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A 4 × non-imaging optically concentrated solar thermoelectric generator (STEG) was simulated and its layout was optimized depending on materials characteristics. The performances of seven state-of-the-art thermoelectric materials were realistically compared considering direct normal irradiances (DNI) between 400 and 900 W/m2 and temperature dependence of the thermoelectric parameters. The model was tested with experimental data from literature and leg aspect ratios, fill factor (or thermal concentration), and leg number per STEG unit area were also used as variables. Due to the high values of thermal concentrations at maximum efficiency, different materials filling the gap among STEG legs were also considered. Maximum efficiency weakly decreases for filler thermal conductivities typical of common insulating materials, opening novel opportunities for STEGs not requiring vacuum. Results of the analysis show that skutterudites, lead telluride and bismuth telluride exhibit the highest efficiencies (≈7%) in the studied range of thermal concentrations and for a DNI equal to 900 W/m2. However, skutterudites and lead telluride were found to be very sensitive on the DNI level, differently from bismuth telluride, which therefore qualifies as the best solution for energy conversion. Moreover, optimal layouts for STEGs based on bismuth telluride more easily meet manufacturing constraints.

Over the last few years, a growing interest has surfaced about the possibility of enhancing solar harvester efficiency by coupling photovoltaic (PV) cells with thermoelectric generators (TEGs). To be effective solutions, hybrid thermoelectric-photovoltaic (HTEPV) solar harvesters must not only increase the solar conversion efficiency but should also be economically competitive. The aim of this paper is to estimate the profitability of HTEPV solar harvesters with no reference to specific materials, relating it instead to their physical properties only and thus providing a tool to address research effort toward classes of HTEPV systems able to compete with current PV technologies. An economic convenience index is defined and used to assess the economic sustainability of hybridization. It is found that, although hybridization often leads to enhanced solar power conversion, power costs (USD/W) may not always justify HTEPV deployment at the current stage of technology. An analysis of the cost structure shows that profitability requires largely enhanced thermoelectric stages, concentrated solar cells, or PV materials with favorable temperature efficiency coefficients, such as perovskite solar cells.

Silicon nanowires, whose thermal conductivity is strongly reduced with respect to that of the bulk silicon, are very promising for high-efficient thermoelectric conversion. This work focuses on the development of a technique for the fabrication of thermoelectric generators which are based on vertical silicon nanowire forests, achieved through a metal-assisted chemical etch. As heavily doped nanowires are essential in thermoelectric applications, this chemical process has been applied both on lightly and on highly doped (> 1019 cm−3) silicon substrates. A comparison of the results shows that the etch behaves in a completely distinct way when applied to the differently doped substrates. The results of this comparison and a preliminary insight into the diverse behavior occurred are reported. The different initial nucleation of silver, which determines the hole injection, essential to the etching of silicon, seems to be the key point of this different behavior.

PdGe contact fabrication on Ge(001) wafers doped with Ga is investigated using conventional complementary metal-oxide-semiconductor processes. Despite a p-type doping level of ~1.4 × 1020 cm−3, the resistivity of the PdGe contact is found to be twice higher than that of undoped Ge. Ga doping has no influence on the Pd reaction with Ge. However, the doping process and the Salicide process led to the formation of Ga-Pd defects in both sides of the PdGe/Ge interface, resulting from Ga and Pd co-segregation on Ge dislocation loops.

The decrease of solar cell efficiency with temperature is a known problem for photovoltaics (PV). Temperature sensitivity can lead to a considerable amount of energy losses over the lifetime of solar panels. In this perspective Hybrid Thermoelectric-Photovoltaic (HTEPV) systems, which recover solar cell heat losses to produce an additional power output, can be a suitable option. However only hybridization of wide-gap solar cells is convenient in terms of efficiency gains and deserves investigation to evaluate HTEPV devices effectiveness. In this work we report the modeling and the development of customized bismuth telluride thermoelectric generators, optimized to be hybridized with amorphous silicon (aSi), Gallium Indium Phosphide (GaInP) or Perovskites solar cells. The model results showed in all three cases efficiency gains with a maximum of +3.1% for Perovskites (from 16.4% to 19.5%). These enhancements were then experimentally validated for the case of Perovskites solar cells, for which maximum gains were found to occur at typical operating temperatures of conventional PVs. This experimental evaluation demonstrated in an accurate fashion the real potential of thermoelectric hybridization of solar cells.

