| 1. |
- Bortoluzzi, Marco, et al.
(författare)
-
Luminescent lanthanide complexes with phosphoramide and arylphosphonic diamide ligands
- 2020
-
Ingår i: Chemické zvesti. - : Springer. - 0366-6352 .- 1336-9075. ; 74:11, s. 3693-3704
-
Tidskriftsartikel (refereegranskat)abstract
- The sensitization of Eu(III) luminescence by the phosphoramide and arylphosphonic diamide ligands OP(NMe2)2Ind, OP(NMe2)2Cbz, OP(NMe2)2Ph, OP(NMe2)2(1-Naph) and OP(NMe2)2(2-Naph) (Ind = indol-1-yl; Ph = phenyl; Cbz = carbazol-9-yl; 1-Naph = naphtalen-1-yl; 2-Naph = naphtalen-2-yl) was verified by coordination to the [Eu(NO3)3] metal fragment. The emission spectra of the corresponding complexes showed only the 5D0 → 7FJ transitions of the metal centre, with the exception of the carbazolyl derivative. Some of the ligands were also able to sensitize Tb(III) luminescence, in agreement with the triplet state energies estimated from the phosphorescence spectra of the analogous Gd(III) nitrates. On the basis of the photoluminescence results achieved using nitrate as ancillary ligand, heptacoordinate Eu(III) complexes having general formula [Eu(β-dike)3L] (β-dike = dibenzoylmethanate, tenoyltrifluoroacetonate; L = phosphoramide or arylphosphomic diamide ligand) were prepared and characterized. All the complexes exhibited bright red emission upon excitation with near-UV and violet-blue light, with intrinsic quantum yields ranging between 18 and 36%.
|
|
| 2. |
- Afanasiev, Sergey V., et al.
(författare)
-
Experimental apparatus to study crystal channeling in an external SPS beamline
- 2007
-
Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6634
-
Tidskriftsartikel (refereegranskat)abstract
- For the new generation of high intensity hadronic machines as, for instance, LHC, halo collimation is a necessary issue for the accelerator to operate at the highest possible luminosity and to prevent the damage of superconductor magnets.1 We propose an experiment aimed to systematic study of the channeling phenomenology and of the newly observed "volume reflection" effect. This experiment will be performed for an external SPS beamline and will make use of a primary proton beam with 400 GeV/c momentum and very small (∼ 3 μrad) divergence. The advantage of a proposed experiment is precise tracking of particles that interacted with a crystal, so that to determine the single-pass efficiency for all the processes involved. For this purpose, a telescope equipped with high-resolution silicon microstrip detectors will be used. New generation silicon crystals and an extra-precise goniometer are mandatory issues. Main goal of the experiment is to get the precise information on channeling of relativistic particles and, ultimately, on the feasibility of such technique for halo collimation at LHC. In this contribution we review the status of the setting-up of experimental apparatus and its future development in sight of the planned run in September 2006.
|
|
| 3. |
- Boscarino, Diego, et al.
(författare)
-
Deposition of silica-silver nanocomposites by magnetron cosputtering
- 2005
-
Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 23:1, s. 11-19
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films have been grown on silicon and silica substrates by cosputtering of silica and silver in Ar, Ar+2.5% O2, and Ar+5% O2 gas mixtures. Rutherford backscattering spectrometry showed that the films have Ag atomic fractions xAg in the range of ∼1 to ∼10 at. %, and, by valence considerations, that the fraction of oxidized Ag in the films deposited in presence of oxygen is limited. Transmission electron microscopy images revealed the presence of Ag nanoclusters, with a mean size diameter not larger than 5 nm. The clusters are preferentially arranged along columns. It is suggested that the columns are regions with diameter in the nanometer range in which the density of the dielectric matrix is lower, thus favoring the formation of metal clusters. In presence of O2, the clusters were observed to have a more regular spherical shape. The optical absorption spectra of films grown in presence of O2 are distinguished from those grown in Ar by specific features, which are attributed to oxidation at the cluster surface. © 2005 American Vacuum Society.
|
|
| 4. |
- Maggioni, Gianluigi, et al.
(författare)
-
Effects of heat treatments on the properties of copper phthalocyanine films deposited by glow-discharge-induced sublimation
- 2006
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 18:17, s. 4195-4204
-
Tidskriftsartikel (refereegranskat)abstract
- Copper phthalocyanine films have been deposited by glow-discharge-induced sublimation. The films have undergone postdeposition heat treatments in air at 250 and 290°C for different times, ranging from 30 min to 14 h. The properties of as-deposited and heated films have been investigated by different techniques in order to determine the effects of heat treatments on the film properties. Fourier transform infrared analysis and UV-visible optical absorption analysis point out a gradual evolution of the film structure from a mixture of α and β polymorphs to the only β polymorph in the sample heated at 290°C for 14 h. A pronounced decrease of carbon and nitrogen atomic percentages against an oxygen increase in the heated films are shown by ion beam analyses (Rutherford backscattering spectrometry and nuclear reaction analysis) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy and XPS indicate that part of the copper phthalocyanine molecules decompose during heat treatments and the formation of copper oxide takes place. The replacement of copper phthalocyanine by copper oxide in the heated films accounts for the change of their surface electrical conductance and of their electrical response to NO 2. © 2006 American Chemical Society.
|
|
| 5. |
- Maggioni, Gianluigi, et al.
(författare)
-
Production and characterization of thin film materials for indoor optical gas sensing applications
- 2006
-
Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 41:1, s. 531-534
-
Tidskriftsartikel (refereegranskat)abstract
- Pure and Nile-Red-doped polyimide and porphyrin films have been deposited and their optical response to different organic vapours has been tested. Polyimide films were obtained by spin coating a solution containing 4, 4'-4, 4'-(hexafluoroisopropylidene) diphthalic anhydride and 2, 3, 5, 6-tetramethyl-1, 4-phenylenediamine. Free, cobalt and iron chloride 5, 10, 15, 20 meso-tetraphenyl porphyrin films were deposited by spin coating and by high vacuum evaporation. Exposure to water, ethanol and isopropanol vapours produce reversible changes of the fluorescence features of both pure and doped polyimide films. Exposure to methanol, ethanol and isopropanol vapours gives rise to changes of the optical absorption of porphyrin films. The results of the optical measurements point out that the synthesized films can be used for the detection of volatile organic compounds. © 2006 IOP Publishing Ltd.
|
|
| 6. |
- Scandale, Walter, et al.
(författare)
-
Apparatus to study crystal channeling and volume reflection phenomena at the SPS H8 beamline
- 2008
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 79:2
-
Tidskriftsartikel (refereegranskat)abstract
- A high performance apparatus has been designed and built by the H8-RD22 collaboration for the study of channeling and volume reflection phenomena in the interaction of 400 GeVc protons with bent silicon crystals, during the 2006 data taking in the external beamline H8 of the CERN SPS. High-quality silicon short crystals were bent by either anticlastic or quasimosaic effects. Alignment with the highly parallel (8 μrad divergence) proton beam was guaranteed through a submicroradian goniometric system equipped with both rotational and translational stages. Particle tracking was possible by a series of silicon microstrip detectors with high-resolution and a parallel plate gas chamber, triggered by various scintillating detectors located along the beamline. Experimental observation of volume reflection with 400 GeVc protons proved true with a deflection angle of (10.4±0.5) μrad with respect to the unperturbed beam, with a silicon crystal whose (111) planes were parallel to the beam. © 2008 American Institute of Physics.
|
|
| 7. |
- Scandale, Walter, et al.
(författare)
-
Deflection of 400GeV/c proton beam with bent silicon crystals at the CERN Super Proton Synchrotron
- 2008
-
Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 11:6
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a detailed study of the deflection phenomena of a 400GeV/c proton beam impinging on a new generation of bent silicon crystals; the tests have been performed at the CERN Super Proton Synchrotron H8 beam line. Channeling and volume reflection angles are measured with an extremely precise goniometer and with high resolution silicon microstrip detectors. Volume reflection has been observed and measured for the first time at this energy, with a single-pass efficiency as large as 98%, in good agreement with the simulation results. This efficiency makes volume reflection a possible candidate for collimation with bent crystals at the CERN Large Hadron Collider. © 2008 The American Physical Society.
|
|
| 8. |
- Scandale, Walter, et al.
