Nanoribbon Heterostructures Research Articles

Hydrogen production of overall water splitting with direct Z-scheme driven by antimonene and arsenide nanoribbon heterostructures: Insight from electronic properties and carrier nonadiabatic dynamics

Two nanoribbon heterostructures are suitable for driving efficient direct Z-schemes of the photocatalytic overall water splitting for hydrogen production and are screened out of nine heterostructures constructed from edge-passivated antimonene (SbNR-X) and arsenide (AsNR-X, X = F, Cl, CN) nanoribbons. The solar-to-hydrogen (STH) efficiency and the Gibbs free energies (ΔGs) of the redox reactions at different sites are calculated to identify the preferable Z-schemes. Meanwhile, the transfer and recombination of the photogenerated carriers are explored by using nonadiabatic molecular dynamics (NAMD) simulations. The obtained band alignments and built-in electric fields of the two considered heterostructures can match the requirements of the photocatalytic Z-scheme, and the corresponding STH efficiencies can reach 15.04 % and 30.53 %, respectively. The oxidation evolution reactions can proceed spontaneously, and hydrogen evolution reactions are feasible in thermodynamics. NAMD simulations show that the SbNR-CN/AsNR-CN nanoribbon heterostructure has faster interlayer recombination but slower transfer of the photogenerated electron from the SbNR-CN to AsNR-CN nanoribbons and of the photogenerated hole along the reversible direction, indicating that this heterostructure has a higher carrier utilization rate. These findings confirm that the SbNR-CN/AsNR-CN nanoribbon heterostructure is a promising candidate for developing high STH efficiency materials with direct Z-schemes.

Thermal rectification through the topological states of asymmetrical length armchair graphene nanoribbons heterostructures with vacancies

We present a theoretical investigation of electron heat current in asymmetrical length armchair graphene nanoribbon (AGNR) heterostructures with vacancies, focusing on the topological states (TSs). In particular, we examine the 9-7-9 AGNR heterostructures where the TSs are well-isolated from the conduction and valence subbands. This isolation effectively mitigates thermal noise of subbands arising from temperature fluctuations during charge transport. Moreover, when the TSs exhibit an orbital off-set, intriguing electron heat rectification phenomena are observed, primarily attributed to inter-TS electron Coulomb interactions. To enhance the heat rectification ratio (η Q ), we manipulate the coupling strengths between the heat sources and the TSs by introducing asymmetrical lengths in the 9-AGNRs. This approach offers control over the rectification properties, enabling significant enhancements. Additionally, we introduce vacancies strategically positioned between the heat sources and the TSs to suppress phonon heat current. This arrangement effectively reduces the overall phonon heat current, while leaving the TSs unaffected. Our findings provide valuable insights into the behavior of electron heat current in AGNR heterostructures, highlighting the role of topological states, inter-TS electron Coulomb interactions, and the impact of structural modifications such as asymmetrical lengths and vacancy positioning. These results pave the way for the design and optimization of graphene-based devices with improved thermal management and efficient control of electron heat transport.

Transition Metal Dichalcogenides Heterostructures Nanoribbons

The integration of two-dimensional van der Waals (vdW) heterostructures breaks through the constraints of lattice matching and symmetry, offering substantial opportunities in the development of advanced materials. After the width is reduced, one-dimensional vdW heterostructures show rich band structures and strong spin–orbit coupling behaviors, widening the applications in optoelectronics and spintronics. However, the synthesis of one-dimensional vdW heterostructure nanoribbons has rarely been reported yet. Herein, we report a general approach to realizing transition metal dichalcogenide (TMD) heterostructure nanoribbons for the first time by unzipping self-assembled TMD heterostructure nanoscrolls. As demonstrated by MoS2/WS2 nanoribbons, the obtained TMD heterostructure nanoribbons with alternating stacked layers possess flat edge structures and high quality. Meanwhile, this strategy can be extended to create diverse vdW TMD nanoribbons, demonstrating its versatility. Our work thus shows great potential to prepare TMD heterostructure nanoribbons with various compositions and stacking modes, and new structures can be customized with targeted properties.

