Non-linear statics and dynamics of nanoelectromechanical systems based on nanoplates and nanowires

2005 ◽  
Vol 219 (1) ◽  
pp. 29-40 ◽  
Author(s):  
N Pugno
Keyword(s):  
Free Energy ◽  
Van Der Waals ◽  
Hessian Matrix ◽  
Three Dimensional ◽  
Van Der Waals Forces ◽  
Structural Instability ◽  
Nanoelectromechanical Systems ◽  
Statics And Dynamics ◽  
Dimensional Element ◽  
Thermal Vibrations

An analysis of the three-dimensional nanoelectromechanical systems (NEMS) is presented. Nanotubes could be a key one-dimensional element in future NEMS device; but they would be inadequate when two- or three-dimensional structures are required. A general free-energy-based formulation to treat statics and dynamics of three-dimensional NEMS, according to classical or quantum mechanics, is derved and presenteed; the method is then applied to nanoplates and nanowires. The equilibrium and stability of an elastic (e.g., graphene sheet) nanoplate-based NEMS under an electrical field and van der Waals forces (pauli's repulsion and large displacements are also discussed) are evaluated by minimizing the free energy and by the sign of the determinant of its Hessian matrix. The structural instability, arising at ythre so-called pull-in voltage, would correspond to the switch of the device. The amplitude and frequency of the thermal vibrations of the nanoplate are evaluated as a function of the applied voltage. The effect of the van der Waals forces on the NEMS dynamics is also presented. The amplitude and frequency of the oscillations at O K, from the uncertainty principle, are estimated.

Van der Waals forces in oil–water systems from the study of thin lipid films - I. Measurement of the contact angle and the estimation of the van der Waals free energy of thinning of a film

1975 ◽  
Vol 347 (1649) ◽  
pp. 141-159 ◽  
Keyword(s):  
Free Energy ◽  
Van Der Waals ◽  
Monochromatic Light ◽  
Van Der Waals Forces ◽  
Contact Angles ◽  
Steric Interaction ◽  
Isotropic Layer ◽  
Free Energies ◽  
Lipid Film ◽  
Lipid Films

Free energies of formation of ‘black’ lipid films have been determined from measurements of their contact angles. The contact angles were calculated from the interference fringes formed in monochromatic light reflected from either the Plateau–Gibbs border or from lenses of bulk lipid solution trapped in the films. It is concluded that the electrostatic repulsion between the two surfaces of a film is negligibly small and that the ‘ steric’ interaction between the adsorbed monolayers of lipid molecules is of such short range that the free energy change during film formation originates almost entirely from work done by the van der Waals forces. The free energies determined for a range of different films all agree to within a factor of three with the free energy calculated from Lifshitz theory for water phases interacting across an isotropic layer of liquid hydrocarbon. Nevertheless, a systematic trend in the experimental data suggests that this picture of the lipid film is too simple and that either the polar groups of the lipid or the structure of the hydrocarbon region (or both) of the film have a significant influence on the results.

On the free energy of nematic wetting layers

1988 ◽  
Vol 66 (4) ◽  
pp. 553-556 ◽  
Author(s):  
Donald E. Sullivan ◽  
Reinhard Lipowsky
Keyword(s):  
Free Energy ◽  
Layer Thickness ◽  
Order Parameter ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
Wetting Layer ◽  
Nematic Director ◽  
The Mean ◽  
Wetting Layers

The contributions to the free energy of a nematic wetting layer as a function of its thickness l are analyzed. The longest-range contribution is due to distortion of the nematic director across the film, resulting from different preferred molecular orientations at the two interfaces bounding the film. Van der Waals forces as well as the decaying tails of the interfacial order-parameter profiles yield contributions to the free energy of successively shorter range. These effects lead to crossovers between different scaling régimes for variation of the mean wetting-layer thickness with temperature. Experimental implications of the results are described.