(författare)
-
Double volume reflection of a proton beam by a sequence of two bent crystals
- 2008
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 658:4, s. 109-111
-
Tidskriftsartikel (refereegranskat)abstract
- The doubling of the angle of beam deflection due to volume reflection of protons by a sequence of two bent silicon crystals was experimentally observed at the 400 GeV proton beam of the CERN SPS. A similar sequence of short bent crystals can be used as an efficient primary collimator for the Large Hadron Collider.
|
|
| 9. |
|
|
| 10. |
- Scrivanti, Alberto, et al.
(författare)
-
Luminescent europium(III) complexes containing an electron rich 1,2,3-triazolyl-pyridyl ligand
- 2018
-
Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 42:13, s. 11064-11072
-
Tidskriftsartikel (refereegranskat)abstract
- An improved synthesis of the electron-rich N,N-chelating ligand, 2-(1-t-butyl-1H-1,2,3-triazol-4-yl)pyridine (L), has been developed by coupling t-butyl-azide with ethynylpyridine in the presence of a Cu(I) catalyst. L has been employed in the preparation of lanthanide coordination compounds having formulae [Ln(κ2-NO3)3L2] and [Eu(dbm)3L] (Ln = Eu, Tb; dbm = dibenzoylmethanate). The molecular structure of [Eu(dbm)3L] has been determined by X-ray diffraction studies. All the new complexes exhibit good photoluminescence properties and [Eu(dbm)3L] has been successfully used as the dopant for the preparation of luminescent plastic materials.
|
|
| 11. |
- Vomiero, Alberto, et al.
(författare)
-
Effects of thermal annealing on the structural properties of sputtered W-Si-N diffusion barriers
- 2004
-
Ingår i: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 7:4-6 SPEC. ISS., s. 325-330
-
Tidskriftsartikel (refereegranskat)abstract
- W-Si-N thin films were deposited via rf-magnetron sputtering from a W 5Si3 target in Ar/N2 reactive gas mixtures over a large range of compositions, obtained by varying the partial flow of nitrogen within the reaction chamber. The samples of each set were then thermally annealed in vacuum at different temperatures up to 980°C. Film composition was determined by Rutherford backscattering spectrometry (RBS), surface film morphology by scanning electron microscopy (SEM), micro-structure by transmission electron microscopy (TEM), vibrational properties by FT-IR absorption and Raman scattering spectroscopy, and electrical resistivity by four-point probe measurements. Independently of the deposition conditions, all the as-deposited films have an amorphous structure, while their composition varies, showing an increase of Si/W ratio from 0.1 up to 0.55 when the nitrogen concentration in the films increases from 0 to 60 at%. Thermal treatments in vacuum induce an important loss of nitrogen in the nitrogen-rich samples, especially at temperatures higher than 600°C. Samples with high nitrogen content preserve their amorphous structure even at the highest annealing temperature, despite the chemical bonding ordering observed by means of FTIR measurements. Raman spectroscopy of as-deposited films rich in nitrogen suggests the presence of an important amorphous silicon nitride component, but fails to detect any structural rearrangement either within the composite matrix of film or within silicon nitride component. Segregation of metallic tungsten was detected by TEM in the annealed sample with lowest nitrogen content (W 58Si21N21). Finally, the resistivity of the films increases with the N content, while the loss of nitrogen accompanies the decrease of resistivity especially of samples with high nitrogen content. © 2004 Elsevier Ltd. All rights reserved.
|
|
| 12. |
- Vomiero, Alberto, et al.
(författare)
-
Structural and functional characterization of W-Si-N sputtered thin films for copper metallizations
- 2004
-
Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 812, s. 153-158
-
Tidskriftsartikel (refereegranskat)abstract
- Ternary W-Si-N thin films have been reactively sputter-deposited from a W5Si3 target at different nitrogen partial pressures. The composition has been determined by 2.2 MeV 4He+ beam, the structure by x-ray diffraction and transmission electron microscope, the chemical bonds by Fourier transform - infrared spectroscopy and the surface morphology by scanning electron microscopy. Electrical resistivity was measured by four point probe technique on the as grown films. The film as-deposited is amorphous with the Si/W ratio increasing from about 0.1 up to 0.55 with the nitrogen content going from 0 to 60 at%. The heat treatments up to 980°C induce a loss of nitrogen in the nitrogen rich samples. Segregation of metallic tungsten occurs in the sample with low nitrogen content (W58Si 21N21). Samples with high nitrogen content preserve the amorphous structure, despite of the precipitation of a more ordered phase inferred by FT-IR absorbance spectrum of the layer treated at highest temperature. The surface morphology depends upon the nitrogen content; the loss of nitrogen induces the formation of blistering and in the most nitrogen rich sample the formation of holes. Electrical resistivity preliminary results on the as grown layers range between 500 and 4750 μΩcm passing from the lowest to the highest N concentration.
|
|
| 13. |
- Vomiero, Alberto, et al.
(författare)
-
Structure and morphology of surface of silicon crystals to be applied for channeling at relativistic energies
- 2006
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 249:1-2 SPEC. ISS., s. 903-906
-
Tidskriftsartikel (refereegranskat)abstract
- Bent crystals can be successfully applied for extraction/collimation of relativistic particles. A crucial feature to obtain high extraction efficiencies is the treatment of the surfaces being encountered by the beam, since mechanical operations induce considerable lattice imperfections. In order to remove the superficial damaged layer a planar etching can be applied on the surface exposed to the beam. This work presents a systematic study of the morphology and the crystalline perfection of the surface of the samples that have been used in accelerators with high efficiency. Crystals with different surface treatments have been investigated. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied on the characterisation of surface morphology. Low energy backscattering channeling of 2-MeV α particles or protons was used as a probe for the crystalline structure. The presence of a superficial damaged layer in the samples just after mechanical treatment was unveiled, while, in contrast, chemical etching leaves a surface with high crystalline perfection that can be related to the record efficiency. © 2006 Elsevier B.V. All rights reserved.
|
|
| 14. |
- Adeel, Muhammad, et al.
(författare)
-
2D metal azolate framework as nanozyme for amperometric detection of glucose at physiological pH and alkaline medium
- 2021
-
Ingår i: Microchimica Acta. - : Springer. - 0026-3672 .- 1436-5073. ; 188:3
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis of Co-based two-dimensional (2D) metal azolate framework nanosheets (MAF-5-CoII NS) is described using a simple hydrothermal method. The product was isostructural to MAF-5 (Zn). The as-prepared MAF-5-CoII NS exhibited high surface area (1155 m2/g), purity, and crystallinity. The MAF-5-CoII NS–modified screen-printed electrode (MAF-5-CoII NS/SPE) was used for nonenzymatic detection of glucose in diluted human blood plasma (BP) samples with phosphate buffer saline (PBS, pH 7.4) and NaOH (0.1 M, pH 13.0) solutions. The MAF-5-CoII NS nanozyme displayed good redox activity in both neutral and alkaline media with the formation of CoII/CoIII redox pair, which induced the catalytic oxidation of glucose. Under the optimized detection potential, the sensor presented a chronoamperometric current response for the oxidation of glucose with two wide concentration ranges in PBS-diluted (62.80 to 180 μM and 305 to 8055 μM) and NaOH-diluted (58.90 to 117.6 μM and 180 to 10,055 μM) BP samples, which were within the limit of blood glucose levels of diabetic patients before (4.4–7.2 mM) and after (10 mM) meals (recommended by the American Diabetes Association). The sensor has a limit of detection of ca. 0.25 and 0.05 μM, respectively, and maximum sensitivity of ca. 36.55 and 1361.65 mA/cm2/mM, respectively, in PBS- and NaOH-diluted BP samples. The sensor also displayed excellent stability in the neutral and alkaline media due to the existence of hydrophobic linkers (2-ethyl imidazole) in the MAF-5-CoII NS, good repeatability and reproducibility, and interference-free signals. Thus, MAF-5-CoII NS is a promising nanozyme for the development of the disposable type of sensor for glucose detection in human body fluids.
|
|
| 15. |
- Aftab, Umair, et al.
