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The fine control over the surface of lead sulfide colloidal quantum dots (PbS CQDs) is increasingly important to achieve enhanced device performance. In particular, the in-gap trap state resulting from the surface hydroxylation of PbS CQDs is considered detrimental to photovoltaic performance. In this study, we developed a method to avoid hydroxyl formation on the PbS CQD surface by using an in situ solution-phase ligand-exchange process. The complete elimination of protic solvents and other hydroxyl sources from the CQD synthesis to device fabrication produced PbS CQD films without undesired hydroxyl ligands with a reduced trap density. In this process, the purification process, which accounts for nearly 60% of the synthesis cost, is completely excluded. The presence of trap states verified through optical analysis and the hydroxylation observed via surface analysis clearly agreed with the device characterization obtained by transient photovoltage and photocurrent. Consequently, the open-circuit voltage of the PbS CQD solar cells is improved by up to 10%, yielding a certified power-conversion efficiency of 11.6%.

Solution-processed semiconductors are promising materials to realize optoelectronic devices that combine high performance with inexpensive manufacturing. In particular, the exploitation of colloidal quantum dots (CQDs) capable of harvesting infrared photons, in conjunction with visible-absorbing organic chromophores, has been demonstrated as an interesting route. Unfortunately, CQD/organic hybrid photovoltaics have been limited to power conversion efficiencies (PCEs) below 10% due to chemical mismatch and difficulties in facilitating charge collection. Here we devise a hybrid architecture that overcomes these limitations by introducing small molecules into the CQD/organic stacked structure. The small molecule complements CQD absorption and creates an exciton cascade with the host polymer, thus enabling efficient energy transfer and also promoting exciton dissociation at heterointerfaces. The resulting hybrid solar cells exhibit PCEs of 13.1% and retain over 80% of their initial PCE after 150 h of continuous operation unencapsulated, outperforming present air-processed solution-cast CQD/organic photovoltaics. Colloidal quantum dots and organics have complementary properties apt for photovoltaics, yet their combination has led to poor charge collection. Here, Baek et al. introduce small molecules that act as a bridge between quantum dots and polymers, thus improving device efficiency and stability.

Gallium oxide films were grown with nitrogen on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Nitrogen and oxygen gases supplied simultaneously through one plasma source were used to grow gallium oxide films with nitrogen. All the films had monoclinic β-Ga2O3 structure; however, their surface roughness increased with increasing nitrogen supply. The incorporation of nitrogen was confirmed by x-ray photoelectron spectroscopy. The average transmittance of the films was over 85% in the visible range and over 95% in the ultraviolet range. The as-deposited films had decreased bandgap energies from 4.92 eV to 4.35 eV, with increased nitrogen rate. That is, the bandgap energies of the gallium oxide films can be tuned simply by increasing nitrogen supply during their growth without any post-annealing process under nitrogen condition.

We introduce indium arsenide colloidal quantum dot films for photovoltaic devices, fabricated by two-step surface modification. Native ligands and unwanted oxides on the surface are peeled off followed by passivating with incoming atomic or short ligands. The near-infrared-absorbing n-type indium arsenide colloidal quantum dot films can be tuned in energy-level positions up to 0.4 eV depending on the surface chemistry, and consequently, they boost collection efficiency when used in various emerging solar cells. As an example, we demonstrate p–n junction between n-type indium arsenide and p-type lead sulfide colloidal quantum dot layers, which leads to a favorable electronic band alignment and charge extraction from both colloidal quantum dot layers. A certified power conversion efficiency of 7.92% is achieved without additionally supporting carrier transport layers. This study provides richer materials to explore for high-efficiency emerging photovoltaics and will broaden research interest for various optoelectronic applications using the n-type covalent nanocrystal arrays., Existing n-type colloidal quantum dot materials easily lose their doping polarity in air. Here Song et al. passivate the reactive covalent surface of indium arsenide quantum dots to gain the energy-level tunability and show p–n junction type solar cells with 7.92% certified efficiency.

Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [\(11\overline{2} 0\)] Al2O3//[\(1\overline{1} 00\)] AlN//[\(1\overline{1} 00\)] GaN//[102] β-Ga2O3 and [\(1\overline{1} 00\)] Al2O3//[\(11\overline{2} 0\)] AlN//[\(11\overline{2} 0\)] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (\(\overline{2} 01\)) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

The effect of growth pressure on the morphology of the ZnO nanostructures in chemical vapor transport by using Zn powder and oxygen as source materials has been investigated. Highly uniform aligned ZnO nanorods or multifaceted tripod structures were grown depending on the growth pressure. The mechanism governing the morphology change was explained by the relative concentration of Zn vapor and supersaturation based on experimental observations. It was concluded that heterogeneous nucleation on the substrate is enhanced at low growth pressure, while homogeneous nucleation from vapor phase is enhanced at high growth pressure. The difference resulted in different morphology of ZnO nanostructures. ZnO nanorods grown at optimized condition were used for the fabrication of gas sensor for the detection of H 2 gas.

In this report, we explore the underlying mechanisms by which doped organic thin films as a top hole-selective layer (HSL) improve the performance and stability of colloidal quantum dot (CQD)-based solar cells. Molecular dynamics-based theoretical studies prove that the hydro/oxo-phobic properties of the HSL serve to efficiently passivate the CQD solid. Furthermore, the robust and outstanding electrical properties of the HSL, simultaneously ensure a high power conversion efficiency (PCE) and increase the stability performance of CQD-based solar cells. As a result, a best PCE of 11.7% in a lead sulfide (PbS)-based CQD solar cell is achieved and over 90% of the initial performance is retained after 1 year storage under ambient conditions.

Colloidal quantum dots (CQDs) have attracted attention as a next-generation of photovoltaics (PVs) capable of a tunable band gap and low-cost solution process. Understanding and controlling the surface of CQDs lead to the significant development in the performance of CQD PVs. Here we review recent progress in the realization of low-cost, efficient lead chalcogenide CQD PVs based on the surface investigation of CQDs. We focus on improving the electrical properties and air stability of the CQD achieved by material approaches and growing the power conversion efficiency (PCE) of the CQD PV obtained by structural approaches. Finally, we summarize the manners to improve the PCE of CQD PVs through optical design. The various issues mentioned in this review may provide insight into the commercialization of CQD PVs in the near future.

We present a one-step layer deposition procedure employing ammonium iodide (NH4I) to achieve photovoltaic quality PbS quantum dot (QD) layers. Ammonium iodide is used to replace the long alkyl organic native ligands binding to the QD surface resulting in iodide terminated QDs that are stabilized in polar solvents such as N,N-dimethylformamide without particle aggregation. We extensively characterized the iodide terminated PbS QD via UV-vis absorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), FT-IR transmission spectroscopy, and X-ray photoelectron spectroscopy (XPS). Finally, we fabricated PbS QD photovoltaic cells that employ the iodide terminated PbS QDs. The resulting QD-PV devices achieved a best power conversion efficiency of 2.36% under ambient conditions that is limited by the layer thickness. The PV characteristics compare favorably to similar devices that were prepared using the standard layer-by-layer ethandithiol (EDT) treatment that had a similar layer thickness.

The surface modified lithium electrode is prepared by coating an ionic conductive poly(vinylene carbonate-co-acrylonitrile) layer as a solid electrolyte interphase on lithium metal. The thin protective polymer layer with strong adhesion to the lithium electrode suppresses the corrosion of lithium metal and stabilizes the interface of lithium electrode in prolonged contact with organic electrolyte. Cycling performance of the Li/LiCoO2 cells can be improved by using the surface modified lithium electrode. SEM analysis of lithium electrodes after repeated cycling reveals that the use of a surface modified lithium electrode effectively suppresses dendrite growth during cycling, which results in stable cycling characteristics compared to that of the cell with an un-modified lithium electrode.

The improvement of power conversion efficiency, especially current density (Jsc), for nanocrystal quantum dot based heterojunction solar cells was realized by employing a trenched ZnO film fabricated using nanoimprint techniques. For an optimization of ZnO patterns, various patterned ZnO films were investigated using electrical and optical analysis methods by varying the line width, interpattern distance, pattern height, and residual layer. Analyzing the features of patterned ZnO films allowed us to simultaneously optimize both the pronounced electrical effects as well as optical properties. Consequently, we achieved an enhancement in Jsc from 7.82 to 12.5 mA cm(-2) by adopting the patterned ZnO with optimized trenched shape.

