Materials Science and NanoEngineering Publications

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    Atomically precise nanoclusters predominantly seed gold nanoparticle syntheses
    (Springer Nature, 2023) Qiao, Liang; Pollard, Nia; Senanayake, Ravithree D.; Yang, Zhi; Kim, Minjung; Ali, Arzeena S.; Hoang, Minh Tam; Yao, Nan; Han, Yimo; Hernandez, Rigoberto; Clayborne, Andre Z.; Jones, Matthew R.
    Seed-mediated synthesis strategies, in which small gold nanoparticle precursors are added to a growth solution to initiate heterogeneous nucleation, are among the most prevalent, simple, and productive methodologies for generating well-defined colloidal anisotropic nanostructures. However, the size, structure, and chemical properties of the seeds remain poorly understood, which partially explains the lack of mechanistic understanding of many particle growth reactions. Here, we identify the majority component in the seed solution as an atomically precise gold nanocluster, consisting of a 32-atom Au core with 8 halide ligands and 12 neutral ligands constituting a bound ion pair between a halide and the cationic surfactant: Au32X8[AQA+•X-]12 (X = Cl, Br; AQA = alkyl quaternary ammonium). Ligand exchange is dynamic and versatile, occurring on the order of minutes and allowing for the formation of 48 distinct Au32 clusters with AQAX (alkyl quaternary ammonium halide) ligands. Anisotropic nanoparticle syntheses seeded with solutions enriched in Au32X8[AQA+•X-]12 show narrower size distributions and fewer impurity particle shapes, indicating the importance of this cluster as a precursor to the growth of well-defined nanostructures.
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    Kramers nodal lines and Weyl fermions in SmAlSi
    (Springer Nature, 2023) Zhang, Yichen; Gao, Yuxiang; Gao, Xue-Jian; Lei, Shiming; Ni, Zhuoliang; Oh, Ji Seop; Huang, Jianwei; Yue, Ziqin; Zonno, Marta; Gorovikov, Sergey; Hashimoto, Makoto; Lu, Donghui; Denlinger, Jonathan D.; Birgeneau, Robert J.; Kono, Junichiro; Wu, Liang; Law, Kam Tuen; Morosan, Emilia; Yi, Ming
    Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy connecting time-reversal invariant momenta. KNLs are robust to spin orbit coupling and are inherent to all non-centrosymmetric achiral crystal structures, leading to unusual spin, magneto-electric, and optical properties. However, their existence in in real quantum materials has not been experimentally established. Here we gather the experimental evidence pointing at the presence of KNLs in SmAlSi, a non-centrosymmetric metal that develops incommensurate spin density wave order at low temperature. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and magneto-transport methods, we provide evidence suggesting the presence of KNLs, together with observing Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. We discuss the nesting possibilities regarding the emergent magnetic orders in SmAlSi. Our results provide a solid basis of experimental observations for exploring correlated topology in SmAlSi
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    Three-dimensional covalent organic frameworks with pto and mhq-z topologies based on Tri- and tetratopic linkers
    (Springer Nature, 2023) Zhu, Dongyang; Zhu, Yifan; Chen, Yu; Yan, Qianqian; Wu, Han; Liu, Chun-Yen; Wang, Xu; Alemany, Lawrence B.; Gao, Guanhui; Senftle, Thomas P.; Peng, Yongwu; Wu, Xiaowei; Verduzco, Rafael
    Three-dimensional (3D) covalent organic frameworks (COFs) possess higher surface areas, more abundant pore channels, and lower density compared to their two-dimensional counterparts which makes the development of 3D COFs interesting from a fundamental and practical point of view. However, the construction of highly crystalline 3D COF remains challenging. At the same time, the choice of topologies in 3D COFs is limited by the crystallization problem, the lack of availability of suitable building blocks with appropriate reactivity and symmetries, and the difficulties in crystalline structure determination. Herein, we report two highly crystalline 3D COFs with pto and mhq-z topologies designed by rationally selecting rectangular-planar and trigonal-planar building blocks with appropriate conformational strains. The pto 3D COFs show a large pore size of 46 Å with an extremely low calculated density. The mhq-z net topology is solely constructed from totally face-enclosed organic polyhedra displaying a precise uniform micropore size of 1.0 nm. The 3D COFs show a high CO2 adsorption capacity at room temperature and can potentially serve as promising carbon capture adsorbents. This work expands the choice of accessible 3D COF topologies, enriching the structural versatility of COFs.