The development and commercialization of Photovoltaic (PV) cells with good cost-efficiency trade-off not using critical raw materials (CRMs) is one of the strategies chosen by the European Community (EC) to address the Energy Roadmap 2050. In this context Cu2ZnSnS4 (CZTS) solar cells are attracting a major interest since they have the potential to combine low price with relatively high conversion efficiencies. Although a ≈9% lab scale efficiency has already been reported for CZTS this technology is still far from being competitive in terms of cost per peak-power (€/Wp) with other common materials. One possible near-future solution to increase the CZTS competiveness comes from thermoelectrics. Actually it has already been shown that Hybrid Thermoelectric-Photovoltaic Systems (HTEPVs) based on CIGS, another kesterite very similar to CZTS, can lead to a significant efficiency improvement. However it has been also clarified how the optimal hybridization strategy cannot come from the simple coupling of solar cells with commercial TEGs, but special layouts have to be implemented. Furthermore, since solar cell performances are well known to decrease with temperature, thermal decoupling strategies of the PV and TEG sections have to be taken. To address these issues, we developed a model for two different HTEPV solutions, both coupled with CZTS solar cells. In the first case we considered a Thermally-Coupled HTEPV device (TC-HTEPV) in which the TEG is placed underneath the solar cell and in thermal contact with it. The second system consists instead of an Optically-Coupled but thermally decoupled device (OC-HTEPV) in which part of the solar spectrum is focused by a non-imaging optical concentrator on the TEG hot side. For both solutions the model returns conversion efficiencies higher than that of the CZTS solar cell alone. Specifically, increases of ≈30% are predicted for both kind of systems considered. Copyright © 2017 American Scientific Publishers All rights reserved.

Thermoelectricity offers a sustainable path to recover and convert waste heat into readily available electric energy, and has been studied for more than two centuries. From the controversy between Galvani and Volta on the Animal Electricity, dating back to the end of the XVIII century and anticipating Seebeck’s observations, the understanding of the physical mechanisms evolved along with the development of the technology. In the XIX century Ørsted clarified some of the earliest observations of the thermoelectric phenomenon and proposed the first thermoelectric pile, while it was only after the studies on thermodynamics by Thomson, and Rayleigh’s suggestion to exploit the Seebeck effect for power generation, that a diverse set of thermoelectric generators was developed. From such pioneering endeavors, technology evolved from massive, and sometimes unreliable, thermopiles to very reliable devices for sophisticated niche applications in the XX century, when Radioisotope Thermoelectric Generators for space missions and nuclear batteries for cardiac pacemakers were introduced. While some of the materials adopted to realize the first thermoelectric generators are still investigated nowadays, novel concepts and improved understanding of materials growth, processing, and characterization developed during the last 30 years have provided new avenues for the enhancement of the thermoelectric conversion efficiency, for example through nanostructuration, and favored the development of new classes of thermoelectric materials. With increasing demand for sustainable energy conversion technologies, the latter aspect has become crucial for developing thermoelectrics based on abundant and non-toxic materials, which can be processed at economically viable scales, tailored for different ranges of temperature. This includes high temperature applications where a substantial amount of waste energy can be retrieved, as well as room temperature applications where small and local temperature differences offer the possibility of energy scavenging, as in micro harvesters meant for distributed electronics such as sensor networks. While large scale applications have yet to make it to the market, the richness of available and emerging thermoelectric technologies presents a scenario where thermoelectrics is poised to contribute to a future of sustainable future energy harvesting and management. This work reviews the broad field of thermoelectrics. Progress in thermoelectrics and milestones that led to the current state-of-the-art are presented by adopting an historical footprint. The review begins with an historical excursus on the major steps in the history of thermoelectrics, from the very early discovery to present technology. A panel on the theory of thermoelectric transport in the solid state reviews the transport theory in complex crystal structures and nanostructured materials. Then, the most promising thermoelectric material classes are discussed one by one in dedicated sections and subsections, carefully highlighting the technological solutions on materials growth that have represented a turning point in the research on thermoelectrics. Finally, perspectives and the future of the technology are discussed in the framework of sustainability and environmental compatibility.