We investigated the CdS/Cu(In,Ga)Se2 interface characteristics of Cu(In,Ga)Se2 (CIGS) thin-film solar cells by using photoreflectance spectroscopy and their influence on the photovoltaic performance. We prepared CIGS solar cells with CdS and CIGS layers fabricated by using different methods of chemical bath deposition (CBD). The thiourea concentration in the CBD-CdS process was varied from 0.025 M to 0.1 M. The final In-Ga-Se deposition time for the CIGS film’s deposition was varied from 300 s to 490 s. We fabricated solar cells with thin films fabricated by using a combination of these conditions. The transition energies changed from 2.277 eV to 2.387 eV and the conversion efficiencies changed from 14.13% to 15.81% depending on the fabrication process. The formation of different states in CdS/CIGS resulted in different conversion efficiencies, as well as different band alignments at the CdS/CIGS interface.

The composition modulation of in In-rich InxGa1−xN layers with an indium content as high as ∼67% was suppressed in plasma-assisted molecular beam epitaxy on c-sapphire substrates. It was found that the higher nitrogen plasma flow rate was very effective in suppression of composition modulation in In-rich InGaN layers. X-ray diffraction, X-ray energy dispersive spectroscopy, and transmission electron microscopic images clearly showed disappearance of composition modulation with increasing the nitrogen flow rate.

Very well aligned vertical ZnO nanorods with high optical quality were successfully synthesized by sequentially employing an aqueous solution method on a ZnO seed layer and a thermal chemical vapor deposition (CVD). The process is growing the upper ZnO nanorods by using CVD on top of the bottom nanorods synthesized by using an aqueous solution method on a Si substrate with a ZnO seed layer. These double-structured-nanorods showed a significant improvement of optical quality. The CVD re-grown upper nanorods showed orders-of-magnitude enhancement of the band edge emission and complete compression of the deep level emissions, compared with the solution-grown bottom nanorods. By comparing emission spectra from the series of samples with and without the seed layer or the second CVD growth, we can conclude that the improvement can only be achieved by combining the CVD, the solution-based synthesis technique, and the seed layer.

Tubular solid oxide fuel cells (SOFCs) have many desirable advantages compared to other SOFC applications. Recently, micro-tubular SOFCs were studied to apply them into APU systems for future vehicles. In this study, electrochemical properties of the micro-tubular SOFCs (1.6 mm O.D.) have been characterized. Electrochemical analysis showed excellent performance with a maximum power density of 1.3 W/cm2 at 550 °C. The impedance information gained at cell operating temperatures of 450, 500, and 550 °C showed individual cell ohmic resistances of 1.0, 0.6, and 0.2 Ω respectively. Within the operating temperature range of 450–550 °C, the ceria based micro-tubular SOFCs (cathode length: 8 mm) were found to have power densities ranging between 0.263 and 1.310 W/cm2. The mechanical properties of the tubes were also analyzed through internal burst testing and monotonic compressive loading on a c-ring test specimen. The two testing techniques are compared and related, and maximum hoop stress values are reported for each of the fabrication parameters. This study showed feasible electrochemical properties and mechanical strength of micro-tubular SOFC for APU applications.

The ability to create and manipulate large arrays of inorganic semiconductor micro/nanostructures for integration on unconventional substrates provides new possibilities in device engineering. Here, simple methods are described for the preparation of structures of single crystalline silicon in suspended and tethered configurations that facilitate their deterministic assembly using transfer-printing techniques. Diverse shapes (e.g., straight or curved edges), thicknesses (between 55 nm and 3 μm), and sizes (areas of 4000 μm(2) to 117 mm(2) ) of structures in varied layouts (regular or irregular arrays, with dense or sparse coverages) can be achieved, using either flat or cylindrical roller-type stamps. To demonstrate the technique, printing with 100% yield onto curved, rigid supports of glass and ceramics and onto thin sheets of plastic is shown. The fabrication of a printed array of silicon p(+) -i-n(+) junction photodiodes on plastic is representative of device-printing capabilities.

Structural and optical properties of nonpolar a -plane ZnO films grown with different II/VI ratios on r -plane sapphire substrates by plasma-assisted molecular beam epitaxy were investigated. Even by increasing the II/VI ratio across the stoichiometric flux condition a consistent surface morphology of striated stripes along the ZnO 〈0 0 0 1〉 direction without any pit formation was observed, which is contrary to polar c -plane ZnO films. Root mean square surface roughness, full width at half maximum values of X-ray rocking curves, defect densities, and photoluminescence were changed with the II/VI ratio. The sample grown with stoichiometric flux condition showed the lowest value of rms roughness, the smallest threading dislocation and stacking fault densities of ∼4.7×10 8 cm −2 and ∼9.5×10 4 cm −1 , respectively, and the highest intensity of D o X peak. These results imply that the stoichiometric flux growth condition is suitable to obtain superior structural and optical properties compared to other flux conditions.

