Wide Nanoribbons Research Articles

Morphology evolution of supramolecular aggregates from C3-symmetric peptide amphiphiles

During the aging of supramolecular systems, new stable materials with different morphologies, molecular packing, and hierarchical organization may form from the initial assembly. Understanding the mechanisms and pathways accompanying age-related changes may allow for the controlled synthesis of multiple materials from a single molecule in a nature-inspired manner. Herein, we demonstrate the multi-stage evolution of a single solution of C3-symmetric peptide amphiphile containing diphenylalanine fragment and benzyl-1,3,5-tricarboxamide core. Transmission electron microscopy reveals the rapid formation of 20–40 nm wide nanoribbons in an aqueous solution within 60 s after preparation. The lateral edges of nanoribbons contain solvent-exposed aromatic residues that tend to merge via an unconventional edge-to-edge zipping mechanism, leading to the nanoribbon’s growth in width. After reaching a critical width and flexibility, “sticky edges” on the same nanoribbon may merge via a self-zipping mechanism, forming rigid nanotubes. Eventually, mechanical perturbations cause buckling and fracture of nanotubes into shorter nanotubes via flexural or tensile failure. This work reports new evolution pathways in soft 2D assemblies and introduces solution ageing as a promising method to control morphology of peptide amphiphiles.

Bioinspired Flexible Hydrogelation with Programmable Properties for Tactile Sensing.

Tactile sensing requires integrated detection platforms with distributed and highly sensitive haptic sensing capabilities along with biocompatibility, aiming to replicate the physiological functions of the human skin and empower industrial robotic and prosthetic wearers to detect tactile information. In this regard, short peptide-based self-assembled hydrogels show promising potential to act as bioinspired supramolecular substrates for developing tactile sensors showing biocompatibility and biodegradability. However, the intrinsic difficulty to modulate the mechanical properties severely restricts their extensive employment. Herein, by controlling the self-assembly of 9-fluorenylmethoxycarbonyl-modifid diphenylalanine (Fmoc-FF) through introduction of polyethylene glycol diacrylate (PEGDA), wider nanoribbons are achieved by untwisting from well-established thinner nanofibers, and the mechanical properties of the supramolecular hydrogels can be enhanced 10-fold, supplying bioinspired supramolecular encapsulating substrate for tactile sensing. Furthermore, by doping with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and 9-fluorenylmethoxycarbonyl-modifid 3,4-dihydroxy-l-phenylalanine (Fmoc-DOPA), the Fmoc-FF self-assembled hydrogels can be engineered to be conductive and adhesive, providing bioinspired sensing units and adhesive layer for tactile sensing applications. Therefore, the integration of these modules results in peptide hydrogelation-based tactile sensors, showing high sensitivity and sustainable responses with intrinsic biocompatibility and biodegradability. The findings establish the feasibility of developing programmable peptide self-assembly with adjustable features for tactile sensing applications.

Quantum transport regimes in quartic dispersion materials with Anderson disorder

Mexican-hat-shaped quartic dispersion manifests itself in certain families of single-layer two-dimensional hexagonal crystals such as compounds of groups III–VI and groups IV–V as well as elemental crystals of group V. A quartic band forms the valence band edge in various of these structures, and some of the experimentally confirmed structures are GaS, GaSe, InSe, SnSb, and blue phosphorene. Here, we numerically investigate strictly one-dimensional and quasi-one dimensional (Q1D) systems with quartic dispersion and systematically study the effects of Anderson disorder on their transport properties with the help of a minimal tight-binding model and Landauer formalism. We compare the analytical expression for the scaling function with simulation data to distinguish the domains of diffusion and localization regimes. In one dimension, it is shown that conductance drops dramatically at the quartic band edge compared to the quadratic case. As for the Q1D nanoribbons, a set of singularities emerge close to the band edge, suppressing conductance and leading to short mean-free-paths and localization lengths. Interestingly, wider nanoribbons can have shorter mean-free-paths because of denser singularities. However, the localization lengths sometimes follow different trends. Our results display the peculiar effects of quartic dispersion on transport in disordered systems.

