AVS2011 Session EN-ThP: Energy Frontiers Poster Session

Thursday, November 3, 2011 6:00 PM in East Exhibit Hall

Thursday Evening

Time Period ThP Sessions | Topic EN Sessions | Time Periods | Topics | AVS2011 Schedule

EN-ThP-1 Development of Analysis System for Evaluating Carrier Lifetime in Organic Thin Film Solar Cell
Kyohei Naito (KAST, Chuo Univ., Japan); Munetoshi Sakai, Hiroko Takei (KAST, Japan); Kazuya Nakata (KAST, Tokyo Univ. Sci., Japan); Kenji Katayama (Chuo University, Japan); Katsuhiko Takagi (KAST, Japan); Akira Fujishima (KAST, Tokyo Univ. Sci., Japan)
Recently, photovoltaic cell is expected as new green technology replacing fossil fuel. Because of a next-generation photovoltaic cell with flexibility, portability and low cost, organic thin film solar cell (OTFSC) is currently the subject of great interest and intensive study. OTFSC is composed of organic electronic materials, which have differences in electron affinity and ionization energy, between two metallic conductive electrodes. The layer of the material with higher electron affinity and ionization potential is electron acceptor, and the other layer is electron donor. The hole-electron pairs (exciton) generated in either material, when OTFSC was photoinduced. When most of excitons reach the interface of the electron acceptor and electron donor, excitons break into carriers of electrons and holes efficiently. Electrons and holes move in the acceptor and donor, respectively. The carriers are collected by the electrode in contact with each layer. In the latest report, OTFSC has exceeded 8 percent of conversion efficiency. However, it was difficult to increase the area of OTFSC with high conversion efficiency. For instance, the conversion efficiency depended on the layer defects, which was caused by contamination of dust and H2O, oxidation and inhomogeneous coating. The defects influenced the carrier lifetime in OTFSC. Hence, the inspection technique, which was evaluated in two dimensions XY, was required to measure the carrier lifetime. The present inspection technique (Laser beam induced current method) had to contact electrodes with electric wires and pass an electric current through OTFSC. Because the carrier lifetime was measured by the decay of electric current, the value was influenced by every interface of circuitry in OTFSC. Therefore, it was necessary to detect the pure carrier lifetime in the organic semi conductivity layer. In this study, to investigate the pure carrier lifetime in the OTFSC, we developed the analysis system employing micro wave photoconductivity decay (μPCD). The carrier life time was discussed from the viewpoints of electrochemistry and quantum mechanics.
EN-ThP-2 Reactivation of Thermionic Electron Emission from Nitrogen Doped Diamond Films by Atomic Hydrogen Exposure
Marko Zumer, Vincenc Nemanic, Bojan Zajec (Jozef Stefan Institute, Slovenia); Franz Koeck, Robert Nemanich (Arizona State University)

Thermionic electron emission from nitrogen doped hydrogen terminated diamond film has been evaluated 18 months after it had been deposited on a 25 mm diameter molybdenum substrate by microwave plasma assisted chemical vapour deposition. A hydrogen enriched surface layer, enabling a negative electron affinity, was formed during the film deposition procedure. The initial thermionic emission current density of the aged film obtained at 500 °C and 0.2 V/micrometer electric field was stable but relatively low compared to the value measured on a freshly deposited film. The value at a base pressure of 2x10-7 mbar was ~ 1.4x10-9A/cm2. Such a low current density is presumed to be a consequence of oxidation, surface adsorption of contaminats and hydrogen depletion from the surface layer, all processes which proceed during ambient atmosphere exposure since the manufacturing date. Reactivation of the surface was achieved by introducing atomic hydrogen, generated by the hot filament cathode of the ionization gauge. A stable current density of ~ 2x10-6 A/cm2 (an increase factor of ~1400) was achieved after exposure to hydrogen at the base pressure of 2.2x10-4 mbar for 2 hours again at 500 °C and 0.2 V/micrometer. The atomic hydrogen exposure rate was estimated by subsequent measurement of the change in optical transmittance of the tungsten phosphate glass plates. The increase in emission with hydrogen was ascribed to two effects: 1) reactivation of the surface, and 2) molecular assisted emission.

