2015 MRS Spring Meeting

Apr 6, 2015 ‐ Apr 10, 2015


The 2015 MRS Spring Meeting and Exhibit was held in San Francisco, California. Technical symposia were held within the following topical clusters: Energy, Nanomaterials, Electronics and Photonics, Soft and Biomaterials, and General – Fabrication and Characterization. Access to all of the content below is free – simply login with your MRS username and password for complete access. Don’t have a username and password? Create a free account.


Sessions

Light Emitting Diodes in the Experimental Practice for the Characterization of Novel Photovoltaics

Apr 7, 2015 2:15pm ‐ Apr 7, 2015 2:30pm

Identification: E2.03

Light Emitting Diodes (LEDs) have recently gained importance in the experimental practice of novel photovoltaic (PV) devices. Tunability of peak wavelengths and the high efficiency of light emission have finally shown LEDs full potential in a variety of techniques. In this work, the following applications in the indoor characterization of PV cells and modules are presented, some of which are consolidated, while some others are totally novel. LEDs have recently been introduced as an alternative to conventional xenon or halogen based solar simulators. High intensity LEDs are now on the market and the authors show preliminary results and related challenges in the indoor characterization with a LED-based, steady state solar simulator for cells and commercial size modules. The continuous source is of fundamental importance in testing novel devices (e.g. organic PV, dye sensitized solar cells, capacitive and high-efficiency c-Si modules) where few millisecond pulsed simulators are no-longer reliable. Most importantly, the standard IEC 60904-9 Class A spectral irradiance requirement can be reached with a set of different LEDs and can be improved, for example via overlapping commercial halogen bulbs. The dependence of the electrical parameters on the Average Photon Energy (APE) is a new insight that emerged in the last years, giving interesting information for energy rating: the combination of powerful LED lamps with a conventional Class AAA large area solar simulator is also presented in this work, showing that a wide range of target APE values can be easily obtained. Comparison with the results from the outdoor field is shown. Multi-junction PV structures take also advantage of the use of coloured LEDs in experimental tools. Indeed, the standard IEC 60904-9 Class A spectral irradiance requirement can be really poor for such devices, which easily exhibit current limitation under artificial spectra and the consequent measurement artifacts that are widely studied in the literature. This work shows how the use of powerful LEDs can transform a conventional, single source pulsed solar simulator in a tunable simulator for spectral characterization of multi-junction modules, thus enhancing the spectral mismatch correction when measuring such devices. From the same point of view, the importance of LEDs as additional bias light (superimposed over a pulsed solar simulator) is also shown for a number of applications, such as spectral responsivity of multi-junction modules and the investigation of the dependence of the electrical parameters on the angle of incidence. With the revision and introduction of all the experimental challenges above, this paper represents a useful tool for any research centre dealing with the characterization of PV devices, with special interest in pre-normative techniques of measurements where standard procedure are still under discussion.

Speaker(s):
  • Mauro Pravettoni, University Appl. Sciences and Arts of Southern Switzerland, University of Pavia

Carbon-Coated ZnFe2O4 Nanocrystals for Advanced Lithium-Ion Anodes

Apr 7, 2015 2:15pm ‐ Apr 7, 2015 2:30pm

Identification: I2.03

As the leading battery technology, lithium-ion batteries (LIBs) have been widely used in consumer electronics. However, for future large-scale applications in electric or hybrid vehicles, further improvement would require concerning power and energy density demanded by such applications. Compared with the theoretical specific capacity of commercialized graphite (372 mAh/g) which is widely used as anode material in LIBs, the transition metal oxide shows great promise as they can provide much higher capacities and rate capabilities. For example, Zinc Ferrite (ZnFe2O4), which can be regarded as the replacement of one iron atom of Fe3O4 by zinc element, can provide an enhanced theoretical capacity of 1000mAh/g. To date, many efforts have been put on developing transition metal oxide based nanostructured-materials to enhance the rate performance. These nanostructures, such as nanoparticles, hollow nanospheres, nanotubes, etc., are effective in facilitating the Li ion diffusion due to a reduced diffusion length within the active materials and an increased electrolyte/electrode contact area. Moreover, carbon-based nanocomposites formed by carbon coating proved to enhance not only the ionic but also the electronic conductivity of electrode, which is very promising for high rate performances. Here we propose a general method to synthesize carbon-coated ZnFe2O4 nanocrystals with various nanostructures templated by star-like poly (acrylic acid)-block-polystyrene (PAA-PS) diblock copolymer and polystyrene-block-poly(acrylic acid)-block-polystyrene (PS-PAA-PS) triblock copolymer. Through a strong coordination bonding between the metal moiety of inorganic precursors and the functional groups of PAA (-COOH), ZnFe2O4 nanocrystals can be selectively incorporated into the space formed by the PAA block in star-like block copolymer templates. As a result, ZnFe2O4 nanoparticles and hollow nanospheres can be synthesized guided by the star-like PAA-PS and PS-PAA-PS templates, respectively. In addition, the size of ZnFe2O4 nanocrystals could be easily changed by varying the molecular weight of templates. The soft template not only serves as an easy control over the size and shape of ZnFe2O4 nanocrystals, but also acts as carbon source when calcinated at high temperature at argon atmosphere. We demonstrated that the carbon-coated ZnFe2O4 nanoparticles and hollow nanospheres obtained by the templating method would be superior anode materials for LIBs.

