Nanoribbons Research Articles

Electronic and magnetic properties of 1 T-TiSe2 nanoribbons

Motivated by the recent synthesis of single layer TiSe2, we used state-of-the-art density functional theory calculations, to investigate the structural and electronic properties of zigzag and armchair-edged nanoribbons (NRs) of this material. Our analysis reveals that, differing from ribbons of other ultra-thin materials such as graphene, TiSe2 NRs have some distinctive properties. The electronic band gap of the NRs decreases exponentially with the width and vanishes for ribbons wider than 20 Å. For ultranarrow zigzag-edged NRs we find odd–even oscillations in the band gap width, although their band structures show similar features. Moreover, our detailed magnetic-ground-state analysis reveals that zigzag and armchair edged ribbons have non-magnetic ground states. Passivating the dangling bonds with hydrogen at the edges of the structures influences the band dispersion. Our results shed light on the characteristic properties of T phase NRs of similar crystal structures.

Enhanced Electrochemical H2 Evolution by Few‐Layered Metallic WS2(1−x)Se2x Nanoribbons

As an effective alternative to noble platinum electrocatalyst, earth abundant and inexpensive layered transition metal dichalcogenides (TMDs) are investigated for the hydrogen evolution reaction (HER). Compared with binary TMDs, the tunably composed ternary TMDs have hitherto received relatively little attention. Here, few‐layered ternary WS2(1−x)Se2x nanoribbons (NRs) with metallic 1T phases, much more catalytically active in HER, are prepared for the first time. The favorable ΔGHo introduced by the tensile region on the surface, along with the presence of local lattice distortions of the WS2(1−x)Se2x nanoribbons with metallic 1T phases, greatly promotes the HER process. These ternary NRs achieve the lowest overpotential of ≈0.17 V at 10 mA cm−2 and a Tafel slope of ≈68 mV dec−1 at a low catalyst loading (≈0.30 ± 0.02 mg cm−2). Notably, the long‐term durability suggests the potential of practical applications in acid electrolytes. The results here suggest that the ternary WS2(1−x)Se2x NRs with 1T phases are prominent alternatives to platinum‐based HER electrocatalysts.

Prediction and Synthesis of Strain Tolerant RbCuTe Crystals Based on Rotation of One-Dimensional Nano Ribbons within a Three-Dimensional Inorganic Network.

A unique possibility for a simple strain tolerant inorganic solid is envisioned whereby a set of isolated, one-dimensional (1D) nano objects are embedded in an elastically soft three-dimensional (3D) atomic matrix thus forming an interdimensional hybrid structure (IDHS). We predict theoretically that the concerted rotation of 1D nano objects could allow such IDHSs to tolerate large strain values with impunity. Searching theoretically among the 1:1:1 ABX compounds of I-I-VI composition, we identified, via first-principles thermodynamic theory, RbCuTe, which is a previously unreported but now predicted-to-be-stable compound in the MgSrSi-type structure, in space group Pnma. The predicted structure of RbCuTe consists of ribbons of copper and telluride atoms placed antipolar to one another throughout the lattice with rubidium atoms acting as a matrix. A novel synthetic adaptation utilizing liquid rubidium and vacuum annealing of the mixed elemental reagents in fused silica tubes as well as in situ (performed at the Advanced Photon Source) and ex situ structure determination confirmed the stability and predicted structure of RbCuTe. First-principles calculations then showed that the application of up to ∼30% uniaxial strain on the ground-state structure result in a buildup of internal stress not exceeding 0.5 GPa. The increase in total energy is 15-fold smaller than what is obtained for the same RbCuTe material but in structures having a contiguous set of 3D chemical bonds spanning the entire crystal. Furthermore, electronic structure calculations revealed that the HOMO is a 1D energy band localized on the CuTe ribbons and that the 1D insulating band structure is also resilient to such large strains. This combined theory and experiment study reveals a new type of strain tolerant inorganic material.

Synthesis of 4H/fcc-Au@Metal Sulfide Core-Shell Nanoribbons.

Although great advances on the synthesis of Au-semiconductor heteronanostructures have been achieved, the crystal structure of Au components is limited to the common face-centered cubic (fcc) phase. Herein, we report the synthesis of 4H/fcc-Au@Ag2S core-shell nanoribbon (NRB) heterostructures from the 4H/fcc Au@Ag NRBs via the sulfurization of Ag. Remarkably, the obtained 4H/fcc-Au@Ag2S NRBs can be further converted to a novel class of 4H/fcc-Au@metal sulfide core-shell NRB heterostructures, referred to as 4H/fcc-Au@MS (M = Cd, Pb or Zn), through the cation exchange. We believe that these novel 4H/fcc-Au@metal sulfide NRB heteronanostructures may show some promising applications in catalysis, surface enhanced Raman scattering, solar cells, photothermal therapy, etc.

