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Nanoscale sliding friction involving a polystyrene melt near its glass transition temperature Tg (373 K) exhibited dissipation phenomena that provide insight into the underlying molecular relaxation processes. A dissipative length scale that shows significant parallelism with the size of cooperatively rearranging regions (CRRs) could be experimentally deduced from friction-velocity isotherms, combined with dielectric loss analysis. Upon cooling to ∼10 K above Tg, the dissipation length Xd grew from a segmental scale of ∼3 Å to 2.1 nm, following a power-law relationship with the reduced temperature Xd∼T R-[lowercase_phi_synonym]. The resulting [lowercase_phi_synonym]=1.89±0.08 is consistent with growth predictions for the length scale of CRRs in the heterogeneous regime of fragile glass formers. Deviations from the power-law behavior closer to Tg suggest that long-range processes, e.g., the normal mode or ultraslow Fischer modes, may couple with the α relaxation, leading to energy dissipation in domains of tens of nanometers. [ABSTRACT FROM AUTHOR]

A modulated nanoindentation technique has been developed for thermal transition analysis of polymer thin films. The procedure was applied to glass transition measurements of poly-t-butylacrylate, with results that compare well with shear-modulated force microscopy and differential scanning calorimetry. The advantages of the modulated indentation technique are twofold: (i) it provides in situ experimental access to material properties in nanoscopically confined geometries, and (ii) it incorporates well-defined indenter geometries, which provide a means for quantitative thermorheological analysis that is not available with conventional scanning probe microscopy. The experimental procedure and critical test parameters are detailed. [ABSTRACT FROM AUTHOR]

Interfacial glass transition temperature (T[sub g]) profiles in spin cast, ultrathin films of polystyrene and derivatives were investigated using shear-modulated scanning force microscopy. The transitions were measured as a function of film thickness (δ), molecular weight, and crosslinking density. The T[sub g](δ) profiles were nonmonotonic and exhibited two regimes: (a) a sublayer extending about 10 nm from the substrate, with T[sub g] values lowered up to ∼10 °C below the bulk value, and (b) an intermediate regime extending over 200 nm beyond the sublayer, with T[sub g] values exceeding the bulk value by up to 10 °C. Increasing the molecular weight was found to shift the T[sub g](δ) profiles further from the substrate interface, on the order of 10 nm/kDa. Crosslinking the precast films elevated the absolute T[sub g] values, but had no effect on the spatial length scale of the T[sub g](δ) profiles. These results are explained in the context of film preparation history and its influence on molecular mobility. Specifically, the observed rheological anisotropy is interpreted based on the combined effects of shear-induced structuring and thermally activated interdiffusion. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Resistive random access memory (ReRAM) devices are emerging candidates for the next generation of nonvolatile high-density memory (Sills et al., 2014). The value proposition for this technology is bit alterability, high speed operation, long retention and high endurance. In addition, low-power and low-current operation is highly desirable for high-density memory systems targeting the growing mobile market. This paper presents various challenges in engineering a ReRAM cell suitable for high-density applications such as material selection, programming algorithms, noise issues and scaling path. [ABSTRACT FROM AUTHOR]

The underpinnings of material properties in nanoscopic polymer systems are reviewed in light of the relaxation modes available for molecular motion. When motion is altered due to the presence of constraints, a rich variety of material and transport behaviors become apparent. On the one hand, external constraints imposed by interfaces and system boundaries generate structural and dynamical anisotropies that can propagate over device-relevant length scales. On the other hand, the ability to cater relaxation behavior through molecularly-engineered internal constraints offers a path to optimize material properties in nanoscopic systems. These two aspects are highlighted throughout the review, and their technological implications are discussed for MEMS/NEMS operations, including frictional and mechanical loading of polymer thin films. In this regard, material performance attributes and feedback for molecular designs are drawn from perturbation techniques that provide access to the energetic signatures and characteristic scales of molecular relaxation. In particular, the importance of the operating time scale in nanoscopic devices is emphasized with examples of both quasi-static and dynamic operations. Material responses have been found to change significantly when the drive velocity or loading rate was either comparable to or in excess of the characteristic molecular frequencies. Correspondingly, intrinsic molecular modes were found to either couple with the external mechanical disturbance, thus establishing channels for energy transport, or to remain passive, leading to apparent material stiffening. Findings such as these suggest that comprehensive investigations of the spatial distribution of molecular relaxation spectra in confined systems are necessary in order to match (or mismatch) molecular response times with system operating times. Along this line, this review provides examples for cognitive engineering of functional materials, with molecular structures that are tailored to system constraints and employed in nanoscale device technologies. [ABSTRACT FROM AUTHOR]

Resistive switching memory (RRAM) features many optimal properties for future memory applications that make RRAM a strong candidate for storage-class memory and embedded nonvolatile memory. This paper addresses the cycling-induced degradation of RRAM devices based on a HfO2 switching layer. We show that the cycling degradation results in the decrease of several RRAM parameters, such as the resistance of the low-resistance state, the set voltage V\mathrm{ set} , the reset voltage V\mathrm{ reset} , and others. The degradation with cycling is further attributed to enhanced ion mobility due to defect generation within the active filament area in the RRAM device. A distributed-energy model is developed to simulate the degradation kinetics and support our physical interpretation. This paper provides an efficient methodology to predict device degradation after any arbitrary number of cycles and allows for wear leveling in memory array. [ABSTRACT FROM AUTHOR]

Resistive-switching memory (RRAM) based on metal oxide is currently considered as a possible candidate for future nonvolatile storage and storage-class memory. To explore possible applications of RRAM, the switching variability and the cycling endurance are key issues that must be carefully understood. To this purpose, we studied the switching variability and the endurance in pulsed regime for HfOx-based RRAM. We found that the resistance window, the set/reset variability, and the endurance are all controlled by the maximum voltage Vstop , which is applied during the negative-reset operation. We demonstrate that the endurance failure is triggered by a negative-set event, where the resistance suddenly decreases during the reset. Cycling endurance is studied as a function of time, compliance current and Vstop , allowing to develop an Arrhenius-law model, which is capable of predicting device lifetime under various conditions. [ABSTRACT FROM PUBLISHER]

DNA nanostructures routinely self-assemble with sub-10 nm feature sizes. This capability has created industry interest in using DNA as a lithographic mask, yet with few exceptions, solution-based deposition of DNA nanostructures has remained primarily academic to date. En route to controlled adsorption of DNA patterns onto manufactured substrates, deposition and placement of DNA origami has been demonstrated on chemically functionalized silicon substrates. While compelling, chemical functionalization adds fabrication complexity that limits mask efficiency and hence industry adoption. As an alternative, we developed an ion implantation process that tailors the surface potential of silicon substrates to facilitate adsorption of DNA nanostructures without the need for chemical functionalization. Industry standard 300 mm silicon wafers were processed, and we showed controlled adsorption of DNA origami onto boron-implanted silicon patterns; selective to a surrounding silicon oxide matrix. The hydrophilic substrate achieves very high surface selectivity by exploiting pH-dependent protonation of silanol-groups on silicon dioxide (SiO2), across a range of solution pH values and magnesium chloride (MgCl2) buffer concentrations. [ABSTRACT FROM AUTHOR]