Liangbing Hu, University of Maryland
Guihua Yu, University of Texas at Austin
Leif Nyholm, Uppsala University
Horacio D. Espinosa, Northwestern University
Rusen Yang, University of Minnesota
R2: Energy Harvesting II
Tuesday PM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
2:30 AM - *R2.01
Stretchable Transparent Nanogenerators Based on 1D/2D Piezoelectric and Triboelectric Nanostructures
Sang-Woo Kim 1
1Sungkyunkwan University (SKKU) Suwon Republic of KoreaShow Abstract
Energy harvesting systems based on piezoelectric and triboelectric nanomaterials are in great demand, as they can provide routes for the development of self-powered devices which are highly flexible, stretchable, mechanically durable, and can be used in a wide range of applications. Our recent research interest mainly focuses on the fabrication of nanogenerators (NGs) based on 1D/2D nanomaterials such as zinc oxide nanowire/nanosheets and graphene. Furthermore, the efforts towards developing triboelectric NGs using those materials are in progress.
3:00 AM - R2.02
Sponge-Like Piezoelectric Polymer Film for Scalable and Integratable Nanogenerators and Self-Powered Electronic Systems
Yanchao Mao 1 2 Ping Zhao 3 Geoffrey McConohy 4 Hao Yang 2 Yexiang Tong 2 Xudong Wang 1
1University of Wisconsin-Madison Madison USA2Sun Yat-sen University Guangzhou China3University of Minnesota-Duluth Duluth USA4University of Wisconsin-Madison Madison USAShow Abstract
Nanogenerator (NG) is a promising new concept for harvesting mechanical energy from ambient sources and developing self-powered electronic systems. Here, we report a development of flexible NGs from sponge-like nanoporous piezoelectric polyvinylidene fluoride (PVDF) thin films that were fabricated by a casting-etching method in wafer-scale. The nanoporous PVDF NGs can be directly attached to the surface of an electronic device (e.g. a cell phone), and effectively convert mechanical energy from ambient surface oscillations to electricity using the device&’s own weight to enhance the amplitude. An output voltage of 11.0 V and current of 9.8 mu;A was demonstrated using a 2 cm2 sized PVDF NG. Multiple PVDF NGs were integrated in series and operate synchronically to raise the output power for the operation of electronic devices. In conclusion, a novel integratable NG design based on sponge-like nanoporous piezoelectric PVDF thin films was successfully demonstrated. This type of NG can generate significantly electrical energy by harvesting mechanical energy from surface oscillations. This technique is considerably scalable and integratable, providing a promising solution for developing practical self-powered electronic devices.
3:15 AM - *R2.03
Piezo-Nano-Devices on Flexible Substrates: Challenges and Opportunities
Christian Falconi 1
1University of Tor Vergata Rome ItalyShow Abstract
Piezoelectric nanodevices can offer crucial advantages for energy harvesting, mechanical sensing/actuation, biomedical devices, optoelectronics, and more. In fact, in comparison with conventional piezoelectric materials, nanostructures can be highly deformed by tiny forces, exhibit outstanding mechanical properties, and can have substantially higher piezoelectric coefficients.
However, many issues must be addressed, both at the theoretical and at the technological level, in order to design and fabricate optimal piezo-nano-devices on flexible substrates.
In the first part of this presentation, I show how shape, electrical boundary conditions, position of contacts, type of mechanical input, and charge transport properties can all crucially affect the piezopotential, the mechanical-to-electrical conversion efficiency, and the on-off ratios of piezoelectric nanodevices. As an example, for a given mechanical input, laterally deflected cylindrical nanowires with total bottom contacts result in lower piezopotential and mechanical-to-electrical conversion efficiency than vertically compressed nanowires; as another example, the mechanical-to-electrical static conversion efficiency of vertically compressed nanowires is almost independent of strain at small strains and increases at higher strains, thus confirming that the ability of nanostructures to withstand extreme deformations without fracture may be a key for increasing the efficiency of nanogenerators. As another example, conical nanowires may prove advantageous for nanogenerators, piezotronics, and piezophototronics.
In the second part I will highlight the challenges to overcome for taking full advantage of piezoelectric nanodevices on flexible substrates, with special reference to both modeling (e.g. parasitic impedances, transient phenomena, and scaling of the electro-mechanical properties, including the Young modulus and piezoelectric coefficients) and fabrication (e.g. low-temperature processing and complexity of in-liquids real-time monitoring).
Finally, I will illustrate some piezoelectric nanodevices on flexible substrates.