Speaker(s):

Monitoring the Size and the Stability of Zinc Oxide Quantum Dots in Biological Media: A Soft Ionization Mass Spectrometry Technique (MALDI-TOF-MS)

Apr 7, 2015 2:30pm ‐ Apr 7, 2015 2:45pm

Identification: GG2.05

With the development of material sciences, the characterization of nanomaterials has become a critical issue in managing their fascinating size-dependent physical and chemical properties. Controlling these properties from the synthesis to the application phase, and consequently to their fate as a worldwide environmental and societal concern is becoming more and more imperative. The potential toxicity of nanoparticles needs to be evaluated when developing applications in a responsible way. Zinc oxide ZnO nanoparticles can be found largely as powders and dispersions with antibacterial, anti-corrosive, antifungal and UV filtering properties. ZnO nanoparticles can also be used for various applications ranging from food and cosmetics up to coatings agent and in the manufacturing of concrete. Research is actively being conducted towards in solar cells, photocatalysis, optical devices and sensors which have already started to show economic potential worldwide. The principal techniques currently used to achieve the characterization of nanoparticles are physical and physico-chemical methods, such as Transmission Electron Microscopy (TEM), X-ray diffraction, and optical spectroscopies. All these analytical tools are excellent for global analyses of clusters and nanomaterials. Soft ionization mass spectrometry (MS) methods such as Matrix Assisted Laser Desorption Ionization coupled with Time of Flight MS (MALDI-TOFMS) have already proven their potential as tools in the nanometrology of small-sized II-VI quantum dots (QDs) such as CdS, CdSe, ZnS and ZnSe. Mass spectra of these nanocrystals are consistent with TEM and optical spectroscopy measurements [1-2]. In this paper, we present a joint physical/physico-chemical study and, more specifically, the first application of MALDI-TOF-MS to analyze small-sized ZnO QDs (3-3.5 nm diameter range) synthesized by sol-gel chemistry and stabilized through an aminosilane coating. The organic shell increases the QDs stability and dispersibility in aqueous solution. The ligands were first quantified by thermogravimetric analysis (TGA), then a careful investigation of the stability of ZnO QDs was initiated once these QDs were dispersed in different media (water, biological buffer,�) for a period up to 6 weeks. Positive ion mode mass spectra showed a decrease in mass and consequently in diameter during aging, which can be ascribed to the degradation of ZnO QDs. In conclusion, the unique combination of MALDI-TOF-MS and physico-chemical techniques brings new insights concerning the structure analysis, the stability and consequently the potential toxicity of ZnO QDs. This new strategy in nanometrology will be extended to other II-VI materials in the near future. [1] A. Aboulaich, D. Billaud, M. Abyan, L. Balan, J.J. Gaumet, G. Medjahdi, J. Ghanbaja, R. Schneider ACS Appl. Mater. Interfaces, 4 (5) 2561-2569 (2012). [2] M. Fregnaux, J.J. Gaumet, S. Dalmasso, J.P. Laurenti, R. Schneider Microelectron. Eng. 108, 187-191 (2013).

Speaker(s):

Water-Free Titania-Bronze Thin Films with Superfast Lithium Ion Transport

Apr 7, 2015 2:30pm ‐ Apr 7, 2015 2:45pm

Identification: I2.04

The bronze polymorph of titanium dioxide (TiO2-B) is interesting for many applications including high rate lithium ion batteries (LIBs), solar cells, photocatalysis, thermoelectrics and sensing, owing to its uniquely layered structure with open channels and highly asymmetric unit cell. However, such a metastable phase is extremely hard to obtain with high purity and crystallinity, significantly impeding its development in these fields. After more than 30 years since the first synthesis of TiO2-B in 1980, hydrothermal methods are still the dominant route to produce this material in powder form, with limited purity, randomized crystal orientation and unavoidable presence of lattice water. Here we report the discovery of a waterless process to synthesize hetero-epitaxial crystalline thin films of TiO2-B using pulsed laser deposition (PLD) onto its more stable variant, Ca:TiO2-B (CaTi5O11), which serves as a template. The growth mechanism and various microstructures in the thin films are clearly shown at the atomic scale. By aligning the more open channels to out-of-plane directions, extremely high rates of lithium ion transport, up to 600C, with extraordinary structural stability can be achieved. As the methods and equipment required are readily accessible to the extended research community, we anticipate our report may stimulate further studies on and applications of these materials, which are attractive in realms that extend beyond LIBs.

