Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D66: Adsorption, Growth and CatalysisRecordings Available
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Chair: Robert Klie, University of Illinois Chicago Room: Hyatt Regency Hotel -Grant Park D |
Monday, March 14, 2022 3:00PM - 3:12PM |
D66.00001: An Investigation of Various Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating Alexander W Auner, Jonathan C Crowhurst, David G Weisz, Zurong Dai, Kim Knight Ta2O5 exists in multiple crystalline and amorphous phases and is used in a variety of applications (e.g. microelectronics, optics). In this work, we show that different phases of Ta2O5 can be generated in high-temperature laser experiments by varying input laser parameters. In our experiments, we used both CW and nanosecond pulse Nd:YAG lasers (1064 nm), which were focused onto a Ta metal target to generate particulates via local ablation/vaporization. Scanning electron microscopy (SEM) and Raman spectroscopy of particulates formed by nanosecond laser ablation show the presence of two distinct oxide phases. The first phase comprised micrometer-sized particulates having a Raman spectrum consistent with a previously observed amorphous Ta2O5 phase. The second phase comprised particulates ~5-10 micrometers in diameter having Raman spectra similar, but not identical, to that of known crystalline β-Ta2O5. Transmission electron microscopy (TEM) of particulates from CW laser processing yielded good agreement with a monoclinic H-Ta2O5 crystalline phase. Additionally, the unique Raman signature was observed proximate to the point of laser impingement in the CW laser experiments that confirms this structure. Further from that point produced particulate with a Raman spectrum that matched β-Ta2O5. We discuss these results in the context of different oxide cooling histories. |
Monday, March 14, 2022 3:12PM - 3:24PM |
D66.00002: Do partial atomic charges matter for the adsorption of molecules on a substrate when using Molecular Mechanics? It depends. Andreas Riemann, Lauren Rankin, Dylan Henry Molecular Mechanics (MM) calculations offer powerful tools to explore adsorption geometries and energies. Various force fields can be used for different combinations of adsorbates and substrates. These MM calculations can be advantageous over purely quantum chemistry approaches due to requirements of less computational power. Suitable MM calculations rely on the charge distributions within a molecule. In order to study several configurations, the molecules are optimized using quantum mechanical calculations and various charge schemes. |
Monday, March 14, 2022 3:24PM - 3:36PM |
D66.00003: Modeling Atomic Layer Deposition of Alumina as an Ultra-thin Tunnel Barrier using Reactive Molecular Dynamics Devon T Romine, Ridwan Sakidja, Judy Z Wu In this study, we have utilized the reactive molecular dynamics (MD) simulations to model the Atomic Layer Deposition (ALD) process that forms an ultra-thin film of a tunnel barrier made of amorphous alumina. The reactive MD simulation is advantageous in comparison to the ab-initio MD simulation since it offers lower computational cost and the capability to model over a relatively longer simulation period and for a larger scale. To further refine and parameterize the existing ReaxFF potentials, we used the Density Functional based Tight Binding (DFTB) -based in conjunction with the Python toolkit as implemented in the Amsterdam Modeling Suite (AMS) program package. The additional training sets were made from evaluations of the potential energy surface (PES) scans of various ALD-relevant species including H2O, OH, and the ALD precursors trimethylaluminum (TMA) and Bis(20ethyl-1,3-cyclopentadien-1-yl) magnesium (C14H18Mg), as well as the bond-dissociation energies during the reactions that occur when they interact. We systematically evaluated the role of the various ALD precursors including the TMA and C14H18Mg and the water pulse toward the chemical reactions that take place on the surface during ALD. We additionally evaluated the role of experimentally- observable parameters including the operating temperature and precursor concentrations for the internal structure of the amorphous alumina/magnesium as the final deposition products. Lastly, we systematically assessed the role of wetting layers as the means to improve the quality and performance of the tunnel barrier. |
Monday, March 14, 2022 3:36PM - 3:48PM |
