Metal/Self-Assembled Monolayer/Metal Junctions for Magnetoelectronic Applications.
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Metal/Self-Assembled Monolayer/Metal Junctions for Magnetoelectronic Applications. Y.A Ovchenkov , Chunjuan Zhang 1 , J. Redepenning 1 , B. Doudin Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE 685880111 1
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304 ABSTRACT
Metal/organic self-assembled monolayer/metal junctions were investigated for junction areas 10-2 to 102 µm2. Several types and thickness of monolayers are investigated, and magnetic electrodes were made. Electroless deposition was used to make the top metal without disrupting the organic film. This deposition is activated with Pd clusters obtained by evaporation or by chemical reduction of a Pd-based catalyst. This method allows us to obtain a high yield of junctions that are not electrically shorted and are mechanically and electrically stable over a wide temperature range. Low-temperatures investigations reveal strong non-linearity in the IV curves and an increase of resistance with decreasing temperature. Zero bias anomalies observed at low temperatures are attributed to a Coulomb blockade associated with the Pd clusters. INTRODUCTION Metal-Insulator-Metal (MIM) tunnel junctions are of great interest for applications as magnetic sensors and memory devices. If both metals are ferromagnetic, the tunnel resistance of the system depends on the relative magnetic orientations of the two magnetic layers [1]. The magnitude of this effect (typically reaching 40%) depends on the properties of the insulator. The main desirable properties are the possibility to make very thin barriers (smaller than 1 nm), with atomically sharp interfaces. To date, the vast majority of tunnel magnetic junctions have been constructed using Al2O3 barriers. We intend to examine the possibility to use organic films as an alternative to Al2O3 in MIM structures. It is well-documented that a variety organic thiols can be used to construct self assembled monolayers (SAM) on metallic surfaces [2]. However, significant synthetic difficulties are encountered when trying to deposit a top metallic electrode without disrupting the organic substructure. Evaporated and sputtered metal layers are often not stable on organic thiol monolayers [3]. High diffusibility of thiols [4], as well as low structural stability of evaporated/sputtered films, usually destroys the MIM structure. We have successfully used electroless deposition (ELD) to plate ferromagnetic metal films on top of self-assembled organic tunnel barriers. Such metal films can show better structural stability than their evaporated or sputtered counterparts [5]. Mechanical and thermal damage to the organic layers is avoided. We can also tailor the distal end of alkanethiols with functional groups capable of activating ELD growth. This method is known as selective ELD [6].
We report here the preparation and characterization of two types of MIM junctions (Figure.1 ). The first, which was pattern using lithographic techniques, has a planar cross geometry with junction a
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