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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2020

Transition-metal phthalocyanine monolayers as new Chern insulators

To explore new materials for the realization of the quantum anomalous Hall effect (QAHE), we studied the electronic, magnetic and topological properties of transition-metal phthalocyanine (TMPc) monolayers in a square lattice. Many of them have large topologically nontrivial band gaps and integer Chern numbers. In particular, the Fermi level of MoPc lies right in the band gap (E g = 8.1 meV) and has large magnetic anisotropy energy (MAE = 2.0 meV per Mo atom) and a Curie temperature of 16 K, showing its usefulness for applications. The presence of the topologically protected edge state in a MoPc nanoribbon further confirms it as a new two-dimensional topological insulator. This much widens the search for QAHE materials for the design of quantum devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Ir 6 In 32 S 21 , a polar, metal-rich semiconducting subchalcogenide

Subchalcogenides are uncommon, and their chemical bonding results from an interplay between metal–metal and metal–chalcogenide interactions. Herein, we present Ir 6 In 32 S 21 , a novel semiconducting subchalcogenide compound that crystallizes in a new structure type in the polar P31m space group, with unit cell parameters a = 13.9378(12) Å, c = 8.2316(8) Å, α = β = 90°, γ = 120°. The compound has a large band gap of 1.48(2) eV, and photoemission and Kelvin probe measurements corroborate this semiconducting behavior with a valence band maximum (VBM) of –4.95(5) eV, conduction band minimum of –3.47(5) eV, and a photoresponse shift of the Fermi level by ~0.2 eV in the presence of white light. X-ray absorption spectroscopy shows absorption edges for In and Ir do not indicate clear oxidation states, suggesting that the numerous coordination environments of Ir 6 In 32 S 21 make such assignments ambiguous. Electronic structure calculations confirm the semiconducting character with a nearly direct band gap, and electron localization function (ELF) analysis suggests that the origin of the gap is the result of electron transfer from the In atoms to the S 3p and Ir 5d orbitals. DFT calculations indicate that the average hole effective masses near the VBM (1.19m e ) are substantially smaller than the average electron masses near the CBM (2.51m e ), an unusual feature for most semiconductors. The crystal and electronic structure of Ir 6 In 32 S 21 , along with spectroscopic data, suggest that it is neither a true intermetallic nor a classical semiconductor, but somewhere in between those two extremes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Green synthesis of reduced Ti 3 C 2 T x MXene nanosheets with enhanced conductivity, oxidation stability, and SERS activity

Transition metal carbides (MXenes) are an emerging family of highly conductive two-dimensional materials with additional functional properties introduced by surface terminations. Further modification of the surface terminations makes MXenes even more appealing for practical applications. Herein, we report a facile and environmentally benign synthesis of reduced Ti 3 C 2 T x MXene (r-Ti 3 C 2 T x ) via a simple treatment with L-ascorbic acid at room temperature. r-Ti 3 C 2 T x shows a six-fold increase in electrical conductivity, from 471 ± 49 for regular Ti 3 C 2 T x to 2819 ± 306 S m -1 for the reduced version. Additionally, we show an enhanced oxidation stability of r-Ti 3 C 2 T x as compared to regular Ti 3 C 2 T x . An examination of the surface-enhanced Raman scattering (SERS) activity reveals that the SERS enhancement factor of r-Ti 3 C 2 T x is an order of magnitude higher than that of regular Ti 3 C 2 T x . The improved SERS activity of r-Ti 3 C 2 T x is attributed to the charge transfer interaction between the MXene surface and probe molecules, re-enforced by an increased electronic density of states (DOS) at the Fermi level of r-Ti 3 C 2 T x . The findings of this study suggest that reduced MXene could be a superior choice over regular MXene, especially for the applications that employ high electronic conductivity, such as electrode materials for batteries and supercapacitors, photodetectors, and SERS-based sensors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The optimal co-doping of SrFe 1-x Co x O 3-δ oxygen carriers in redox applications

