Validity of Molecular Dynamics in Heat Transfer


Molecular Dynamics (MD) is commonly used in computational heat transfer to determine the thermal response of nanostructures. MD is based on classical statistical mechanics with the thermal energy of the atom related to its momentum by the equipartition theorem. Momenta of atoms in an ensemble are determined by solving Newton’s equations with inter-atomic forces derived from Lennard-Jones potentials.  Statistical mechanics implicitly assumes the atom has heat capacity as otherwise the temperature of the atom cannot be related to its thermal energy.  Moreover, statistical mechanics assumes atoms in nanostructures have the same heat capacity as at the macroscale.

For bulk materials, MD heat transfer based on atoms in submicron computation boxes having macroscopic heat capacity is valid provided periodic boundary conditions are imposed in the MD solution. The statistical mechanics requirement of macroscopic heat capacity is satisfied because the atoms in submicron boxes under periodic boundary conditions are equivalent to atoms in the bulk that do indeed have heat capacity.

In contrast, quantum mechanics (QM) precludes atoms in submicron nanostructures from having the capacity to conserve heat by an increase in temperature.  Nevertheless, MD simulations are commonly performed by assuming atoms in discrete or non-periodic nanostructures have heat capacity. Although consistent with statistical mechanics, MD of discrete nanostructures is unequivocally invalid by QM. By QM, atoms in discrete nanostructures lacking heat capacity cannot conserve heat by an increase in temperature, and therefore Fourier’s heat conduction equation that depends on temperature has no meaning. Instead, conservation in discrete nanostructures proceeds by the creation of QED induced non-thermal EM radiation that charges the nanostructure by the photoelectric effect. QED stands for quantum electrodynamics and EM for electrodynamics. Examples of MD simulations that by QM are valid or invalid are presented and recommendations made for how MD heat transfer simulations of discrete nanostructures may be made consistent with QM.  See Paper and Press Release
 


QED Induced Heat Transfer


 Over the past century, Fourier’s transient heat conduction equation including the notions of heat capacity of Lavosier and Laplace .have served well in our understanding heat transfer in macroscopic systems. Modern day heat transfer assumes phonons are the heat carriers solids based on theories formulated by Einstein and Debye at the time systems were macroscopic. Today, the heat transfer systems are no longer typically macroscopic, but include the nanoscale. Macroscopic heat capacity in Fourier’s equation is routinely applied in heat transfer simulations at the nanoscale, the consequence of which has led to unphysical results, e.g. standard mixing rules are violated for nanofluids; thermal conductivity of thin films is reduced depending on thickness; the memristor is thought necessary to complete symmetry to the circuit elements of resistor, capacitor, and inductor; molecular polymers in nanoscale electronics have thermal conductivity; unlikely molecular signaling by the lock and key mechanism olfaction, and so forth.
 
Unphysical observations from application of classical heat transfer to nanostructures may be traced back to Einstein’s and Debye’s theories of heat capacity based on phonons. In contrast, nanoscale heat transfer based on QED by Planck’s photons avoids the unphysical, i.e. thin film conductivity remains at bulk as thickness decreases, nanofluids obey mixing rules, the memristor is a quantum size effect, molecular conductivity is meaningless, olfaction reduces to signaling of the odorant molecule by its unique vibration spectrum, etc. QED stands for quantum electrodynamics. Supporting QED physics is based on quantum mechanics from the Einstein-Hopf relation for the harmonic oscillator in terms of temperature and EM confinement. Both Einstein and Debye phonon theories based on classical statistical mechanics permit the atom at the nanoscale to have the heat capacity necessary to conserve absorbed EM energy by an increase in temperature. But quantum mechanics requires the heat capacity to vanish thereby precluding conservation by a temperature increase at the nanoscale. Instead, conservation proceeds by the creation of non-thermal photons inside the nanostructure by the QED induced frequency up-conversion of absorbed EM energy to the TIR confinement of the nanostructure. TIR stands for total internal reflection. The TIR confinement of the QED photons occurs because the high surface to volume ratio of nanostructures naturally concentrates the absorbed EM energy in the TIR mode, thereby effectively supporting photon confinement. The QED photons may excite phonons, but the absorbed EM energy is primarily conserved by the prompt creation of QED photons that may be converted to electric charge by Einstein‘s photoelectric effect, or lost to the surroundings. Examples of QED physics are presented to illustrate the fact the QED physics extends far beyond nanoscale heat transfer. See Press Release and Presentation



Invalidity of Near-Field Heat Transfer

Over the past decade, extensive research in near-field heat transfer has suggested the EM radiation at submicron distances < 100 nm from a surface is orders of magnitude larger than the limit given by Planck's theory of BB radiation. BB stands for blackbody. But Planck never stated his theory set an upper limit on radiative heat transfer, although he was surely aware bringing BB surfaces close together does not increase their thermal energy. 

However, experimental support for near-field enhancement is limited to micron and not nanoscale gaps, and therefore support for claims that near-field enhancement in submicron gaps exceeds the  Planck limit relies almost entirely on classical EM analysis of evanescent waves by the Maxwell equations.But near-field enhancement based on Maxwell’s equations is refuted because temperature fluctuations in the surfaces of nanoscale gaps as required by the FDT are precluded by QM. FDT stands for the fluctuation-dissipation theorem and QM for quantum mechanics.

