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

Morphological Control and Charge Recombination Kinetics for Perovskite Solar Cells

Apr 9, 2015 3:30pm ‐ Apr 9, 2015 4:00pm

Identification: C9.01

The development of all solid-state thin-film solar cells has reached a new milestone when the devices made of organometallic lead halide perovskite materials were reported with power conversion efficiency (PCE) exceeding 19 %. The key issue to make a device with a great photovoltaic performance for perovskite solar cells is to control the film morphology of perovskite under different experimental conditions. Diverse processing techniques were reported according to either a one-step or a sequential method to synthesize the required perovskite layer on top of the contact electrode with either a mesoscopic or a planar interface. In this lecture, I will demonstrate how the film morphology of perovskite can be controlled via varied synthetic approaches. For example, the perovskite layer can be produced under the condition of fast crystallization deposition using either toluene or chlorobenzene as an anti-solvent to induce a fast crystallization. The other approach is to use a proper additive such as hydroiodic acid (HI) to produce homogeneous precursor solutions prior to the following spin-coating step. Without adding the HI additive, one-dimensional dendroid microcrystals were produced with a poor surface coverage. When the HI additive was added in the perovskite stock solution, uniform and pinhole-free perovskite nanocrystals with full surface coverage were observed. For a p-type planar device ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Ag fabricated using such a synthetic approach to generate the CH3NH3PbI3 layer, the power conversion efficiency attained 8 % with the short-circuit current density over 18 mA cm-2. Photo-induced absorption (PIA) spectra and nanosecond transient absorption (ns-TAS) kinetics were also performed to understand the electron-hole recombination rates responsible for the corresponding device performances.

Speaker(s):

Improvement of Reliability by Inserting Un-Doped Poly-Si to Bottom of Floating Gate for Sub-20nm NAND Flash Memory

Apr 9, 2015 3:30pm ‐ Apr 9, 2015 3:45pm

Identification: CC11.07

NAND flash memory technology has been scaled down continuously for more productivity, but at the same time reliability properties have become worse due to increase in trap generation in tunnel oxide and inter-poly dielectrics as well as cell-to-cell interference and disturbance. For the reliability enhancement, n-type poly Si floating gate (FG) has been replaced with p-type poly-Si. By adopting p-type poly-Si FG, the virgin threshold voltage increases and charge loss of programed cells in NAND flash memory devices decreases. Because p-type poly-Si FG may increase charge gain of erased cells, however, cautious approach is needed. Also, diffusion of boron atoms in the p-type poly-Si FG into tunnel oxide (Tox) makes Tox quality worse, leading to degradation of reliability properties. To simultaneously reduce the virgin Vth of cells and boron diffusion into Tox, a thin layer of un-doped poly-Si is inserted at the bottom of p-type poly-Si FG. We profile boron concentration using secondary ion mass spectroscopy(SIMS) and achieve the decreased boron concentration in Tox. To evaluate the improvement on reliability properties, electrical characteristics such as time dependent dielectric breakdown(TDDB), stress-induced leakage current(SILC), random telegraph noise(RTN), endurance and data retention have also been measured. The results indicate that inserting un-doped poly-Si produces lower trap density in Tox and better reliability as compared to the conventional process.

Speaker(s):

In-situ TEM Study on the Tunnel Evolution during Lithiation of Single Crystalline Alpha-MnO2 Nanowires

Apr 9, 2015 3:30pm ‐ Apr 9, 2015 3:45pm

Identification: I8.06

Manganese dioxide (MnO2) is widely known to possess various allotropic forms such as ?-, ?- and ?-phases, which are constructed by combination of octahedral [MnO6] building blocks to form different tunneled structures. These special structures are believed to account for the various characteristics of MnO2 when it is employed as electrode material in lithium (ion) batteries. There is, however, lack of direct proof demonstrating the role of tunneled structure during electrochemical lithiation/delithiation of MnO2. In this work, by applying high resolution scanning transmission electron microscopy (HRSTEM) to single ?-MnO2 nanowire along both axial and radial directions, the tunneled structure is clearly shown and characterized. The ?-MnO2 nanowire is proved to be single crystalline and grow along [001] direction. Cross-sectional HRSTEM images have shown that the nanowire has a squared cross section and 2x2 tunnels align parallelly along its growth direction [001], matching very well with simulated crystal structure. An in-situ TEM setup for study of MnO2�s dynamic lithiation/delithiation process is also designed and demonstrated. It is found that upon lithiation, the ?-MnO2 nanowire shows different orientation-sensitive morphologies. That is, ?-MnO2 unit cell expands asynchronously along [100] and [010] directions, resulting in macroscopic difference under [010] and [100] zone axes observations. DFT simulation demonstrates that such an asynchronous expansion originates from the specific Li-occupancy sequence at Whckoff 8h sites inside ?-MnO2�s 2�2 tunnels.