Although the oxygen carrier SrCoO 3 has higher redox activity than SrFeO 3 , cobalt is both more expensive and scarcer than iron, which would hinder the wide implementation of SrCoO 3 . For these reasons, doping SrFeO 3 with Co is a potential compromise, benefitting the redox properties of SrFeO 3 , while still limiting the overall amount of cobalt being used. In this work, to find the optimal level of Co-doping, density functional theory calculations were performed to investigate the Co-doping effect on the oxygen vacancy formation and oxygen migration in SrFe 1- x Co x O 3- δ ( x = 0, 0.125, 0.25, 0.375, 0.5). Our findings show that the oxygen vacancy formation energies ( E f ) decrease with the increase of Co content resulting from the increased composition of the O-2p band at the Fermi level upon Co doping. In particular, the E f decreases nearly 0.5 eV between the x = 0 and x = 0.25 samples while E f only decreases 0.1 eV further as Co content is increased to x = 0.5. We obtain that x = 0.25 is an optimal cost/benefit ratio for Co doping, which is preserved at both low oxygen vacancy concentrations ( δ = 0.0625 values listed above) and at high concentrations of δ = 0.1875 and 0.375. Kinetically, the oxygen migration barrier has slight change upon Co doping due to the similar size of Co and Fe. Therefore, considering both redox activity and economics in reversible oxygen storage applications, x = 0.25 is suggested as the optimal Co-doping value in SrFe 1- x Co x O 3- δ .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

How well do self-interaction corrections repair the overestimation of static polarizabilities in density functional calculations?

Herein, we examine the effect of removing self-interaction error (SIE) on the calculation of molecular polarizabilities in the local spin density (LSDA) and generalized gradient approximations (GGA). To this end, we utilize a database of 132 molecules taken from a recent benchmark study [Hait and Head-Gordon, Phys. Chem. Chem. Phys. , 2018, 20 , 19800] to assess the influence of SIE on polarizabilities by comparing results with accurate reference data. Our results confirm that the general overestimation of molecular polarizabilities by these density functional approximations can be attributed to SIE. However, removing SIE using the Perdew–Zunger self-interaction-correction (PZ-SIC) method, implemented using the Fermi–Löwdin Orbital SIC approach, leads to an underestimation of molecular polarizabilities, showing that PZ-SIC overcorrects when combined with LSDA or GGA. Application of a recently proposed locally scaled SIC [Zope, et al., J. Chem. Phys. , 2019, 151 , 214108] is found to provide more accurate polarizabilities. We attribute this to the ability of the local scaling scheme to selectively correct for SIE in the regions of space where the correction is needed most.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ultrafast relaxation dynamics in bimetallic plasmonic catalysts

Combining a plasmonic metal, such as gold, with other popular catalysts, such as Ni or Pt, can extend its benefits to many energy-extensive reactions catalyzed by those metals. The efficiency of a plasmon-enhanced catalytic reaction is mainly determined by the light absorption cross section and the photoexcited charge carrier relaxation dynamics of the nanoparticles. Here we have investigated the charge carrier relaxation dynamics of gold/nickel (Au/Ni) and gold/platinum (Au/Pt) bimetallic nanoparticles. We found that the addition of Ni or Pt to gold can reduce light absorption in gold nanoparticles. However, electron–phonon coupling rates of Au/Ni and Au/Pt nanoparticles are significantly faster than that of pure Au nanoparticles. This is due to the fact that both Ni and Pt possess significantly larger electron–phonon coupling constants and higher densities of states near the Fermi level in comparison with Au. Additionally, the phonon–phonon coupling rate of bimetallic Au/Pt and Au/Ni nanoparticles was significantly different from that of pure gold nanoparticles, due to the acoustic impedance mismatch at the nanoparticle/substrate interface. Our findings provide important insights into the rational design of bimetallic plasmonic catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Hexagonal layered group IV–VI semiconductors and derivatives: fresh blood of the 2D family

New phases of group IV–VI semiconductors in 2D hexagonal structures are predicted and their unusual physical properties are revealed. The structures of monolayer group IV–VI semiconductors are similar to those of blue phosphorene and each unit has the same ten valence electrons. The band gap of 2D hexagonal group IV–VI semiconductors depends on both the thickness and stacking order. Atomic functionalization can induce ferromagnetism, and the Curie temperature can be tuned. Gapped Dirac fermions with zero mass are developed and this makes it exceed that of graphene. Finally, the Fermi velocity can be compared to or even above that of graphene.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Gapped metals as thermoelectric materials revealed by high-throughput screening