Speaker(s):

Performance and Service Behavior of ZnO Based Energy Conversion Nanodevices

Apr 7, 2015 2:30pm ‐ Apr 7, 2015 3:00pm

Identification: P2.04

One dimensional ZnO nanostructures are envisioned as fundamental building blocks of future electronic, electromechanical, electro-optomechanical nanodevices. Meanwhile, the service behavior and damage in nanomaterials and nanodevices it vital for practical applications. The recent developments in our group for designs, fabrication of energy conversion devices based on ZnO nanomaterials, and some effective approaches for performance enhancement will be presented in this talk. We will focus on the major progress in three area. Firstly, we present the fabrication of wurtzite nanostructures and the property modulation. Then, we introduce the progresses on the piezotronic properties of ZnO nano-materials and prototype piezotronic devices, including piezoelectric field effect transistors, piezoelectric diodes, strain sensors and nanogenerators. Finally, the investigations of property degrading and damage of nanomaterials, and functional degrading and failure of these nanodevices will be presented for future electronic applications.

Speaker(s):
  • Yue Zhang, University of Science and Technology Beijing

On the Mechanics of an Engineered Living 1D Swimmer at Low Reynolds Number from Cardiomyocytes

Apr 7, 2015 2:45pm ‐ Apr 7, 2015 3:00pm

Identification: L2.05

There is a rich diversity of flagellar swimmers in nature. In general, they use a long tail, known as flagellum or celia, to propel themselves in fluids. Due to their small size, the fluid around them appears as viscous, resulting in low Reynolds number dynamics. Thus, there is no inertial component in the propulsion. Until to date, there is no engineered low Reynolds number swimmer that can propel itself autonomously. Earlier efforts resulted in swimmers that are driven by external magnetic fields. Here we present a swimmer that propels itself autonomously by using live rat cardiomyocytes. The swimmer consists of a flexible tail and a rigid head. Cardiomyocytes are plated on the tail near the head. The cells self-organize themselves by interacting with the flexible tail substrate, and with each other, and emerge as a group all beating in synchrony. The cell forces bend and deform the tail with time against the viscous drag of the fluid. This fluid-structure interaction results in a bending wave that travels from head to the tail end giving rise to a time irreversible dynamics. Such motion results in a net propulsive force on the swimmer. The swimmer moves forward by overcoming the longitudinal viscous drag. The swimmer dynamics is modeled within the framework of slender body hydrodynamics. The model predictions match within 10 percent of the experimental observation. The future potentials of such biological machines will be discussed.

Speaker(s):
  • Taher Saif, University of Illinois at Urbana-Champaign

Electrical Characterization of Gate Traps in FETs with Ge and III-V Channels

Apr 7, 2015 3:15pm ‐ Apr 7, 2015 3:45pm

Identification: CC4.01

Many Ge and III-V-based MOSFETs as well as GaN-based HEMTs and MOS-HEMTs are significantly compromised in performance and reliability by their high densities of interface, border, and bulk oxide traps. Problems may also arise when characterizing traps in FETs made on modern high mobility channels, due to their device structures and material properties that are different from their conventional counterparts. In this talk, we present the results of our study of these traps as obtained by the use of several electrical characterization techniques. In particular, we will review the novel ac transconductance technique that we recently introduced, which enables us to probe interface traps in the band gap as well as border and bulk traps in the gate dielectrics even without a body contact. We will also show that the Inelastic Electron Tunneling Spectroscopy (IETS) offers the unique capability to provide spatial and energy information about traps, as well as to distinguish between two types of traps: those that give rise to trap-assisted conduction and those that simply trap carriers. Ionizing radiation-induced trapping of charges in MOS-FETs and MOS-HEMTs made on III-V semiconductors are also reported and discussed.

Speaker(s):

Atomic-Scale Investigation of the Role of Twin Boundary in Lithiation Process in SnO2 Nanowires

Apr 7, 2015 3:15pm ‐ Apr 7, 2015 3:30pm

Identification: I2.05

During the past two decades, it has become clear that structural defects can greatly alter the behavior of nanoscale materials. With increased use of nanomaterials in the electrode architecture of Li-ion batteries, one should take into account how such defects can influence the electrochemical response of battery electrodes. In spite of this need, our fundamental understanding about the kinetics of lithium ions at microstructural defects is at its infancy. Here, we report, for the first time, the lithiation behavior of the individual SnO2 nanowires containing twin boundary (TB). Comparing with the single crystal SnO2 nanowire, in which the lithium ions preferred to diffusion along the [001] direction, our in situ TEM study indicates that the lithium transport pathway will totally change when the TB exists inside the SnO2 nanowires. Direct atomic-scale imaging of the initial lithiation stage of the TB-SnO2 nanowire and the DFT simulations prove that the lithium ions prefer to intercalate in the vicinity of the TB, which acts as a conduit for lithium ion diffusion inside the nanowires. Our results should lead to working out the great impact of interfaces on mass transfer, transport and storage and guide the development of high performance electrochemical devices that rely on ion transport by microstructure engineering.

