bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) The Role of Defects in Van Der Waals Epitaxy of Transition Metal Dichalcogenides
Authors: Zhang Xiaotian , Choudhury Tanushree , Chubarov Mikhail , Bansal Anushka , Redwing Joan M.
Published: February 2020

Direct growth of transition metal dichalcogenides (TMDs) such as WS2 and WSe2 on graphene and hexagonal boron nitride (hBN) is of interest for the fabrication of 2D heterostructures as an alternative to exfoliation and 2D layer stacking. This can be challenging, however, given the low surface energy of the basal plane in 2D layered materials which inhibits nucleation and lateral growth of TMD domains. In addition, it is equally probable for TMD domains to orient in two rotational directions (referred to as 0o and 180o domains) on pristine surfaces of hBN and graphene which gives rise to inversion domain boundaries (IDBs) in coalesced films. However, the presence of defects in hBN and graphene can dramatically alter the energy landscape providing a route to control nucleation and epitaxy.

Our recent studies have focused on the epitaxial growth of WSe2, WS2 and related TMD monolayer films by gas source chemical vapor deposition (CVD) on hBN and epitaxial graphene. The CVD process is carried out in a cold-wall reactor using metal hexacarbonyls and hydride chalcogen precursors in a hydrogen carrier gas. In the case of epitaxial graphene, nucleation of WS2 occurs primarily at step edges and terrace defects resulting in different WS2 rotational orientations. In the case of WSe2 growth on hBN, however, single atom vacancies in the hBN were found to act as sites for metal atom trapping which facilitates the nucleation of WSe2 domains on the surface. In this case, the TMD nucleation density can be controlled by manipulating the density of surface atom vacancies which can be achieved through plasma irradiation and annealing in NH3. In addition, the metal atoms break the surface symmetry which leads to a preferred orientation (~95%) for WSe2 domains on hBN. Through careful control of nucleation and extended lateral growth time, fully coalesced WSe2 monolayer films on hBN were achieved which exhibit optical and transport properties superior to comparable films grown on sapphire substrates. The results demonstrate the important role of defects in nucleation and epitaxial growth of 2D heterostructures.
Epitaxial and Atomically Thin Graphene–Metal Hybrid Catalyst Films—the Dual Role of Graphene As the Support and the Chemically-Transparent Protective Cap
Authors: Abdelhafiz Ali , Alamgir Faisal M.
Published: February 2020

Commercialization of polymer electrolyte membrane (PEM) fuel cell materials has been of a great interest over the past decade. At the cathode side, the oxygen reduction reaction (ORR) is the key reaction where sluggish kinetics is present, for which Pt remains the catalyst of choice. In order to leapfrog the current limits to Pt use, three main objectives have to be achieved. First, is a reduction of Pt loading; second, is an enhancement of the mass activity per Pt atom; and third is an increase the catalyst durability. Herein, we demonstrate the dual role of single graphene layer, both as a growth template and as a protective cap for 2D Pt monolayers catalysts, where all three objectives can be achieved.

Using iterative under potential deposition (UPD), atomic layers of Pt catalyst are grown on top of a single layer graphene. X-ray absorption spectroscopic (XAS) and scanning transmission electron microscopy (STEM) analyses show that Pt growth is dictated by the graphene-templated epitaxy. Pt/graphene intimacy induces a localized compressive strain on Pt monolayers ranges 3-10%, owing to structural defects, with an overall compressive strain of 3.5% according to extended x-ray absorption fine structure (EXAFS) analysis. In addition, cyclic voltammetry (CV) analysis shows fully-wetted Pt monolayers coverage of graphene under-layer with only a ~1 nm ultra-thin layer of Pt, while ripening was suppressed as shown through STEM images. Atomic Force Microscopy (AFM) analysis demonstrates that Pt monolayers prefer to follow Frank-van der Merwe growth (i.e. layer-by-layer growth mode) rather than Volmer-Weber growth (i.e. island growth mode), where root mean square (rms) of surface roughness remains quite similar while increasing Pt loading is increased.

Pt/graphene hybrid catalysts show superior catalytic activity for ORR relative to the graphene-free counterparts or state of the art Pt commercial catalyst. A combination of the graphene-imposed compressive strain and electron transfer, push the Pt d-band center up, lowering the overpotential needed for ORR to occur. Furthermore, the graphene/Pt cap hybrid shows the graphene protecting Pt MLs from both dissolution and from ripening, with no Pt loss after 1000 fuel cell operating cycles. Our demonstration of a graphene-Pt hybrid opens the door for graphene/metal or metal/graphene architectures with potential applications in, and not limited to, energy, thermo-electric and electronics field.
Alkali Metal Doped Mono- and Bilayer Graphene: Band Structure, Raman Spectrum and Electronic Transport
Authors: Hell Martin , Ehlen Niels , Falke Yannik , Senkovskiy Boris V. , Petaccia Luca , Szkopek Thomas , Grueneis Alexander
Published: February 2020

