Trivalent ion overcharging on electrified graphene

The structure of the electrical double layer (EDL) formed near graphene in aqueous environments strongly impacts its performance for a plethora of applications, including capacitive deionization. In particular, adsorption and organization of multivalent counterions near the graphene interface can promote nonclassical behaviors of EDL including overcharging followed by co-ion adsorption. In this paper, we characterize the EDL formed near an electrified graphene interface in dilute aqueous YCl3 solution using in situ high resolution x-ray reflectivity (also known as crystal truncation rod (CTR)) and resonant anomalous x-ray reflectivity (RAXR). These interface-specific techniques reveal the electron density profiles with molecular-scale resolution. We find that yttrium ions (Y3+) readily adsorb to the negatively charged graphene surface to form an extended ion profile. This ion distribution resembles a classical diffuse layer but with a significantly high ion coverage, i.e., 1 Y3+ per 11.4 ± 1.6 Å2, compared to the value calculated from the capacitance measured by cyclic voltammetry (1 Y3+ per ~240 Å2). Such overcharging can be explained by co-adsorption of chloride that effectively screens the excess positive charge. The adsorbed Y3+ profile also shows a molecular-scale gap (≥5 Å) from the top graphene surfaces, which is attributed to the presence of intervening water molecules between the adsorbents and adsorbates as well as the lack of inner-sphere surface complexation on chemically inert graphene. We also demonstrate controlled adsorption by varying the applied potential and reveal consistent Y3+ ion position with respect to the surface and increasing cation coverage with increasing the magnitude of the negative potential. This is the first experimental description of a model graphene-aqueous system with controlled potential and provides important insights into the application of graphene-based systems for enhanced and selective ion separations.

Temperature, strain and charge mediated multiple and dynamical phase changes of selenium and tellurium

Trigonal-Se and -Te change to a metallic or a simple cubic structure under thermal excitation, compressive strain and excess positive charge, or to metallic, body-centered tetragonal and body-centered orthorhombic structures under negative charging.

An investigation of the generation and properties of laboratory-produced ball lightning

The experiments revealed that ball lightning is a self-confining quasi-neutral in a whole plasma system that rotates around its axis. Ball lightning has a structure of a spherical electric domain, consisting of a kernel with excess negative charge and an external spherical layer with excess positive charge. The excess of charges of one sort and the lack of charges of the other sort in the kernel or in the external spherical layer significantly reduces the possibility of electron capture by means of an electric field, created by the nearest ions and leads to a drastic slowdown of recombination process. Direct proof has been obtained that inside of ball lightning – in an external spherical layer that rotates around the axis – there is a circular current of sub-relativistic particles. This current creates and maintains its own poloidal magnetic field of ball lightning, i.e. it carries out the function of magnetic dynamo. The kernel of ball lightning is situated in a region with minimum values of induction of the magnetic field. The inequality of positive and negative charges in elements of ball lightning also significantly reduces losses of the charged plasma on bremsstrahlung. Ball lightning generation occurs in a plasmic vortex. The ball lightning energy in the region of its generation significantly differs from the ball lightning energy, which is drifting in space. The axial component of kinetic energy of particles slightly exceeds 100 keV and the rotational component of the ions energy is a bit greater than 1 MeV. Ball lightning is ‘embedded’ in atmosphere autonomous accelerator of charged particles of a cyclotron type due to self-generation of strong crossed electric and magnetic fields. A discussion of the conditions of stability and long-term existence of ball lightning is given.

Carrier Accumulation in Silicon-On-Insulator Structures Containing Ge Nanocrystals in the Burried SiO2 Layer

Electro-physical properties of metal-oxide-silicon (MOS) structures and MOS transistors, prepared in the top silicon layer of silicon-on-insulator (SOI) structures containing Ge nanocrystals in the buried SiO2 layers, have been studied. It was obtained that carrier accumulation in MOS structures depend on the direction of built-in electrical field in MOS structures. Accumulation of the excess negative charges in the case of p-channel transistors is associated with electron trapping on Ge nanocrystals synthesized in the buried dielectric. In the case of n-channel transistor, positive charge related to the Si/SiO2 interface or to the charged oxide is accumulated. The Ge atoms diffused to the SiO2/Si interface can stimulate the formation of the excess positive charge.

The adsorption of CH 4 , C 2 H 6 and neo-C 5 H 12 on (111), (100) and (110) faces of nickel observed by l. e. e. d. and by photoelectric work-function measurement

Low-energy electon diffraction and photoelectric work-function measurements have been made with(111), (110) and (100) nickel surfaces, and the results of adsorption of methane, ethane and neopentane on these surfaces have been studied. Diffraction patterns from ordered structures were observed in all cases of hydrocarbon absorption at 20 °C; however, these were also accompanied by appreciable diffuse scattering from disordered adsorption. The ordered arrays formed initially at 20 °C were from various (2×2) structures, and it is concluded that in all cases the adsorbed entities in the ordered arrays were C 1 units, probably CH 2 . Treatments at higher exposures and higher temperatures resulted in a sequence of surface structures of which the high temperature (> 350 °C) end products were: for (111) and (110), ‘pseudo-clean’ surfaces, where the term ‘pseudo-clean’ refers to a surface covered with carbon atoms in a P (1×1) structure forming the same mesh as that of the surface nickel atoms, and with the carbon atoms probably in the normal surface crystallographic sites; for (100), P (2×2) where the adsorbed entities were again probably carbon atoms. Some apparently complex structures formed on (111) and (110) before the ‘pseudo-clean’ surfaces were probably coincidence lattice structures. Hydrocarbon adsorption resulted in all cases in work-function reductions. From an interpretation of these data it is concluded that an (isolated) adsorbed CH 2 residue has a surface dipole of about 0.2 to 0.3 D (Debye unit) on (100), while on (110) and (111) the corresponding figures are both about 0.7 to 0.8 D. The origin of this dipole is discussed in terms of the likely surface bonding. For the ultimate high temperature surfaces (i. e. 350 °C) the work-functions were about 0.2 to 0.3 eV below the clean surface values, and this is interpreted as resulting from carbon atoms with a net excess positive charge situated a little above the plane of the outermost nickel atoms.