Properties Of Ribbons Research Articles

Strain-induced valley conductance recovery in four-terminal graphene device

We investigated the valley dependent transport properties of a zigzag graphene ribbon attached with two strained side arms. The conductance of the zigzag ribbon for each valley is increased by the strain of the side arms. On the curves of conductance versus energy, step-like structures appear in some energy intervals, and in such intervals, the conductance does not decay when increasing the length of the intersection region. By applying a strain exceeding a critical amount, the conductance of valley K (K′) for the negative (positive) energies can be recovered to that of a graphene ribbon without side arms attached. The critical strain is compressive and is evaluated as about −10%. We explained all the features by means of the energy dispersion of the injection ribbon and that of the strained region.

On the magnetic anisotropy in Fe78Si9B13 ingots and amorphous ribbons: Orientation aligning of Fe-based phases/clusters

Magnetic anisotropy in Fe-based amorphous ribbon plays an important role in various applications and is still not fully understood. To gain an in-depth understanding of this phenomenon, the structure and magnetic properties of Fe78Si9B13 master alloy ingots and melt-spun amorphous ribbons were measured by various techniques. For the ingot samples, both the <100>α-Fe and <001>Fe2B axes are aligned parallel with the radial direction (RD) of the original cylindrical ingot, i.e. the maximum temperature gradient direction, and their other orthogonal axes have several preferred directions in the plane vertical to RD. The hard magnetic axis of the ingot samples is parallel to RD, which is due to the large magnetocrystalline anisotropy energy difference between <001> and {001} of the Fe2B phase. For the amorphous ribbons, there is an in-plane magnetic anisotropy: the easy or hard axis of magnetization is aligned on the plane of the ribbon, and parallel to or at an angle of about 60° to its width direction, respectively. According to the structural heredity between the melts and glasses/crystals during solidification, we deduce that the magnetic anisotropy in the ribbon plane is ascribed to the orientation alignment of Fe-Si and Fe-B clusters, i.e. a hidden order beyond short-range order, in Fe78Si9B13 amorphous ribbons.

Effect of Nb and Cu on the crystallization behavior of under-stoichiometric Nd–Fe–B alloys

In this work, we present a complete study of the influence of Nb and Cu addition on the crystallization behavior of Nd-lean Nd–Fe–B melt-spun alloys. Alloys with compositions Nd10−x−yFe84B6NbxCuy (x = 1, y = 0 and x = 0.5, y = 0.5) were melt-spun at different wheel speeds (15–40 m s−1) to obtain samples in amorphous, highly disordered and nanocrystalline structures. The crystallization process, induced by different heat treatments, was studied by means of differential thermal analysis and x-ray powder thermodiffraction. Magnetic properties of as-made and heat-treated ribbons were measured by magnetometry. The as-made amorphous samples showed a crystallization to the 2:14:1 hard magnetic phase at T1 ~ 350 °C. Doping with Nb results in an increase of T1, and addition of Cu lowers T1. This behavior is explained in terms of an inhibition of grain growth by Nb and a nucleation enhancement by Cu additions. During the crystallization process, a secondary phase (identified as a bcc-Fe-rich phase) is formed. The amount of such a phase increases with the annealing temperature. Coercivity increases upon annealing reaching maxima at 700–750 °C. This can be explained in terms of competition between the two phases formed: the 2:14:1 hard phase and the soft bcc-Fe-rich phase. The highest coercivity of the Nd-lean samples is observed when the microstructure is appropriate and both phases are exchange-coupled.

Thermomechanical properties and two-way shape memory effect in melt spun Ni57Mn21Al21Si1 ribbons

Thermomechanical properties of Ni57Mn21Al21Si1 melt-spun ribbons were studied as functions of temperature and applied stress. A one-time plastic deformation of the ribbons in the martensitic state brings about a two-way shape memory effect which is highly stable against number of thermocycling and is reproducible at least up to 1000 thermocycles. Influence of internal stresses on martensitic transformations was described theoretically in the terms of minimum conditions for Gibbs potential and it was shown that both internal axial stress induced by the axial deformation and internal pressure introduced during thermocycling of the alloy specimen are important for the appearance of two-way shape memory effect.