Microstructural analyses of of ZnO films on (1 1 1) Si substrates grown by plasma-assited molecualr beam epitaxy were performed in this study. Zn pre-deposition and its subsequent oxidation, in which either oxygen gas or oxygen-plasma was used as the oxygen source, were employed before ZnO growth. Both reflection high energy electron diffraction and x-ray pole figure showed the single crystalline features in the ZnO films with both post-oxidation of deposited Zn. Detailed transmission electron microscopy (TEM), however, revealed a locally multi-crystalline feature with 30 degrees-rotated domians at the near-interface regions in the ZnO film with oxidation by oxygen gas. ZnO film with oxidation of pre-deposited Zn by oxygen-plasma was observed to be single crystalline through the whole thickness by TEM. We observed a new epitaxial relationship, (0 0 0 1)ZnO//(1 1 1)Si and [0 1 1¯ 0]ZnO//[1 1¯ 0]Si, with a crystallographic rotation of ZnO with respect to Si by 30 degrees, which is energitically more favorable because of a lower lattice misfit (2.2%). No cracks were observed from the ZnO film with a thickness of 1.5 μm, supporting the mechanical integrity of the film prepared in this study.

In this paper, a graded Ni/YSZ cermet anode, an 8 mol.%YSZ electrolyte, and a lanthanum strontium manganite (LSM) cathode were used to fabricate a solid oxide fuel cell (SOFC) unit. An anode-supported cell was prepared using a tape casting technique followed by hot pressing lamination and a single step co-firing process, allowing for the creation of a thin layer of dense electrolyte on a porous anode support. To reduce activation and concentration overpotential in the unit cell, a porosity gradient was developed in the anode using different percentages of pore former to a number of different tape-slurries, followed by tape casting and lamination of the tapes. The unit cell demonstrated that a concentration distribution of porosity in the anode increases the power in the unit cell from 76 mW cm−2 to 101 mW cm−2 at 600 °C in humidified hydrogen. Although the results have not been optimized for good performance, the effect of the porosity gradient is quite apparent and has potential in developing superior anode systems.

In this work, we studied a NiO/GDC-GDC-LSCF micro-tubular SOFC system using saturated hydrogen at 450-550 oC. The systems were electrochemically and mechanically tested using a number of different methodologies, and were modeled using a 2D axial symmetric steady state non-isothermal computational model incorporating radiation heat transfer, flow and species transport.

Nanostructured ZnO films were fabricated on nanopored Si(001) surfaces through reactive ion etching and plasma-assisted molecular-beam epitaxy techniques. Nanowall-like nanostructures were formed on the ZnO film surfaces depending on the thickness of the ZnO films. Significant enhancement of the photoluminescence intensity up to 15 fold was observed from the nanostructured ZnO films. We found that the emission properties of the film changed very sensitively with the nanostructure on the surface and the enhancement is closely related to the formations of nanostructures on the surface of the ZnO films, not at the interface between the films and the substrate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An anode-supported yttria-stabilized zirconia (YSZ) electrolyte was fabricated using tape casting and co-sintering techniques for use in a solid oxide fuel cell (SOFC). Nickel/YSZ, lanthanum strontium manganite (La 0.85 Sr 0.15 MnO 3 ) and 8 mol% Y 2 O 3 –ZrO 2 were used for the anode, the cathode and the electrolyte, respectively. The anode-supported electrolyte was prepared with a tape casting technique followed by hot pressing lamination. Co-sintering between the anode and the electrolyte was applied at 1350 °C under pressurized conditions to fabricate the anode-supported electrolyte of the unit cell. Scanning electron microscopy (SEM) revealed the crack-free and dense structure of the electrolyte in the unit cell. The open circuit voltage (OCV) of the unit cell was 1.08 V at 750 °C, indicating negligible leakage of fuel through the electrolyte layer. The active layer was applied to the interface between the anode and the electrolyte layer to increase the three-phase boundary, the electrochemical reaction site of the anode. The unit cell having an active layer exhibits good performance due to the drastic reduction of polarization resistance.

