There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Many metal–insulator–metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.

http://chialvo.org/Curso/UBACurso/DIA7/Papers/Aono_NatMat_07_Ionic%20Switching%20Memory.pdf

Nanoionics-based resistive switching memories

Nanoscale metal/oxide/metal switches have the potential to transform the market for nonvolatile memory and could lead to novel forms of computing. However, progress has been delayed by difficulties in understanding and controlling the coupled electronic and ionic phenomena that dominate the behaviour of nanoscale oxide devices. An analytic theory of the ‘memristor’ (memory-resistor) was first developed from fundamental symmetry arguments in 1971, and we recently showed that memristor behaviour can naturally explain such coupled electron–ion dynamics. Here we provide experimental evidence to support this general model of memristive electrical switching in oxide systems. We have built micro- and nanoscale TiO2 junction devices with platinum electrodes that exhibit fast bipolar nonvolatile switching. We demonstrate that switching involves changes to the electronic barrier at the Pt/TiO2 interface due to the drift of positively charged oxygen vacancies under an applied electric field. Vacancy drift towards the interface creates conducting channels that shunt, or short-circuit, the electronic barrier to switch ON. The drift of vacancies away from the interface annilihilates such channels, recovering the electronic barrier to switch OFF. Using this model we have built TiO2 crosspoints with engineered oxygen vacancy profiles that predictively control the switching polarity and conductance. Nanoscale metal/oxide/metal devices that are capable of fast non-volatile switching have been built from platinum and titanium dioxide. The devices could have applications in ultrahigh density memory cells and novel forms of computing.

Memristive switching mechanism for metal/oxide/metal nanodevices.

The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.

Synthetic molecular motors and mechanical machines.

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Die Erfindung betrifft eine Vorrichtung fur ein Raster-Kraft Mikroskop (AFM) zur Untersuchung und/oder Modifikation von Materialoberflachen (11). Die Vorrichtung umfasst einen Cantilever (Biegebalken) (1) mit einem integrierten, piezoresistiven Sensor (8) und einem integrierten Bimorph-Aktuator (7), sowie eine Messspitze (5). Die Messspitze (5) tragt mindestens zwei metallische Elektroden (4), die uber elektrische Anschlusse (2) ansteuerbar sind. Die Messspitze (5) und/oder der Cantilever (1) besitzen mindestens ein nanoskopisches Loch (6), durch welches Synchrotronstrahlung oder Laserlicht (3) auf die zu untersuchende Materialoberflache (11) gerichtet wird. Die Erfindung betrifft weiterhin ein Verfahren zur Untersuchung und Modifikation von Materialoberflachen und oberflachennahen Eigenschaften, welches mit einer solchen Vorrichtung ausfuhrbar ist. Dabei werden Raster-Kraft Mikroskopie (AFM), resonante Raman-Streuung (SERS), Photoemissionsspektroskopie(XPS, XAS) und Materialmodifikation durch lokale Belichtung nacheinander oder gleichzeitig mit ein und derselben Vorrichtung ausgefuhrt.

Vorrichtung und verfahren für ein raster-kraft mikroskop zur untersuchung und modifikation von oberflächeneigenschaften

A novel approach to dry development of exposed photo resist is described in which a photo resist layer is exposed to a visible light source in order to remove the resist in the areas of exposure. The class of compounds used as the resist material, under the influence of the light source, undergoes a chemical/structural change such that the modified material becomes volatile and is thus removed from the resist surface. The exposure process is carried out for a time sufficient to ablate the exposed resist layer down to the layer below. A group of compounds found to be useful in this process includes aromatic calixarenes.

Lithographic dry development using optical absorption

In scanning electron microscopy (SEM), imaging nanoscale features by means of the cross-sectioning method becomes increasingly challenging with shrinking feature sizes. However, obtaining high quality images, at high magnification, is crucial for critical dimension and patterned feature evaluation. Therefore, in this work, we present a new sample preparation method for high performance cross-sectional secondary electron (SE) imaging, targeting features at the deep nanoscale and into the sub-10 nm regime. Different coating architectures including conductive and non-conductive polymer, carbon and metal are compared on their ability to discern etching feature profiles and materials interfaces of densely packed nano-patterned features. A stacked coating of polymer and metal produced better visibility mainly due to enhancement of contrast between feature and background. Contrast was evaluated by using histograms of intensity of gray levels directly derived from SE images, obtained by the SE in-lens detector. In polymer–metal coatings (PMC), optimization of contrast is explored by varying the thickness of the metal layer and results are discussed in terms of the effectiveness of the metal layer in reducing the escape of secondary electrons (SE) generated in the polymer layer and feature. Other advantages of PMCs are their cleanroom compatibility and ease of coating removal.

Polymer–metal coating for high contrast SEM cross sections at the deep nanoscale

Density of up to 2 Tdpsi (Figure 2) have been fabricated. Subsequent media fabrication involves transferring the nano features from a template into magnetic thin films by NIL and ion-beam etching (IBE). Using this approach, HDMR media with fully functional integrated servo features has been successfully fabricated on 2.5” disks with areal density of up to 2.0 Tdpsi. On a spinstand, track-following capability and basic read-write functionality of a 1.5 Tdpsi HDMR media has been demonstrated.

Deirdre L. Olynick

Papers

Vorrichtung und verfahren für ein raster-kraft mikroskop zur untersuchung und modifikation von oberflächeneigenschaften

Lithographic dry development using optical absorption

Polymer–metal coating for high contrast SEM cross sections at the deep nanoscale

Heated Dot Magnetic Recording Media - Path to 10 Tdots/in 2