Study of Nitrogen terminated doped zigzag GNR FET exhibiting negative differential resistance

This paper presents the study of Gallium and Aluminum doped Nitrogen terminated zigzag Graphene Nano Ribbon (GNR) FET with high-k dielectric. The GNR FET structure has been designed and simulated using Quantumwise Atomistix Toolkit software package. The presented GNR FET with n-type (Nitrogen doped) electrodes and p-type (Gallium or Aluminum doped) scattering region are simulated and analyzed using Density Functional Theory combined with NEGF formalism and Device Density of States (DDOS). The device shows a negative differential resistance phenomenon which can be controlled by the gate of the zigzag GNR FET. It is found that doping of Gallium and Aluminum in scattering region provides higher drain current, higher ION/IOFF and IP/IV ratios as compared to that of Boron doped zigzag GNR FET. The potential applications of the device are in logical, high frequency, and memory devices.

Surface plasmon propelled high-performance CdSe nanoribbons photodetector.

In this work, we present a plasmonic photodetector (PPD) with high sensitivity to red light illumination. The ultrasensitive PPD was composed of high-crystalline CdSe nanoribbons (NRs) decorated with plasmonic hollow gold nanoparticles (HGNs) on the surface, which were capable of coupling the incident light due to localized surface plasmon resonance (LSPR). Device analysis reveals that after modification of HGNs, both responsivity and detectivity were considerably improved. Further device performance analysis and theoretical simulation based on finite element method (FEM) find that the optimized performance is due to HGNs induced localized field enhancement and direct electron transfer.

Divacancy-induced ferromagnetism in graphene nanoribbons

Zigzag graphene nanoribb ons have spin-polarized edges, anti-ferromagnetically coupled in the ground state with total spin zero. Customarily, these ribbons are made ferromagnetic by producing an imbalance between the two sublattices. Here we show that zigzag ribbons can be ferromagnetic due to the presence of reconstructed divacancies near one edge. This effect takes place despite the divacancies are produced by removing two atoms from opposite sublattices, being balanced before reconstruction to 5-8-5 defects. We demonstrate that there is a strong interaction between the defect-localized and edge bands which mix and split away from the Fermi level. This splitting is asymmetric, yielding a net edge spin-polarization. Therefore, the formation of reconstructed divacancies close to the edges of the nanoribbons can be a practical way to make them partially ferromagnetic.

Room temperature ppb level H2S detection of a single Sb-doped SnO2 nanoribbon device

Sb-doped SnO2 nanoribbons (NRs) with a single crystal structure are synthesized via thermal evaporation. H2S gas sensor is developed based on a single Sb-SnO2 NR through dual-ion beam sputtering deposition with a mask template. The response of the Sb-SnO2 NR sensor has been measured up to 56–100ppm of H2S at 150°C. More importantly, this sensor shows a response of 10(1.6) toward 100ppb of H2S at 150°C(25°C), which promotes the detection limit of H2S. The NR-based sensor also exhibits a high sensitivity, good selectivity and long-term stability with a prompt response time, demonstrating good sensing capabilities at room temperature. The mechanism for enhanced sensing performance of Sb-doped SnO2 nanoribbon is discussed.

Ultraviolet nano-photodetector based on ZnS:Cl nanoribbon/Au Schottky junctions

We report on a semiconductor nanostructures/metal Schottky junction for optoelectronic device application. The n-type ZnS nanoribbons (NRs) with an electron mobility of 64.9 cm V−1 s−1 and electron concentration of 5.7 × 1017 cm−3 were synthesized by using Cl as dopant via a thermal co-evaporation method. Electrical analysis reveals that the Schottky barrier diodes (SBD) based on the ZnS:Cl NRs/Au junctions exhibited typical rectifying behavior (rectification ratio >103) with Schottky barrier height of .64 eV and a small ideality factor of ~1.05 at 320 K. Interestingly, n-ZnS:Cl NR/Au nano-SBD device exhibited pronounced negative photoresponse at forward bias, but positive photoresponse at reverse bias under 365 nm UV light irradiation. Finally, the detailed reason for this phenomenon was explained by the energy band diagram.

MoO3 Nanodots Decorated CdS Nanoribbons for High-Performance, Homojunction Photovoltaic Devices on Flexible Substrates.