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    Large enhancement of thermal conductivity of aluminum-reduced graphene oxide composites prepared by a single-step method
    (Oxford University Press, 2023) Mitra, Arijit; Sahoo, Mihir Ranjan; Samal, Aiswarya; Pradhan, Sunil Kumar; Polai, Balaram; Sahoo, Krishna Rani; Kar, Subrat; Satpathy, Bijoy Kumar; Narayanan, Tharangattu N; Ajayan, Pulickel M; Satyam, Parlapalli V; Nayak, Saroj K
    Metal matrix composites have attracted extensive attention from both the research and industrial perspective. In this study, we prepared aluminum-reduced graphene oxide (Al–rGO) composites with enhanced thermal conductivity in an easy single-step process. Pristine Al shows a thermal conductivity of 175 Wm−1K−1 (standard deviation <5%), which increases to 293 Wm−1K−1 for an Al–rGO composite with 1% rGO. Analysis of theoretical models shows that a higher percentage of rGO inside the Al matrix creates a continuous network resulting in more available phase space through which heat carrier phonons travel with less scattering, and hence thermal conductivity of the composite increases. Furthermore, Al–rGO composites show an ∼5% increase in microhardness compared with pristine Al. The electrical resistivity of the composite is comparable to that of pristine Al for a narrow weight percentage of rGO, whereas a 70% enhancement in the thermal conductivity of the composite is observed for the same weight percentage range, suggesting possibilities for exploiting both high electrical and thermal conductivities for various applications.
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    Magneto-structural phase transition in exfoliated pyrrhotite (Fe7S8) ultra-thin sheets
    (Oxford University Press, 2023) Puthirath Balan, Aravind; Oliveira, Eliezer F; Costin, Gelu; Gray, Tia; Chakingal, Nithya; Biswas, Abhijit; Puthirath, Anand B
    Non-van der Waals (n-vdW) 2D materials are gaining popularity due to their exciting confinement-enhanced properties for magnetic, catalytic and optoelectronic applications. The recent discovery of mechanical and liquid exfoliation of n-vdW materials along the cleavage planes, owing to the very low scission energies, is encouraging and opens the avenue for further exploration of n-vdW materials having exceptional properties. Herein, we successfully isolated a few layers of pyrrhotite (Fe7S8) nanosheets from bulk mineral ore by means of liquid phase exfoliation in organic solvent and studied the magnetic ordering at bulk and exfoliated samples. Both experimental and first principle theoretical investigations point out confinement-induced magneto-structural phase transition from ferromagnetic monoclinic (4M) to antiferromagnetic hexagonal (3T) characterized by the suppression of Besnus transition.
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    The role of graphene in new thermoelectric materials
    (Royal Society of Chemistry, 2023) Mulla, Rafiq; White, Alvin Orbaek; Dunnill, Charles W.; Barron, Andrew R.
    Graphene has high electrical conductivity, making it an attractive material for thermoelectric applications. However, its high thermal conductivity is a major challenge, and initial studies indicate that using pristine graphene alone cannot achieve optimal thermoelectric performance. Therefore, researchers are exploring ways to improve thermoelectric materials by either leveraging graphene's high intrinsic electrical conductivity or compounding graphene with additives to reduce the intrinsic thermal conductivity of the materials. Therefore, the research focus is now being shifted to graphene composites, primarily with polymer/organic conductors. One promising avenue of research is the development of graphene composites with polymer or organic conductors, which have shown some improvements in thermoelectric performance. However, the achieved “dimensionless figure of merit (ZT)” values of these composites are still far lower than those of common inorganic semiconductors. An alternative approach involves incorporating a very small amount of graphene into inorganic materials to improve their overall thermoelectric properties. These new concepts have successfully addressed the detrimental effects of graphene's intrinsic thermal conductivity, with the added interfaces in the matrix due to the presence of graphene layers working to enhance the properties of the host material. The use of graphene presents a promising solution to the longstanding challenge of developing high-performance and cost-effective thermoelectric materials. This paper discusses these innovative research ideas, highlighting their potential for revolutionizing the field of thermoelectric materials.