Thermal conductivity of quasi-bilayer graphene without and with perfluorophenylazide molecules

The obstacles in further improving the heat-transport performance of the graphene-based films root in the random stacking configuration of the graphene flakes and their agglomeration in solvents. In order to overcome these obstacles, we design one kind of quasi-bilayer graphene device composed of one upper narrow nanoribbon and one lower wide nanoribbon with absorbed perfluorophenylazide (PFPA) molecules. By investigating the thermal conductivity (TC) of the quasi-bilayer graphene without absorbed PFPA molecules, we find the TC will increase as the length and width increase, while the TC will decrease with the increase of the layer number. This indicates that a quasi-bilayer graphene flake of a large area and a small layer number will be beneficial to increasing its TC. Furthermore, in the presence of the PFPA molecules, the TC of the quasi-bilayer graphene, albeit suppressed by the PFPA molecules, is found to decrease slowly with the increase of the PFPA molecule number. This demonstrates a feasible way to fabricate the high-quality graphene-based films based on the technology of absorbing PFPA molecules. This research should be an important reference for designing the graphene-based thermal functional devices.

Electronic structures, transport properties, and optical absorption of bilayer blue phosphorene nanoribbons.

Based on first-principles density functional theory and nonequilibrium Green's function, we study the electronic band structures, the electronic transport properties, and the optical absorption of bilayer blue phosphorene nanoribbons (BPNRs). Both bilayer armchair BPNRs (a-BPNRs) and zigzag BPNRs (z-BPNRs) behave as semiconductors in the narrow nanoribbon case and metals in the wide nanoribbon case, sharply different from their monolayer counterparts where the monolayer a-BPNRs (z-BPNRs) are always semiconducting (metallic). This indicates that interlayer couplings or the increasing layer number may induce the switching of the conductivity of the monolayer BPNRs, which is absent in graphene and phosphorene nanoribbons. Furthermore, we explore the edge states of the energy bands near Fermi energy, and find that there are almost no pure edge-state band branches in the bilayer BPNRs, which can be attributed to the interlayer couplings between the edge-states in one layer and the bulk-states in the other. Consequently, the resulting complex band structures cannot be directly analyzed any more in the framework of the two-body coupling picture just according to the simple band structures of the monolayer BPNRs. Finally, we present the current-voltage characteristics and the optical absorption of the bilayer a-BPNRs and z-BPNRs. The influences of the nanoribbon width and the interlayer couplings on the current and the anisotropic optical absorption can be understood based on the complex energy band structures. This research should be an important reference of extending the field of BPNRs from the monolayer to the bilayer case, and deepen the understanding of the difference between the monolayer and bilayer nanoribbons in different materials.

Self-assembly of wide peptide nanoribbons via the formation of nonpolar zippers between β-sheets

Because zipper motifs between complementary sidechains can allow molecular order to be maintained over larger length scales, they hold great promise for the preparation of hierarchical peptide self-assemblies with long-range ordering. Although polar zippers based on sidechain-sidechain hydrogen bonding have been demonstrated to promote significant lamination of β-sheets into wide and flat nanoribbons, it remains a challenge to achieve such well-defined nanostructures through nonpolar zippers. In this study, we designed a series of short amphiphilic peptides Ac-I3XGK-NH2, where X at the intramolecular hydrophobic/hydrophilic interface denotes different hydrophobic residues. Microscopic imaging and neutron scattering measurements indicated that only Ac-I3VGK-NH2 could self-assemble into wide and uniform nanoribbons. Spectroscopic and solid-state NMR analyses revealed that the peptide adopted an anti-parallel β-sheet secondary structure with a two-residue shifting. Under such a molecular conformation and alignment, homogenous and extensive nonpolar zippers between β-sheets, consisting of alternating Val4-Ile3 and Ile2-Ile1 sidechain contacts, would be formed, leading to significant β-sheet lamination that can cause wide and flat nanoribbon assembly. Finally, the failure of the peptide variants to form wide and flat nanoribbons indicated a stringent requirement of extensive nonpolar zipper formation between β-sheets for primary sequence, especially the interaction mode of hydrophobic sidechains.