Comparative study of magnetic and magnetoimpedance properties of CoFeSiB-based amorphous ribbons of the same geometry with Mo or W additions

Amorphous ribbons with the following compositions Co68.5Fe4.0Si15.0B12.5, Co68.6Fe3.9Mo3.0Si12.0B12.5, Co65.9Fe3.5W3.1Si16.5B11.0 and Co64.3Fe3.5W4.7Si16.5B11.0 and the same geometry were prepared by melt spinning technique despite the technological difficulties usually related to the fabrication of the tungsten containing rapidly quenched materials. The structure, magnetic properties and giant magnetoimpedance effect (GMI) measured in 0.1–100 MHz frequency range were comparatively analyzed. All of the ribbons showed soft magnetic properties but different magnetostriction coefficients, Curie temperatures, saturation magnetizations and GMI features. Both Co65.9Fe3.5W3.1Si16.5B11.0 and Co64.3Fe3.5W4.7Si16.5B11.0 ribbons showed reasonably high Curie temperature above 200 °C suitable for possible applications. Despite very small composition differences of the tungsten containing ribbons, their GMI responses were distinct due to the difference of the effective magnetostriction coefficient evaluated from the shape of the hysteresis loops measured under stress. The Co68.6Fe3.9Mo3.0Si12.0B12.5 ribbon showed the best corrosion stability and the maximum MI of 320% at 15 MHz frequency. For sensor applications, Co64.3Fe3.5W4.7Si16.5B11.0 ribbons are eligible for frequency interval above 6 MHz.

Reverse rectification and negative differential resistance effects in doped armchair graphene ribbons device

In the present work, we perform first-principles calculations based on density functional theory and non-equilibrium Green’s function to study the electronic transport properties of the 10-armchair graphene ribbons devices doped by boron and phosphorus atoms. Two kinds of device show a strong inverse rectification and negative differential resistance (NDR) effect. The effect of doping position on rectifying phenomenon are analyzed by calculating the transmission spectra and the energy band structures of the related electrodes as well as the projected density of states for two devices at different bias. And the observed NDR effect is explained by the local density of states. The results indicate that the asymmetric doping of the impurity atom contributes to the electron transport of the device, being used to design a molecular rectifier with good performance.

Symmetry breaking induced excitations of dark plasmonic modes in multilayer graphene ribbons.

Multilayer graphene can support multiple plasmon bands. If structured into graphene ribbons, they can support multiple localized plasmonic modes with interesting optical properties. However, not all such plasmonic modes can be excited directly due to the constrains of the structural symmetry. We show by numerical simulations that by breaking the symmetry all plasmonic modes can be excited. We discuss the general principles and properties of two-layer graphene ribbons and then extend to multilayer graphene ribbons. In multilayer graphene ribbons with different ribbon widths, a tunable broadband absorption can be attained due to the excitations of all plasmonic modes. Our results suggest that these symmetry-broken multilayer graphene ribbons could offer more degrees of freedom in designing photonic devices.

Tailoring the Electronic and Magnetic Properties of Two-Dimensional Silicon Carbide Sheets and Ribbons by Fluorination

Fluorination has been instrumental for tuning the properties of several two-dimensional (2D) materials, including graphene, h-BN, and MoS2. However, its potential application has not yet been explored in 2D silicon carbide (SiC), a promising material for nanoelectronic devices. We investigate the structural, electronic, and magnetic properties of fully and partially fluorinated 2D SiC sheets and nanoribbons by means of density functional theory combined with cluster expansion calculations. We find that fully fluorinated 2D SiC exhibits chair configurations and a nonmagnetic semiconducting behavior. Fluorination is shown to be an efficient approach for tuning the band gap. Four ground states of partially fluorinated SiC, SiCF2x with x = 0.0625, 0.25, 0.5, 0.75, are obtained by cluster expansion calculations. All of them exhibit nanoroad patterns, with the x = 0.5 structure identified as the most stable one. The x = 0.0625 structure is a nonmagnetic metal, while the other three are all ferromagnetic half-me...