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    Transition from Diffusive to Superdiffusive Transport in Carbon Nanotube Networks via Nematic Order Control
    (American Chemical Society, 2023) Wais, Michael; Bagsican, Filchito Renee G.; Komatsu, Natsumi; Gao, Weilu; Serita, Kazunori; Murakami, Hironaru; Held, Karsten; Kawayama, Iwao; Kono, Junichiro; Battiato, Marco; Tonouchi, Masayoshi
    The one-dimensional confinement of quasiparticles in individual carbon nanotubes (CNTs) leads to extremely anisotropic electronic and optical properties. In a macroscopic ensemble of randomly oriented CNTs, this anisotropy disappears together with other properties that make them attractive for certain device applications. The question however remains if not only anisotropy but also other types of behaviors are suppressed by disorder. Here, we compare the dynamics of quasiparticles under strong electric fields in aligned and random CNT networks using a combination of terahertz emission and photocurrent experiments and out-of-equilibrium numerical simulations. We find that the degree of alignment strongly influences the excited quasiparticles’ dynamics, rerouting the thermalization pathways. This is, in particular, evidenced in the high-energy, high-momentum electronic population (probed through the formation of low energy excitons via exciton impact ionization) and the transport regime evolving from diffusive to superdiffusive.
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    Frequency independent damped outrigger systems for multi-mode seismic control of super tall buildings with frequency independent negative stiffness enhancement
    (Wiley, 2023) Wang, Meng; Sun, Fei-Fei; Koetaka, Yuji; Chen, Lin; Nagarajaiah, Satish; Du, Xiu-Li
    Damped outrigger system is effective for improving energy dissipation for tall buildings. However, conventional damped outrigger (CDO) system with viscous damping has two limitations: (i) its maximum damping ratio cannot be improved when outrigger/column stiffness is inadequate; (ii) different modes achieve their maximum damping ratios at different outrigger damping values, and thus the dampers cannot be optimized to simultaneously reduce vibrations of multiple modes of concern to their minimum. In this paper, a purely frequency-independent negative stiffness damped outrigger (FI-NSDO) system is proposed by combining frequency-independent damper (FID) and negative stiffness device (NSD). The damped outrigger with FID can achieve the maximum damping ratio for all modes as compared to frequency-dependent damper like viscous damper. As the NSD has the features of assisting and enhancing motion and frequency-independence, the utilization of NSD will considerably improve the maximum damping ratios when outrigger/column stiffness is inadequate and maintain the frequency-independent feature of the whole system. Therefore, the FI-NSDO has the capability of simultaneously increasing the damping ratios of all target modes to their maximum values. Analysis in frequency domain and time domain, demonstrate that the proposed FI-NSDO performs better in controlling the multi-mode vibration of seismic responses.
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    Mesoscale Modeling of Distributed Water Systems Enables Policy Search
    (Wiley, 2023) Zhou, Xiangnan; Duenas-Osorio, Leonardo; Doss-Gollin, James; Liu, Lu; Stadler, Lauren; Li, Qilin; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    It is widely acknowledged that distributed water systems (DWSs), which integrate distributed water supply and treatment with existing centralized infrastructure, can mitigate challenges to water security from extreme events, climate change, and aged infrastructure. However, it is unclear which are beneficial DWS configurations, i.e., where and at what scale to implement distributed water supply. We develop a mesoscale representation model that approximates DWSs with reduced backbone networks to enable efficient system emulation while preserving key physical realism. Moreover, system emulation allows us to build a multiobjective optimization model for computational policy search that addresses energy utilization and economic impacts. We demonstrate our models on a hypothetical DWS with distributed direct potable reuse (DPR) based on the City of Houston's water and wastewater infrastructure. The backbone DWS with greater than 92% link and node reductions achieves satisfactory approximation of global flows and water pressures, to enable configuration optimization analysis. Results from the optimization model reveal case-specific as well as general opportunities, constraints, and their interactions for DPR allocation. Implementing DPR can be beneficial in areas with high energy intensities of water distribution, considerable local water demands, and commensurate wastewater reuse capacities. The mesoscale modeling approach and the multiobjective optimization model developed in this study can serve as practical decision-support tools for stakeholders to search for alternative DWS options in urban settings.
