Showing papers by "Claes-Göran Granqvist published in 2014"

Thermochromic undoped and Mg-doped VO2 thin films and nanoparticles: Optical properties and performance limits for energy efficient windows

Abstract: Undoped and Mg-doped thermochromic VO2 films with atom ratios z equivalent to Mg/(Mg + V) of 0 <= z < 0.21 were deposited by reactive DC magnetron sputtering onto heated glass and carbon subs ...

On the security of the Kirchhoff-law---Johnson-noise (KLJN) communicator

Abstract: A simple and general proof is given for the information theoretic (unconditional) security of the Kirchhoff-law---Johnson-noise key exchange system under practical conditions. The unconditional security for ideal circumstances, which is based on the second law of thermodynamics, is found to prevail even under slightly non-ideal conditions. This security level is guaranteed by the continuity of functions describing classical physical linear, as well as stable non-linear, systems. Even without privacy amplification, Eve's probability for successful bit guessing is found to converge toward 0.5--i.e., the perfect security level--when ideal conditions are approached.

New Approaches for Improving Selectivity and Sensitivity of Resistive Gas Sensors: A Review

Abstract: New Approaches for Improving Selectivity and Sensitivity of Resistive Gas Sensors: A Review

Do Electromagnetic Waves Exist in a Short Cable at Low Frequencies? What Does Physics Say?

Abstract: We refute a physical model, recently proposed by Gunn, Allison and Abbott (GAA) [http://arxiv.org/pdf/1402.2709v2.pdf], to utilize electromagnetic waves for eavesdropping on the Kirchhoff-law–Johnson-noise (KLJN) secure key distribution. Their model, and its theoretical underpinnings, is found to be fundamentally flawed because their assumption of electromagnetic waves violates not only the wave equation but also the second law of thermodynamics, the principle of detailed balance, Boltzmann's energy equipartition theorem, and Planck's formula by implying infinitely strong blackbody radiation. We deduce the correct mathematical model of the GAA scheme, which is based on impedances at the quasi-static limit. Mathematical analysis and simulation results confirm our approach and prove that GAA's experimental interpretation is incorrect too.

Oxide-based chromogenic coatings and devices for energy efficient fenestration: Brief survey and update on thermochromics and electrochromics

Abstract: Modern buildings often have large windows and glass facades in order to achieve good day-lighting and desirable indoors–outdoors contact. These glazings are challenging with regard to the buildings' energy efficiency and frequently let in or out too much energy; this phenomenon has to be balanced by energy guzzling cooling or heating. In particular, the cooling requirement has grown strongly in recent years. Chromogenic glazings, based on thermochromism or electrochromism, are emerging technologies that can regulate the inflow of visible light and solar energy between widely separated limits and create better energy efficiency than is possible with static solutions. Thermochromic thin films—in practice based on vanadium dioxide—have a transmittance of infrared solar radiation that is smaller at high temperature than at low temperature. Electrochromic multilayer structures—often incorporating nanoporous thin films of tungsten oxide and nickel oxide—are able to vary the transmittance of visible light and solar energy when a low voltage is applied for a short time so as to shuttle charge between the two oxide films. Furthermore, and importantly, the new chromogenic fenestration technologies are able to improve indoor comfort. This brief tutorial review surveys the fields of oxide-based thermochromics and electrochromics with particular attention to recent advances.

Current and voltage based bit errors and their combined mitigation for the Kirchhoff-law---Johnson-noise secure key exchange

Abstract: We classify and analyze bit errors in the current measurement mode of the Kirchhoff-law---Johnson-noise (KLJN) key distribution. The error probability decays exponentially with increasing bit exchange period and fixed bandwidth, which is similar to the error probability decay in the voltage measurement mode. We also analyze the combination of voltage and current modes for error removal. In this combination method, the error probability is still an exponential function that decays with the duration of the bit exchange period, but it has superior fidelity to the former schemes.

Elimination of a Second-Law Attack, and All Cable-Resistance-Based Attacks, in the Kirchhoff-Law-Johnson-Noise (KLJN) Secure Key Exchange System

Abstract: We introduce the so far most efficient attack against the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange system. This attack utilizes the lack of exact thermal equilibrium in practical applications and is based on cable resistance losses and the fact that the Second Law of Thermodynamics cannot provide full security when such losses are present. The new attack does not challenge the unconditional security of the KLJN scheme, but it puts more stringent demands on the security/privacy enhancing protocol than for any earlier attack. In this paper we present a simple defense protocol to fully eliminate this new attack by increasing the noise-temperature at the side of the smaller resistance value over the noise-temperature at the side with the greater resistance. It is shown that this simple protocol totally removes Eve’s information not only for the new attack but also for the old Bergou-Scheuer-Yariv attack. The presently most efficient attacks against the KLJN scheme are thereby completely nullified.

