Electrical resistivity and Hall effect measurements of pellets compacted from fullerene-like WS 2 nanoparticles (IF-WS 2 ) and bulk 2H-WS 2 powder were carried out using the van der Pauw method over a wide temperature range. In addition IF-WS 2 pellets were annealed at elevated temperatures under vacuum in a specially designed system. Arrhenius plots for the conductivities of the WS 2 samples (2H, IF and IF+annealing) exhibit marked uprise of ∂ ln (s T -1 )/∂T -1 with temperature. The resistivity of the nonannealed IF-WS 2 pellets is higher by 2 -8 orders of magnitude than that of 2H-WS 2 pellets, whereas the resistivity of the annealed IF pellets is higher than that of the non-annealed ones. Hall Effect measurements at 300 K show p-type conductivity and similar carrier concentration for both types of materials. The carrier mobility of 2H-WS 2 platelets is found to be in the range of the reported values. However, IF-WS 2 pellets have shown an unusually low mobility for a semiconducting material. The experimental data was found to be in a good agreement with a model used for analyzing the conductivity of polycrystalline semiconductors, which takes into consideration fluctuations of the barrier heights among the different nanoparticles as well as within a single nanoparticle boundary.

Organic conducting polymers can be synthesized inside the pores of a track‐etch membrane, and the resulting hollow tubules are shown to have enhanced electrical properties compared to their corresponding bulk materials. The polymerization of monomers (e.g., pyrrole, thiophenes) inside the confined space of these pores, combined with electrostatic interaction, ensures the alignment of the organic polymers on the interior, leading to higher conductivity. The application of these conducting tubes in the development of amperometric glucose sensors is discussed. Due to the special properties of conducting polymers inside a track‐etch membrane, biosensors with a unique electron‐transfer mechanism have been developed.

Photosystem I (PSI) and photosystem II (PSII) are the primary solar-energy-converting enzymes of oxygenic photosynthetic organisms.[1] PSI is a robust, potent, and highly efficient photosensitizer capable of providing electrons at a high reduction potential (À0.55 V vs. normal hydrogen electrode, NHE) from its reducing end.[2] These properties have prompted many attempts to integrate PSI into biohybrid systems for solar energy conversion and storage.[3] In a biological setting, water photooxidation by PSII provides a source of electrons for the reductive processes driven by PSI, but in contrast to PSI, integration of PSII into nonbiological systems is very difficult.[4] Both photosystems were successfully "wired" to conductive electrode surfaces, but their integration into a photocatalytic bioelectrochemical device has not been reported to date.[5]Herein we demonstrate a simple scheme for mediated coupling of PSII and PSI in solution; this coupling enables electron flow from water photooxidized by PSII all the way to the reducing end of PSI. Furthermore, we show that the same scheme can be reconstituted either when both photosystems are coencapsulated in sol-gel glasses, or when one photosystem is encapsulated and the other is in solution. The solgel trapping technique is a proven method for encapsulating a wide variety of biological materials, from intact whole cells to functional individual enzymes. [6,7] In addition, sol-gel systems are porous and optically transparent, [8] which makes them ideal scaffolds for photoinduced electron transfer systems such as the photosynthetic machinery.[9] The main difference between the sol-gel and solution samples is that the photosystem complexes are immobilized within the sol-gel cavities instead of diffusing freely in solution. This property suggests interesting possibilities of segregating PSI and PSII in distinct microenvironments while maintaining electron flow between the photosystems. PSII is not naturally directly coupled to PSI (Figure 1, top). Instead, electrons flow from PSII to a pool of membrane-soluble plastoquinones that diffuse between the acceptor and donor sides of PSII, and cytochrome b 6 f (b6f), respectively.[10] Only a fraction of the electrons extracted from water at the oxygen-evolving complex of PSII end up at the acceptor side of PSI. The rest are cycled between PSII and b6f whereby directed diffusion of quinones, the release of protons on the water oxidizing face, and their consumption on the reducing face of the membrane actively pumps protons across the membrane, and generates proton-motive force.[11]By using the amphipathic quinone analogue 2,6-dichlorophenolindophenol (DCPIP) as an electron carrier, we were able to bypass b6f and set up an alternative pathway of electron flow from PSII to PSI (Figure 1, bottom). Although it is well established that DCPIP can be reduced by PSII, and the reduced form DCPIPH 2 is an electron donor to PSI, [12] DCPIP-mediated electron flow from PSII to PSI was not reported to date, to the best of our knowledge. Th...