This study investigated the ionic transport and water dissociation phenomena with current densities in a continuous electrodeionization (CEDI). Current–voltage ( I – V ) relationships exhibit the ionic transport and water dissociation phenomena in a CEDI system. A high ionic removal rate was attained at the transition current from ionic transport to water dissociation indicating minimized water dissociation is sufficient for ionic removal. The pH variation with current densities was observed due to the mixed effects of convection and electromigration. An FT-IR spectrum study on anion exchange textile (AIET) indicated that the pH increase in a CEDI system was due to the structural change of functional groups.

Electrical impedance spectroscopy was used for the characterization of electroregeneration in a continuous electrodeionization (CEDI) system packed with cation-exchange resin (CIX). CEDI process usually operates in two regimes of enhanced transfer and electroregeneration. The current efficiency decreased in the second regime of a CEDI system due to the water dissociation. Therefore, it is necessary to minimize the second regime to maximize the current efficiency by controlling the operating parameters even though the second regime is essential for regeneration of the resin. It was suggested to monitor the ionic state of the bed during the operation by observing current distribution along the column. The measurement of the resistance of CIX beads at high frequency, based on the equivalent circuit, provided information on the extent of electrical regeneration of the bed. The optimal current density was estimated at the minimized area of second regime, and the operation at the optimal current density showed the 100% of metal removal, indicating the effectiveness of this method.

Performances of electromembrane systems were investigated for removal of the hardness materials in a tap water. Six cells of ED, EDR, and EDIR systems with an electrode area of 12.5cm x 8.0 cm were operated. The results showed scaling formation due to water dissociation on the surface of cation exchange membrane, but EDR and EDIR enabled to avoid the scaling problem. EDIR operation lowered the resistance and power consumption compared to EDR due to the conductance of ion exchange resins. This study demonstrated the feasibility of EDR and EDIR processes for water softening.

The transport of cobalt ion in a continuous electrodeionization (CEDI) system was investigated in terms of electrochemical properties of ion exchange textile. The porous plug model and an extended Nernst‐Plank equation were applied to describe the transport of Co2+ through an ion exchange textile. The transport characteristics of Co2+ during CEDI operation suggested the transport mechanism was due mainly to the increased current induced by the high conductivity in the ion exchange textile, not accelerated ionic mobility. This study suggested the important parameter for the high performance of the CEDI system is the conductivity of the ion exchange media.

An RO-CEDI (Reverse osmosis-continuous electrodeionization) hybrid process was investigated to pro- duce high purity water. The RO system, with an effective membrane area of 1.1 m 2 , was operated using tap water with conductivity of 64 µs·cm −1 , and the CEDI system experiments were carried out in a cell-pair stack consisting of 3 com- partments. During the parametric study of the RO-CEDI hybrid system, the optimal operating conditions were deter- mined based on the water purity. The electrical resistivity and water dissociation of the ion exchange resins and ion exchange membrane were verified as the key mechanisms of the CEDI system in the water purification. The produced water met the quality requirements as a make-up water in a nuclear power plant with a resistivity of 10-16.7 MΩ·cm.

We have investigated the optical response of periodic arrays of metallic (gold) nanoparticles composed of a pair of particles on each lattice site. By varying the interparticle separation within the pairs from dielectric proximity to conductive contact on a nanometer scale, we observe an abrupt, large renormalization as well as a splitting of the surface plasmon polariton energy. These spectral anomalies are ascribed to a transition whereupon the interparticle dipole−dipole interaction is shunted and the plasmon polaritons exhibit multipolar behavior, including a very high local concentration of electromagnetic energy in the vicinity of their conductive contact.

This study investigated the production of high-purity water in the primary coolant of a nuclear power plant via the continuous electrodeionization (CEDI) process, using ion exchange resins as ion-conducting media between ion exchange membranes. The effectiveness of this method was examined with respect to the removal of heavy metals. The study was carried out on a laboratory scale with an effective area of 20 cm(2). The CEDI system was operated with a layered bed of cation exchange resins, anion exchange resins, and mixed-bed ion exchange resins. The stack configuration was designed to prevent a reaction between metal ions and hydroxide ions. The CEDI operation with the layered bed removed more than 99% of the ions at 30% of the current efficiency. The results showed that, with an inlet conductivity of 40 microScm(-1), a linear velocity of 4.17 cms(-1), and an applied current density of 17 mAcm(-2), the CEDI process yielded an outlet conductivity of 0.5 microScm(-1), thereby preventing the precipitation of metal ions. This study therefore successfully demonstrated the feasibility of the CEDI operation for the removal of heavy metals at a very low concentration.

