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Sequential DC magnetron sputtering and rapid thermal processing appear very promising to fabricate CZTS-based thin-film photovoltaic (PV) solar cells with regards to existent environmental and industrial issues. However, their state-of-the-art efficiency remains limited to about 10% to date. In this work, we aim at optimizing the optical and electrical properties of the CZTS absorber by an extensive screening of their correlation with the material composition. This is widely varied by different deposition (i.e. thickness of precursors) and process (i.e. RTP) conditions. We assess the impact of absorber composition on the energy bandgap, absorption coefficient, p-type carrier concentration and mobility. The most important results lie in the extensive analysis of the inverse power-law trend for carrier concentration versus mobility and logarithmic trend versus bandgap. Our conclusions point the optimal composition ratios towards Cu-poor and less than actual target Zn-rich range. As a result, a potential roadmap is drawn up based on presented experimental results and SCAPS simulations in order to reach more than 10% cell efficiency with the target technology.

This review deals with our long-range goal of determining why the Prussian blue pigments, typically either the “soluble” KFeIII[FeII(CN)6]·xH2O or the alternative “insoluble” FeIII4[FeII(CN)6]3·xH2O compounds, used by artists from shortly after the discovery of Prussian blue in 1704 and well into the early twentieth century, often fade when exposed to light. In order to achieve this goal it was decided that first, for comparison purposes, we had to prepare and fully characterize Prussian blues prepared by various, often commercially successful, synthetic methods. The characterization has employed a large variety of modern methods to determine both the stoichiometry of the Prussian blues and the arrangement of the voids found in the latter “insoluble” Prussian blues. The refinement of synchrotron radiation derived X-ray powder diffraction data obtained for a formally soluble and an insoluble Prussian blue required refinement in the Pmm space group and lead to the K1.9[FeIII4FeII3(CN)18]·{1.9 OH + 7.0H2O}, 1, and FeIII4FeII3(CN)18·11.0H2O, 2, stoichiometries. The former compound, 1, exhibits an apparently random iron(II) long-range void arrangement, whereas 2 exhibits a more non-random long-range arrangement, however, a pair distribution function analysis indicates a short-range ordering of the voids in both compounds. After further detailed characterization of many Prussian blue samples, painted samples on linen canvas, were subjected to accelerated light exposure for up to 800 hours either as pure Prussian blues or mixed with (PbCO3)2Pb(OH)2, ZnO or TiO2, the white pigments often used by artists to lighten the intense Prussian blue colour. The results indicate that the first two of these white pigments play a significant role in the fading of the colour of Prussian blues. In order to achieve our long-range goal, several Prussian blue samples were prepared from “ancient” recipes published in 1758 and 1779. These so-called “ancient” samples, painted in a dark and a pale blue shade, were also subjected to accelerated light exposure. The colorimetric results, in conjunction with X-ray powder diffraction refinements, pair distribution analysis and Mossbauer spectral results, indicate that, depending on the exact method of ancient preparation, the Prussian blue pigments were sometimes badly contaminated with alumina hydrate and/or ferrihydrite, a contamination which leads to extensive fading or decolourization of the Prussian blue pigments. The presence of ferrihydrite was subsequently confirmed in the study of a surface paint fragment from an eighteenth-century polychrome sculpture.

A range of titanium silicates (ETS-4 and CTS-1) with interesting gas separation properties were studied as CO2 adsorbents. Some of these adsorbents, in particular NaMg-CTS-1, showed the ability to ...

Two highly porous γ-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol–gel-based process were investigated by 27Al nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for γ-aluminas. TEM studies revealed that rod-shaped particles with about 5nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50nm in the commercial catalyst and are considerably shorter in the sol–gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a ~1nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of γ-alumina, independent of precursor and synthesis conditions. The concentration of “non-spinel” Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous γ-alumina.

