The goal of the study was to characterize the limestone that was used extensively in the ancient city of Pella (Macedonia, Greece), the birthplace of Alexander the Great. An on-site examination of the building material was carried out to record the types of damage and to select sampling areas. A variation in the nature of the stone and the degree of deterioration, even between the stones that comprise a specific monument structure, was observed, with water absorption and biological colonization being the main factors resulting in the deterioration of the stone. A comprehensive microanalysis and testing scheme was conducted to fully characterize the mineralogical, chemical, mechanical and thermal properties of the stones collected from various areas of the archaeological site. Optical microscopy, XRD and SEM–EDX were used to investigate the chemical composition and the structure of the stone samples. Finally, other properties, such as porosity, specific gravity and water absorption, were measured. Surface alterations, material degradation and biological deterioration were observed in most samples. The results obtained using XRD showed that the dominant mineral phase of the limestone is calcite, with quartz and clay minerals also detected in traces. The microscopic examination of the samples showed that the main natural stone at the archaeological site is a marly limestone. Thermographical measurements showed that the decay of the stones due to ambient temperature variation and corresponding contraction/expansion phenomena may be relatively limited, as the stone exhibited a low thermal diffusivity. Moreover, high porosity values (12.06–21.09%) and low compressive strength (11.3–27.7 MPa) were recorded, indicating the vulnerability of the stone and the need to take conservation measures.

We measured sorption isotherms for helium and nitrogen in wide temperature ranges and for a series of porous silicon samples, both native samples and samples with reduced pore mouth, so that the pores have an ink-bottle shape. Combining volumetric measurements and sensitive optical techniques, we show that, at a high temperature, homogeneous cavitation is the relevant evaporation mechanism for all samples. At a low temperature, the evaporation is controlled by meniscus recession, the detailed mechanism being dependent on the pore length and mouth reduction. Native samples and samples with ink-bottle pores shorter than 1 μm behave as an array of independent pores. In contrast, samples with long ink-bottle pores exhibit long-range correlations between pores. In this latter case, evaporation takes place by a collective percolation process and not by heterogeneous cavitation as previously proposed. The variety of evaporation mechanisms points to porous silicon being an anisotropic three-dimensional pore network rather than an array of straight independent pores.

The sanctuaries of Demeter and Asklepios are part of the Dion archaeological site that sits among the eastern foothills of Mount Olympus. The main building materials are limestones and conglomerates. Sandstones, marbles, and ceramic plinths were also used. The materials consist mainly of calcite and/or dolomite, whereas the deteriorated surfaces contain also secondary and recrystallized calcite and dolomite, gypsum, various inorganic compounds, fluoroapatite, microorganisms and other organic compounds. Cracks and holes were observed in various parts of the stones. The influence of specific weathering agents and factors to the behavior of the materials was examined. The particular environmental conditions in Dion combine increased moisture and rain fall, insolation and great temperature differences, abundance of intensive surface and underground water bodies in the surrounding area, an area full of plants and trees, therefore, they can cause extensive chemical, biological and mechanical decay of the monuments. The following physical characteristics of the building materials have been studied: bulk density, open porosity, pore size distribution, water absorption and desorption, capillary absorption and desorption. The chemical composition of bulk precipitation, surface and underground water was investigated. The salts presence and crystallization was examined. The influence of the water presence to the behavior of the materials was examined by in situ IR thermometer measurements. Temperature values increased from the lower to the upper parts of the building stones and they significantly depend on the orientation of the walls. The results indicate the existence of water in the bulk of the materials due to capillary penetration. The existence of water in the bulk of the materials due to capillary penetration, the cycles of wet-dry conditions, correlated with the intensive surface and underground water presence in the whole surrounding area, lead to partial dissolution-recrystallization of the carbonate material and loss of the structural cohesion and the surface stability.

High resolution measurements reveal that condensation isotherms of (4)He in high porosity silica aerogel become discontinuous below a critical temperature. We show that this behavior does not correspond to an equilibrium phase transition modified by the disorder induced by the aerogel structure, but to the disorder-driven critical point predicted for the athermal out-of-equilibrium dynamics of the random-field Ising model. Our results evidence the key role of nonequilibrium effects in the phase transitions of disordered systems.

Metal silicides formed by means of thermal annealing processes are employed as contact materials in microelectronics. Control of the structure of silicide/silicon interfaces becomes a critical issue when the characteristic size of the device is reduced below a few tens of nanometers. Here, we report on silicide clustering occurring within the channel of PtSi/Si/PtSi Schottky-barrier transistors. This phenomenon is investigated through atomistic simulations and low-temperature resonant-tunneling spectroscopy. Our results provide evidence for the segregation of a PtSi cluster with a diameter of a few nanometers from the silicide contact. The cluster acts as a metallic quantum dot giving rise to distinct signatures of quantum transport through its discrete energy states.