Research at ASU is supported through the Office of Naval Research and at JSI through the Slovenian Research Agency (grant BI-US/09-12/021).

EN-ThP-3 Self-powered Environmental Sensor System Driven by Nanogenerators
Minbaek Lee, Joonho Bae (Georgia Institute of Technology); Joohyung Lee (Seoul National University, Republic of Korea); Churl-Seung Lee (Korea Electronics Technology Institute, Republic of Korea); Seunghun Hong (Seoul National University, Republic of Korea); ZhongLin Wang (Georgia Institute of Technology)
A self-powered sensor for toxic materials can be the most desirable and promising prototype of the future monitoring systems for environmental protection/detection. Wiring power-source to sensors that are placed in every corner of our surroundings not only causes a vast amount of labours, resources and budget, but also potential contamination to be produced by the batteries. Although solar energy is most attractive, it depends on the weather, season and has day and night difference. However, regardless of day and night, mechanical energy is one of the most abundant/sustainable sources practically to be utilized through piezoelectric materials. ZnO nanowires (NWs) not only have piezoelectricity, but also are environmental friendly and biological compatible, which make it a strong candidate for energy-harvesting for environmental sensors. Here, we have demonstrated a fully stand-alone, self-powered environmental sensor driven by nanogenerators with harvesting vibration energy. Such a system is made of ZnO nanowire-based nanogenerator, a rectification circuit, a capacitor for charge storage, a signal transmission LED light and a carbon nanotube-based Hg2+ ion sensor. The circuit lights up the LED indicator when it detects mercury ions in water solution. It is the first demonstration of nanomaterial-based, self-powered sensor system for detecting a toxic polluter.
EN-ThP-4 Effect of Inserting a Thin Buffer Layer on Obtainable Efficiency in n-ZnO/p-Cu2O Heterojunction Solar Cells
Tadatsugu Minami, Toshihiro Miyata, Yuki Nishi, Jun-ichi Nomoto (Kanazawa Institute of Technology, Japan)

The effect of inserting a thin-film buffer layer on the obtainable efficiency in n-ZnO/p-Cu2O heterojunction solar cells was investigated with a transparent conducting Al-doped ZnO (AZO) thin film/Cu2O sheet structure. To improve conversion efficiency, various heterojunction solar cells were fabricated by forming an AZO/thin-film buffer layer/Cu2O structure on the front surface of thermally oxidized Cu2O sheets that function as the active layer as well as the substrate. It was found that achieving higher efficiency Cu2O-based heterojunction solar cells fabricated by depositing various thin films on Cu O sheets requires that the surface of the Cu2O sheets always be treated using a low-damage deposition technology at a low deposition temperature .

The Cu2O sheets, with electrical properties such as resistivity on the order of 103 Ωcm, hole concentration on the order of 1013 cm-3 and Hall mobility above 100 cm2/Vs, were prepared by a thermal oxidization of copper sheets under appropriate conditions. The AZO thin film and the thin-film buffer layer were prepared by a pulsed laser deposition (PLD) using an ArF excimer laser. As an example of AZO/buffer layer/Cu2O heterojunction solar cells, AZO/ non-doped ZnO (ZO)/Cu2O solar cells were fabricated by inserting a ZO thin film as the buffer layer. It was found that the obtainable conversion efficiency in AZO/ZO/Cu2O heterojunction solar cells increased markedly as the deposition temperature of the AZO and ZO thin films was decreased from approximately 300oC to room temperature (RT) , i.e., non-intentionally heated Cu2O sheets. In addition, when the ZO thin films were prepared on non-intentionally heated Cu2O sheets by PLD, the efficiency (η) increased considerably as the introduced O2 gas pressure was increased; η, approximately 3 % with a ZO thin-film layer deposition at an O gas pressure of 0.1 Pa, gradually increased as the O2 gas pressure was increased up to approximately 1.2 Pa, and then decreased markedly at a pressure of approximately 1.5 Pa. The optimal thickness of the ZO thin-film layer was in the range from 30 to 50 nm. The obtained increase of η as the ZO film thickness was increased up to approximately 50 nm may be attributable to an improvement of film quality; in contrast, the decrease of η as the ZO film thickness was increased above approximately 50 nm may be attributable to the short lifetime of minority carriers in the n-ZO thin film. An AZO/ZO/Cu2O heterojunction solar cell fabricated under optimal preparation conditions exhibited an efficiency of 3.83% under simulated AM1.5G solar.
EN-ThP-5 Surface Texturing of Silicon for Solar Cells for CMOS Technology
Audrey R. Silva, Juliana Miyoshi, Fabio Cavarsan, Lucas P.B. Lima, José A. Diniz (State University of Campinas, Brazil)