D66.00004: Two-Dimensional Transition Metal Silicate Formed on Ru (0001) by Hydrogenation Kayahan Saritas, Eric I Altman, Nassar Doudin, Sohrab Ismail-Beigi Two-dimensional transition metal silicates are dynamically stable materials with interesting magnetic and piezoelectric properties which can render them useful for further applications [1]. Bottom-up synthesis of these materials has been challenging due to strong overlayer-substrate interactions, which prevents the exfoliation of the overlayer. Here, using density functional theory calculations, we systematically investigate the hydrogenation of the overlayer as a way to decrease the substrate and overlayer interactions [2]. Using the Fe2Si2O8·O/Ru(0001) structure as our starting point from Wlodarczyk et al.[3], we study hydrogenation levels up to Fe2Si2O9H4·Ru(0001). Structural and thermodynamical properties are studied at different hydrogenation levels to show under which conditions, the exfoliation can be feasible. Simulated core-level shifts show that Fe is primarily in a 3+ state through the hydrogenation of Fe2Si2O8·O/Ru(0001). Simulated reflection adsorption infrared spectroscopy (RAIRS) yields distinctive shifts in vibrational properties with increasing hydrogenation which can guide experiments. |
Monday, March 14, 2022 3:48PM - 4:00PM |
D66.00005: Theoretical Study of Bonding for Au Adatoms on Ge(110) and its Implications for the Observed Motion of Au-Ge Alloy Ad-Clusters Shirley Chiang, Ruikuan Xie, Talat S Rahman, Ching-Yao Fong Using DFT, we explore the microscopic physical origins of experimentally observed motion of Au-Ge alloy droplets on Ge(110). Our earlier studies showed no bonds forming between Au adatoms or between an Au adatom and its nearest neighbor (nn) Ge atom, while a strong covalent bond formed between a Ge adatom and its nn Ge. We use 4 model clusters with 2 to 5 Au adatoms alloying with 1 Ge adatom on a substrate model defined by [001] a axis, [1,-1,0] b axis, and [110] c axis directions of the fcc structure. By using 3 schemes for displacements of ad-clusters at the top plane of the substrate along a, a-b, and b directions, we did 72 sets of calculations. When the displacement is <3.50% of the Ge bond length, the b-direction is preferred. When the displacements increased to 6.88%, the Ge adatom changes its nn as a result of bond-breaking and reforming. The preferred direction for motion changes from b-axis to a-b direction. The surface structure plays a role in the preferred moving direction of clusters, regardless of cluster size and whether or not Au and Ge adatoms move together or separately. The direction change is due to the bond breaking of the Ge adatom and the surface Ge atom. |
Monday, March 14, 2022 4:00PM - 4:12PM |
D66.00006: Growth and Characterization of Stoichiometry-Varied MnxCo3-xO4 Manganese-Cobalt Spinel Thin Films Miles D Blanchet, Jibril Ahammad, Steve M Heald, Jerzy Sadowsky, Bethany Matthews, Steven Spurgeon, Tiffany Kaspar, Tamara Isaacs-Smith, Wencan Jin, Ryan B Comes The cobalt-manganese spinels MnCo2O4 and CoMn2O4 have shown strong catalysis behavior through oxygen reduction reactivity (ORR). These materials can perform ORR at levels on par with ubiquitous but expensive materials such as platinum. Despite their impressive catalytic properties, little has been done in the way of thin film characterization on these materials. Additionally, phase segregation has been observed in nanoparticle studies due to a miscibility gap between Jahn-Teller active tetragonal CoMn2O4 and cubic MnCo2O4. Thin film studies enable further analysis of phase composition, degree of inversion, and charge transfer within the crystal. We have grown and studied the properties of cobalt-manganese spinel thin films at varying cation stoichiometries (MnxCo3-xO4 from x = 0 to 2.1). Films were grown using molecular beam epitaxy. In-situ X-ray photoelectron spectroscopy, X-ray diffraction and K-edge/L-edge X-ray absorption spectroscopy were performed. The experiments allowed us to determine information such as cation valence states, spinel inversion parameters, cation-oxygen bond lengths and magnetization properties. The results allow us to create a map of material properties as a function of cation stoichiometry for the entire cobalt-manganese spinel system. |
Monday, March 14, 2022 4:12PM - 4:24PM |
D66.00007: On the development of order and interfaces during growth of ultrathin La2CuO4 films by molecular beam epitaxy Hawoong Hong, Xinyue Fang, Friederike Wrobel, Meng-Kai Lin, Zhan Zhang, Kevin Peterson, Anand Bhattacharya, Dillon D Fong, Tai-Chang Chiang While the atomic structure of interfaces in complex oxide heterostructures created by epitaxial growth has been investigated extensively, few studies have been conducted on how interfaces form and restructure at the initial stage of film growth. The dynamic aspects of the growth behavior can strongly influence the final interfacial atomic structure, which may lead to the emergence of interface-specific properties, such as the rise of interfacial superconductivity between certain Ruddlesden-Popper oxide materials. Here, the structural development of La2CuO4 thin films grown by molecular beam epitaxy on a LaSrAlO4 substrate is investigated by X-ray diffraction measurements with rapid scans over a volume of reciprocal space. This method provides far more detailed information on interface formation than traditional fixed-point measurements. The results show that the atomic structure of the interface becomes fully established after just a single unit cell of growth. Interestingly, restructuring continues to occur within the topmost half- to one unit cell of the film during the deposition process. However, diffraction intensity oscillations from both reflection high energy electron and X-ray measurements stabilize only after the growth of two unit cells, indicating that the growth front morphology continues to evolve until the start of the third unit cell. This multimodal investigation provides insights into the atomic processes taking place during layered oxide interface formation, including the dynamical rearrangement of LaO and CuO2 layers. Such information is not only relevant to the engineering and optimization of functional layer structures, but can be critical for ultrathin films. |
