This PDF file contains the front matter associated with SPIE Proceedings Volume 8377, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The requirement for power and energy in a modernized, highly digital and network-centric Army is growing exponentially. In addition to the ongoing demand for improved soldier portable power sources, the need for more electric capabilities for combat and unmanned platforms and the requirements of emerging Operational Energy doctrine are driving development of high density, energy efficient power technologies. The Army Research Laboratory (ARL) is addressing these needs through developing a number of underpinning power and energy component technologies at the fundamental research level. ARL is leveraging core expertise in microelectronics and micro-electro-mechanical systems (MEMS), energy conversion, energy storage, and wideband gap materials and devices to advance selected niche areas that address military demands beyond commercial needs in partnership with the Army Research, Development and Engineering centers (RDECs), other services, other agencies, industry, and academia. The technologies under development can be broadly characterized under power generation and energy conversion, energy storage, power distribution, and thermal management. This discussion outlines progress, approach and the way ahead for ARL efforts.

Size reduction in nanocrystals leads to a variety of unexpected exciting phenomena due to enhanced surface-to-volume ratio and reduced length for the transport [1, 2]. Here, we consider the effects of nano-size on the kinetics and thermodynamics and study its bearing on the lithium storage performance in insertion and conversion based Li storage mechanism. Firstly, we investigate the storage performance of nanocrystalline LiMnPO₄ by insertion reaction. Ball milling of LiMnPO₄ synthesized by soft-template method with carbonaceous materials helps to reduce the grain size as well as formation of a thin layer of carbon coating. Nanostructuring by ball milling process promotes high surface area of the active electrode material for improved electrolyte wetting, short transport length for Li diffusion while the carbon coatings facilitates electronic wiring all of which contribute to the enhanced storage performance. Additionally, we show that combining nanostructuring with divalent cation doping further improves the storage performance of the system which make them potential high voltage cathodes for real applications. Secondly, we discuss the size effect on thermodynamics during the conversion reaction, considering Fe₂O₃ as an example. The process of Li storage by conversion induces drastic size reduction, leading to stabilization of metastable phase of γ-Fe₂O₃. We show here that apart from kinetics, thermodynamics at nanosize also limit the rate of conversion reaction. Finally, we show that Fe₂O₃ can be a potential anode material for practical applications as they demonstrate a high degree of reversibility ~ 90% and excellent high rate performance.

There is a strong need for small, lightweight energy storage devices that can satisfy the ever increasing power and energy demands of micro unmanned systems. Currently, most commercial and developmental micro unmanned systems utilize commercial-off-the-shelf (COTS) lithium polymer batteries for their energy storage needs. While COTS lithium polymer batteries are the industry norm, the weight of these batteries can account for up to 60% of the overall system mass and the capacity of these batteries can limit mission durations to the order of only a few minutes. One method to increase vehicle endurance without adding mass or sacrificing payload capabilities is to incorporate multiple system functions into a single material or structure. For example, the body or chassis of a micro vehicle could be replaced with a multifunctional material that would serve as both the vehicle structure and the on-board energy storage device. In this paper we present recent progress towards the development of carbon nanotube (CNT)-based structural-energy storage devices for micro unmanned systems. Randomly oriented and vertically aligned CNT-polymer composite electrodes with varying degrees of flexibility are used as the primary building blocks for lightweight structural-supercapacitors. For the purpose of this study, the mechanical properties of the CNT-based electrodes and the charge-discharge behavior of the supercapacitor devices are examined. Because incorporating multifunctionality into a single component often degrades the properties or performance of individual structures, the performance and property tradeoffs of the CNT-based structural-energy storage devices will also be discussed.

Recent development in miniaturized electronic devices has increased the demand for power sources that are sufficiently compact and can potentially be integrated on a chip with other electronic components. Miniaturized electrochemical capacitors (EC) or micro-supercapacitors have great potential to complement or replace batteries and electrolytic capacitors in a variety of applications. Recently, we have developed several types of micro-supercapacitors with different structural designs and active materials. Carbon-Microelectromechanical Systems (C-MEMS) with three dimensional (3D) interdigital structures are employed both as electrode material for electric double layer capacitor (EDLC) or as three dimensional (3D) current collectors of pseudo-capacitive materials. More recently, we have also developed microsupercapacitor based on hybrid graphene and carbon nanotube interdigital structures. In this paper, the recent advances in design and fabrication of on-chip micro-supercapacitors are reviewed.