Dual Dirac points and odd–even oscillated energy gap in zigzag chlorinated stanene nanoribbon

Stanene has been predicted to be a two-dimensional topological insulator, providing an ideal platform for the realization of quantum spin Hall effect even at room temperature. Based on first-principles calculations, we studied the topological edge states in zigzag chlorinated stanene nanoribbon. From our calculations, dual Dirac points can be found near Fermi level. One Dirac point is localized at the edges and emerges in a narrow nanoribbon, while another is widespread and can only be found in a wide nanoribbon due to the coupling of two opposite edges. At the localized Dirac point, there is an interesting odd–even oscillated energy gap with the change of the width of nanoribbon. The energy gaps at both Dirac points and the coupling of two opposite edges can be modified by edge adsorption. Asymmetric adsorption of two edges was also discussed. Our calculations may be helpful for the potential applications of tin-based topological nanoribbons in nanodevices.

Subbands in a nanoribbon of topologically insulating MoS2 in the 1T′ phase

Continuous miniaturization has brought the feature size of silicon technology down into the nanometer scale, where performance enhancement cannot easily be achieved by further size reduction. The use of new materials with advanced properties has become mandatory to meet the needs for higher performance at reduced power. Topological insulators possess highly conductive topologically protected edge states which are insensitive to scattering and thus suitable for energy efficient high-speed devices. Here, we evaluate the subband structure in a narrow nanoribbon of 1T′ molybdenum disulfide by employing an effective k·p Hamiltonian. Highly conductive topologically protected edge modes whose energies lie within the bulk band gap are investigated on equal footing with traditional electron and hole subbands. Due to the interaction between the edge modes at opposite sides, a small gap in their linear spectrum opens up in a narrow nanoribbon. This gap is shown to sharply increase with the perpendicular out-of-plane electric field, in contrast to the behavior in a wide nanoribbon with negligible edge modes interaction. The gap between the traditional electron and hole subbands also increases with the perpendicular electric field. The increase of both gaps leads to a rapid decrease of the ballistic nanoribbon conductance and current with the electric field, which can be used for designing molybdenum disulfide nanoribbon-based current switches.

Quantum electronic transport across ‘bite’ defects in graphene nanoribbons

On-surface synthesis has recently emerged as an effective route towards the atomically precise fabrication of graphene nanoribbons (GNRs) of controlled topologies and widths. However, whether and to what degree structural disorder occurs in the resulting samples is a crucial issue for prospective applications that remains to be explored. Here, we experimentally visualize ubiquitous missing benzene rings at the edges of 9-atom wide armchair nanoribbons that form upon cleavage of phenyl groups in the precursor molecules. These defects are referred to as ‘bite’ defects. First, we address their density and spatial distribution on the basis of scanning tunnelling microscopy and find that they exhibit a strong tendency to aggregate. Next, we explore their effect on the quantum charge transport from first-principles calculations, revealing that such imperfections substantially disrupt the conduction properties at the band edges. Finally, we generalize our theoretical findings to wider nanoribbons in a systematic manner, hence establishing practical guidelines to minimize the detrimental role of such defects on the charge transport. Overall, our work portrays a detailed picture of ‘bite’ defects in bottom-up armchair GNRs and assesses their effect on the performance of carbon-based nanoelectronic devices.

