Amorphous Quartz Research Articles

An XPS investigation on the influence of the substrate and growth conditions on pyrite thin films surface composition

Abstract Pyrite thin films have been prepared by sulfuration of Fe thin films deposited on sodalime glass substrates. Sulfuration temperatures have ranged from 200 °C to 500 °C and sulfuration time has been 20 h in all cases. It has been found that, during the sulfuration process, Na from the substrate diffuses through the formed pyrite thin film and reaches its surface where it reacts with some components of the sulfuration atmosphere to form sodium sulfate (Na 2 SO 4 ). The Na concentration at the film surface has been measured as a function of the film sulfuration temperature. Obtained experimental data show that Na surface concentration increases up to a sulfuration temperature of 350 °C but, on passing from this temperature to 400 °C, a drastic reduction is produced. For higher sulfuration temperatures ( T s > 400 ° C) the Na surface concentration slightly increases. Besides, a chemical variation of the pyrite surface composition related to an excess of sulfur is measured as a function of the sulfuration temperature showing a quite parallel behavior to that shown by the Na surface concentration. This excess of sulfur appears regardless the type of substrate (sodalima glass, alumina or amorphous quartz) used. The obtained results have been correlated with the variations of other parameters (grain and crystallite size, thickness, etc.) of the sulfurated films. After these investigations, it has been concluded that the Na concentration evolution at the film surface closely reflects the pyrite thin film grain crystallization (and size) which takes place during the sulfuration process. As a consequence, it is proposed that a change of the Na diffusion mechanism through the film (from diffusion through the grain boundaries to diffusion through the grain bulk) takes place at the indicated critical sulfuration temperatures. The reported excess of sulfur might be also related to this crystallization, although no further evidence has been obtained from our results. The consequences of this conclusion are discussed on the light of present pyrite thin film knowledge, mainly those aspects concerning to possible doping effects of Na and electrical transport processes in pyrite thin films.

Structural Characterizations of Aluminosilicates in Two Types of Fly Ash Samples from Shanxi Province, North China

In order to determine the structural characterization of aluminosilicates in two types of fly ashes, two samples from Shanxi Province, China were selected for study. One was from a pulverized coal boiler (FA-1), and the other from a circulating fluidized bed boiler (FA-2). FA-1 had a much higher content of silicon dioxide (SiO2) (70.30%) than FA-2(42.19%), but aluminum oxide (Al2O3) was higher in FA-2 (25.41%) than in FA-1 (17.04%). The characterizations were investigated using various methods including X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), magic angle spinning nuclear magnetic resonance (MAS–NMR) spectrometry, and X-ray photoelectron spectroscopy (XPS). The XRD analysis showed that FA-1 contained aluminosilicate glass, quartz and mullite, while FA-2 contained significant amounts of amorphous aluminosilicate, quartz and gypsum. The FTIR results showed an increased substitution of Al3+ for Si4+ as the band of asymmetric stretching vibrations Si–O(Si) (1100 cm−1) moved to 1090 cm−1 for FA-2, much lower than for FA-1(1097 cm−1). Moreover, the sharpness of the bands in the 1250–1000 cm−1 region for FA-2 indicates that the silicate structure of FA-2 was more ordered than for FA-1. It can be understood from the 29Si MAS–NMR results that Q4(mAl) (Q4 are connected via 4 bridging O atoms to mAl) is the main structural type in FA-1 and FA-2, and that FA-2 contains more Al, which substitutes for Si in the Q4 structure. 27Al MAS–NMR demonstrated that a combination of tetrahedral, pentahedral, and octahedral Al existed in FA-1 and FA-2. The Si 2p XPS spectra suggested that there were three forms of Si, including bridging Si (Si–O2), non–bridging Si (Si–O), and SiO2 gel. The content of Si–O2 for FA-1 was 37.48% higher than Si–O (28.57%), while the content of Si–O2 was 30.21% lower than Si–O (40.15%) for FA-2. The Al 2p XPS spectra showed that octahedral Al was the dominant form for FA-1 with a content of 40.25%, while the main phase was tetrahedral Al for FA-2 with a proportion of 37.36%, which corresponds well with the 27Al MAS–NMR results.