The solar cell efficiency is hardly connected with device fabrication processes, such as texturing silicon surface, which increases the surface absorption area of incident radiation on the cell and, consequently, reduces the substrate reflectance. Nowadays, solar cells based on silicon substrate are fabricated with texturing surfaces to increase the device efficiency. These surfaces are obtained by anisotropic wet etching in KOH and NaOH alkaline solutions [1]. The disadvantage of these solutions are K+ and Na+ ions from KOH and NaOH, which are mobile charges in Metal-Oxide-Silicon structures. Thus, these solutions are not compatible for CMOS technology, which is used for integration circuits and devices on silicon surface. As an advantage, using these alkaline solutions, the <111> planes of silicon substrate with (100) crystallographic orientation are exposed, resulting in groups of pyramid on silicon surface. The pyramids induce many reflections and scatterings of the incident radiation, which increase the light absorption on the surface. This effect is defined as light trapping [1]. In this work, the silicon substrate texturing is carried out by an anisotropic wet etching, with an alkaline solution based on NH4OH,because this solution can form pyramids on the surface, does not release alkaline products/reagents on the silicon surface and is fully compatible with the CMOS technology. With this solution (concentration of 9%wt of NH4OH and four magnetic stirring velocities) the <111> planes of silicon substrate with (100) crystallographic orientation are exposed and theses planes can form some pyramids on surface. Scanning Electron Microscopy analysis presents that these pyramids are observed all long on the surface, indicating that the wet etching was uniform on the substrate. Furthermore, the pyramid height values are between 3.5 and 7.2 µm, and the silicon etching wet rate was about of 0.7 µm/minute. The reflectance measurements show that the surfaces with and without texturing present reflectance values of about 16% and 38%, respectively. The reflectance values of about 16% with texturing are similar to the results from references [1], which have used KOH solution. This result indicated that our texturing process based on NH4OH, which is fully compatible with the CMOS technology, can be used to fabricate Si-based solar cells [2].

REFERENCES

[1]L.A. Dobrzański, A.Drygała, Surface texturing of multicrystalline silicon solar cells, JAMME,Volume 31 ISSUE1,November 2008.

[2J J.Lu, W.Liu, C.H.M. van der Werf,A.Y.Kovalgin,Y. Sun, R. E. I. Schropp and J.Schmitz, Above-CMOS a-Si and CIGS Solar Cells for Powering Autonomous Microsystems, IEDM, December 2010