(författare)
-
Two step synthesis of TiO2–Co3O4 composite for efficient oxygen evolution reaction
- 2021
-
Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 46:13, s. 9110-9122
-
Tidskriftsartikel (refereegranskat)abstract
- For an active hydrogen gas generation through water dissociation, the sluggish oxygen evolution reaction (OER) kinetics due to large overpotential is a main hindrance. Herein, a simple approach is used to produce composite material based on TiO2/Co3O4 for efficient OER and overpotential is linearly reduced with increasing amount of TiO2. The scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) investigations reveal the wire like morphology of composite materials, formed by the self-assembly of nanoparticles. The titania nanoparticles were homogenously distributed on the larger Co3O4 nanoparticles. The powder x-ray diffraction revealed a tetragonal phase of TiO2 and the cubic phase of Co3O4 in the composite materials. Composite samples with increasing TiO2 content were obtained (18%, 33%, 41% and 65% wt.). Among the composites, cobalt oxide-titanium oxide with the highest TiO2 content (CT-20) possesses the lowest overpotential for OER with a Tafel slope of 60 mV dec−1 and an exchange current density of 2.98 × 10−3A/cm2. The CT-20 is highly durable for 45 h at different current densities of 10, 20 and 30 mA/cm2. Electrochemical impedance spectroscopy (EIS) confirmed the fast charge transport for the CT-20 sample, which potentially accelerated the OER kinetics. These results based on a two-step methodology for the synthesis of TiO2/Co3O4 material can be useful and interesting for various energy storage and energy conversion systems.
|
|
| 16. |
- Ahdikari, Rajesh, et al.
(författare)
-
High Efficiency, Pt-free Photoelectrochemical Cells for Solar Hydrogen Generation based on “Giant” Quantum Dots
- 2016
-
Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 27, s. 265-274
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum dot (QD) sensitized TiO2 is considered as a highly promising photoanode material for photoelectrochemical (PEC) solar hydrogen production. However, due to its limited stability, the photoanode suffers from degradation of its long-term PEC performance. Here, we report the design and characterization of a high-efficiency and long-term stable Pt-free PEC cell. The photoanode is composed of a mesoporous TiO2 nanoparticle film sensitized with “giant” core@shell QDs for PEC solar hydrogen generation. The thick shell enhances light absorption in the visible range, increases the stability of the QDs and does not inhibit charge separation, injection and transport, needed for proper operation of the device. We prepared thin films of Cu2S nanoflakes through a simple and reproducible procedure, and used them as counter-electrodes replacing the standard Pt film, resulting in equivalent performances of the PEC cell. We obtained an unprecedented photocurrent density (~10 mA/cm2) for “giant” QDs based PEC devices (and corresponding H2 generation) and a very promising stability, indicating that the proposed cell architecture is a good candidate for long-term stable QD-based PEC solar hydrogen generation.
|
|
| 17. |
- Akbar, Kamran, et al.
(författare)
-
Carbon Dots for Photocatalytic Degradation of Aqueous Pollutants : Recent Advancements
- 2021
-
Ingår i: Advanced Optical Materials. - : John Wiley & Sons. - 2162-7568 .- 2195-1071. ; 9:17
-
Forskningsöversikt (refereegranskat)abstract
- The immense progress of humanity on the technological, domestic, and industrial fronts comes at the cost of polluting the planet. Aquatic pollution is particularly dangerous since all life forms are directly linked to it. Each year tons of industrial and domestic pollutants make their way into aqueous systems. Efficient removal/degradation of these pollutants is of prime importance for the sustainable future. Among many technologies, photodegradation is an emerging and promising method for the successful removal of aqueous pollutants since it is powered by abundant solar light. The last decade had shown that carbon dots are among the most promising materials that can be utilized as an efficient tool to derive various solar-driven chemical reactions. Carbon dots possess unique photophysical and chemical properties such as light-harvesting over a broad-spectrum region, upconversion photoluminescence, photosensitizers, chemical inertness, and bivalent redox character, etc. The ease of synthesis of carbon dots at low cost also contributes hugely to their utilizations as an efficient photocatalyst for the degradation of aqueous pollutants. This review summarizes the recent progress made in the field of photodegradation of aqueous pollutants with the aid of carbon dots and their hybrids, highlighting the critical role carbon dots can play in the field.
|
|
| 18. |
- Alberoni, Chiara, et al.
(författare)
-
Ceria doping boosts methylene blue photodegradation in titania nanostructures
- 2021
-
Ingår i: Materials Chemistry Frontiers. - : Royal Society of Chemistry. - 2052-1537. ; 5:11, s. 4138-4152
-
Tidskriftsartikel (refereegranskat)abstract
- Ceria-doped titania photocatalysts (ceria loading 0.25–5.0 wt%) were synthesized by hydrothermal methods for water remediation. Nanotubes (CeTNTx) and nanoparticles (CeTNPx) were obtained. Ceria doping was applied to tune the electronic properties of nanostructured titania, boosting its photocatalytic activity. CeTNT nanostructures contained anatase as the only titania phase, whereas the CeTNP series consisted of both anatase and rutile polymorphs. The Ce addition induced a decrease in the energy gap, allowing enhancement of visible light harvesting. The photodegradation of methylene blue, MB, in aqueous solution was chosen to study the influence of the morphology and the ceria loading on the photocatalytic response, under UV and solar light. Both CeO2–TiO2 nanoparticles and nanotubes were found to be very active under UV light. The highest MB degradation rates were obtained for the 0.25 wt% CeO2 doping, for both nanotubes and nanoparticles (0.123 and 0.146 min−1, respectively), able to photodegrade completely the dye after 120 min. The two samples are stable after a 3-cycle reusability test. The photo-response under simulated solar light confirmed that doping titania with ceria allows harvesting visible light absorption, enhancing its photoactivity. A maximum efficiency of 85% under simulated sunlight at a degradation rate of 0.054 min−1 was obtained. Transient photoluminescence confirmed that MB acts as a charge scavenger for the composite system. These results pointed out ceria-doped titania nanostructures as a promising class of photocatalysts for the degradation of dyes and other hazardous organic compounds in wastewater.
|
|
| 19. |
- Alvi, Sajid Ali, et al.
(författare)
-
Adaptive nanolaminate coating by atomic layer deposition
- 2019
-
Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 692
-
Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) was used to deposit ZnO/Al2O3/V2O5 nanolaminate coatings to demonstrate a coating system with temperature adaptive frictional behaviour. The nanolaminate coating exhibited excellent conformity and crack-free coating of thickness 110 nm over Inconel 718 substrate. The ALD trilayer coating showed a hardness and elastic modulus of 12 GPa and 193 GPa, respectively. High-temperature tribology of the nanolaminate trilayer was tested against steel ball in dry sliding condition at 25 °C (room temperature, RT), 200 °C, 300 °C, and 400 °C. It was found that the nanolaminate coating showed a low coefficient of friction (COF) and wear rate at RT and 300 °C. The trilayer coating was found intact and stable at all temperatures during the friction tests. The adaptability of nanolaminate coating with the temperature was verified by performing the cyclic friction test at 300 °C and RT. The low COF and wear rate had been attributed to the (100) and (002) basal plane sliding of ZnO top layer, and the interlayer sliding of weakly bonded planes parallel to (001) plane in V2O5 bottom layer. Furthermore, even after the removal of ZnO coating during the tribotest, the bottom V2O5 layer coating stabilized the COF and wear rate at RT and 300 °C.
|
|
| 20. |
- Alvi, Sajid, et al.
(författare)
-
Enhanced mechanical, thermal and electrical properties of high‐entropy HfMoNbTaTiVWZr thin film metallic glass and its nitrides
- 2022
-
Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 24:9
-
Tidskriftsartikel (refereegranskat)abstract
- The inception of high-entropy alloy promises to push the boundaries for new alloy design with unprecedented properties. This work reports entropy stabilisation of an octonary refractory, HfMoNbTaTiVWZr, high-entropy thin film metallic glass, and derived nitride films. The thin film metallic glass exhibited exceptional ductility of ≈60% strain without fracture and compression strength of 3 GPa in micro-compression, due to the presence of high density and strength of bonds. The thin film metallic glass shows thermal stability up to 750 °C and resistance to Ar-ion irradiation. Nitriding during film deposition of HfMoNbTaTiVWZr thin film of strong nitride forming refractory elements results in deposition of nanocrystalline nitride films with compressive strength, hardness, and thermal stability of up to 10 GPa, 18.7 GPa, and 950 °C, respectively. The high amount of lattice distortion in the nitride films leads to its insulating behaviour with electrical conductivity as low as 200 S cm−1 in the as-deposited film. The design and exceptional properties of the thin film metallic glass and derived nitride films may open up new avenues of development of bulk metallic glasses and the application of refractory-based high entropy thin films in structural and functional applications.
|
|
| 21. |
- Alvi, Sajid, et al.