In this chapter, we will describe triple cogeneration technologies for solar conversion. The costs of solar conversion technologies are determined by the efficiency of power conversion, the lifetime and reliability of its components, the cost of the raw materials, potentially including storage, and any fabrication or construction required. Recently, photovoltaics and solar thermal have emerged as viable candidates for low cost power production; they each have losses that vary across the solar spectrum, with realized and theoretical efficiencies that are well below fundamental thermodynamic limits. Thus, it is desirable to split the solar spectrum to utilize both technologies in parallel over their respective optimal wavelength ranges. This chapter will present promising triple co-generation solutions that have been developed and implemented to provide electric power generation by a combination of photovoltaic and thermal generation. In particular, we show that splitting the solar spectrum, and then using high-energy solar photons for photovoltaics and medium-energy solar photons for thermoelectrics with a bottoming Rankine cycle has potential to achieve 50% solar-to-electricity conversion using existing materials. Also, over 50% of the harvested energy goes to thermal storage for generation after sunset, which could enable highly efficient baseload solar electricity and heat generation at all hours of the day.

A summary of the main issues covered in the previous chapters will serve a comparative analysis of the current and perspective possibilities that the hybridization of thermoelectric and photovoltaic generators provides. Materials demand, technological open questions, and market-related issues will be discussed. Also concerning the competition with alternate hybridization strategies, an analysis of HTEPV cost-effectiveness will be outlined. It will be shown that HTEPV may have a key role in the development of renewable energy sources, provided that a careful selection of photovoltaic materials is made. The importance of rethinking the layout of thermoelectric generators will be stressed, along with the merits of hybridization in concentrated solar generators. As an overall conclusion, pairing thermoelectric generators to photovoltaic cells will be proved to be profitable for third-generation PV materials, where hybridization might support the differentiation of the solar module market, currently pinned to silicon-based technology.

The most common and efficient way to covert solar power into useful work is by photovoltaic generation. Photovoltaic cells are devices that convert radiative energy into electric energy. This chapter outlines the mechanism of photovoltaic conversion. The physical principles are introduced and described, and their implementation in real devices (cells and modules) is discussed with reference to the so called three solar cell generations, namely bulk cells, thin film cells, and cells based on dye sensitization. The role played by materials in each cell generation is also examined.

The performances of two hybrid thermoelectric photovoltaic systems are compared. In the first instance, a photovoltaic (PV) device and a thermoelectric generator (TEG) are optically coupled using a vacuumâ sealed compound parabolic concentrator (CPC). As an alternative, PV and TEG devices are thermally coupled putting them directly in contact to each other. Singleâ junction aâ Si and heterojunction Cu2ZnSnS4 (CZTS) have been considered as PV systems. The two systems are studied by varying the heat transfer coefficient of the cooling system between the TEG cold side and the ambient, the TEG device fill factor, and the optical concentration. Hybridization, in both configurations, always enhances the efficiencies, up toÂâ Â57% for single-junction a-Si and up toÂâ Â35% for the heterojunction CZTS. It will be shown that while direct thermal contact enables larger efficiencies, optical coupling grants lower temperatures at the PV side, enhancing reliability and lifetime. Further advantages and limitations of both configurations will be discussed.

Exploitation of solar energy conversion has become a fundamental aspect of satisfying a growing demand for energy. Thus, improvement of the efficiency of conversion in photovoltaic (PV) devices is highly desirable to further promote this source. Because it is well known that the most relevant efficiency constraint, especially for single-junction solar cells, is unused heat within the device, hybrid thermo-photovoltaic systems seem promising . Among several hybrid solutions proposed in the literature, coupling of thermoelectric and PV devices seems one of the most interesting. Taking full advantage of this technology requires proper definition and analysis of the thermal losses occurring in PV cells. In this communication we propose a novel analysis of such losses, decoupling source-dependent and absorber-dependent losses. This analysis enables an evaluation of the actual recoverable amount of energy, depending on the absorber used in the PV cell. It shows that for incoming solar irradiation of $$1000\,\hbox {W}/\hbox {m}^{2}$$ , and depending on the choice of material, the maximum available thermal power ranges from $$380\,\hbox {W}/\hbox {m}^{2}$$ (for single-crystal silicon) to $$130\,\hbox {W}/\hbox {m}^{2}$$ (for amorphous silicon).