The p-n homojunctions are essential components for high-efficiency optoelectronic devices. However, the lack of p-type doping in CdS nanostructures hampers the fabrication of efficient photovoltaic (PV) devices from homojunctions. Here we report a facile solution-processed method to achieve efficient p-type doping in CdS nanoribbons (NRs) via a surface charge transfer mechanism by using spin-coated MoO3 nanodots (NDs). The NDs-decorated CdS NRs exhibited a hole concentration as high as 8.5 × 10(19) cm(-3), with the p-type conductivity tunable in a wide range of 7 orders of magnitude. The surface charge transfer mechanism was characterized in detail by X-ray photoelectron spectroscopy, Kelvin probe force microscopy, and first-principle calculations. CdS NR-homojunction PV devices fabricated on a flexible substrate exhibited a power conversion efficiency of 5.48%, which was significantly better than most of the CdS nanostructure-based heterojunction devices, presumably due to minimal junction defects. Devices made by connecting cells in series or in parallel exhibited enhanced power output, demonstrating the promising potential of the homojunction PV devices for device integration. Given the high efficiency of the surface charge transfer doping and the solution-processing capability of the method, our work opens up unique opportunities for high-performance, low-cost optoelectronic devices based on CdS homojunctions.

Mechanical Properties of Graphene Nano Ribbon and Their Nanocomposites

Mechanical Properties of Graphene Nano Ribbon and Their Nanocomposites

Modeling the Charge Transport in Graphene Nano Ribbon Interfaces for Nano Scale Electronic Devices

In this research work we have modeled, simulated and compared the electronic charge transport for Metal-Semiconductor-Metal interfaces of Graphene Nano Ribbons (GNR) with different geometries using First-Principle calculations and Non-Equilibrium Green's Function (NEGF) method. We modeled junctions of Armchair GNR strip sandwiched between two Zigzag strips with (Z-A-Z) and Zigzag GNR strip sandwiched between two Armchair strips with (A-Z-A) using semi-empirical Extended Huckle Theory (EHT) within the framework of Non-Equilibrium Green Function (NEGF). I-V characteristics of the interfaces were visualized for various transport parameters. The distinct changes in conductance and I-V curves reported as the Width across layers, Channel length (Central part) was varied at different bias voltages from -1V to 1 V with steps of 0.25 V. From the simulated results we observed that the conductance through A-Z-A graphene junction is in the range of 10-13 Siemens whereas the conductance through Z-A-Z graphene junction is in the range of 10-5 Siemens. These suggested conductance controlled mechanisms for the charge transport in the graphene interfaces with different geometries is important for the design of graphene based nano scale electronic devices like Graphene FETs, Sensors.

Effect of external strain on electronic structure of stanene

In this article we study the effect of applied strain on the electronic and mechanical properties of stanene, the Tin counterpart of graphene. Due to the relatively large intrinsic spin–orbit coupling we used the fully-relativistic pseudo-potentials to consider the effect of spin–orbit in the density functional calculations. The spin–orbit interaction opens a 70meV energy gap in the K point but by applying strain the energy gap in the band structure is closed. The density functional theory and simple molecular mechanic models are used to estimate the Young’s modulus of stanene. According to our calculations we estimate the in-plane stiffness of stanene Ys=40N/m. By matching DFT and molecular mechanic results of stanene, we investigate the size and chirality effects on the in-plane stiffness of stanene nano ribbons.

Fabrication of Pyrene and Tetraphenylethylene Nanostructures by a Hydrolysis‐Assisted Co‐Assembly

AbstractThe poly(allylamine hydrochloride)‐g‐pyrene‐tetraphenylethylene (PAH‐g‐Py‐g‐TPE) copolymers with different ratios of Py and TPE are synthesized by grafting 1‐pyrenecarboxaldehyde (Py‐CHO) and tetraphenylethylenecarboxaldehyde (TPE‐CHO) to PAH via a Schiff base reaction in methanol. The PAH‐g‐Py‐g‐TPE forms spherical micelles in water regardless of the ratios of Py and TPE, which can transform into different nanostructures after being incubated in pH 0 and pH 2 solutions, respectively. These nanomaterials including nanoparticles (NPs), nanorods (NRs), nanotubes (NTs) and nanoribbons (NBs) are composed of Py‐CHO and TPE‐CHO with different ratios, and emit fluorescence with colors different from the pure Py NRs and NTs, and TPE NPs.

