| 1. |
- Borgani, Riccardo, et al.
(författare)
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Fast Multifrequency Measurement of Nonlinear Conductance
- 2019
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 11:4
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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.
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| 2. |
- Dobryden, Illia, et al.
(författare)
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Nanoscale characterization of an all-oxide core-shell nanorod heterojunction using intermodulation atomic force microscopy (AFM) methods
- 2021
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 3:15, s. 4388-4394
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Tidskriftsartikel (refereegranskat)abstract
- The electrical properties of an all-oxide core-shell ZnO-Co3O4nanorod heterojunction were studied in the dark and under UV-vis illumination. The contact potential difference and current distribution maps were obtained utilizing new methods in dynamic multifrequency atomic force microscopy (AFM) such as electrostatic and conductive intermodulation AFM. Light irradiation modified the electrical properties of the nanorod heterojunction. The new techniques are able to follow the instantaneous local variation of the photocurrent, giving a two-dimensional (2D) map of the current-voltage curves and correlating the electrical and morphological features of the heterostructured core-shell nanorods.
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| 3. |
- Enrichi, Francesco, et al.
(författare)
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Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics
- 2018
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 84, s. 668-674
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the study of down-shifting silica-zirconia glass and glass-ceramic films doped by Tb3+ ions and Ag nanoaggregates, which combine the typical spectral properties of the rare-earth-ions with the broadband sensitizing effect of the metal nanostructures. Na-Tb co-doped silica-zirconia samples were obtained by a modified sol-gel route. Dip-coating deposition followed by annealing for solvent evaporation and matrix densification were repeated several times, obtaining a homogeneous crack-free film. A final treatment at 700 °C or 1000 °C was performed to control the nanoscale structural properties of the samples, resulting respectively in a glass (G) or a glass-ceramic (GC), where tetragonal zirconia nanocrystals are surrounded by an amorphous silica matrix. Ag introduction was then achieved by ion-exchange in a molten salt bath, followed by annealing in air to control the migration and aggregation of the metal ions. The comparison of the structural, compositional and optical properties are presented for G and GC samples, providing evidence of highly efficient photoluminescence enhancement in both systems, slightly better in G than in GC samples, with a remarkable increase of the green Tb3+ PL emission at 330 nm excitation: 12 times for G and 8 times for GC samples. Furthermore, after Ag-exchange, the shape of Tb3+ excitation resembles the one of Ag ions/nanoaggregates, with a broad significant absorption in the whole UV-blue spectral region. This broadband enhanced downshifting could find potential applications in lighting devices and in PV solar cells.
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| 4. |
- Adeel, Muhammad, et al.
(författare)
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2D metal azolate framework as nanozyme for amperometric detection of glucose at physiological pH and alkaline medium
- 2021
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Ingår i: Microchimica Acta. - : Springer. - 0026-3672 .- 1436-5073. ; 188:3
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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.
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| 5. |
- Aftab, Umair, et al.
(författare)
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Two step synthesis of TiO2–Co3O4 composite for efficient oxygen evolution reaction
- 2021
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Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 46:13, s. 9110-9122
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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.
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| 6. |
- Ahdikari, Rajesh, et al.
(författare)
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High Efficiency, Pt-free Photoelectrochemical Cells for Solar Hydrogen Generation based on “Giant” Quantum Dots
- 2016
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 27, s. 265-274
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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.
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| 7. |
- Alvi, Sajid Ali, et al.
(författare)
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Adaptive nanolaminate coating by atomic layer deposition
- 2019
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 692
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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.
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| 8. |
- Alvi, Sajid, et al.
(författare)
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Synthesis and Mechanical Characterization of a CuMoTaWV High-Entropy Film by Magnetron Sputtering
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:18, s. 21070-21079
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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.
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| 9. |
- Amin, Sidra, et al.
(författare)
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A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles
- 2019
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 9:25, s. 14443-14451
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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.
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| 10. |
- Amin, Sidra, et al.
(författare)
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A sensitive enzyme-free lactic acid sensor based on NiO nanoparticles for practical applications
- 2019
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Ingår i: Analytical Methods. - : Royal Society of Chemistry. - 1759-9660 .- 1759-9679. ; 11, s. 3578-3583
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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.
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