We use ultra-high vacuum (UHV) Raman spectroscopy in tandem with angle-resolved photoemission (ARPES) to investigate the doping-dependent Raman spectrum of epitaxially grown graphene. The evolution of the Raman spectra from pristine to heavily Cs doped graphene up to a carrier concentration of 4.4x10^14 cm-2 is investigated [1]. Renormalization effects reduce the electronic bandwidth at this doping level when graphene is at the onset of the Lifshitz transition. Ultraviolet (UV) light allows to probe the optical transition at the saddle point in the Brillouin zone achieving resonance Raman conditions in close vicinity to the van Hove singularity in the joint density of states. The position of the Raman G band of fully doped graphene/Ir(111) shifts down by 60 cm-1 and the G band asymmetry of Cs doped epitaxial graphene on Ir(111) assumes an unusual strong Fano asymmetry opposite to that of the G band of doped graphene on insulators. We compare these results on Cs doped monolayer graphene to studies of Cs doped bilayer graphene. Growth of bilayer graphene is realized by intercalation of carbon atoms under monolayer graphene using molecular beam epitaxy. We probe each step of the intercalation process using UHV Raman which reveals distinct changes in the linshape. Finally, the graphene is transferred from the metal substrate onto Si wafers and probed by UHV electronic transport during alkali metal deposition. Our work demonstrates high sensitivity towards sensing of alkali atoms and a giant decrease of the four-point resistance by three orders of magnitude upon Cs doping.

[1] M.G.Hell at al. Nano Letters 2018
18 (9), 6045-6056

Figure 1
First-Principles Understanding of Strong Auger Recombination in Hybrid Perovskites
Authors: Shen Jimmy , Zhang Xie , Van de Walle Chris G.
Published: February 2020

The radiative recombination coefficient of the hybrid perovskites is as high as in typical direct-gap semiconductors [1], facilitating strong light absorption in solar cells and potentially enabling their application in light-emitting diodes (LEDs). Since LEDs operate at higher carrier densities than solar cells, higher-order electron–hole recombination processes can critically affect their efficiency. We have computed Auger recombination coefficients in the prototypical halide perovskite [2], CH3NH3PbI3 (MAPbI3), using first‐principles calculations. Our computed nonradiative Auger coefficients show that strong Auger recombination may suppress the LED’s efficiency. Fortunately, our insights into the origins of the strong Auger recombination indicate potential avenues for engineering to reduce the effect of Auger recombination.

This work was supported by DOE.

[1] Zhang, X, et al. ACS Energy Lett. 3, 2329 (2018).

[2] Shen, J.-X., et al. Adv. Energy Mater. 8, 1801027 (2018).
(Invited) High Optical Absorbance Multilayer Film of Au and TiO2: Charge Generation Dynamics Under Plasmon Excitation
Authors: Furube Akihiro , Takahata Toshihiko , Yanagiya Shinichiro
Published: February 2020

Metal-insulator-metal (MIM) structure using gold nanoparticles, titanium dioxide (TiO2), and gold (Au) film was fabricated. The optical absorption nature of the films in visible and NIR region with different TiO2 thickness were studied by steady-state extinction spectra and femtosecond transient absorption data. The Au nanoparticles were deposited on silane-treated glass by wet process, which showed enhancement of optical absorption of visible light due to its surface plasmon resonance (SPR). On the AuNP self-assembly, the titanium dioxide was deposited by magnetron sputtering. The extinction spectra of multilayer film showed the absorbance of the wide range of visible light. Further coating by Au film resulted in very broad absorption covering whole visible and NIR region. Transient absorption study proved that the generation of the conductive electrons by plasmon induced electron transfer from Au to the conduction band. The electron lifetimes in picosecond timescale depended on the film thickness the of TiO2 layer, suggesting that thicker film is appropriate to obtain long-lived carriers.

Authors appreciate Prof. Retsuo Kawakami in Tokushima Univ. for kind help while preparing the TiO2 films.
(Invited) Electrochemical Oxygen Reduction Catalyzed at Pt–Ni Nanostructured Electrocatalysts Immobilized on Nitrogen-Doped Carbon Supports
Authors: Kato Masaru , Ogura Kazuya , Nakagawa Shogo , Li Tianchi , Nakahoshiba Ryota , Tokuda Shoichi , Yagi Ichizo
Published: February 2020

Oxygen reduction reaction (ORR) is the key reaction in future energy generation devices such as polymer electrolyte fuel cells (PEFCs) and metal–air batteries. To drive the ORR in state-of-the-art PEFCs, carbon-supported Pt–M alloys (M = Ni and Co) are used. Since platinum is rare and expensive, there is a need to develop ORR electrocatalysts with not only high catalytic activity but also high durability. Under electrocatalytic conditions, catalyst degradation mechanisms are known to involve many processes including particle detachment, agglomeration and metal dissolution.[1] These phenomena can be suppressed by increase metal/support interactions. Carbon black is typically used as the catalyst support and can be chemically modified by heteroatom-doping. Heteroatom-doped carbon supports can show strong metal/support interactions with Pt nanoparticles.[2]

Herein, we report the enhancement of electrocatalytic ORR activity and durability of Pt–Ni alloy nanoframes by immobilization on nitrogen-doped carbon supports. Strong metal/support interactions between the nanoframe and the support caused the downshift of the d-band center position of the surface Pt, proved by X-ray photoelectron spectroscopy and surface-enhanced infrared absorption spectroscopy.[3] In situ X-ray absorption spectroscopy also revealed that the Pt surface oxide formation was suppressed by the immobilization on nitrogen-doped carbon supports. Our findings demonstrate that tuning the electronic structure of nanostructured Pt alloy electrocatalysts via strong metal/support interactions will allow the development of highly active and robust electrocatalysts for the ORR.

References

[1] N. Hodnik, G. Dehm, K.J.J. Mayrhofer, Acc. Chem. Res., 49, 2015–2022 (2016).

[2] Q. Wang, Y. Tian, G. Chen, J. Zhao, Appl. Surf. Sci. 397, 199–205 (2017).