Palladium nanoparticles have been immobilized into an amino-functionalized metal-organic framework (MOF), MIL-101Cr-NH2, to form Pd@MIL-101Cr-NH2. Four materials with different loadings of palladium have been prepared (denoted as 4-, 8-, 12-, and 16wt%Pd@MIL-101Cr-NH2). The effects of catalyst loading and the size and distribution of the Pd nanoparticles on the catalytic performance have been studied. The catalysts were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), N-2-sorption isotherms, elemental analysis, and thermogravimetric analysis (TGA). To better characterize the palladium nanoparticles and their distribution in MIL-101Cr-NH2, electron tomography was employed to reconstruct the 3D volume of 8wt%Pd@MIL-101Cr-NH2 particles. The pair distribution functions (PDFs) of the samples were extracted from total scattering experiments using high-energy X-rays (60keV). The catalytic activity of the four MOF materials with different loadings of palladium nanoparticles was studied in the Suzuki-Miyaura cross-coupling reaction. The best catalytic performance was obtained with the MOF that contained 8wt% palladium nanoparticles. The metallic palladium nanoparticles were homogeneously distributed, with an average size of 2.6nm. Excellent yields were obtained for a wide scope of substrates under remarkably mild conditions (water, aerobic conditions, room temperature, catalyst loading as low as 0.15mol%). The material can be recycled at least 10times without alteration of its catalytic properties. AuthorCount:9

Two families of metal–organic frameworks (MOFs), MIL-88 and MIL-101 built by trinuclear transition metal (TM) clusters (TM = Cr, Fe, or Sc), have been known for several years, but their syntheses are often reported separately. In fact, these MOFs are polymorphs, or framework isomers: they are assembled from the same metal secondary building units and organic linkers, but the connectivity of these components differs. Here we report for the first time the synthesis of the vanadium MOF MIL-88B(V) and compare its synthesis parameters to those of MIL-47(V) and the recently reported MIL-101(V). The properties of MIL-88B(V) and MIL-101(V) are remarkably different. MIL-88B(V) can “breathe” and is responsive to different solvents, while MIL-101(V) is rigid and contains mesoporous cages. MIL-101(V) exhibits the highest specific surface area among vanadium MOFs discovered so far. In addition, both MIL-88B(V) and MIL-101(V) transform to MIL-47 at higher temperatures. We have also identified the key synthesis paramete...

Prussian blue pigments, highly insoluble mixed-valence iron(III) hexacyanoferrate(II) complexes of typical stoichiometry Fe-4(III)[Fe-II(CN)(6)](3)center dot xH(2)O or KFeIII[Fe-II(CN)(6)]center do ...

Prussian blue, a hydrated iron(III) hexacyanoferrate(II) complex, is a synthetic pigment discovered in Berlin in 1704. Because of both its highly intense color and its low cost, Prussian blue was widely used as a pigment in paintings until the 1970s. The early preparative methods were rapidly recognized as a contributory factor in the fading of the pigment, a fading already known by the mid-eighteenth century. Herein two typical eighteenth-century empirical recipes have been reproduced and the resulting pigment analyzed to better understand the reasons for this fading. X-ray absorption and Mössbauer spectroscopy indicated that the early syntheses lead to Prussian blue together with variable amounts of an undesirable iron(III) product. Pair distribution functional analysis confirmed the presence of nanocrystalline ferrihydrite, Fe10O14(OH)2, and also identified the presence of alumina hydrate, Al10O14(OH)2, with a particle size of ∼15 Å. Paint layers prepared from these pigments subjected to accelerated light exposure showed a tendency to turn green, a tendency that was often reported in eighteenth- and nineteenth-century books. The presence of particles of hydrous iron(III) oxides was also observed in a genuine eighteenth-century Prussian blue sample obtained from a polychrome sculpture.

Silicon-based substrates for the epitaxy of HgCdTe are an attractive low-cost choice for monolithic integration of infrared detectors with mature Si technology and high yield. However, progress in heteroepitaxy of CdTe/Si (for subsequent growth of HgCdTe) is limited by the high lattice and thermal mismatch, which creates strain at the heterointerface that results in a high density of dislocations. Previously we have reported on theoretical modeling of strain partitioning between CdTe and Si on nanopatterned silicon on insulator (SOI) substrates. In this paper, we present an experimental study of CdTe epitaxy on nanopatterned (SOI). SOI (100) substrates were patterned with interferometric lithography and reactive ion etching to form a two-dimensional array of silicon pillars with ∼250 nm diameter and 1 μm pitch. MBE was used to grow CdTe selectively on the silicon nanopillars. Selective growth of CdTe was confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Coalescence of CdTe on the silicon nanoislands has been observed from the SEM characterization. Selective growth was achieved with a two-step growth process involving desorption of the nucleation layer followed by regrowth of CdTe at a rate of 0.2 A s−1. Strain measurements by Raman spectroscopy show a comparable Raman shift (2.7 ± 2 cm−1 from the bulk value of 170 cm−1) in CdTe grown on nanopatterned SOI and planar silicon (Raman shift of 4.4 ± 2 cm−1), indicating similar strain on the nanopatterned substrates.