3:45 AM - R2.04
Semiconductor Nanowire Laser: Fabrication, Tuning and Applications
Xiaowei Liu 1 Yuanpeng Wu 1 Pengfei Xu 1 Weisong Yang 1 Qing Yang 1 Shan Jiang 1
1Zhejiang University Hangzhou ChinaShow Abstract
High flexibility and easy tunability have been important advantages for one-dimensional nanowires (NWs) in wide applications of nanoscale integrated circuits and high sensitive sensor etc. We present our work on NW lasers from fabrication, tuning to applications. First of all, we fabricated various NW lasers: semiconductor NW-microfiber hybrid lasers , semiconductor NW-microdisk cavity hybrid lasers , and semiconductor NW-microfiber ultraviolet-green-red three color lasers . The hybrid structure laser combine the high gain of semiconductor and high quality factor of micro cavity, offering low threshold and easily manipulation properties. Secondly, we focus on achieving tuning/modulating/enhancing the afore-mentioned NW lasers. We demonstrate an efficient way to achieve wide wavelength tunable lasers on single non-doped CdSe NWs . The laser wavelengths are tuned from 746 nm to 706 nm by changing the length of a single NW (402-nm-diameter), spanning a range as large as 40 nm. The length dependent wavelength tuning is attributed to absorption-emission-absorption (AEA) of the propagating light in the NWs. We also utilize the bending effects to modulate the polarization of NW lasers . Furthermore, we work on the modulation of polarization and modes of NW lasers by electrical tuning. Finally, we use the tunable laser to achieve super-resolution microscope and investigate the behind new physical mechanism. Our work pioneered in the NW lasers may provide a way of fabricating ultra-compact nanophotonic devices and may find its applications in single molecule detection, integrated optical circuits, and optical communications etc.
Q. Yang, X. Jiang, X. Guo, Y. Chen, L. Tong, “Hybrid structure laser based on semiconductor nanowires and a silica microfiber knot cavity”, Appl. Phys. Lett. 94 (2009) 101108.
G. Wang, X. Jiang, M. Zhao, Y. Ma, H. Fan, Q. Yang, L. Tong, M. Xiao, “Microlaser based on a hybrid structure of a semiconductor nanowire and a silica microdisk cavity”, Opt. Express 20 (2012) 29472-29478.
Y. Ding, Q.Yang, X.Guo, S. Wang, F. Gu, J. Fu, Q. Wan, J. Cheng, and L. Tong, “Nanowires/microfiber hybrid structure multicolor laser”, Opt. Express 17 (2009) 21813.
J. Li , C. Meng , Y. Liu , X. Wu , Y. Lu , Y. Ye , L. Dai , L. Tong, X. Liu, Q. Yang “Wavelength Tunable CdSe Nanowire Lasers Based on the Absorption-Emission-Absorption Process” Adv. Mater. DOI: 10.1002/adma.201203692 (2012)
W. Yang, Y. Ma, Y. Wang, C. Meng, X.Wu, Y. Ye, L. Dai, L. Tong, X. Liu, Q. Yang, “Bending effects on lasing action of semiconductor nanowires”, Opt. Express 21 (2013) 2025-2031
4:30 AM - *R2.05
Stretchable Inorganic Photovoltaics and Mechanical Energy Harvesters
John Rogers 1
1University of Illinois Urbana USAShow Abstract
Large interconnected collections of small, ultrathin inorganic solar cells and piezoelectric elements provide routes to high performance energy production systems in flexible, and even stretchable, designs. This talk describes materials, techniques for assembly and concepts in mechanics for this type of technology. Device examples built using silicon, compound semiconductors and piezoelectric materials derived from wafer-scale sources of material illustrate an ability to achieve, simultaneously, high efficiency operation in energy conversion and extreme levels of flexibility and stretchability.
5:00 AM - R2.06
M13 Phage-Based Piezoelectric Energy Generation
Kwang Heo 1 2 Seung-Wuk Lee 1 2
1Univ. California, Berkeley Berkeley USA2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Piezoelectric materials can convert mechanical energy into electrical energy, and piezoelectric devices made of various inorganic materials and organic polymers have been demonstrated. However, synthesizing such materials often requires toxic materials, harsh conditions and/or complex procedures. Recently, it was shown that hierarchically organized natural materials, such as bones, collagen fibrils and peptide nanotubes, can display piezoelectric properties. In this paper, we will demonstrate our innovative approach to produce biomaterial-based piezoelectric energy generation. Recently, we establish that the piezoelectric and liquid crystalline properties of M13 bacteriophage (phage) can be used to generate electrical energy. Using piezoresponse force microscopy, we characterized the structure-dependent piezoelectric properties of phage at the molecular level. We then showed that self-assembled thin films of phage could exhibit piezoelectric strengths of up to 7.8 pm/V. It is also possible to modulate the dipole strength of phage, and hence tune their piezoelectric response by genetically engineering the phage&’s major coat proteins. Finally, we developed a phage-based piezoelectric generator that produces up to 100 nA of current and 900 mV of potential, and use it to operate a liquid crystal display. Because biotechnology techniques enable large-scale production of genetically modified phages, phage-based piezoelectric materials potentially offer a simple and environment-friendly approach to piezoelectricity generation.