[3] M. Kato, K. Ogura, S. Nakagawa, S. Tokuda, K. Takahashi, T. Nakamura, I. Yagi, ACS Omega, 3, 9052–9059 (2018).
Electrochemical and Chemical Reactivity of Octahalogenated Meso-Tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)Porphyrins
Authors: Cong Lei , Chahal Mandeep K , Osterloh Ryan , Sankar Muniappan , Kadish Karl M.
Published: February 2020

Two highly non-planar octahalogenated nickel(II) porphyrins were characterized for the first time as to their electrochemical and spectroscopic properties as well as their chemical reactivity in nonaqueous media. The complexes have the structures shown in Chart 1.

Chart 1. Structures of investigated porphyrins.

The UV-vis spectra of NiPorCl8 and NiPorBr8 vary with solvent and degree of axial coordination and are substantially different than spectra of the unhalogenated NiPor parent porphyrin. The NiPorBr8 and NiPorCl8 spectra are stable with time and interpreted in terms of four or six-coordinated derivatives in 14 different nonaqueous solvents but this is not the case for NiPorCl8 in DMF or DMSO where a transient 6-coordinate solvated complex is initially formed upon dissolving the compound followed by formation of a porphodimethene in solution. The combination of eight β-halogens and four meso-t-butyl-hydroxyphenyl groups on the NiPorX8 complexes exerts a powerful influence on the electrochemistry which is characterized by up to five redox reactions, the first 2 or 3 of which are irreversible at room temperature and assigned as involving the easily reducible meso-hydroxyphenyl groups followed by reduction of the π-conjugated system at more negative potentials. A rapid homogeneous chemical reaction occurs after the first electron transfer giving as the final product a nickel(II) porphodimethane at the electrode surface. This was confirmed by comparisons between redox potentials and UV-visible spectra of the in situ generated electroreduction products with that of chemically synthesized porphodimethenes formed in a reaction between NiPorCl8 and the added anions F-, CN-, OAc- or H2PO4
-.
Synthesis, Structural, Spectral and Electrochemical Redox Properties of Monofused Porphyrins Derived from Trans-Chlorins
Authors: Chaudhri Nivedita , Grover Nitika , Sankar Muniappan
Published: February 2020

The core of photosynthetic pigments consist of chlorophylls having chlorin skeleton and associated pigments which are responsible for light harvesting on Earth. Chlorins are utilized as photosensitizers in PDT since they exhibit intense long wavelength absorption ≥ 600 nm [1]. The advancement in synthetic methodologies over the past few years brought classical methods to bring functionalized chlorins [2,3]. Several methods are available in literature for the synthesis of tetraphenylchlorins (TPCs) from tetraphenylporphyrins (TPPs). However, there are only a few reports on smooth conversion of functionalized chlorins into porphyrins [4,5]. The interconversion of chlorins into porphyrins is of great interest since it opens a new synthetic route to access a wide variety of nonviable β-functionalized porphyrinoids [4,5]. In this regard, several ruffled
β-to-ortho-phenyl monofused metalloporphyrins (MIIMFPs) with 1,3-indanedione functionality have been synthesized by oxidative fusion of free base trans-chlorins via nickel insertion followed by the skeletal rearrangement of macrocycle. The synthesized monofused porphyrins exhibited red shifted electronic spectral features as compared to precursor, trans-chlorins or structurally related unfused porphyrins (mono/tri-β-substituted porphyrins) due to extended π-conjugation and nonplanar conformation of the macrocyclic core. Four of the synthesized porphyrins were structurally characterized by X-ray diffraction analysis. Ring fusion resulted into twisted macrocyclic conformation. NiMFP(IND)Ph2 (3b) exhibited modestly ruffled conformation of the macrocyclic core which was further confirmed by higher Δ24 (0.362 Å) and ΔC
β
(0.279 Å) values. Free base monofused porphyrins have shown upfield shifted inner core NHs as compared to trans-chlorins, whereas much downfield shifted as compared to H2TPP. Electron rich Ni(II) complexes exhibited metal centered oxidation (NiII/NiIII) due to electron donating β-substituents and extended π-conjugation of macrocyclic core. In this presentation, we will describe the facile synthesis, structural, spectral and intriguing electrochemical redox properties of monofused porphyrins.

Figure 1
Pentacene Fused Porphyrin Dimer Exhibiting High Stability and Solubility
Authors: Hu Yi , Wang Hong
Published: February 2020

Acenes have the potential to be used in the next gengeration of electronic devices due to their unique electronic properties. Pentacene is one of the most widely utilized organic compounds for organic-filed effect transistor (OFET) because of its high charge mobility. However, solubility and stability are two critical factors that limit their use in practical application. Ethynylation has shown to be one of the best strategies to stabilize pentacene. Our group is interested in linearly fusing another aromatic chromophore such as porphyrin with alkynyl-substituted pentacene to further increase its stability and solubility.

In this work, a new pentacene fused porphyrin dimer with high stability and solubility was prepared and characterized. The new pentacene fused porphyrin dimer exhibits a narrow energy gap up to 1.4 eV. Photodegradation studies using UV-Vis and 1H NMR reveal that the new pentacene derivative exhibits an increased solubility and stability up to 16 times compared to 6,13-bis(phenyethynyl)pentacene.