Speaker(s):

Enhancing Optoelectronic Properties of Semiconductor Devices with Piezoelectric Substrates

Apr 9, 2015 3:30pm ‐ Apr 9, 2015 4:00pm

Identification: P8.05

Piezoelectrics with their permanent polarization and its change with temperature can be used to enhance optoelectronic properties of semiconductor devices. Here we present several exemplary devices to illustrate the benefits of piezoelectric substrates. The first example is an optothermal field effect transistor (FET) based on the pyroelectric effect of the piezoelectric substrates. The device is a graphene-lead zirconate titanate (PZT) system utilizing the high optical transparency and conductance of graphene.1 Under the incidence of an infrared (IR) laser beam, the drain current can be increased or decreased depending on the direction of the polarization of the PZT substrate. The drain current sensitivity of the optothermal FET can reach up to 360 nA/mW at a drain field of 6.7 kV/m more than 5 orders of magnitude higher than that of the photogating transistors based on carbon nanotube on SiO2/Si substrate. A similar device using single zinc oxide nanowire and PZT (ZnO NW�PZT) was also demonstrated.2 Recently, we combined the transparent and conductive properties of graphene with the optical and photovoltaic properties of Poly(3-hexylthiophene) (P3HT) as a hybrid composite.3 Based on the inherent nature of the band alignment between graphene and P3HT, the photogenerated holes are able to transfer to the graphene layer and improve the photoresponse. When the graphene was deposited on a piezoelectric Pb(Zr0.2Ti0.8)O3 (PZT) substrate, the photoresponse of such composite photodetectors was found to be ten times larger than on SiO2 substrate. It was demonstrated that the electric field of the polarization of piezoelectric substrate helped the spatial separation of photogenerated electrons and holes and promoted the hole doping of graphene to enhance the photoconduction. Moreover, with the replacement of P3HT by a thin layer of bulk heterojunction of polymer and fullerene, the photosensitivity can be further increased by more than one order of magnitude. More recently, we replaced the P3HT with graphene quantum dots (GQDs). Preliminary results showed that the photoresponse of the GQD-graphene composite on PZT was even higher than that of P3HT-graphene system. More updated results will also be presented. References C.-Y. Hsieh, Y.-T. Chen, W.-J. Tan, Y.-F. Chen, W. Y. Shih, and W.-H. Shih, �Graphene-PZT Optothermal Field Effect Transistors,� Appl. Phys. Lett., 100, 113507 (2012) C.-Y. Hsieh, M.-L. Lu, J.-Y. Chen, Y.-T. Chen, Y.-F. Chen, W. Shih, and W.-H. Shih, "Single ZnO nanowire-PZT Optothermal Field Effect Transistors," Nanotechnology, 23, 355201 (2012) W.-C. Tan, W.-H. Shih, and Y.-F. Chen, �Highly Sensitive Graphene-Organic Hybrid Photodetector with Piezoelectric Substrate,� Advanced Functional Materials, DOI: 10.1002/adfm.201401421

Speaker(s):

The Nexus of Energy, Water, Health and Food: Thinking Small to Solve Global Quality of Life Challenges