A Raman micro-spectroscopy study of 77,000 to 71,000\xa0year old ochre processing tools from Sibudu, KwaZulu-Natal, South Africa

Many Middle Stone Age sites in South Africa yielded hundreds, even thousands, of ochre pieces sometimes showing use traces. Less attention has been paid to the tools used for their processing. Here, seven tools excavated from the oldest layers (71,000 to 77,000 years ago) of Sibudu rock shelter were studied non-invasively to identify the micro-residues on them. The tools were first examined with optical microscopy to detect areas of interest. Then, Raman micro-spectroscopy was performed on the residues present, as well as on random areas of tool surfaces. These Raman signatures were compared to those obtained from the sediments and ochre samples recovered from the same layers. All tools exhibited red, orange and brown stains on their surfaces and these comprised iron oxides (haematite and maghemite) and oxyhydroxide (goethite). The other compounds detected include amorphous carbon, quartz, anatase and manganese oxides. All of these can occur within ochre, but they may alternatively be natural components of other rocks and sediments, formed secondarily by decay processes. However, the large and thick residues present on the surfaces of the artefacts imply their use for ochre processing (microscopic observations and chemical analyses of the sediments and the local rocks showed that they contain only traces of haematite). Ochre seems to have been the only material processed with these old Sibudu artefacts whereas in younger occupations, items such as bone were also processed with grindstones. The grinding tools are morphologically varied and the ochre pieces are both morphologically and chemically diverse.

Bulk-like magnetization and improved microwave properties of polycrystalline YIG (Y3Fe5O12) films grown on quartz substrates by pulsed laser deposition

Yttrium iron garnet (YIG) thin films with thickness 110 nm ≤ t ≤ 530 nm were grown on amorphous quartz substrates using pulsed laser deposition (PLD). The films show an improved magnetic and microwave performance. The value of saturation magnetization (4πMS) and ferromagnetic resonance (FMR) linewidth were found to be dependent on the thickness (t) of the film. The film with t = 530 nm shows a 4πMS value of 1725 (98% of the bulk value of YIG) and a minimum value for FMR linewidth of 57 Oe and 78 Oe respectively for the magnetic field applied perpendicular and parallel to the film plane. An almost linear relation between linewidth and coercivity is observed, which suggests a positive correlation between magnetic anisotropy, coercivity, and linewidth. The results demonstrated that YIG films prepared on quartz substrates can be beneficial to the application of YIG films to semiconductor integrated devices.

Synthesis, characterization and catalytic methanation performance of modified kaolin-supported Ni-based catalysts

Kaolin as a raw material for mesoporous support was firstly modified by calcination, acid treatment, and then was used to prepare nickel catalysts. The amount of alumina which was activated in kaolin during thermal treatment and then leached out in the acid was different. XRD pattern of the kaolin calcined at 600 °C or 900 °C exhibited only the diffraction peaks for amorphous silica and quartz while that calcined at 1100 °C showed obvious peaks for γ-Al2O3. Therefore, the nickel-based catalysts exhibited different physic-chemical properties. Atmospheric syngas methanation over the catalysts clarified an activity order of CA-1100 > CA-900 > CA-1400 > CA-600 > KA ≈ 0 at temperatures of 350–650 °C and a space velocity of 120 L·g−1·h−1. Metallic nickel with small diameter which has medium interaction with the modified kaolin and is well dispersed on the support would have reasonably good activity and carbon-resistance for syngas methanation.