Figure 1
Site-Specific Coordination Chemistry and Beyond: Novel Properties in Low Dimensional Supramolecular Architectures of Porphins at Surfaces
Authors: Girovsky Jan , Baljozovic Milos , Nowakowska Sylwia , Nowakowski Jan , Wäckerlin Christian , Dreiser Jan , Lobo Checa Jorge , Gade Lutz , Decurtins Silvio , Liu Shi-Xia , Oppeneer Peter , Ballav Nirmalya , Jung Thomas A.
Published: February 2020

In our work, we establish porphin based on-surface architectures which exhibit extraordinary properties e.g. electronic, magnetic and quantum properties originating from the reduced dimensionality of the self-assembled and atomically precise architectures. Unconventional H-bonding as well as the direct site-specific interaction of the porphin’s center metal with the substrate direct the 2D architectures. The coordination and magneto-chemistry of binary 2D assemblies can be investigated by combining scanning probe microscopy / spectroscopy, photoelectron and photoabsorption spectroscopy and density functional theory. Complex electronic [1] and magnetic [2] interactions arise from the 2D periodicity which are also dependent on the state of adsorbed to physisorption and chemical reactivity. Sub-lattices in 2D ‘checkerboard’ architectures of magnetic molecules on magnetic substrates can be selectively switched by chemical ligation [3]. Also we have observed the first example of 2D ferrimagnetic long-range order and remanence for such a 2D architecture on non-magnetic Au(110) [2]. Uniquely, self-assembled 2D architectures contribute to our understanding of fundamental interactions involved in host-guest systems and allow for the specific operation of quantum states with a partial delocalization across the supramolecular on-surface architecture [4]. Thereby we unravel more and more of the on-surface chemistry [5] required to engineer low dimensional materials with unprecedented properties by controlling their architecture. In particular this involves the on-surface supramolecular, the on-surface coordination and the on-surface magneto-chemistry.

[1] Lobo-Checa, J. et al., Science 325:300 (2009)

[2] Girovsky, J. et al., Nat. Commun., DOI: 10.1038/ncomms15388 (2017).

[3] C. Waeckerlin et al, 10.1002/adma.201204274

[4] Nowakowska, S. et al., 10.1021/acsnano.7b07989

[5] Ballav N., et al., JPCL 4:2303 (2013) [4]

Figure 1
Star-Shaped Magnesium Tetraethynylporphyrin Bearing Four Peripheral Electron-Accepting Functionalities for Organic Solar Cell
Authors: Matsuo Yutaka , Wang Huan
Published: February 2020

Magnesium tetraethynylporphyrins bearing four electron-deficient diketopyrrolopyrrole (DPP; Mg-TEP-DPP4) units were synthesized by Sonogashira coupling, andtheir optical and electrochemical properties were investigated. The energy levels were effectively tuned by DPP with or without electron-withdrawing end-caps. Importantly, all the Mg-TEP-DPP4moleculeshave broad absorption bands across the visible and near-infrared regions. The time-dependent excited state features of Mg-TEP-DPP4molecules and their kinetics wereinvestigatedby femtosecond transient absorption spectroscopy in combination with multiwavelength and global/target analyses of time-resolved spectra. Importantly, the charge-separated state was demonstrated to undergo recombination within 253 ps in benzonitrile. Bulk heterojunction organic solar cells fabricated with Mg-TEP-DPP4:PC61BM exhibited a power conversion eﬃciencyof 7.40% after solvent vapor annealing, which enabled balanced charge carrier transport, reduced charge recombination, and favorable charge separation and collection.
Light Triggers Molecular Shuttling in Rotaxanes
Authors: Guldi Dirk M.
Published: February 2020

In this work on rotaxanes comprising a strapped-porphyrin as a ring molecule and a dumbbell bearing one fullerene stopper, coordination forces are crucial for the excited state behavior. Distinct differences in the lifetime of the charge-separated state and the presence of more than a single lifetime were observed. Here, the coordinating properties and the polarity of the solvent have the strongest impact. For example, in apolar, non-coordinating toluene, a single lifetime was found for the charge-separated state, whereas in polar, coordinating PhCN, a short-lived and a long-lived charge-separated state evolved. In toluene and PhCl, these effects were also induced when a coordinating species, such as pyridine, was added.

Depending on the solvent polarity, the shuttling is either directional or random. In apolar toluene and in the presence of pyridine, Coulombic interactions in the ZnP•+-C60
•-radical ion pair dominate and, in turn, force a close proximity between the oxidized porphyrin and the reduced fullerene. This sets up the means for a directional molecular shuttling, which results in a drastically reduced lifetime of the charge-separated state. In highly polar benzonitrile, shuttling is random and allows the fullerene anion to move further away from the porphyrin cation. This enables the system to overcome the barrier of Coulombic attractions. As such, larger porphyrin-to-fullerene distances go hand-in-hand with a longer lifetime of the charge-separated state in a high-polarity coordinating solvent; longer relative to that in either non-coordinating solvents or low-polarity solvents. Independent confirmation for our hypothesis came from the absence of a longer and/or a shorter-lived charge-separated state in the presence of a coordinating solvent in analogous experiments with a system, which features a strapped free-base porphyrin rather than a zinc porphyrin.

Our results emphasize the importance of coordination interactions. To gain further insight, rotaxanes with longer, more rigid axles, which should enhance the effects on the distribution of lifetimes, are currently being designed and studied in our laboratories. Finally, a porphyrin with a metal center that binds pyridine more strongly than zinc, such as ruthenium, could exhibit interesting behavior.
Supramolecular Assemblies Recognized Gastric Cancer Biomarkers in Biological Fluids
Authors: Stefan-van Staden Raluca-Ioana
Published: February 2020

Molecular recognition of gastric cancer biomarkers is essential for fast and early diagnosis of gastric cancer. To date, the standard methods are unable to detect most of these biomarkers in biological fluids.