Apr 9, 2015 3:45pm ‐ Apr 9, 2015 4:15pm

Identification: GG7.07

In the past decade and half, we have gained incredible insight into the workings of Nature at the smallest scales as we developed the ability to manipulate, control and interrogate matter at the atomic scale. But much of the promise of establishing new industry and economies founded on these scientific achievements has not come to pass. This is all about to change. With the foundations laid, the next 15 years is destined to see the application of these scientific advances into technologies that directly improve the human condition creating both economic and societal wealth. The ability to use machines to manipulate matter a single molecule at a time renders many things possible that were impossible before. Living systems do this on a regular basis. The core challenge is how to transform a labile molecule that exists in a fragile living organism and to transfer that functionality into a stable system that is economically scalable. The most significant difficulties revolve around environmental stability and the inherent structural limitations of the molecule. Ingenuity Lab was created to bring together researchers from many disciplines to capitalize on the molecular interactions found in living systems and, through molecular manipulation, incorporate this functionality into complex systems to yield technology for solving many of the worlds societal challenges. Presented is the concept of convergent technology, the intersection of the precision assembly of matter, nanotechnology, coupled with the functional building blocks of nature, biotechnology, and fused by the network flow of spatiotemporal information, informatics. We will present the details of the technological demands and the results of efforts associated with the production of a new class of functional material and devices. Elements of the discussion will include the genetic engineering of active biological molecules into engineering building blocks and the incorporation of �metabolism� into engineered devices and materials through precision assembly of these molecules into stable �active� materials. Finally, we will provide exemplars using these building blocks to engineer systems that address issues surrounding energy, environment and human health: the societal grand challenges of our age.

Speaker(s):

Polycrystalline-Silicon Ferroelectric Memory Thin-Film Transistors with a Large-Single Grained Pb(Zr,Ti)O3

Apr 9, 2015 4:00pm ‐ Apr 9, 2015 4:15pm

Identification: CC11.09

We have successfully fabricated metal-ferroelectric-insulator-silicon (MFIS)-type memory thin-film transistors (TFTs) with a large single-grained Pb(Zr,Ti)O3 (PZT) on glass substrate. The single-grain of (PZT) was obtained by separating the temperature of nucleation and growth. An artificially controlled nucleation seeds were formed in a 40 ?m row and the location of polycrystalline-silicon (poly-Si) channel were 10 ?m offset from the nucleation seeds. The growth of the PZT seeds was carried out by post-annealing until the single-grained covers the poly-Si channel. The device exhibits a good performance in terms of large memory window (3.5 V), ultra-fast programming and erasing (P/E) switching, long data retention, and an excellent P/E fatigue cycles. Comparing with the poly-grained MFIS-type memory (TFTs), the single-grained MFIS-type TFTs showed a high reliability performance due to its non-grain boundary effect. As a result, achieving a single-grained PZT is a important factor for high performance of ferroelectric memory transistors and useful for the display applications.

Speaker(s):

Characterizing Ionic/Electrochemical Effects in the Resistive Switching of TiO2 Film by Using Advanced Scanning Probe Microscopy Techniques

Apr 9, 2015 4:00pm ‐ Apr 9, 2015 4:15pm

Identification: TT14.02

Resistive switching in transition metal oxides has attracted great attention due to the potential for Resistance Random Access Memories (RRAM) with high speed and density. Even though a great number of researches on resistive switching behavior of oxides have been conducted, it is still not fully understood the detail mechanisms such as electroforming and subsequent resistive switching in different materials, and such understanding is important to develop the new generation non-volatile memory materials or devices. TiO2, as a potential memristive material, has been largely studied and reported in the literature and it is an ideal candidate to study the mechanism of the resistive switching. On the other hand, TiO2 is an electronic-ionic semiconductor and it is reported that the formation and ordering of oxygen vacancies (ionic species) in the TiO2 thin film were resulted from the electrochemical reactions, which might lead to the phase change and finally the resistance switching. However, there are so far few studies to directly provide experimental basis for this ionic/electrochemical effects in the resistive switching processes of TiO2. In this study, the resistive switching behaviour of TiO2 thin film are studied by using Electrochemical Strain Microscopy (ESM) and conductive Atomic Force Microscopy (C-AFM) techniques. ESM is a new type of scanning probe microscopy technique, and it is an effective tool to study the local electrochemical phenomena such as surface deformation due to the electrochemical reactions, the ionic mobility and distribution, and the electrochemical activity. In this work, the TiO2 samples with various thicknesses were prepared on Pt/TiO2/Si substrates by pulsed laser deposition technique with different oxygen partial pressures. By combining ESM and C-AFM measurements, the ionic/electrochemical effects in the resistive switching processes of TiO2 are studied. The results have shown the direct correlations between the ionic/electrochemical processes and different stages of the resistive switching, including the electroforming, set, or reset. In addition, the possible mechanisms for the resistive switching in TiO2 are studied and discussed.