Hole-containing silicon has been regarded as a viable candidate thermoelectric material because of its low thermal conductivity. However, because voids are efficient scattering centers not just for phonons but also for charge carriers, achievable power factors (PFs) are normally too low for its most common form, i.e. porous silicon, to be of practical interest. In this communication we report that high PFs can, indeed, be achieved with nanoporous structures obtained from highly doped silicon. High PFs, up to a huge 22 mW K-2 m(-1) (more than six times higher than values for the bulk material), were observed for heavily boron-doped nanocrystalline silicon films in which nanovoids (NVs) were generated by He+ ion implantation. In contrast with single-crystalline silicon in which He+ implantation leads to large voids, in polycrystalline films implantation followed by annealing at 1000A degrees C results in homogeneous distribution of NVs with final diameters of approximately 2 nm and densities of the order of 10(19) cm(-3) with average spacing of 10 nm. Study of its morphology revealed silicon nanograins 50 nm in diameter coated with 5-nm precipitates of SiB (x) . We recently reported that PFs up to 15 mW K-2 m(-1) could be achieved for silicon-boron nanocomposites (without NVs) because of a simultaneous increase of electrical conductivity and Seebeck coefficient. In that case, the high Seebeck coefficient was achieved as a result of potential barriers on the grain boundaries, and high electrical conductivity was achieved as a result of extremely high levels of doping. The additional increase in the PF observed in the presence of NVs (which also include SiB (x) precipitates) might have several possible explanations; these are currently under investigation. Experimental results are reported which might clarify the reason for this paradoxical effect of NVs on silicon PF.

The spectacular growth of networks of intercommunicating sensing nodes has generated a request for alternate, renewable power sources. Thermoelectric generators (TEGs), either conventional or integrated, are possible candidates. This paper analyzes the usability of TEGs as alternate power sources for wireless sensor network. It is shown how TEGs meet power requirements of low-power sensing nodes and how they outperform batteries as of the installation costs. Factors still hampering TEG wider use are also reviewed and commented upon, and an outlook at specific applications where TEGs might be rapidly deployed is provided.

In this work we perform a theoretical analysis of the thermoelectric performance of polycrystalline Si nanowires (NWs) by considering both electron and phonon transport. The simulations are calibrated with experimental data from monocrystalline and polycrystalline structures. We show that heavily doped polycrystalline NW structures with grain size below 100 nm might offer an alternative approach to achieve simultaneous thermal conductivity reduction and power factor improvements through improvements in the Seebeck coefficient. We find that deviations from the homogeneity of the channel and/or reduction in the diameter may provide strong reduction in the thermal conductivity. Interestingly, our calculations show that the Seebeck coefficient and consequently the power factor can be improved significantly once the polycrystalline geometry is properly optimized, while avoiding strong reduction in the electrical conductivity. In such a way, ZT values even higher than the ones reported for monocrystalline Si NWs can be achieved.

This paper discusses enhancements of solar energy conversion by photovoltaic (PV) cells using thermoelectric (TE) generators harvesting the heat released by the PV cell. To optimize the TE–PV coupling, PV efficiency losses are analyzed by decoupling source- and absorber-dependent losses. This shows that the implementation of a tandem PV–TE device leads to a substantial increase of available power densities depending on the PV material. We further show that a major increase of the conversion efficiency can be achieved by adding an intermediate layer between the PV and the TE stage capable of absorbing the under-the-gap fraction of the solar spectrum. This increase of efficiency is discussed and commented upon also in view of the constraints PV–TE coupling imposes to the TE generator layout and to its material characteristics. The critical importance of effective heat dissipation will also be addressed. The conclusion is reached that not only could tandem PV–TE cells improve the conversion rate of existing solar cells but also that they could enable the use of lower cost PV materials, currently not considered because of their marginal PV efficiency.

Silicon is the reference material of microelectronics, is readily available, relatively unexpensive, and its use may take profit of a fantastic technology. This may explain why a substantial effort has focused on improving its thermoelectric efficiency, either by top-down nanostructuring or through suitable processing. In this paper we report an analysis of the electronic transport properties of heavily boron-doped nanocrystalline silicon films. High-temperature thermal treatments are confirmed to remarkably increase its thermoelectric power factor. Electrical conductivity and Hall effect measurements were carried out over the temperature range 20–300 K along with Seebeck coefficient measurements. We provide evidence of the occurrence of low-temperature hopping conduction between impurity subbands. Dopant ionization was studied as a function of temperature. Freeze-out temperature was found to correlate with the Seebeck coefficient in agreement with Pisarenko equation. This brings to the conclusion that, while untreated samples are weakly degenerate, the thermal processing reverts them into non-degenerate semiconductors, in spite of the high doping level.