The weight and volume of conventional energy storage technologies greatly limits their performance in mobile platforms. Traditional research efforts target improvements in energy density to reduce device size and mass. Enabling a device to perform additional functions, such as bearing mechanical load, is an alternative approach as long as the total mass efficiency exceeds that of the individual materials it replaces. Our research focuses on structural composites that function as batteries and supercapacitors. These multifunctional devices could be used to replace conventional structural components, such as vehicle frame elements, to provide significant system-level weight reductions and extend mission times. Our approach is to design structural properties directly into the electrolyte and electrode materials. Solid polymer electrolyte materials bind the system and transfer load to the fibers while conducting ions between the electrodes. Carbon fiber electrodes provide a route towards optimizing both energy storage and load-bearing capabilities, and may also obviate the need for a separate current collector. The components are being integrated using scalable, cost-effective composite processing techniques that are amenable to complex part shapes. Practical considerations of energy density and rate behavior are described here as they relate to materials used. Our results highlight the viability as well as the challenges of this multifunctional approach towards energy storage.

Biological fuel cells hold promise as an alternative energy source to batteries for unattended ground sensor applications due to the fact that they can be extremely long lived. This lifetime can be extended over batteries by scavenging fuel from the deployed environment. Microbial fuel cells (MFC) are one class of such sources that produce usable energy from small organic compounds (i.e. sugars, alcohols, organic acids, and biopolymers) which can be easily containerized or scavenged from the environment. The use of microorganisms as the anodic catalysts is what makes these systems unique from other biofuel cell designs. One of the main drawbacks of engineering a sensor system powered by an MFC is that power densities and current flux are extremely low in currently reported systems. The power density is limited by the mass transfer of the fuel source to the catalyst, the metabolism of the microbial catalysts and the electron transfer from the organism to the anode. This presentation will focus on the development of a new style of microbially-modified anodes which will increase power density to a level where a practical power source can be engineered. This is being achieved by developing a three dimensional matrix as an artificial, conductive biofilm. These artificial biofilms will allow the capture of a consortium of microbes designed for efficient metabolism of the available fuel source. Also it will keep the microbes close to the electrode allowing ready access by fuel and providing a low resistance passage of the liberated electrons from fuel oxidation.

Photoelectrochemical cells are devices that can convert solar radiation to hydrogen gas through a water decomposition process. In this process, energy is converted from incident photons to the bonds of the generated H₂ molecules. The solar radiation absorption, electron-hole pair splitting, and photoelectrolysis half reactions all occur in the vicinity of the electrode-electrolyte interface. As a result, engineering the electrode material and its interaction with the electrolyte is important in investigating and improving the energy conversion process in these devices. III-V nitride materials are promising candidates for photoelectrochemical energy applications. We demonstrate solar-to-hydrogen conversion in these cells using p-type GaN and n-type InGaN as a photocathode and photoanode material, respectively. Additionally, we demonstrate heteroepitaxial MOCVD growth of GaP on Si, enabling future work in developing GaPN as a photocathode material.

Harvesting electrical energy from thermal energy sources using pyroelectric conversion techniques has been under investigation for over 50 years, but it has not received the attention that thermoelectric energy harvesting techniques have during this time period. This lack of interest stems from early studies which found that the energy conversion efficiencies achievable using pyroelectric materials were several times less than those potentially achievable with thermoelectrics. More recent modeling and experimental studies have shown that pyroelectric techniques can be cost competitive with thermoelectrics and, using new temperature cycling techniques, has the potential to be several times as efficient as thermoelectrics under comparable operating conditions. This paper will review the recent history in this field and describe the techniques that are being developed to increase the opportunities for pyroelectric energy harvesting. The development of a new thermal energy harvester concept, based on temperature cycled pyroelectric thermal-to-electrical energy conversion, are also outlined. The approach uses a resonantly driven, pyroelectric capacitive bimorph cantilever structure that can be used to rapidly cycle the temperature in the energy harvester. The device has been modeled using a finite element multi-physics based method, where the effect of the structure material properties and system parameters on the frequency and magnitude of temperature cycling, and the efficiency of energy recycling using the proposed structure, have been modeled. Results show that thermal contact conductance and heat source temperature differences play key roles in dominating the cantilever resonant frequency and efficiency of the energy conversion technique. This paper outlines the modeling, fabrication and testing of cantilever and pyroelectric structures and single element devices that demonstrate the potential of this technology for the development of high efficiency thermal-toelectrical energy conversion devices.