The typical strategy to design high performance thermoelectric materials is to dope a semiconducting material until optimal properties are obtained. However, some known thermoelectric materials such as La 3 Te 4 , Mo 3 Sb 7 , Yb 14 MnSb 11 , and NbCoSb are actually gapped metals,i.e., their band structure displays a gap slightly above or below the band crossed by the Fermi level. This key feature makes these metals comparable to degenerate semiconductors and thus suitable for thermoelectric applications. In this work, we perform a computational high-throughput search for such gapped metals exhibiting attractive thermoelectric properties. Several thousands of metals are found to present this key feature, and about one thousand of them show decent thermoelectric properties as evaluated by a computed zT. We present the different chemistry of gapped metals we discovered such as clathrates, Chevrel phases, or transition metal dichalcogenides and discuss their previous studies as thermoelectric and their potential as new thermoelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The effect of elastic strains on the adsorption energy of H, O, and OH in transition metals

The influence of elastic strains on the adsorption of H, O, and OH on the (111) surfaces of 8 fcc (Ni, Cu, Pd, Ag, Pt, Au, Rh, Ir) and on the (0001) surfaces of 3 hcp (Co, Zn, Cd) transition metals was analyzed by means of density functional theory calculations. To this end, surface slabs were subjected to different strain states (uniaxial, biaxial, shear, and a combination of them) up to strains dictated by the mechanical stability limits indicated by phonon calculations. It was found that the adsorption energy followed the predictions of the d-band theory but – surprisingly – the variations in the adsorption energy only depended on the area of the adsorption hole and not on the particular elastic strain tensor applied to achieve this area. The analysis of the electronic structure showed that the applied strains did not modify the shape of the Projected Density of States (PDOS) of the d-orbitals of the transition metals but only led to a shift in the energy levels. Moreover, the presence of the adsorbates on the surfaces led to negligible changes in the PDOS. Thus, the adsorption energies were a function of the Fermi energy which in turn was associated with the change of the area of the adsorption through a general linear law that was valid for all metals. Furthermore, the information in this paper allows the immediate and accurate estimation of the effect of any elastic strain on the adsorption energies of H, O, and OH in 11 transition metals with more than half-filled d-orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Computational investigations of Dienes defect- and vacancy-induced changes in the electronic and vibrational properties of carbon fiber structural units

Carbon fiber (CF) is a promising lightweight alternative to steel and is of significant interest for energy applications. As CF continues to find new uses and is exposed to new external conditions, a noninvasive method of monitoring its structural integrity is critical. Raman spectroscopy is a commonly used method for this monitoring; however, it is highly inferential, and the interpretation of the data is not always straightforward. In this work, we perform density functional theory (DFT) calculations to investigate changes in the vibrational properties of CF structural units (i.e., graphene and graphite) caused by monovacancy and Dienes defects as a foundation for modeling more complex defects that move our model toward that of realistic CF. Using large computational supercells, we can understand how these defects change the electronic structure and vibrational properties of graphene and graphite for interdefect distances near those of the lower experimental limit. The monovacancy opens an electronic bandgap at the K point. Although no such electronic gap is opened by the Dienes defect, both defects introduce flat defect bands near the Fermi energy. The Dienes defect creates long-range deviations of the phonons, leading to substantial broadening of the highest frequency optical modes in the band structure compared to that of the pristine material. In contrast, the phonon changes caused by the monovacancy are short range, and only minor changes in the band structure or phonon density of states were observed. These findings can assist in the interpretation of experimental results by providing atomic-scale insight into key electronic and vibrational features.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Engineering of flat bands and Dirac bands in two-dimensional covalent organic frameworks (COFs): relationships among molecular orbital symmetry, lattice symmetry, and electronic-structure characteristics