The FDT that relates the strength of the oscillations of the dipoles inside a body to the temperature fluctuations cannot be assumed in the solution of Maxwell’s equations because QM precludes atoms in the surfaces of nanoscale gaps to respond to absorption of heat by changes in temperature. Solutions of Maxwell’s equations for  by evanescent waves showing Planck theory is exceeded are unphysical because the FDT is no longer valid at the nanoscale.

Given that the thermal energy of a body is not increased by bringing it close to another body, near–field enhancement by tunneling of evanescent waves simply does not exist. Instead, conservation of EM energy proceeds by QED induced heat transfer, and therefore Planck’s theory is indeed an upper bound to near-field radiative heat transfer at the nanoscale.   See  Paper,  Presentation and Press Release


Johnson-Nyquist Noise 

 The validity of Maxwell's solutions in near-field heat transfer by tunneling of evanescent waves through nanoscale gaps is of great importance in the hope a breakthrough of a large enhancement in energy harvesting can be realized. However, atoms in the surface of nanoscale gaps are under high EM confinement that by QM are precluded from having the heat capacity necessary to conserve heat flow by a change in temperature, and therefore the temperature fluctuations required by the FDT do not occur in nanoscale gaps suggesting solutions of Maxwell's equations that rely on temperature fluctuations are invalid. See above "Invalidiity of Near-Field Heat Transfer," 2012.

One way of assessing whether the FDT is satisfied is to estimate the effect of EM confinement on the strength of the Johnson-Nyquist (J-N) noise signals from a hypothetical resistor in the surface atoms of nanoscale gaps. See Press Release and Paper.

The  J-N signals of V(f) under EM frequencies > 3E+15 Hz ( Gap < 50 nm) show the noise is at least 100 orders of magnitude less than that of a surface free of EM confinement. See above Plot. Since Maxwell solutions require gaps of about 10 nm to achieve enhancements consistent with breakthorughs in energy havesting, the tunneling of evanescent waves through nanoscale gaps is likely to be difficult to achieve in practice. 


1/f Noise in Nanowires


he 1/f frequency spectrum is commonly observed in the measurements of power in electronic circuits comprising semiconductors, resistors, vacuum tubes, and transistors. However, no recognized physical explanation of 1/f noise has been proposed. Indeed, the ubiquity of 1/f noise is one of the oldest puzzles of contemporary physics.

In 1925, Johnson and Nyquist discovered electronic or white noise from vacuum tubes. White noise power has a constant frequency f spectrum generated by the thermal agitation of the charges inside a resistor independent of any applied voltage. In contrast, 1/f noise shown above is sometimes called pink noise differs in that under applied voltage the power frequency f spectrum is not constant, but rather shows a slope of -1 on a log-log plot consistent with the frequency f raised to the -1 exponent.

Nanoelectronics comprise nanostructures that by QM create charge upon dissipating Joule heat. QM stands for quantum mechanics. QM precludes atoms in nanostructures from having the heat capacity necessary to conserve Joule heat by an increase in temperature, and therefore the Joule heat under EM confinement is induced by QED to produce non-thermal radiation that by Einstein’s photoelectric effect creates charge inside the nanostructure. EM stands for electromagnetic and QED for quantum electrodynamics. In this regard, QED induced charge in nanowires finds similarity with memristors including the Ovshinsky Effect in PCRAM devices whereby charge is created in amorphous GST films from excitons (holes and electrons) by the photoelectric effect that locally reduce the film resistance to allow encoding. See this page at Memristors and the Ovshinsky Effect, 2011.

In nanowires, absorption of Joule heat is conserved by the creation of QED photons instead of by an increase in temperature. The QED photons are under the TIR confinement of the diameter d of the nanowire. TIR stands for total internal reflection. The QED photons have Planck energy E = hc/2nd, where h is Planck’s constant, c is the speed of light, and n is the refractive index of the nanowire. Typically, E > 6 eV, and therefore charges in the form of excitons (holes and electrons) are produced by Einstein’s photoelectric effect. What this means is current flow through the nanowire spontaneously creates a step change in charge that reduces the resistance and increased current that eventually  dissipated in the otherwise macroscopic electronic circuit. Equivalently, current flow may be considered to produce a steady step change in power, the Fourier transform of which gives the 1/f response in the frequency domain.

Nanowires that naturally produce a steady step change in power may be considered to be a summation of a train of individual steps in the manner of Markov chain. See Press Release and preliminary Paper 


Immunogenicity by QED Radiation 

Protein therapeutics is used in the treatment of diabetes and various forms of cancer. A major concern is that repeated administration to patients often leads to immunogenicity by the immune system responding by formation of antidrug antibodies (ADAs) that reject the otherwise beneficial drug in treating the treatment of the disease.  Immunogenicity (or an adverse response of the immune system to a drug) is of great interest as the rejection of the drug may be life threatening. Generally, the ADAs are triggered by the tendency of the beneficial monomer form of the protein molecules to aggregate, although why aggregation occurs is not understood.  In protein deposition diseases such as Alzheimer and Parkinson, protein aggregates enhance stronger immunogenicity.

Typically, the aggregates known to elicit ADA response are globular proteins having molecular weights from 6 to 100 kDa and diameters from 3 – 10 nm comparable to NPs that based on QM have been linked to DNA damage by the natural emission of low-level QED induced EM radiation at levels beyond the UV. Similarity suggests the toxicity to the immune system by protein aggregation is caused by the UV radiation created as the protein aggregates conserve absorbed EM energy from collisions of water molecules in body fluids. See Press Releases on DNA damage by inanimate and biological NPs.   