Quantum-structured photovoltaic devices incorporating III-V quantum wells or quantum dots have the potential to dramatically increase the performance of energy harvesting devices. In this work, the dark current of high-voltage InGaAs quantum well structures is characterized, and the underlying saturation current density analyzed as a function of effective energy gap. Analysis of the current-voltage characteristics suggests that these advanced quantum well device structures are operating in a regime of suppressed radiative recombination. High-voltage output from quantum-structured energy harvesting devices, coupled with advances in the field of light trapping, provides a pathway for achieving ultra-high conversion efficiencies.

Over the past several decades, research in organic semiconductors has progressed steadily to the point that commercial applications have been realized in areas such as organic light emitting diodes (OLEDs) for solid state lighting and displays, as well as organic field effect transistors (OFETs) for RFIDs, e-paper and flexible electronics. The use of organic semiconductors for photo-voltaics (PV) has also seen tremendous progress over the past decade with power conversion efficiencies that have risen from 1% to above 10% as reported recently. The urgency for developing low-cost, high-efficiency renewable energy sources is very pressing since worldwide demand for energy is expected to triple by the end of the century. Organic PV provides advantages in its very low-cost manufacturing processes that utilize room temperature techniques, unlike crystalline Si and other inorganic PV technologies that are not cost-effective. Other advantages of OPV includes the use of environmentally friendly materials, and compatibility with roll-toroll processing for the realization of solar cells in a flexible and conformable platform.

Recent development efforts on thermoelectric (TE) power converters comprised of low-to-mid-temperature (25-400°C), and high-temperature (400-750°C) materials have achieved >60 Watts electrical power with a thermal-to-electric conversion efficiency of ~8%. This paper will focus on thermoelectric devices fabricated from these materials, and also on cascaded power converters that enable the high power and efficiency to be obtained. In addition, work is underway to explore the use of more advanced low- to mid-temperature TE materials that have achieved over 10% efficiency in a single junction converter.

Accuracy of thermal conductivity measurements is an ongoing area of controversy in thermoelectric materials development. In this work, we demonstrate a novel steady-state method for characterizing thermal conductivity of bulk materials and devices under isothermal and near-isothermal conditions. The isothermal condition is achieved by exactly balancing Peltier heat flow against an externally imposed heat flow in the material. Under steady-state, isothermal conditions, heat flow in the material can be determined with high accuracy because external parasitic heat flows become negligible. We compare our results with conventional measurement techniques and also with measured thermoelectric device performance. Agreement between predicted and measured thermoelectric cooler performance is within 2%. Results for thermoelectric power generators will also be discussed.

In this paper, development of single crystalline n- and p- type PbTe crystals and PbTe bulk nanocomposites using PbTe nano powders and emerging field assisted sintering technology (FAST) are discussed. Materials requirements for efficient thermoelectric power generation using waste heat at intermediate temperature range (6500 to 8500 K) will be discussed. Recent results on production of n- and p- type PbTe crystals and their thermoelectric characterization will be presented. Relative characteristics and performance of PbTe bulk single crystals and nano composites for thermoelectric power generation will be discussed.

Computational models for the transport properties of nanostructured thermoelectric materials predicted vast improvements in the thermoelectric power factor (PF) values over bulk due to discretization of the electron density-of-states function as the result of confinement. We have developed a model that bridges bulk and nanostructure PF data. The model is analyzed in the framework of the relaxation time approximation, considering different scattering mechanisms. The model shows that the PF of nanowires in fact falls below the bulk value for most of the experimentally-accessible size range. Under the constant relaxation time approximation, universal scaling relations are obtained for all single-carrier semiconductors.

The addition of advanced sensors, targeting systems and electronic countermeasures to military vehicles has created a strategic need for additional electric power. By incorporating a thermoelectric (TE) waste heat recovery system to convert available exhaust heat to electricity, increased electric power needs can be met without reducing the energy efficiency of the vehicle. This approach allows existing vehicles to be upgraded without requiring a complete re-design of the engine and powertrain to support the integration of advanced electronic sensors and systems that keep the performance at the state of the art level. RTI has partnered with General Dynamics Land Systems and Creare, Inc. under an Army Research Lab program to develop a thermoelectric exhaust waste heat recovery system for the M1 Abrams tank. We have designed a reduced-scale system that was retrofitted to the tank and generated 80W of electric power on the vehicle operating on a test track by capturing a portion of the exhaust heat from the Honeywell/Lycoming AGT-1500 gas turbine engine.