5:15 AM - R2.07
Flexible Giant Magnetostrictive GaFe Films on Cylindrical, Nanoporous and Planar Substrates for Energy Harvesting Devices
Matt Hein 1 Eliot Estrine 1 Jung Jin Park 2 Sai Madhukar Reddy 1 Alison Flatau 3 Bethanie Stadler 1 2
1University of Minnesota Twin Cities Minneapolis USA2University of Minnesota Twin Cities Minneapolis USA3University of Maryland College Park USAShow Abstract
A number of unique and interesting energy harvesting devices utilizing materials with extremely large magnetostrictive constants (lambda;) such as TbFe (Terfenol) have been demonstrated in literature. When compared to piezoelectric devices though the number paper dealing with these materials is only a small fraction. The reason for this may be due to a lack of materials with suitable properties. Magnetostrictive materials can change the direction of their magnetization with the application of a stress which is referred to as the Villari effect. This action is analogous to rotating a magnet. By using Maxwells equations it can be seen that this rotation of magnetic moment can be used to harvest energy. GaFe (Galfenol) overcomes many limitations of typical magnetostrictive materials in that it has a large lambda;, is rare-earth-free, and ductile. In addition to that, our group has pioneered electrodeposition of the material which allows us to deposit thin films directly onto various substrates and structures. To date we have demonstrated deposition on planar substrates of glass, metals, Si, GaAs and into high aspect ratio nanoporous films using a rotating disc electrode (RDE). Recently, a technique for depositing directly onto a cylindrical substrate using a rotating cylinder electrode (RCE) has been developed with allows for direct integration of energy harvesting materials onto a shaft or tubular structure. EDS results of our cylindrical films show that we can control the composition of our alloy (10%-40% at.% Ga ) by adjusting the deposition potential 1.4 to 1.8V, the rotation rate 100 to 1000rpm, and by adjusting the ratio of Ga:Fe in solution. As deposited films have been measured using a capacitance bridge to have a lambda; between 50 and 120ppm, while our nanowires have been measured via atomic force microscopy to have a lambda; of 40ppm. With this unique ability to electrodeposit magnetostrictive material onto a wide range of substrates, new opportunity exist for developing integrated energy harvesting micro and nano-structured devices.
5:30 AM - R2.08
Output Power Enhancement of Flexible ZnO Nanogenerator By a CuO-ZnO P-N Junction Formation
Sung-Ho Shin 1 Min-Hyung Lee 3 Joo-Yun Jung 2 Junghyo Nah 1
1Chungnam National University Daejeon Republic of Korea2Korea Institute of Machinery and Materials Daejeon Republic of Korea3Kyung Hee University Yongin Republic of KoreaShow Abstract
Among several piezoelectric materials, ZnO has been considered as one of the most promising candidates for the realization of nanogenerator due to their nontoxicity and cost effectiveness by comparison to other materials. However, the performance of ZnO piezoelectric nanogenerator (NG) has been limited largely due to excessive electrons existing in ZnO, which screens piezoelectric potential generated by mechanical deformation of the crystal structure. Nominally undoped intrinsic ZnO exhibits n-type behavior due to defect levels induced by interstitials and oxygen vacancies, leading to Fermi level close to the conduction band edge. Thus, large excessive electrons can be easily found even at room temperature. To alleviate this issue, several attempts have been made up to date. In our report, as an alternate solution, we investigated CuO, p-type metal oxide semiconductor with a bandgap of 1.35 eV, to form a metal oxide only CuO-ZnO p-n junction, where CuO naturally demonstrates p-type behavior due to cation-deficiency, acting as a hole conductor. In this approach, we demonstrated greatly enhanced piezoelectric energy conversion performance of ZnO flexible piezoelectric NG, exhibiting 7-fold higher output voltages and one order of magnitude higher output currents by comparison to the devices without CuO layer.
5:45 AM - R2.09
Multilayer Stacked Flexible BatiO3 Nano-Composite Based Piezoelectric Nanogenerator for Enhanced Output Power Generation
Sung-Ho Shin 1 Min-Hyung Lee 2 Joo-Yun Jung 3 Junghyo Nah 1
1Chungnam National University Daejeon Republic of Korea2Korea Institute of Machinery and Materials Daejeon Republic of Korea3Kyung Hee University Yongin Republic of KoreaShow Abstract
ZnO nanogenerators(NGs) have gained great attentions as a material system to fabricate NGs due to nontoxicity and cost effectiveness of ZnO by comparison to other materials. However, relatively low piezoelectric dipole moment coupled with potential screening effect by excess electrons in ZnO (wurtzite crystal structure) necessitates additional process steps to realize high performance NGs. In this respect, several attempts have been made to fabricate NGs with perovskite ceramic materials such as PZT and BaTiO3. Inherent piezoelectric properties of these materials are superior to ZnO, providing a more advantageous platform to realize high performance NGs. Several reports have been made based on these material systems. In our work, we investigated NGs based on BaTiO3 nanoparticle composite, which is more environmental friendly material compared with PZT. The NGs were fabricated by forming a multilayer structure with BaTiO3-PVDF composite. Compared with previously demonstrated BaTiO3 composite based NG, our approach provides relatively simple fabrication process, allowing multiple layer stacking, which results in enhanced output power per unit area. After polling process at high electric field, the NGs consistently exhibits over 8 V peak-to-peak output voltage with a current density fo ~1.3 uA/cm^2 at normal bending conditions on a bending stage. Upon the applied pressure with a finger tip normal to the device surface, the devices show the output voltage and current density of ~50 V and ~10 uA/cm^2, respectively. Our simple approach allows to realize large scale high performance NGs with high flexibility and reliability.
