The structure of graphite oxide (GO) has been systematically studied using various tools such as SEM, TEM, XRD, Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), (13)C solid-state NMR, and O K-edge X-ray absorption near edge structure (XANES). The TEM data reveal that GO consists of amorphous and crystalline phases. The XPS data show that some carbon atoms have sp(3) orbitals and others have sp(2) orbitals. The ratio of sp(2) to sp(3) bonded carbon atoms decreases as sample preparation times increase. The (13)C solid-state NMR spectra of GO indicate the existence of -OH and -O- groups for which peaks appear at 60 and 70 ppm, respectively. FT-IR results corroborate these findings. The existence of ketone groups is also implied by FT-IR, which is verified by O K-edge XANES and (13)C solid-state NMR. We propose a new model for GO based on the results; -O-, -OH, and -C=O groups are on the surface.

We report the fabrication of nickel nanospaced electrodes by electroplating and electromigration for nanoelectronic devices. Using a conventional electrochemical cell, nanogaps can be obtained by controlling the plating time alone and after a careful optimization of electrodeposition parameters such as electrolyte bath, applied potential, cleaning, etc. During the process, the gap width decreases exponentially with time until the electrode gaps are completely bridged. Once the bridge is formed, the ex situ electromigration technique can reopen the nanogap. When the gap is ∼ 1 nm, tunneling current-voltage characterization shows asymmetry which can be corrected by an external magnetic field. This suggests that charge transfer in the nickel electrodes depends on the orientation of magnetic moments.

We report the fabrication and characterization of copper microelectrodes obtained by a homemade lithography technique and after gold electroless deposition. For the fabrication, planes consisting of arrays of electrodes (black in color) with bow tie shape were designed and printed on a transparent paper (Canson ltd.). Using an embroidery frame with a silk fabric, a photographic emulsion was spread on the silk and simultaneously pressing the Canson paper on it. The system was introduced into a closed box and exposed with a UV light. The designed electrode templates prevented direct exposition of the UV light over copper films and indelible ink was spread over it. After the ink was dried, the copper film is immersed into ferric acid to attack the uncovered copper parts (where there is no ink). In this way, we obtained copper electrodes with initial gap separation of ~142μm and subsequently, they followed electroless deposition of gold to make the copper electrodes to contact. For the characterization, electrical measurements were performed. They present ohmic resistance values in the order of 10 6 Ω produced by surface scattering of the electrons within the gold microwire and enhanced by oxidation of the copper electrodes.

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En este trabajo se estudia la morfología y cristalización de la superficie de películas delgadas de Cu (expuestos al medio ambiente) sobre sustratos de SiO2/Si. Las muestras fueron sometidas a tratamientos térmicos mediante el uso de un horno tubular, en un rango de temperaturas comprendidas entre 250ºC y 1000ºC durante 3 horas para luego ser enfriadas a razón de 1.4ºC/min. La cristalización de las muestras luego de los tratamientos térmicos fueron caracterizadas mediante difracción de Rayos X (DRX), mientras que la morfología de la superficie se analizo usando Microscopia Electrónica de Barrido (MEB). Los resultados obtenidos fueron analizados y encontramos que la temperatura de recocido mas optima que mejor la dirección (111) en la pelicula de cobre y que permite conocer la dinámica de los átomos de la superficie del sistema Cu/SiO2 con respecto a la temperatura, está comprendida en el rango de 400 y 500ºC. Durante todo el proceso de recocido las superficies de las muestras se oxidan y notamos la presencia de siliciuros de cobre