We have designed, modeled, fabricated and tested novel MEMS variable capacitors with two air cavities (two capacitors) for electrostatic power harvesting utilizing mechanical vibration in environment. The device is unique in the use of an innovative two-cavity design and electroplated nickel as the main structural material, which allows using both up and down directions to generate energy. The prototype of two-cavity MEMS variable capacitors have been successfully fabricated using surface micromachining. The initial testing for investigating electrical dynamic behaviors and power generation from the fabricated devices was implemented.

The modeling, fabrication and testing of a two-cavity MEMS capacitor utilizing inertial forces from unwanted ambient vibrations has been performed. The device was designed with two air cavities and a thick movable metallic plate in order to increase the efficiency of the energy conversion from mechanical vibration. The moving plate was sandwiched between two fixed plates to construct a two cavity capacitor. The improved model verified the fact that that two-cavity model enhances the average output power by 2 to 5 times of a single cavity model. The device was designed with soft suspension beams and with a thick plate in order to achieve a natural frequency close to the ambient vibration frequencies. The FEM analysis showed that a thick electroplated nickel plate and beams can results in a natural frequency less than 1 kHz. The behavior of the plate under damping was also calculated using FEM analysis. The MEMS converters were fabricated using surface micromachining technology, nickel electroplating and photoresist sacrificial layer. The moving plate and suspension beams were grown on the photoresist sacrificial layer and nickel anchors. The structure was released by removing the photoresist sacrificial layers using photoresist strip remover. To form the top cavity, nickel bonding tabs with sufficient thickness were grown by electroplating on another substrate followed by indium electroplating with a thickness of 1 μm. The two substrates were then aligned and bonded together. A good control of the height of the two cavity MEMS capacitor is possible with the control of Ni deposition and sacrificial layer thicknesses.

Isotope batteries offer solutions for long-lived low-power sensor requirements. Alpha emitting isotopes have energy per decay 10³ times that of beta emitters. Alpha particles are absorbed within 20 μm of most materials reducing shielding mitigation. However, damage to materials from the alphas limits their practical use. A Schottky Barrier Diode (SBD) geometry is considered with an alpha emitting contact-layer on a diamond-like crystal semiconductor region. The radiation tolerance of diamond, the safety of alpha particles, combined with the internal field of the SBD is expected to generate current useful for low-power electronic devices over decades. Device design parameters and calculations of the expected current are described.

Wireless sensor networks (WSNs) have emerged as means of providing automated monitoring, target tracking, and intrusion detection. Solar-powered WSNs that adopt innovative sensors with low power consumption and forefront networking technologies can provide rapidly deployable situational awareness and effective security control at the border at low cost. In our paper, we introduce the prototype of our new solar-powered WSN platform for Border Security. We consider practical issues in WSNs, including sensing environment classification, survivability under harsh weather conditions, and efficient solar energy harvesting. Experimental results demonstrate the performance of our new solar-powered WSN.

A methodology that allows for the coupling of biology and electronic materials is presented, where double stranded DNA will ultimately serve as a template for electronic material growth. Self-assembled DNA structures allow for a variety of patterns to be achieved on the nanometer size scale that is difficult to achieve using conventional patterning techniques. DNA self assembly under non-aqueous conditions has yet to be presented in literature, and is necessary if unwanted oxidation of certain electronic substrates is to be avoided. Solubilization of the DNA in non-aqueous solvents is achieved by replacing charge stabilizing salts with the surfactant cetyl trimethyl ammonium chloride (CTAC). Herein, the procedures for the creation of self-assembled DNA nanostructures in aqueous and non-aqueous media are described, and these structures are subsequently deposited (drop cast, spin cast, and physically adsorbed) onto freshly cleaved mica or silicon wafers. The DNA architectures are characterized either in solution (circular dichroism spectroscopy (CD)) or on the surface (AFM). These studies illustrate the retention of DNA hierarchical structure under both conditions and this data will be presented by observing the structures using AFM imaging and CD spectroscopic studies