The UV created in the aggregates dissociates native disulfide bonds causing drastic conformational changes that expose the hydrophobic residues in partially unfolded molecules. Subsequently, the partially unfolded molecules self-assemble into globular protein aggregates by the formation of intermolecular disulfide bonds driven by intermolecular hydrophobic interactions. The combined effects from both the hydrophobic interaction and the formation of intermolecular disulfide bonds dominate this process. See Paper and Press Release 


2012 International Conference

Biomedical Engineering and Biotechnology

(iCBEB)

 28th to 30th May 2012, Macau 

Selff-Assembly of Protein Aggregate

The 2012 International Conference on Biomedical Engineering and Biotechnology (iCBEB 2012) held on 28th to 30th May 2012, in Macau, China, sponsored by The Institute of Electrical and Electronics Engineers (IEEE), and co-sponsored by University of Macau, IEEE Macau Section and Macau Society of BioMedical Engineering.are published in the IEEE Xplore® online. See  Paper

Protein therapeutics is used in the treatment of diabetes and various forms of cancer. A major concern is that repeated administration to patients often leads to undesirable antidrug antibodies with a wide range of life threatening consequences that induce immunogenicity or an adverse response of the immune system. The antibodies are generally thought triggered by the tendency of monomer protein molecules to aggregate, although why aggregation occurs is not known.

A molecular dynamics (MD) simulation of protein aggregation was presented at Macao in support of the immunogenicity by QED induced EM radiation. The MD simulation considered 108 - 2 nm NP granules under perioidic boundary conditions. The polarization force  was derived based on the polarizabiity of the NP and the EM energy density gradient produced by the NPs themselves. The polarizability of each NP was taken as 1x10^-30 cubic meters. It is noted that the attraction between NPs does not depend on van der Waals forces as is commonly assumed in the assembly of nanostructures. Once started, aggregation is very rapid. The partially assembled blobular protein is illustrated with VMD. See Paper  , Presentation, and Press Release

 

Global Warming and the Second Law of Thermodynamics

Global warming claims that solar radiation absorbed in the Earth’s surface is re-radiated back in the IR and absorbed by CO2 in the atmosphere only to be conserved by the emission of EM radiation as “backradiation” that further warms the Earth. IR stands for infrared and EM for electromagnetic. Global warming argues the Earth therefore warms more by backradiation from CO2 than otherwise, the consequence of which has resulted in the controversy that CO2 emissions need to be regulated to avoid climate change in a warming Earth.

In the global warming controversy, skeptics argue backradiation requires heat to be transferred from the CO2 in the cold atmosphere to the warm surface of the Earth, and therefore the Second Law that requires heat to only flow from hot to cold surfaces is violated. Skeptics therefore claim that backradiation is unphysical and does not occur. Hence, the economic costs of avoiding global warning by restricting CO2 emissions are unjustified. See Paper

However, backradiation does not violate the Second law. Indeed, the CO2 molecule does absorb the IR radiation from the Earth, but conservation proceeds by the emission of EM radiation at the vibration frequencies of the CO2 molecule. Since the EM emissions are independent of temperature, backradiation occurs without violating the Second Law. See Press Release

An important issue is whether  BB radiation from the Earth is absorbed by the CO2 in the atmoshere.  For the Earth at 300K, Wien’s law gives the peak BB emission at about 9.66 microns. Since CO2 absorbs at 14 microns, skeptics say BB radiation at 9.66 microns is not absorbed by CO2, and therefore CO2 cannot cannot undergo backraddiation to the Earth. Hence, CO2 canot contribute to global warming and should not be legislated. However, BB radiation is broadband and has content at 14 microns. How much of the BB radiation content at 300 K is at 14 microns can be determined from Planck’s theory, and is illustrated in Paper1 

 


The Red Rectangle 

 Astronomers have extensively studied the ERE of the Red Rectangle (RR) Nebula in the Milky Way for nearly a century. ERE stands for extended red emission. Today, controversy surrounds the mechanism by which the ERE is produced. Two competing mechanisms: PL and BB radiation have emerged, both of which rely on the UV emission from a pair of stars in the RR Nebula:. PL stands for photoluminescence and BB for blackbody.

Cosmic dust in the interstellar medium (ISM) comprised of discrete nanoparticles (NPs) separated by large distances. In the ISM, PL may only occur by the absorption of a single UV photon in a NP. Since the PL conversion efficiency < 100%, it may be safely concluded PL from single UV photon absorptions in cosmic dust is not the ERE mechanism.

Since PL in cosmic dust is highly unlikely, PL as the source of ERE was proposed supplemented by thermal BB radiation in Paper1  The stars in the RR Nebula have temperatures of about 7000 K that by Wien’s law limits the BB emission peak to about 0.41 microns or 3 eV, and therefore it can be concluded that BB radiation cannot produce UV photons having Planck energy > 10.5 eV necessary to explain the ERE in the RR.  