The influence of heat treatment on the structure and thermal properties of metallic glasses

This paper presents the structure and chosen properties of Fe-based ribbons with specified composition, after casting and heat treating. The aim of this work was to produce amorphous ribbons and study the influence of heat treatment on the structure and thermal properties before and after annealing. The base alloy ingot was prepared by induction melting of pure Fe, Co, B, Si and Nb elements in argon atmosphere. Then, the station for ultra-fast cooling of molten alloy with high vacuum pumps, designed for the production of metallic glasses in the form of ribbons by Buhler Melt Spinner SC was used. Also, the X-ray diffraction analysis system PANalytical X’Pert PRO was used. As-cast ribbons and metallic glasses after annealing were examined by differential scanning calorimetry (DSC) method, with the use of DSC822 Mettler Toledo. Annealing was done at different temperature. On the basis of obtained dependence, the glass transition temperature (Tg), onset crystallization temperature (onset—Tx) and peak crystallization temperature (peak—Tp) were determined. The supercooled liquid region (ΔTx), specific heat and the crystallization enthalpy (ΔH) were calculated as well. The microscopic observation of cross section of ribbons was carried out by means of the Zeiss Supra 35 scanning electron microscope. Based on experimental data, the discussion on the correlation between thermal properties, structure, annealing and future application was carried out.

Electric gating induced bandgaps and enhanced Seebeck effect in zigzag bilayer graphene ribbons

We theoretically investigate the effect of a transverse electric field generated by side gates and a vertical electric field generated by top/back gates on energy bands and transport properties of zigzag bilayer graphene ribbons (Bernal stacking). Using atomistic tight binding calculations and Green’s function formalism we demonstrate that a bandgap is opened when either field is applied and even enlarged under simultaneous influence of the two fields. Interestingly, although vertical electric fields are widely used to control the bandgap in bilayer graphene, here we show that transverse fields exhibit a more positive effect in terms of modulating a larger range of bandgap and retaining good electrical conductance. The Seebeck effect is also demonstrated to be enhanced strongly—by about 13 times for a zigzag bilayer graphene ribbon with 16 chain lines. These results may motivate new designs of devices made of bilayer graphene ribbons using electric gates.

Magnetic properties of melt-spun MM–Fe–B ribbons with different wheel speeds and mischmetal contents

In this study, the effect of wheel speed and mischmetal (MM) content on the magnetic properties of MMFeB ribbons was investigated. The samples were prepared via direct solidification technique. The nominal composition of the alloy ingots is MM x Fe92−x B8 with x varying from 9 to 15 in steps of 2. Experimental results show the overall magnetic properties of the ribbons. Analysis of the results shows that the magnetic properties first improve and then degrade with the wheel speed and MM content increasing. Increase in MM content leads to better formation of crystal texture in the ribbons, indicating that the α-Fe phase might undermine the formation of crystal texture. Magnetic properties results show that the coercivity of the ribbons rises with an appropriate increase in both MM content and wheel speed during melt-spun process. The strongest magnetic properties of the ribbons (remanence of M r = 0.72 T, intrinsic coercivity of H cj = 352.58 kA·m−1, and maximum energy product of (BH)max = 72.14 kJ·m−3) are obtained for compositions where x = 13 and a wheel speed of v = 20 m·s−1. The variation in maximum remanence (M r), coercivity (H cj), and maximum energy product ((BH)max) values were analyzed as a function of wheel speed for the MM13Fe79B8 melt-spun ribbons. All of the ribbons’ magnetic properties (M r, H cj, and (BH)max) first increase as the wheel speed increases up to 20 m·s−1 and then decrease gradually. The best magnetic properties are obtained at a wheel speed of 20 m·s−1, achieving M r value of 0.72 T, H cj value of 352.58 kA·m−1, and (BH)max value of 72.14 kJ·m−3.