Photoresponse of Solution-Synthesized Graphene Nanoribbon Heterojunctions on Diamond Indicating Phototunable Photodiode Polarity

Graphene nanoribbon heterostructures and heterojunctions have attracted interest as next-generation molecular diodes with atomic precision. Their mass production via solution methods and prototypical device integration remains to be explored. Here, the bottom-up solution synthesis and characterization of liquid-phase-processable graphene nanoribbon heterostructures (GNRHs) are demonstrated. Joint photoresponsivity measurements and simulations provide evidence of the structurally defined heterostructure motif acting as a type-I heterojunction. Real-time, time-dependent density functional tight-binding simulations further reveal that the photocurrent polarity can be tuned at different excitation wavelengths. Our results introduce liquid-phase-processable, self-assembled heterojunctions for the development of nanoscale diode circuitry and adaptive hardware.

Ordered Van der Waals Hetero-nanoribbon from Pressure-Induced Topochemical Polymerization of Azobenzene.

Pressure-induced topochemical polymerization of molecular crystals with various stackings is a promising way to synthesize materials with different co-existing sub-structures. Here, by compressing the azobenzene crystal containing two kinds of intermolecular stacking, we synthesized an ordered van der Waals carbon nanoribbon (CNR) heterostructure in one step. Azobenzene polymerizes via a [4 + 2] hetero-Diels-Alder (HDA) reaction of phenylazo-phenyl in layer A and a para-polymerization reaction of phenyl in layer B at 18 GPa, as evidenced by in situ Raman and IR spectroscopies, X-ray diffraction, as well as gas chromatography-mass spectrometry and the solid-state nuclear magnetic resonance of the recovered products. The theoretical calculation shows that the obtained CNR heterostructure has a type II (staggered) band gap alignment. Our work highlights a high-pressure strategy to synthesize bulk CNR heterostructures.

Band structure engineering and transport properties of graphene/BN van der Waals heterostructures

It is an important topic in spintronics to find regulable half-metallic materials. In this work, by using density functional theory and nonequilibrium Green’s functional method, we find that the van der Waals heterostructures formed by zigzag-edged boron nitride nanoribbons and zigzag-edged graphene nanoribbons (ZGNRs) are spin splitting semiconductors. The energy band gap of the heterostructures can be regulated by applying a local voltage and the semiconductor–metal–semiconductor phase transition can be realized. Two spin-dependent transport devices are constructed based on the heterostructures. One device can generate a fully spin-polarized current within a small bias range, and the other device can generate high spin polarization within a large bias range. Moreover, based on zigzag-edged graphene/boron nitride nanoribbon (ZGBNNR) heterostructures, a dual-probe device with double vertical gates in the electrode regions is designed, which can form a metal–semiconductor–metal tunneling device. These findings indicate that ZGBNNRs can be used in excellent spintronic devices.

Tuning the thermoelectric properties of doped silicene nanoribbon heterostructures

In this work, we investigate the thermoelectrical properties of a silicene nanoribbon heterostructure composed of a central conductor fully doped with ad-atoms and connected to two pristine leads of the same material. Using a tight-binding Hamiltonian, we have calculated the system’s thermoelectric properties as a function of the geometrical confinement and external field. Our results exhibit an enhancement of the thermopower when a transverse electric field is applied to the conductor region for different temperatures. In addition, a violation of the Wiedemann–Franz law is observed around the ad-atom energy. Our results suggest the thermoelectric properties of doped silicene nanoribbons can be efficiently tuned with external perturbations.

Two‐Step Magnetic‐Pulling Chemical Vapor Deposition Growth of CdS1−xSex Lateral Nanoribbon Heterostructures for High‐Performance Photodetectors

Bandgap integration in a single semiconductor nanostructure is an important task for their applications in photonics and photoelectronics. Herein a two‐step growth of CdS x Se1−x alloy nanoribbon heterostructures along the lateral direction by an improved two‐step magnetic‐pulling chemical vapor deposition (CVD) method is reported. Microstructural characterizations further demonstrate that these ribbons are formed by two separate components along the lateral direction of the nanoribbons, including CdS0.76Se0.24 at the central region and CdS0.44Se0.56 at both lateral sides, respectively. Under a laser excitation, photoluminescence spectrum and 2D emission mapping at the junctions show two different emission bands at 555 and 603 nm, which show agreement with the structural characterization results. More importantly, under 355 nm laser illumination, room‐temperature dual‐wavelength lasing with peak center at 542.3 and 605.2 nm is realized using these sandwich‐like nanoribbons. Additionally, photodetectors based on these achieved nanoribbons are fulfilled with great performance of high responsivity (2.4 × 104 A W−1), high external quantum efficiency of 2.9 × 105%, fast response speed (rise ≈25 ms, decay ≈21 ms), and high I on/I off ratio (106). These structures may offer an interesting system for exploring new applications in multifunctional nanophotonic and optoelectronic devices, such as high‐performance detectors, miniature tunable lasers, and high‐density color displays.