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    Phonon-Assisted Intertube Electronic Transport in an Armchair Carbon Nanotube Film
    (American Physical Society, 2023) Adinehloo, Davoud; Gao, Weilu; Mojibpour, Ali; Kono, Junichiro; Perebeinos, Vasili; The Smalley-Curl Institute
    The electrical conductivity of a macroscopic assembly of nanomaterials is determined through a complex interplay of electronic transport within and between constituent nano-objects. Phonons play dual roles in this situation: their increased populations tend to reduce the conductivity via electron scattering, while they can boost the conductivity by assisting electrons to propagate through the potential-energy landscape. We identified a phonon-assisted coherent electron transport process between neighboring nanotubes in temperature-dependent conductivity measurements on a macroscopic film of armchair single-wall carbon nanotubes. Through atomistic modeling of electronic states and calculations of both electronic and phonon-assisted junction conductances, we conclude that phonon-assisted conductance is the dominant mechanism for observed high-temperature transport in armchair carbon nanotubes. The unambiguous manifestation of coherent intertube dynamics proves a single-chirality armchair nanotube film to be a unique macroscopic solid-state ensemble of nano-objects promising for the development of room-temperature coherent electronic devices.
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    Impregnation of KOAc on PdAu/SiO2 causes Pd-acetate formation and metal restructuring
    (Royal Society of Chemistry, 2023) Jacobs, Hunter P.; Elias, Welman C.; Heck, Kimberly N.; Dean, David P.; Dodson, Justin J.; Zhang, Wenqing; Arredondo, Jacob H.; Breckner, Christian J.; Hong, Kiheon; Botello, Christopher R.; Chen, Laiyuan; Mueller, Sean G.; Alexander, Steven R.; Miller, Jeffrey T.; Wong, Michael S.
    Potassium-promoted, oxide-supported PdAu is catalytically active for the gas-phase acetoxylation of ethylene to form vinyl acetate monomer (VAM), in which the potassium improves long-term activity and VAM selectivity. The alkali metal is incorporated into the catalyst via wet impregnation of its salt solution, and it is generally assumed that this common catalyst preparation step has no effect on the catalyst structure. However, in this work, we report evidence to the contrary. We synthesized a silica-supported PdAu (PdAu/SiO2, 8 wt% Pd, 4 wt% Au) model catalyst containing Pd-rich PdAu alloy and pure Au phases. Impregnation with potassium acetate (KOAc) aqueous solution and subsequent drying did not cause XRD-detectible changes to the bimetal structure. However, DRIFTS indicated the presence of Pd3(OAc)6 species, which is correlated to up to 2% Pd loss after washing of the dried KOAc-promoted PdAu/SiO2. Carrying out the impregnation step with an AcOH-only solution and subsequent drying caused significant enlargement of the pure Au grain size and generated a smaller amount of Pd3(OAc)6. During co-impregnation of AcOH and KOAc, grain sizes were enlarged slightly, and substantial amounts of K2Pd2(OAc)6 and Pd3(OAc)6 were detected by DRIFTS and correlated to up to 32% Pd loss after washing. Synchrotron XAS analysis showed that approximately half the Pd atoms were oxidized, corroborating the presence of the Pd-acetate species. These results indicate wet-impregnation-induced metal leaching can occur and be substantial during catalyst preparation.