(författare)
-
Synthesis and Mechanical Characterization of a CuMoTaWV High-Entropy Film by Magnetron Sputtering
- 2020
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:18, s. 21070-21079
-
Tidskriftsartikel (refereegranskat)abstract
- Development of high-entropy alloy (HEA) films is a promising and cost-effective way to incorporate these materials of superior properties in harsh environments. In this work, a refractory high-entropy alloy (RHEA) film of equimolar CuMoTaWV was deposited on silicon and 304 stainless-steel substrates using DC-magnetron sputtering. A sputtering target was developed by partial sintering of an equimolar powder mixture of Cu, Mo, Ta, W, and V using spark plasma sintering. The target was used to sputter a nanocrystalline RHEA film with a thickness of ∼900 nm and an average grain size of 18 nm. X-ray diffraction of the film revealed a body-centered cubic solid solution with preferred orientation in the (110) directional plane. The nanocrystalline nature of the RHEA film resulted in a hardness of 19 ± 2.3 GPa and an elastic modulus of 259 ± 19.2 GPa. A high compressive strength of 10 ± 0.8 GPa was obtained in nanopillar compression due to solid solution hardening and grain boundary strengthening. The adhesion between the RHEA film and 304 stainless-steel substrates was increased on annealing. For the wear test against the E52100 alloy steel (Grade 25, 700–880 HV) at 1 N load, the RHEA film showed an average coefficient of friction (COF) and wear rate of 0.25 (RT) and 1.5 (300 °C), and 6.4 × 10–6 mm3/N m (RT) and 2.5 × 10–5 mm3/N m (300 °C), respectively. The COF was found to be 2 times lower at RT and wear rate 102 times lower at RT and 300 °C than those of 304 stainless steel. This study may lead to the processing of high-entropy alloy films for large-scale industrial applications.
|
|
| 22. |
- Amin, Sidra, et al.
(författare)
-
A practical non-enzymatic urea sensor based on NiCo 2 O 4 nanoneedles
- 2019
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 9:25, s. 14443-14451
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo 2 O 4 ) nanoneedles. These nanoneedles are used for the first time for highly sensitive determination of urea with the lowest detection limit (1 μM) ever reported for the non-enzymatic approach. The nanoneedles were grown through a simple and low-temperature aqueous chemical method. We characterized the structural and morphological properties of the NiCo 2 O 4 nanoneedles by TEM, SEM, XPS and XRD. The bimetallic nickel cobalt oxide exhibits nanoneedle morphology, which results from the self-assembly of nanoparticles. The NiCo 2 O 4 nanoneedles are exclusively composed of Ni, Co, and O and exhibit a cubic crystalline phase. Cyclic voltammetry was used to study the enhanced electrochemical properties of a NiCo 2 O 4 nanoneedle-modified GCE by overcoming the typical poor conductivity of bare NiO and Co 3 O 4 . The GCE-modified electrode is highly sensitive towards urea, with a linear response (R 2 = 0.99) over the concentration range 0.01-5 mM and with a detection limit of 1.0 μM. The proposed non-enzymatic urea sensor is highly selective even in the presence of common interferents such as glucose, uric acid, and ascorbic acid. This new urea sensor has good viability for urea analysis in urine samples and can represent a significant advancement in the field, owing to the simple and cost-effective fabrication of electrodes, which can be used as a promising analytical tool for urea estimation.
|
|
| 23. |
- Amin, Sidra, et al.
(författare)
-
A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles
- 2019
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 9:25, s. 14443-14451
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo2O4) nanoneedles. These nanoneedles are used for the first time for highly sensitive determination of urea with the lowest detection limit (1 mu M) ever reported for the non-enzymatic approach. The nanoneedles were grown through a simple and low-temperature aqueous chemical method. We characterized the structural and morphological properties of the NiCo2O4 nanoneedles by TEM, SEM, XPS and XRD. The bimetallic nickel cobalt oxide exhibits nanoneedle morphology, which results from the self-assembly of nanoparticles. The NiCo2O4 nanoneedles are exclusively composed of Ni, Co, and O and exhibit a cubic crystalline phase. Cyclic voltammetry was used to study the enhanced electrochemical properties of a NiCo2O4 nanoneedle-modified GCE by overcoming the typical poor conductivity of bare NiO and Co3O4. The GCE-modified electrode is highly sensitive towards urea, with a linear response (R-2 = 0.99) over the concentration range 0.01-5 mM and with a detection limit of 1.0 mu M. The proposed non-enzymatic urea sensor is highly selective even in the presence of common interferents such as glucose, uric acid, and ascorbic acid. This new urea sensor has good viability for urea analysis in urine samples and can represent a significant advancement in the field, owing to the simple and cost-effective fabrication of electrodes, which can be used as a promising analytical tool for urea estimation.
|
|
| 24. |
- Amin, Sidra, et al.
(författare)
-
A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles
- 2019
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 9:25, s. 14443-14451
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo2O4) nanoneedles. These nanoneedles are used for the first time for highly sensitive determination of urea with the lowest detection limit (1 μM) ever reported for the non-enzymatic approach. The nanoneedles were grown through a simple and low-temperature aqueous chemical method. We characterized the structural and morphological properties of the NiCo2O4 nanoneedles by TEM, SEM, XPS and XRD. The bimetallic nickel cobalt oxide exhibits nanoneedle morphology, which results from the self-assembly of nanoparticles. The NiCo2O4 nanoneedles are exclusively composed of Ni, Co, and O and exhibit a cubic crystalline phase. Cyclic voltammetry was used to study the enhanced electrochemical properties of a NiCo2O4 nanoneedle-modified GCE by overcoming the typical poor conductivity of bare NiO and Co3O4. The GCE-modified electrode is highly sensitive towards urea, with a linear response (R2 = 0.99) over the concentration range 0.01–5 mM and with a detection limit of 1.0 μM. The proposed non-enzymatic urea sensor is highly selective even in the presence of common interferents such as glucose, uric acid, and ascorbic acid. This new urea sensor has good viability for urea analysis in urine samples and can represent a significant advancement in the field, owing to the simple and cost-effective fabrication of electrodes, which can be used as a promising analytical tool for urea estimation.
|
|
| 25. |
- Amin, Sidra, et al.
(författare)
-
A sensitive enzyme-free lactic acid sensor based on NiO nanoparticles for practical applications
- 2019
-
Ingår i: Analytical Methods. - : Royal Society of Chemistry. - 1759-9660 .- 1759-9679. ; 11, s. 3578-3583
-
Tidskriftsartikel (refereegranskat)abstract
- A facile and efficient electrochemical sensing platform has been successfully exploited for the first time for the determination of lactic acid using a nickel oxide (NiO) nanoparticle-modified glassy carbon electrode (GCE). Nickel oxide nanoparticles were prepared by a chemical growth method using different quantities of arginine as a soft template. The structural and morphological properties of NiO nanoparticles were characterized by Raman spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cyclic voltammetry (CV) was used to study the electrochemical properties of various samples. The modified electrode is highly sensitive and presents a linear response over a wide range (0.005–5 mM) of lactic acid concentrations in 0.1 M NaOH. The detection limit for the sensor was found to be 5.7 μM, and it exhibits good stability. Furthermore, the sensor shows excellent selectivity in the presence of common interfering species. The lactic acid sensor showed good viability for lactic acid analysis in real samples (milk, yogurt and red wine) and demonstrated significant advancement in sensor technology for practical applications.
|
|
| 26. |
- Amin, Sidra, et al.
