Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S01: Surfaces and Nanoscience of Solids |
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Sponsoring Units: DCP Chair: David Chandler, Sandia Natl Labs Room: LACC 150A |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S01.00001: Stabilization of Cubic Crystalline Phase in Organo-metal Halide Perovskite Quantum Dots via Surface Energy Manipulation Som Sarang, Sara Bonabi Naghadeh, Parveen Kumar, Edwin Betady, Vincent Tung, Michael Scheibner, Jin Zhang, Sayantani Ghosh Surface functionalization of nanoscale materials significantly impact their properties due to their large surface-to-volume ratio. We have studied temperature dependent crystal phase transitions in CH3NH3PbBr3 perovskite quantum dots (PQDs) ligated with octylaminebromide (P-OABr) and 3-aminopropyl triethoxysilane (P-APTES), using a framework of static and dynamic spectroscopy. P-OABr undergoes the expected structural phase transition from tetragonal to orthorhombic phase at ~ 140 K, established by the emergence of a higher energy band at 2.64 eV in the photoluminescence (PL) spectrum, while no phase transition was observed in the case of P-APTES. Such phase stabilization is a result of variation in their respective surface energies, an important contributing factor to the Gibbs free energy for nanomaterials. On further investigation, using time-resolved PL, excitation power dependent PL and Raman microscopy over a range of 300 – 20 K, we observe significant differences in recombination rates and charge carrier types between P-APTES and P-OABr. Our findings highlight aspects of PQD phase stabilization linked to nanoscale morphology and surface energy manipulation of the crystal phase diagram. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S01.00002: Iron oxides for the removal of water contaminants: A theoretical approach Samuel Baltazar, Aldo Romero The presence of metalloids and heavy metals in aqueous sources is a major concern in many countries. Several pollutants such methylated arsenicals are already associated to different human health issues, demanding new alternatives to purify water resources. One of these solutions involves the use of iron nanoparticles due to their affinity with arsenic species. We study the interaction of arsenic complexes with iron oxide surfaces at the atomic scale from first principle calculations. From the considered anionic species, a higher adsorption energy was found for the complexation of Fe3O4(001) with As(III) being 1.3 eV higher than the adsorption energy for As(V). In the case of As(III), a large partial band charge density was found, which was associated to the O-Fe bond formation, while more delocalized electron density was found in the adsorption of As(V) subspecies, with the formation of two Fe-O bonds in the most stable configuration. Finally, we envisage the sorption capacity of other iron oxide surfaces as well as the adsorption of other pollutant compounds. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S01.00003: First-principles study on the lithiation/delithiation reactions of Si-doped iron oxide nanoparticles Masaaki Misawa, Subodh Tiwari, Fuyuki Shimojo, Kenji Tsuruta, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta Iron oxidizing bacteria produce iron oxide based sludge-like matter (biogenous iron oxide, BIOX) assembled with nanoparticles (NP) that is doped with silicon in ambient environment. BIOX has been considered as unwanted substance in the environment for a long time, but it was proved recently that this material has great potential to be a functional material. For example, it is found that BIOX exhibits good performance as an anode material for lithium-ion battery. However underlying atomistic mechanisms remain elusive. In this study, we have investigated the lithiation/delithiation reactions to elucidate the microscopic reaction mechanism and effect of the impurity element on the reaction based on the first-principles molecular dynamics (FPMD) method. Our FPMD simulations show rapid charging and discharging of NP within 100 fs, with associated surface lithiation and delithiation, respectively. In this presentation, an essential role of Si-doping on the lithiation/delithiation reaction will be discussed with the simulation results. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S01.00004: Investigation of the Exciton Formation in a Single Molecule with a Scanning Tunneling Microscope Kensuke Kimura, Hiroshi Imada, Kuniyuki Miwa, Miyabi Imada, Shota Kawahara, Jun Takeya, Maki Kawai, Yousoo Kim The recombination of holes and electrons in organic molecules produce excitons and the radiative decay from the excitons is used in organic light emitting diodes (OLEDs). Controlling the exciton formation is one of the primary strategy for improving the device properties of OLEDs. Thus, it is required to investigate and describe the exciton formation process at well-defined molecular systems. In this study, we prepared single molecule system, which is ultimate well-defined system, and conducted experiments with a scanning tunneling microscope (STM). Recent progress in STM experiment enables to detect luminescence from a single molecule on ultrathin insulating film. Here, we applied this technique to 3,4,9,10-perylenetetracarboxyricdianhydride (PTCDA) adsorbed on NaCl ultrathin film grown on Ag(111). PTCDA is known as a prototypical n-type organic semiconductor with strong optical response, and we succeeded in detecting luminescence from PTCDA. The precise bias voltage dependent electroluminescence measurement and differential conductance measurement revealed the exciton formation mechanism in this system. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S01.00005: Yarn-Shaped Hybrid Carbon Nanotube Supercapacitor with Enlarged Surface Area by ZnO Nanorod Forest Containing Pseudo-Capacitive Material Suong Le, Dongseok Suh Recently, the fiber supercapacitor based on carbon nanotube (CNT) yarn has been reported in many literatures. CNT yarn has owned high-strength, high thermal-electrical conductivity, and flexibility. Zinc oxide nanorods (ZnO-NR) can provide an enlarged surface area, which can enhance an electrochemical performance. Nickel-cobalt layered double hydroxide (NiCo-LDH) is well known as pseudo-material with high theoretical capacitance, low-toxicity and diverse nanostructures. The NiCo-LDH coated ZnO-NR grown on CNT yarn electrode achieve maximum capacitance of 1051 mF cm-2 (1261 F g-1) at scan rate of 5 mV s-1. It also shows excellent cycling stability with 60.5% capacitance retention after 7000 charge-discharge cycles at a current density of 75 mA cm-2. Moreover, we also fabricate a flexible symmetric supercapacitor (NiCo-LDH/ZnO-NR/CNT// NiCo-LDH/ZnO-NR/CNT) with PVA–LiOH gel as separator and electrolyte. It can open large potential window up to 1.2 V. Furthermore, the device remains more than 90% capacitance after applying 150o bending angle. Finally, we have successfully fabricated a flexible electrode based on NiCo-LDH/ZnO-NR/CNT yarn by a hydrothermal method that has the potential candidate for the flexible and high performance supercapacitor. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S01.00006: Structural Investigation of Aluminum Nanoparticles as Energetic Materials Chi-Chin Wu, Dylan Smith, Michelle Pantoya
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Thursday, March 8, 2018 12:27PM - 12:39PM |
S01.00007: Superconductivity of monolayer Mo2C: The key role of functional groups Jun-Jie Zhang, Shuai Dong Two-dimensional (2D) graphene-like MXenes have attracted enormous interest for their novel chemical and physical properties. Recently, 2D layered Mo2C as a new member of Mxenes was formed from Mo2Ga2C thin films, which was found to be a promising candidate as a high-performance thermoelectric material. As the allotrope of 2D layered Mo2C, the superconductivity was discovered in bulk α-Mo2C. However, its superconducting transition temperature (TC) was depressed from 4 K (thick film) to near 0 K when its thickness is less than 3.5 nm. In this report, according to the electron-phonon interaction, it is predicted that monolayer Mo2C could be a quasi-two-dimensional superconductor and the effects of functional-groups are crucially important considering its unsaturated surface. Despite the suppressed superconductivity by chalcogen adsorption, our most interesting prediction is that the electron-phonon interaction of monolayer Mo2C can be greatly enhanced by bromine absorption, suggesting that Mo2CBr2 as a good candidate for a nanoscale superconductor. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S01.00008: Scattering-Type Scanning Near-field Optical Microscopy and Spectroscopy for Nanoscale Chemical Analysis Max Eisele, Adrian Cernescu, Andreas Huber Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) is an optical microscopy and spectroscopy approach based on scanning probe technology, bypassing the ubiquitous diffraction limit of light to achieve a spatial resolution below 20nanometers. s-SNOM employs the strong confinement of light at the apex of a sharp metallic AFM tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties (absorption, reflectivity) of the sample directly below the tip and yields nanoscale resolved images and nanoscale spectroscopy (hyperspectral nano-FTIR) information simultaneous to topography. This presentation we will introduce the basic principle of near-field microscopy and hyperspectral nano-FTIR for imaging and spectroscopy with 10 nanometer spatial resolution. In addition we will summarize the latest achievements in the field of near-field microscopy and spectroscopy on polymers, biomaterials and 2D materials and will focus on applications in chemical analysis and material identification at the nanoscale. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S01.00009: Parahydrogen Induced Polarization of Water and other Neat Liquids by Heterogeneous Catalysis Evan Zhao, Raghu Maligal-Ganesh, Yong Du, Wenyu Huang, Clifford Bowers We have discovered a heterogeneous catalyst for the alignment of proton magnetic moments in water molecules (as well as methanol and ethanol molecules) from parahydrogen, the metastable singlet spin isomer of dihydrogen. After simply bubbling para-enriched H2 gas through a suspension of the catalyst particles in water, the water protons yield intense stimulated emission NMR signals, corresponding to a negative spin temperature. The phenomenon is dubbed SWAMP (Surface Water Acquires Magnetized Protons from Parahydrogen). Parahydrogen induced polarization (PHIP) of water by heterogeneous catalysis has not been previously reported in the past three decades of PHIP research. Details about the catalyst and the molecular mechanism for the interfacial process, including a density operator model for the spin dynamics, will be presented. SWAMP is a fast and scalable method for producing hyperpolarized pure liquid water, free from polarizing radicals or catalyst residues, which could be transformative to the advancement of MRI and other applications. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S01.00010: Calculating binding energy shifts in core level XPS from first principles: a case study of adsorbates on Cu(111) Juhan Matthias Kahk, Johannes Lischner X-ray Photoelectron spectroscopy is one of the most widely used experimental techniques in surface science, yet in spite of over forty years of research, the interpretation of core level spectra of chemically complex systems remains extremely challenging. Whilst theoretical calculations could help in this regard, at present almost all published core level XPS spectra are analyzed without the aid of first principles modelling. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S01.00011: First-principles study of oxygen reduction reaction on defective TiO2 surfaces Yoshiyuki Yamamoto, Shusuke Kasamatsu, Osamu Sugino Some oxides (TiO2, ZrO2, …) have been proposed as promising electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells. The oxides can be made active by introducing defects such as Nb or oxygen vacancies (Vos), and some of them have high activities in acid media comparable to Pt. However, little is known about the microscopic mechanisms of the ORR . To improve our understanding of the ORR at defective oxide surfaces, we have studied the ORR on Nb-doped and oxygen-deficient TiO2 surfaces using density functional theory with PBE+U functional. Thorough calculating the free energies of the reaction intermediates on the rutile (110), anatase (101), (100), (001) and (001)-(1x4) reconstructed surfaces, we found the followings. (1) At Nb-doped surface, the intermediates adsorb too strongly on the surface due to charge transfer from Ti3+. (2) At oxygen-deficient surface, adsorbates bind too strongly to the Vo site due to the existence of 2Ti3+s. On the other hand, (3) if the excess electrons in Ti3+ are removed by charge transfer to adjacent OH* adsorbates, then the intermediates moderately bind to the Vo. These results indicate that the surface Vo site without any excess electron is a candidate for the catalytic sites of the ORR. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S01.00012: Adsorption of Polar Molecules onto Electrodes Driven By the Combined Effects of Dielectric Inhomogeneity and Electrostatic Correlation Hongbo Chen, Issei Nakamura A recent atomistic molecular dynamics simulation suggested that water molecules in ionic liquids are significantly adsorbed onto electrodes, but an understanding of this mechanism is limited. To clarify the simulation data, we highlight the effects of the dielectric contrast among the species by developing the mean-field theory that accounts for molecular polarization. We then demonstrate that polar molecules such as water may be enriched in the vicinity of electrodes and even markedly bound onto the charged surfaces when the electrostatic correlations are combined. Furthermore, we show that the energy efficiency may be improved through tuning the dielectric contrast within a certain range of the applied voltage. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S01.00013: Oxidation and tribopolymerization mechanisms of Pt3Si(001) surface Jing Yang, Yubo Qi, Andrew Rappe Platinum sillicides are a class of material to replace pure metal when using on Micro- and Nano-electromechanical system (MEMS and NEMS) devices due to their high conductivity and low surface oxidation. MEMS and NEMS devices are small scale, non-volatile and low-power consuming; and hence, they are considered to be the future generation of computational devices. However, tribopolymer formed on electrode contact surfaces with adsorbed ambient molecules under mechanical stress could contaminate the device and obstruct the way of MEMS and NEMS for massive production. Here, we focused on Pt3Si surface material and determined thermodynamically stable surface to be Pt3Si(001) with Pt2Si2 as termination structure. Similar to experimental observation, the study of binding strength of oxygen shows that the matierial is inert to surface oxidation. Furthermore, the density functional theory calculation on surface reaction with applied normal stress demonstrates that partially oxidized Pt3Si surface presents low tendency of tribobopolymer formation when using benzene gas as the initial contamination source. Our study has further proved that the Pt3Si could be a promising material for MEMS and NEMS switching devices. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S01.00014: Graphene-like materials from Coal – Microwave Treatments Christoffer Masi, Rabindra Dulal, Joann Hilman, Gaurab Rimal, Te-Yu Chien Since discovery in 2004, graphene has attracted plenty of attentions owing to its excellent physical properties. Many ways for producing graphene have been developed, such as mechanical exfoliation, chemical exfoliation, and chemical vapor deposition etc. Here, making use of one of our planet’s most abundant natural resources, coal, graphene-like materials are synthesized through very simple and easy processes. In this presentation, a low cost and environmental friendly method to produce graphene-like materials directly from coal will be discussed. With the use of a reduced environment, copper foil, and 900 W microwave oven, we have found evidences of the graphene-like materials through Raman spectroscopy, SEM, and TEM images. Further refinement on producing higher quality and quantity of graphene-like and graphene materials directly from raw coal will be pursued. |
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