Modeling of a vertical tunneling transistor based on Gr-hBN- χ 3 borophene heterostructure

We present a computational study on the electrical behavior of the field-effect transistor based on vertical graphene-hBN-χ3 borophene heterostructure and vertical graphene nanoribbon-hBN-χ3 borophene nanoribbon heterostructure. We use nonequilibrium the Green function formalism along with an atomistic tight-binding (TB) model. The TB parameters are calculated by fitting tight-binding band structure and first-principle results. Also, electrical characteristics of the device, such as ION/IOFF ratio, subthreshold swing, and intrinsic gate-delay time, are investigated. We show that the increase of the hBN layer number decreases subthreshold swing and degrades the intrinsic gate-delay time. The device allows current modulation 177 at room temperature for a 1.2 V gate-source bias voltage.

Thermoelectric transport properties of armchair graphene nanoribbon heterostructures

In this paper, we numerically analyze the thermoelectric (TE) properties of recently synthesized graphene nanoribbon (GNR) heterostructures that are obtained as extensions of pristine armchair graphene nanoribbons (AGNRs). After simulating their band structure through a nearest-neighbor tight-binding model, we use the Landauer formalism to calculate the necessary TE coefficients, with which we obtain the electrical conductance G, thermopower S, thermal conductance K e , linear-response thermocurrent , and figure of merit ZT (using literature results for the phonon thermal conductance K ph ), at room temperature. We then compare the results for the nanoribbon heterostructures with those for the pristine AGNR nanoribbons. The comparison shows that the metallic AGNRs become semiconducting (with much higher ZT values) after the inclusion of the extensions that transform them into heterostructures and that some heterostructures have higher values of ZT when compared to the semiconducting pristine AGNRs from which they have originated.

Charge transport in topological graphene nanoribbons and nanoribbon heterostructures

The structure of graphene nanoribbons crucially affects their electronic properties and transport. Here, the authors elucidate the transport in various nanoribbons and nanoribbon heterostructures via transport measurements with the scanning tunneling microscope and theoretical modeling based on an atomistic mean-field Hubbard model. This reveals an intricate interplay between transport, topology, eigenstate localization, magnetism, and emergent negative differential resistance.

Ferromagnetism in armchair graphene nanoribbon heterostructures

We study the properties of flat-bands that appear in a heterostructure composed of strands of different widths of graphene armchair nanoribbons. One of the flat-bands is reminiscent of the one that appears in pristine armchair nanoribbons and has its origin in a quantum mechanical destructive interference effect, dubbed `Wannier orbital states' by Lin et al. in Phys. Rev. B 79, 035405 (2009). The additional flat-bands found in these heterostructures, some reasonably closer to the Fermi level, seem to be generated by a similar interference process. After doing a thorough tight-binding analysis of the band structures of the different kinds of heterostructures, focusing in the properties of the flat-bands, we use Density Functional Theory to study the possibility of magnetic ground states when placing, through doping, the Fermi energy close to the different flat-bands. Our DFT results confirmed the expectation that these heterostructures, after being appropriately hole-doped, develop a ferromagnetic ground state that seems to require, as in the case of pristine armchair nanoribbons, the presence of a dispersive band crossing the flat-band. In addition, we found a remarkable agreement between the tight-binding and DFT results for the charge density distribution of the so-called Wannier orbital states.

Expanding the Conjugate Structure of Polymeric Carbon Nitride for Enhanced Light Absorption and Photothermal Conversion.

The development of efficient and inexpensive materials for light energy conversion is very important for achieving sustainable energy supply and carbon neutrality. Polymeric carbon nitride has become a promising material for light energy conversion due to its advantages of simple preparation and high physical and chemical stability. However, the pristine polymeric carbon nitride only absorbs light with a wavelength of less than 450nm, and the energy conversion for low-energy photons is very limited. Here, by introducing the pyromellitic dianhydride component to construct an in-plane heterostructure, the conjugated structure of polymeric carbon nitride is successfully expanded. This in-plane carbon nitride-carbon nanoribbon (C3 N4 -C) heterostructure has an ultrawide absorption range from 200 to 2000nm. Compared with the original material, the photothermal conversion performance of C3 N4 -C is significantly improved under the irradiation of Xe lamp or infrared laser. Furthermore, C3 N4 -C exhibits good potential for synergistic photothermal and chemotherapy. This work provides a simple strategy to construct expanded conjugate structure for improved light absorption and energy conversion materials based on polymeric carbon nitride.