Effect of Substrate Properties on Nanostructure and Optical Properties of CdTe Thin Films

Cadmium telluride (CdTe) nanoparticles were deposited on amorphous glass and crystal quartz as nonconductive films, indium tin oxide and fluorine doped tin oxide as transparent conducting films, and silver as a metal at 100°C under pressure of 2 × 10−5 mbar. CdTe thin films prepared by a thickness about 80 nm. The results of x-ray diffraction analysis show the grain size of preferential orientation was between 5.48 nm and 15.37 nm. Also, the preferential orientation changed from (111) for non-conducting substrates to (220) for conducting substrates. The investigation of texture coefficient (TC) has indicated the deviation of TC from unity for metals substrates is further than the other substrates. The optical properties of CdTe thin films such as the optical band gap, extinction coefficient and refractive index, real and imaginary parts of dielectric constant were investigated by ultraviolet–visible spectroscopy (UV–Vis) as a function of photon energy in the wavelength range of 600–1600 nm. These measurements indicated the increasing of optical band gap by increasing the conductivity of substrates. Scanning electron microscopy analysis used to investigate the morphology of thin films.

A micro-Raman and X-ray study of erupted submarine pyroclasts from El Hierro (Spain) and its' astrobiological implications

The pumice volcanic samples could have possible connections to the evolution of life and give us insight about their bio-geochemical processes related. In this regard, the samples from the volcanic eruption from La Restinga (El Hierro, Spain) in 2011 have been mainly studied by means of Raman spectroscopy. The research also includes analysis of XRD, Scanning Electron Microscopy and Optical Microscopy to support the Raman analysis. The results show that the Raman methods and mineral analyses are in strong agreement with the results obtained from other authors and techniques. The internal white foamy core (WFC) of the studied pumice samples shows amorphous silica, Fe-oxides, Ti-oxides, quartz, certain sulfates, carbonates, zeolites and organics. On the other hand, the external part (dark crust – DC) of these samples mainly presents primary-sequence mineralogy combined with some secondary alteration minerals such as olivine, feldspar, pyroxene, amorphous silica, and Fe-oxide. Raman spectroscopy detected other minerals not yet reported on these samples like barite, celestine and lepidocrocite. Also, the different chemometric and calibration methods for Raman spectroscopy in elemental composition, mineral classification and structural characterization has been successfully applied.From the astrobiological perspective, the research was also complemented with comparisons to other similar samples from terrestrial analogs. The main consideration was taking into account the proposed hypothesis regarding the potential behavior of the pumice as a substrate for the evolution of life. Furthermore, the detailed analysis from La Restinga eruption is coherent with the mineral phases and processes discussed from previous literature. The white internal part fulfills the conditions to work as an organic reservoir, confirmed by the detection of organic matter and selected minerals that could be used as energy sources for bacterial communities. The external layers of the samples work as a shielding layer to protect the organics from decay in extreme conditions. Finally, here we have demonstrated that the characteristics and advantages of Raman spectroscopy could help to assess and understand the possible biogenicity and alteration processes of any geological sample to be found on Mars.

Absence of ferromagnetism in transition metal (Co, Ni and Cu) doped ZnO films

Structural, optical and magnetic properties of oriented Zn0.95TM0.05O (TM = Co, Ni, Cu) films prepared on amorphous quartz substrate using RF magnetron sputtering have been studied. X-ray diffraction patterns show that all films are single phase and are preferably oriented in (002) direction. An analysis of transmission spectra shows that the optical band gap is reduced for all doped ZnO films with respect to that of bulk ZnO single crystal. With increase in thickness of Cu doped ZnO films, the band gap reduces further (3.00 eV for 200 nm film and 2.86 eV for 400 nm film). A strong absorption is observed at 665 nm for Co doped ZnO film due to transitions of tetrahedrally coordinated Co2+ from 4A2 (4F) → 2E (2G). A pre-edge peak observed in TM K-edge XANES spectra of each film confirms that TM ions get substituted in Zn site of ZnO hexagonal wurtzite structure. No room temperature ferromagnetism is observed in any of doped films.

MoS2-OH Bilayer-Mediated Growth of Inch-Sized Monolayer MoS2 on Arbitrary Substrates.

