are in contact This continuity of n and Pc is the main point of the theoretical analysis by Crowley et al. [31], and they showed that when the osmotic pressure rises to little as 1% of the equilibrium vapour pressure of water, the force should be sufficirait to densify the film. 

Figure 4.35 Schematic representation of dip-pen nanoiithography. An AFM tip is loaded by thioi moiecuies in this case, 16-thiohexadecanoic acid). Because of the presence of a naturai water meniscus, the thiols are transported onto a gold surface...

Due to ambient humidity, one or very few layers of absorbed water formed due to condensation results in the formation of water meniscus between the conductive tip and the substrate. Thus highly resistive electrolyte is formed by a thin water film in wet gas atmosphere which facilitates formation of nanostructures by oxidation of the metal substrate. The introduction of reference electrode in the electrochemical nanocell is not at all possible due to space constraint. A large potential drop in the electrolyte and at the counter electrode, i.e., AFM tip is encountered due to the absence of reference electrode. Several attempts have been made for nanostructure formation on metal substrates such as Si,... 

If the inside surface of each tube were coated with wax, would the general shape of the water meniscus change Would the general shape of the mercury meniscus change ... 

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