Generalized van der Waals theory. I. Basic formulation and application to uniform fluids

1980 ◽  
Vol 33 (9) ◽  
pp. 2013 ◽  
Author(s):  
S Nordholm ◽  
ADJ Haymet
Keyword(s):  
Free Energy ◽  
Equation Of State ◽  
Particle Density ◽  
Van Der Waals ◽  
Three Dimensional ◽  
Energy Functional ◽  
Coarse Grained ◽  
Uniform Structure ◽  
Free Energy Functional ◽  
Van Der Waals Theory

A generalized van der Waals theory is derived on the basis of simple physical and mathematical arguments. The derivation results in a free- energy functional wherein the independent variable is a coarse-grained particle density. It is assumed that a well defined particle density dominates the free energy and this density is to be obtained by minimizing the free energy functional. The variational theory so obtained can be applied to non-uniform fluids. In the present work the possibility of stable non-uniform structure is neglected and the theory is applied to uniform fluids. It then produces an equation of state identical in form to that proposed originally by van der Waals but the excluded volume is only about half as large in the three-dimensional case. Applications to several two- and three-dimensional systems indicate that the new equation of state is a distinct improvement over the traditional van der Waals theory when the full range of fluid densities is considered. The quantitative accuracy in the case of simple uniform fluids is sufficient to warrant further development and exploitation of the theory.

Physical aspects of wear of the piston-ring—cylinder set of combustion engines

2008 ◽  
Vol 222 (11) ◽  
pp. 2103-2119 ◽  
Author(s):  
A Kazmierczak
Keyword(s):  
Free Energy ◽  
Surface Free Energy ◽  
Piston Ring ◽  
Van Der Waals ◽  
Cylinder Liner ◽  
Van Der Waals Forces ◽  
Real Object ◽  
Lubricating Oil ◽  
Combustion Engines ◽  
The Real

The research presented in this paper has shown that the physical aspects of interfacial phenomena, described by the total value of surface free energy and the values of its components, make it possible to select more suitable materials for sliding pairs. The total value of surface free energy depends on the molecular structure and the bonds characteristic of a given material, and determines its hardness. In order to reduce friction losses in a sliding pair that is being designed, it is proposed to match such materials for the pair in such a way that the surface of one of them has a high sum of surface free energy components originating from van der Waals interactions, while the other material's surface has a possibly low value of the sum. Furthermore, proper values of the components of surface free energy ensure proper wettability with lubricating oil. In order to minimize friction in a sliding contact, the element with the larger surface area (e.g. a cylinder sleeve) should have larger dispersion and van der Waals forces compared with those of the oil, while the element with the smaller area (e.g. a piston ring) has to have smaller (as low as possible) dispersion and van der Waals forces compared with those of the lubricating oil. Thus a basis for reducing friction losses, particularly during mixed friction and boundary friction, has been created. Pursuing the practical goal of this research, a new cylinder liner sliding pair of a piston-ring—cylinder (PRC) set (in which the ring has a titanium nitride (TiN) coating and the cylinder liner has a surface layer with varying properties, applied by vacuum nitriding) of a piston packing ring—combustion engine was designed and made. The sliding pair can be used in self-ignition combustion engines and in spark-ignition engines. The sliding pair is the result of the research carried out as part of this paper, including tests in a tribotester and three-stage testing embracing numerical simulations, preliminary tests on the real object, and tests proper on the real object.

Self-Assembly of a Chiral Cubic Three-Connected Net from the High Symmetry Molecules C60 and SnI4

2020 ◽  
Author(s):  
Daniel B. Straus ◽  
Robert J. Cava
Keyword(s):  
Organic Synthesis ◽  
Self Assembly ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
High Symmetry ◽  
Molecular Chirality ◽  
Chiral Materials ◽  
Self Assembled ◽  
Chiral Centers

The design of new chiral materials usually requires stereoselective organic synthesis to create molecules with chiral centers. Less commonly, achiral molecules can self-assemble into chiral materials, despite the absence of intrinsic molecular chirality. Here, we demonstrate the assembly of high-symmetry molecules into a chiral van der Waals structure by synthesizing crystals of C<sub>60</sub>(SnI<sub>4</sub>)<sub>2</sub> from icosahedral buckminsterfullerene (C<sub>60</sub>) and tetrahedral SnI4 molecules through spontaneous self-assembly. The SnI<sub>4</sub> tetrahedra template the Sn atoms into a chiral cubic three-connected net of the SrSi<sub>2</sub> type that is held together by van der Waals forces. Our results represent the remarkable emergence of a self-assembled chiral material from two of the most highly symmetric molecules, demonstrating that almost any molecular, nanocrystalline, or engineered precursor can be considered when designing chiral assemblies.

scholarly journals On the Kirchhoff-Love Hypothesis (Revised and Vindicated)

