Hyperbranched polymers: from synthesis to applications

Nanotechnology is the science of understanding matter and the control of matter at dimensions of 100 nm or less. Encompassing nanoscale science, engineering, and technology, nanotechnology involves imaging, measuring, modeling, and manipulation of matter at this level of precision. An important aspect of research in nanotechnology involves precision control and manipulation of devices and materials at a nanoscale, i.e., nanopositioning. Nanopositioners are precision mechatronic systems designed to move objects over a small range with a resolution down to a fraction of an atomic diameter. The desired attributes of a nanopositioner are extremely high resolution, accuracy, stability, and fast response. The key to successful nanopositioning is accurate position sensing and feedback control of the motion. This paper presents an overview of nanopositioning technologies and devices emphasizing the key role of advanced control techniques in improving precision, accuracy, and speed of operation of these systems.

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A Survey of Control Issues in Nanopositioning

“Life is branched” was the motto of a special issue of Macromolecular Chemistry and Physics1 on “Branched Polymers”, indicating that branching is of similar importance in the world of synthetic macromolecules as it is in nature. The significance of branched macromolecules has evolved over the last 30 years from just being considered as a side reaction in polymerization or as a precursor step in the formation of networks. Important to this change in perception of branching was the concept of “polymer architectures”, which formed on new starand graft-branched structures in the 1980s and then in the early 1990s on dendrimers and dendritic polymers. Today, clearly, controlled branching is considered to be a major aspect in the design of macromolecules and functional material. Hyperbranched (hb) polymers are a special type of dendritic polymers and have as a common feature a very high branching density with the potential of branching in each repeating unit. They are usually prepared in a one-pot synthesis, which limits the control on molar mass and branching accuracy and leads to “heterogeneous” products with a distribution in molar mass and branching. This distinguishes hyperbranched polymers from perfectly branched and monodisperse dendrimers. In the last 20 years, both classes of dendritic polymers, dendrimers as well as hb polymers, have attracted major attention because of their interesting properties resulting from the branched architecture as well as the high number of functional groups.2 The challenging synthesis of the dendrimers attracted especially scientists with a strong organic chemistry background and led to beautifully designed macromolecules, which allowed a deeper insight into the effect of branching and functionality. Dendrimers have been considered as perfect “nano-objects” where one can control perfectly size and functionality, which is of high interest in nanotechnology and biomedicine. hb polymers, however, were considered from the beginning as products suitable for larger-scale application in typical polymer fields like coatings and resins, where a perfect structure is sacrificed for an easy and affordable synthetic route. Thus, the first structures that were reported paralleled the chemistry used for linear polymers like typical polycondensation for polyester synthesis. More recently, unconventional synthetic methods have been adopted also for hb polymers and related structures. Presently, a vast variety of highly branched structures have been realized and studied regarding their properties and potential application fields. Excellent reviews appeared covering synthesis strategies, properties, and applications, like the very recent tutorial by Carlmark et al.,3 the comprehensive book on hyperbranched polymers covering extensively synthesis and application * E-mail: voit@ipfdd.de; lederer@ipfdd.de. Chem. Rev. 2009, 109, 5924–5973 5924

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Hyperbranched and highly branched polymer architectures--synthetic strategies and major characterization aspects.

The practical realization of nanoscale electronics faces two major challenges: the precise engineering of the building blocks and their assembly into functional circuits. In spite of the exceptional electronic properties of carbon nanotubes, only basic demonstration devices have been realized that require time-consuming processes. This is mainly due to a lack of selective growth and reliable assembly processes for nanotubes. However, graphene offers an attractive alternative. Here we report the patterning of graphene nanoribbons and bent junctions with nanometre-precision, well-defined widths and predetermined crystallographic orientations, allowing us to fully engineer their electronic structure using scanning tunnelling microscope lithography. The atomic structure and electronic properties of the ribbons have been investigated by scanning tunnelling microscopy and tunnelling spectroscopy measurements. Opening of confinement gaps up to 0.5 eV, enabling room-temperature operation of graphene nanoribbon-based devices, is reported. This method avoids the difficulties of assembling nanoscale components and may prove useful in the realization of complete integrated circuits, operating as room-temperature ballistic electronic devices.

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Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography

Recent advancements in computational inverse-design approaches — algorithmic techniques for discovering optical structures based on desired functional characteristics — have begun to reshape the landscape of structures available to nanophotonics. Here, we outline a cross-section of key developments in this emerging field of photonic optimization: moving from a recap of foundational results to motivation of applications in nonlinear, topological, near-field and on-chip optics. Starting with a desired optical output it is possible to use computational algorithms to inverse design devices. The approach is reviewed here with an emphasis on nanophotonics.