On the “Cracking” Scheme in the Paper “A Directional Coupler Attack Against the Kish Key Distribution System” by Gunn, Allison and Abbott

Abstract: Recently, Gunn, Allison and Abbott (GAA) [http://arxiv.org/pdf/1402.2709v2.pdf] proposed a new scheme to utilize electromagnetic waves for eavesdropping on the Kirchhoff -law –Johnson- noise (KLJN) secure key distribution. We proved in a former paper [ Fluct. Noise Lett. 13 (2014) 1450016 ] that GAA’s mathematical model is unphysical. Here we analyze GAA’s cracking scheme and show that, in the case of a loss -free cable, it provides less eavesdropping information than in the earlier (Bergou)-Scheuer-Yariv mean-square- based attack [Kish LB, Scheuer J, Phys. Lett. A 37 4:2140 –2142 (2010)], while it offers no information in the case of a lossy cable. We also investigate GAA’s claim to be experimentally capable of distinguishing —using statistics over a few correlation times only —the distributions of two Gaussian noises wit h a relative variance difference of less than 10 –8 . Normally such distinctions would require hundreds of millions of correlations times to be observable. We identify several potential experimental artifacts as results of poor KLJN design, which can lead to GAA’s assertions: deterministic currents due to spurious harmonic components caused by ground loops, DC offset, aliasing, non -Gaussian features including non-linearities and other non- idealities in generators, and the timederivative nature of GAA’s schem e which tends to enhance all of these artifacts.

On the "Cracking" Experiments in the Paper "A Directional Coupler Attack against the Kish Key Distribution System" by Gunn, Allison and Abbott

Abstract: On the "Cracking" Experiments in the Paper "A Directional Coupler Attack against the Kish Key Distribution System" by Gunn, Allison and Abbott

Bit Errors in the Kirchhoff-Law-Johnson-Noise Secure Key Exchange

Abstract: We classify and analyze bit errors in the voltage and current measurement modes of the Kirchhoff-law–Johnson-noise (KLJN) secure key distribution system. In both measurement modes, the error probability decays exponentially with increasing duration of the bit sharing period (BSP) at fixed bandwidth. We also present an error mitigation strategy based on the combination of voltage-based and current-based schemes. The combination method has superior fidelity, with drastically reduced error probability compared to the former schemes, and it also shows an exponential dependence on the duration of the BSP.

Elimination of a Second-Law-attack, and all cable-resistance-based attacks, in the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange system

Abstract: We introduce the so far most efficient attack against the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange system. This attack utilizes the lack of exact thermal equilibrium in practical applications and is based on cable resistance losses and the fact that the Second Law of Thermodynamics cannot provide full security when such losses are present. The new attack does not challenge the unconditional security of the KLJN scheme, but it puts more stringent demands on the security/privacy enhancing protocol than for any earlier attack. In this paper we present a simple defense protocol to fully eliminate this new attack by increasing the noise-temperature at the side of the smaller resistance value over the noise-temperature at the at the side with the greater resistance. It is shown that this simple protocol totally removes Eve's information not only for the new attack but also for the old Bergou-Scheuer-Yariv attack. The presently most efficient attacks against the KLJN scheme are thereby completely nullified.

Thermochromic vanadium oxide thin films: Electronic and optical properties

Abstract: Vanadium dioxide, VO2, is a widely studied thermochromic material with potential applications in energy efficient window technology. It undergoes a first-order metal-to- insulator transition, accompanied by a crystal structure transformation from monoclinic to tetragonal rutile, at a critical temperature of 68 °C. Below this temperature, VO2 is semiconducting and infrared transmitting whereas it is metallic and infrared reflecting above the transition temperature. However, in order to achieve significant thermochromic switching, the luminous transmittance of thin films will typically be less than 50%. Here we report on recent research to improve the luminous transmittance as well as the transmittance change at the transition temperature. We systematically evaluate the effect of antireflection coatings, doping with Mg and the performance of coatings comprising thermochromic nanoparticles in a transparent matrix. The last option is shown to give the best performance and holds great promise for practical applications.

Cyclic voltammetry on sputter-deposited films of electrochromic Ni oxide : Power-law decay of the charge density exchange

Abstract: : Ni-oxide-based thin films were produced by reactive direct-current magnetron sputtering and were characterized by X-ray diffraction and Rutherford backscattering spectroscopy. Intercalati ...

Analysis of an attenuator artifact in an experimental attack by gunn–allison–abbott against the kirchhoff-law– johnson-noise (kljn) secure key exchange system

Abstract: A recent paper by Gunn–Allison–Abbott (GAA) [L.J. Gunn et al., Scientific Reports 4 (2014) 6461] argued that the Kirchhoff-law–Johnson-noise (KLJN) secure key exchange system could experience a severe information leak. Here we refute their results and demonstrate that GAA’s arguments ensue from a serious design flaw in their system. Specifically, an attenuator broke the single Kirchhoffloop into two coupled loops, which is an incorrect operation since the single loop is essential for the security in the KLJN system, and hence GAA’s asserted information leak is trivial. Another consequence is that a fully defended KLJN system would not be able to function due to its built-in current-comparison defense against active (invasive) attacks. In this paper we crack GAA’s scheme via an elementary current comparison attack which yields negligible error probability for Eve even without averaging over the correlation time of the noise.

Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization

Abstract: Conversion of acetaldehyde to crotonaldehyde on anatase TiO2 films was studied by in situ Fourier transform infrared spectroscopy (FTIR) and by density functional theory (DFT) calculations. In situ ...

Demons: Maxwell's demon, Szilard's engine and Landauer's erasure-dissipation

Abstract: This talk addressed the following questions in the public debate at HoTPI: (i) energy dissipation limits of switches, memories and control; (ii) whether reversible computers are possible, or does their concept violate thermodynamics; (iii) Szilard's engine, Maxwell's demon and Landauer's principle: corrections to their exposition in the literature; (iv) whether Landauer's erasure–dissipation principle is valid, if the same energy dissipation holds for writing information, or if it is invalid; and (v) whether (non-secure) erasure of memories, or the writing of the same amount of information, dissipates most heat.

Preferential Orientation and Surface Oxidation Control in Reactively Sputter Deposited Nanocrystalline SnO2:Sb Films: Electrochemical and Optical Results

Abstract: Antimonydopedtinoxideisaversatiletransparentelectricalconductor.Manyofitspropertiesdependontheelectronicbandstructure at the surface of a thin film‐such as the position of the Fermi level, ionization potential Ip, optical gap energy, etc.‐which in its turn is related to the surface termination given by the crystallographic orientation of the film. We prepared SnO2:Sb films by reactive DC magnetron sputtering at different oxygen/argon ratios and found by X-ray diffraction that the crystallographic orientation could be changed from tetragonal (101) to tetragonal (110) as the oxygen content was raised. Electrochemical measurements showed that this change in preferential orientation was accompanied by an increase of Ip by more than 1 eV as a result of the modification of the oxidation state of tin atoms at the film’s surface. Such alterations of Ip have a large impact on the electrochemical, photocatalytic and gas sensing behavior of the material. Moreover, preferential orientation control‐and hence Ip tuning‐allow the tailoring of SnO2:Sb electrodes for various application by reducing the Schottky barrier.

Electronic density-of-states of amorphous vanadium pentoxide films: Electrochemical data and density functional theory calculations

Abstract: Thin films of V2O5 were prepared by sputter deposition onto transparent and electrically conducting substrates and were found to be X-ray amorphous. Their electrochemical density of states was determined by chronopotentiometry and displayed a pronounced low-energy peak followed by an almost featureless contribution at higher energies. These results were compared with density functional theory calculations for amorphous V2O5. Significant similarities were found between measured data and computations; specifically, the experimental low-energy peak corresponds to a split-off part of the conduction band apparent in the computations. Furthermore, the calculations approximately reproduce the experimental band gap observed in optical measurements.

Critical Remarks on Landauer's principle of erasure-dissipation

Abstract: We briefly address Landauer's Principle and some related issues in thermal demons. We show that an error-free Turing computer works in the zero-entropy limit, which proves Landauer's derivation incorrect. To have a physical logic gate, memory or information-engine, a few essential components necessary for the operation of these devices are often neglected, such as various aspects of control, damping and the fluctuation-dissipation theorem. We also point out that bit erasure is typically not needed or used for the functioning of computers or engines (except for secure erasure).

Durability of VO2-based thin films at elevated temperature: Towards thermochromic fenestration

Abstract: An explorative study was performed on sputter-deposited thermochromic VO2 films with top coatings of Al oxide and Al nitride. The films were exposed to dry air at a high temperature. Bare 80-nm-thick VO2 films rapidly converted to non-thermochromic V2O5 under the chosen conditions. Al oxide top coatings protected the underlying VO2 films and, expectedly, increased film thickness yielded improved protection. Specifically, it was found that a 30-nm-thick sputter-deposited Al oxide top coating delayed the oxidation by more than one day upon heating at 300°C. The results demonstrate the importance of protective layers in thermochromic windows for practical application.

On the "cracking" scheme in the paper "A directional coupler attack against the Kish key distribution system" by Gunn, Allison and Abbott

Abstract: Recently, Gunn, Allison and Abbott (GAA) [this http URL] proposed a new scheme to utilize electromagnetic waves for eavesdropping on the Kirchhoff-law-Johnson-noise (KLJN) secure key distribution. We proved in a former paper [Fluct. Noise Lett. 13 (2014) 1450016] that GAA's mathematical model is unphysical. Here we analyze GAA's cracking scheme and show that, in the case of a loss-free cable, it provides less eavesdropping information than in the earlier (Bergou)-Scheuer-Yariv mean-square-based attack [Kish LB, Scheuer J, Phys. Lett. A 374 (2010) 2140-2142], while it offers no information in the case of a lossy cable. We also investigate GAA's claim to be experimentally capable of distinguishing - using statistics over a few correlation times only - the distributions of two Gaussian noises with a relative variance difference of less than 10^-8. Normally such distinctions would require hundreds of millions of correlations times to be observable. We identify several potential experimental artifacts as results of poor KLJN design, which can lead to GAA's assertions: deterministic currents due to spurious harmonic components caused by ground loops, DC offset, aliasing, non-Gaussian features including non-linearities and other non-idealities in generators, and the time-derivative nature of GAA's scheme which tends to enhance all of these artifacts.