2021 ◽  
Author(s):  
Olivier Ozenda ◽  
Epifanio G. Virga
Keyword(s):  
Free Energy ◽  
Dimension Reduction ◽  
Three Dimensional ◽  
Energy Functional ◽  
The Other ◽  
Variational Model ◽  
Two Dimensional ◽  
Elastic Plates ◽  
Kinematic Constraint ◽  
Free Energy Functional

AbstractThe Kirchhoff-Love hypothesis expresses a kinematic constraint that is assumed to be valid for the deformations of a three-dimensional body when one of its dimensions is much smaller than the other two, as is the case for plates. This hypothesis has a long history checkered with the vicissitudes of life: even its paternity has been questioned, and recent rigorous dimension-reduction tools (based on standard $\varGamma $ Γ -convergence) have proven to be incompatible with it. We find that an appropriately revised version of the Kirchhoff-Love hypothesis is a valuable means to derive a two-dimensional variational model for elastic plates from a three-dimensional nonlinear free-energy functional. The bending energies thus obtained for a number of materials also show to contain measures of stretching of the plate’s mid surface (alongside the expected measures of bending). The incompatibility with standard $\varGamma $ Γ -convergence also appears to be removed in the cases where contact with that method and ours can be made.

scholarly journals Boundary conditions in topological AdS4/CFT3

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Pietro Benetti Genolini ◽  
Matan Grinberg ◽  
Paul Richmond
Keyword(s):  
Field Theory ◽  
Free Energy ◽  
Boundary Conditions ◽  
Smooth Solution ◽  
Three Dimensional ◽  
Field Theories ◽  
Legendre Transformation ◽  
Generating Functional ◽  
Holographic Duals

Abstract We revisit the construction in four-dimensional gauged Spin(4) supergravity of the holographic duals to topologically twisted three-dimensional $$ \mathcal{N} $$ N = 4 field theories. Our focus in this paper is to highlight some subtleties related to preserving supersymmetry in AdS/CFT, namely the inclusion of finite counterterms and the necessity of a Legendre transformation to find the dual to the field theory generating functional. Studying the geometry of these supergravity solutions, we conclude that the gravitational free energy is indeed independent from the metric of the boundary, and it vanishes for any smooth solution.

scholarly journals Superconducting contact and quantum interference between two-dimensional van der Waals and three-dimensional conventional superconductors

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Michael R. Sinko ◽  
Sergio C. de la Barrera ◽  
Olivia Lanes ◽  
Kenji Watanabe ◽  
Takashi Taniguchi ◽  
...  
Keyword(s):  
Quantum Interference ◽  
Van Der Waals ◽  
Three Dimensional ◽  
Two Dimensional

scholarly journals Nanotube‐Based 1D Heterostructures Coupled by van der Waals Forces

Small ◽  
2021 ◽  
pp. 2102585
Author(s):  
Sofie Cambré ◽  
Ming Liu ◽  
Dmitry Levshov ◽  
Keigo Otsuka ◽  
Shigeo Maruyama ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Van Der Waals Forces

Van der Waals Epitaxy of GaSe on GaAs(111)

1994 ◽  
Vol 340 ◽  
Author(s):  
L. E. Rumaner ◽  
F.S. Ohuchi
Keyword(s):  
Lattice Mismatch ◽  
Van Der Waals ◽  
Three Dimensional ◽  
Structured Materials ◽  
Lattice Matching ◽  
Molecular Beam Deposition ◽  
Crystal Films ◽  
Low Dimensional ◽  
Matching Constraints ◽  
Lattice Matched

ABSTRACTAlthough heteroepitaxy of lattice-matched and lattice-mismatched materials leading to artificially structured materials has resulted in impressive performance in various electronics devices, material combinations are usually limited by lattice matching constraints. A new concept for fabricating material systems using the atomically abrupt and low dimensional nature of layered materials, called van der Waals epitaxy (VDWE), has been developed. GaSe (Eg = 2.1 eV) has been deposited on the three dimensional surface of GaAs (111) using a molecular beam deposition system. GaSe was evaporated from a single Knudsen source, impinging on a heated substrate. Even with a lattice mismatch of 6% between the substrate and the growing film, good quality single crystal films were grown as determined by RHEED. The films have further been analyzed using a complementary combination of XPS and X-ray reflectivity.

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