Materials based on solid-supported nanoparticles are used in a range of applications, spanning from catalysis to sensing. Controlling the inter-nanoparticle distance is essential in property optimization of these materials. To achieve such control, nanoparticle gradient surfaces, where nanoparticles are attached in a number density gradient on the support, show great promise. This study presents a tunable method for the preparation of gold nanorod gradient surfaces, exploiting nanoparticle adsorption kinetics to control the surface coverage. The method involves immersing a mercapto silane-functionalized substrate in a gold nanorod suspension, which is then withdrawn at a fixed rate. We show that the gradient dynamics can be tuned by changing the withdrawal rate, and that the gradients exhibit a linear increase in surface coverage along the distance of the support. The changes in optical properties and influence of plasmon coupling with the surface coverage of gold nanorods were evaluated using extinction spectroscopy. Additionally, by assessing the photothermal properties of the gradients upon irradiation with a near-infrared laser, through thermal imaging and in situ X-ray diffraction, we show that a temperature gradient is achieved, correlating with the increased surface coverage of gold nanorods.

The orbital Hall effect provides a promising route for generating angular-momentum currents beyond conventional spin Hall physics. PtCr alloys exhibit unusually large current-induced torques, but the contribution of orbital transport and the ability of these torques to sustain coherent nonlinear magnetization dynamics remain unresolved. Here we demonstrate spin-orbital Hall nano-oscillators by exploiting a homogeneous heavy-metal/light-metal alloy in which orbital Hall currents generated by Cr are converted by Pt into spin currents, producing giant spin-orbit torques. Using PtCr/NiFe heterostructures, the effective torque efficiency increases from 0.14 in Pt/NiFe to 0.40 in Pt0.38Cr0.62/NiFe despite substantial Pt dilution, enabling coherent auto-oscillations with the threshold current density reduced from 1.07 x 10^12 to 4.4 x 10^11 A m^-2. First-principles calculations show that Cr alloying suppresses the intrinsic spin Hall conductivity while enhancing the orbital Hall conductivity, and reproduce the observed torque enhancement only when orbital transport is included. Our combined experimental and first-principles results show that alloy engineering enables giant spin-orbit torques through an intrinsic orbital-mediated contribution, enabling coherent auto-oscillations without engineered multilayers and establishing a scalable materials platform for low-power nonlinear spintronic and orbitronic devices.

Gold nanoparticles possess unique photothermal properties and have gained considerable interest in biomedical research, particularly for photothermal therapy (PTT). This study focuses on evaluating the photothermal properties of gold nanorods (AuNRs) supported on glass substrates upon excitation with near-infrared (NIR) light. Two aspect ratios of AuNRs were electrostatically immobilized onto glass with controlled coverage. In situ X-ray diffraction (XRD) was performed to evaluate the photothermal behavior and morphological changes of the supported AuNRs during NIR laser irradiation. The XRD data sets were corroborated with scanning electron microscopy and Vis-NIR spectroscopy characterization. XRD revealed a linear temperature increase with laser power, aligning with theoretical predictions, and a slope dependent on the AuNR coverage, until the onset of morphology transformations around 120 degrees C. This study provides valuable insights into the photothermal properties of supported AuNRs, crucial for their application in PTT.

The accident tolerant fuel (ATF) concept has emerged in the years after the 2011 Fukushima accident as part of a renewed effort in research for light water reactors. The primary focus is to further improve safety measures under and beyond design basis accident conditions, and to improve fuel cladding performance in normal operation. The application of a coating on zirconium claddings can achieve both these aims without extensive changes to the reactor design. Metallic chromium coatings have been profusely studied as solution for pressurized water re-actors, but the search for an effective ATF coating able to withstand the environment inside boiling water re-actors (BWRs) is still ongoing. In this work, two different versions of a novel nitride coating composition were studied. Zirconium claddings coated with 8 & mu;m thick layers of superlattice CrN-NbN and a nanolayered CrN-NbN were tested in autoclave under BWR operating conditions for 60 days. Scanning electron microscopy, trans-mission electron microscopy, energy dispersive x-ray spectroscopy, electron back-scattered diffraction, x-ray diffraction, and atom probe tomography were employed to characterize as-deposited and autoclaved samples of these two materials. During exposure, both coating versions formed a stable, dense and passivating oxide scale (200-300 nm thick) on the surface, demonstrating improved oxidation protection under operating conditions. Some differences in the oxide growth mechanism were observed between the superlattice and the nanolayered CrN-NbN coatings, which allowed to glimpse at the effect of the layer thickness on the oxidation protection provided by these coatings. The nano-structured morphology of both coatings remained unaffected by the autoclave test, but a 35 nm thick Zr-Cr-N phase was found at the coating-substrate interface of the superlattice CrN-NbN coated cladding.