Stochastic sensors represent a promising candidate for the molecular recognition of the biomarkers, because they can perform a qualitative analysis as well as a quantitative analysis of these biomarkers in biological fluids such as whole blood, saliva. Therefore, stochastic sensors based on supramolecular assemblies immobilized on carbon materials such as diamond, graphite, graphene were designed, characterized and validated for fast screening of biological fluids for early diagnosis of gastric cancer. The results obtained proved that they can be used for early diagnosis of gastric cancer.
Accelerated Charge Separation and Stabilization in a Fused Bis Zinc Porphyrin-Quinone Conjugate Via Cation-Quinone Interaction
Authors: Thomas Michael Brandon , Hu Yi , Wang Hong , D'Souza Francis
Published: February 2020

Accelerated singlet excited state charge separation, improved quantum yields, and ultimate charge stabilization upon cation binding to the electron acceptor quinone in a fused bis zinc porphyrin-quinone (zinc porphyrin located on each side of the pentacenequinone) donor-acceptor conjugate has been accomplished. Selective binding of either Mg2+ or Sc3+ to quinone in the donor-acceptor conjugate led to facile reduction of quinone making the charge separation process thermodynamically more feasible. Consequently, increased population of the charge separated state was witnessed in femtosecond transient absorption studies with a near linear trend in population of the charge separated state versus amount of metal-ion added. GloTarAn software was utilized to process the spectral data which enabled determination of the species associated spectrum and population profiles which thereby allowed deconvolution of the femtosecond spectral data and appropriate designations of each state. The present findings may provide further insight into the role of the interaction between quinones and iron metal ions in the electron transport chain of natural photosynthesis, which may have further implications in other biological systems where metal cations are present in electron transport chains.
(Invited) Nano-FTIR Correlation Nanoscopy for Organic and Inorganic Material Analysis
Authors: Mastel Stefan , Hartmann Nicolai F. , Gokus Tobias
Published: February 2020

Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) is a scanning probe approach to optical microscopy and spectroscopy, bypassing the ubiquitous diffraction limit of light to achieve a spatial resolution below 20 nanometers. s-SNOM employs the strong confinement of light at the apex of a sharp metallic atomic force microscopy (AFM) tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties (dielectric function) of the sample directly below the tip and yields nanoscale resolved images simultaneous to topography [1]. In addition, the technology has been advanced to enable Fourier-Transform Infrared Spectroscopy on the nanoscale (nano-FTIR) [2] using broadband radiation from the visible spectral range to THz frequencies.

Recently, the combined analysis of complex nanoscale material systems by correlating near-field optical data with information obtained by other scanning probe microscopy (SPM)-based measurement methodologies has gained significant interest. For example, the material-characteristic nano-FTIR spectra of a phase-separated polystyrene/low-density polyethylene (PS/LDPE) polymer blend verifies sharp material interfaces by measuring a line profile across a ca. 1 µm sized LDPE island (Fig1). Near-field reflection/absorption imaging at 1500cm-1 of the ca. 50nm thin film allows to selectively highlight the distribution of PS in the blend and simultaneously map the mechanical properties like adhesion of the different materials [3,4].

Further, results will be presented that correlate the near-field optical response of semiconducting samples like graphene (2D) or functional SRAM devices (3D) in different frequency ranges (mid-IR & THz) to Kelvin Probe Force Microscopy (KPFM) measurements. Thus, s-SNOM systems represent an ideal platform to gain novel insights into complex material systems by different near-field and AFM-based method.

[1] F. Keilmann, R. Hillenbrand, Phil.
Trans. R. Soc. Lond. A
362, 787 (2004).

[2] F. Huth, et al., Nano Lett.
12, 3973 (2012).

[3] B. Pollard, et al., Beilstein J. of Nanotechn.
7, 605 (2016).

[4] I. Amenabar, et al., Nature Commun.
8, 14402 (2017).

Figure caption:

Fig 1.
Near-field correlation nanoscopy of a thin PS/LDPE polymer film, highlighting the phase separation of the materials by nano-FTIR measurements as well as the different mechanical properties of the polymers.

Figure 1
(Invited) Design of Metal - Carbon Nanotube Structures for Electronic and Optoelectronic Applications
Authors: Li Wangxiang , Chen Mingguang , Bekyarova Elena
Published: February 2020

Interconnecting graphitic surfaces has generated significant interest especially in electronics and optoelectronics motivated by the multi-functionality of the novel carbon structures. Bridging the π-conjugated carbon surfaces of single-walled carbon nanotubes (SWNTs) have special implications in next-generation electronics. We discuss the electrical transport properties of aligned semiconducting SWCNT films and the effect of metal atoms on the film conductivities. Deposition of transition metal and alkali metal atoms on aligned SWNTs increases the film conductivities via distinctly different mechanisms. Hexahapto metal-bridged aligned SWNTs can be engineered as reversible optoelectronic switches. We demonstrate aligned SWNT devices that are reversibly switched between a state of high electrical conductivity (on) by light and low electrical conductivity (off) by applied potential.
(Keynote) Facile Sorting of Single Walled Carbon Nanotubes According to Their Electronic Types
Authors: Chan-Park Mary
Published: February 2020