Disorder effects of vacancies on the electronic transport properties of realistic topological insulator nanoribbons: The case of bismuthene

The robustness of topological materials against disorder and defects is presumed but has not been demonstrated explicitly in realistic systems. In this work, we use state-of-the-art density functional theory and recursive nonequilibrium Green's functions methods to study the effect of disorder on the electronic transport of long nanoribbons, up to $157\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$, as a function of vacancy concentration. In narrow nanoribbons, a finite-size effect gives rise to hybridization between the edge states erasing topological protection. Hence, even small vacancy concentrations enable backscattering events. We show that the topological protection is more robust for wide nanoribbons, but surprisingly it breaks down at moderate structural disorder. Our study helps to establish some bounds on defective bismuthene nanoribbons as promising candidates for spintronic applications.

Narrower Nanoribbon Biosensors Fabricated by Chemical Lift-off Lithography Show Higher Sensitivity.

Wafer-scale nanoribbon field-effect transistor (FET) biosensors fabricated by straightforward top-down processes are demonstrated as sensing platforms with high sensitivity to a broad range of biological targets. Nanoribbons with 350 nm widths (700 nm pitch) were patterned by chemical lift-off lithography using high-throughput, low-cost commercial digital versatile disks (DVDs) as masters. Lift-off lithography was also used to pattern ribbons with 2 μm or 20 μm widths (4 or 40 μm pitches, respectively) using masters fabricated by photolithography. For all widths, highly aligned, quasi-one-dimensional (1D) ribbon arrays were produced over centimeter length scales by sputtering to deposit 20 nm thin-film In2O3 as the semiconductor. Compared to 20 μm wide microribbons, FET sensors with 350 nm wide nanoribbons showed higher sensitivity to pH over a broad range (pH 5 to 10). Nanoribbon FETs functionalized with a serotonin-specific aptamer demonstrated larger responses to equimolar serotonin in high ionic strength buffer than those of microribbon FETs. Field-effect transistors with 350 nm wide nanoribbons functionalized with single-stranded DNA showed greater sensitivity to detecting complementary DNA hybridization vs 20 μm microribbon FETs. In all, we illustrate facile fabrication and use of large-area, uniform In2O3 nanoribbon FETs for ion, small-molecule, and oligonucleotide detection where higher surface-to-volume ratios translate to better detection sensitivities.

Conductance in a Nanoribbon of Topologically Insulating MoS2 in the 1T’ Phase

The use of new materials with advanced properties has become mandatory to meet the needs for higher electronics performance at reduced power. Topological insulators (TIs) possess highly conductive topologically protected edge states which are insensitive to scattering and thus suitable for energy-efficient high-speed devices. Here, we evaluate the subband structure in a narrow nanoribbon of 1 $\text {T}^\prime$ molybdenum disulphide using an effective k.p Hamiltonian. Highly conductive topologically protected edge modes whose energies lie within the bulk band gap are investigated on equal footing with traditional electron and hole subbands. Due to the interaction between the edge modes at opposite sides, a small gap in their linear spectrum opens up in a narrow nanoribbon. This gap is shown to sharply increase with the perpendicular out-of-plane electric field, in contrast to the behavior in a wide nanoribbon with negligible edge modes’ interaction. This increase leads to a rapid decrease in the ballistic nanoribbon conductance and current with the electric field, which can be used for designing molybdenum disulphide nanoribbon-based current switches.

Sub-10 nm patterning of few-layer MoS2 and MoSe2 nanolectronic devices by oxidation scanning probe lithography

The properties of 2D materials devices are very sensitive to the physical, chemical and structural interactions that might happen during processing. Low-invasive patterning methods are required to fabricate devices at the nanoscale. Here we developed a process that combines oxidation scanning probe lithography (o-SPL) and oxygen plasma to fabricate nanoribbon field-effect transistors and nano-constrictions on few-layer MoS2 and MoSe2. The oxygen plasma has a double role in this process. First, it forms a thin, uniform oxide layer on top of the flake surface to enable o-SPL nanopatterning with full control of shape and size. Second, the oxide layer thins down the flake. Both plasma-based and o-SPL oxides are soluble in deionized H2O, which enabled etching and the definition of electrically isolated nano-constrictions and nanoribbons. The accuracy and robustness of the process was applied to pattern sub-10 nm wide constrictions and nanoribbon transistors.