Metal nanoparticles are currently used in a variety of applications, ranging from life sciences to nanoelectronic devices to gas sensors. In particular, the use of palladium nanoparticles is gaining increasing attention due to their ability to catalyze the rapid dissociation of hydrogen, which leads to an excellent response in hydrogen-sensing applications. However, current palladium-nanoparticle-based sensors are hindered by the presence of hysteresis upon hydride formation and decomposition, as this hysteresis limits sensor accuracy. Here, we present a robust colloidal synthesis for palladium–gold alloy nanoparticles and demonstrate their hysteresis-free response when used for hydrogen detection. The obtained colloidal particles, synthesized in an aqueous, room-temperature environment, can be tailored to a variety of applications through changing the size, ratio of metals, and surface stabilization. In particular, the variation of the viscosity of the mixture during synthesis resulted in a highly tunable size distribution and contributed to a significant improvement in size dispersity compared to the state-of-the-art methods.

Grains constitute the building blocks of polycrystalline materials and their boundaries determine bulk physical properties like electrical conductivity, diffusivity and ductility. However, the structure and evolution of grains in nanostructured materials and the role of grain boundaries in reaction or phase transformation kinetics are poorly understood, despite likely importance in catalysis, batteries and hydrogen energy technology applications. Here we report an investigation of the kinetics of (de)hydriding phase transformations in individual Pd nanoparticles. We find dramatic evolution of single particle grain morphology upon cyclic exposure to hydrogen, which we identify as the reason for the observed rapidly slowing sorption kinetics, and as the origin of the observed kinetic compensation effect. These results shed light on the impact of grain growth on kinetic processes occurring inside nanoparticles, and provide mechanistic insight in the observed kinetic compensation effect.

Energy-conversion devices based on the phenomenon of proton conduction, for example, polymer electrolyte membrane fuel cells (PEMFCs), require low cost and sustainable electrolytes with high ionic conductivity and good mechanical properties under anhydrous conditions and at temperatures up to 150 degrees C. Biopolymers possess an intrinsic thermomechanical stability but an insufficient proton conductivity in the dry state, which however may be imparted by a protic ionic liquid (PIL). This work presents the preparation and properties of composite membranes made of cellulose nanocrystals (CNCs) and a PIL. The membranes are thermally stable and display an ionic conductivity within the range 10(-4)-10(-3) S/cm for temperatures between 120 and 160 degrees C. Moreover, the analysis of the biopolymer's apparent dimensions at nanoscale reveals a dependence of the CNCs' defects, twisting, and aggregation in the presence of the PIL. Preliminary tests using a simple fuel cell setup demonstrate a response of the membranes to the inlet of H-2 gas, with a generation of electrical current. These findings provide a solid groundwork for further development and future studies of biopolymer/PIL electrolytes for energy applications.

Alkali carbonate melts are promising high temperature thermal storage media. In this work five alumina forming alloys have been exposed to a ternary LiNaK carbonate melt and CO2 at 800 degrees C. The corrosion propagation was found to depend on the formation of a slow-growing LiAlO2 scale. Furthermore, the two polymorphs contributing to the LiAlO2 phase were monitored for up to 1000 h: a dense alpha-LiAlO2 scale and gamma-LiAlO2 crystallites. We suggest a growth stress assisted formation of alpha-LiAlO2 relaxing into the outwards growing gamma-LiAlO2 phase. This implies a deceleration of the alpha-LiAlO2 scale growth towards a steady state-thickness.

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X-ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre-nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.