Because both PL and BB radiation cannot explain ERE, carbon molecules having < 28 atoms were assumed heated to temperatures in excess of 1500 K by absorption of a single UV photon. Ibid. In support of this assumption, laser heating experiments of soot comprising 30-100 nm carbon NPs deposited on the aluminum foil vanes of a Crookes radiometer are presented in Paper2 Laser irradiation of the soot film produces an emission spectrum that resembles that of the RR. Temperatures were estimated and not measured.  Fits of BB radiation alone did not appr0oximate the measured spectrum. Mie theory gave a better approximation to the spectra at a temperature of 3800 K.           

However, the Mie theory estimate of 3800 K necessary to fit the measured spectrum cannot be correct as the aluminum foil having a melting point of about 960 K would have been exceeded, but foil damage was not reported. Whatever caused the emission spectrum did not require high temperatures as would be expected in Planck’s theory of BB radiation.

Classically, NPs conserve absorbed EM energy of any form by an increase in temperature that in turn is emitted as VIS and IR radiation, but QM differs. QM stands for quantum mechanics. QM requires that UV photon absorption in NPs occurs without a change in NP temperature, i.e., ISM molecules having < 28 carbon atom do not heat to > 1500 K by absorbing UV photons. Further description is given in PressRelease - the conclusions of which are:

1.  Both PL and BB radiation including variants thereof may be safely dismissed as mechanisms for the ERE.

2.  QED induced radiation asserts the VIS and NIR in the ISM are caused by the absorption of UV radiation in cosmic dust NPs. In the ISM, mid and far IR spectra may also be explained by QED induced redshift, but require larger cosmic dust particles. 

3.  The redshift measurements of Supernovae explosions have nothing to do with an expanding Universe, but rather cosmic dust. The RR color by QED induced redshift radiation by cosmic dust clearly shows that high Z redshifts need not be limited to distant Supernovae, but are common in the colors we on Earth observe in the Milky Way. See this page http://www.nanoqed.org/, “Cosmology by Cosmic Dust – Update,” 2010


Superluminality and the Hartman Effect

 The Hartman effect suggests superluminal velocities as the evanescent tunneling time tends to a constant for large barriers. With evanescent tunneling, the barrier may be the gap between double prisms shown above. When the prisms are in contact, the incident photons pass straight through, but when there is a gap, the photons may either tunnel across or follow the refracted path. Since the time for light to travel across large gaps is found the same as for short gaps, the Hartman effect has been interpreted to suggest the incident photons have crossed the gap with superluminal velocity.

However, Winful argues evanescent waves crossing the gap are virtual photons that do not propagate across the gap into the outside world. Since the velocity of non-propagating waves is meaningless, the light in the Hartman effect cannot be moving at superluminal velocity, but rather delayed. If the delay is the time for storing incident photon energy until the barrier can be breached, the Hartman effect may be simply explained without the need for superluminal velocities.

The problem is Winful’s argument based on the stored energy of evanescent waves cannot overcome the fact that irrespective of whether the accumulated stored energy can breach the barrier, the evanescent waves cannot propagated beyond the gap to the outside world, which in fact they do. What this means is tunneling of photons through the double prism gap is caused by a more fundamental mechanism that creates photons capable of propagating across the gap. Evanescent waves are not this mechanism, but rather are only a way of storing the energy of incident photons in the gap. Instead, QED is proposed to convert evanescent energy to QED photons. See  Press Release.
 


The Electrostatic Casimir Force 

 Recently, Yale researchers claimed the measurement of thermal Casimir force between neutral surfaces at ambient temperature for the first time. See Press Release  The thermal Casimir force differs from the ZPE force proposed in 1948 by Casimir who extended the ZPE of quantum mechanics to the field. ZPE stands for zero point energy. However, the thermal Casimir force has a long history and was predicted by Lifshitz in 1955. Like Casimir, Lifshitz only considered the force between neutral plates. The thermal Casimir forces derived with Lifshitz theory are the Drude and Plasma models having different dielectric properties for the plate materials.

However, Lifshitz theory does not predict the charging of neutral surfaces separated from each other by submicron gaps. Similarly, charging of neutral plates is not predicted in Casimir’s theory of the ZPE Casimir force. In fact, experiments to measure the Casimir force are always swamped by electrostatic charges. Indeed, MEMS devices and semiconductors in photolithography commonly show charge is created upon bringing otherwise neutral surfaces within submicron distances of each other. Given that Casimir and Lifshitz theories cannot explain the charge created in the Yale experiment, the force measured may not be the thermal Casimir force, but rather some other effect such as the servo-control using the minimizing potential to compensate for electrostatic charge created during the experiment.

Subsequent to the Yale experiment, the thermal Casimir force was measured at Grenoble using an AFM. Unlike the Yale experiment at ambient temperature, the Grenoble tests were performed at 4.2 K. Like the Yale experiment at ambient temperature, significant charge at 4.2 K was created. Both Yale and Grenoble experiments corrected for the unwanted electrostatic forces using a servo to impose a minimizing potential during force measurements. In this way, it was thought the thermal Casimir force alone would be measured. However, the QED photons having energies > 5 eV created at gaps d < 0.2 microns leave residual charge trapped beneath the gold surface that cannot be removed by minimizing potentials of only a few 100 mV.  See Paper and  Press Release

Conclusions
1. Lifshitz theory cannot explain the charge created by bringing neutral surfaces within submicron gaps of each other, and as such cannot predict the thermal Casimir force. Instead, the QED electrostatic force provides the correct thermal Casimir force.
2. Servo control of unwanted electrostatic forces creates the QED force that follows the inverse square law of classical electrostatics at large gaps changing to the inverse fourth power law at small gaps. However, the inverse fourth power behaviour is caused by the servo having nothing to do with the fourth power law predicted by Casimir in 1948.


