I. Samaras

Optical and electrical characterizations of SnSe, SnS2 and SnSe2 single crystals

Abstract This work reports a study of the optical and electrical properties of tin monoselenide SnSe and tin dichalcogenides SnX2 with X = S and Se . The semiconducting character of the single crystals is investigated by means of resistivity and Hall effect in the temperature range from 90 to 300 K. The energy gap data are obtained by absorption measurements. The far-infrared reflectance spectra of the tin chalcogenide compounds have been measured. The experimental data are fitted using a four-parameter dispersion model based on the factorized form of the dielectric function.

Study of leakage current in n-channel and p-channel polycrystalline silicon thin-film transistors by conduction and low frequency noise measurements

The off-state current in n- and p-channel polycrystalline silicon thin-film transistors (polysilicon TFTs) is investigated systematically by conduction measurements at various temperatures and low-frequency noise measurements at room temperature. It is demonstrated that the leakage current is controlled by the reverse biased drain junction. The main conduction mechanisms are due to thermal generation at low electric fields and Poole–Frenkel accompanied by thermionic filed emission at high electric fields. The leakage current is correlated with the traps present in the polysilicon bulk and at the gate oxide/polysilicon interface which are estimated from the on-state current activation energy data. Analysis of the leakage current noise spectral density confirms that deep levels with uniform energy distribution in the silicon band gap are the main factors in determining the leakage current. The density of deep levels determined from noise analysis is in agreement with the value obtained from conductance acti...

A Modified DPWS Protocol Stack for 6LoWPAN-Based Wireless Sensor Networks

In this paper, a modification of the protocol stack of the device profile for web services (DPWS) is proposed which can be applied in wireless sensor networks (WSNs) that comply with the IPv6 over low-power wireless personal area networks (6LoWPAN) architecture. The modification is based on a new format for the DPWS message exchanges without prohibiting the usage of the web services (WS) and the extensible markup language (XML) set of rules. The modified DPWS was implemented on the SunSPOT wireless sensor mote (WSM) and it was observed that it processes XML documents with a mean computation time less by 53% than the respective computation time of the DPWS while it consumes less EEPROM and RAM by 84% and 85%, respectively. Furthermore, its network performance was assessed by testing it over a real 6LoWPAN-based WSN with its maximum number of WSMs being 12. In order to validate these results and extend them to larger-scale 6LoWPAN-based WSNs, the network simulator 2 (NS-2) was used by enhancing it with a developed 6LoWPAN object. The NS-2 was also utilized for comparing the modified DPWS, the DPWS and a binary-based DPWS in terms of packet delivery ratio and maximum transmission delay. Simulation results have shown that the modified DPWS presents better performance than the DPWS and offers inferior results only when it is compared with the binary-based DPWS which, however, does not retain the WSs interoperability feature as it does not use XML documents.

Structural studies of MoS2 intercalated by lithium

Abstract Defects created by intercalation in MoS2 single crystals were studied by plane and cross-sectional electron microscopy. In the first stage of intercalation the effect is to create extensive dislocations. Further intercalation leads to a structural transformation of the type 2H → 1T , as is evident from the appearance of spots in the diffraction pattern belonging to the new phase. In addition, the transformation is accompanied by a 2a 0 × 2a 0 superstructure. This superstructure is unstable and disappears on heating, while the structural transformation is irreversible.

Integrating Wireless Sensor Networks into Enterprise Information Systems by Using Web Services

This paper proposes an advanced middleware solution to the problem of integrating a Wireless Sensor Network into the information system of an enterprise at a high abstraction level. This is achieved by using the proposed middleware which provides to the wireless sensors a Service Oriented Architecture connection to the Internet. The proposed middleware is based on the Device Profile for Web Services which is a Service Oriented Architecture technology at the device level. Since this technology is based on exchanging eXtensible Markup Language documents, a technique is utilized which compresses and reduces the data volume of such documents at a level that can be handled by the use of the resource constrained environment of the wireless sensors. By utilizing the proposed middleware which implements only the basic functions of the Device Profile for Web Services, we demonstrate how such a Wireless Sensor Network can be connected to the Internet achieving in this way its integration into an enterprise information system in which all its components conform to a Service Oriented Architecture standard.

Lithium insertion in layered materials as battery cathodes

Abstract Results are presented for discharge processes of lithium electrochemical cells containing layered chalcogenide materials. Systematic and precise studies of the voltage-composition relation were made of lithium insertion in InSe, In 2 Se 3 , MoS 2 , TiS 2 and NiPS 3 . The stability of the intercalated phases is discussed on the basis of electrochemical potential spectroscopy measurements, and the inverse derivative composition-voltage is analysed using the lattice gas model. Using galvanostatic experiments, the chemical diffusion coefficient D(x) and the Darken factor K 1 (x) of the solid solution electrodes are determined.

Vibrational modifications on lithium intercalation in MoS2

Abstract Raman scattering and IR absorption were studied in lithium-intercalated MoS 2 at room temperature. After intercalation, new Raman peaks were observed on the low frequency sides of the high-frequency original Raman peaks and around a rigid layer mode. This fact indicates the formation of superlattice structure along the c axis. An intercalation mode in which lithium atoms vibrate strongly against the host lattice was observed at about 205 cm −1 . Two new broad bands grow in the high frequency region as the concentration of lithium increases. The corresponding bands were observed by IR absorption.

Lithium insertion into indium sesquiselenide

Abstract The effects of lithium intercalation in In 2 Se 3 have been studied using different methods. Electrochemical properties of the non-stoichiometric Li x In 2 Se 3 phase are given in the range 0 ⩽ × ⩽ 1 for either quenched or annealed compounds. Electronic conductivity has been measured during the insertion process in n -butyl lithium and suggests weak charge transfer. The relation between the morphology of samples and insertion mechanism have been discussed.

Lithium insertion in indium selenide films: application to microbatteries

Indium selenide films are formed on silica slides and silicon wafers using a flash evaporation technique in which the material source stoichiometry is modified to obtain InpSeq films with various compositions. The structural and optical properties of indium selenide films are reported. These characterizations have shown that, using different growth conditions, either single phases, such as InSe, In4Se3 or In2Se3, are formed or a mixture of these compounds is present in the film structure. The products are examined by X-ray diffraction, and Raman and IR spectroscopies. The electrochemical properties of lithium-intercalated films are presented. It is observed that the morphology and stoichiometry play an important role in the lithium insertion process. The thermodynamics and kinetics of the insertion reaction are reported. Li/Li+ -borate glass/InSe microbatteries have been built, and their characteristics are reported and discussed using a Butler-Volmer relationship.

Synthesis and characterization of LiMn2O4 for use in Li-ion batteries

Lithiated spinel manganese dioxide was synthesised from electrochemical MnO 2 and Li2CO 3 with deficiency or excess lithium (Li x Mn 2 O 4 , 0.8 <x < 1.3) for use in Li/Li x Mn 2 O 4 and Li-ion cells. Micron-sized Li 1.05 Mn 2 O 4 prepared at 730°C showed high Li utilization, excellent cyclability and good rate capability with an initial discharge capacity of 123 mA h/g and 10% discharge capacity reduction after 20 cycles. Different types of commercial carbonaceous materials were also investigated with respect to their electrochemical performance vs. Li. Unoptimised Li-ion cells, using Li 1.05 Mn 2 O 4 prepared at 730°C as the cathode material, EC-DMC-LiPF 6 electrolyte and carbon fibres, showed promising performance characteristics.