Due to remarkable electronic property, optical transparency, and mechanical flexibility, monolayer molybdenum disulfide (MoS2) has been demonstrated to be promising for electronic and optoelectronic devices. To date, the growth of high-quality and large-scale monolayer MoS2 has been one of the main challenges for practical applications. Here we present a MoS2-OH bilayer-mediated method that can fabricate inch-sized monolayer MoS2 on arbitrary substrates. This approach relies on a layer of hydroxide groups (-OH) that are preferentially attached to the (001) surface of MoS2 to form a MoS2-OH bilayer structure for growth of large-area monolayer MoS2 during the growth process. Specifically, the hydroxide layer impedes vertical growth of MoS2 layers along the [001] zone axis, promoting the monolayer growth of MoS2, constrains growth of the MoS2 monolayer only in the lateral direction into larger area, and effectively reduces sulfur vacancies and defects according to density functional theory calculations. Finally, the hydroxide groups advantageously prevent the MoS2 from interface oxidation in air, rendering high-quality MoS2 monolayers with carrier mobility up to ∼30 cm2 V-1 s-1. Using this approach, inch-sized uniform monolayer MoS2 has been fabricated on the sapphire and mica and high-quality monolayer MoS2 of single-crystalline domains exceeding 200 μm has been grown on various substrates including amorphous SiO2 and quartz and crystalline Si, SiC, Si3N4, and graphene This method provides a new opportunity for the monolayer growth of other two-dimensional transition metal dichalcogenides such as WS2 and MoSe2.

Identification and Characterization of Ti-Spheres (Titanspheres) in Cork Powder Fly Ash

During the treatment of cork powder from different products, for example, the production of cork stoppers, cork powder is generated and used as fuel. However, the combustion of cork powder produces ash, specifically fly ash, which is the object of this study, with the aim of valorization. Previous studies showed that this ash contains, Ti-spheres (hereinafter referred to as titanspheres), among other morphotypes, which may be the most valuable ash component if they have application in ink industry as white pigment. Therefore, cork powder fly ash was sampled in the combustion unit of the champagne stoppers producer “RELVAS II”. Wet and dry sieving trials combined with ultrasound and a polycarboxylate bath were performed to obtain size fractions and concentrations of the titanspheres. A combination of analytical techniques (SEM/EDS, XRD, XRF, ICP-MS, reflected light microscopy, and Raman microspectroscopy) was used to characterize the bulk ash, size fractions, and, in particular, titanspheres. It was concluded that dry sieving is not an efficient method for cork powder fly ash size fractionating. However, with a combination of wet sieving, ultrasound, a polycarboxylate solution and acid reflux, it was possible to obtain a < 25 µm concentrate that mostly comprised amorphous aluminosilicate material, quartz, and titanspheres. The titanspheres in this concentrate have a 15–25 µm diameter, and the phases determined by XRD include rutile, perovskite and priderite.

Pollution from uncontrolled coal fires: Continuous gaseous emissions and nanoparticles from coal mines

In this investigation, the coal fires in different Colombian coal mines were studied using advanced electron beam and X-ray diffraction techniques. The results were compared with information from high-resolution transmission electron microscopy (HR-TEM) equipped with a dispersive X-ray detector (EDS). Amorphous phases, salammoniac, anatase, muscovite, goethite, jarosite, calcite, gypsum, kaolinite, illite, and quartz are the dominant mineral matter constituents in almost all of the coal fires, with minute quantities of native sulfur, magnetite, siderite, pyrite, pickeringite, epsomite, hexahydrite, halotrichite being present in around half of the investigated coal fire samples. Other minerals that are present in some particular samples are chlorite, ankerite, and dolomite. Fe-sulfides were also detected particularly in the pyrite-bearing coal fires, possibly indicating oxidation of the Fe-sulfides occurring with coal fires. Exhaust discharge data indicate an overall trend of reducing carbon dioxide (CO2) and carbon monoxide (CO) releases (between 1.5 and 34%) from the coal fires. This is the first report on Colombian coal fires, which would be important for different perspectives of the research in the area.