R1: Energy Harvesting I
Horacio D. Espinosa
Tuesday AM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 13-14
9:00 AM - R1.01
High Power Triboelectric Nanogenerator and Its Hybridization with Li-Ion Battery as Sustainable Flexible-Power-Unit
Sihong Wang 1 Zhong Lin Wang 1
1Georgia Institute of Technology Atlanta USAShow Abstract
The emergence of electronic devices/systems with unprecedented functionalities mandatorily requires portable, flexible and sustainable power sources. Energy harvesting technology that can efficiently generate electricity from ambient environmental energy is the prerequisite for the realization of such new power sources. But due to their intrinsic limitation of unstable and uncontrollable electrical output, it is desirable to hybridize them with energy storage devices into single units, which could be capable of sustainably providing a stable output through utilizing the energy in the environment.
For the electricity generation, mechanical energy is one of the best choices as energy source owing to its universally-existence in our living environment and human bodies. A new type of devices—triboelectric nanogenerators (TENGs)—based on contact electrification has been recently invented as an effective and adaptive technology to generate electricity from motions. However, because the device structure and material properties have not been optimized, the output is still insufficient for sustainably driving electronic devices/systems. Here, we demonstrated a rationally designed arch-shaped TENG as a flexible mechanical energy harvester with extremely-high power output. Through purposely introducing thermal stress on the surface, a flexible substrate was made into a naturally-bent shape, so that a steady gap formed between two triboelectric layers at strain-free conditions. This design facilitates the separation of the opposite tribo-charges, thus maximizes the electrical driving force. This unique structure, together with the surface modification of tribo-layers, helps to largely enhance the output voltage, and power density to 230 V and 128 kW/m3, respectively, with an efficiency as high as 10~39%. For the first time, it realized the instantaneous driving of tens of regular electronic devices (LEDs), and also the fully charging of a Li-ion battery. 
For the development of sustainable power sources, we further hybridized the arch-shaped TENG with a flexible Li-ion-battery into as a single device—a flexible self-charging power unit (SCPU), which allows a battery to be charged directly by ambient mechanical motion. This physical hybridization enables a new operation mode: the “sustainable mode”, in which the environmental mechanical energy is scavenged to charge the battery while the battery keeps driving an external load. In this mode, the demonstrated SCPU can provide a continuous and sustainable DC current of 2 µA at a stable voltage of 1.55 V for as long as there is mechanical motion/agitation. It can be used to continuously drive a UV sensor for extended period of time. Thus, the SCPU can serve as an independent and sustainable power unit, which will meet the general requirement of almost any electronic device. 
 Wang, S. H.; Wang, Z. L. et al. Nano Lett. 2013, 13, 2226-2233.
 Wang, S. H.; Wang, Z. L. et al. ACS Nano Under review.
R3: Poster Session I: Energy Conversion and Storage
Tuesday PM, April 22, 2014
Marriott Marquis, Yerba Buena Level, Salons 8-9
9:00 AM - R3.02
Preparation and Orange-Red Emission of Hierarchical PbTiO3/ZnO Nanostructures
Shan Jiang 1 Hui Zhao Ren 1 Gang Xu 1 Rong Gao Han 1
1Zhejiang University Hangzhou ChinaShow Abstract
One-dimensional (1D) piezoelectric and ferroelectric nanomaterials, such as PZT, ZnO nanowires, have attracted great attention due to their fascinating properties and potential applications ranging from high-density ferroelectric random access memory (FeRAM) and high performance nanogenerators [1,2]. In particular, hierarchical complex structure on the basis of ZnO nanowires has been designed and prepared to realize novel nanodevices in the recent work [3,4]. In this study, we apply a two-step hydrothermal process to fabricate hierarchical PbTiO3/ZnO (PTOZ) nanostructures. Unique brush-like three-dimensional (3D) nanostructures of the samples was achieved, where secondary ZnO nanorods grew on the surface of the single-crystal nanowires of ferroelectric tetragonal PbTiO3. The number density and the length/diameter ratio of the secondary ZnO can be easily tailored by changing the reaction time. Photoluminescence (PL) properties of the as-prepared and post-annealing treated samples were studied at room temperature. Compared with pure ZnO nanorods, such hybrid nanostructures show a stronger broad visible emission centered at 632nm. Moreover, after annealing treatment in air, the visible emission intensity of the samples was significantly enhancemed, accompanied with a red shift in the peak center.