Monday, March 14, 2022 4:24PM - 4:36PM |
D66.00008: Two-dimensional electron gas on the Gd2C electride surface: A first-principles study Gunn Kim, Jinwoong Chae, Youngtek Oh, Junsu Lee Electrides are interesting ionic compounds in which electrons behave as anions in the interior of a positively charged framework. Gd2C is a type of stable layered electrides. Although previous research has focused on the bulk properties of Gd2C, few studies have focused on ultrathin layers or surfaces for two-dimensional (2D) characteristics. In this talk, we present our first-principles study of the electronic properties of few-layer Gd2C structures. We show that Gd2C has a work function of 3.35 eV. Because the interlayer region has changed to the surface by exfoliation, the properties of the electron gases once located in the interlayer in the past will also change. We found that the surface anionic electrons accounted for about 25% of the number of electrons in the interlayer region in the absence of an external electric field. When we applied an external electric field, the number of surface electrons increased, and the increase was proportional to the square of the field intensity. Since the electronic properties of 2D materials can be understood through scanning tunneling spectroscopy (STS), we also performed the STS simulations. At −0.9eV, the STS image was blurred because of surface anionic electrons. In contrast to the spin-up electron, an interlayer band of the spin-down electron crossed the Fermi level in the ultrathin Gd2C layers. Our findings open a possibility that the spin-polarized electronic gas in the few-layer electride could be used for spintronics. |
Monday, March 14, 2022 4:36PM - 4:48PM |
D66.00009: Preparation of Crystalline Hydroxyapatite Thin Films by PLD for Biomedical Implant Coating Applications Salizhan Kylychbekov, Bektur Abdisatarov, Somon Hakimov, Zikrulloh Khuzhakulov, Ali Oguz Er All major precursors for the orthopedic implants: stainless steel (316L), cobalt-based alloys, and titanium-based alloys have main problems at the long-term functioning. Key problems are degradation of metals in human body’s fluid, corrosion of implants, and release of toxic elements. Coating of the metallic implants with inorganic ceramic-based materials such as hydroxyapatite (HAP): Ca10(PO4)6OH2 can efficiently diminish the listed hazards. Since HAP partially exists in human bone, it can enhance biocompatibility, bone-implant adhesion, and reduce the release of toxic elements. However, conventional techniques of coatings such as RF Magnetron Sputtering, Plasma Spraying, Ion-Beam deposition struggle in producing crystalline structure, which is an essential parameter for the resistance against degradation in saline human body environment. In this work, we report the possibility of obtaining crystalline HAP films by the Pulsed Laser Deposition technique. We also analyze the film’s crystallinity and microstructure depending on annealing and substrate temperatures ranging from 25º C to 900º C. The XRD results show that substrate temperature directly influences the crystallinity, as at higher substrate temperatures more Bragg diffraction planes have emerged. Furthermore, the analysis of surface topography, composition, and structure of HAP coatings by SEM with energy dispersive x-ray, and FTIR will be presented. We propose these films for further study on biodegradation and fatigue resistance tests on Biomedical implants. |
Monday, March 14, 2022 4:48PM - 5:00PM |
D66.00010: Stabilization of Metastable Polymorphs on Single Crystal Oxide Substrates via Substrate Induced Strain in 2D/3D TMD/TMO Heterostructures: A case of Epitaxial MoS2 Thin-film by Pulsed Laser Deposited, Role of Surface Chemistry and Structure Swati Parmar Structural polymorphs of two-dimensional 2D layered Van der Waal solids like MoS2 hold great potential for major applications in the advanced electronics and energy sectors. Here, we have grown MoS2 thin-film on different single crystal metal oxide substrates (SrLaAlO4, c-Al2O3, SrTiO3, LaAlO3) by Pulsed Laser Deposition (PLD). We observe that on the structurally compatible tetragonal SrLaAlO4 (001) substrate mixed 1T´+2H phase MoS2 grows with a dominant (~75%) 1T´ phase, while on hexagonal c-Al2O3 (0001) substrate pure 2H phase grows, whereas 1T´ phase contribution varies in order SLAO>STO>LAO. Further, the chemical role of Sr is elucidated in the early growth on SLAO and STO. XRD, Raman spectroscopy, XPS, VBS, and EFM are used to analyse the properties of these films and phases.The pivotal role of lattice strain in stabilizing the initial layer(s) on SLAO has also observed. The mixed 1T´+2H phase in ultrathin film shows high room temperature resistivity (~2 mΩ cm) with respect to that of pure 2H phase (~14 mΩ cm). This substrate selective polymorphism with distinct electronic features provides an approach to stabilization of metastable phases of even soft Van der Waal solids on hard substrates for integration into novel device functions. |