Ti3 C2 Tx MXene Conductive Layers Supported Bio-Derived Fex -1 Sex /MXene/Carbonaceous Nanoribbons for High-Performance Half/Full Sodium-Ion and Potassium-Ion Batteries.

Owing to their cost-effectiveness and high energy density, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are becoming the leading candidates for the next-generation energy-storage devices replacing lithium-ion batteries. In this work, a novel Fex -1 Sex heterostructure is prepared on fungus-derived carbon matrix encapsulated by 2D Ti3 C2 Tx MXene highly conductive layers, which exhibits high specific sodium ion (Na+ ) and potassium ion (K+ ) storage capacities of 610.9 and 449.3mAhg-1 at a current density of 0.1Ag-1 , respectively, and excellent capacity retention at high charge-discharge rates. MXene acts as conductive layers to prevent the restacking and aggregation of Fex -1 Sex sheets on fungus-derived carbonaceous nanoribbons, while the natural fungus functions as natural nitrogen/carbon source to provide bionic nanofiber network structural skeleton, providing additional accessible pathways for the high-rate ion transport and satisfying surface-driven contribution ratios at high sweep rates for both Na/K ions storages. In addition, in situ synchrotron diffraction and ex situ X-ray photoelectron spectroscopy measurements are performed to reveal the mechanisms of storage and de-/alloying conversion process of Na+ in the Fex -1 Sex /MXene/carbonaceous nanoribbon heterostructure. As a result, the assembled Na/K full cells containing MXene-supported Fex -1 Sex @carbonaceous anodes possess stable large-ion storage capabilities.

Improvement of electronic and transport properties of graphene nanoribbon by simultaneous substitution of graphane and fluorographane

We investigate the electronic and transport properties of the graphene heterostructure nanoribbons terminated by H/H and F/F atoms, which are formed by partially substituting graphane and fluorographane nanoribbons into both edge parts of graphene nanoribbons, using the nonequilibrium Green's functions (NEGF) combined with the density functional theory (DFT). The calculated structural stability shows that all hybrid systems are stable than pristine GNRs. In particular, the hybrid systems terminated by F/F atoms are structurally more favorable than that of H/H ones. Our results indicate that armchair hybrid systems are nonmagnetic semiconductors with wide direct band gaps regardless of their spin polarizations, whereas zigzag systems have the half-metal or half-semiconducting behavior according to their spin polarizations. With the increase of nanoroad, band gaps increase (decrease) to different attributes. Interestingly, h-ZGAx/G8-2xNR/FGxNRs may produce from half-metal to half-semiconducting behavior transition, due to chemical potential change according to ribbon widths and nanoroads. Moreover, the calculated I–V curve exhibits negative differential resistance, which can be used for application in molecular spin electronic device.

Thermal conductivity of graphene/graphane/graphene heterostructure nanoribbons: Non-equilibrium molecular dynamics simulations

We investigate thermal conductivity of graphene/graphane/graphene heterostructure nanoribbons, which are constructed by substituting graphane nanoribbons into middle part of the armchair graphene nanoribbons, using non-equilibrium molecular dynamics. Effects of hydrogen atoms in middle graphane nanoribbons, H-termination on edge, width, and H coverage on thermal conductivity of the heterostructure nanoribbons were clarified. The thermal conductivity of the heterostructure nanoribbons are at least one order less than that of graphene nanoribbons. Reduction of thermal conductivity decreases, as width of the heterostructure nanoribbons and adsorption width increase. Reduction of thermal conductivity in graphene by hydrogen-functionalization can be used to control the thermal transportation properties. The graphene/graphane/graphene heterostructure nanoribbons may be candidate for high merit of figure thermoelectric conversion material with low thermal conductivity and high electric conductivity.