Two-dimensional covalent organic frameworks (2D-COFs), also referred to as 2D polymer networks, display unusual electronic-structure characteristics, which can significantly enrich and broaden the fields of electronics and spintronics. In this Focus article, the objective of this report is to lay the groundwork for the conceptual description of the fundamental relationships among the COF electronic structures, the symmetries of their 2D lattices, and the frontier molecular orbitals (MOs) of their core and linker components. We focus on monolayers of hexagonal COFs and use tight-binding model analyses to highlight the critical role of the frontier-MO symmetry, in addition to lattice symmetry, in determining the nature of the electronic bands near the Fermi level. We rationalize the intriguing feature that, when the core unit has degenerate highest occupied MOs [or lowest unoccupied MOs], the COF highest valence band [or lowest conduction band] is flat but degenerate with a dispersive band at a high-symmetry point of the Brillouin zone; the consequences of having such band characteristics are briefly described. Multi-layer and bulk 2D COFs are found to maintain the salient features of the monolayer electronic structures albeit with a reduced bandgap due to the interlayer coupling. This Focus article is thus meant to provide an effective framework for the engineering of flat and Dirac bands in 2D polymer networks.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Solar cell contacts: quantifying the impact of interfacial layers on selectivity, recombination, charge transfer, and V oc

Interfacial layers (IFLs) are ubiquitous in solar cells, but their precise impact on carrier transfer rates and the relation of these rates to performance metrics and the concepts of selectivity and recombination is lacking. We report the use of a well-defined interdigitated back-contact (IBC) silicon solar cell to determine the precise role of such IFLs. We characterize the action of the common IFL spiro-OMeTAD by making it a third contact to the IBC cell. This architecture creates three solar cells within a single structure that, with numerical simulation, provide the exchange current densities (i.e., charge transfer rates) for electrons ( J 0n ) and holes ( J 0p ) and the quasi Fermi-level splitting in the absorber, which measures the balance of generation and recombination. Further, we describe the relation of V oc to contact recombination, the asymmetry in electron/hole collection rates at a single contact (contact selectivity), and the asymmetry in collection rates of the same carrier at separate contacts (carrier selectivity). Relative to bare gold, neat spiro-OMeTAD reduces J 0n and J 0p (their geometric mean ( J 0n J 0p ) 0.5 decreases by 10 4 ), decreasing contact recombination. Addition of the common dopant Li-TFSI and air increase J 0p / J 0n by 10 6 with little effect on ( J 0n J 0p ) 0.5 , increasing contact hole selectivity. The significant increase in V oc observed by introducing spiro-OMeTAD/Li-TFSI IFLs into the cells studied, however, is due to an increase in the carrier selectivity rather than the contact selectivity or recombination of the spiro-OMeTAD-modified contact. Operando measurements further show voltage-dependent changes in the J 0 s, demonstrating that spiro-OMeTAD contributes to hysteresis. Broader context : Solar cells operate by photogenerating excess charge carriers in an absorber material and, in competition with recombination, asymmetrically extracting them at so-called carrier-selective contacts, one that ideally collects only electrons and the other, only holes. Particularly in emerging photovoltaics such as perovskites, thin layers of organic semiconductors or related materials are introduced between the absorber and contact to improve power conversion efficiency. In terms of interfacial charge transfer, a prevailing view is that such interfacial layers improve performance by helping block the collection of the undesired carrier, considered a form of recombination. We use a novel platform to study the simultaneous impact of spiro-OMeTAD, a common interfacial layer, on the collection of electrons, the collection of holes, and on the recombination of electrons and holes. We quantitatively demonstrate that spiro-OMeTAD layers indeed passivate the contact toward recombination, but that larger improvements in the open-circuit voltage, a key cell metric, can come not only from this but also from increasing the asymmetry of the collection of electrons in the system. Further, operando measurements show transient changes in the properties of spiro-OMeTAD which suggest that it contributes to hysteresis phenomena commonly observed in perovskite and other solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Materials design, synthesis, and transport properties of disordered rare-earth Zintl bismuthides with the anti -Th 3 P 4 structure type