(författare)
-
Functional Nickel Oxide Nanostructures for Ethanol Oxidation in Alkaline Media
- 2020
-
Ingår i: Electroanalysis. - : John Wiley & Sons. - 1040-0397 .- 1521-4109. ; 32:5, s. 1052-1059
-
Tidskriftsartikel (refereegranskat)abstract
- Nickel oxide (NiO) nanostructures are employed in the basic medium for the oxidation of ethanol. A variety of NiO nanostructures are synthesized by wet chemical growth method, using different hydroxide (OH−) ion sources, particularly from ammonia, hexamethylenetetramine, urea and sodium hydroxide. The use of urea as (OH−) ion source results in flower‐like NiO structures composed by extremely thin nanowalls (thickness lower than 10 nm,), which demonstrated to be the most active for ethanol oxidation. All the samples exhibit NiO cubic phase, and no other impurity was detected. The cyclic voltammetry (CV) curves of NiO nanostructures were found linear over the concentration range 0.1–3.5 mM (R2=0.99) of ethanol, with the limit of detection estimated to be 0.013 mM for ethanol. The NiO nanostructures exhibit a selective signal towards ethanol oxidation in the presence of different members of alcohol family. The proposed NiO nanostructures showed a significant practicality for the reproducible and sensitive determination of ethanol from brandy, whisky, mixture of brandy and rum, and vodka samples. The nanomaterial was used as a surface modifying agent for the glassy carbon electrode and it showed a stable electro‐oxidation activity for the ethanol for 16 days. These findings indicate that the presented NiO nanomaterial can be applied in place of noble metals for ethanol sensing and other environmental applications (like fuel cells).
|
|
| 27. |
- Banari, Mohammad, et al.
(författare)
-
Effect of the seed layer on the UV photodetection properties of ZnO nanorods
- 2021
-
Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5107 .- 1873-4944. ; 272
-
Tidskriftsartikel (refereegranskat)abstract
- The ZnO seed layer, acting as nucleation center for the growth of ZnO nanorods (NRs), has strong impact on the optical and photodetection properties of ZnO-based UV photodetectors (PDs). In this paper, vertically aligned ZnO NRs were grown by varying the thickness of the seed layer in the range 50–125 nm, to investigate its influence on the recovery time of the PD. Single crystalline ZnO NRs were obtained as indicated by combined electron microscopy and X-ray diffraction analysis. The photoluminescence (PL) spectra proved that the lowest PL intensity (i.e.: the lowest recombination) belongs to the sample with seed layer thickness of 100 nm (labeled as NR-7). The carrier concentration of ZnO NR films was estimated from the slope of the Mott–Schottky plot. It was 1.49 × 10+20 cm−3 for seed layer thickness of 65 nm (NR-5), which was dramatically reduced to 5.44 × 10+17 cm−3 in the sample NR-9 (seed layer thickness 125 nm). Furthermore, the current-voltage (I-V) and chronoamperometric (I-t) analysis indicate a high UV responsivity under a UV irradiation. The fastest recovery time (0.1 s time decay constant) occurs in sample NR-7 (seed layer 100 nm thick). These results indicate that effective control of the electronic and optical properties in ZnO NRs can be obtained by proper tuning of the seed layer, enabling a simple and straightforward strategy to optimize NR functionality, depending on their planned use.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Baricordi, S., et al.
(författare)
-
Low-energy-channeling surface analysis on silicon crystals designed for high-energy-channeling in accelerators
- 2005
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:9
-
Tidskriftsartikel (refereegranskat)abstract
- Channeling of relativistic particles in bent Si crystals is a powerful technique for use with accelerators. Its efficiency can be found to be highly dependent on the state of the surface of the crystal steering the particles. We investigated the morphology and structure of the surface of the samples that have been used with high efficiency for channeling in accelerators. Low-energy channeling of 2 MeVα particles or protons was used as a probe. We found that mechanical treatment of the samples leads to a superficial damaged layer, which is correlated to efficiency limitations of the crystal in accelerators. In contrast, chemical etching, which was used to treat the surface of the most efficient crystals, leaves a surface with superior perfection. © 2005 American Institute of Physics.
|
|
| 31. |
- Baricordi, S., et al.
(författare)
-
Optimal crystal surface for efficient channeling in the new generation of hadron machines
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:6
-
Tidskriftsartikel (refereegranskat)abstract
- The new generation of hadron machines may profitably take advantage of channeling for steering and collimation of high-energy particle beams. In that case, the requirements on the quality of the crystal surface are rather stringent in terms of both lattice perfection and roughness. Here, the authors show the structural and morphological characterizations of crystals fabricated through a method to achieve a surface that fulfills all needed specifications for application in hadron machines. © 2007 American Institute of Physics.
|
|
| 32. |
- Basu, Kaustubh, et al.
(författare)
-
Enhanced photovoltaic properties in dye sensitized solar cells by surface treatment of SnO2 photoanodes
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- We report the fabrication and testing of dye sensitized solar cells (DSSC) based on tin oxide (SnO2) particles of average size ~20 nm. Fluorine-doped tin oxide (FTO) conducting glass substrates were treated with TiOx or TiCl4 precursor solutions to create a blocking layer before tape casting the SnO2 mesoporous anode. In addition, SnO2 photoelectrodes were treated with the same precursor solutions to deposit a TiO2 passivating layer covering the SnO2 particles. We found that the modification enhances the short circuit current, open-circuit voltage and fill factor, leading to nearly 2-fold increase in power conversion efficiency, from 1.48% without any treatment, to 2.85% achieved with TiCl4 treatment. The superior photovoltaic performance of the DSSCs assembled with modified photoanode is attributed to enhanced electron lifetime and suppression of electron recombination to the electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS) carried out under dark condition. These results indicate that modification of the FTO and SnO2 anode by titania can play a major role in maximizing the photo conversion efficiency
|
|
| 33. |
- Belay Ibrahim, Kassa, et al.
(författare)
-
Emerging 2D materials beyond mxenes and TMDs: Transition metal carbo-chalcogenides
- 2024
-
Ingår i: Progress in Materials Science. - : Elsevier Ltd. - 0079-6425 .- 1873-2208. ; 144
-
Forskningsöversikt (refereegranskat)abstract
- Interestingly, it opens the door for the development of the 2D materials family, which includes different classes of 2D materials. Among them, transition metal dichalcogenides (TMDs) and transition metal carbide MXenes (TMCs) have emerged. TMDs have unique layered structures, low cost, and are composed of earth abundant elements, but their poor electronic conductivity, poor cyclic stability, their structural and morphological changes during electrochemical measurements hinder their practical use. Recently, TMC MXenes have garnered attention in the 2D material world, but the issue of restacking and aggregation limits their direct use in large-scale energy conversion and storage. To address these challenges, hetero structures based on conductive TMCs MXenes and electrochemically active TMDs have emerged as a promising solution. However, understanding the solid/solid interface in heterostructured materials remains a challenge. To tackle this, 2D single component crystals with high capacity, low diffusion barrier, and good electronic conductivity are highly sought. The emergence of transition metal carbo-chalcogenides (TMCCs) has provided a potential solution, as these 2D nanosheets consist of TM2X2C, where TM represents transition metal, X is either S or Se, and C atom. This new class of 2D materials serves as a remedy by avoiding the challenges related to solid/solid interfaces often encountered in heterostructures. This review focuses on the latest developments in TMCCs, including their synthetic strategies, surface/interface engineering, and potential application in batteries, water splitting, and other electro-catalytic processes. The challenges and future perspectives of the design of TMCCs for electrochemical energy conversion and storage are also discussed.
|
|
| 34. |
- Bemmerer, D., et al.