Pyrite thin films on amorphous substrates: Interaction with the substrate and doping effects

Recent published literature dealing with FeS2 pyrite (thin films and single crystals) faces a few and relevant issues: the low photovoltage presented by pyrite (mainly related to the singular nature of its surface), the not yet clearly defined way of making available n and p type reliable samples and the relevance of their stoichiometry. To address the second and third issues, Fe thin films, Ti/Fe and Co/Fe bilayers deposited on sodalime glass and amorphous quartz substrates have been sulfurated at different temperatures (Ts) (Ts ≲ 600°C) during 20 h to obtain pyrite thin films. Seebeck coefficient and Hall Effect measurements have been carried out at room temperature with the sulfurated samples. It has been found that sulfurated Ti/Fe on sodalime glass presents a change of the Seebeck coefficient sign (from negative to positive) due to a strong interaction of the Ti layer with the substrate, which is not present in the Ti/Fe samples deposited on amorphous quartz. As a consequence of the interaction, a new TiO2 layer is formed between the sodalime glass substrate and the pyrite layer. Sulfurated Co/Fe bilayers on sodalime glass show a coherent behavior according to the obtained results and previously published works. They all appear to be n-type semiconductors when Ts ≳ 175°C. Non-intentionally doped Fe thin films on sodalime glass behave in a non-conclusive fashion from the point of view of their electrical transport characterization. The Seebeck coefficient (S) of the sulfurated films appear to be S > 0 for all values of Ts. However, the value and sign of the Hall constant behave in a non-reproducible way. Results are discussed on the light of present knowledge of synthetic pyrite thin films growth and doping.

Large Room Temperature Magnetic Moment in Mn${_{1-x}}$ Zn${x}$ Fe2O4 Thin Films for ${x \geq0.4 }$

Mn ${_{1-x}}$ Zn x Fe2O4 ( $0.1\le x\le 0.8$ ) thin films with nanocrystalline grains were deposited on amorphous quartz substrate using pulsed laser ablation technique, at a substrate temperature of 650 °C. For $x\le 0.3$ , the room temperature spontaneous magnetization ( $4\pi M_{S}$ ) of thin films was observed to be lower than the bulk composition. For $x=0.7$ , the room temperature $4\pi M_{S}$ value (~6.1 kG) is 7.5 times the bulk value for same x. This value is only 1.4 times of the bulk at 10 K, signifying a large enhancement in the exchange constant for thin films. The exchange stiffness constant (D) values were evaluated by fitting the $4\pi M_{S}$ data to the Bloch equation. The D values of thin films were always higher than that of the bulk. This result can be explained on the basis of occupancy of nonmagnetic Zn2+ on both the tetrahedral (A) and octahedral (B) sites. This is unlike in the bulk, where all the Zn2+ ions occupy only A site.

Mechanical Properties of Build-Up Layers on Failed Ceramic Roller

The paper describes degradation process of ceramic rollers. Rollers behavior under mechanical and thermal load was evaluated using available methods like XRD, instrumented hardness measurement and compressive strength. The influence of residual stresses was also discussed. The first phase during the degradation crystalize from amorphous silica tridymite, cristobalite and quartz, then due to the contact and pressure of the steel strip to the surface roller iron diffuses and forms fayalite. Measured values of compression strength of roller of 55-61 MPa agree with producer documentation declared minimal values. Hardness and Young´s modulus of buildup phases identified from surface into depth were determined. Wüstite was present up to 100 mm, with hardness 6±1 GPa, Young´s modulus 75±6 GPa, fayalite, cristobalite, up to 500 mm, with hardness 5.4±0.6 GPa, Young´s modulus 51±2 GPa, tridymite over 500 mm, with the hardness 7±4 GPa and Young´s modulus 58±25 GPa.

