33 research outputs found
Suivi de la formation dâun film de type polyphosphazĂšne sur InP dans lâammoniac liquide (- 55°C) : Couplage Ă©lectrochimie / XPS
Indium phosphide (InP) is a III-V semiconductor, which represents an ideal candidate for optoelectronic applications. However, its spontaneous oxidation in air leads to the loss of its electrical properties. The surface passivation becomes a key step for its integration in attractive optoelectronic devices. As part of this thesis, we are interested in studying the passivation of the InP surface by nitridation. We reproducibly realized the formation of a polyphosphazene-like (H2N-P=NH)n film on InP by electrochemical treatment in liquid ammonia (-55°C). The monitoring of the film formation was performed using a systematic coupling between electrochemical measurements (J = f(E), J = f(t), E = f(t), and C = f(E)) and XPS analysis (X-ray photoelectron spectroscopy) to follow the chemical composition of the surface. These techniques provide some answers about the nitridation mechanism of InP surface by a wet process (anodization in NH3 liq), leading to the formation of the phosphazene film through an ECE mechanism âElectrochemical-Chemical-Electrochemicalâ. The study of the air ageing of the modified surface using XPS analysis revealed the protective nature of the film. The high value of the interfacial capacity after the anodic treatment suggests that the modified interface (Electrolyte-Insulator-Semiconductor-like) is in accumulation state and behaves like a "real" capacitor.Le phosphure dâindium (InP) est un semiconducteur III-V aux propriĂ©tĂ©s adaptĂ©es aux applications optoĂ©lectroniques. Toutefois, son oxydation spontanĂ©e Ă lâair engendre une dĂ©gradation de ses propriĂ©tĂ©s Ă©lectriques. La passivation de sa surface devient donc une Ă©tape clĂ© pour son intĂ©gration dans des dispositifs optoĂ©lectroniques attractifs. Dans le cadre de ce travail de thĂšse, nous nous sommes intĂ©ressĂ©s Ă lâĂ©tude de la passivation de surface de InP par nitruration. Nous avons rĂ©alisĂ© de maniĂšre reproductible la formation dâun film de type polyphosphazĂšne ( H2N-P=NH )n sur InP par voie Ă©lectrochimique dans lâammoniac liquide (-55°C). Le suivi de la croissance du film sur InP a Ă©tĂ© effectuĂ© grĂące au couplage systĂ©matique de mesures Ă©lectrochimiques (J = f(E), J = f(t), E = f(t) et C = f(E)) avec des analyses de composition chimique de surface par XPS (X-ray photoelectron spectroscopy). Chacune de ces techniques apporte des Ă©lĂ©ments sur la comprĂ©hension du mĂ©canisme de nitruration de la surface de InP en solution (anodisation en milieu NH3 liq), nous permettant ainsi de proposer un mĂ©canisme de formation du film de phosphazĂšne de type ECE « Electrochimique-Chimique-Electrochimique ». LâĂ©tude par XPS de la stabilitĂ© Ă lâair de la composition chimique de surface de InP traitĂ© a rĂ©vĂ©lĂ© le caractĂšre protecteur du film. La valeur Ă©levĂ©e de la capacitĂ© interfaciale aprĂšs traitement anodique suggĂšre que lâinterface modifiĂ©e (de type Electrolyte-Insulator-Semiconductor) est en rĂ©gime d'accumulation et se comporte comme un « vrai » condensateur
Gas phase synthesis and adsorption properties of a 3D ZIF-8 CNT composite
The metal organic framework structure ZIF-8 has been grown directly on vertically aligned carbon nano tubes (VACNT) by a solid vapour transformation of a ZnO@VACNT composite with gaseous 2-methylimidazole. The ZnO@VACNT composite was synthesised by atomic layer deposition (ALD) using diethylzinc and water as precursors resulting in a homogeneous distribution of crystalline ZnO particles with an average size of 13 nm within the 3D VACNT host structure. The ZnO@VACNT composite was transformed to ZIF-8 by reaction with 2-methyl-imidazole (Hmim) while maintaining the 3D VACNT structure employing a solid vapour transformation reaction. Reaction time and temperature were identified as key parameters to control the generated surface area and the degree of conversion of the nanoscaled ZnO particles. 80 °C and 72 h were found to be sufficient for a complete conversion while longer reaction times result in even higher surface areas of the formed ZIF-8@VACNT composite. Surface areas of up to 1569 m g could be achieved. Temperatures below 80 °C led to an incomplete conversion even under longer reaction times of up to 6 weeks. Finally, the CO adsorption properties of the ZIF-8@VACNT composite were evaluated. A composite with a 27 w% content of CNTs and a surface area of 1277 m g shows an adsorption of 6.05 mmol g CO at 30 bar. From the comparison with the pristine materials ZIF-8 and VACNT alone the observed overall CO adsorption behaviour of the composite is a combination of the behaviour of the individual components, ZIF-8 and VACNTs. Namely the typical steep rise of the ZIF-8 in the low-pressure regime with a nearly linear steady progression in the medium pressure size regime, the latter typical for VACNTs, proves that the combination of both components leads to enhanced adsorption properties of the ZIF-8@VACNT composite compared to the sole components ZIF-8 and VACNTs
Electrochemical study on nickel aluminum layered double hydroxides as high-performance electrode material for lithium-ion batteries based on sodium alginate binder
Nickel aluminum layered double hydroxide (NiAl LDH) with nitrate in its interlayer is investigated as a negative electrode material for lithium-ion batteries (LIBs). The effect of the potential range (i.e., 0.01â3.0 V and 0.4â3.0 V vs. Li+/Li) and of the binder on the performance of the material is investigated in 1 M LiPF6 in EC/DMC vs. Li. The NiAl LDH electrode based on sodium alginate (SA) binder shows a high initial discharge specific capacity of 2586 mAh gâ1 at 0.05 A gâ1 and good stability in the potential range of 0.01â3.0 V vs. Li+/Li, which is better than what obtained with a polyvinylidene difluoride (PVDF)-based electrode. The NiAl LDH electrode with SA binder shows, after 400 cycles at 0.5 A gâ1, a cycling retention of 42.2% with a capacity of 697 mAh gâ1 and at a high current density of 1.0 A gâ1 shows a retention of 27.6% with a capacity of 388 mAh gâ1 over 1400 cycles. In the same conditions, the PVDF-based electrode retains only 15.6% with a capacity of 182 mAh gâ1 and 8.5% with a capacity of 121 mAh gâ1, respectively. Ex situ X-ray photoelectron spectroscopy (XPS) and ex situ X-ray absorption spectroscopy (XAS) reveal a conversion reaction mechanism during Li+ insertion into the NiAl LDH material. X-ray diffraction (XRD) and XPS have been combined with the electrochemical study to understand the effect of different cutoff potentials on the Li-ion storage mechanism