(författare)
-
Feasibility of low-energy radiative-capture experiments at the LUNA underground accelerator facility
- 2005
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 24:2, s. 313-319
-
Tidskriftsartikel (refereegranskat)abstract
- The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, with 50 and 400 kV maximum voltage, in combination with solid and gas target setups allowed to measure the total cross-sections of the radiative-capture reactions 2H2H(p, γ) 3He3Heand 14N14N(p, γ) 15O15Owithin their relevant Gamow peaks. We report on the gamma background in the Gran Sasso laboratory measured by germanium and bismuth germanate detectors, with and without an incident proton beam. A method to localize the sources of beam-induced background using the Doppler shift of emitted gamma rays is presented. The feasibility of radiative-capture studies at energies of astrophysical interest is discussed for several experimental scenarios. © Società Italiana di Fisica/Springer-Verlag 2005.
|
|
| 35. |
- Benavides, Vicente
(författare)
-
Synthesis and characterization of nanocarbons as reinforced particles in metal composites
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work, several scientific problems related to high pressure–high temperature (HP–HT) synthesis of new materials using fullerite as a precursor were studied: first, the mechanism of the transformation of C60 crystal into a nano-clustered graphene phase (NGP) at a pressure of 8 GPa; and second, the effect of disorder introduced into C60 crystals by ball milling prior to HP–HT synthesis on the structure and properties of the NGP. A separate set of experiments was devoted to compression of C60 precursor at unexplored before pressure of 25 GPa and elevated temperatures in search for new type of disordered carbon-based materials.In the first study, Raman spectroscopy, HRSTEM-EELS, and indentation hardness demonstrate that, under pressure, C60 exhibits a path of transformation from polymerized C60 to NGP. This phase exhibits a short-range order and preferential orientation of nano-clusters of graphene assembled in a highly disordered carbon matrix. In our studies, we observe that the mechanism of C60 transformation into NGP could be understood in terms of nucleation and growth mechanism as opposed to the pseudomartensitic mechanism. Changes in Raman intensity of the Ag(2) C60 mode monitored in polished incompletely transformed carbon particles reveal different steps of transformation. Moreover, the polishing reveals the distribution of shear bands resulting from plastic deformation of the C60 monomer and following the direction of the <110> slip planes in FCC system.HRSTEM analysis reveals the presence of disorder as an intermediate state between the parent C60 and the nano-graphene units. EELS spectra show that C60 molecules in such state are present as monomers, and the intermediate phase is an sp2–sp3 disordered phase, in which the sp2 fraction is by up to 20% lower than that of graphene nanoclusters. The findings suggest that, after the collapse, the polymer structure breaks down with the formation of a disordered (sp2–sp3) carbon phase containing some fraction of residual C60 molecules. The graphene nanoclusters further nucleate and grow in the intermediate disordered phase. Thus, a nucleation and growth mechanism is proposed for the formation of NGP phase from C60 upon HP-HT action.For the second problem, highly disordered systems were obtained from ball-milled C60 through HP–HT demonstrating a promising technique to create hard (hardness > 30 GPa) disordered carbons at relatively low pressure (up to 8 GPa).The nanoarchitecture of NGP and disordered systems was studied using multi-wavelength Raman spectroscopy, HRSTEM, and indentation techniques. The Raman data treatment was carefully studied following the three-stage amorphization trajectory of amorphous carbon. The Raman model consists of G and D bands and data from semi-empirical models that include peak position, FWHM, and intensity ratio. A new approach proposed by the research team includes the presence of carbon pentagons (F band) and carbon heptagons as defects in the graphene clusters and are eventually present in the disordered carbon matrix as well. A peak deconvolution considering the G, D, F and heptagon bands is the model that allows building an empirical correlation between the Raman spectra features and hardness. Using peak deconvolution model based on G, D, F heptagon and sp3 carbon-derived bands allowed us to build an empirical correlation that can be used for a semi-quantitative estimation/prediction of hardness of an arbitrary disordered sp2 carbon-based system based on their spectroscopic (Raman) data.Finally, experiments on compressed C60 at 25 GPa, previously unexplored pressure, produce superhard 3D-C60 polymers at temperatures below 600 oC. As the temperature increases, sp3 carbon starts dominating the disordered structures. The synthesized materials are semiconductors exhibiting ultra-high hardness that in a particular case exceeds that of single crystalline diamond. UV-Raman spectroscopy reveals a high intensity of T band and a G band position typically observed in tetrahedral amorphous carbon (ta-C)-based thin films. The phase has a residual fraction of sp2 carbons, mainly linear chains and fused aromatic rings.In summary, the results demonstrate that a whole class of novel materials with outstanding physical properties - superelastic-hard and ultrahard semiconducting carbons - can be produced for demanding technological applications at HP-HT by using C60 as a precursor and tuning its microstructure.
|
|
| 36. |
- Benetti, Daniele, et al.
(författare)
-
Direct Measurement of Electronic Band Structure in Single Quantum Dots of Metal Chalcogenide Composites
- 2018
-
Ingår i: Small (Weinheim an der Bergstrasse, Germany). - : John Wiley & Sons. - 1613-6810 .- 1613-6829. ; 14:51
-
Tidskriftsartikel (refereegranskat)abstract
- Metal chalcogenide quantum dots (QDs) are among the most promising materials as light harvesters in all-inorganic systems for applications in solar cells and production of solar fuels. The electronic band structure of composite QDs formed by lead and cadmium chalcogenides directly grafted on highly oriented pyrolytic graphite surfaces through successive ionic layer absorption and reaction is investigated. Atomic force microscopy and Kelvin probe force microscopy (KPFM) are applied to investigate PbS, CdS, and PbS/CdS QD systems. The variation of the surface potential of individual QDs is measured, investigating the evolution of the electronic band structure as a function of QD size and composition. A shift of the Fermi level toward more negative values occurs when QD size is increased. The shift is more pronounced in CdS than in PbS, while the composite PbS/CdS exhibits an intermediate behavior. The calculated shift is in good agreement with the experiments. These results highlight the ability of KPFM to directly measure the electronic band structure in individual QDs of metal chalcogenide composites. This feature regulates charge dynamics in composite systems, thereby affecting device performance. This work provides valuable insights for applications in several fields, in which charge injection plays a major role.
|
|
| 37. |
- Benetti, Daniele, et al.
(författare)
-
Functionalized multi-wall carbon nanotubes/TiO2 composites as efficient photoanodes for dye sensitized solar cells
- 2016
-
Ingår i: Journal of Materials Chemistry C. - 2050-7526 .- 2050-7534. ; 4:16, s. 3555-3562
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the effects of incorporation of different concentrations of carboxyl group (COOH)-functionalized multi-wall carbon nanotubes (F-MWCNTs) into TiO2 active layers for dye-sensitized solar cells (DSSCs). Standard DSSCs with bare TiO2 exhibit a photo-conversion efficiency (PCE) of 6.05% and a short circuit current density (Jsc) of 13.3 mA cm−2. The presence of 2 wt% F-MWCNTs in the photoanodes increases the PCE up to 7.95% and Jsc up to 17.5 mA cm−2. The photoanodes were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The electrochemical behaviour of the solar cells was investigated by electrochemical impedance spectroscopy (EIS). We attribute the improved performances to the combined effect of increased dye loading and reduced charge recombination (as clarified by dye loading and EIS measurements), due to the conformal coverage of F-MWCNTs, which allows fast and efficient charge collection in operating solar cells. These results can help in improving the PCE in DSSCs in an elegant and straightforward way, minimizing the need of additional steps (e.g. pre- and post-treatment with TiCl4) for photoanode preparation.
|
|
| 38. |
- Benetti, Daniele, et al.
(författare)
-
Hole-extraction and photostability enhancement in highly efficient inverted perovskite solar cells through carbon dot-based hybrid material
- 2019
-
Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 62, s. 781-790
-
Tidskriftsartikel (refereegranskat)abstract
- We report the effect of the integration of carbon dots (Cdots) in high-performance inverted planar-heterojunction (PHJ) perovskite solar cells (PSCs). We used Cdots to modify the hole-transport layer in planar PSC devices. By introducing Cdots on graphene oxide (GO) as hole-transporting layer, the efficiency of the PSC improved significantly from 14.7% in the case of bare GO to 16.2% of the best device with optimized Cdots content. When applying Cdots with an engineered absorption in the UV range as downshifting layer, the device performance was further improved, attaining a maximum PCE of 16.8% (+14%); the stability of the device was also enhanced of more than 20%. Kelvin probe force microscopy (KPFM) and cyclic voltammetry (CV) were employed to analyze the electronic band alignment at the interface between GO/Cdots and the perovskite film. Holes were extracted and transferred to the conductive substrate more efficiently in the presence of Cdots, thus delaying charge recombination. Photoluminescence (PL), transient PL decays and transient photovoltage (TPV) decays investigated the charge-transfer kinetics and proved the retardation of charge recombination. This work reveals an effective enhancement of the performance of planar PSCs by using Cdots/GO as hole transport material.
|
|
| 39. |
- Bhatti, Adeel Liaquat, et al.