Improving the thermoelectric properties of graphene through zigzag graphene–graphyne nanoribbon heterostructures

Thermoelectric materials can convert thermal energy and electrical energy into each other, which have attracted extensive attention in recent years. In this paper, we systematically investigate the ballistic thermoelectric performance of four zigzag graphene–graphyne nanoribbon heterostructures M $$i(i=1{-}4)$$ through utilizing non-equilibrium Green’s function method. Our results show that heterostructures possess superior thermoelectric properties with respect to pristine graphene nanoribbon. Especially, the ZT value of M4 reaches 1.5 at 700 K, which is about 15 times that of graphene. Such improvement mainly originates from the reduction of phononic and electronic thermal conductance and the increase of Seebeck coefficient. Meanwhile, because M4 has the lowest phonon thermal conductance and favorable thermal power, its thermoelectric figure of merit is the best. These findings in this paper demonstrate that heterostructure is a viable approach to optimize the thermoelectric performance of graphene, which provides useful guidance for the design and fabrication of nanoscale thermoelectric devices.

Microbe-Assisted Assembly of Ti3C2Tx MXene on Fungi-Derived Nanoribbon Heterostructures for Ultrastable Sodium and Potassium Ion Storage.

As a typical family of two-dimensional (2D) materials, MXenes present physiochemical properties and potential for use in energy storage applications. However, MXenes suffer some of the inherent disadvantages of 2D materials, such as severe restacking during processing and service and low capacity of energy storage. Herein, a MXene@N-doped carbonaceous nanofiber structure is designed as the anode for high-performance sodium- and potassium-ion batteries through an in situ bioadsorption strategy; that is, Ti3C2Tx nanosheets are assembled onto Aspergillus niger biofungal nanoribbons and converted into a 2D/1D heterostructure. This microorganism-derived 2D MXene-1D N-doped carbonaceous nanofiber structure with fully opened pores and transport channels delivers high reversible capacity and long-term stability to store both Na+ (349.2 mAh g-1 at 0.1A g-1 for 1000 cycles) and K+ (201.5 mAh g-1 at 1.0 A g-1 for 1000 cycles). Ion-diffusion kinetics analysis and density functional theory calculations reveal that this porous hybrid structure promotes the conduction and transport of Na and K ions and fully utilizes the inherent advantages of the 2D material. Therefore, this work expands the potential of MXene materials and provides a good strategy to address the challenges of 2D energy storage materials.

Far-infrared photodetection in graphene nanoribbon heterostructures with black-phosphorus base layers

We propose far-infrared photodetectors with the graphene nanoribbon (GNR) array as the photosensitive element and the black phosphorus (bP) base layer (BL). The operation of these GNR infrared photodetectors (GNR-IPs) is associated with the interband photogeneration of the electron–hole pairs in the GNR array followed by the tunneling injection of either electrons or holes into a wide gap bP BL. The GNR-IP operating principle is akin to that of the unitraveling-carrier photodiodes based on the standard semiconductors. Due to a narrow energy gap in the GNRs, the proposed GNR-IPs can operate in the far-, mid-, and near-infrared spectral ranges. The cut-off photon energy, which is specified by the GNR energy gap (i.e., is dictated by the GNR width), can be in the far-infrared range, being smaller that the energy gap of the bP BL of ΔG ≃ 300 meV. Using the developed device models of the GNR-IPs and the GNR-IP terahertz photomixers, we evaluate their characteristics and predict their potential performance. The speed of the GNR-IP response is determined by rather short times: the photocarrier try-to-escape time and the photocarrier transit time across the BL. Therefore, the GNR-IPs could operate as terahertz photomixers. The excitation of the plasma oscillations in the GNR array might result in a strong resonant photomixing.

High performance terahertz anisotropic absorption in graphene–black phosphorus heterostructure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61865009 and 61927813).

Graphene and black phosphorus have attracted tremendous attention in optics due to their support of localized plasmon resonance. In this paper, a structure consisted of graphene–black phosphorus heterostructure is proposed to realize terahertz anisotropic near-perfect absorption. We demonstrate that strong plasmonic resonances in graphene–black phosphorus heterostructure nanoribbons can both be provided along armchair and zigzag directions, and dominated by the distance between the graphene and black phosphorus ribbons. In particular, the maximum absorption of 99.6% at 10.2 THz along armchair direction can be reached. The proposed high performance anisotropic structure may have promising potential applications in photodetectors, biosensors, and terahertz imaging.