The synthesis, structural elucidation, and transport properties of the extended series Ca 4–x RE x Bi 3 (RE = Y, La–Nd, Sm, Gd–Tm, and Lu; x ≈ 1) and Ca 4–x RE x Bi 3–δ Sb δ (RE = La, Ho, Er, and Lu; x ≈ 1, δ ≈ 1.5) are presented. Structural elucidation is based on single-crystal X-ray diffraction data and confirms the chemical drive of Ca4Bi3 with the cubic anti-Th 3 P 4 structure type (space group I4 ¯3d, no. 220, Z = 4) into a Zintl phase by the introduction of trivalent rare-earth atoms. The structure features complex bonding, heavy elements, and electron count akin to that of valence-precise semiconductors, making it an ideal target for thermoelectrics development. Introducing crystallographic site disorders at the cation site for the Ca 4–x RE x Bi 3 phase and both the cation and anion sites for the Ca 4–x RE x Bi 3–δ Sb δ phase brings about additional desirable characteristics for thermoelectric materials in the context of tuning knobs for lowering thermal conductivity. Electronic structure calculations of idealized Ca 3 YBi 3 and Ca 3 LaBi 3 compounds indicate the opening of indirect bandgaps at the Fermi level with magnitudes Eg = 0.38 eV and 0.57 eV, respectively. The electrical resistivity ρ(T) of some of the investigated phases measured on single crystals evolve in a metallic manner with magnitudes of order 1.4 mΩ cm near 500 K, thus supporting the notion of a degenerate semiconducting state, with the temperature dependence of the Seebeck coefficient α(T) suggesting the p-type behavior. Furthermore, the low electrical resistivity and the realization of a degenerate semiconducting state in the title phases present a window of opportunity for optimizing their carrier concentrations for enhanced thermoelectric performance.

36 MATERIALS SCIENCE↗
DOE OSTI2022

First-principles study of the defect-activity and optical properties of FAPbCl 3

With promising solar cell applications, organic–inorganic lead halide perovskites belong to a novel and rapidly developing class of semiconducting materials. Unlike its well-investigated iodide counterparts, formamidinium lead chloride (FAPbCl 3 ) is a much less studied perovskite that shows superior stability and surprisingly high selectivity and sensitivity towards certain gas analytes. The origin of the sensing ability of this perovskite material can be traced to its high defect tolerance and the existence of some defects which act as the “lock” to a certain gas analyte's “key”. In this work, we deepen the understanding of this proven perovskite sensor through first-principles computational study of its defect formation energies, charge transition energies, and optical properties. These studies are done with the widely used GGA exchange–correlation functional PBE and the newer meta-GGA functional SCAN, both incorporating the Grimme's D3 dispersion correction. Additionally, we also consider experimental conditions and the effect of temperature on electron screening in the simulations, which demonstrates that screening is particularly important when considering high oxidation states of the defects. We also note the importance of antisites in the Fermi Pinning as well as the importance of FA disorder, which are previously unreported insights.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Modulation of the coordination environment enhances the electrocatalytic efficiency of Mo single atoms toward water splitting

Here, enhancing the catalytic efficiency through engineering active site environments is expected to work pronouncedly for single atom catalysts (SACs) because of intense atomic scale interactions involved between SAs and their coordination environments. Taking Mo SACs for catalyzation of the hydrogen evolution reaction (HER) as an example, three SACs of different coordination environments, namely Mo-O 2 N 2 , Mo-O 2 N 1 C 1 , and Mo-O 2 C 2 , were successfully created for demonstration. The HER performances are in an increasing order of Mo-O 2 N 2 , Mo-O 2 N 1 C 1 , and Mo-O 2 C 2 , exhibiting η 10 of 98, 71, and 61 mV, η 500 of 340, 248, and 200 mV, Tafel slopes of 95.8, 39.6, and 33.8 mV dec -1 , and current density decays of 9, 6, and 6% after a 50 hour operation at an initial current density of 100 mA cm -2 , respectively. Substituting C with N in the coordination environment results in inferior HER catalytic efficiency and stability. Density functional theory calculations reveal that replacing carbon with nitrogen for coordination with the Mo SA on a carbon substrate of a higher N-doping level shifts the d-band center of Mo more negatively from the Fermi level, thereby increasing the hydrogen adsorption energy and thus decelerating the hydrogen desorption kinetics, giving consequent inferior HER activities.