Single walled carbon nanotubes have interesting electronic properties such as superior semiconducting properties. However, before they can be applied in real electronic transistors, the as-synthesized carbon nanotubes need to be puriifed of the contaminating metallic carbon nanotubes which short circuit the the semi-conducting ones. We had developed various techniques to purify and sort SWNTs according to their electronic types including the use of polymers, and also the application of redox reactions which can directly probe the band gap of metallic nanotubes facilely. This talk shall describe the latest scaleable technique that we have developed that to achieve ultra-high pure semiconducting SWNTs.
Henna Extract As a Corrosion Inhibitor on Carbon Steel with TMSM-PMMA Hybrid Coating
Authors: Rabiei Baboukani Amin , Torkghashghaei Maryam
Published: February 2020

In this study, the effect of green henna as an inhibitor existing in the coating of TMSM-PMMA and its electrochemical study were analyzed. The coating was produced by "sol-gel" method for the corrosion protection of low–carbon steel. TMSM hybrid cell was synthesized by hydrolysis and condensation, Metaacryloxypropyltrimethoxysilane and Tetraetylorthosilicate with 1:1 molar ratio and PMMA hybrid cell was produced by Methylmetaacrylate polymerization. Finally two cells were mixed in 1:1 weight ratio. The carbon steel substrates were prepared by dip coating method. SEM technique was used to evaluate the structure of thin films including different concentrations of henna extract. Adhesion of coating was analyzed by "Pull off" test. Additionally, the experimental results obtained in different concentrations of henna extract using electrochemical methods such as tafel polarization, electrochemical impedance spectroscopy indicating that the concentration of %3 inhibitor in the coating had the maximum inhibition efficiency in 0.1M HCL. In this presentation, the electrochemical performance of the samples will be present.
Corrosion Behavior of Ni-Mo Alloys in CO2-Saturated Salinity Environment at Gas Hydrate Formation Temperatures
Authors: Ozigagu Christopher E , Zhou Ting , Sanders Stephen , Golden Teresa D
Published: February 2020

Gas hydrate formation and corrosion can cause serious safety and flow assurance problems in deep water environments. One aspect that has been given less attention is the corrosion behavior of materials in salinity environment where gas hydrate formation and CO2 (sweet) corrosion can simultaneously occur. This type of environment is common in oil and gas deep water environments. The aim of this work is to investigate the corrosion behavior of Ni-Mo alloy coatings in an environment containing salt and dissolved CO2 gas at gas hydrate formation temperature (5 oC). Even though materials exposed to deep water operations can still experience corrosion at gas hydrate temperatures (low temperatures), previous research have done similar studies in room or higher temperatures using other test materials. Ni-Mo coatings were selected as the test material due to its excellent corrosion resistance in aggressive environments and serves as a based material for many oil and gas materials. A specialty designed jacketed glass cell was used to conduct the immersion test. The immersion test solutions were sweet low-salinity (CO2 + 1 wt% salt + 5 oC) and sweet high-salinity (CO2 + ~24 wt% salt + 5 oC) test solutions, respectively. The as-deposited Ni-Mo alloy coating has the highest corrosion resistance of 33.28 kΩ cm2. The corrosion resistance dropped to 14.36 kΩ cm2 and 11.11 kΩ cm2 after 20 hrs of immersion in the sweet low-salinity and sweet high-salinity test solutions, respectively. From grazing incidence XRD, the (111) reflection peak of the Ni-Mo coating was depressed and broaden after immersion in both test solutions due to increase in oxide layer formation on the surface Ni-Mo coating. SEM revealed a cracked surface morphology after immersion in sweet high-salinity test solution and elemental analysis shows the presence of oxygen after immersion in both test solutions, which is an indication of the formation of oxygen containing compounds on the surface of the Ni-Mo coating. The oxygen content increased from 1.70 wt% after immersion in sweet low-salinity test solution to 2.37 wt% after immersion in sweet high-salinity test solution. This work provides a new corrosion design consideration and solution, and will help in designing models and corrosion prediction software used for simulating materials exposed to salinity environment where gas hydrate formation and CO2 corrosion can both occur. Incorporating this consideration into corrosion design of pipeline will improve offshore pipeline performance and serve as a baseline for initial corrosion allowance for materials exposed to this type of environment.

Figure 1
Magnetic Field Effect on Anodic Dissolution of Axle Steel in Bicarbonate Solution with Chlorides
Authors: Ning Fei , Zhang Kun , Cui Tongming , Ling Sichun , Ma Jiarong , Lu Zhanpeng , Yu Chengbing
Published: February 2020

The vehicle axle in the railway locomotive is a very important component. Localized corrosion is a cause of its degradation. Localized corrosion is usually caused by corrosive environments especially in media containing chloride ions. Harmonic currents in the power supply loops (contact nets and guide rails) of the train during train travel can produce stray current that produces stray magnetic fields. Some studies have shown that magnetic fields can accelerate or inhibit localized corrosion of metals.

In this study, optical microscopy (OM) and electrochemical measurements were used to study the effects of magnetic field on the electrochemical behavior and corrosion morphology of axle steel in sodium bicarbonate solutions with and without chloride ions. Different scan rates were used in the measurements of anodic polarization curves. Potentiostatic polarization measurements were performed with applying or removing a 0.4 T magnetic field. The surface morphologies of the electrodes were observed after potentiostatic polarization.

