Strong magnetoresistance effects are often observed in ferromagnet-nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as-grown on catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of ~10 4 % has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-grown multilayer graphene. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range, and can be qualitatively explained within the framework of "interlayer magnetoresistance" (ILMR).[Keywords: Graphene, Chemical Vapor Deposition, Raman Spectroscopy, Interlayer Magnetoresistance, Current-Perpendicular-to-Plane Transport] 2 Artificial layered structures often exhibit strong magnetoresistance (MR) effects that are exploited in various data storage and magnetic field sensing technologies 1 . Graphite is a naturally occurring layered material in which single graphitic layers (or "graphene") are stacked on each other. Graphene, epitaxially grown on ferromagnets (such as nickel), is particularly attractive for spintronics because such systems can potentially realize perfect spin filtering 2 and giant Rashba splitting 3 . However, CPP (current-perpendicular-toplane) MR properties of such layered graphene/ferromagnet structures are still largely underexplored. Here we consider multilayer-graphene (MLG) as-grown on nickel by chemical vapor deposition (CVD) and show that these structures exhibit large and nearly temperature-independent CPP-MR of ~ 10 4 % for a small magnetic field of ~ 2 kilogauss. This MR effect is correlated with the shape of the 2D peak and also with the occurrence of the D peak in Raman spectrum of as-grown MLG. These Raman features can be controlled by varying the CVD growth parameters. Such large negative CPP-MR, which persists even at room temperature, has hitherto not been reported in any graphitic system 4-14 . Figure 1a shows the device schematic. CVD growth of MLG is performed on 2 cm × 2 cm nickel (Ni) foils, which act as catalyst for graphene growth as well as bottom electrical contact. To ensure uniform current distribution 6 , the second contact is fabricated at the center of the top MLG surface using silver epoxy. Area of the top contact is ~ 1 mm 2 . As shown in Figure S1 (section I, Supplementary Information), the Ni substrate is polycrystalline with primarily (111) grains. Details of the fabrication process are provided in section I of Supplementary Information. Figure 1b shows a FESEM image of the as-grown large-area MLG on Ni. Raman spectra taken from three representative regions of this sample are shown in the top inset of Figure 1b. The top Raman spectrum (black line) is most commonly observed, with few occurren...

Abstract. Anodic aluminum oxide (AAO) or anodic alumina template containing hexagonally ordered nanopores has been widely used over the last decade for the development of numerous functional nanostructures such as nanoscale sensors, computing networks and memories. The long range pore order requires the starting aluminum surface to be extremely smooth. Electropolishing is the most commonly used method for surface planarization prior to anodization. While prevalent, this method has several limitations in terms of throughput, polishing area and requirement of special experimental setups, which introduce additional speed bottlenecks in the intrinsically slow AAO-based nanofabrication process. In this work we report a new generation of the so-called -chemical polishing‖ approach which circumvents these stumbling blocks in the pretreatment phase and offers a viable, simpler, safer and faster alternative to electropolishing. These benefits are obtained without sacrificing the quality of the final AAO template. In this work we have (a) identified the optimum parameter regime for chemical polishing and (b) determined process conditions for which a novel parallel nanoridge configuration self-assembles and extends over a distance of several microns. Such patterns can be used as a mask for fabricating nanocrossbars, which are the main structural components in myriad nanoscale memories and crosspoint architectures.

Template-Assisted Synthesis of π -Conjugated Molecular Organic Nanowires in the Sub-100 nm Regime and Device Implicationsπ -conjugated molecular organics such as rubrene, Alq 3 , fullerene, and PCBM have been used extensively over the last few decades in numerous organic electronic devices, including solar cells, thin-fi lm transistors, and large-area, low-cost fl exible displays. Rubrene and Alq 3 , have emerged as promising platforms for spin-based classical and quantum information processing, which has triggered signifi cant research activity in the relatively new area of organic spintronics. Synthesis of these materials in a nanowire geometry, with feature sizes in the sub-100 nm regime, is desirable as it often enhances device performance and is essential for development of high-density molecular electronic devices. However, fabrication techniques that meet this stringent size constraint are still largely underdeveloped. Here, a novel, versatile, and reagentless method that enables growth of nanowire arrays of the above-mentioned organics in the cylindrical nanopores of anodic aluminum oxide (AAO) templates is demonstrated. This method 1) allows synthesis of high-density organic nanowire arrays on arbitrary substrates, 2) provides electrical access to the nanowire arrays, 3) offers tunability of the array geometry in a range overlapping with the relevant physical length scales of many organic devices, and 4) can potentially be extended to synthesize axially and radially heterostructured organic nanowires. Thus prepared nanowires are characterized extensively with an aim to identify their potential applications in diverse areas such as organic optoelectronics, photovoltaics, molecular nanoelectronics, and spintronics.

Current-perpendicular-to-plane (CPP) magnetoresistance (MR) effects are often exploited in various state-of-the-art magnetic field sensing and data storage technologies. Most of the CPP-MR devices are artificial layered structures of ferromagnets and non-magnets, and in these devices, MR manifests, due to spin-dependent carrier transmission through the constituent layers. In this work, we explore another class of artificial layered structure in which multilayer graphene (MLG) is grown on a metallic substrate by chemical vapor deposition (CVD). We show that depending on the nature of the graphene-metal interaction, these devices can also exhibit large CPP-MR. Magnetoresistance ratios (>100%) are at least two orders of magnitude higher than “transferred” graphene and graphitic samples reported in the literature, for a comparable temperature and magnetic field range. This effect is unrelated to spin injection and transport and is not adequately described by any of the MR mechanisms known to date. The simple fabrication process, large magnitude of the MR and its persistence at room temperature make this system an attractive candidate for magnetic field sensing and data storage applications and, also, underscore the need for further fundamental investigations on graphene-metal interactions

Chemical Vapor Deposition grown multilayer graphene (MLG) exhibits large out-of-plane magnetoresistance due to interlayer magnetoresistance (ILMR) effect. It is essential to identify the factors that influence this effect in order to explore its potential in magnetic sensing and data storage applications. It has been demonstrated before that the ILMR effect is sensitive to the interlayer coupling and the orientation of the magnetic field with respect to the out-of-plane (c-axis) direction. In this work, we investigate the role of MLG thickness on ILMR effect. Our results show that the magnitude of ILMR effect increases with the number of graphene layers in the MLG stack. Surprisingly, thicker devices exhibit field induced resistance switching by a factor of at least ~107. This effect persists even at room temperature and to our knowledge such large magnetoresistance values have not been reported before in the literature at comparable fields and temperatures. In addition, an oscillatory MR effect is observed at higher field values. A physical explanation of this effect is presented, which is consistent with our experimental scenario.