A magnetic filter - continuous electrodeionization (CEDI) hybrid separation system was investigated for the purification of the primary coolant in a nuclear power plant. A magnetic filter system with a 3000 Gauss magnetic field and a CEDI system with a cell consisting of 3 compartments were used for the removal of magnetite and nickel ions, respectively. The hybrid separation system achieved removal rates of 98% for magnetite and 99% for the nickel ions demonstrating its feasibility for the purification of primary coolant.

Ion-exchange textiles (IETs) suitable for use in continuous electrodeionization (CEDI) stacks were prepared using the ultraviolet (UV)-induced grafting of acrylic acid and sodium styrene sulfonate for cation-exchange textiles, or 2-hydroxyethyl methacrylate and vinylbenzyl trimethyl ammonium chloride for anion-exchange textiles, onto nonwoven polypropylene fabric using benzophenone as photoinitiator. Although the ion-exchange capacity (2.2 meq g−1) of the prepared strong acid cation-exchange textile was lower than that of IRN77 strong acid cation-exchange resin (4.2 meq g−1), the overall rate constant of IET was very high due to its low crosslinking and high specific surface area. There was no significant difference between the two different media in terms of the Co(II) removal rate. Furthermore, the current efficiency for IETs was higher than that of IRN77 cation-exchange resin during a CEDI operation, with efficiencies of 60% and 20%, respectively. The IET also showed the faster exchange kinetics. Therefore, IETs prepared in this study proved to have desirable ion-conducting characteristics within the CEDI systems. Also this study revealed that the primary removal mechanism in CEDI is the transport of ions through a medium and not the ionic capacity of a medium. Copyright © 2004 Society of Chemical Industry

Colloidal quantum dots (CQDs) are promising light harvesting materials for realization of solution processible, highly efficient multipurpose photovoltaics (PVs). Here, PbS CQD solar cells are reported with improved certified power conversion efficiency performance of 10.4% by simply controlling protic solvents (alcohols) in ligand exchange process. With shorter chain alcohols, the mobility of charge carriers is an order-of-magnitude improved due to the enhanced interparticle coupling; on the other hand, excessive removal of passivating ligands by very protic solvent, methanol (MeOH) induced undesirable traps on CQD surface. Consequently, it has been found that high performance CQD PVs require a solvent engineering for balance between native leaving ligands with incoming ligands during ligand exchange process for well-controlled surfaces of CQDs and enhanced carrier concentration of conductive CQD films.

The fast degradation of lead selenide (PbSe) nanocrystal quantum dots (NQDs) in ambient conditions impedes widespread deployment of the highly excitonic, thus versatile, colloidal NQDs. Here we report a simple in situ post-synthetic halide salt treatment that results in size-independent air stability of PbSe NQDs without significantly altering their optoelectronic characteristics. From TEM, NMR, and XPS results and DFT calculations, we propose that the unprecedented size-independent air stability of the PbSe NQDs can be attributed to the successful passivation of under-coordinated PbSe(100) facets with atomically thin PbX2 (X = Cl, Br, I) adlayers. Conductive films made of halide-treated ultrastable PbSe NQDs exhibit markedly improved air stability and behave as an n-type channel in a field-effect transistor. Our simple in situ wet-chemical passivation scheme will enable broader utilization of PbSe NQDs in ambient conditions in many optoelectronic applications.

The strain and piezoelectric fields in InGaN blue light-emitting diodes on a GaN layer, which is grown on a planar sapphire substrate or patterned sapphire substrates (PSSs), such as a microsized PSS and a nanosized PSS (NPSS), are investigated by micro-Raman spectroscopy and electroreflectance (ER) spectroscopy. The obtained piezoelectric field in InGaN multiple quantum wells (QWs) grown on the planar substrate is 0.83 MV/cm, and it is 0.70 MV/cm for the case of the NPSS. These results are attributed to the fact that the GaN layers on the PSSs have a smaller residual strain compared to that on the planar sapphire, and thus, strain reduction in the GaN layer can reduce the piezoelectric field in the InGaN QWs grown on top of it.

