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Dr. Mark Topinka
Geballe Laboratory for Advanced Materials, Stanford University

Carbon Nanotube Networks:  Enabling the Next Generation of Flexible, Low-cost Solar Cells and Electronics

Printable, low-cost organic electronics in areas such as solar cells, electronic paper, radio-frequency-ID tags, biological sensors, and flexible organic displays have shown great promise in the past few years. Thin conductive carbon nanotube films are potentially a good match to these technologies in several ways. Carbon nanotube films around 100nm thick are a potential replacement for more expensive, less flexible transparent conductors such as ITO (Indium Tin Oxide) - they can be made both highly transparent and highly conductive and are compatible with low-temperature and low-cost roll-to-roll printing technology. Also, thinner films of carbon nanotubes, about 1nm in thickness, can be used as field effect transistors, demonstrating on/off ratios of over 10^5 while maintaining almost perfect transparency.

In this talk I will present a series of simulations and experiments we have performed to understand the underlying physics of these devices, and to point the way to improving the real-world performance of carbon nanotube films for both transparent electrodes and transparent FETs.

We have successfully fabricated an organic solar cell using CNT-film electrodes which performs similarly to an ITO reference cell. In order to find how to push the films closer to theoretically achievable performance levels, we have modeled the films as both 2 and 3 dimensional networks of wires, and have investigated the effects of tube length, density, alignment, and metal-semiconducting ratios. We have also performed Electric Force Microscopy experiments on thin films of carbon nanotube networks to directly image where the bottlenecks in resistance in these films lie.

Professor Steve Forrest
Department of Electrical Engineering and Applied Physics, University of Michigan

Electronics on plastic: A solution to the energy challenge, or just a pipe dream?

For over 50 years, conjugated organic compounds have been recognized as an important class of electronic semiconductor materials, with potential application to light emission and detection. Very recently, these materials have been shown to generate extremely high efficient white light, and can also have high detection efficiencies. Due to their very low cost and low deposition temperatures, this suggests that organic thin film semiconductor light emitting diodes and solar cells may present a practical solution to mankind’s greatest challenge: the use and generation of low cost renewable, and largely pollution free energy. In this talk, I will address both the reality and fantasy of this suggestion. While organic thin film devices can have extremely high performance, they also suffer from shorter operational lifetime than conventional semiconductor (e.g. silicon) devices. And, although their low cost has yet to be proven in large scale manufacturing environments, the potentially unlimited promise of this materials class is driving a substantial global research effort to determine their ultimate applicability to meeting our energy challenges.

Dr. Volker Schmidt
Max Planck Institute, Halle

Some Aspects Silicon Nanowire Growth

Silicon nanowires, i.e silicon rods with diameters in the nanometer range and lengths that exceeds their diameters, became a very fashionable object for materials research in recent years - mainly caused by the widespread believe that silicon nanowires might have a application in future electronics (see e.g. the ITRS roadmap). Today, the most common method for the synthesis of silicon nanowires employs the so-called vapor-liquid-solid (VLS) growth mechanism, proposed in the 1960s by R.S. Wagner and W. C. Ellis. Herein, a liquid dropet catalyzes nanowire growth by serving as a preferential site for the adhesion of the silicon precursor gas species. In my presentation I will mainly focus on the implications of this growth mechanism for the fundamental properties of silicon nanowires, i.e. growth direction, shape, and length.
 

Professor Paul Alivisatos
Chemistry Department, UC Berkeley

Shock wave studies of solid-solid structural transitions, deformation, and fracture in nanocrystals and hollow nanoparticles

We have investigated shock-induced structural transformations in CdSe nanocrystals of 5 nm diameter and in hollow CdS nanoparticles of 200 nm outer diameter and 20 nm wall thickness.  The shock wave is generated by ablation of aluminum from a multilayer film.  The nanocrystals and nanoparticles are embedded in a polymer layer.  We are investigating the possibility that the nanocrystals undergo the wurtzite-to-rocksalt solid-solid structural transformation within the period of the shock, which has a duration of a few ns.  The hollow particles are comparable in size to the wavelength of the shock, and therefore they experience a large variation in pressure across their diameter; we find that they are shattered by a shock that exceeds a threshold value.  The possibility of using hollow nanoparticles as shock absorbing materials will be discussed.  
 

Professor Tom Jackson
Department of Electrical Engineering, Pennsylvania State University  

Electronics Anywhere

The economic importance of large area active electronics applications, at least in the form of displays, is large (>$50 billion/year) and growing rapidly. This success, and the technical experience and infrastructure behind it, make the possibility of other large area applications of increasing interest. Organic thin film electronics is well suited to large area electronics applications because of the diversity and flexibility of the devices, function, and processing it allows. Organic thin film transistors (OTFTs) are particularly interesting because they can act as enabling devices to allow the integration of other devices in active matrices for displays, sensor arrays, low cost memories, and other applications.