The pyrovanadates $\beta$-Mn$_2$V$_2$O$_7$ and $\beta$-Cu$_2$V$_2$O$_7$ were previously investigated as photoanode materials for water splitting. Neither of them, however, was found to be sufficiently active. In this work we predict the properties of solid solutions of these two structurally similar pyrovanadates via density functional theory calculations to explore the suitability of their band structure for water splitting and to assess their ease of synthesis. We predict that substitution of up to 20\% Cu or Mn into $\beta$-Mn$_2$V$_2$O$_7$ and $\beta$-Mn$_2$V$_2$O$_7$ respectively leads to a narrowing of the band gap, which in the former case is experimentally confirmed by UV-vis spectroscopy. Calculations for solid solutions in the intermediate composition range, however, yield nearly constant band gaps. Moreover, we predict solid-solutions with higher substitution levels to be increasingly difficult to synthesize, implying that solid solutions with low substitution levels are most relevant in terms of band gaps and ease of synthesis.

The pyrovanadates β-Mn2V2O7 and β-Cu2V2O7 were previously investigated as photoanode materials for water splitting. Neither of them, however, was found to be sufficiently active. In this work, we predict the properties of these two structurally similar pyrovanadates upon Cu/Mn substitution in their corresponding lattices via density functional theory calculations to explore the suitability of their band structure for water splitting and to assess their ease of synthesis. We predict that a concentration of up to 20% Cu and Mn into β-Mn2V2O7 and β-Cu2V2O7, respectively, leads to a narrowing of the bandgap, which, in the former case, is experimentally confirmed by UV-vis spectroscopy. Calculations in the intermediate composition range, however, yield nearly constant bandgaps. Moreover, we predict the materials with higher substitution levels to be increasingly difficult to synthesize, implying that low substitution levels are most relevant in terms of bandgaps and ease of synthesis.

The pyrovanadates β-Mn_2V_2O_7 and β-Cu_2V_2O_7 were previously investigated as photoanode materials for water splitting. Neither of them, however, was found to be sufficiently active. In this work we predict the properties of solid solutions of these two structurally similar pyrovanadates via density functional theory calculations to explore the suitability of their band structure for water splitting and to assess their ease of synthesis. We predict that substitution of up to 20% Cu or Mn into β-Mn_2V_2O_7 and β-Mn_2V_2O_7 respectively leads to a narrowing of the band gap, which in the former case is experimentally confirmed by UV-vis spectroscopy. Calculations for solid solutions in the intermediate composition range, however, yield nearly constant band gaps. Moreover, we predict solid-solutions with higher substitution levels to be increasingly difficult to synthesize, implying that solid solutions with low substitution levels are most relevant in terms of band gaps and ease of synthesis.

The ability to tune thin oxide coatings by wet-chemistry is desirable for many applications, yet it remains a key synthetic challenge. In this work, we introduce a general colloidal atomic layer deposition (c-ALD) synthesis to grow an alumina shell with tunable thickness around nanocrystalline cores of various compositions spanning from ionic semiconductors (i.e., CsPbX3, with X = Br, I, Cl) to metal oxides and metals (i.e., CeO2 and Ag). The distinctive characteristics of each core (i.e., emission, facile surface functionalization, stability) allowed us to optimize and to elucidate the chemistry of the c-ALD process. Compared to gas-phase ALD, this newly developed synthesis has the advantage of preserving the colloidal stability of the nanocrystalline core while controlling the shell thickness from 1 to 6 nm. As one example of the opportunities offered by the growth of a thin oxide shell, we study the anion exchange reaction in the CsPbX3 perovskites nanocrystals by in situ X-ray diffraction, which had been impeded so far by the instability of this class of materials and by the fast exchange kinetics.