We investigated the effects of a strain-control layer on piezoelectric fields and indium incorporation in blue-emitting InGaN/GaN quantum wells (QWs) using reverse-biased electroreflectance spectroscopy. With this technique, we could determine the change in both indium incorporation and the piezoelectric field by the inserted buffer layer. We compared two test samples, which have identical structures except for the insertion of an additional InGaN layer at the bottom of the blue-QW. The magnitude of the piezoelectric fields in the QWs with the added layer was significantly smaller even with a slightly higher indium composition. The result shows that the strain in the QW is partially released and can be controlled quantitatively by the strain-control layer underneath. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of silver nanoplates was studied in the modified polyol method, where the nucleation and seed stage occurred in a poly(ethylene glycol) (PEG)–water mixture solution, and the growth stage happened in the PEG environment. The morphological evolution of nanoplates was characterized using UV, SEM, and TEM. Interestingly, plane nanostructures with unusual jagged edges were finally formed in our modified polyol method. Using TEM, we observed the medium state of fusion between two nanoplates, resulting in generating unusual jagged edges. Therefore, a novel two-dimensional oriented attachment occurred in our modified polyol method, which involves smaller nanoplates as the building blocks. Further control experiments showed that the presence of water could break this kinetic preferred reactivity, leading to the formation of nanoparticles.

A simple and mass productive extrusion technique was applied to fabricate anode-supported micro-tubular solid oxide fuel cells (SOFCs). A standard NiO/8YSZ (Nickel oxide/8 mol % yttria stabilized zirconia) cermets anode, 8 YSZ electrolyte, and LSM (Lanthanum strontium manganite) cathode were used as the materials components. SEM (secondary electron microscopy) images indicated vacuum infiltration method successfully generated the thin electrolyte layer (10∼15 μm) with a structurally effective three phase boundaries. Fabricated unit cell showed the open circuit voltage of 1.12 V without any fuel leaking problems. Electrochemical tests showed a maximum power density up to 0.30 W/cm2 at 800 °C, implying the excellent performance as micro-tubular SOFCs. This study verified that the extrusion aided by vacuum infiltration process could be a promising technique for mass production of microtubualr SOFCs.Copyright © 2008 by ASME

It is usually accepted that the doped ceria buffer layer is needed between the conventional yttria-stabilized zirconia (YSZ) electrolytes and the Fe and Co containing cathode materials such as (La,Sr)(Co,Fe)O3-δ (LSCF) to improve the cell performance and to prevent unwanted chemical reactions between them. In this study, the effect of the sintering temperature, cobalt doping amount, and the starting powders of GDC (Gadolinium Doped Ceria) layer were investigated. The cell testing result indicated that it would be desirable to decide the sintering temperature of the GDC layer less than 1250°C to minimize the effect of the solid solutions based on (Zr, Ce)O2 . Furthermore, 5 days operations of the button cell with cobalt doped GDC layer showed the increased ohmic and polarization resistance, indicating the cobalt segregation from the GDC layer during the long term operation.Copyright © 2010 by ASME

Diels-Alder reaction of cyclic sugar dienophiles with cyclopentadiene and cyclohexadiene occurred in totally exo - and face-selective manner to afford single stereoisomers, one of which wa tranformed into a highly substituted cyclopentane.

We investigated the effects of prestrained layers on piezoelectric fields and indium incorporation in blue-emitting InGaN/GaN quantum wells by using reverse-biased electroreflectance spectroscopy. We compared two sets of samples, which have identical structures except an insertion of an additional UV quantum well at the bottom of the blue-quantum well. Indium composition of quantum wells with the additional layer is larger than in the wells without the added layer. In contrast, the magnitude of the piezoelectric fields in the quantum wells with the added well is smaller even with higher In composition. The result shows that the strain in the quantum well is partially released and can be controlled by the insertion of the prestrained layer underneath.

A planar anode-supported electrolyte was fabricated using a tape casting method that involved a single step cofiring process. A standard NiO∕8YSZ cermet anode, 8mol% YSZ electrolyte, and a lanthanum strontium manganite cathode were used for the solid oxide fuel cell unit cell. A pressurized cofiring technique allows the creation of a thin layer of dense electrolyte about 10μm without warpage. The open circuit voltage of the unit cell indicated negligible fuel leakage through the electrolyte film due to the dense and crack-free electrolyte layer. An electrochemical test of the unit cell showed a maximum power density up to 0.173W∕cm2 at 900°C. Approximated electrochemical properties, e.g., activation energy, Ohmic resistance, and exchange current density, indicated that the cell performance was significantly influenced by the electrode properties of the unit cell.