Speaker(s):
  • Anmin Nie, Michigan Technological University

Wrapping Strategy for SnO2 with Porosity-Tuned Graphene for High Rate Lithium-Anodic Performance

Apr 7, 2015 3:30pm ‐ Apr 7, 2015 3:45pm

Identification: I2.06

The previous studies on SnO2 as electrode materials convey a message that the inevitable pulverization of SnO2 particles can be resolved by carbon-based materials. Since graphene has also proved effective for the harmful decrepitation of the particles with an advantage of electronic conductivity, wrapping SnO2 by sufficient amount of graphene seems to be an answer to enhancing its cycle life. On the other hand, severe wrapping of SnO2 by graphene is deleterious to its rate capability due to the sluggish motion of Li+ through the stacked graphene layers. Thus, in order to make graphene sheets favorable for Li-ion diffusion, they were modified to have large porosity with 3-D architectures, by a simple heating-rate control. The porous graphene-wrapped SnO2, having direct diffusion channels for Li+, outperforms the SnO2 with less-porous graphene. Consequently, the excellent performances are fulfilled, showing both stable cyclability (~1100 mAh g-1 up to 100 cycles) and high rate capability (~690 mAh g-1 under 3600 mA g-1). This strategy using porosity-tuned graphene sheet furnishes a valuable insight into the effective encapsulation of active materials, especially for those undergoing pulverization during cycling. [1] Y. Oh, S. Nam, S. Wi, J. Kang, T. Hwang, S. Lee, H. H. Park, J. Cabana, C. Kim and B. Park, J. Mater. Chem. A 2, 2023 (2014). [2] S. J. Yang, T. Kim, H. Jung, and C. R. Park, Carbon 53, 73 (2013). Corresponding Author: Byungwoo Park: byungwoo@snu.ac.kr

Speaker(s):

Applications of Antireflection Coatings for Enhancing Power Output of Solar Panels

Apr 7, 2015 3:45pm ‐ Apr 7, 2015 4:00pm

Identification: E2.06

Nanostructured antireflection (AR) layers on the front sheet of a solar panel can significantly increase the power output of the solar panel, and thereby lower the cost of solar electricity production. Sunlight incident on the front surface of conventional panels undergoes Fresnel reflection due to the mismatch between the refractive indices of air and of the front sheet of the panel. This reflection loss is around 4% at noon and can be greater than 40% at dawn or dusk. An optical interface layer with intermediate refractive indices at the air/front sheet interface can eliminate or greatly reduce the unwanted reflection. Designing the optical interface layer, i.e., antireflection structure is challenging due to the unavailability of material with the required intermediate refractive indices. Recent developments in nanostructured coatings have overcome this limitation and provide new avenues for novel antireflection structures. The need for broadband and wider angle AR structures has been significantly amplified due to recent development of novel PV technologies, such as tandem cells that harvest the entire spectrum of sunlight with greater efficiencies. However, most of the approaches previously developed to create broadband high-performance nanostructured AR coatings have experienced difficulties due to limitations in tuning the refractive index of the coating materials and lack of controllability in achieving the desired thickness of the ultra-low refractive index material. We have developed a scalable self-assembled nanostructure process that overcomes these limitations. Our process has the ability to create ultra-low refractive index (down to 1.08) material with controllability in both layer thickness and refractive index. Our nanostructured AR layers have demonstrated ultra-high, omnidirectional transmittance over the entire accessible portion of the solar spectrum and a wide range of optical incidence angles. In this paper, we review our latest work on high performance nanostructure-based AR coatings, including recent efforts to deposit such AR coatings on large area substrates. The high performance of these coatings has been demonstrated on a variety of front surfaces employed in the production of solar panels, including polyester (PET), polycarbonate, fluorinated ethylene propylene (FEP), and ethylene tetrafluoroethylene (ETFE) films, as well as ridged glass sheets. AR coated front sheets integrated on solar panels demonstrate 3% higher short-circuit current at normal incidence and 22% higher short-circuit current for light incident 80� from the normal. Furthermore, NREL�s System Advisor Model (SAM) predicts based on experimental results that Magnolia�s AR coatings can yield 5.4% and 6.4% greater annual power output for flat installations of solar panels at Tucson, AZ and Albany, NY locations, respectively, and 8.8% and 12.4% higher annual power output for vertical installations in Albany, NY and Honolulu, HI, respectively.

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