Synthesized multiwall MoS2 nanotube and nanoribbon field-effect transistors

We report on the fabrication and characterization of synthesized multiwall MoS2 nanotube (NT) and nanoribbon (NR) field-effect transistors (FETs). The MoS2 NTs and NRs were grown by chemical transport, using iodine as a transport agent. Raman spectroscopy confirms the material as unambiguously MoS2 in NT, NR, and flake forms. Transmission electron microscopy was used to observe cross sections of the devices after electrical measurements and these were used in the interpretation of the electrical measurements, allowing the estimation of the current density. The NT and NR FETs demonstrate n-type behavior, with ON/OFF current ratios exceeding 103, and with current densities of 1.02 μA/μm and 0.79 μA/μm at VDS = 0.3 V and VBG = 1 V, respectively. Photocurrent measurements conducted on a MoS2 NT FET revealed short-circuit photocurrent of tens of nanoamps under an excitation optical power of 78 μW and 488 nm wavelength, which corresponds to a responsivity of 460 μA/W. A long channel transistor model was used to model the common-source characteristics of MoS2 NT and NR FETs and was shown to be consistent with the measured data.

Surface charge transfer induced p-CdS nanoribbon/n-Si heterojunctions as fast-speed self-driven photodetectors

Heterojunctions composed of single p-type CdS nanoribbons (NRs) and n-type silicon (Si) were successfully fabricated and can be applied as fast-speed self-driven visible photodetectors.

Effects of Position and Shape of Atomic Defects on the Band Gap of Graphene Nano Ribbon Superlattices

In this work, we study the behavior of introducing atomic size vacancy in a graphene nanoribbon superlattice. Our investigations are based on the density functional theory (DFT) with the Local Density Approximation in Atomistix Toolkit (ATK). We show that, in addition to its shape, the position of vacancy has a major impact on the electrical properties of a graphene nanoribbon superlattice. We show that the band gap of an armchair graphene nanoribbon may be tuned by introducing an appropriate periodic pattern of vacancies. The band gap changes in a zig-zag manner similar to the variation of band gap of a graphene nanoribbon by changing its width. Keywords—Antidot, Atomistix ToolKit, Superlattice, Vacancy.

Improving Ion/Ioff in dual-gate graphene nanoribbon field-effect transistors using local uniaxial tensile strain

In this work, we present the Dual-Gate Graphene Nano Ribbon Field Effect Transistor (DG-GNRFET) under local uniaxial strain in source and drain regions as a device suitable for switching applications. Our investigations are based on the 2D Poisson based on an atomistic mode-space approach and Schrodinger equations, within the Non-Equilibrium Green’s (NEGF). We show a high on-current and on–off ratio which can be obtained using the combination of techniques such as applying uniaxial strain to the portion of channel/source regions and the gate overlap. We followed an optimization process to find the best performance of the device. Finally, the proposed device shows a higher on-current and on–off ratio becomes about 100 times greater than of the unstrained device.

Silicane nanoribbons: electronic structure and electric field modulation

We present electronic band structure, Gibbs free energy of formation, and electric field modulation calculations for silicane nanoribbons (NRs), i.e., completely hydrogenated or fluorinated silicene NRs, using density functional theory. We find that although the completely hydrogenated silicene (H-silicane) sheet in the chair-like configuration is an indirect-band-gap semiconductor, a direct band gap can be achieved in the zigzag H-silicane NRs by using Brillouin-zone folding. Compared to H-silicane NRs, the band gaps of completely fluorinated silicene (F-silicane) NRs reduce at least by half. For all silicane NRs considered here, the Gibbs free energy of formation is negative but shows different trends by changing the ribbon width for H-silicane NRs and F-silicane NRs. Furthermore, by analyzing the effect of transverse electric fields on the electronic properties of silicane NRs, we show that an external electric field can make the electrons and holes states spatially separated and even render silicane NRs self-doped. The tunable electronic properties of silicane NRs make them suitable for nanotechnology application.

Possible polaron formation of zigzag graphene nano-ribbon in the presence of Rashba spin–orbit coupling

In this article we study the role of Rashba spin–orbit coupling and electron–phonon interaction on the electronic structure of zigzag graphene nanoribbon with different width. The total Hamiltonian of nanoribbon is written in the tight binding form and the electron–electron interaction is modeled in the Hubbard term. We used a unitary transformation to reach an effective Hamiltonian for nano ribbon in the presence of electron–phonon interaction. Our results show that small Rashba spin orbit coupling annihilates the anti-ferromagnetic phase in the zigzag edges of ribbon and the electron–phonon interaction yields small polaron formation in graphene nano ribbon. Furthermore, Rashba type spin–orbit coupling increases (decreases) the polaron formation energy for up (down) spin state.