The orange-red emission is commonly attributed to the presence of excess oxygen in the ZnO . For the PTOZ nanostructures, we proposed that the polarization surface of PbTiO3 nanowires could make additional contribution to the orange-red emission in the hierarchical PTOZ nanostructures by changing absorption of oxygen on their surfaces. These hybrid 3D nanostructures could be ideal candidates for optoelectronic and piezoelectronics nanodevice applications.
1. Xiao, Z.; Ren, Z. H.; Liu, Z. Y.; Wei, X.; Xu, G.; Liu, Y.; Li, X.; Shen, G. and Han, G. R. J.Mater.Chem.,2011, 21, 3562.
2. Wang, Z. L.; Zhu, G.; Yang, Y.; Wang, S. H. and Pan, C. F. Materials Today 2012, 15, 532-543.
3. Cheng, C. W.; Liu, B.; Yang, H. Y.; Zhou, W. W.; Sun, L.; Chen, R.; Yu, S. F.; Zhang, J. X.; Gong, H.; Sun, H. D. and Fan, J. H. ACS Nano. 2009, 10, 3069.
4. Qin, Y.; Wang, X. D. and Wang, Z. L. Nature. 2008, 451, 809.
5. Djuriscaron;icacute;, A. B.; Leung, Y. H.; Tam, K. H.; Hsu, Y. F.; Ding, L.; Ge, W. K.; Zhong, Y. C.; Wong, K. S.; Chan, W. K.; Tam, H. L.; Cheah, K. W.; Kwok, W. M. and Phillips, D. L. Nanotechnology 2007, 18, 095702.
9:00 AM - R3.04
Elucidating the Decomposition of PCBM During Evaporation: A Model Approach for the Evaluation of Small Molecule Semiconductor Films Processed by Physical Vapor Deposition.
Torben Adermann 1 Julia Maibach 2 Tobias Glaser 4 Ralph Eckstein 3 Eric Mankel 2 Norman Mechau 3 5 Annemarie Pucci 4 Manuel Hamburger 1 5 Thomas Mayer 2 Wolfram Jaegermann 2
1Heidelberg University Heidelberg Germany2TU Darmstadt Darmstadt Germany3Karlsruhe Institute of Technology Karlsruhe Germany4Heidelberg University Heidelberg Germany5InnovationLab GmbH Heidelberg GermanyShow Abstract
In the field of organic electronics a major research focus lies on the solution processabilty of organic semiconductor materials. Although some materials are designed for solution processing, i.e. Phenyl-C61-butyric acid methyl ester (PCBM), it is repeatedly reported in literature that deposition of PCBM via thermal evaporation in vacuum is performed to achieve either ultrathin or very clean films suitable for e.g. photoelectron spectroscopy characterization.
We have investigated the effects of thermal evaporation on PCBM in a very interdisciplinary approach, applying physical characterization techniques such as photoelectron (PES) and infrared (IR) spectroscopy in combination with device engineering and chemical analysis using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), ultra performance liquid chromatography-coupled mass spectrometry (UPLC-MS), and nuclear magnetic resonance spectroscopy (NMR). The methods were applied to thin films prepared by both solution based deposition techniques and thermal evaporation. It is found, that evaporation proves to be an inefficient deposition route for thin layers of chemically pure PCBM. Changes in the IR spectrum of the PCBM films already indicate a change in the molecular structure of PCBM. The UPLC chromatogram of the redissolved organic film proves the formation of several molecular species, including bare C60. Especially the crucible residue after evaporation contains a large fraction of disintegration products. 1H-NMR of the crucible residues shows the formation various new functional groups in the side-chain of PCBM. The effect of degradation on the electronic properties was however found to be limited, as an almost unchanged ionization potential of 6.1 eV was determined with UPS for both the solution processed as well as the evaporated films. By simulating the evaporation conditions by TGA, PCBM sample purity was reduced to roughly 90 %. Bulk-heterojunction solar cells were fabricated with pure and thermally treated PCBM samples to investigate their impact on device performance.
9:00 AM - R3.05
Wireless Power Harvesting via Flexible Magnetostrictive Nanoribbons
Huai-An Chin 1 Tian Liang 3 Shiyou Xu 4 Gerald Poirier 4 Nan Yao 4 Sigurd Wagner 1 Michael McAlpine 2
1Princeton University Princeton USA2Princeton University Princeton USA3Princeton University Princeton USA4Princeton University Princeton USAShow Abstract
The development of a method for wirelessly “radiating” power generated by biomechanical motion could enable new fundamental insights and applications in soft robotics, sensor networks and remote medical monitors. Biomechanical power harvesting is gaining interest due to decreasing power requirements in portable electronic devices. Various approaches have been investigated to harvest this biomechanical power, including piezoelectricity and triboelectricity. Significantly less explored is the use of magnetic materials for wireless harvesting of biomechanical power. For example, if a flexible magnetostrictive sample is interfaced with a biomechanical source, the persistent biomechanical motion will continuously deform the sample, which will radiate electromagnetic power.