Unphysical Heat Transfer by Molecular Dynamics 

The MEME conference held in Hong Kong was directed to the frontiers of Mechanical Engineering. One such frontier is heat transfer by Molecular Dynamics (MD).

MD is based on classical physics using the theory of statistical mechanics initiated by Boltzmann in 1870. At that time, statistical mechanics was formulated on the basis the thermal heat capacity of the atom was independent of the size of the body containing the atom. The notion that the heat capacity of the atom depended on the size of the body would come later in the quantum mechanics (QM) developed by Planck in 1910. Indeed, there is no size effect in statistical mechanics even to this day.

Today, the size effect of QM is important in the heat transfer analysis of nanostructures in that the heat capacity of atoms in submicron nanostructures vanishes. Nevertheless, MD simulations of heat transfer in discrete nanostructures are routinely performed and abound in the literature. Not only are discrete MD simulations invalid by QM, but give unphysical results, e.g., thermal conductivity in nanofluids is found to exceed standard mixing rules while in solid metal films depends on thickness.

QM explains the unphysical results by negating the heat capacity of atoms in discrete nanostructures, thereby precluding the usual conservation of absorbed EM energy by an increase in temperature. Unlike classical physics, QM allows the thermal conductivity of thin films to remain at bulk while nanofluids obey mixing rules.

By QM, the absorbed EM energy is conserved by QED inducing the creation of non-thermal EM radiation inside the nanostructure that by the photoelectric effect creates charge in the nanostructure, or is emitted to the surroundings. Examples of unphysical MD simulations are presented and recommendations made for how QM may be included in MD. See Paper and Presentation


1/f Noise in Nanoelectronics 

The ICCSS 2012 international Conference on Circuits, Systems, and Simulations was held in Hong Kong. Simulation of 1/f noise commonly observed in EM measurements of power in circuit elements - capacitors, resistors, and inductors is of importance in future applications of nanoelectronics.

Today, 1/f noise is generally explained by free electrons in the Hooge relation. However, it is difficult to explain low frequency 1/f noise because of the short residence time of the electron in the size of the sample. If 1/f noise is a summation of Lorentzians, the characteristic residence in the sample much longer than a few seconds, but in a 1 cm sample, the electron residence time is only about 0.1 s. For nanoelectronics, the residence s far less, thereby negating the Hooge relation that claims free electrons are the source of 1/f noise.

To provide an alternative to Hooge relation,  the dramatic increase in 1/f noise in nanoelectronic circuit elements, and nanowires in particular suggests the explanation may be found in the size effect of QM and even even extended to submicron regions of ordinary circuit elements. QM stands for quantum mechanics. In nanoelectronics, QM precludes atoms from the heat capacity necessary to conserve Joule heat by an increase in temperature. Instead, conservation proceeds by the creation of charge that produces a step change of power in time, the Fourier transform of which is shown to give the 1/f noise spectrum in the frequency domain.  See Paper and Presentation.


QED Tunneling 

The Stefan-Boltzmann (SB) equation giving the radiative power transmitted between hot and cold surfaces is the consequence of Planck theory of BB radiation. Historically, the SB equation has served as the BB limit to the radiative transfer of heat between gaps large in relation to wavelength of emitted radiation. However, near-field enhancement based on evanescent tunneling through nanoscale gaps has been recently claimed to exceed the BB limit by 3-4 orders of magnitude. Experimental data at the nanoscale are difficult to acquire, and therefore the claim of near-field enhancement rests almost entirely on solutions to Maxwell equations.

However, the Maxwell solutions require the fluctuation-dissipation theorem (FDT) be satisfied.  The FDT is a statement that temperatures are proportional to dipole fluctuations.  But the FDT is questionable in near-field heat transfer because atoms in the surfaces of nanoscale gaps are precluded by QM to have the heat capacity necessary to allow temperatures to fluctuate. Instead, near-field heat transfer proceeds by the creation of QED photons from the thermal energy of surface atoms that tunnel across the gap.

QED tunneling allows Planck theory to remain valid for near-field radiative heat transfer at the nanoscale, although there is no near-field enhancement above the BB limit. Similarities of near-field heat transfer with the Hartman effect are consistent with the Schrodinger equation including the thermal Casimir force is presented. See Press Release and  Paper  


At the IEEE Nano Conference held at Birmingham, the heat transfer in nanoelectronics was actively discussed because of potential melting of circuit elements. Joule heat is commonly assumed to be conserved by increasing the temperature of the resistor, capacitor, or inductor. But it should rememberd that the increase in temperature of a circuit element is based on classical physics of macroscopic circuit elements and is not applicable in nanoelectroncs.

Classical physics assumes the atom always has heat capacity. Quantum mechanics or QM differs by restricting the atom’s heat capacity to vanishing small levels in nanostructures. Conserving absorbed EM energy by the QED induced creation of photons in the nanostructure surface avoids melting of circuit elements, but creates space charge that is likely to cause the element to be inoperational because of excessive noise.