Bulk transport properties of bismuth selenide thin films grown by magnetron sputtering approaching the two-dimensional limit

Transport properties of topological insulator Bi2Se3 thin films are investigated with an emphasis on understanding finite-size effects as the two-dimensional limit is approached. Ultra-smooth, (000l)-orientated Bi2Se3 thin-films fabricated using radio-frequency magnetron sputtering reveal disproportionately large changes in bulk resistivity and Hall mobility below six quintuple layers (QL). We correlate such changes to the bulk (other than surface) electronic structure where a bandgap enlargement is observed below six QL in optical absorption spectroscopy measurements. This effect is strongest at the three and two quintuple layers that show the largest changes in bandgap. Temperature dependent transport measurements reveal the effect of disorder from substrate and high carrier concentration. Films on sapphire substrate demonstrate better transport properties compared to amorphous quartz. While temperature dependence of bulk resistivity is both thickness and substrate sensitive, the temperature dependence of Hall coefficient is determined only by the carrier concentration in films. Our work highlights the influence of the bulk electronic structure on the transport properties of few-layer Bi2Se3 which is of interest in the applied areas of optoelectronics, nanoelectronics, and spintronics.

The use of single-crystal cuvettes with the properties of an optical shutter in X-ray diffractometers

The atomic structure of substances can be studied using X-ray diffraction methods. X-ray diffractometers contains X-ray source and goniometer with a detector of scattered radiation. A sample holder (a cuvette) with the material under study is placed in the center of the goniometer. The diffraction spectrum which represents the structure of the sample under study is recorded upon angular scanning of the sample and detector. Study of crystalline powders, amorphous substances, nanocrystalline and partially crystalline objects is often based on the Bragg-Brentano scheme (θ – 2θ-scanning) with divergent X-ray beams irradiating the entire sample surface. Scattered radiation from the cuvette can also enter the detector and affect the recorded diffraction spectrum. The aforementioned distortion is rather weak for polycrystalline samples due to strong intensity of crystalline reflections. However, when studying amorphous substances, nanocrystalline and partially crystalline objects, contribution of the scattered radiation can be compared with the radiation from the sample and thus interfere with an unambiguous determination of the sample structure. The results of using standard cuvettes for X-ray diffractometers D500, D5000 (Siemens), D8 ADVANCE (Bruker) and DRON are analyzed with a special attention paid to distortion of X-ray spectra attributed to the use of cuvettes made of plastic or amorphous quartz when studying amorphous, nanocrystalline and partially crystalline samples. Special cuvettes, being a kind of optical shutters for background scattering, which do not distort the diffraction spectra of the objects under study are developed: single crystal plates of a special orientation with cylindrical cavities for the samples. The advantages of a single-crystal silicon cuvette compared to plastic cuvette usually supplied for D500 diffractometer are estimated when studying an amorphous sample.

Laser Source Influence on the Preferential Growth and the Inversion Degree in Pulsed Laser CoFe2O4 Films

A comparative study between cobalt ferrite films deposited by pulsed laser deposition as a function of the laser sources, 355 nm (Nd:YAG) and 248 nm (KrF excimer), on amorphous quartz (AQ) and -oriented silicon wafer (SW) at different temperatures (650–800 ∘C) is presented. Also, a quantitative estimation of the preferential crystalline growth orientation as laser source function was made by means of Lotgering factor and Harris texture coefficient, which were obtained from XRD patterns. The inversion degree in spinel-type structure for cobalt ferrite films was calculated through a deconvolution in Raman spectra, where the band A1g vibrating modes in tetrahedral sites were associated with Fe and Co sites (687 and 611 cm−1, respectively). Additionally, saturation magnetization was also calculated from the inversion degree obtained from deconvolution of the Raman spectra in CoFe2O4 films, being compared with experimental results, which is in a good agreement with cobalt ferrite bulk, and we also correlated the preferential growth and the particle size with increment of the coercive field.