Figure 1 show that, for axle steel in 0.05 mol/L NaHCO3 with or without 0.001 mol/L NaCl, the magnetic field increased the peak current, positively shifted the potential for the onset of passivation, and narrowed the passivation range. Chlorides increased the anodic current in the transpassivation region. The synergistic effect of magnetic field and chlorides on breakdown of passivation was more significant at high potential scan rate for the anodic polarization curve measurements. Obvious corrosion pits could be found after polarization, according to the morphology of the axle steel after polarization at a scan rate of 50 mV/min. It is found that the magnetic field significantly accelerated the corrosion. For axle steel in 0.05 mol/L NaHCO3 system, the potentiostatic polarization was carried out at -0.3 V(SCE). The current density decreased with increasing the polarization time. The current decreasing rate was mitigated by applying a 0.4T magnetic field, i.e., the anodic current density tended to be more stable under applied magnetic field, showing a significant magnetic field effect on anodic dissolution and pitting behavior of axle steel in this environments.

Figure 1
Electrochemical Noise Analysis of Aluminum Alloy 6061-T6 in Laminar Flow of Seawater
Authors: Veleva Lucien , Acosta Gloria
Published: February 2020

Aluminum alloy 6061-T6 is widely used in many fields of engineering, especially in marine applications1. In the presence of chlorides localized corrosion occurs2. The goal of this study is characterize the alloy surface and its corrosion resistance in laminar flow conditions (0.1 ms-1), during the exposure in Caribbean seawater of Cozumel channel. As electrochemical techniques, open circuit potential (OCP) monitoring and electrochemical noise (EN) have been employed. OCP was correlated with changes on the alloy surface. The fluctuations of current, considered as EN3, were acquired up to 30 days and were transformed in the frequency domain. Their power spectral density (PSD) plots were obtained in order to gain information concerning dynamic of spontaneous release of energy. At the end of the experiment, the value of β exponent in PSD graph (Fig. 1a) suggests that AA6061-T6 corrosion process occurs as a persistent non-stationary process, which dynamics is controlled by fractional Brownian motion (fBm). The EN data provided the pitting index (PI = 0.95) and Rp value (1.44 kΩ cm2). The PI value indicates that Al6061-T6 presents pitting corrosion. Corrosion current (Icorr = 18.08 μA cm-2) was calculated based on Rp and Stern-Geary coefficient (B = 0.026 V) values.

Removing the corrosion products, SEM-EDX analysis showed undissolved intermetallic particles on the alloys surface, rich in Fe and in the presence of Si, as well as the presence of pit cavities (Fig. 1b).

Figure 1. AA6061-T6 after 30 days of exposure in Caribbean seawater of Cozumel channel with a laminar flow (0.1 ms-1): a) PSD plot of current noise signal and β exponent value and b) SEM-EDS of the surface after remove of the corrosion layer.

References:

1. Davis, J. R., Aluminum and aluminum alloys, alloying: understanding the basics,
ASM International, Materials Park, Ohio, (2001).

2. Szklarska-Smialowska Z., “Pitting Corrosion of Aluminum”, Sci., 41, 1743 (1999).

3. Dawson, J., “Electrochemical noise measurement: the definitive in-situ technique for corrosion applications” in Kearns J., Scully J., Roberge P., Reichert D., Dawson J., E
lectrochemical noise measurement for corrosion applications. West Conshohocken, PA: ASTM STP 1277, (1996).

Figure 1
Electrode Scratching Technique As a Robust Way to Decouple Erosion-Corrosion Components
Authors: Omirkhan Aigerim , Bos Tom , Yang Guoqiang , Stitt Camilla , Riley D. Jason , Ryan Mary P.
Published: February 2020

The substantial number of parameters and their interdependence makes the modelling and prediction of erosion-corrosion rates a rather challenging task, yet owing to increasing computational capacity one that is potentially solvable. To accurately estimate the rate of material loss, universally accepted explanations of the mechanisms of combined erosion and corrosion must be developed. The absence of reliable data can undermine safety and predictability of industrial processes, such as oil and gas transportation. The aim of this work is to demonstrate the application of an electrode scratching technique coupled with microstructural characterisation for improved understanding of synergy in erosion-corrosion.

In this work, a rotating disc electrode scratching setup, with well-defined and controlled flow conditions, was developed to study individual contributions to erosion-corrosion. Linear potentiodynamic and potentiostatic polarization techniques were used to reproducibly monitor the kinetics of dissolution and repassivation of API X65 steel electrodes upon scratching. Samples characterized using high-resolution scanning electron microscopy (SEM) and white-light interferometry (WLI), confirm the synergy; the losses due to erosion-corrosion are larger than that of the summation of the separate contributions of erosion and corrosion. Focused Ion Beam (FIB) milling was implemented for in-situ lift-out of lamellae from scratched samples for Transmission Electron Microscopy (TEM) characterisation. We confirm distinct microstructural changes take place in the vicinity of scratches: with nanoscale grain refinement and orientation changes observed (See Figure 1). These results, coupled with electrochemical data and micro-hardness measurements, suggest time-dependent surface-hardening processes affect material loss rates during mechanical-electrochemical coupled corrosion.