The response of nanoelectronics including the memristor, Ovshinsky effect, and 1/f noise presented at the IEEE Nano conference illustrates how space charge is expected to be central to the conservation of Joule heat in nanoelectronics in the future.  See Press Release , Paper, and Presentation 

On 1 September 2012, the Economist published an article on Phase Change Memory (PCM) called "Altered States" in submicron chalcogenide films making the argument that physical melting causes the resistance change.  See Economist  But quantum mechanics precludes temperature changes in submicron films. For comments to the Econmist article, see Comments 

 

Stiffening of Nanowires


MOLEC 2012

European Conference on Molecular Systems

 Over the past decade, the observation of significant stiffening of nanowires has been reported. Numerous mechanisms  have been proposed including: high surface-to-volume ratio, surface stresses, bulk nonlinear elasticity, surface stiffness, surface tension, surface reconstruction, surface strain and stress, and skin depth energy pinning. The stiffening mechanisms proposed to date find basis in classical physics contrary to the fact stiffening is not observed at the macroscale, but rather a QM effect only observed in < 100 nm diameter nanowires. QM stands for quantum mechanics.

In this regard, stiffening of nanowires by QM is proposed to occur from the QED radiation induced in nanowires from EM energy that under the TIR confinement creates photons within the wire instead of increasing the wire temperature. The QED photons having high Planck energy create charge by the photoelectric effect that pressurizes the nanowire by electrostatic repulsion.

The QM pressure P produced in the tensile specimen is produced from thermal kT energy acquired from the grips. The pressure P may be upper bound by assuming all the atoms in the nanowire acquire kT energy at the support temperature T. Provided the QED photon energy E > 5 eV and charge is created, the pressure P = 3kT/2D^3.

For the silver nanowire with D = 0.26 nm at T = 300 K, P < 3.53 x 10^8 Pa ~ 51000 psi. Taking the yield stress Syo of silver as 6550 psi, P/3Syo = 2.6. The figure shows QM enhances both the Young’s modulus Y/Yo and yield stress Sy/Syo < 25. However, experimental data shows Y/Yo ~ 3 and  Sy/Syo ~ 50.  The QM stiffening mechanism for silver nanowires is reasonably consistent with the enhancement of yield stress, but not the Young’s modulus. However, the flexibility of the supports would reduce the QM enhancement of Young’s modulus, but not the yield stress. More study is required. See Press Release



NAP 2012

Nanomaterials: Applications and Properties
The European Conference on the Dynamics of Molecular Systems ( MOLEC 2012 ) on the experimental and theoretical aspects of MD was held at the Jesus College of Oxford University from the 9 - 14 September 2012. The paper was entitled:

"Heat Capacity of the Atom - A Fundamental Problem in Molecular Dynamics"

Molecular Dynamics (MD) simulations based on classical statistical mechanics always allow the atom to have thermal heat capacity. Quantum mechanics (QM) differs in that the heat capacity of atoms in submicron nanostructures vanishes. Nevertheless, MD simulations of heat transfer in discrete nanostructures are routinely performed and abound in the literature. Not only are discrete MD simulations invalid by QM, but give unphysical results, e.g., thermal conductivity in nanofluids is found to exceed standard mixing rules while in solid metal films depends on thickness.

On the other hand, QM negates the heat capacity of atoms in discrete nanostructures, thereby  precluding the usual conservation of absorbed electromagnetic (EM) energy by an increase in temperature. Instead, conservation proceeds by QED inducing the absorbed EM energy to create non-thermal EM radiation inside the nanostructure that by the photoelectric effect charges the nanostructure, or is emitted to the surroundings. QED stands for quantum electrodynamics. Unphysical results occur because QED induced radiation is not included in the nanoscale heat balance, but if included physical results for discrete nanostructures are found. Examples of unphysical MD simulations are  presented. See Abstract

In contrast, MOLEC 2012 presentations lacking the QED induced radiation mechanism generally provided unphysical explanations of experimental observations. Contrary to the purpose of MOLEC 2012, the fundamental problems of MD such as the heat capacity of the atom were not discussed. For example, collisional quenching of OH radicals and deciphering the mystery of the NO3 photolysis mechanism in the general area of photo dissociation cannot be explained without QED induced radiation. Similarly, energy flow in photo excited ICN and molecular processes in outer space requires QED radiation instead of classical physics in cosmic dust nanoparticles. Intermolecular Coulomb decay in liquid water and water clusters and fundamental photochemistry are more readily explained by QED of discrete molecules. Indeed, QED resolves the question of whether fullerenes are giant atoms or hot metal spheres including photoionization processes in clusters. Fundamental in photolysis problems is the fact that classical physics does not create photons in nano clusters instead of increases in temperature intrinsic in classical physics. Only QM in combination with QED induced radiation can explain photochemical reactions in interactions of discrete molecules.