(författare)
-
Nanostructured Co3O4 electrocatalyst for OER : The role of organic polyelectrolytes as soft templates
- 2021
-
Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 398
-
Tidskriftsartikel (refereegranskat)abstract
- Designing an efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline media is highly needed but very challenging task. Herein, we used organic polyelectrolytes such as (carboxymethyl cellulose) CMC and polyacrylamide polymers for the growth of Co3O4 nanostructures by aqueous chemical growth method. The morphology and composition studies were performed on scanning electron microscopy (SEM), energy dispersive X-ray (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) techniques. The structural properties and the surface chemistry of the Co3O4 electrocatalysts were correlated to the OER performance, and the enhancement mechanism with respect to pristine Co3O4 was observed to be specifically related to the polyelectrolyte templating role.Co3O4@CMC composites displayed reduced crystallite size, producing OER overpotential as low as 290 mV at 10 mAcm−2 in 1.0 KOH and Tafel slope of 71 mVdec−1, suggesting fast transfer of intermediates and electrons during water electrolysis. On the other hand, the use of polyacrylamide and its different templating mechanism resulted in similar crystallite size, but preferential exposed faces and larger surface vacancies content, as demonstrated by HR-TEM and XPS, respectively. Consistently, this material displays cutting-edge OER performance, such as overpotential of 260 mV at 10 mAcm−2 and a low Tafel slope of 63 mVdec−1. The proposed strategy for the preparation of Co3O4 nanostructures in the presence of CMC and polyacrylamide is facile, mass production, thus it could equally contributed towards the realization of hydrogen energy. Therefore, these nanostructures of Co3O4 can be regarded as an alternative and promising materials for the different electrochemical applications including fuel cells, metal air batteries, overall water electrolysis and other energy storage devices.
|
|
| 40. |
- Bianchi, S., et al.
(författare)
-
Indium oxide quasi-monodimensional low temperature gas sensor
- 2006
-
Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 118:1-2, s. 204-207
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the sensing properties of indium oxide nanostructures and tailored the deposition conditions in order to obtain nano-wires of indium oxide. We have comparatively tested the gas sensing properties of nano-wires with micrometric or even nanometric size. The micro-wires feature interesting gas sensitivity at room temperature, particularly in the case of nitrogen dioxide detection. The sensing performance is improved as the lateral dimension of the wire decreases. © 2006 Elsevier B.V. All rights reserved.
|
|
| 41. |
- Borgani, Riccardo, 1989-, et al.
(författare)
-
Fast multifrequency measurement of nonlinear conductance
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Low noise measurement of small currents in nanometer-scale junctions is of central importance to the characterization of novel high-performance devices and materials for applications ranging from energy harvesting and energy conversion to topological materials for quantum computers. The high resistance of these junctions and the stray capacitance of their measurement leads impose speed limitations (tens of seconds) on the traditional methods of measuring their nonlinear conductance, making detailed investigations of change with external fields or maps of variation over a surface impractical, if not impossible. Here we demonstrate fast (milliseconds) reconstruction of nonlinear current-voltage characteristics from phase-coherent multifrequency lock-in data using the inverse Fourier transform. The measurement technique allows for separation of the galvanic and displacement currents in the junction and easy cancellation of parasitic displacement current due to the measurement leads. We use the method to reveal nanometer-scale variations in the electrical transport properties of organic photovoltaic and semiconducting thin films. The method has broad applicability and its wide-spread implementation promises advancement in high-speed and high-resolution characterization for nanotechnology.
|
|
| 42. |
- Borgani, Riccardo, et al.
(författare)
-
Fast Multifrequency Measurement of Nonlinear Conductance
- 2019
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 11:4
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a phase-coherent multifrequency lock-in measurement technique that uses the inverse Fourier transform to reconstruct the nonlinear current-voltage characteristic of a nanoscale junction. The method provides separation of the galvanic and displacement currents in the junction and easy cancellation of the parasitic displacement current from the measurement leads. These two features allow us to overcome traditional limitations imposed by the low conductance of the junction and the high capacitance of the leads, thus providing an increase in measurement speed of several orders of magnitude. We demonstrate the method in the context of conductive atomic force microscopy, acquiring current-voltage characteristics at every pixel while scanning at standard imaging speed.
|
|
| 43. |
- Bortoluzzi, Marco, et al.
(författare)
-
Green-emitting manganese (II) complexes with phosphoramide and phenylphosphonic diamide ligands
- 2018
-
Ingår i: Inorganic Chemistry Communications. - : Elsevier. - 1387-7003 .- 1879-0259. ; 92, s. 145-150
-
Tidskriftsartikel (refereegranskat)abstract
- Tetrahedral manganese(II) complexes having formulae [MnX2{O = PR(NMe2)2}2] (X = Br, I; R = NMe2, Ph) were isolated and characterized, and in the case of [MnBr2{O = PPh(NMe2)2}2] the structure was ascertained by means of single crystal X-ray diffraction. All the complexes showed intense green emission assigned to the Mn(II) 4T1(4G) → 6A1(6S) transition upon excitation with UV light, with photoluminescence lifetimes in the range 100–1000 μs. Bromo-complexes maintain their luminescence features once dispersed in polycaprolactone matrix.
|
|
| 44. |
- Bortoluzzi, Marco, et al.
(författare)
-
Luminescent copper(I) coordination polymer with 1-methyl-1H-benzotriazole, iodide and acetonitrile as ligands
- 2019
-
Ingår i: Inorganic Chemistry Communications. - : Elsevier. - 1387-7003 .- 1879-0259. ; 102, s. 141-146
-
Tidskriftsartikel (refereegranskat)abstract
- The Cu(I) coordination polymer [Cu3(μ3-I)3(μ-btzMe)(NCCH3)]n (btzMe = 1-methyl-1H-benzotriazole) was prepared and characterized by X-Ray diffraction. The compound showed strong green emission upon excitation with wavelengths below 475 nm, with lifetime of 47 μs. The emission was attributed to 3(X,M)LCT transition on the basis of experimental data and DFT calculations.
|
|
| 45. |
- Botella, Pablo, PhD Student, et al.
(författare)
-
High-pressure characterization of multifunctional CrVO4
- 2020
-
Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 32:38
-
Tidskriftsartikel (refereegranskat)abstract
- The structural stability and physical properties of CrVO4 under compression were studied by X-ray diffraction, Raman spectroscopy, optical absorption, resistivity measurements, and ab initio calculations up to 10 GPa. High-pressure X-ray diffraction and Raman measurements show that CrVO4 undergoes a phase transition from the ambient pressure orthorhombic CrVO4-type structure (Cmcm space group, phase III) to the high-pressure monoclinic CrVO4-V phase, which is isomorphic to the wolframite structure. Such a phase transition (CrVO4-type → wolframite), driven by pressure, also was previously observed in indium vanadate. The crystal structure of both phases and the pressure dependence in unit-cell parameters, Raman-active modes, resistivity, and electronic band gap, is reported. Vanadium atoms are sixth-fold coordinated in the wolframite phase, which is related to the collapse in the volume at the phase transition. Besides, we also observed drastic changes in the phonon spectrum, a drop of the band-gap, and a sharp decrease of resistivity. All the observed phenomena are explained with the help of first-principles calculations.
|
|
| 46. |
- Botella, Pablo, et al.
(författare)
-
High-pressure characterization of the optical and electronic properties of InVO4, InNbO4, and InTaO4
- 2019
-
Ingår i: SN Applied Sciences. - : Springer. - 2523-3963 .- 2523-3971. ; 1:5
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the electronic properties at ambient pressure and under high pressure of InVO4, InNbO4, and InTaO4 powders, three candidate materials for hydrogen production by means of photocatalytic water splitting using solar energy. A combination of optical absorption and resistivity measurements and band structure calculations have allowed us to determine that these materials are wide band-gap semiconductors with a band-gap energy of 3.62(5), 3.63(5), and 3.79(5) eV for InVO4, InNbO4, and InTaO4, respectively. The last two compounds are indirect band-gap materials, and InVO4 is a direct band-gap material. The pressure dependence of the band-gap energy and the electrical resistivity have been determined too. In the three compounds, the band gap opens under compression until reaching a critical pressure, where a phase transition occurs. The structural transition triggers a band-gap collapse larger than 1.2 eV in the three materials, being the abrupt decrease in the band-gap energy related to an increase in the pentavalent cation coordination number. The phase transitions also cause changes in the electrical resistivity, which can be correlated with changes induced by pressure in the band structure. An explanation to the reported results is provided based upon ab initio calculations. The conclusions attained are of significance for technological applications of the studied oxides.
|
|
| 47. |
- Botella, Pablo, et al.