Synergistic effects at metal/metal oxide interfaces often give rise to highly active and selective catalytic motifs. So far, such interactions have been rarely explored to enhance the selectivity in the electrochemical CO2 reduction reaction (CO2RR). Herein, Cu/CeO2-x, heterodimers (HDs) are synthesized and presented as one of the prime examples where such effects promote CO2RR, A colloidal seeded-growth synthesis is developed to connect the two highly mismatched domains (Cu and CeO2-x) through an interface. The Cu/CeO2-x HDs exhibit state-of-the-art selectivity toward CO2RR (up to similar to 80%) against the competitive hydrogen evolution reaction (HER) and high faradaic efficiency for methane (up to similar to 54%) at -1.2 V-RHE, which is similar to 5 times higher than that obtained when the Cu and CeO2-x nanocrystals are physically mixed. Operando X-ray absorption spectroscopy along with other ex-situ spectroscopies evidences the partial reduction of Ce4+ to Ce3+ in the HDs during CO2RR A Density Functional Theory (DFT) study of the active site motif in reducing condition reveals synergistic effects in the electronic structure at the interface. The proposed lowest free energy pathway utilizes an O-vacancy site with intermediates binding to both Cu and Ce atoms, a configuration which allows one to break the CHO*/CO* scaling relation. The suppression of HER is attributed to the spontaneous formation of CO* at this interfacial motif and subsequent blockage of the Cu-sites.

Understanding nucleation phenomena is crucial across all branches of physical and natural sciences. Colloidal nanocrystals are among the most versatile and tunable synthetic nanomaterials. While huge steps have been made in their synthetic development, synthesis by design is still impeded by the lack of knowledge of reaction mechanisms. Here, we report on the investigation of the reaction intermediates in high temperature syntheses of copper nanocrystals by a variety of techniques, including X-ray absorption at a synchrotron source using a customized in situ cell. We reveal unique insights into the chemical nature of the reaction intermediates and into their role in determining the final shape of the metal nanocrystals. Overall, this study highlights the importance of understanding the chemistry behind nucleation as a key parameter to predict synthetic pathways for shape-controlled nanocrystals.

Laboratory of Nanochemistry for Energy (L and Engineering, École Polytechnique F Switzerland. E-mail: raffaella.buonsanti@ep Department of Chemical Sciences and Engi Lausanne, CH-1950 Sion, Switzerland † Electronic supplementary information synthesis procedure, ligand stripping pro and experimental details for SEM, TEM, ex situ XRD, UV-Vis spectroscopy, FTIR See DOI: 10.1039/c8sc01314d Cite this: Chem. Sci., 2018, 9, 5658

Nanocrystal-seeded synthesis relies on the reaction of nanocrystal seeds with a molecular precursor and it can be regarded as the link between sol–gel and solid-state chemistries.

Materials Copper (I) acetate (CuOAc, 97%), hexane (anhydrous, 95%) was purchased from TCI Deutschland GmbH. Sodium hydroxide (NaOH, 97%), Toluene (anhydrous), Dimethylformamide (DMF, anhydrous) and Acetonitrile (ACN, anhydrous) were purchased from abcr GmbH. Oleic acid (OLAC, ), Oleylamine (OLAM, 70%), Vanadyl acetylacetonate (VO(acac)2, 98%) , Trioctylamine (TOA, 98%), tetradecylphosphonic acid (TDPA, 97%), trimethyloxonium tetrafluoroborate (Me3OBF4, 95%), sodium sulphite (Na2SO3, 98%) and ethanol (anhydrous) were purchased from Sigma-Aldrich and used as received. Boric acid (H3BO3, 99.8%) was purchased from ROTH AG.

Tuning interfaces is crucial to improve charge separation in inorganic bulk heterojunctions.

Copper vanadates have been proposed as promising photoanodes for water-splitting photoelectrochemical cells, but their performance has recently been shown to be severely limited. To understand this behavior, we study the electronic structure and the optical properties of β-Cu2V2O7 both experimentally and computationally. The measured absorption spectrum shows an absorption peak at 1.5 eV followed by the onset of an apparent continuum at 2.26 eV, as generally found for this class of materials. We perform calculations within the framework of the QS GW̃ method and the Bethe-Salpeter equation while including effects of magnetic ordering, nuclear quantum motion, and thermal vibrations. We demonstrate the occurrence of two kinds of excitons with high binding energies upon optical excitation in β-Cu2V2O7, which account for the first absorption peak and the lower edge of the apparent continuum. The results are confirmed by photoluminescence measurements, where sub-band-gap emissions are found for both excitons. These results provide an explanation for the low photocatalytic efficiencies of copper vanadates, despite the favorable size of their optical band gaps.