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    Precise Cation Separations with Composite Cation-Exchange Membranes: Role of Base Layer Properties
    (American Chemical Society, 2023) DuChanois, Ryan M.; Mazurowski, Lauren; Fan, Hanqing; Verduzco, Rafael; Nir, Oded; Elimelech, Menachem; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT)
    Separation of specific ions from water could enable recovery and reuse of essential metals and nutrients, but established membrane technologies lack the high-precision selectivity needed to facilitate a circular resource economy. In this work, we investigate whether the cation/cation selectivity of a composite cation-exchange membrane (CEM), or a thin polymer selective layer on top of a CEM, may be limited by the mass transfer resistance of the underlying CEM. In our analysis, we utilize a layer-by-layer technique to modify CEMs with a thin polymer selective layer (∼50 nm) that has previously shown high selectivity toward copper over similarly sized metals. While these composite membranes have a CuCl2/MgCl2 selectivity up to 33 times larger than unmodified CEMs in diffusion dialysis, our estimates suggest that eliminating resistance from the underlying CEM could further increase selectivity twofold. In contrast, the CEM base layer has a smaller effect on the selectivity of these composite membranes in electrodialysis, although these effects could become more pronounced for ultrathin or highly conductive selective layers. Our results highlight that base layer resistance prevents selectivity factors from being comparable across diffusion dialysis and electrodialysis, and CEMs with low resistance are necessary for providing highly precise separations with composite CEMs.
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    Size-Induced Ferroelectricity in Antiferroelectric Oxide Membranes
    (Wiley, 2023) Xu, Ruijuan; Crust, Kevin J.; Harbola, Varun; Arras, Rémi; Patel, Kinnary Y.; Prosandeev, Sergey; Cao, Hui; Shao, Yu-Tsun; Behera, Piush; Caretta, Lucas; Kim, Woo Jin; Khandelwal, Aarushi; Acharya, Megha; Wang, Melody M.; Liu, Yin; Barnard, Edward S.; Raja, Archana; Martin, Lane W.; Gu, X. Wendy; Zhou, Hua; Ramesh, Ramamoorthy; Muller, David A.; Bellaiche, Laurent; Hwang, Harold Y.
    Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high-energy-density storage applications, understanding their size effects will provide key information for optimizing device performances at small scales. Here, the fundamental intrinsic size dependence of antiferroelectricity in lead-free NaNbO3 membranes is investigated. Via a wide range of experimental and theoretical approaches, an intriguing antiferroelectric-to-ferroelectric transition upon reducing membrane thickness is probed. This size effect leads to a ferroelectric single-phase below 40 nm, as well as a mixed-phase state with ferroelectric and antiferroelectric orders coexisting above this critical thickness. Furthermore, it is shown that the antiferroelectric and ferroelectric orders are electrically switchable. First-principle calculations further reveal that the observed transition is driven by the structural distortion arising from the membrane surface. This work provides direct experimental evidence for intrinsic size-driven scaling in antiferroelectrics and demonstrates enormous potential of utilizing size effects to drive emergent properties in environmentally benign lead-free oxides with the membrane platform.
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    Spontaneous hydrogen production using gadolinium telluride
    (Cell Press, 2023) Kumbhakar, Partha; Parui, Arko; Dhakar, Shikha; Paliwal, Manas; Behera, Rakesh; Gautam, Abhay Raj Singh; Roy, Soumyabrata; Ajayan, Pulickel M.; Sharma, Sudhanshu; Singh, Abhishek K.; Tiwary, Chandra S.
    Developing materials for controlled hydrogen production through water splitting is one of the most promising ways to meet current energy demand. Here, we demonstrate spontaneous and green production of hydrogen at high evolution rate using gadolinium telluride (GdTe) under ambient conditions. The spent materials can be reused after melting, which regain the original activity of the pristine sample. The phase formation and reusability are supported by the thermodynamics calculations. The theoretical calculation reveals ultralow activation energy for hydrogen production using GdTe caused by charge transfer from Te to Gd. Production of highly pure and instantaneous hydrogen by GdTe could accelerate green and sustainable energy conversion technologies.