Effect of P addition on glass forming ability and soft magnetic properties of melt-spun FeSiBCuC alloy ribbons

The dependency of phosphorous content on the glass forming ability, thermal stability and soft magnetic properties of Fe83.4Si2B14−xPxCu0.5C0.1 (x=0,1,2,3,4) alloys was investigated. The experimental results showed that the substitution of B by P increased the glass forming ability in this alloy system. The Fe83.4Si2B10P4Cu0.5C0.1 alloy shows a fully amorphous character. Thermal stability of melt-spun ribbons increases and temperature interval between the first and second crystallization peaks enlarges with the increase of P content. And the saturation magnetic flux density (Bs) shows a slight increase with the increase of P content. The Fe83.4Si2B11P3Cu0.5C0.1 nanocrystalline alloy exhibits a high Bs about 200.6emu/g. The Bs of fully amorphous alloy Fe83.4Si2B10P4Cu0.5C0.1 drops dramatically to 172.1emu/g, which is lower than that of other nanocrystallines. Low material cost and excellent soft magnetic properties make the FeSiBPCuC alloys promise soft magnetic materials for industrial applications.

Production feature of soft magnetic amorphous alloys

Methods for making nanocrystalline alloys have been discussed. Temperature dependences of the surface tension (σ), electric resistivity (ρ), magnetic susceptibility (χ) and kinematic viscosity (ν) have been obtained. Comparison of the properties of amorphous ribbons obtained by the pilot and serial technologies has been conducted. Science-based technology of multi-component alloy smelting makes it possible to prepare equilibrium smelt, the structure of which has a significant effect on the properties of the amorphous ribbon before spinning and kinetics of its crystallization has been offered.

Determination of the Nip Angle in Roller Compactors With Serrated Rolls

In roller compaction, the nip angle defines the critical transition interface between the slip and nip regions which is used to model material densification behavior and the properties of compacted ribbons. Current methods to determine the nip angle require either sophisticated instrumentation on smooth rolls or input parameters that are difficult to obtain experimentally. In this study, a practical method to determine nip angles for serrated rolls was developed based on mass balance considerations established around the nip region. Experimental input relating to roll geometry, powder density, and mass output from the compactor were required and they could be obtained reliably. The calculated nip angles were validated against those obtained from physical measurements during actual roll compaction. These nip angles were in agreement for various powder formulations containing plastic and brittle materials. The nip angles ranged from 4° to 12° and decreased significantly when the proportion of brittle material increased. Nip angles were also calculated using the widely used Johanson model. However, wall friction measurement on serrated roll surfaces could be impractical. The Johanson model-derived nip angles could differ by 3°-8° just by altering the roughness of the reference wall and this had compromised their reliability.

Response of Mg Addition on the Dendritic Structures and Mechanical Properties of Hypoeutectic Al-10Si (Wt Pct) Alloys

Rapidly solidified hypoeutectic Al-10Si-xMg (x = 0, 5, 10 wt pct) alloys were produced by the melt-spinning method. The phase composition was identified by X-ray diffractometry, and the microstructures of the alloys were characterized by scanning electron microscopy. The melting characteristics were studied by differential scanning calorimetry and differential thermal analysis under an Ar atmosphere. The mechanical properties of the melt-spun and conventionally solidified alloys were tested by tensile-strength and Vickers microhardness tests. The results illustrate that the cooling rate and solidification time of 89 μm thick melt-spun ribbon were estimated to be 2.97 × 107 K s−1 and 9.31 × 10−6 s, respectively. Nanoscale Si spot particles were observed growing on the surface of the dendritic α-Al matrix and the average sizes of these spots ranged from 10 to 50 nm. The improvement in the tensile properties and microhardness was related to structural refinement and the supersaturated α-Al solid solution; the nanoscale-dispersed Si spot particles made a significant improvement to the mechanical properties of the melt-spun ribbon. Detailed electrical resistivity tests of the ribbons were carried out at temperatures of 300 K to 800 K (27 °C to 527 °C).