Micro-tubular Solid Oxide Fuel Cells (SOFCs) are fabricated and tested for analysis of electrochemical properties. The impedance spectra from individual 1.8 mm diameter, 1.2 cm length micro-tubular SOFCs are obtained for the intermediate temperature range of 450–550°C. The micro-tubular SOFC used is anode supported, consisting of a NiO and Gd0.2 Ce0.8 O2−x (GDC) cermet anode, thin GDC electrolyte, and a La0.6 Sr0.4 Co0.2 Fe0.8 O3−y (LSCF) and GDC composite cathode. The impedance information gained at cell operating temperatures of 450, 500, and 550°C yielded power density losses of 0.8, 2.3, and 4.6% respectively. Within the operating temperature range of 450–550 °C, the ceria based 1.8 mm micro-tubular SOFCs were found to have a power densities ranging between 180–740 mW/cm2 .Copyright © 2008 by ASME

Micro tubular solid oxide fuel cells (SOFCs) have many desirable advantages compared to general SOFC. Recently, microtubualr SOFC are now studied to apply into APU system in a future generation vehicles. In this study, electrochemical and mechanical properties of the micro tubular SOFCs (less than 1 mm O.D.) have been characterized. Electrochemical characterization showed the excellent performance of MT SOFC with the power density of 1 W/cm2 at 600°C. Impedance measurement indicated that the contribution of contact resistance on the cell performance was still high and there were many possibilities to improve the cell performance. Mechanical test of the MT-SOFC using burst testing apparatus indicated the mechanical properties were mainly dependent on porosity and wall thickness, i.e. physical properties of anode support. This study examined the properties of micro-tubular SOFC using the novel characterization method for APU application.

Nanoengineered fluorescent response is reported in semiconductor core-shell (CdSe/ZnS) quantum dots in proximity to the surface plasmon field of periodic silver nanoparticle arrays. Tuning the surface plasmon resonance to the quantum dot exciton emission band results in an /spl sim/50-fold enhancement of the fluorescence.

Li22Si5 alloy powder was synthesized by mechanical alloying and its electrochemical performance was investigated for use in solid-state battery anodes. Two types of anode powder were prepared: 1) Li–Si alloy powder after mechanical alloying with Li-granules and Si-powder, and 2) Li–Si alloy powder from the first process followed by additional ball milling for reduction of particle size. Using these anode materials, all-solid-state lithium batteries were assembled with Li4Ti5O12 (LTO) as cathode and Li2S–P2S5 as electrolyte. Impedance spectra of the two types of cells were measured, and the results showed that the non-ohmic resistance was less in the case of the cell with the secondary ball-milled, fine anode powder. Galvanostatic charge/discharge tests were also performed, and capacity was increased about two times by the additional powder milling process; which is consistent with the impedance results. Thus, the results from the present work indicate that using the secondary milling process to refine the electrode powder is an effective way to increase the kinetics of alloying and de-alloying with improvement in interfacial properties in all-solid-state lithium secondary batteries.

We investigated the effect of double air gaps embedded between sapphire and undoped GaN on the strain reduction in the InGaN/GaN-based green LED structure. Selective GaN growth and electrochemical etching were exploited to achieve embedded air gaps. Raman spectroscopy and photoluminescence were employed to demonstrate the relation between strain relaxation and indium incorporation. The double air gaps caused strain relaxation and led to a higher In incorporation in InGaN layers, which in turn caused a redshift of the PL spectra. As a result, three different peak wavelengths according to the existence of air gaps were observed.

The authors have characterized the CdS layer in Cu(In,Ga)Se2 thin-film solar cells using photoreflectance (PR) spectroscopy and investigated its influence on the photovoltaic performance. The CdS layer was fabricated by chemical bath deposition with various concentrations of ammonia (1.0–3.0 M), thiourea (0.025–0.1 M), and Cd-salt (0.0004–0.003 M) as well as various thicknesses (30–90 nm). The PR transition energy in CdS increased from 2.282 to 2.366 eV as the thiourea concentration increased from 1.0 to 3.0 M, whereas it decreased as the thickness of CdS increased. The conversion efficiency depended on neither the ammonia and the Cd-salt concentrations nor the thickness of CdS, whereas it changed from 14.72% to 15.81% as the thiourea concentration decreases from 3.0 to 1.0 M.