Aim of this paper is to validate a modified Schottky barrier model accounting for the electrical properties of metal - self-assembled layer - semiconductor structures. To this end, the effect of the dynamic modulation of the dipole moment of the organic layer was studied. The system was a junction built on Si(1 0 0) surfaces modified by grafting an organic layer by wet chemistry reactions. As the metallic electrode, a thin, porous gold layer was deposited, enabling gas diffusion through it. In such a geometry, a polar gas was allowed to adsorb onto the Si surface, and the variation of the barrier height could be measured and correlated with the dipole moment of the gas molecule and its partial pressure. © 2006 Elsevier B.V. All rights reserved.

The thermoelectric properties of doped polycrystalline silicon nanowires have been investigated using doping techniques that impact grain growth in different ways during the doping process. In particular, As- and P-doped nanowires were fabricated using a process flow which enables the manufacturing of surface micromachined nanowires contacted by Al/Si pads in a four-terminal configuration for thermal conductivity measurement. Also, dedicated structures for the measurement of the Seebeck coefficient and electrical resistivity were prepared. In this way, the thermoelectric figure of merit of the nanowires could be evaluated. The As-doped nanowires were heavily doped by thermal doping from spin-on-dopant sources, whereas predeposition from POCl3 was utilized for the P-doped nanowires. The thermal conductivity measured on the nanowires appeared to depend on the doping type. The P-doped nanowires showed, for comparable cross-sections, higher thermal conductivity values than As-doped nanowires, most probably because of their finer grain texture, resulting from the inhibition effect that such doping elements have on grain growth during high-temperature annealing.

An efficient use of solar energy as a renewable power source has been the subject of an enduring research effort, still challenging scientists and technologists worldwide. Beyond standard photovoltaic (PV) and thermodynamic solar power plants, the increase of conversion efficiency achieved in thermoelectric generators (TEGs) has opened a new, lively research front aimed at the direct conversion of solar power into electricity. Although the efficiency of thermoelectric (TE) materials cannot rival that of PV materials yet, TEGs allow concentrating solar power without requiring bulky and expensive optical devices. Also, TEGs may be deployed in harsh environments (e.g. deserts) where maintenance of PV cells is often unaffordable. However, it is realistic to consider today TEGs as tools to improve, not to replace, PV generators. PV efficiency losses will be analyzed in details by decoupling source- and absorber-dependent losses, showing that the implementation of a tandem PV-TE device might lead to a substantial increase of available power densities. Specifically, it will be shown that the proper choice of the TEG geometry and layout remarkably depends on the PV material. In addition, since the efficiency of the tandem device depends on the energy gap and then on the working temperature of its PV stage, a major increase of the conversion efficiency can be achieved by adding an intermediate layer between the PV an the TE stage capable of absorbing the under-the-gap fraction of the solar spectrum. This increase of efficiency will be discussed and commented upon also in view of the constraints they impose to the TEG layout and to its material characteristics. The critical importance of effective heat dissipation will also be addressed. The conclusion will be reached that not only could tandem PV-TE cells improve the conversion rate of existing solar cells but also that they could enable the use of lower cost PV materials, currently not considered because of their marginal PV efficiency.

We have modeled the thermoelectric power factor enhancement by energy barriers in a one-dimensional composite semiconductor using the Boltzmann transport equation within the relaxation time approximation. The effective transport coefficients of the composite structure are calculated assuming two-phases connected in series: (i) the grain and (ii) the barrier.For the grains, bulk properties are assumed. For the barriers, the transport coefficients are calculated within Boltzmann transport equationand assuming thermionic emission over an energy barrier. The power factor enhancement is calculated as function of the relevant parameters of the material. It is found that power factor enhancement is possible in the presence of energy barriers. The role of the non-uniformity in the thermal conductivity is considered. Moreover, the occurrence of simultaneous increase of the conductivity and Seebeck with carrier density and its effect on the power factor enhancement is discussed.