EN-ThP-7 Carrier Life Time of Several Organic Photovaltanic Cells by using Micro Wave Photoconductive Decay
Munetoshi Sakai (Kanagawa Academy of Science and Technology (KAST), Japan); Kyohei Naito (KAST, Chuo Univ., Japan); Hiroko Takei (KAST, Japan); Kazuya Nakata (KAST, Tokyo Univ. Sci., Japan); Kenji Katayama (Chuo University, Japan); Katsuhiko Takagi (KAST, Japan); Akira Fujishima (KAST, Tokyo Univ. Sci., Japan)
Recently, the importance of developing the future energy is recognized in various industries. In one of the green innovations, there are great expectations to develop organic photovoltaic cells; Dye sensitized solar cell (DSSC) and Organic thin film solar cell (OTFSC). Organic photovoltaic cells with inexpensive and low resource constraint are currently the subject of great interest and intensive study. DSSC is composed of photo-sensitized anode using molecular dye placed on a porous layer of titanium dioxide nanoparticles, and an electrolyte solution. The photo electrochemical system was known as the Grätzel cell. Electrons at the dye excited because of sunlight move into the titanium dioxide, and are collected by the electrode. On the other hands, OTFSC is composed of organic electronic materials, which have differences in electron affinity and ionization energy, between two metallic conductive electrodes. The layer of the material with higher electron affinity and ionization potential is electron acceptor, and the other layer is electron donor. The hole-electron pairs (excitons) generated in either material, when OTFSC was photoinduced. When most of excitons reach the interface of the electron acceptor and electron donor, excitons break into carriers of holes and electrons efficiently. Electrons and holes move in the acceptor and donor, respectively. The carriers are collected by the electrode in contact with each layer. In either solar cell, the carrier life time would influence the performance of the solar cell, because the carriers (electrons) move through the semiconductor and reach the electrode. Therefore, we investigated the carrier life time of several organic photovoltaic cells by using micro wave photoconductive decay (μPCD). The difference of the carrier life time was discussed from the viewpoints of electrochemistry and quantum mechanics.
EN-ThP-8 Making Molecular Multilayers using "Click" Chemistry: Growth, Characterization, and Application in p-Type Dye Sensitized Solar Cells
Peter Palomaki, Peter Dinolfo (Rensselaer Polytechnic Institute)
Bottom-up approaches to creating molecular multilayer assemblies using layer-by-layer (LbL) techniques give one the ability to tailor the surface properties of an interface through molecular control. LbL assembly methods can provide molecular level control of structure in one dimension from simple solution deposition processes. We have developed a versatile LbL fabrication method using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) or “click” chemistry in the construction of multilayer assemblies on oxide surfaces.1,2 These reactions occur in minutes at room temperature allowing for the facile creation of complex, covalently attached multilayer assemblies. Multilayers containing synthetic porphyrins, perylenes, and mixtures of the two have been constructed in order to highlight the versatility of this method. The fabrication of this new type of molecular multilayer thin film will be discussed along with characterization of the photophysical, electrochemical, and structural properties. Initial results pertaining to the use of these films as light harvesting systems in p-type dye sensitized solar cells will be presented.
 
1. Palomaki, P.K.B. and Dinolfo, P.H. Langmuir 2010, 26 (12), 9677-9685.
2. Palomaki, P.K.B.; Krawicz, A.; Dinolfo, P.H. Langmuir 2011, 27 (8), 4613-4622.
 