Organic thin film transistor (OTFT) device performance rivals or exceeds that of a-Si:H devices, and low OTFT processing temperature allows fabrication on a variety of surfaces including cloth, paper, or polymeric substrates. Many organic device applications are likely to be cost sensitive and solution-deposited organic semiconductors offer important advantages for low-cost processing. However, solution processed semiconductors often lack the molecular-level order important for good carrier transport and large field-effect transistor mobility. Working with J. Anthony (University of Kentucky) we have investigated functionalized pentacenes and pentacene derivatives that can provide both solution processiblity and molecular ordering. These materials use bulky molecular side groups to control molecular packing and allow solubility in a range of common solvents. Solution-deposited films of many of these materials show strong molecular ordering. Using triisopropylsilylethynyl (TIPS) pentacene films deposited by drop casting we have fabricated OTFTs with mobility >1.5 cm2/V s and simple circuits including ring oscillators. Using fluorinated 5,11-Bis(triethylsilylethynyl) anthradithiophene (F-TES-ADT) films deposited by simple spin casting we have fabricated OTFTs with mobility >1 cm2/V s. F-TES-ADT films also display differential microstructure on surfaces or surface features with varying surface energy. Using SAM-treated electrodes that encourage large well-ordered F-TES-ADT grains we have fabricated spin-cast OTFTs with mobility that increases with decreasing gate length. We have also fabricated spin-cast circuits including ring oscillators on both glass and polymeric substrates with propagation delay <5 sec/stage. Solution-processed organic semiconductors also allow printing or other non-conventional approaches for material patterning. Using TIPS-pentacene and F-TES-ADT we have used surface energy modification to demonstrate non-relief pattern lithography (no photoresist used), including organic semiconductor patterning for OTFTs and simple circuits.

The technological landscape appears ripe for an explosion of large area organic electronic applications. Details of device structure, function, and performance are critically related to the success of various application possibilities and organic thin film electronic offers unique advantages. The wide range of device and application possibilities as well as physical phenomena makes this an interesting and exciting area of device physics and engineering with potentially large economic and societal impact.
 

Ultrafast Thermometry and the Measurement of Thermal Transport Properties at the Nanoscale  

We normally think of heat conduction as a relatively slow process; the diffusion of heat across 1 cm of material occurs in 1 second in Ag and 1000 seconds in plastic. Since this thermal transit-time scales as the square of the length, heat diffusion across 10 nm of materials occurs in only 1-1000 picoseconds. To measure and understand heat conduction at the nanoscale therefore requires thermometry with ultrafast time response and, ideally, high spatial resolution. A variety of physical mechanisms can provide such fast thermometers: e.g., changes in optical reflectivity or absorption; inelastic light scattering; x-ray or electron diffraction; and non-linear optical reflectivity and spectroscopy. We have recently advanced the state-of-the-art of time-domain-thermoreflectance (TDTR) measurements of thermal transport and are using TDTR as a robust tool for studies of heat transport across interfaces and in a variety of nanostructured thin film materials—including “disordered-layered-crystals” of WSe2 that have the lowest thermal conductivity ever observed in a dense solid. We are studying the fast evolution of temperature within buried layers of epitaxial semiconductors by time-resolved x-ray diffraction at the Advanced Photon Source. Sum-frequency vibrational spectroscopy provides a unique probe of heat transport across a self-assembled alkane-thiol monolayer with picosecond time resolution.

Professor Aaron Lindenberg
Department of Materials Science and Engineering, Stanford University  

Ultrafast characterization and control of materials properties:
From THz to X-rays

The ability to capture atomic-resolution snapshots of materials as they move opens up new avenues in both the characterization of materials properties and their control. In this talk, I will discuss our recent work and provide a vision for the future of ultrafast materials science, encompassing both structural and electronic processes, with applications to information processing, energy storage and conversion, and nanoscale materials processing. New ultrafast light sources extending from the far infrared to the x-ray regime are now being utilized to probe the first steps in these processes, and are providing new tools for engineering and manipulating materials on atomic length-scales and femtosecond time-scales.

Dr. Sang Il Park
Park Systems Corporation, Korea

Nanoscale metrology and characterization with advanced AFM/SPM

As the design rules become smaller, it is becoming increasingly difficult to meet the metrology requirements of tomorrow’s industrial applications. Traditional tools, such as stylus profiler, optical microscope, and CD-SEM are proving to be insufficient. In their stead, Atomic Force Microscopes (AFM) are gaining attention as the tool of choice in nanoscale metrology.

In a nanoscale measurement, accuracy, repeatability, and reproducibility are just as important as resolution. Conventional AFM systems, based on piezoelectric tube scanners, cannot meet these metrology requirements, suffering from a significant background curvature and destructive imaging mode.

In order to overcome these limitations, the XE-AFM was introduced. The innovative metrology platform of completely decoupled, flexure based XY and Z scanners overcomes non-linearity and non-orthogonality associated with conventional piezotube based AFM, achieving a highly flat and linear XY scan, optimized for precision nanometrology. The high speed Z-scanner with minimized drive mass attains a fast Z-servo response, enabling the industry’s only true Non-Contact mode AFM.

The unique design of the XE-series AFM represents a major step forward in the advancement of nanometrology, rapidly expanding its application base, especially in the Pole Tip Recession (PTR) metrology of hard drive manufacturing. It also allowed the development of a series of new techniques to image previously inaccessible overhang features and in-liquid cells, and new modes of high resolution Scanning Thermal Microscopy (SThM), and variable frequency Scanning Capacitance Microscopy (SCM).