Nanoribbon self-assembly and hydrogel formation from an N[sbnd]Octanoyl octapeptide derived from the antiparallel β-Interface of a protein homotetramer

The effect of installing different lipid chains (C6, C8, C10, and C16) on the N-terminus of an octapeptide derived from the antiparallel β-interface of the diaminopimelate decarboxylase protein homotetramer has been investigated. Notably, the C8 peptide conjugate assembled into wide twisted nanoribbons and formed hydrogels, which to the best of our knowledge constitutes the first example of a peptide containing an eight carbon alkyl chain that demonstrates these properties, a space typically occupied by peptide amphiphiles with long lipid chains. Furthermore, this self-assembling lipopeptide exhibited pH and temperature stability with shear thinning properties suitable for biomedical applications. Importantly, in this work the application of the polystyrene-based sorbent Diaion™ HP20SS for the simple large-scale purification of self-assembling peptides is presented as an alternative to the use of time-consuming and labor-intensive reverse-phase high-performance liquid chromatography. Statement of SignificancePeptides that can self-assemble into defined nanostructures are highly attractive for many biomedical applications given their unique physical and chemical properties. It is recognized that self-assembling peptides derived from naturally occurring proteins offer an unlimited source of functionalities and structures, which are hard to uncover with designed sequences. In this study, we have investigated the effect of installing different lipids chains on the N-terminus of an octapeptide derived from the antiparallel β-interface of the diaminopimelate decarboxylase protein homo tetramer. We also reported the use of polymeric DiaionⓇ HP20SS beads as an alternative solid support to purify self-assembling peptides.

Tuning electronic transport properties of wide antimonene nanoribbon via edge hydrogenation and oxidation

In this paper, we study the electronic structures and electronic transport properties of wide buckled and puckered antimonene nanoribbions (SbNRs) via edge hydrogenation and oxidation by using a first principle method. The calculated results show that the edge passivations play an important role in the band structures of wide buckled and puckered SbNRs. The current-voltage characteristics of buckled and puckered SbNRs consistent with their band structures. The currents of buckled and puckered SbNR devices via edge hydrogenation are nearly zero at low bias region, but the edge oxidation can enlarge the device’s conductance obviously. More importantly, the tunable negative differential resistance behavior can be found in the buckled and puckered SbNR devices via edge oxidation. Our researches are of great significance for the subsequent application of SbNR devices.

Progression of Self-Assembly of Amelogenin Protein Supramolecular Structures in Simulated Enamel Fluid.

Mechanisms of protein-guided mineralization in enamel, leading to organized fibrillar apatite nanocrystals, remain elusive. In vitro studies reveal recombinant human amelogenin (rH174), a matrix protein templating this process, self-assembles into a variety of structures. This study endeavors to clarify the self-assembly of rH174 in physiologically relevant conditions. Self-assembly in simulated enamel fluid was monitored up to 2 months. At alkali (7.3-8.7) and acidic (5.5-6.1) pH ranges, a distinct progression in formation was observed from nanospheres (17-23 nm) to intermediate-length nanorods, concluding with the formation of long 17-18 nm wide nanoribbons decorated with nanospheres. Assembly in acidic condition progressed quicker to nanoribbons with fewer persistent nanospheres. X-ray diffraction exhibited reflections characteristic of antiparallel β-sheets (4.7 and 9.65 Å), supporting the model of amyloid-like nanoribbon formation. This is the first observation of rH174 nanoribbons at alkaline pH as well as concurrent nanosphere formation, indicating both supramolecular structures are stable together under physiological conditions.