EN-ThP-9 Powder-Sputtered Cu(In,Ga)Se2 Thin Films: Nonstoichiometric Influences on Optical and Electrical Characteristics
Nam-Hoon Kim, JiEun Jeon, Woo-Sun Lee (Chosun University, Republic of Korea)
The thin film solar cell efficiency of 19.2% (0.41 cm2) was accomplished by using Cu(In,Ga)Se2 (NREL, 2003), which has been fabricated by using the three stage co-evaporation process. There are two general methods for Cu(In,Ga)Se2 thin film fabrication: selenization after sputtering and thermal co-evaporation. The novel method of powder-sputtering was employed for the preparation of Cu(In,Ga)Se2 to deposit the thin film over the large area with a good uniformity without selenization of toxic H2Se because the co-evaporation method requires very strict controls during the deposition process of Cu(In,Ga)Se2 thin film. This method has the advantages of the production of target, change of stoichiometry, and easy doping of impurities. The composition of the starting powder target was changed by x = 0.1, 0.3, 0.5, 0.7, and 0.9 in the deposition process of Cu(Inx,Ga1-x)Se2 thin film while Cu/(In+Ga) ratio was ‘1’. The compositions of the starting powder target and the deposited samples with 1 μm-thickness were comparatively analyzed by electron probe microanalysis (EPMA). The crystal structure, surface morphology, optical properties, and electrical characteristics of Cu(Inx,Ga1-x)Se2 thin films were analyzed by using X-ray diffraction (XRD), atomic force microscope (AFM), UV-Visible spectrophotometer, and a Hall effect measurement system to investigate the influence of nonstoichiometry on the characteristics. The optimized composition was selected through the comprehensive analysis of the characteristics.
EN-ThP-10 Indium-Doped CdS Thin Film by He-Ne Laser Exposure for CIGS Solar Cells
KukDo Myung, Nam-Hoon Kim, Woo-Sun Lee (Chosun University, Republic of Korea)
Cadmium sulfide (CdS) is a direct and wide band gap (2.42 eV at room temperature) II-VI semiconductor, which is a very desirable window layer for many photovoltaic solar cells including CIGS solar cell. CdS thin film has been paid to the considerable attention due to its band gap, high absorption coefficient, reasonable conversion efficiency, stability and low cost. It is generally known that the undoped CdS thin film has the high electrical resistivity. Some impurities were employed for doping CdS to produce less resistive films. Expecially, indium (In) showed the improvement of resistivity and optical transmittance when it was doped into the sputtering-deposited CdS thin film. In this study, the structural, optical, electrical, and morphological properties of indium-doped CdS thin films prepared by the effective method with He-Ne laser at room temperature. Indium was deposited on the 200 nm-thickness of CdS thin film by the sputtering method with 10 nm-thickness. He-Ne laser (632.8 nm) was exposured with a small energy by a change of exposure time. The remained indium layer was removed with the chemical solutions. The doping effects of indium on the CdS thin films were investigated by analyzing the structural, optical, electrical, and morphological properties of CdS thin films by using X-ray diffraction (XRD), Auger electron spectroscopy (AES), UV-Visible spectrophotometer, Hall effect measurement system, and atomic force microscope (AFM). AES depth profile was employed to examine the indium-doped CdS thin film with a change of He-Ne laser exposure time. The doping uniformity and amount of indium into the depth of CdS thin film was compared to the characteristics of CdS thin film. The optimization of indium-doping process was achieved to enhance the electrical and optical characteristics including resistivity and optical transmittance.
EN-ThP-11 Three-Terminal Tandem Devices for PV, TPV and CPV Applications
Mahieddine Emziane (Masdar Institute, United Arab Emirates)
One of the key approaches for achieving very-high efficiency for photovoltaic (PV) devices is to use, instead of single junctions, double or multi-junction devices due to an extended solar spectral coverage leading to an enhanced overall power output from the multi-junction PV devices.
 
In this study, we investigated two-junction solar cells based on group IV materials, i.e. Si and Ge, for top and bottom sub-cell, respectively. Unlike the conventional and widely used monolithic series-connected two-terminal device configuration that was shown to deliver a slightly lower output, these double-junction cells were assembled with three terminals and operated independently [1, 2].
The main advantages of choosing these materials and device configuration are: (i) cheapest, largest and easiest group IV substrates; (ii) extended spectral coverage leading to more photons being converted; and (iii) no current matching or the associated tunnel junctions between the two sub-cells.
 
We have undertaken a comprehensive modeling analysis for the device optimization and performance prediction. n/n/p as well as p/p/n device structure configurations were investigated and optimized with regard to the thicknesses and doping levels of both top and bottom active junctions that lead to the highest device performance. Due to the split of the incident solar spectrum between the top and bottom sub-cells, the latter only receives the light to which the former is transparent (mainly in the near infrared) and therefore behaves differently from the single-junction cell counterpart.
 
Optimal current-voltage and power-voltage characteristics were generated for individual cells together with the corresponding quantum efficiency spectra. The applications of these devices in conventional PV, concentrator PV and thermal PV were assessed and the output PV parameters were predicted as a function of the simulated operating conditions.
 
References:
[1] M. Emziane, R. J. Nicholas, Journal of Applied Physics, 102 (2007) 074508.
[2] M. Emziane, Mater. Res. Soc. Symp. Proc., Vol 1165 (2009) M08-13.
EN-ThP-12 The Advantage of State of the Art DC Power Supplies Over the Pulsed DC Power Supplies for TCO Magnetron Sputtering
Piotr Rozanski, Pawel Ozimek, Marcin Zelechowski, Piotr Lach, Wojciech Glazek, Jacob Abraham (Huettinger Electronic Company, Poland)

Non-pulsing DC power supplies for highly arcing processes are gaining more and more interest slowly pushing out older pulsing DC power supplies as more efficient and more cost optimal. The importance of arc management in DC power supplies is taking on a new meaning as most advanced DC generators are more and more successful in sputtering highly arcing and difficult materials, providing high deposition rates at competitive investment.

