Nanofabrication with metallopolymers ‐ recent developments and future perspectives

Synthetic polymers containing metals and metal centers have experienced rapid growth in the last two decades. Metal‐containing polymers have an unprecedented role to play in modern high‐tech applications including nanomanufacturing, sensing, separation and catalysis. Advancement in synthetic strategies for macromolecules has enabled the synthesis of novel, exotic and use‐inspired metallopolymers. Using state‐of‐the‐art design strategies, it is now possible to perform targeted synthesis of macromolecules with varied complexity that contain a range of metal centers either in the backbone or in the side chains of the organic moiety. The presence of an inorganic element (metals and metal centers) in organic moieties has led to a number of new physicochemical properties while implementing novel functionality to the polymer matrix. This review covers nanotechnology influenced by distinctive features of metal‐containing macromolecular systems, particularly in developing flexible, functional materials. © 2013 Society of Chemical Industry     

Dielectric‐Screening Reduction‐Induced Large Transport Gap in Suspended Sub‐10 nm Graphene Nanoribbon Functional Devices

The predicted quasiparticle energy gap of more than 1 eV in sub‐6 nm graphene nanoribbons (GNRs) is elusive, as it is strongly suppressed by the substrate dielectric screening. The number of techniques that can produce suspended high‐quality and electrically contacted GNRs is small. The helium ion beam milling technique is capable of achieving sub‐5 nm patterning; however, the functional device fabrication and the electrical characteristics are not yet reported. Here, the electrical transport measurement of suspended ≈6 nm wide mono‐ and bilayer GNR functional devices is reported, which are obtained through sub‐nanometer resolution helium ion beam milling with controlled total helium ion budget. The transport gap opening of 0.16–0.8 eV is observed at room temperature. The measured transport gap of the different edge orientated GNRs is in good agreement with first‐principles simulation results. The enhanced electron–electron interaction and reduced dielectric screening in the suspended quasi‐1D GNRs and anti‐ferromagnetic coupling between opposite edges in the zigzag GNRs substantiate the observed large transport gap.     

Highly Reproducible and Regulated Conductance Quantization in a Polymer‐Based Atomic Switch

A detailed understanding of the conductance quantization and resistive switching phenomena in redox‐based memories is crucial for realizing atomic‐scale memory devices and for finding the adequate design principles on which they can be based. Here, the emergence of quantized conductance states and their correlation with resistive switching characteristics in polymer‐based atomic switches are investigated using combinations of current–voltage measurements and first‐principles density functional theory (DFT) simulations. Various conductance states, including integer and half‐integer multiples of a single atomic point contact and fractional conductance variations, are observed in an Ag/polyethylene oxide/Pt device under sweeping of bias voltage. Moreover, highly controllable and reproducible quantized conductance behaviors by tuning the voltage sweep rate and the sweep voltage range, suggesting well‐controlled formation of the atomic point contact, are demonstrated. The device also exhibits longer retention times for higher conductance states. The DFT simulations reveal the transmission eigenstate of geometrically optimized atomic point contact structures and the impact of the atomic configurations and structural stability on the conductance state, which also explains their resistive switching behaviors. The well‐defined, multiple quantized conductance states observed in these polymer‐based atomic switches show promise for the development of new multilevel memory devices.     

Stress analysis of perforated graphene nano-electro-mechanical (NEM) contact switches by 3D finite element simulation

Microsystem Technologies - In this article, we report the finite element method (FEM) simulation of the suspended double-clamped graphene beam-based NEM switches with standard and perforated beam...     

A QRD-RLS-Based Predistortion Scheme for High-Power Amplifier Linearization

A digital baseband predistortion (PD) scheme for high-power amplifier (HPA) linearization is proposed and analyzed in this brief. The proposed approach utilizes the QR-decomposition-based recursive least squares (QRD-RLS) algorithm to estimate the memoryless complex polynomial coefficients that characterize the HPA. The inverse polynomial model coefficients corresponding to the PD are similarly extracted using QRD-RLS. The performance of the proposed PD scheme is analyzed via simulations and compared with previously published techniques. Results show that the QRD-RLS-based solution offers improved performance over its comparatives     

Asymmetric morphology from an organic/organometallic block copolymer

Block copolymer self-assembly is a burgeoning subject in polymer and materials science driven by both fundamental and applied inspirations. Whereas the vast majority of block copolymer studies have focused on highly symmetric morphologies, here we report the first observation of an unusual asymmetric cylindrical phase in thick films of an organic/organometallic block copolymer, poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS). Microscopy and X-ray scattering data establish the lack of symmetry in this structure and reveal an unusual 3-D network organization. Following selective removal of the PS matrix, the remaining nanoporous film has characteristics of potential value in separation applications such as substantial interconnection (mechanical strength), uniform pore size, and chemical and physical stability.     

A Computationally Efficient QR-Successive Interference Cancellation Scheme for Simplified Receiver Implementation in SFBC-OFDM Systems

In this paper, we propose a computationally efficient square-root and division free recursive QR (SDRQR) decomposition based successive interference cancellation (SIC) receiver for space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) transmit diversity schemes. The performance of the proposed SDRQR-SIC receiver is semi- analytically evaluated taking into account the effects of channel estimation errors and error propagation during SIC. In addition, performance and complexity comparisons are drawn with previously proposed approaches. These comparisons show an excellent performance-complexity tradeoff achieved by SDRQR-SIC over the previous solutions under various channel conditions.     

Foam films as thin liquid gas separation membranes

In this letter, we testify the feasibility of using freestanding foam films as a thin liquid gas separation membrane. Diminishing bubble method was used as a tool to measure the permeability of pure gases like argon, nitrogen, and oxygen in addition to atmospheric air. All components of the foam film including the nature of the tail (fluorocarbon vs hydrocarbon), charge on the headgroup (anionic, cationic, and nonionic) and the thickness of the water core (Newton black film vs Common black film) were systematically varied to understand the permeation phenomena of pure gases. Overall results indicate that the permeability values for different gases are in accordance with magnitude of their molecular diameter. A smaller gaseous molecule permeates faster than the larger ones, indicating a new realm of application for foam films as size selective separation membranes.     

Simple orientational control over cylindrical organic-inorganic block copolymer domains for etch mask applications

Bottom-up patterning methodologies, predicated on chemical self-assembly, have the potential to transcend limitations associated with more traditional lithographies. By controlling the domain orientation of a cylinder-forming organic-inorganic block copolymer, poly(styrene-block-ferrocenyldimethylsilane), it is possible to straightforwardly fabricate massive arrays of either nanoscale dots or wires out of a film composed of a wide variety of materials. In the work reported here, orientational control is achieved by manipulating the polymer film thickness in concert with the annealing treatment. For films much thinner than the equilibrium periodicity of the microdomains, the cylinders spontaneously orient themselves perpendicular to the substrate. Films with thickness close to the equilibrium periodicity exhibit the more common in-plane orientation following thermal annealing. Solvent annealing leads to an in-plane orientation for the full range of film thicknesses studied. As a demonstration of the effectiveness of this method, semiconductor substrates were patterned with arrays of posts and wires, respectively, using the same starting polymeric material as the etch mask. Compatibility of this polymer with various substrate materials is also demonstrated.