25 ENERGY STORAGE↗
DOE OSTI2023

Two-dimensional ruthenium boride: a Dirac nodal loop quantum electrocatalyst for efficient hydrogen evolution reaction

Catalysts with high carrier mobility, high activity, and an active basal plane have been highly sought for the hydrogen evolution reaction (HER). However, combining these advantages into one single material is a grand challenge. Herein, using first principles computations, we predicted that a two-dimensional (2D) Dirac nodal loop semimetal, namely the RuB 4 monolayer, is promising as a superior catalyst for the HER. Our systematic computations showed that the single layer RuB 4 is thermodynamically, dynamically, mechanically, and thermally stable and presents multiple Ru and B sites for the HER on the basal plane. The estimated Gibbs free energy for hydrogen adsorption at a Ru site is approaching zero (–8.8 meV), suggesting its excellent HER performance. The RuB 4 monolayer is a Dirac nodal loop semimetal with high Fermi velocities, which can accelerate charge transfer between catalysts and reaction intermediates. The RuB 4 monolayer is an auxetic material with an out-of-plane negative Poisson's ratio, implying its novel mechanical properties. Finally, this work provides an example of using a Dirac nodal loop semimetal for high-performance HER catalysts, which is a promising alternative to the known catalysts with trivial metallic properties.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Structure, electrical and thermal properties of single-crystal BaCuGdTe 3

Single crystals of the quaternary chalcogenide BaCuGdTe 3 were obtained by direct reaction of elements allowing for a complete investigation of the intrinsic electrical and thermal properties of this previously uninvestigated material. The structure was investigated by high-resolution single-crystal synchrotron X-ray diffraction, revealing an orthorhombic crystal structure with the space group Cmcm. Although recently identified as a semiconductor suitable for thermoelectric applications from theoretical analyses, our electrical resistivity and Seebeck coefficient measurements show metallic conduction, the latter revealing strong phonon-drag. Temperature dependent hole mobility reveals dominant acoustic phonon scattering. Heat capacity data reveal a Debye temperature of 183 K and a very high density of states at the Fermi level, the latter confirming the metallic nature of this composition. Thermal conductivity is relatively high with Umklapp processes dominating thermal transport above the Debye temperature. The findings in this work lay the foundation for a more detailed understanding of the physical properties of this and similar multinary chalcogenide materials, and is part of the continuing effort in investigating quaternary chalcogenide materials and their suitability for use in technological applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Carbon Kagome nanotubes—quasi-one-dimensional nanostructures with flat bands

In recent years, a number of bulk materials and heterostructures have been explored due their connections with exotic materials phenomena emanating from flat band physics and strong electronic correlation. The possibility of realizing such fascinating material properties in simple realistic nanostructures is particularly exciting, especially as the investigation of exotic states of electronic matter in wire-like geometries is relatively unexplored in the literature. Motivated by these considerations, we introduce in this work carbon Kagome nanotubes (CKNTs)—a new allotrope of carbon formed by rolling up Kagome graphene, and investigate this material using specialized first principles calculations. We identify two principal varieties of CKNTs—armchair and zigzag, and find both varieties to be stable at room temperature, based on ab initio molecular dynamics simulations. CKNTs are metallic and feature dispersionless states (i.e., flat bands) near the Fermi level throughout their Brillouin zone, along with an associated singular peak in the electronic density of states. We calculate the mechanical and electronic response of CKNTs to torsional and axial strains, and show that CKNTs appear to be more mechanically compliant than conventional carbon nanotubes (CNTs). Additionally, we find that the electronic properties of CKNTs undergo significant electronic transitions—with emergent partial flat bands and tilted Dirac points—when twisted. We develop a relatively simple tight-binding model that can explain many of these electronic features. We also discuss possible routes for the synthesis of CKNTs. Overall, CKNTs appear to be unique and striking examples of realistic elemental quasi-one-dimensional materials that may display fascinating material properties due to strong electronic correlation. Distorted CKNTs may provide an interesting nanomaterial platform where flat band physics and chirality induced anomalous transport effects may be studied together.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

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