It has been developed as the answer to the market’s demand to limit arc energy during an arc occurrence in sputtering. Industrial implementation has been already successfully performed with air-cooled DC power supplies that have been on the market for years. The possibility of using DC power supplies for sputtering highly-arcing materials is the result. It is the beginning of a new age in magnetron sputtering technology. Further improvement and optimization by using more efficient water cooling and faster transistors has resulted in a new generation of power supplies with state-of-the-art arc management parameters. A complementary feature of the newly-developed arc management circuitry is software that supports efficient arc handling: self-adjusting arc management settings and an internal oscilloscope.

EN-ThP-14 The Science of Precision Multifunctional Nanostructures for Electrical Energy Storage
Ashley Predith (University of Maryland, College Park)
Nanostructures for Electrical Energy Storage (NEES) is a five-year Energy Frontier Research Center investigating nanoscale behavior in lithium-ion battery materials. Funded by the US Department of Energy, the Center studies the properties of composite nanostructures containing an oxide or silicon as a charge storage material and low dimensional forms of carbon as an electronic conductor or mechanical support. NEES is particularly interested in nanostructures that are precise and regularly ordered. These structures provide a unique test bed for uncovering to the science of electrochemistry at the nanoscale.
 
The two Science Thrusts of the Center investigate nanotubes, nanowires, and layers of MnO2, silicon, and carbon electrode materials as well as nanoporous membranes in an electrolyte. They examine the mechanical behavior, electrochemical properties, and interfacial phenomena that arise in heterogeneous material combinations. The two Enabling Thrusts of the Center develop model systems and characterization instruments for the nanoscale. Ultra high vacuum scanning probe microscopy and first principles modeling provide for the study of pristine systems, and in situ transmission electron microscopy and microelectromechanical systems are allowing members of NEES to observe electrochemical processes as they unfold.
 
NEES is a collaboration of 19 senior investigators, ~35 postdoctoral associates and graduate research assistants, and many staff members at six institutions. The Center integrates their perspectives to pursue a comprehensive examination of electrical energy storage using precision, multifunctional nanostructures. Members include Philip Collins (University of California-Irvine), Michael Fuhrer (University of Maryland), Sang Bok Lee (UMD), Charles Martin (University of Florida), Reginald Penner (UCI), Zuzanna Siwy (UCI), John Cumings (UMD), S. Thomas Picraux (Los Alamos National Laboratory & Center for Integrated Nanotechnologies), Mark Reed (Yale University), Chunsheng Wang (UMD), YuHuang Wang (UMD), Kevin Leung (Sandia National Laboratories), Janice Reutt-Robey (UMD), Kevin Zavadil (SNL), Reza Ghodssi (UMD), Jianyu Huang (SNL, CINT), Robert Hwang (SNL), Gary W. Rubloff (UMD), John Sullivan (SNL, CINT), and Ashley Predith (UMD).
 
 
EN-ThP-15 Photosystem I-Based Solar Cells
Darlene Gunther, David Cliffel, Kane Jennings (Vanderbilt University)
The long-term success of photosynthetic organisms has resulted in their global superabundance, which is sustained by their widespread, continual mass-production of the integral proteins that photocatalyze the chemical processes of natural photosynthesis. Here, a fast, general method to assemble wet and dry solar cells composed of one such photocatalytic protein complex, Photosystem I (PSI), onto a variety of electrode substrates, including gold, nanoporous gold, and graphene is reported. The resulting PSI films consist of a protein matrix that is permeable to electrochemical mediators in a wet cell and conducting for electron transfer in a dry cell. These results demonstrate how the assembly of micron-thick coatings of PSI on non-biological substrates yields a biohybrid ensemble that manifests the photocatalytic activity of the film’s individual protein constituents, and represent signifi cant progress toward affordable, biologically-inspired renewable energy conversion platforms.
EN-ThP-18 Microbial Fuel Cells Development on the Base of Desulfuromonas Acetoxidans Bacteria
Oresta Vasyliv, Oleksandr Bilyy, Svitlana Hnatush (Ivan Franko National University of Lviv, Ukraine)