Speaker(s):

Special Characteristics and Challenges of Top Performing Silicon Microwire Anodes for Li Ion Batteries

Apr 9, 2015 4:15pm ‐ Apr 9, 2015 4:30pm

Identification: I8.09

A new concept of Si microwire anodes for Li ion batteries, which consists of an array of Si microwires embedded at one end in a Cu current collector, has been lately developed [1]. The process for the production of the wires is fully scalable, allowing the production of anodes as large as a silicon wafer, with wires as long as the thickness of the wafer [2]. The method is based in the electrochemical etching of macropores and a chemical over-etching step, what makes it very economical. The capacity of the anodes is very stable over 100 cycles [3], and breaks all the records when considering the capacity per area (mAh/cm2), with wires of 70 micron in length [4]. This capacity can be even larger when preparing longer wires. Nevertheless, it is not known which may be the limit for scaling up the wires. In the paper for this conference, an electrical and mechanical description of the wires will be given, explaining which are the charging rate limits of the wires. A model based on the series resistance, aging and state of charge will be discussed. Comments of the future development of the wires will be given. [1] E. Quiroga-Gonz�lez, E. Ossei-Wusu, J. Carstensen, H. F�ll, J. Electrochem. Soc., 158 (2011) E119. [2] E. Quiroga-Gonz�lez, E. Ossei-Wusu, J. Carstensen, H. F�ll, Nanoscale Res. Lett. 9 (2014) 417. [3] E. Quiroga-Gonz�lez, J. Carstensen, H. F�ll, Electrochim. Acta, 101 (2013) 93. [4] E. Quiroga-Gonz�lez, J. Carstensen, H. F�ll, Energies, 6 (2013) 5145.

Speaker(s):

Photoelectric Property Change Caused by Additional Nano-Confinement: A Study of Half-Dimensional Nanomaterial

Apr 9, 2015 4:15pm ‐ Apr 9, 2015 4:45pm

Identification: P8.07

Nanomaterials majorly fall into three categories according to the nano-confinment dimension: two dimensional (2D), one dimensional (1D), zero dimensional (0D). Among them, 1D and 0D nanomaterials attract most research interest because the multi nano-confinment effects enable novel properties. Up to present, all the studies on 1D and 0D nanomaterials are limited in their own dimensions. There is no research about the vast blank area that connects 1D and 0D nanomaterials. When reducing the dimension of 1D nanomaterial, previously not within nanometer scale, the property will undergo significantly changes. The research field that covers the intermediate scale between 1D and 0D nanomaterials will attract much more research interest and cover most of the materials. Here, we named the intermediate nanoscale materials between 1D and 0D Half-Dimensional (0.5D) nanomaterials and we systematically investigate the photoelectric property change of ZnO in that dimension and found the photoelectric property does not follow the Ohm�s Law. [i] We build a theoretical model based on semi-classical physics and well explained this unique phenomena. This is the first time that 0.5D nanomaterial concept is defined and the first preliminary result has ever been reported. The research in this paper initiates a brand new research field, which covers all properties for 0.5 nanomaterials and is applied to all materials, such as semiconducting materials, carbon nanotube, grapheme, etc. [i] "Significant Photoelectric Property Change Caused by Additional Nano-confinement: A Study of Half-Dimensional Nanomaterials" Chengming Jiang and Jinhui Song Small, DOI: 10.1002/smll.201400704.

Speaker(s):

Palladium Memory Devices for Bio-Driven Sensing

Apr 9, 2015 4:30pm ‐ Apr 9, 2015 4:45pm

Identification: AA10.10

With the recent physical demonstration of memristive-based devices, low-power two terminal devices with memory and learning functions have advanced electronics and computing. In memristive devices, typically slow moving ions are coupled with fast moving electrons. Ionic motion affords memory, with electronic current as the output signal. Here, we present fully ionic memory devices in which protons (H+) provide both memory and output signal. We describe the development of 1D and 2D grid-based memory elements. These devices function by storing and passing protons between adjacent palladium bits, in a mechanism similar to electron transfer in a CCD. This transfer allows for the serial measurement of parallel analog inputs. Digital input or output can easily be accomplished by assigning logic values to threshold values of proton concentration. Energy consumption is dependent on device volume: the current 10�m x 30 �m device consumes 35 �J per switching operation, but a 40nm x 40nm bit is expected to consume less than 50fJ.

Speaker(s):
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