The 2nd International Conference on Nanomaterials: Applications and Properties ( NAP 2012 ) was held on 17-20 September 2012 at the Black Sea city of Alushta, The Crimea, Ukraine. The paper delivered was entzitled:

"The Invalidity of Moleculelar Dynamics in Heat Transfer"

Molecular Dynamics (MD) simulations based on classical statistical mechanics always allow the atom to have thermal heat capacity. Quantum mechanics (QM) differs in that the heat capacity of atoms in submicron nanostructures vanishes. Nevertheless, MD simulations of heat transfer in discrete nanostructures are routinely performed and abound in the literature. Not only are discrete MD simulations invalid by QM, but give unphysical results, e.g., thermal conductivity in nanofluids is found to exceed standard mixing rules while in solid metal films depends on thickness. QM negates the heat capacity of atoms in discrete nanostructures, thereby  precluding the usual conservation of absorbed electromagnetic (EM) energy by an increase in temperature. Instead, conservation proceeds by QED inducing the absorbed EM energy to create non-thermal EM radiation inside the nanostructure that by the photoelectric effect charges the nanostructure, or is emitted to the surroundings. QED stands for quantum electrodynamics. Unphysical results occur because QED induced radiation is not included in the nanoscale heat balance, but if included physical results for discrete nanostructures are found. Examples of unphysical MD simulations are  presented.  See Paper and Presentation




 Molecular Dynamics of Nanowires


Over the past decade, the observation of significant stiffening of nanowires or NW’s has been reported, although some findings suggest there is no stiffening. Because of this uncertainty, research on the mechanism for stiffening has been a subject of great interest. Numerous mechanisms have been proposed that depend on high surface-to-volume ratio of NW’s including surface stress and strain – all of which rely on classical physics. However, classical physics in the interpretation of nanoscale behavior typically leads to unphysical results that are avoided by quantum mechanics or QM.

In NW’s, QM precludes the atoms from having the heat capacity to conserve the absorption of EM energy of any form and specifically thermal energy from macroscopic supports or the Joule heat from loading and unloading cycles by an increase in temperature. Instead, absorbed EM energy is conserved by frequency up-conversion to the TIR resonance of the NW by QED, the consequence of which is the production of photons that create charge by the photoelectric effect.

Molecular dynamics simulations show the stiffening of NW’s is caused by charge repulsion between atoms creating a state of hydrostatic tension that changes  the uniaxial stress common in macroscopic tenisle specimens to a ulti-axial stress state. The VMD representation of the NW chosen for MD analysis consists of 550 silver atoms in a FCC configuration having a 8 A square cross-section x 87.9 A length.  Hence, the longitudinal strain is reduced by the Poisson effect that subsequently stiffens the NW by increasing the Young's modulus consistent with conventional elasticity theory. See Press Release and Paper

Unlike the reduction in diameter of the conventional tensile specimen under the uniaxial stress state, the MD simulation of the nanowire under the QED induced triaxial stress state causes the cross-section to expand because of hydrostatic tension that subsequently leads to the Coulomb explosion of silver atoms into the surroundings.The VMD simuland the off-colored atomsation of the nanowire cross-section at its midpoint for the initial and final configurations is shown below.  The cyan and off-colored atoms atoms mark the respective initial and final geometries. Differences between final and initial geometries geometry are amplified by a factor 50X. The QED induced expansion under triaxial stress is illustrated in  VMD movie
Validity of Wiedemann-Franz Law

In 1853, Wiedermann and Franz (W-F) proposed the ratio of thermal to electrical conductivity of metals to be proportional to the absolute temperature as shown above.Although the W-F law is verified for the bulk, theoretical arguments  based on the Boltzmann transport equation includfing electron scatttering have for some time claimed the validity of the W-F law even for very thin film thicknesses. Since electrons are thought the dominant carriers of charge and heat in metallic samples,  a decrease of electron mobility due to scattering should reduce both thermal and electrical conductivity by the same factor, and consequently their ratio should be equal to the bulk W-F ratio.

Recently, the W-F law for Pt was found reduced 30% from bulk in experiments on 100 nm diameter nanowires (NWs). The electrical conductivity was measured directly and found reduced from bulk. However, a direct measurement of the thermal conductivity based on measurements of temperatures could not be made because of the nanoscale size of the NW. Therefore, the temperatures along the NW were inferred from solutions of the Fourier equation based on balancing the Joule heat by conductive heat flow along the NW and the thermal radiation loss to the surroundings. The Fourier solutions for the NW showed radiation losses to be negligible leaving Joule heat to be conserved solely by thermal conduction.  Based on the calculated temperature differences over the NW length, the thermal conductivity of Pt was found reduced by larger amount than the electrcal conductivity giving a a 30 % Lorenz number from the bulk. 

However, the Fourier equation by assuming the NW has fiinite heat capacity is invalid as QM requires heat capacity at the nanoscale to vanish. QM stands for quantum mechanics. Explanations of reduced thermal conductivity by electron scattering at grain boundaries are simply not correct. In contrast, the theory of QED radiation asserts the Joule heat is conserved at the TIR frequency of the NW by the creation of charge and QED radiation inside the NW. QED stands for quantum electrodynamics. Unlike the thermal radiation, the QED radiation is significant being almost entirely equal to the Joule heat. See Press Release, the conlcusions of  which are:

1.  By QM, NWs having vanishing heat capacity preclude the conservation of Joule heat by an increase in temperature. Instead, conservation proceeds by the creation of QED radiation inside the NW at its TIR resonance. The QED radiation produces charge by the photoelectric effect or is emitted to the surroundings as non-thermal EM radiation.
 
2.  The QED radiation created at the speed of light is far faster than phonons can respond at acoustic velocities, thereby effectively negating conductive heat flow Q along the NW. What this means is the Joule heat is almost totally conserved by the creation of QED radiation.
 
3. In the NW experiments, the thermal conductivity should remain at bulk, and therefore there is no temperature difference across the length of the NW.  The electrical conductivity of the NW is indeed reduced by electron scattering at grain boundaries, but otherwise is not affected by the QM restriction on the heat capacity of the atom.  .
 