Microbial fuel cells (MFCs) are able to capture the electrons produced during different biochemical microbial processes to generate electricity. They offer the promise of a new sustainable source of energy, produced from biodegradable and reduced compounds. Increased shortcoming of unrenewable fossil fuels causes the need for it’s less dendence. The enhance of use of renewable fuels requires the development of alternative sources of energy such as waste biomass for environmental benefits. MFCs investigations have attracted substantial interest in development of different devices for generating electricity and removing wastes. The development of processes that can apply bacteria of normal environmental microflora to produce electricity represents a highly effective method for bioenergy production as bacteria are self-replicating, and thus the catalysts for organic matter oxidation are self-sustaining.

Nowadays MFCs is considered to be applied as highly effective and self-sustaining model of wastewater treatment which contains energy in the form of biodegradable organic matter. At the same time wastewater contains high concentrations of xenobiotics, such as different heavy metal ions that have an overwhelming harmful effect towards all living organisms. These elements even in small concentration in the environment cause the intensive inhibiton of physiological and biochemical properties of most bacteria. Despite that, some genuses of bacteria possess high toxic heavy metals resistance because of highly-efficient defensive systems functioning. There are Feroplasma, Streptomyces, Thiobacillus etc.

Desulfuromonas acetoxidans are uncoloured gram-negative sulfur-reducing bacteria. These bacteria are considered to be used as the substrate for microbial-anode fuel cells with high electron recovery, which is more than 80%, to electric current by the interaction between proceses of acetate oxidation and S0 or Fe3+ - reduction. Sulfurbacteria have a great effect on the biogeochemistry of aquatic environments because of their ability to reduce and precipitate toxic heavy metals compounds. It’s a result of their particular binding with the final product of bacterial dissimilative sulfur-reduction ­– H2S, and formation of the unsoluble metal sulfides. It also serves as self-defensive mechanism of these bacteria against toxic influence of toxic heavy metal ions.

The influence of diferent of Ni2+ and Cu2+ concentrations on size distribution and relative content of D. acetoxidans bacteria during their life cycle on the base of cells’ light scattering properties changes by the new method of measurement has been investigated. The ability of this bacteria to produce electric current in microbial-anode fuel cells under the specific cultivation condition has been shown. Particular heavy metals resistance of D. acetoxidans bacteria has been observed. Distibution curves of the cells’ size distribution changes were in the range from 0.3 to 1.9 µm under the influence of investigated metal ions. The maximum of cells’ size distribution of investigated bacteria was changed from 0.55 to 0.62 µm under the influence of 0.01-10 mM of NiCl2×6H20 and CuCl2×2H20 during five days of bacterial growth.
EN-ThP-19 Investigating CdTe/CdS/TCO Inter-diffusion by AES and XPS
L. Le Tarte, A. Barbuto, J. Cournoyer, K. Dovidenko, H. Piao (General Electric, Global Research Center)
CdTe has recently received a lot of attention as the material of choice for thin film solar cells as it converts light to electricity more cost effectively than traditional semiconductors and is compatible with manufacturing scale-up. An in-depth understanding of film composition, morphology and interface integrity is critical for CdTe thin film process development. Clear depth profiles of the buried layers by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) are difficult to obtain due to the rough, and thick (~3µm ± 0.5µm), upper CdTe layer. Sputtering through this layer leads to broadened depth profile interfaces which reduces information about inter-diffusion. We have developed a polishing method to thin and smooth this layer prior to analysis. In this poster we will present how this method has improved the Auger depth resolution and therefore the understanding of inter-diffusion between the CdTe, CdS and TCO layers. A novel FIB preparation method for Auger will also be discussed. XPS imaging analyses on AES sputter crater sidewalls provides additional chemical information about the buried layers and interfaces.
Time Period ThP Sessions | Topic EN Sessions | Time Periods | Topics | AVS2011 Schedule