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    Enhanced thermoelectricity in Bi-sprayed bismuth sulphide particles
    (Elsevier, 2023) Mulla, Rafiq; Kiani, Sajad; White, Alvin Orbaek; Dunnill, Charles W.; Barron, Andrew R.
    Bismuth sulphide (Bi2S3), an n-type semiconductor that critically demonstrates the Seebeck effect with Seebeck coefficients of about 300 μVK−1. However, its poor electrical conductivity makes it unsuitable for thermoelectric applications. In this study, we present a facile preparation method for fabricating Bi-sprayed Bi2S3 particles that alters their thermoelectric properties. Samples were created with differing Bi concentrations into the Bi2S3 compound to test for enhanced thermoelectric properties of the resulting Bi/Bi2S3 composites. The incorporation of excess Bi into Bi2S3 significantly improves the compound's electrical conductivity and optimises overall thermoelectric performance. The electrical conductivity of the Bi/Bi2S3 composites improved from 6.5 Scm−1 (for pristine Bi2S3) to 154 Scm−1 (for highest Bi added Bi2S3). Although the Seebeck coefficient of samples decreased with Bi incorporation, a high power factor (∼390 μWm−1K−2) has been achieved for an optimised composition of the composite. Incorporation of metallic Bi has led to an increase in the thermal conductivity of the samples, but the increase is not significant for the optimised composition of the composites where a high thermoelectric performance has been observed. Therefore, enhanced power factor and moderate thermal conductivity have resulted in a peak ZT value of 0.11 at room temperature. The strategy proposed here improves the thermoelectricity in Bi2S3 and shows excellent potential for developing better-performing thermoelectric compounds with excess elemental contents.
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    Theory of sigma bond resonance in flat boron materials
    (Springer Nature, 2023) Qiu, Lu; Zhang, Xiuyun; Kong, Xiao; Mitchell, Izaac; Yan, Tianying; Kim, Sung Youb; Yakobson, Boris I.; Ding, Feng
    In chemistry, theory of aromaticity or π bond resonance plays a central role in intuitively understanding the stability and properties of organic molecules. Here we present an analogue theory for σ bond resonance in flat boron materials, which allows us to determine the distribution of two-center two-electron and three-center two-electron bonds without quantum calculations. Based on this theory, three rules are proposed to draw the Kekulé-like bonding configurations for flat boron materials and to explore their properties intuitively. As an application of the theory, a simple explanation of why neutral borophene with ~1/9 hole has the highest stability and the effect of charge doping on borophene’s optimal hole concentration is provided with the assumption of σ and π orbital occupation balance. Like the aromaticity theory for carbon materials, this theory greatly deepens our understanding on boron materials and paves the way for the rational design of various boron-based materials.
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    Superior mechanical properties of multilayer covalent-organic frameworks enabled by rationally tuning molecular interlayer interactions
    (PNAS, 2023) Fang, Qiyi; Pang, Zhengqian; Ai, Qing; Liu, Yifeng; Zhai, Tianshu; Steinbach, Doug; Gao, Guanhui; Zhu, Yifan; Li, Teng; Lou, Jun
    Two-dimensional (2D) covalent-organic frameworks (COFs) with a well-defined and tunable periodic porous skeleton are emerging candidates for lightweight and strong 2D polymeric materials. It remains challenging, however, to retain the superior mechanical properties of monolayer COFs in a multilayer stack. Here, we successfully demonstrated a precise layer control in synthesizing atomically thin COFs, enabling a systematic study of layer-dependent mechanical properties of 2D COFs with two different interlayer interactions. It was shown that the methoxy groups in COFTAPB-DMTP provided enhanced interlayer interactions, leading to layer-independent mechanical properties. In sharp contrast, mechanical properties of COFTAPB-PDA decreased significantly as the layer number increased. We attributed these results to higher energy barriers against interlayer sliding due to the presence of interlayer hydrogen bonds and possible mechanical interlocking in COFTAPB-DMTP, as revealed by density functional theory calculations.
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    Electronic Properties of Functionalized Diamanes for Field-Emission Displays
    (Amerian Chemical Society, 2023) Tantardini, Christian; Kvashnin, Alexander G.; Azizi, Maryam; Gonze, Xavier; Gatti, Carlo; Altalhi, Tariq; Yakobson, Boris I.