Electronic transport in graphene nanoribbons with disorder look at the pseudo-spin polarization: Dirac versus tight-binding model

We have compared results of electronic transport using two different approaches: Dirac vs tight-binding (TB) Hamiltonians to assesses disorder-induced effects in graphene nanoribbons. We apply the proposed Hamiltonians to calculate the density of states, the transmission along the ribbon, and the pseudo-spin polarization (P(E)) in metallic armchair graphene nanoribbons. We clearly show differences between these two approaches in the interference processes, especially in the low-lying energy limit, when the systems are found in the presence of random impurities (disorder). This allows us to find fingerprints associated with each model used. As the disorder increases, more robust electronic transmission (through polarized states in a given sublattice) arises when one is dealing with the Dirac model only. We also find with this model unexpected peaks in the P(E) far from the Dirac point for wider nanoribbons. In the other hand, the model TB show the Dirac limit with disturbances of the hyperboloid subbands for certain potentials of the impurities. In general, our study is indicating that a P(E) spectroscopy (analyzing the line width and intensity) can be used to detect fingerprints of the increase of asymmetry in the scattering processes and the transport limits where hyperboloid subbands are important.

Quantum phase transitions in effective spin-ladder models for graphene zigzag nanoribbons

We examine the magnetic correlations in quantum spin models that were derived recently as effective low-energy theories for electronic correlation effects on the edge states of graphene nanoribbons. For this purpose, we employ quantum Monte Carlo simulations to access the large-distance properties, accounting for quantum fluctuations beyond mean-field-theory approaches to edge magnetism. For certain chiral nanoribbons, antiferromagnetic inter-edge couplings were previously found to induce a gapped quantum disordered ground state of the effective spin model. We find that the extended nature of the intra-edge couplings in the effective spin model for zigzag nanoribbons leads to a quantum phase transition at a large, finite value of the inter-edge coupling. This quantum critical point separates the quantum disordered region from a gapless phase of stable edge magnetism at weak intra-edge coupling, which includes the ground states of spin-ladder models for wide zigzag nanoribbons. To study the quantum critical behavior, the effective spin model can be related to a model of two antiferromagnetically coupled Haldane-Shastry spin-half chains with long-ranged ferromagnetic intra-chain couplings. The results for the critical exponents are compared also to several recent renormalization group calculations for related long-ranged interacting quantum systems.

Normal and skewed phosphorene nanoribbons in combined magnetic and electric fields

The energy spectrum and eigenstates of single-layer black phosphorus nanoribbons in the presence of a perpendicular magnetic field and an in-plane transverse electric field are investigated by means of a tight-binding method, and the effect of different types of edges is examined analytically. A description based on a continuum model is proposed using an expansion of the tight-binding model in the long-wavelength limit. The wave functions corresponding to the flatband part of the spectrum are obtained analytically and are shown to agree well with the numerical results from the tight-binding method for both narrow (10 nm) and wide (100 nm) nanoribbons. Analytical expressions for the critical magnetic field at which Landau levels are formed and the ranges of wave numbers in the dispersionless flatband segments in the energy spectra are derived. We examine the evolution of the Landau levels when an in-plane lateral electric field is applied, and we determine analytically how the edge states shift with magnetic field. For wider nanoribbons, the conductance is shown to have a characteristic staircase shape in combined magnetic and electric fields. Some of the stairs in zigzag and skewed armchair nanoribbons originate from edge states that are found in the band gap.

From Half-Metal to Semiconductor: Electron-Correlation Effects in Zigzag SiC Nanoribbons From First Principles

Are we really sure about the electronic properties of zigzag silicon carbide nanoribbons (NRs)? Density-functional calculations at the mean-field level have predicted them to be intrinsically half-metallic. However, the authors' refined results, including electronic correlations and excitonic effects, show that wide NRs are semiconductors with spin-polarized states at the band gap, which could be useful for spintronic devices. Meanwhile, narrow NRs have strongly bound excitons that make them interesting for optoelectronics.