(författare)
-
Investigation on the Luminescence Properties of InMO4 (M = V5+, Nb5+, Ta5+) Crystals Doped with Tb3+ or Yb3+ Rare Earth Ions
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:5, s. 2148-2158
-
Tidskriftsartikel (refereegranskat)abstract
- We explore the potential of Tb- and Yb-doped InVO4, InTaO4, and InNbO4 for applications as phosphors for light-emitting sources. Doping below 0.2% barely change the crystal structure and Raman spectrum but provide optical excitation and emission properties in the visible and near-infrared (NIR) spectral regions. From optical measurements, the energy of the first/second direct band gaps was determined to be 3.7/4.1 eV in InVO4, 4.7/5.3 in InNbO4, and 5.6/6.1 eV in InTaO4. In the last two cases, these band gaps are larger than the fundamental band gap (being indirect gap materials), while for InVO4, a direct band gap semiconductor, the fundamental band gap is at 3.7 eV. As a consequence, this material shows a strong self-activated photoluminescence centered at 2.2 eV. The other two materials have a weak self-activated signal at 2.2 and 2.9 eV. We provide an explanation for the origin of these signals taking into account the analysis of the polyhedral coordination around the pentavalent cations (V, Nb, and Ta). Finally, the characteristic green (5D4 → 7FJ) and NIR (2F5/2 → 2F7/2) emissions of Tb3+ and Yb3+ have been analyzed and explained.
|
|
| 48. |
- Botella, Pablo, PhD Student, 1988-
(författare)
-
Physical Properties of Ternary Metal Oxides and Carbon Nanomaterials Under Pressure
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Found in nature or synthesized, materials present amazing properties such as superconductivity, super-hardness, lightweight, or high-energy-density, among others. All these properties can be used in our benefit to improve or develop new applications. Although, many of these properties are not noticeable in the ambient conditions of pressure and temperature. Therefore, only when the materials are exposed to extreme conditions of temperature, pressure, radiation, etc., become notable. For those reasons, it is fundamental to understand their properties and how they are affected by different parameters such as the synthesis process, morphology, doping or external parameters (e.g. pressure, temperature).High-pressure studies have been shown to be an excellent tool for proving and study the robustness of material properties as well as for the synthesis of new materials. Changes as extreme and spectacular as converting oxygen gas into a superconducting metal or the well-known graphite to diamond conversion among others have been made under high-pressure conditions.Among all the materials, and due to their interesting properties, in this doctoral thesis we have studied four ternary metal oxide semiconductors (InVO4, CrVO4, InNbO4 and InTaO4) and carbon nanostructure materials (single-walled carbon nanotubes (SWCNTs)) at ambient conditions as well as under high-pressure (static or dynamic compression) using different characterization techniques such as X-ray diffraction (XRD), Raman spectroscopy (RS), optical absorption, transmission electron microscopy (TEM), photoluminescence (PL) and electrical measurements.InVO4, InNbO4 and InTaO4 are wide metal oxide semiconductors having band-gap energy of 3.62(5), 3.63(5) and 3.79(5) eV, respectively, being InVO4 a direct band-gap semiconductor and, InNbO4 and InTaO4 indirect band-gap semiconductors. These compounds undergo, under pressure, to a structural phase transition from orthorhombic, in the case of InVO4, or monoclinic, in the case of InNbO4 and InTaO4, to another monoclinic system. This structural phase transition triggers interesting phenomena due to the modification of the electronic band structure of the compounds. Phenomena observed under compression include bandgap collapse about 1-1.5 eV depending on the compound, band crossing due to the change to the local maximum on top of the valence band and colour change. Also, the electrical resistivity of the materials is affected by this change in the band structure. All these results are discussed based on our theoretical band structure calculations.On the other hand, doping these compounds below 0.2% using Tb or Yb rare-earth elements, the crystal structure is barely affected as well as their phonon structure, but the band structure does, giving rise optical excitation and emission properties in the visible and near-infrared (NIR) spectral region. From optical reflectivity measurements, the two first direct transitions are reported at 3.7/4.2 eV in InVO4, 4.7/5.3 eV in InNbO4 and 5.6/6.1 eV in InTaO4. All the compounds present self-activated photoemission signals which are discussed in terms of the distorted polyhedral coordination around V, Nb and Ta atoms. Finally, the characteristic emission of Tb atoms in the green region (5D4→7FJ) and the Yb atoms in the NIR region (2F5/2→2F7/2) are analysed and discussed based on our theoretical calculations.Even though, being a prototype structure of a family of compounds denoted as CrVO4-type materials, there is still scarce information on the behaviour under pressure of the CrVO4 compound. Here, it is also studied CrVO4 having an orthorhombic structure under pressure up to 10 GPa. Crystal structure, phonon band structure, optical and electrical properties are analysed showing a structural phase transition similar to that in InVO4 with an increase in the vanadium atoms coordination from 4 to 6. This phase transition triggers also a band-gap collapse of 1.1 eV, a change in the phonon structure and a sharp decrease in the resistivity of the material. All these results are discussed in terms of our theoretical calculations and comparison with its isostructural partner InVO4.To conclude, we study the effects of the dynamic pressure of 0.5 Mbar (50 GPa) on SWCNTs which is way beyond the limit of their structural stability in quest of new forms of carbon nanostructures. Thus, no nanotubes survived to this pressure. The recovered material is composed of two types of material which are classified in a multi-layer graphene phase (MLG) with high defect concentration and multi-phase material which dominates the sample. Even the reached conditions during the shock-compression were favourable for the diamond formation, we were unable to find traces of diamond-like carbon in the very inhomogeneous sample. The crystal size of both materials has been estimated at 13 nm for disordered carbon and 30 nm for MLG phase. The dispersion of the Raman modes was also studied using several lasers and the observations were supported by TEM analysis.
|
|
| 49. |
- Braga, Antonio, et al.
(författare)
-
Panchromatic sensitized solar cells based on metal sulfide quantum dots grown directly on nanostructured TiO2 electrodes
- 2011
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 2:5, s. 454-460
-
Tidskriftsartikel (refereegranskat)abstract
- The use of narrow band gap semiconductors such as PbS may expand the light absorption range to the near-infrared region in quantum-dot-sensitized solar cells (QDSCs), increasing the generated photocurrent. However, the application of PbS as a sensitizer in QDSCs causes some problems of stability and high recombination. Here, we show that the direct growth of a CdS coating layer on previously deposited PbS by the simple method of successive ionic layer adsorption and reaction (SILAR) minimizes these problems. A remarkable short-circuit current density for PbS/CdS QDSCs is demonstrated, ∼11 mA/cm2, compared to that of PbS QDSCs, with photocurrents lower than 4 mA/cm2, using polysulfide electrolyte in both cells. The cell efficiency reached a promising 2.21% under 1 sun of simulated irradiation (AM1.5G, 100 mW/cm2). Enhancement of the solar cell performance beyond the arithmetic addition of the efficiencies of the single constituents (PbS and CdS) is demonstrated for the nanocomposite PbS/CdS configuration. PbS dramatically increases the obtained photocurrents, and the CdS coating stabilizes the solar cell behavior. © 2011 American Chemical Society.
|
|
| 50. |
- Caciolli, A., et al.
(författare)
-
Revision of the 15N(p, γ)16O reaction rate and oxygen abundance in H-burning zones
- 2011
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 533
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T ≈ 30 × 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the red giant branch (RGB) phase of the star or to the pollution of the primordial gas by an early population of massive asymptotic giant branch (AGB) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. Aims. The activation of this cycle depends on the rate of the 15N(p, γ)16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. Methods. We present a new measurement of the 15N(p, γ)16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 × 106 K and 780 × 106 K. This range includes the 15N(p, γ)16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. Results. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level. © 2011 ESO.
|
|