    Ultrathin diamond films, or diamanes, are promising quasi-2D materials that are characterized by high stiffness, extreme wear resistance, high thermal conductivity, and chemical stability. Surface functionalization of multilayer graphene with different stackings of layers could be an interesting opportunity to induce proper electronic properties into diamanes. Combination of these electronic properties together with extraordinary mechanical ones will lead to their applications as field-emission displays substituting original devices with light-emitting diodes or organic light-emitting diodes. In the present study, we focus on the electronic properties of fluorinated and hydrogenated diamanes with (111), (110), (0001), (101̅0), and (2̅110) crystallographic orientations of surfaces of various thicknesses by using first-principles calculations and Bader analysis of electron density. We see that fluorine induces an occupied surface electronic state, while hydrogen modifies the occupied bulk state and also induces unoccupied surface states. Furthermore, a lower number of layers is necessary for hydrogenated diamanes to achieve the convergence of the work function in comparison with fluorinated diamanes, with the exception of fluorinated (110) and (2̅110) films that achieve rapid convergence and have the same behavior as other hydrogenated surfaces. This induces a modification of the work function with an increase of the number of layers that makes hydrogenated (2̅110) diamanes the most suitable surface for field-emission displays, better than the fluorinated counterparts. In addition, a quasi-quantitative descriptor of surface dipole moment based on the Tantardini–Oganov electronegativity scale is introduced as the average of bond dipole moments between the surface atoms. This new fundamental descriptor is capable of predicting a priori the bond dipole moment and may be considered as a new useful feature for crystal structure prediction based on artificial intelligence.
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    Slippery Alkoxysilane Coatings for Antifouling Applications
    (Amerian Chemical Society, 2023) Apsey, Henry; Hill, Donald; Barron, Andrew R.; Alexander, Shirin
    Herein, we report the wettability and antifouling behavior of a range of different siloxane coatings on plastic and glass substrates. The films investigated are prepared using trimethoxysilane precursors with different alkyl chain lengths (1–18 C atoms) in order to study how the nature of the hydrophobic group affects the different parameters used to characterize wettability (contact angles, sliding angles, and contact angle hysteresis). Atomic force microscopy analysis shows that the coatings possess low surface topography [root mean squared roughness (rms) < 50 nm] and are highly transparent as studied using UV–vis spectroscopy. The sliding properties of H2O, CH2I2, methanol, and ethylene glycol were observed to be strongly influenced by the chain length of the alkoxysilane precursor used. The coatings formed from the longer chain analogues show comparable water sliding angles to superhydrophobic surfaces. These coatings show similar performance to analogous alkoxysilane coating-bearing fluorinated groups, indicating that they could act as viable environmentally friendly alternatives to some of the fluorinated films that have been widely adopted. Furthermore, these surfaces are highly durable toward common forms of abrasion and are observed to show low adhesion toward synthetic feces, indicating that their utility extends further than repelling liquids alone. Consequently, these coatings could show promise for potential use in applications in the medical sector where fouling by biological mixtures leads to an unsustainable use of materials.
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    Directing and Understanding the Translation of a Single Molecule Dipole
    (Amerian Chemical Society, 2023) Simpson, Grant J.; García-López, Víctor; Boese, A. Daniel; Tour, James M.; Grill, Leonhard; Smalley-Curl Institute; NanoCarbon Center
    Understanding the directed motion of a single molecule on surfaces is not only important in the well-established field of heterogeneous catalysis but also for the design of artificial nanoarchitectures and molecular machines. Here, we report how the tip of a scanning tunneling microscope (STM) can be used to control the translation direction of a single polar molecule. Through the interaction of the molecular dipole with the electric field of the STM junction, it was found that both translations and rotations of the molecule occur. By considering the location of the tip with respect to the axis of the dipole moment, we can deduce the order in which rotation and translation take place. While the molecule–tip interaction dominates, computational results suggest that the translation is influenced by the surface direction along which the motion takes place.