The synthesis of a metal-organic framework (UiO-67) functionalised simultaneously with two different transition metal complexes (Ir and Pd or Rh) through a one-pot procedure is reported for the first time. This has been achieved by an iterative modification of the synthesis parameters combined with characterisation of the resulting materials using different techniques, including X-ray absorption spectroscopy (XAS). The method also allows the first synthesis of UiO-67 with a very wide range of loadings (from 4 to 43 mol%) of an iridium complex ([IrCp*(bpydc)(Cl)Cl](2-); bpydc=2,2'-bipyridine-5,5'-dicarboxylate, Cp* = pentamethylcyclopentadienyl) through a pre-functionalisation methodology. AuthorCount:5

The fading of modern laboratory-synthesized and commercial Prussian blue, iron(III) hexacyanoferrate (II), based pigments in a linseed oil medium during exposure to light has been investigated. The Prussian blue pigments were painted with linseed oil, as a pure pigment and mixed with white lead, (PbCO3)(2)Pb (OH)(2), zinc white, ZnO, or titanium white, TiO2, pigment. The samples were subjected to accelerated ageing for 800 h and the light fastness of the Prussian blue pigment was evaluated by reference to blue wool standards. Pure Prussian blue is extremely light fast whilst it strongly fades when mixed with a white pigment, especially with lead white or zinc oxide. The painted samples were studied by UV-visible, iron K-edge X-ray absorption, iron-57 transmission Mossbauer, and attenuated total reflectance infrared spectroscopy. X-ray absorption results reveal a decrease in the iron coordination number in aged samples in the presence of white pigment. The Mossbauer spectra of the pure Prussian blue and the unaged and aged mixtures of Prussian blue and lead white or zinc oxide at 1 : 100 and 1 : 10 dilution ratios, respectively, indicate the presence of iron(II) and iron(III) in a ratio close to one as expected for the bulk stoichiometric KFeIII[Fe-II(CN)(6)]; no change in the spectral parameters was observed upon ageing. Combined with the X-ray near edge absorption and infrared studies, these results suggest reduction of the surface iron ions in the Prussian blue with ageing upon exposure to light.

Prussian blue, a mixed valence pigment, typically KFeIII[FeII(CN)6]·xH2O, was the most widely used blue artistic pigment from ca. 1720 to the 1970's but, unfortunately, its paint layers, especially when used in conjunction with a white pigment, tend to fade or turn green upon extended exposure to light. In order to identify the mechanism underlying these changes, paint layers have been prepared with differing amounts of these white pigments and subjected to accelerated light exposure fading. The resulting unfaded and faded paint layers as well as both the Berlin white pigment, Fe2II[FeII(CN)6], and the partially oxidized Berlin green pigment, {KFeIII[FeII(CN)6]}x{FeIII[FeIII(CN)6]}1−x, have been characterized by Raman and iron-57 Mossbauer spectroscopy. The results indicate that, upon fading, the Prussian blue pigment painted with a linseed oil binder and (PbCO3)2Pb(OH)2 or ZnO, and to a lesser extent with TiO2, undergoes a reduction at the exposed paint surface and an oxidation in the bulk of the paint layer. This combined reduction and oxidation disrupts, at least in part, the FeIII–N–C–FeII intervalent electron transfer pathways in Prussian blue thus leading to pigment fading through a reduction in the intervalent electron transfer absorbance at about 700 nm.

The authors have studied selective growth of cadmium telluride on Si(211) by molecular beam epitaxy (MBE). Patterned substrates were produced by optical lithography of MBE-grown CdTeAsSi (211). Photoemission microscopy was used as the main tool to study selective growth. This is very powerful because Si or Si O2 can be very easily distinguished from areas covered with even small amounts of CdTe due to contrast from work function differences. It was found that CdTe grows on CdTe without sticking on bare Si areas if the temperature is sufficiently high. Based on the analysis of the temperature dependence of the growth rate of CdTe, we suggest that different physisorption energies on Si and CdTe are the main cause of this selective growth.

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