Dimensional confinement in silicon nanowires (NWs) is well-known for enhancing phonon scattering, thus leading to a pronounced reduction of thermal conductivity κ with respect to bulk material. The effect of confinement on phonon scattering in nanolayers (NLs), however, has not been fully understood. In this work, thermal conductivity on polycrystalline silicon NLs with roughened surfaces and thicknesses ranging from 30 to 100 nm has been experimentally investigated. For measurement purposes, the nanostructures were fabricated with a dedicated surface nano-machining process, thus producing vertical silicon nanostructures suspended on Al/Si electrodes on a silicon substrate, using SiO2 as a sacrificial layer. By designing such structures in a four-terminal configuration, their κ could be determined by the current-voltage method. Boron doped silicon NLs were examined, at resistivity ranging between 2 and 10 m $$\Upomega$$ cm. We found an increase of phonon scattering from the confinement, since κ decreased steadily with the thickness from values typical of thick films (around 30 W m−1 K−1) down to

The ability to tune the thermal conductivity of semiconductor materials is of interest for thermoelectric applications, in particular, for doped silicon, which can be readily integrated in electronic microstructures and have a high thermoelectric power factor. Here, we examine the impact of nanovoids on the thermal conductivity of highly doped, high-power factor polysilicon thin films using time-domain thermoreflectance. Voids are formed through ion implantation and annealing, evolving from many small (∼4 nm mean diameter) voids after 500 °C anneal to fewer, larger (∼29 nm mean diameter) voids with a constant total volume fraction after staged thermal annealing to 1000 °C. The thermal conductivity is reduced to 65% of the non-implanted reference film conductivity after implantation and 500 °C anneal, increasing with anneal temperature until fully restored after 800 °C anneal. The void size distributions are determined experimentally using small-angle and wide-angle X-ray scattering. While we believe multiple physical mechanisms are at play, we are able to corroborate the positive correlation between measurements of thermal conductivity and void size with Monte Carlo calculations and a scattering probability based on Matthiessen's rule. The data suggest an opportunity for thermal conductivity suppression combined with the high power factor for increased material zT and efficiency of nanostructured polysilicon as a thermoelectric material.

This special issue of Nanoscale Research Letters is a collection of selected papers presented at the Nano and Giga Challenges in Electronics, Photonics and Renewable Energy (NGC2011) conference in Moscow and Zelenograd which addresses both theoretical and experimental achievements and provide a stimulating outlook for technological developments in these highly topical fields of research.

The possibility of enhancing the thermoelectric figure of merit ZT by damping the material thermal conductivity (e.g. by quantum confinement) rather than by increasing its power factor has generated a surge of interest toward the use of nanostructures in thermoelectric generators (TEGs). Actually, while ZT is an appropriate performance index when optimizing the rate of heat conversion in the presence of small thermal power inputs, it may turn out to be misleading when used as a general criterion. Under fixed heat flow conditions, the optimization of ZT may actually proceed only by maximizing the power factor, since materials with low κ may be unable to duly dissipate heat. However, also when operating between heat reservoirs at fixed temperature it is shown that the highest electric power a TEG can output may be obtained by increasing κ, not decreasing it. In addition, it will be presented an equation allowing to determine the TE efficiency over temperature ranges where transport parameters are no longer temperature-independent. © 2012 American Institute of Physics.

Energy filtering has been widely considered as a suitable tool to increase the thermoelectric performances of several classes of materials. In its essence, energy filtering provides a way to increase the Seebeck coefficient by introducing a strongly energy-dependent scattering mechanism. Under certain conditions, however, potential barriers may lead to carrier localization, that may also affect the thermoelectric properties of a material. A model is proposed, actually showing that randomly distributed potential barriers (as those found, e.g., in polycrystalline films) may lead to the simultaneous occurrence of energy filtering and carrier localization. Localization is shown to cause a decrease of the actual carrier density that, along with the quantum tunneling of carriers, may result in an unexpected increase of the power factor with the doping level. The model is corroborated toward experimental data gathered by several authors on degenerate polycrystalline silicon and lead telluride.

An experimental investigation about the thermoelectric properties of heavily doped p ad n-type nanocrystalline silicon nanowires (NWs) is described. The NWs are produced with low cost CMOS compatible processes, highly customizable in terms of cross-section and placement, which enables the fabrication of both stacked NWs in nearly vertical arrays within nanostructured templates built with SiO2/Si3N4 thin films and individual, freestanding NWs suited for thermal conductivity measurements. The cross-section dimensions of the investigated NWs range between 30 and 120 nm in size and up to about 2 cm in length. The structure of the NWs, as shown by SEM/TEM observations, is nanocrystalline with average size of the nanocrystals in one dimension that is comparable with the nanowire diameter. On the NWs, Seebeck coefficient, electrical resistivity and thermal conductivity have been measured, yielding thermoelectric figure of merit (ZT) values of 0.2 at 300 K for the best case.