An all-in-one nanoprinting approach for the synthesis of a nanofilm library for unclonable anti-counterfeiting applications
In addition to causing trillion-dollar economic losses every year, counterfeiting threatens human health, social equity and national security. Current materials for anti-counterfeiting labelling typically contain toxic inorganic quantum dots and the techniques to produce unclonable patterns require tedious fabrication or complex readout methods. Here we present a nanoprinting-assisted flash synthesis approach that generates fluorescent nanofilms with physical unclonable function micropatterns in milliseconds. This all-in-one approach yields quenching-resistant carbon dots in solid films, directly from simple monosaccharides. Moreover, we establish a nanofilm library comprising 1,920 experiments, offering conditions for various optical properties and microstructures. We produce 100 individual physical unclonable function patterns exhibiting near-ideal bit uniformity (0.492â±â0.018), high uniqueness (0.498â±â0.021) and excellent reliability (>93%). These unclonable patterns can be quickly and independently read out by fluorescence and topography scanning, greatly improving their security. An open-source deep-learning model guarantees precise authentication, even if patterns are challenged with different resolutions or devices
An all-in-one nanoprinting approach for the synthesis of a nanofilm library for unclonable anti-counterfeiting applications
In addition to causing trillion-dollar economic losses every year, counterfeiting threatens human health, social equity and national security. Current materials for anti-counterfeiting labelling typically contain toxic inorganic quantum dots and the techniques to produce unclonable patterns require tedious fabrication or complex readout methods. Here we present a nanoprinting-assisted flash synthesis approach that generates fluorescent nanofilms with physical unclonable function micropatterns in milliseconds. This all-in-one approach yields quenching-resistant carbon dots in solid films, directly from simple monosaccharides. Moreover, we establish a nanofilm library comprising 1,920 experiments, offering conditions for various optical properties and microstructures. We produce 100 individual physical unclonable function patterns exhibiting near-ideal bit uniformity (0.492â±â0.018), high uniqueness (0.498â±â0.021) and excellent reliability (>93%). These unclonable patterns can be quickly and independently read out by fluorescence and topography scanning, greatly improving their security. An open-source deep-learning model guarantees precise authentication, even if patterns are challenged with different resolutions or devices
The Effect of Single versus Polycrystalline Cathode Particles on AllâSolidâState Battery Performance
Lithium-thiophosphate-based all-solid-state batteries (ASSBs) are increasingly attracting attention for high-density electrochemical energy storage. In this work, the cycling performance of single and polycrystalline forms of LiNiCoMnO (NCM, with â„83% Ni content) cathode active materials in ASSB cells with an LiTiO composite anode is explored, and the advantages and disadvantages of both morphologies are discussed. The virtual lack of grain boundaries in the quasi-single-crystalline material is found to contribute to improved stability by eliminating the tendency of Ni-rich NCM particles to crack during cycling, due to volume differences between the lithiated and delithiated phases. Although the higher crack resistance mitigates effects of chemical oxidation of the lithium thiophosphate solid electrolyte, the cells suffer from electrochemical side reactions occurring at the cathode interfaces. However, coating the single-crystal particles with a protective LiNbO overlayer helps to stabilize the interface between cathode active material and solid electrolyte, leading to a capacity retention of 93% after 200 cycles (with q â 160 mAh g or 1.7 mAh cm at C/5 rate and 45 °C). Overall, this work highlights the importance of addressing electro-chemo-mechanical phenomena in ASSB electrodes
Polyoxometalate Modified Separator for Performance Enhancement of MagnesiumâSulfur Batteries
The magnesiumâsulfur (MgâS) battery has attracted considerable attention as a candidate of postâlithium battery systems owing to its high volumetric energy density, safety, and cost effectiveness. However, the known shuttle effect of the soluble polysulfides during charge and discharge leads to a rapid capacity fade and hinders the realization of sulfurâbased battery technology. Along with the approaches for cathode design and electrolyte formulation, functionalization of separators can be employed to suppress the polysulfide shuttle. In this study, a glass fiber separator coated with decavanadateâbased polyoxometalate (POM) clusters/carbon composite is fabricated by electrospinning technique and its impacts on battery performance and suppression of polysulfide shuttling are investigated. MgâS batteries with such coated separators and nonâcorrosive Mg[B(hfip)4]2 electrolyte show significantly enhanced reversible capacity and cycling stability. Functional modification of separator provides a promising approach for improving metalâsulfur batteries