Monday, March 14, 2022 5:00PM - 5:12PM |
D66.00011: Metastable SrNbO3 : Growth Challenges and Future Applications for High Mobility 2DEGs Suresh Thapa, Patrick T Gemperline, Sydney R Provence, Steve M Heald, Marcelo A Kuroda, Ryan B Comes Two-dimensional electron gases in complex oxide interfaces offer great promise for high-speed electronics. BaSnO3 (BSO) is well known for its high mobility due to an availability of unoccupied 5s bands in Sn. SrNbO3 (SNO) is a 4d transition metal oxide serving as a good donor material in oxide interface. Synthesis is challenging, however, due to the metastable nature of the d1 Nb4+ cation and the challenges of delivery of refractory Nb. To that end, SNO thin films were grown using hybrid MBE (hMBE) for the first time using a TDTBN precursor for Nb and an elemental Sr source on GdScO3 and as prepared BaSnO3 films on different substrates. Varying thicknesses of SrHfO3 (SHO) capping layers were deposited using a precursor for Hf on top of SNO films to preserve the metastable surface. Grown films were transferred in vacuo for XPS to quantify elemental composition and Nb oxidation state. Ex situ studies by XANES illustrates the SHO capping plays vital role in preserving the Nb 4d1 metastable charge state in atmospheric conditions. These studies help to understand the high-quality SNO film growth by hMBE approach and quantify the carrier concentration and mobility in SNO/BSO interface opening the door for promising alternatives for traditional semiconductor in high mobility devices. |
Monday, March 14, 2022 5:12PM - 5:24PM |
D66.00012: Development of Si and SiO2 interfacial layers for growing photoconductive GaN on Au Phadindra Wagle Gallium nitride films deposited by high-temperature atomic layer deposition (HT-ALD) are |
Monday, March 14, 2022 5:24PM - 5:36PM |
D66.00013: Atomic-scale description of tensile-induced desintering and formation of monatomic wires in nanostructured ceramics Rodrigo B Capaz, Tanna Fiuza, Bruno Focassio, Jefferson Bettini, Gabriel R Schleder, Murillo Rodrigues, João Souza Jr., Adalberto Fazzio, Edson R Leite We employ in situ high-resolution transmission electron microscopy (HRTEM) to observe desintering between ZrO2 nanoparticles at room temperature with unprecedented spatial and temporal resolutions. At the atomic scale, contrary to macroscopic descriptions, no instability is observed. Instead, a stable nano-bridge (with a single grain boundary) is formed, then evolving to an ionic atomic wire. To our knowledge, this is the first observation of an ionic monatomic wire. Density-functional theory (DFT) calculations reveal the key role of oxygen vacancies in the stability and rupture of such wires. Our work provides insights on both the rupture of ceramic materials and on atomic-level control of densification processes. |
Monday, March 14, 2022 5:36PM - 5:48PM |
D66.00014: Enhanced surface wettability in Cu-doped TiO2 thin films for solar driven catalytic applications Manish K Vishwakarma, Manjeet ., Puneet Jain Currently, the development of the resources to pollution-free energy like the solar-driven hydrogen generation methods are the utmost priority to slow down the current rate of global warming. Metal oxide semiconductors say TiO2, based photocatalyst materials, has proved themselves a better candidate for the solar driven water splitting. TiO2 is a cost-effective wide bandgap semiconductor with a bandgap of 3.2 eV. Herein, we demonstrate that Cu doping in TiO2 can significantly enhance surface wettability. The redshift in absorption spectra indicates a reduction in the bandgap. The enhanced hydrophilic nature of the photocatalyst material results in improving the surface area available for the photon induced reaction. The absorption spectra' redshift ensures that more solar spectrum should be utilized for hydrogen production via water splitting. Water contact angle measurement of TiO2 surfaces reduces from 33.829° to 18.053° after copper doping. Our study concludes that transition metal doping (Cu) can help in tuning the bandgap and the surface wetting nature of the photocatalyst, which opens the pathways for developing more efficient photocatalytic materials for the cost-efficient hydrogen production. |
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