We present a new scanning-probe-based data-storage concept called the "millipede" that combines ultrahigh density, terabit capacity, small form factor, and high data rate. Ultrahigh storage density has been demonstrated by a new thermomechanical local-probe technique to store, read back, and erase data in very thin polymer films. With this new technique, nanometer-sized bit indentations and pitch sizes have been made by a single cantilever/tip into thin polymer layers, resulting in a data storage densities of up to 1 Tb/in 2 . High data rates are achieved by parallel operation of large two-dimensional (2-D) atomic force microscope (AFM) arrays that have been batch-fabricated by silicon surface-micromachining techniques. The very large-scale integration (VLSI) of micro/nanomechanical devices (cantilevers/tips) on a single chip leads to the largest and densest 2-D array of 32 32 (1024) AFM cantilevers with integrated write/read/erase storage functionality ever built. Time-multiplexed electronics control the functional storage cycles for parallel operation of the millipede array chip. Initial areal densities of 100-200 Gb/in 2 have been achieved with the 32 32 array chip, which has potential for further improvements. A complete prototype system demonstrating the basic millipede functions has been built, and an integrated five-axis scanner device used in this prototype is described in detail. For millipede storage applications the polymer medium plays a crucial role. Based on a systematic study of different polymers with varying glass-transition temperatures, the underlying physical mechanism of bit writing has been identified, allowing the correlation of polymer properties with millipede-relevant parameters. In addition, a novel erase mechanism has been established that exploits the metastable nature of written bits.Index Terms-Atomic force microscope (AFM) array chips, microscanner, millipede, nano-indentation, polymer films, scanning probe data storage, thermomechanical write/read/erase.

Packaging electronic devices is a growing challenge as device performance and power levels escalate. As device feature sizes decrease, ensuring reliable operation becomes a challenge. Ensuring effective heat transfer from an integrated circuit and its heat spreader to a heat sink is a vital step in meeting this challenge. The projected power density and junction-toambient thermal resistance for high-performance chips at the 14 nm generation are >100 Wcm −2 and <0.2 °CW −1 , respectively. The main bottleneck in reducing the net thermal resistance are the thermal resistances of the thermal interface material (TIM). This review evaluates the current state of the art of TIMs. Here, the theory of thermal surface interaction will be addressed and the practicalities of the measurement techniques and the reliability of TIMs will be discussed. Furthermore, the next generation of TIMs will be discussed in terms of potential thermal solutions in the realisation of Internet of Things.

Graphene and related two-dimensional materials have shown unusual and exceptional mechanical properties, with similarities to origami-like paper folding and kirigami-like cutting demonstrated. For paper analogues, a critical difference between macroscopic sheets and a two-dimensional solid is the molecular scale of the thin dimension of the latter, allowing the thermal activation of considerable out-of-plane motion. So far thermal activity has been shown to produce local wrinkles in a free graphene sheet that help in theoretically understanding its stability, for example, and give rise to unexpected long-range bending stiffness. Here we show that thermal activation can have a more marked effect on the behaviour of two-dimensional solids, leading to spontaneous and self-driven sliding, tearing and peeling from a substrate on scales approaching the macroscopic. We demonstrate that scalable nanoimprint-style contact techniques can nucleate and direct the parallel self-assembly of graphene ribbons of controlled shape in ambient conditions. We interpret our observations through a simple fracture-mechanics model that shows how thermodynamic forces drive the formation of the graphene-graphene interface in lieu of substrate contact with sufficient strength to peel and tear multilayer graphene sheets. Our results show how weak physical surface forces can be harnessed and focused by simple folded configurations of graphene to tear the strongest covalent bond. This effect may hold promise for the patterning and mechanical actuating of devices based on two-dimensional materials.

We report on the first controlled alternation between memory and threshold resistance switching (RS) in single Ni/NiO core-shell nanowires by setting the compliance current (I(CC)) at room temperature. The memory RS is triggered by a high I(CC), while the threshold RS appears by setting a low I(CC), and the Reset process is achieved without setting a I(CC). In combination with first-principles calculations, the physical mechanisms for the memory and threshold RS are fully discussed and attributed to the formation of an oxygen vacancy (Vo) chain conductive filament and the electrical field induced breakdown without forming a conductive filament, respectively. Migration of oxygen vacancies can be activated by appropriate Joule heating, and it is energetically favorable to form conductive chains rather than random distributions due to the Vo-Vo interaction, which results in the nonvolatile switching from the off- to the on-state. For the Reset process, large Joule heating reorders the oxygen vacancies by breaking the Vo-Vo interactions and thus rupturing the conductive filaments, which are responsible for the switching from on- to off-states. This deeper understanding of the driving mechanisms responsible for the threshold and memory RS provides guidelines for the scaling, reliability, and reproducibility of NiO-based nonvolatile memory devices.

