ABSTRACT
Integration of electrochemical capacitors with silicon-based electronics is a major challenge, limiting energy storage on a chip. We describe a wafer-scale process for manufacturing strongly adhering carbide-derived carbon films and interdigitated micro-supercapacitors with embedded titanium carbide current collectors, fully compatible with current microfabrication and silicon-based device technology. Capacitance of those films reaches 410 farads per cubic centimeter/200 millifarads per square centimeter in aqueous electrolyte and 170 farads per cubic centimeter/85 millifarads per square centimeter in organic electrolyte. We also demonstrate preparation of self-supported, mechanically stable, micrometer-thick porous carbon films with a Young's modulus of 14.5 gigapascals, with the possibility of further transfer onto flexible substrates. These materials are interesting for applications in structural energy storage, tribology, and gas separation.
ABSTRACT
The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe3-xO4, i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x=1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization Ms and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.
Subject(s)
Ferrosoferric Oxide/chemistry , Magnetics , Metal Nanoparticles/chemistry , Particle Size , X-Ray DiffractionABSTRACT
Liquid-liquid phase transfer has been used to synthesize platinum nanocrystals with a cubic morphology. By finely tuning the parameters controlling the nucleation and growth processes, nanometric truncated cubes or perfect cubes may be obtained. To our knowledge, this is the first time such shapes are obtained with this procedure. The importance of both the length of the capping agent to control the growth process and the bromide anions as poison for the (111) facet is shown. The low degree of size polydispersity allows these nanocrystals to self-assemble with a long-range ordering in two-dimensional and three-dimensional supracrystals. According to the nanocrystal shape, simple cubic or face-centered cubic supracrystals are observed. It is remarkable to notice that well-faceted supracrystals with sizes on the order of 10 microm may be obtained.
ABSTRACT
Controlled synthesis of magnetic nanoparticles with a well-known size and composition is always a challenge. A soft chemical synthesis was developed to obtain magnetic alloy nanocrystals with a high ability to control composition, size, and polydispersity. Cobalt-platinum alloy nanocrystals were synthesized using a colloidal approach by the liquid-liquid phase transfer method. Structural characterization using HRTEM and XRD was carried out on nanocrystals in the range of 25-75% cobalt composition, which indicated the formation of nanoalloy bimetallic CoxPt100-x. Adjusting the alkylamine capping agent and the kinetics of the reduction process allowed tuning of the size in the range of 1.8-4 nm while keeping an equiatomic composition. The narrow size distribution led to the possibility of inducing nanoparticle self-organization over a long range. The magnetic properties of the Co50Pt50 nanoalloy in the disordered face-centered cubic phase A1 were studied for different nanoparticle sizes.