PurposeThe purpose of this paper is to study the stress corrosion cracking (SCC) behaviour of anodized 1050 Al‐alloy in marine environments at different concentrations of sulphate ions.Design/methodology/approachThe SCC experiments were performed by measuring the time to failure in 3.5% NaCl solution, or in the presence of three different concentrations of sulphate ions under conditions of applied anodic current. For the interpretation of the results, changes in potential during SCC tests and optical microscope micrographs of stress corrosion tested specimens at various periods of time, were obtained.FindingsThe influence of seawater composition on the SCC behaviour of the anodized 1050 Al‐alloy depends on the concentration of sulphate ions, the oxide thickness and the stress level. At the higher stress levels and low concentrations of sulphate ions, increased times to failure were observed. These results were attributed to the inhibitory action of sulphate ions. At a low stress level and higher concentration of sulphate ions, the increased times of exposure and the more intensive corrosive environment led to partial destruction of the anodic coatings and a decrease in the time to failure. Better protective properties were observed at an oxide thickness of 10 μm. The thicker oxides did not protect so well because they were more brittle, cracking under strain and allowing corrosive species to reach the metal surface.Research limitations/implicationsThe hypothesised mechanism of the effect of seawater composition on the SCC behaviour of anodized Al‐alloys depended on the concentration of sulphate ions and the stress level remains yet to be confirmed.Practical implicationsThe selection of suitable anodic coatings for the protection of aluminium alloys against stress corrosion cracking depends on the composition of the marine environment.Originality/valueThe paper provides information regarding the influence of sulphate ions on the anticorrosive properties of electrolytically prepared anodic coatings on aluminium alloys.

We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature-dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be effective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid helium temperature. By independently tuning the effective Schottky barrier heights, a variety of reconfigurable device functionalities could be obtained. In particular, the same nanowire device could be configured to work as a Schottky barrier transistor, a Schottky diode, or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one.

Back-scattered Scanning Electron Microscopy (BSEM) has been used to identify weathering mechanisms occurring in two oolitic limestones from urban areas in London and Cambridge, United Kingdom. From a petrographical point of view, the two stones can be described as oosparite and oomicrite, their main distinctive feature being the crystal size of the cement binding the limestone grains together. The sulphation mechanism, i.e. the replacement of calcium carbonate (calcite: CaCO3) by calcium sulphate dehydrate (gypsum: CaSO4 2H2O), at the surface and within the stone fabric is confirmed as the general decay process. Differences in macroporosity/permeability distribution in the two limestones lead to different weathering patterns. BSEM provides evidence that gypsum patinas still commonly found on limestone facades in polluted urban locations are advancing inside the diseased stone and that their removal is urgently needed to arrest the growth of the in-growing weathering front.

The aim of this paper is the study of the effect of environmental factors on the deterioration of marble monuments and the selection of a suitable and effective cleaning method. One of the main deterioration problems of the monuments is biodeterioration. It was obvious the presence of thick layers of biological patina, covering all almost surfaces of these. The growth of microorganisms, bacteria and plants is enhanced from the particular environmental conditions, that combine increased moisture, insolation and temperature, an area full of plants and trees and can cause extensive chemical and mechanical decay of the monuments. The growth of microorganisms, bacteria, plants and lichens was observed and determined. The influence of specific weathering agents and factors to the behavior of the materials was examined. The chemical composition of bulk precipitation and also the physicochemical characteristics of the surface and underground water were investigated. The environmental conditions and the growth of physical microorgamisms on the surface of the materials led to loss of the structural cohesion and the surface instability of the building materials. A series of various mechanical and chemical cleaning methods were tested in the laboratory containing the use of distilled water, microsandblast, organic solvents, absorbing clays, NH4HCO3 solution, biocides (desogen, hydrogen peroxide). In situ tests were carried out with satisfactory results in the monuments when a method of combination of hydrogen peroxide solutions, EDTA, NH4HCO3 solution and organic solvent was applied in various steps on the monument surface.

The sanctuaries of Demeter and Asklepios are part of the Dion archaeological site that sits among the eastern foothills of Mount Olympus and covers roughly 100 hectares. The excavations finds from this area are dated since the Hellenistic, Roman and Early Christian times. The main building materials are limestones and conglomerates. Sandstones, marbles, and ceramic plinths were also used. The materials consist mainly of calcite and/or dolomite, whereas the deteriorated surfaces contain also secondary and recrystallized calcite and dolomite, gypsum, various inorganic compounds, fluoroapatite, microorganisms and other organic compounds. Cracks and holes were observed in various parts of the stones. The most proper approach to select effective methods for the structural and surface consolidation, the cleaning, the protection and the overall conservation of these structures is the knowledge of the processes contributing to their deterioration. The influence of the water presence to the behavior of the materials was examined by in situ IR thermometer measurements. Temperature values increased from the lower to the upper parts of the building stones and they significantly depend on the orientation of the walls. The results indicate the existence of water in the bulk of the materials due to capillary penetration. To confirm these observations measurements of the following physical characteristics of the building materials have been studied: open porosity, pore size distribution, water absorption and desorption, capillary absorption and desorption. The existence of water in the bulk of the materials due to capillary penetration, the cycles of wet-dry conditions, correlated with the intensive surface and underground water presence in the whole surrounding area, lead to partial dissolution-recrystallization of the carbonate material and loss of the structural cohesion and the surface stability.