Here we demonstrate the feasibility of wirelessly harvesting power from biomechanical motion using flexible magnetostrictive Terfenol-D nanoribbons, which were deposited, fabricated and transfer printed onto biocompatible silicone. A Terfenol-D film was sputterer-deposited onto an oxidized Si wafer substrate containing photolithographically patterned resist lines. Terfenol-D nanoribbons were obtained following lift-off. The transfer involved complete removal of the Si substrate, rendering the sample flexible. The flexible nanoribbons exhibited excellent magnetic characteristics; indeed, the observed saturation magnetization value of ~1.3 Tesla is, to our knowledge, the highest value reported to date for any sputtered Terfenol-D film. As a proof of principle for demonstrating the potential of the magnetostrictive nanoribbons to wirelessly harvest biomechanical power, flexible nanoribbon generators were attached to a wind-up toy capable of generating a flapping motion. The power wirelessly radiated from this system was then measured. The result indicates that magnetostrictive nanoribbons which are deformed periodically can transmit power to a receiver without any physical contact, enabling new advances in wirelessly harvesting power from a biomechanical source.
9:00 AM - R3.06
Polymer-Oxide Interface Delamination and Reliability in Protective Barriers
Scott G. Isaacson 1 Reinhold H. Dauskardt 1
1Stanford University Stanford USAShow Abstract
Interfaces between polymers and inorganic materials can be found at all levels of flexible organic electronics and photovoltaics, including in the active electronic or photovoltaic layers, at electrical contacts or interconnection lines, and within the protective encapsulation and transparent barrier layers. In the case of flexible protective barriers, the integrity of such polymer-inorganic interfaces are of critical importance to the lifetime of devices and their modules, since interfacial damage in the form of loss of adhesion or delamination can degrade device performance and create fast diffusion pathways for potentially harmful environmental species such as moisture and oxygen.
We present research methodologies for quantifying the effect of interfacial chemistry together with the role of environment, temperature and mechanical stress on the adhesion of model polymer-oxide interfaces. Measurements of adhesive strength are reported as a function of pre-exposure to accelerated aging conditions, including elevated temperature, ambient humidity, and irradiation with ultraviolet light. We demonstrate that adhesive strength is degraded after exposure to ultraviolet light, and use XPS measurements to correlate this degradation to photo-induced chemical changes at the interface. Importantly, we also show that the wavelength of the UV irradiation (UVA vs. UVB) affects many properties of the polymer-oxide system, including delamination behavior, adhesive strength, and the polymer yellowing rate. The importance of understanding such mechanisms of environmentally-assisted degradation of polymer-inorganic interfaces is underscored by the need for improved accelerated life testing procedures, which form the basis for more accurate lifetime predictions.
9:00 AM - R3.07
Enhanced Transparent Barrier Film Through Nanoscale Interface Structuring
Can Cai 1 Reinhold H Dauskardt 1
1Stanford University Stanford USAShow Abstract
The development of a cheap, flexible, and reliable barrier film technology is critical for the integration and commercialization of flexible photovoltaics and organic electronics devices. A promising emerging barrier technology utilizes multiple thin films of alternating organic/inorganic layers that is amenable to roll-to-roll processing while maintaining the desired ultra-low diffusion barrier properties. In operation, the barrier films are subject to weathering effects such as diurnal temperature cycling, moisture and chemical erosion, and UV degradation. The organic/inorganic interfaces are highly susceptible to damage from these degradation sources and limit the operational lifetime of the barrier film. We demonstrate a novel method to increase the organic/inorganic interfacial adhesion strength in a model system of poly (methyl methacrylate) (PMMA) and silicon oxide through interfacial patterning. An array of nanoscale patterns is etched into the PMMA through the use of nanosphere lithography. A thin layer of silicon oxide is conformally deposited onto the patterned PMMA through plasma enhanced chemical vapor deposition. The patterned interface exhibit an order of magnitude increase in adhesion strength over that of a non-patterned interface. X-ray photoelectron spectroscopy (XPS) of the delamination surface shows that the fracture pathway changes from the oxide/PMMA interface in the unpatterned system to within the PMMA in the patterned system. Absorption spectroscopy was used to determine the effect of the nanostructured interface on the optical transmission of the samples. Applied to barrier films, interfacial patterning can be used to increase adhesion between the organic/inorganic layers and resistance of delamination under environment degradation.