Tuning magneto-structural properties of Ni44Co6Mn39Sn11 Heusler alloy ribbons by Fe-doping

Microstructure, martensitic transformation behavior and magnetic properties of Ni44−xFexCo6Mn39Sn11 (x=0, 1, 2at.%) melt spun ribbons have been investigated. The influence of iron addition has been thoroughly studied by means of electron microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that addition of 1at.% of iron into quaternary Ni–Co–Mn–Sn Heusler alloy drastically decreases the martensitic transformation temperature by more than 100K. Higher concentration of iron leads to complete suppression of martensitic transition. The structure of samples change from fully martensite (12M) through mixed austenite-martensite (L21+10M) to fully austenite (L21) with increase of iron content. Addition of 1at.% of iron leads to enhance magnetization of both austenitic and martensitic phases and also a small increase of Curie temperature occurs. The largest change of magnetic entropy under 15kOe measured 2.9 and 0.65Jkg−1K−1 for alloys where x=0 and 1, respectively.

Special Features of Friction Treatment of Steels of the Spring Class

The influence of surface friction deformation on the structure and properties of malleated ribbons from spring steels of martensitic and austenitic types is studied. X-ray diffraction and electron microscopic analyses are performed. A “sliding preform – immobile indenter” loading scheme providing friction deformation of long-length ribbon preforms is discussed.

Effect of edge-hydrogen passivation and nanometer size on the electronic properties of phagraphene ribbons

Based on a first-principles approach, the structures and electronic properties are investigated for both pure zigzag phagraphene nanoribbons (ZPHAGNRs) and mixture phagraphene nanoribbons (MPAHGNRs) terminated edges with hydrogen atoms or bare edges. There are many differences between bare and passivated phagraphene nanoribbons (PHAGNRs) in structure parameters after geometry optimization, although they still keep the two-dimensional plane structures. The edge states and quantum confined effect play crucial roles in the electronic properties for PHAGNRs. Our results show that ZPHAGNRs and bare MPHAGNRs are metallic, while the MPHAGNRs terminated edges with hydrogen atoms with direct band gap arise from quantum confined effect. The electronic properties of MPHAGNRs with passivated by hydrogen are further probed with the variation of width (NM=4–21). Our works indicate that all of the calculated H-MPHAGNRs are direct band gap, and 4-H-MPHAGNR has the largest band gap is 1.02eV. Generally, the band gaps decreased with respect to the ribbon widths increasing. However, the variation in band gaps exhibits three distinct family behaviors. The band gap sequence is gap3q>gap3q+1>gap3q+2.

Two-dimensional germanane and germanane ribbons: density functional calculation of structural, electronic, optical and transport properties and the role of defects

We have performed first principles calculations combined with non-equilibrium Green’s function to study the structural, electronic, optical and transport properties of two-dimensional germanane and germanane ribbons.

A Smart Polymer Composite Based on a NiTi Ribbon and a Magnetic Hybrid Material for Actuators with Multiphysic Transduction

A smart composite material constituted of a magnetic hybrid film and a NiTi shape memory alloy (SMA) ribbon was obtained and characterized. The magnetic hybrid film was joined to the NiTi ribbon in order to combine the properties of both materials. This new composite material combines magnetic properties of the hybrid film, (Fe2O3-CMC)/(polyvinyl butyral), and the shape memory properties of the NiTi ribbon, which has a chemical composition of Ti-50.13 at. % Ni. This smart composite material has a mass of 18.3% NiTi ribbon and 81.7% magnetic hybrid film. Results obtained by DSC show that the smart composite material presents a small delay of transformation during warming and cooling because the magnetic hybrid film acts like a thermal insulator. Thermomechanical results indicate that the hybrid material also acts as a mechanical reinforcement, since it is observed that the Stress-Assisted Two-Way Memory Effect (SATWME) of the smart composite is lower than the SATWME of the SMA ribbon. The density current values of phase transformations were clearly identified with a thermomechanical apparatus developed in our laboratory. Finally, displacements of the smart composite material in cantilever configuration are obtained by applying an external magnetic field. All these results demonstrate that the smart composite material can be activated by temperature, electrical current, stress, and/or magnetic field, offering good expectations for actuating applications with multiphysic transduction.