4.  In NWs, the dependence of electron mobility in thermal conductivity by grain boundary scattering may be safely dismissed by QM. 



Quantum Corrections of Heat Capacity

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Molecular Dynamics

 MD finding based on statistical mechanics always assumes the atom has heat capacity. In heat transfer simulations of bulk materials, MD assumes the atoms have heat capacity. Under periodic boundary conditions, MD simulations are valid by QM because atoms in the bulk do indeed have heat capacity. QM stands for quantum mechanics. However, MD simulations of heat transfer in discrete nanostructures differ in that QM precludes atoms in nanostructures under TIR confinement from having the heat capacity necessary to conserve absorbed EM energy by an increase in temperature.  TIR stands for total internal reflection. What this means is the uncountable number of heat transfer solutions of nanostructures derived by MD are invalid by QM.

The theory of QED radiation avoids the invalidity of MD by QM. QED stands for quantum electrodynamics. QM based on the Einstein-Hopf relation for the QM harmonic oscillator shows the heat capacity given by the thermal kT energy of the atom vanishes at the submicron TIR wavelengths of nanostructures. Lacking heat capacity, conservation of absorbed EM energy proceeds by the QED induced creation of non-thermal EM radiation inside the nanostructure at its TIR frequency – the EM radiation having the necessary Planck energy to charge the nanostructure by the photoelectric effect, and if not, is emitted to the surroundings. Numerous papers have argued that MD heat transfer simulations of discrete nanostructures based on SM are invalid by QM. See “Validity of Molecular Dynamics in Heat Transfer”, “Unphysical Heat Transfer by Molecular Dynamics”, “MOLEC 2012”, and “NAP 2012” on this homepage.

In support of QED radiation theory, QCs of classical thermodynamic variables in MD solutions may be made to show the heat capacity of the atoms does indeed vanish in nanostructures.  QC stands for quantum correction. Indeed, the MD book by Allen & Tildesley (“Quantum Corrections” Sect. 2.9) gives procedures for performing QCs. The QCs for the energy E, constant volume heat capacity Cv, Helmholtz free energy A, and entropy S of any QM system are summarized in the above figure.

The figure gives the QC weighting function W = Q – C is the difference “delta” between the quantum Q and classical C values of the thermodynamic variable. See Paper The bottom abscissa is u = h * Nu / kT, where h is Planck’s constant and Nu = TIR frequency of the nanostructure. The top abscissa is the wave number equivalent to the parameter u at 300 K. All W go to zero for u < 1 is consistent with the anharmonic low frequency region of classical statistical mechanics; whereas, W for u > 1 corresponds to the harmonic approximation where QCs are significant.

The QC for heat capacity is consistent with the theory of QED radiation that relies on the vanishing heat capacity in the Einstein-Hopf relation of QM. See Paper and Press Release.


Light Activated Spin-Valves


 
Spin-valves comprise alternating nanoscale layers of ferromagnetic FM layers separated by non-magnetic NM s[pacers. Spin-polarized current is produced by passing un-polarized current through a first FM layer that remains polarized in passing through the NM spacer. Upon interaction with the second FM layer, a giant magnetoresistance GMR is thought to transfer the spin angular momentum that tends to produce parallel spins in both FMs thereby creates an effective electrical short-circuit that significantly lowers the GMR. By this process, information may be stored spatially by discrete changes in resistance as on the surface of a hard disk drive by magnetic random access memory or MRAM.

Although spin-valves resistance changes are thought caused by aligning electron spin, the spins absorbed in the second FM more likely transfer their angular momentum as torque to the relatively rigid lattice and not to the electron spins that are effectively shielded by the lattice. Moreover, the spin-torque propagates by phonons through the second FM lattice at frequencies < 10 GHz while the electron spins respond on a sub-picosecond time scale. Clearly, spin-valve switching is occurring by a faster mechanism than the transfer of angular momentum through the lattice by phonons, say by light activation.

In nanoelectronics, QM requires the heat capacity of atoms in circuit elements like memristors and PC-RAM devices to vanish thereby precluding conservation of Joule heat by an increase in temperature. Spin-valves are no different. Instead, Joule heat is conserved by the creation of non-thermal EM radiation. Provided the RI of the circuit element is greater than that of the surroundings, EM radiation at EUV levels is created by the frequency up-conversion of Joule heat to the TIR confinement frequency of the circuit element. RI stands for refractive index, EUV for extreme ultraviolet, and TIR stands for total internal reflection. Memristors and PC-RAM devices  comprise titanium dioxide and GST films if having thicknesses < 10 nm create EUV > 40 eV, and therefore excitons (holes and electrons) are readily created by the photoelectric effect, the positive holes of which act as photo carriers that significantly reduce the nominal resistance of the circuit element. For the FMs in spin-valves, the EUV may directly change the spin and even demagmetize the FM, but this is irrelevant as the GMR is reduced by the dramatic increase in photoconductivity.

In summary, electron-spins most likely have nothing to do with the lowering of the GMR. Instead, the MRAM mechanism is that of memristors and PC-RAM devices where resistance is dramatically changed by the significant increase in photoconductivity brought about by the QED induced photoelectric effect in the conversion of Joule heat to EUV radiation. See Press Release and Paper