Purpose – The purpose of this paper is to study of the effect of carboxylic acids additions to the anodising bath on the subsequent corrosion and stress corrosion cracking (SCC) tendencies of anodised 1050 Al‐Alloy in 3M NaCl solution.Design/methodology/approach – The study was carried out using SCC tests and electrochemical cyclic potentiodynamic measurements at a high or a slow scan rates. The anodic coatings were prepared electrolytically in a bath of 4 M H2SO4, with and without additions of 0.015 M oxalic, malonic, tartaric, maleic, or citric acids. The consequent thicknesses and packing densities of the coatings were measured.Findings – The SCC behaviour was found to vary with both anodising conditions and stress level. The addition of carboxylic acids in the anodising bath increased the protective properties of the coating. In corrosion conditions without stress, the addition of the carboxylic acids decreased the susceptibility to pitting corrosion, the effect depending on the presence or absence of...

The fabrication and operation of V-based superconducting nanorefrigerators is reported. Specifically, electrons in an Al island are cooled thanks to hot-quasiparticle extraction provided by tunnel-coupled V electrodes. Electronic temperature reduction down to 400 mK starting from 1 K is demonstrated with a cooling power ~20 pW at 1 K for a junction area of 0.3 micron^2. The present architecture extends to higher temperatures refrigeration based on tunneling between superconductors and paves the way to the implementation of a multi-stage on-chip cooling scheme operating from above 1 K down to the mK regime.

We report the fabrication and characterization of superconducting quantum interference devices (SQUIDs) based on InAs nanowires and vanadium superconducting electrodes. These mesoscopic devices are found to be extremely robust against thermal cycling and to operate up to temperatures of ∼ 2.5 K with reduced power dissipation. We show that our geometry allows one to obtain nearly-symmetric devices with very large magnetic field modulation of the critical current. All these properties make these devices attractive for sensitive magnetometry applications and quantum circuit implementation.

We report on a technique enabling electrical control of the contact silicidation process in silicon nanowire devices. Undoped silicon nanowires were contacted by pairs of nickel electrodes, and each contact was selectively silicided by means of the Joule effect. By a real-time monitoring of the nanowire electrical resistance during the contact silicidation process we were able to fabricate nickel-silicide/silicon/nickel-silicide devices with controlled silicon channel length down to 8 nm.

A prominent branch of spintronics aims at exploiting the electronic spin degree of freedom either for encoding and manipulating quantum information or for switching the state of transistors in a more efficient way. While ground-breaking achievements could be made mainly on GaAs-based heterostructures, the importance of exploring alternative material systems with favourable properties such as long spin coherence is now widely recognized. Si and Ge are attractive materials because in these materials electronic spins can have a long coherence time due to the absence of hyperfine interaction (in isotopically purified crystals). Here we report for the first time the realisation of single-hole transistors based on individual self-assembled SiGe quantum dots. Transport spectroscopy reveals largely anisotropic and electrically tunable hole g-factors, which make SiGe self-assembled QDs an interesting material system for performing all-electrical spin coherent manipulations.

Aim of the present work is the study of corrosion and stress corrosion cracking behaviour of 1050 Al-Alloy anodised in a 3M H2SO4 anodising bath with the presence in it of malonic acid, in various concentrations and anodising current densities. The investigation was carried out by SCC (Stress Corrosion Cracking) tests and electrochemical measurements. The influence of applied potential on SCC behaviour was also examined. The corrosion and SCC behaviour of anodised 1050 Al-Alloy was found to vary with malonic acid concentration, anodising conditions, applied potential and stress level. In SCC conditions all prepared coatings protected the bare alloy, with better protective properties in the case of 0.015M concentration of malonic acid prepared with a 6 A.dm-2 anodising current density. The coating prepared in these conditions had better mechanical properties as indicated from the increased protection at a high stress level and also the better behaviour in corrosion, without stress, conditions of coatings prepared in different conditions of malonic acid concentration and anodising current density. For the interpretation of the results, properties of the anodic coatings as thickness, packing density, coating ratio, roughness, were also studied. The anodic coating formed in a electrolytic bath of 0.015M concentration of malonic acid and a 6 A.dm-2 anodising current density was found to be less porous, more compact and rough, with better oxide structure. Prepared coatings were found to increase protective properties in an area of applied potentials slightly more anodic than the free corrosion potential values.