Study of short range structure of amorphous Silica from PDF using Ag radiation in laboratory XRD system, RAMAN and NEXAFS

At present synchrotron and neutron sources are the preferred choices for the Pair Distribution Function (PDF) analysis, but there is a need to explore PDF in a laboratory XRD system for quick feedback about the short range structure of the amorphous materials. Present work considered both crystalline (quartz) and amorphous silica to study the structural differences in silica by PDF analysis using Ag radiations in laboratory XRD. The structural information about short range ordering of the oxygen (O) atoms around silicon (Si) atoms as obtained by the PDF were compared with the results as obtained by Near Edge X-ray Absorption Fine Structure (NEXAFS) and RAMAN experiments. The PDF studies showed that the amorphous silica possessed short range periodicity within the basic unit of (SiO4)4− tetrahedra with a SiO & OO distance are of about 1.622 Å and 2.713 Å while the short range as well as long range ordered structure present in quartz with SiO & OO distance are 1.562 Å and 2.661 Å respectively. Raman spectra showed some asymmetry in amorphous silica which corresponds to the defects present in the lattice and thus forming the n-fold ring structure with Si and O resulting in the wide variation of bridging bond angle SiOSi in amorphous silica. NEXAFS studies revealed the structure of amorphous silica and quartz in the intermediate range (3–5 Å) at the Si L and O K edges. The structural information about short range ordering of the O around Si atoms as obtained by these methods were found to be in good match with the results as obtained by PDF, suggesting this technique may be used as a screening tool for routine PDF studies of amorphous materials.

Optical response of thin amorphous films to infrared radiation

We briefly review the electrical-optical response of materials to radiative forcing within the formalism of the Kramers-Kronig relations. A commensurate set of criteria is described that must be met by any frequency-domain model representing the time-domain response of a real (i.e., physically possible) material. The criteria are applied to the Brendel-Bormann (BB) oscillator, a model that was originally introduced for its fidelity at reproducing the non-Lorentzian peak broadening experimentally observed in the infrared absorption by thin amorphous films but has since been used for many other common materials. We show that the BB model fails to satisfy the established physical criteria. Taking an alternative approach to the model derivation, a physically consistent model is proposed. This model provides the appropriate line-shape broadening for modeling the infrared optical response of thin amorphous films while adhering strictly to the Kramers-Kronig criteria. Experimental data for amorphous alumina (${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$) and amorphous quartz silica (${\mathrm{SiO}}_{2}$) are used to obtain model parametrizations for both the noncausal BB model and the proposed causal model. The proposed model satisfies consistency criteria required by the underlying physics and reproduces the experimental data with better fidelity (and often with fewer parameters) than previously proposed permittivity models.

The braunite (3Mn2O3·MnSiO3)-rich mineralization in the metasedimentary succession from southern Apennines (Italy): Genesis constraints

A massive Mn-bearing mineralization, extensively exploited until the 70 s, locally occurs in the metasedimentary succession of the southern Apennines (at Mormanno site, Calabria-Lucania border, Italy). The mineralization mainly consists of three types distinguished by the relative percentages of the principal mineral phases: braunite, quartz, Mn oxi-hydroxides and Mn-rich epidote (piemontite). Petrographic observations revealed that the ore underwent medium- to high-grade metamorphism that was responsible of the growth of braunite at the expense of “primary” amorphous Mn oxi-hydroxides and quartz. During metamorphism, piemontite also formed where altered phyllosilicates are present in addition to braunite and quartz, suggesting that the aluminosilicates were source of Al necessary to the epidote crystallization. The most important geochemical features of the ore are high Mn contents (up to 71.6 wt% of MnO), low concentrations of transitional elements (Co + Ni+Cu + Zn < 0.1 wt%), high Ba (up to 4455 ppm) and variable total REEs (14.7 < ΣREEs < 329.7 ppm) contents. These are the typical characteristics of the ocean-floor hydrothermal Mn deposits, similarly to what observed in braunite ores occurring in the Alps and northern Apennines. The high LREE/HREE fractionations and the negative Ce and Eu anomalies characterizing the studied ore, suggest the mineralizing fluid was formed by a mixing solution consisting of a Mn-rich hydrothermal fluid and seawater, which attained the ideal condition for the ore precipitation in a distal oceanic area, far from the submarine hydrothermal vent.