9:00 AM - R3.08
Preparation and Properties Study of Mo Thin Film Electrode Materials on Flexible Polyimide Substrates
Chao Li 1 2 Daqin Yun 2 Ran Zhang 2 Fengyan Zhang 2
1Auburn University Auburn USA2Xiamen University Xiamen ChinaShow Abstract
Molybdenum (Mo) thin films were prepared on flexible polyimide (PI) substrates by direct current (DC) magnetron sputtering method. Mo thin films prepared at different sputtering gas pressures and powers have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), four-probe resistivity meter and adhesion test, respectively. The influence of different deposition factors on the crystal structures, surface morphology, electrical and adhesion properties of Mo thin films have been discussed. The experiment results indicate that increasing sputtering gas pressures lead to worse crystal structures, worse electrical properties and better adhesion; the design of a bilayer Mo thin films can achieve better electrical and adhesion properties; increasing sputtering powers result in better electrical and adhesion properties, but it will lead to worse crystal structures and electrical and adhesion properties after beyond a certain power value. Therefore, a bilayer Mo thin film deposited at a higher sputtering power is more suitable for the back contact electrode of CIGS thin film solar cells.
9:00 AM - R3.09
Recharging Electric Vehicles During Motion to Extend the Range
Hal Gokturk 1
1Ecoken San Francisco USAShow Abstract
Range anxiety is considered as one of the major hurdles in the acceptance of a pure electric vehicle (EV) by the mass market. In order to alleviate this concern, auto makers are researching batteries which can store more energy per unit weight. However it might take decades of development to reach the energy density of gasoline even with the advanced formulations under consideration. The objective of this research is to consider an alternative approach which refreshes the batteries of an EV by delivering energy to the vehicle while in motion. Methods of directing intense energy beams to a moving target have been developed by Directed Energy Weapons Systems Program of the military and some of those can be adopted to EVs .
A typical EV has a large cross-sectional area (~10 m2) and a roof area which is about a third of the total cross-section (~3 m2). Three recharging schemes which take advantage of these aspects of the vehicle are proposed:
(a) By AC magnetic induction while the EV is moving at very slow speed, for example through a toll gate or temporarily stationary, for example waiting at a red light. AC current is provided to coils placed on the ground to create a time varying magnetic field perpendicular to the road surface. This magnetic field induces current in receiver coils wrapped around the EV. Frequency of the AC input needs to be set high (600 Hz or more) in order to provide a significant amount power during the brief presence of the vehicle over the coils.
(b) By permanent magnets placed on the road surface along highways. A static magnetic field perpendicular to the road surface is generated by sheets of magnets placed on the road surface. High speed motion of the vehicle over the magnetic field induces a current at receiver coils wrapped around the EV. Since this is a passive method which does not provide power, magnetic sheets are placed at downhill locations along the highway where the EV can maintain its motion with minimal battery usage.
(c) By a pulsed laser directed at photovoltaic (PV) panels placed on the roof of the EV. Diode lasers which are small and relatively inexpensive are installed on overhead structures such as traffic signs. The laser sends high power (kW) pulses to the roof of the EV as it approaches and passes below the laser unit. A conversion efficiency of 50% can be attained with a PV panel matched to the nearly monochromatic light of the laser.
Technical requirements necessary to refresh 1-3% of the energy stored in a typical EV battery will be provided during the presentation.
 R.J. Katt, "Selected Directed Energy Research and Development for U.S. Air Force Aircraft Applications," National Academies Press, Publication 18497, Washington, DC 2013
9:00 AM - R3.10
Reduced Graphene Oxide Thin Films as Ultrabarriers for Organic Electronics
Hisato Yamaguchi 1 2 Jimmy Granstrom 3 Wanyi Nie 1 Hossein Sojoudi 3 Takeshi Fujita 4 Damien Voiry 2 Mingwei Chen 4 Gautam Gupta 1 Aditya D Mohite 1 Manish Chhowalla 2
1Los Alamos National Laboratory Los Alamos USA2Rutgers University Piscataway USA3Georgia Institute of Technology Atlanta USA4Tohoku University Sendai JapanShow Abstract
Encapsulation of electronic devices based on organic materials that are prone to degradation even under normal atmospheric conditions with hermetic barriers is crucial for increasing their lifetime. A challenge is to develop “ultrabarriers” that are impermeable, flexible, and preferably transparent. Another important requirement is that they must be compatible with organic electronics fabrication schemes (i.e. must be solution processable, deposited at room temperature and be chemically inert). Here, we report lifetime increase of 1,300 hours for poly(3-hexylthiophene) (P3HT) films encapsulated by uniform and continuous thin (~10 nm) films of reduced graphene oxide (rGO). This level of protection against oxygen diffusion is substantially better than conventional polymeric barriers such as CytopTM, which degrades after only 350 hours despite being 400 nm thick. Analysis using atomic force microscopy, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy suggest that the superior oxygen gas barrier property of rGO is due to the close interlayer distance packing and absence of pinholes within the impermeable sheets. These material properties can be correlated to the enhanced lag time of 500 hours. Our results provide new insight for the design of high performance and solution processable transparent “ultrabarriers” for a wide range of encapsulation applications.