WS 2 inorganic fullerene-like (IF) nanoparticles were subjected to intercalation with potassium, sodium, and rubidium atoms in heated sealed ampules. The product of the intercalation process was not pure and was composed of both intercalated and nonintercalated phases. X-ray diffraction measurements under inert conditions of the intercalated powders showed that the interlayer expansion was correlated with the alkali metal radius. Small increase of the a-axis was observed as well and was explained on the grounds of the WS 2 band structure. The XPS analysis of the rubidium intercalated material showed a rise in the Fermi energy as a result of the intercalation, endowing the originally p-type nanoparticles an n-type character.

No abstract

Inorganic fullerene-like nanoparticles of WS2 (IF-WS2), are synthesized by a reaction of tungsten oxide with molecular hydrogen and hydrogen sulfide. The synthesized nanoparticles appear as large agglomerates (>40 microns), each one counting thousands of IF nanoparticles. 1H nuclear magnetic resonance study of these nanoparticles is reported. The measurements show that the prepared product contains water (and possibly some hydrogen) molecules that occupy the voids in the central part of the fullerene-like nanoparticles and the nanopores between the adhering IF-WS2 particles. Defects in the IF-WS2 structure, arising due to the strain release during the folding of the layers, may result in additional sites for the absorbed water. Vacuum annealing of the powder leads to substantial reduction in the amount of absorbed water molecules.

Photosystem I (PSI) and photosystem II (PSII) are the primary solar-energy-converting enzymes of oxygenic photosynthetic organisms. [1] PSI is a robust, potent, and highly efficient photosensitizer capable of providing electrons at a high reduction potential (À0.55 V vs. normal hydrogen electrode, NHE) from its reducing end. [2] These properties have prompted many attempts to integrate PSI into biohybrid systems for solar energy conversion and storage. [3] In a biological setting, water photooxidation by PSII provides a source of electrons for the reductive processes driven by PSI, but in contrast to PSI, integration of PSII into nonbiological systems is very difficult. [4] Both photosystems were successfully "wired" to conductive electrode surfaces, but their integration into a photocatalytic bioelectrochemical device has not been reported to date. [5] Herein we demonstrate a simple scheme for mediated coupling of PSII and PSI in solution; this coupling enables electron flow from water photooxidized by PSII all the way to the reducing end of PSI. Furthermore, we show that the same scheme can be reconstituted either when both photosystems are coencapsulated in sol-gel glasses, or when one photosystem is encapsulated and the other is in solution. The solgel trapping technique is a proven method for encapsulating a wide variety of biological materials, from intact whole cells to functional individual enzymes. [6,7] In addition, sol-gel systems are porous and optically transparent, [8] which makes them ideal scaffolds for photoinduced electron transfer systems such as the photosynthetic machinery. [9] The main difference between the sol-gel and solution samples is that the photosystem complexes are immobilized within the sol-gel cavities instead of diffusing freely in solution. This property suggests interesting possibilities of segregating PSI and PSII in distinct microenvironments while maintaining electron flow between the photosystems. PSII is not naturally directly coupled to PSI (Figure 1, top). Instead, electrons flow from PSII to a pool of membrane-soluble plastoquinones that diffuse between the acceptor and donor sides of PSII, and cytochrome b 6 f (b6f), respectively. [10] Only a fraction of the electrons extracted from water at the oxygen-evolving complex of PSII end up at the acceptor side of PSI. The rest are cycled between PSII and b6f whereby directed diffusion of quinones, the release of protons on the water oxidizing face, and their consumption on the reducing face of the membrane actively pumps protons across the membrane, and generates proton-motive force. [11] By using the amphipathic quinone analogue 2,6dichlorophenolindophenol (DCPIP) as an electron carrier, we were able to bypass b6f and set up an alternative pathway of electron flow from PSII to PSI (Figure 1, bottom). Although it is well established that DCPIP can be reduced by PSII, and the reduced form DCPIPH 2 is an electron donor to PSI, [12] DCPIP-mediated electron flow from PSII to PSI was not reported to date, to the best of our knowl...

Current-voltage characteristics measured using STM on fullerene-like WS2 nanoparticles show zero-bias current and contain segments in which the tunneling current flows opposite to the applied bias voltage. In addition, negative differential conductance peaks emerge in these reversed current segments, and the characteristics are hysteretic with respect to the change in the voltage sweep direction. Such unusual features resemble those appearing in cyclic voltammograms, but are uniquely observed here in tunneling spectra measured in vacuum, as well as in ambient and dry atmosphere conditions. This behavior is attributed to tunneling-driven electrochemical processes.