Figure 1
Passivation Layer Tailoring Using Laser Powder-Bed Fusion Additive Manufacturing: A Tribocorrosion Study
Authors: Chiu Tse-Ming , Castaneda Homero
Published: February 2020

Laser powder-bed fusion is an additive manufacturing high-energy laser beam creating near-end shape parts directly from a digital computer model. This technique has revealed new trends in manufacturing industry by producing parts with complex geometry and with topology optimizing the weight to strength ratio of structures. In this research, we characterize the corrosion behavior of a Ti6Al4V and AlSi12 alloy fabricated by using laser powder-bed fusion (L-PBF) when they were exposed to corrosive and tribocorrosion conditions. Two synthesis pathways (vertical and horizontal) were employed to produce alloy disks by using high and low laser power resulting in four different thermo-history profiles. The superfine microstructure of L-PBFed Ti6Al4V was revealed using EBSD and XRD, identified as α’ structure (an oversaturated HCP phase) with an n-type titanium oxide passive layer. The surface property was tailored by different 3D printing parameter resulting in a 30% increase in hardness 60% in wear loss and 28% decrease in the oxygen vacancies. The difference in oxygen vacancies tuned the corrosion to wear ratio from 25% to 15% at 2N normal load in simulated body fluid. The corrosion behavior of L-PBFed AlSi12 was tested in simulated acid water. The two different melt pool microstructure (shown in Fig1 (a) and (b)) engineered by the L-PBF building direction results in a difference in the suspiciously of pitting corrosion. The horizontal built specimens show better in pitting resistance, but with a broader probability distribution, which increases the uncertainty in engineering structurer design. The coarse grain silicon precipitation at melt pool boundary result in localized cathode barrier that deflects the pit propagation resulting in shallow pits. However, the heterogeneity of grain boundaries leads to the weakness in forming a protective surface layer under Cl- attack.

Figure 1 (a) Pit morphology and (b) melt pool structure and (c) accumulated pitting probability of AM-AlSi12 in dilute Harrison’s solution

Figure 1
Structure of the Oxide Films Formed on Hydrogen-Charged and Uncharged 316L Stainless Steels in Oxygenated High Temperature Water
Authors: Cui Tongming , Zhang Kun , Ma Jiarong , Jia Yibo , Ning Fei , Lu Zhanpeng
Published: February 2020

Austenitic stainless steels (SSs) are commonly used in pressurized water reactors (PWRs) nuclear power systems as key structural materials. The corrosion resistance are closely related to the passive film formed on the surfaces of austenitic alloys in high-temperature aqueous environments. It has been reported that hydrogen can affect corrosion, localized corrosion as well as stress corrosion cracking of materials in aqueous solutions. It is necessary to investigate the influence of hydrogen on the corrosion behavior of stainless steels material in high temperature water environments. In the present study, the oxide films formed on 316L SS with uncharged (316L) and hydrogen-charged (316L-H) in oxygenated simulated PWR primary water at 300℃were investigated. Oxygen was added in high temperature water to simulated occlude region condition or faulted water chemistry. The aim of this work is to clarify the effect of hydrogen in stainless steel on the corrosion behavior.

The surface morphologies of the oxide films formed on 316L (uncharged) and 316L-H (charged) specimens after exposure to oxygenated PWR primary water at 300 oC for168 h were observed. The regular and irregular oxides particles homogeneous distributed on the outer surface of 316L specimen, and compact filamentary oxides in the sub-surface. On 316L-H specimen, large oxides dispersed and inhomogeneous distributed on the outer surface, and compact minor polyhedral oxide particles packed on the sub-surface. The number of the large oxides on the outermost surface of 316L specimen was more than that on the 316L-H sample. The cross-section of the oxide films formed on 316L specimens after exposed to oxygenated PWR primary water was analyzed by FIB-TEM. The interface front between the inner oxide layer and the base metal was wavy-shaped. There were compact Cr-rich oxides in the inner layer, and filamentary (Fe, Ni)-rich oxides in the outer layer. There was slightly Ni-enrichment near the inner oxides/matrix interface and Fe-enrichment beneath the inner oxides/matrix interface from EDS line scan profile.

Some discontinuous cellular oxides distributed on the inner oxides/matrix interface on 316L-H after the exposure test, which was Fe-rich oxides identified by EDS maps and line scan. Similar to the 316L specimen, the inner layer oxide was compact and Cr-edriched, showing a slightly Fe-enriched beneath the inner oxides/matrix interface, but no Ni-enrichment close to the interface of inner oxides/matrix was observed.

Figure 1
(Invited) Recent Advances in SiC CMP
Authors: Rhoades Robert L.
Published: February 2020

The need for high-quality single crystal SiC substrates continues to grow as the demand for SiC-based power and RF devices increases. The physical properties of SiC result in better thermal conductivity, higher breakdown voltage, faster switching performance and lower resistivity when compared to similar devices based on silicon. Even with the performance advantages, the adoption rate of SiC is slowed by high cost and inherent difficulty of processing the material. Conventional processing of SiC substrates involves double-sided batch lapping followed by batch diamond polishing then final polishing with a non-diamond slurry to achieve an epi-ready surface. This process flow involves multiple process tools and is fraught with issues including the need for wafer sorting to group wafers by thickness, manual loading and unloading of wafers, low yields, and unacceptable risk of batch loss (an entire batch of wafers may be scrapped if even one wafer cracks or breaks during process).

This paper presents an improved process for single-wafer CMP during SiC substrate manufacturing or backside thinning. In contrast to batch polishing, key improvements include individual wafer processing, fully-automated handling, and elimination of the need for wafer sorting and grouping by thickness. Recent development efforts have achieved removal rates for the 4H Si face up to 2.5 µm/hour for the first step CMP. Removal rates for the C-face can be as much as 3-4x higher consistent with other findings in the industry. Fig 1 shows surface finish after the polishing sequence is complete which is consistently at or below 1 Å Ra as measured by AFM. The combination of an optimized grind followed by an optimized CMP process provides a viable path to both improving wafer yield and reducing costs for SiC wafer manufacturing or backside thinning process sequences.

Figure 1