Heat conduction governs the ultimate writing and reading capabilities of a thermomechanical data storage device. This work investigates transient heat conduction in a resistively heated atomic force microscope cantilever through measurement and simulation of cantilever thermal and electrical behavior. The time required to heat a single cantilever to bit-writing temperature is near 1 μs and the thermal data reading sensitivity ΔR/R is near 1×10−4 per vertical nm. Finite-difference thermal and electrical simulation results compare well with electrical measurements during writing and reading, indicating design tradeoffs in power requirements, data writing speed, and data reading sensitivity. We present a design for a proposed cantilever that is predicted to be faster and more sensitive than the present cantilever.

The squeezing of polymers in narrow gaps is important for the dynamics of nanostructure fabrication by nanoimprint embossing and the operation of polymer boundary lubricants. We measured stress versus strain behavior while squeezing entangled polystyrene films to large strains. In confined conditions where films were prepared to a thickness less than the size of the bulk macromolecule, resistance to deformation was markedly reduced for both solid-glass forging and liquid-melt molding. For melt flow, we further observed a complete inversion of conventional polymer viscosity scaling with molecular weight. Our results show that squeeze flow is accelerated at small scales by an unexpected influence of film thickness in polymer materials.

In thermomechanical data writing, a resistively-heated atomic force microscope (AFM) cantilever tip forms indentations in a thin polymer film. The same cantilever operates as a thermal proximity sensor to detect the presence of previously written data bits. This paper uses recent progress in thermal analysis of the writing and reading modes to develop new cantilever designs for increased speed, sensitivity, and reduced power consumption in both writing and reading operation. Measurements of cantilever electrical resistance during heating reveals physical limits of cantilever writing and reading, and verifies a finite-difference thermal and electrical simulation of cantilever operation. This work proposes two new cantilever designs that correspond to fabrication technology benchmarks. Simulations predict that the proposed cantilevers have a higher data rate and are more sensitive than the present cantilever. The various cantilever designs offer single-bit writing times of 0.2 s-25 s for driving voltages of 2-25 V. The thermal reading 1 sensitivity is as high as 4 10 4 per vertical nm in near steady-state operation. Analysis of the adaptable operation of a single cantilever bounds the operation of a cantilever array. The present cantilever operates with an array data rate as high as 35 Mbit sec 1 at a power of 330 mW and can operate at less than 100 mW. Proposed cantilevers offer a factor of 10 improvements in both data rate and power consumption. By considering their thermal, mechanical and electrical design, and by optimizing cantilevers for both writing and reading, this work aims to guide the future development of AFM cantilevers for thermomechanical data storage systems.

We have measured forces between an atomically defined W(111) tip and an Au(111) sample in ultrahigh vacuum at 150 K. The W tips are manipulated and characterized on an atomic scale both before and after sample approach by field ion microscopy. Forces between the tip and the sample are measured by an in situ differential interferometer. We observe strong attractive adhesion forces, which turn repulsive upon the further approach of the tip towards the Au surface. Unexpected for a metallic system, there is no spontaneous jump to contact. The force versus tip-sample distance curve shows only modest hysteresis, and the field ion microscopy images reveal an atomically unchanged tip apex.[S0031-9007 (98) Many physical phenomena are believed to be governed by the effects of metallic adhesion. The study of those interactions can shed light on the fields of powder metallurgy, machining, and tribology, and will advance our understanding of molecular-scale lubrication. Furthermore, the study of force interactions between a tip and a sample plays a key role in understanding imaging mechanisms in scanning tunneling microscopy [1] and atomic force microscopy [2]. Moreover, tip-sample forces constitute the basic mechanism for atomic [3] and molecular-scale manipulation [4]. Tip-sample adhesion has been investigated previously [5][6][7]. Although the geometrical shape of the tip as well as the chemical composition of the apex surface [6,8] have a significant effect on the strength and character of the interaction, in all previous investigations the structure of the tip was in fact unknown. Hence, tip fabrication and characterization on the atomic level in combination with local probe microscopies are a prerequisite for attaining full control over imaging and manipulation processes. We have taken a first step in this direction by investigating the adhesion interaction between an atomically characterized W(111) trimer tip and a Au(111) surface.Experiments were conducted under ultrahigh vacuum (UHV) conditions (p , 2 3 10 211 mbar) and at a temperature of 150 K. The apparatus [9] (see Fig.