Inverse design in nanophotonics

Ultrahigh storage densities can be achieved by using a thermomechanical scanning-probe-based data-storage approach to write, read back, and erase data in very thin polymer films. High data rates are achieved by parallel operation of large two-dimensional arrays of cantilevers that can be batch fabricated by silicon-surface micromachining techniques. The very high precision required to navigate the storage medium relative to the array of probes is achieved by microelectromechanical system (MEMS)- based x and y actuators. The ultrahigh storage densities offered by probe-storage devices pose a significant challenge in terms of both control design for nanoscale positioning and read-channel design for reliable signal detection. Moreover, the high parallelism necessitates new dataflow architectures to ensure high performance and reliability of the system. In this paper, we present a small-scale prototype system of a storage device that we built based on scanning-probe technology. Experimental results of multiple sectors, recorded using multiple levers at 840 Gb/in2 and read back without errors, demonstrate the functionality of the prototype system. This is the first time a scanning-probe recording technology has reached this level of technical maturity, demonstrating the joint operation of all building blocks of a storage device.

Probe-based ultrahigh-density storage technology

Disks are among the most frequently failing components in today's IT environments. Despite a set of defense mechanisms such as RAID, the availability and reliability of the system are still often impacted severely. In this paper, we present a highly accurate SMART-based analysis pipeline that can correctly predict the necessity of a disk replacement even 10-15 days in advance. Our method has been built and evaluated on more than 30000 disks from two major manufacturers, monitored over 17 months. Our approach employs statistical techniques to automatically detect which SMART parameters correlate with disk replacement and uses them to predict the replacement of a disk with even 98% accuracy.

Predicting Disk Replacement towards Reliable Data Centers

Low-loss optical waveguides have been fabricated from fluorinated copolymers designed to incorporate photochemical amplification based on acid catalysis. Core and cladding layers were made, for single-mode (SM) channel waveguides, from the poly(pentafluorostyrene-co-glycidyl methacrylate) copolymer series and, for multimode (MM) ridge waveguides, from poly(tert-butyl methacrylate-co-glycidyl methacrylate) as the cladding and poly(pentafluorostyrene-co-glycidyl methacrylate) as core layer. The reactivity ratios for PFS and GMA monomers have been measured to be r(PFS) = 0.38 ± 0.01 and r(GMA) = 0.89 ± 0.01 in free radical polymerization. Variation of the copolymer composition allowed precise control over the refractive index measured at 589, 633, 1320, and 1550 nm. These amorphous copolymers were photo-cross-linked by contact printing and developed by wet etching to produce high quality ridge waveguides with very smooth top surfaces. Low loss single-mode (SM) waveguides exhibit averaged losses over eight ch...

Low-Loss Passive Optical Waveguides Based on Photosensitive Poly(pentafluorostyrene-co-glycidyl methacrylate)

We present the first realization of a Bragg grating apodization based on a concatenation of different duty cycles. The gratings were fabricated in SiON planar waveguides. The reflected signal exhibits a sidelobe suppression better than -20 dB outside a bandwidth of 1.36 nm. At the same time the reflection is stronger than 99.9%, i.e., the resonant light is suppressed better than -30 dB in transmission over 0.22 nm. The gratings are perfectly suited to serve as the wavelength-selective element of a Mach-Zehnder add/drop filter.

Apodized surface-corrugated gratings with varying duty cycles

One approach to ultrahigh-density data storage involves the use of arrays of atomic force microscope probes to read and write data on a thin polymer film, but damage to the ultrasharp silicon probe tips caused by mechanical wear has proved problematic. Here, we demonstrate the effective elimination of wear on a tip sliding on a polymer surface over a distance of 750 m by modulating the force acting on the tip-sample contact. Friction measurements as a function of modulation frequency and amplitude indicate that a reduction of friction is responsible for the reduction in wear to below our detection limit. In addition to its relevance to data storage, this approach could also reduce wear in micro- and nanoelectromechanical systems and other applications of scanning probe microscopes.

Dorothea Wiesmann

Papers

Probe-based ultrahigh-density storage technology

Predicting Disk Replacement towards Reliable Data Centers

Low-Loss Passive Optical Waveguides Based on Photosensitive Poly(pentafluorostyrene-co-glycidyl methacrylate)

Apodized surface-corrugated gratings with varying duty cycles

Dynamic superlubricity and the elimination of wear on the nanoscale