H.Yamaguchi et al. "Reduced Graphene Oxide Thin Films as Ultrabarriers for Organic Electronics" Adv. Energy Mater. (2013), Article first published online: 10 OCT 2013, doi: 10.1002/aenm.201300986
9:00 AM - R3.11
Origin of "Temporal Tail" in Decay Dynamics of MEH-PPV Films
Rajarshi Chakraborty 1 Lewis J Rothberg 2
1University of Rochester Rochester USA2University of Rochester Rochester USAShow Abstract
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) has been considered as one of the potential and useful conducting polymers for various optoelectronic applications because of its solubility, flexibility, low cost and conductivity. It is accepted that quantum yield of films are less than their solution counterparts and has a “temporal tail” in the decay dynamics. We try to understand if a correlation exists between the “temporal tail” and quantum yield in films. We investigate the origin of a “temporal tail” by a temperature dependent study of the spectra. We also study the electric-field effect on the “tail” and describe the results on the basis of a model that implies that the long-lived `tail&’ luminescence in film is a result of energy transfer from “ H-like aggregates” present in the film.
9:00 AM - R3.12
Effective Piezo-Phototronic Enhancement of Solar Cell Performance by Tuning Material Properties
Xiaonan Wen 1 Wenzhuo Wu 1 Zhong Lin Wang 1 2
1Georgia Institute of Technology Atlanta USA2National Institute for Materials Science Tsukuba JapanShow Abstract
Piezo-phototronic effect is demonstrated in the ZnO/P3HT solar cell system and detailed study is conducted regarding the influence of crystallization and doping level of ZnO on the strength of piezo-phototronic effect as well as the overall solar cell performance. By testing and comparing five groups of samples prepared under different conditions, optimized parameters are determined for the most efficient piezo-phototronic enhancement of solar cell performance. The general principles and regularities provided in this study are universal and applicable to all solar cell systems involving piezoelectric semiconductor materials and could provide substantial guidance on further increasing performances of commercial solar cells based on CdTe, GaAs etc. and also spur the development of flexible solar cells for smart applications in various situations.
9:00 AM - R3.13
Photoemission Studies on the Effects of Micro/Nano Fillers in HEMT GaN Encapsulants
Viswas Purohit 1 2 Laurence Chevalier 2 Kaouther Daoud 2
1Alliance College of Engineering and Design Bangalore India2Universitamp;#233; de Rouen , Facultamp;#233; des Sciences et Techniques - Technopamp;#244;le du Madrillet Saint Etienne du Rouvray cedex FranceShow Abstract
Failures in electronic devices can be classified as i) catastrophic failures which destroy the device or ii) degradation failures which causes a reduction in device performance. Device bias, resultant channel temperature, passivation, and material interactions may all cause or contribute to failure. For the analysis of such types of defects, it is very important to access the ‘heart&’ of the device and to observe the front side of the die. This is done by removing the epoxy resin which plays an important part in insulation between the electrical parts of the device as well as to provide protection against atmospheric corrosion. The most widely used solution is to use the laser decapsulation process along with chemical depackaging technique to obtain a good surface of the die for further analysis. The use of silica for reinforcement of polymeric insulation like epoxy resin in microelectronic packaging industry is essential for its dielectric and thermal properties since, addition of silica improves the thermal dissipation . However, decapsulation of chips, tend to leave behind minute traces of this epoxy which remain bound to crevices of the semiconductor device.
In this paper, decapsulation studies were carried out on Gallium Nitride High Electron Mobility Transistor (GaN HEMT) devices and the physics of degradation attributed to epoxy was analyzed. Although the sealant materials are supposedly electrically inactive, a contribution to the device performance is observed. These electrically active traces are believed to contribute to the degradation in the performance of the device as evident by the IV measurements for different gate voltages. The use of photoemission microscopy for the analysis of this particular type of packaging related failure has been put forward in this work. The main aim of this paper is to study the effects of the remnant material on the performance of the component and to analyze its contribution towards electrical degradation by using photoemission microscopy.
9:00 AM - R3.14
Flexible Carbon Nanotube Based Power Fabrics for Harvesting Thermoelectricity to Operate an Electrochromic Sensor
Suk Lae Kim 1 Choongho Yu 1
1Texas Aamp;M University College Station USAShow Abstract
Single wall carbon nanotubes (CNT) were functionalized to p- or n-type materials, and a thermoelectric power generating device made of CNT films was designed and fabricated to operate a glucose sensor. The electronic transport properties were optimized by adjusting the amount of surfactants on CNTs for p-type films as well as reducing CNTs with multiple dopants for n-type. The thermopower and electrical conductivity of optimized n-type nanotubes were measured to be -86 µV/K and 5,200 S/m, respectively. The p-type nanotube samples have a thermopower and electrical conductivity value of +100 µV/K and 11,000 S/m, respectively. Electronic band structures with the Fermi level and carrier mobilities of the CNTs were experimentally investigated, which have elucidate