Heavily boron-doped polycrystalline silicon has been reported to be characterized by somewhat unexpectedly high power factor. High Seebeck coefficients are however unexpected in materials with high carrier densities. A semiquantitative model was proposed, showing that the potential barrier structure at grain boundaries, along with the nanometric grain size, leads to an unusual mechanism of carrier filtering, named adiabatic energy filtering. Actually, the presence of potential barriers associated with segregated boron disables charge transport by holes in the band deep tail. This leads to a decrease of the actual carrier density, as in the case of standard energy filtering. However, the nanometric grain size along with the inefficiency of the hole-hole relaxation mechanism in degenerate semiconductors actually prevents carriers from relaxing, causing an increase of the average (macroscopic) drift mobility. Thus, in spite of the decrease of drifting hole density the electrical conductivity is found to increase. In this communication a refinement of the model is presented, that will be discussed and corroborated with an extended body of experimental data gathered by several authors on degenerate polycrystalline silicon films. © 2012 American Institute of Physics.

The control of the chemical state of the inner surfaces of nanocavities (NCs) produced by the annealing of helium-implanted silicon has influence on lifetime control, gettering and wafer bonding. In this work it is demonstrated that the etching in HFaq of (1 0 0) silicon containing a buried array of NCs produces a giant injection of hydrogen with the consequent passivation of the inner surfaces, mainly via the formation of silicon monohydride at (1 1 1) faces and monohydride dimers at 2 × 1 reconstructed (1 0 0) faces. These terminations are very stable and survive heat treatments at 700 °C. © 2009 IOP Publishing Ltd.

Nanotechnologies are one of the two most prominent actors of the scientific revolution marking the beginning of the new Millennium. As for biotechnology, nanotechnologies are the outcome of an interdisciplinary, new approach to old technological issues ranging from device manufacturing to energy conversion, from sensing to signal amplification and transmission. The discovery of unexpected physical and chemical behavior of matter at the nanometer scale has paved the way to a number of exploitations (some current, most real but prospective). In this paper I will briefly review the nanotechnologies, showing most promise for Medicine and Veterinary Medicine. In this specific area, I will discuss current techniques and soon-to-come applications in nano-pharmaceuticals (i.e. pharmaceuticals based on the specific chemistry of nanoparticles), in vivo targeted nanodispensers, and nanoactuators. Some closing remarks will be made on how this will affect animal health control and healing in the near future. © Springer 2007.

Boron diffusivity in single‐crystal diamond has been investigated. To this aim, a novel method using impedance spectroscopy for the study of the atomic diffusivity in wide‐gap semiconductor has been developed, along with a model for the analysis of the dielectric response function. The advantages of this procedure are discussed. Boron diffusivity in diamond has been determined to be 6.9×10−20 cm2 s−1 at 800 °C. A discussion of the results and a comparison with previous estimates are presented.

In this paper we report results concerning the use of Reflectance Infrared Spectroscopy for the study of film structure and morphology. Analyses were performed on tin dioxide and silicon dioxide thin films. For tin dioxide samples, film thickness and surface roughness could be determined. Also, evidence was obtained of preferential crystallographic orientation, that was confirmed by Transmission Electron Microscopy. On silicon dioxide, usability was proved of infrared reflectance spectra for quantitative analyses of water content in the films.

The durability of a device is determined by the stability of its interfaces. The aim of this paper is to compare and to discuss problems connected with interphase stability, as they reflect on chemical-sensor design and operation. Case studies will be considered, concerning issues such as the degradation of the interface between the electrolyte and the auxiliary layer and interface-related degradation in semiconductor sensors. In the former the active mechanism of response degradation is the formation of an interface at the electrolyte-auxiliary layer interface, while in the latter the slow migration of defects throughout the grain dominates. All discussion will be carried out with reference to the relationship between preparation procedures and device structure and chemistry.

Electron spin resonance and ultraviolet and visible absorption techniques have been used to study the optical and structural properties of RuIII and TiIII in TiO–2 and RuO2-based phosphate glasses as a way of investigating the role of transition-metal oxides on the electronic properties of these glasses. From the spectroscopic and thermodynamic analysis of the results it could be inferred that strong metal–metal interactions predominate in TiO2-containing glasses, while metal–matrix interactions play the major role in RuO2-containing glasses, demonstrating that the distribution of the transition-metal ions inside the matrix is essentially determined by the structure of the matrix.