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The electronic and optical properties of armchair germanene nanoribbons
摘要： The electronic and optical properties of armchair germanene nanoribbons (AGeNRs) are studied using the first principles calculations. The band structure, band-gap size, projected density of states (PDOS), and dielectric function of AGeNRs are calculated. Moreover, the variation of these parameters as a function of various ribbon widths is investigated. By increasing the width of ribbons the band-gap size of pristine AGeNRs is decreased according to three different trends. Based on these trends, it is extracted that the AGeNRs can be divided into three categories named as n=3P, n=3P+1, n=3P+2, here n is the number of germanium atoms in the width and P is an integer. Moreover, all these categories are direct band-gap materials and the order of band-gap size is changed as: EG (3P+2) < EG (3P) < EG (3P+1). Due to the direct band-gap size, it can be extracted that all of AGeNR categories are proper for optical applications. Based on the simulation results of this work, it is demonstrated that the AGeNRs are appropriate for optical devices in the range of infrared applications. In addition, the effect of uniaxial tensile and compressive strain on the band-gap size and the dielectric function of AGeNRs is investigated and it is shown that the electronic and optical properties of AGeNRs can be tuned by strain in a wide range.
关键词： electronic and optical properties,silicene,band gap size,graphene,germanene nanoribbons
更新于2025-09-10 09:29:36
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Termini effects on the optical properties of graphene nanoribbons
摘要： We investigate from first principles the optical response of finite-length armchair-edged graphene nanoribbons (AGNRs) within the framework of many-body perturbation theory. As a result of the explicit inclusion of zigzag extremities, we identify low-energy and low-intensity excitations that are expected to be almost independent of the GNR length. These excitations coexist with bulk-like excitations, which have the same origin as the ones characterizing infinite AGNRs. Our results are used to rationalize termini effects on the optical response of GNRs and to shed light on recent photoluminescence data.
关键词： graphene nanoribbons,optical properties,photoluminescence,many-body perturbation theory,zigzag extremities
更新于2025-09-10 09:29:36
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Bandgap Tunability in a One-Dimensional System
摘要： The ability to tune the gaps of direct bandgap materials has tremendous potential for applications in the ?elds of LEDs and solar cells. However, lack of reproducibility of bandgaps due to quantum con?nement observed in experiments on reduced dimensional materials, severely affects tunability of their bandgaps. In this article, we report broad theoretical investigations of direct bandgap one-dimensional functionalized isomeric system using their periodic potential pro?le, where bandgap tunability is demonstrated simply by modifying the potential pro?le by changing the position of the functional group in a periodic supercell. We found that bandgap in one-dimensional isomeric systems having the same functional group depends upon the width and depth of the deepest potential well at global minimum and derived correlations are veri?ed for known synthetic as well as natural polymers (biological and organic), and also for other one-dimensional direct bandgap systems. This insight would greatly help experimentalists in designing new isomeric systems with different bandgap values for polymers and one-dimensional inorganic systems for possible applications in LEDs and solar cells.
关键词： one-dimensional systems,polymers,nanoribbons,density functional theory,bandgap
更新于2025-09-09 09:28:46
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Size and strain effects on mechanical and electronic properties of green phosphorene nanoribbons
摘要： Recently, a phosphorus isomer named green phosphorus was theoretically predicted with a similar interlayer interaction compared to that of black phosphorus, thus indicating that individual layers can be mechanically exfoliated to form two-dimensional (2D) layers known as green phosphorene. In this work, we investigated the properties of green phosphorene nanoribbons along both armchair and zigzag directions with ribbon widths up to 57 ? using density functional theory. Effects of ribbon width and strain on the mechanical and electronic properties of the ribbons were studied. The Young’s modulus, effect of quantum con?nement on the band gap, and effect of strain on the band structures of the ribbons were investigated. The green phosphorene ribbons were found to exhibit prominent anisotropic properties, with the Young’s modulus in the range of 10-35 GPa for the armchair green phosphorene nanoribbons (AGPNR) and 160-170 GPa for the zigzag green phosphorene nanoribbons (ZGPNR), which are the same order of magnitude as those of the 2D sheets. The work function was found to be between 5 eV ～ 5.7 eV for the range of widths studied. Both size and strain trigger direct-indirect band gap transitions in the ribbons and their transition mechanisms were discussed.
关键词： green phosphorene,mechanical properties,nanoribbons,electronic properties,density functional theory
更新于2025-09-09 09:28:46
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Alkaline Hydrothermal Synthesis, Characterization, and Photocatalytic Activity of TiO <sub/>2</sub> Nanostructures: The Effect of Initial TiO <sub/>2</sub> Phase
摘要： One-dimensional (1D) titanate nanostructures were synthesized by hydrothermal route, using commercially available TiO2 (P25) and anatase powders as precursor materials and strong NaOH solution as catalyzer. The prepared titanates were calcined, followed by protonation to produce TiO2 nanostructures having enhanced photocatalytic and photovoltaic properties. The synthesized TiO2 1D nanostructures were characterized using field-emission scanning electron microscope, high-resolution electron microscope, X-ray diffraction analysis, and UV-Vis photospectroscopy to understand the effect of initial TiO2 phase on morphological and crystallographic features, and bandgap. Methylene blue degradation test was applied to evaluate the photoactivity of the products obtained after different stages of the process. The findings indicate that 1D TiO2 nanostructures form by different mechanisms from dissolved aggregates during hydrothermal process, depending on the crystal structure of the initial precursor used. Photocatalytic test results reveal that protonated titanates have considerable adsorption capability, while photocatalytic degradation depends on TiO2 transformation.
关键词： TiO2,Photocatalytic Activity,1D Structure,Hydrothermal Process,Nanoribbons
更新于2025-09-04 15:30:14
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Strain engineering of chevron graphene nanoribbons
摘要： In this work, we theoretically investigate the material and transport properties of strained chevron graphene nanoribbons (CGNRs) which can be easily synthesized by the bottom-up fabrication technology. Because of the unique atomic structures, the energy and pressure of the CGNRs vary asymmetrically along compressive and tensile strains. Under the two strain directions, the CGNRs’ bandgaps and carrier effective masses in the conduction band minimum and the valence band maximum are all reduced. The transport properties are promoted accordingly, except some negative differential conductance behaviors caused by energy state localizations. When the tensile strains exceed a criterion value, the C–C bonds in the inner sides of the CGNR corners will be broken in sequence. Meanwhile, the CGNRs can restore their initial unstrained states rapidly when the strains are removed. However, if the broken bonds are saturated by foreign atoms, such as H, a novel kind of stable carbon structure will be obtained. The investigations suggest possible applications of strain engineered CGNRs in transport devices.
关键词： carrier effective masses,strain engineering,transport properties,chevron graphene nanoribbons,bandgap
更新于2025-09-04 15:30:14
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Biodissolution and cellular response to MoO <sub/>3</sub> nanoribbons and a new framework for early hazard screening for 2D materials
摘要： Two-dimensional (2D) high-aspect-ratio sheet-like materials are a broad class of synthetic ultra-thin sheet-like solids whose rapid pace of development motivates systematic study of their biological effects and safe design. A challenge for this effort is the large number of new materials and their chemical diversity. Recent work suggests that many 2D materials will be thermodynamically unstable and thus non-persistent in biological environments. Such information could inform and accelerate safety assessment, but experimental data to confirm the thermodynamic predictions are lacking. Here we propose a framework for early hazard screening of nanosheet materials based on biodissolution studies in reactive media, specially chosen for each material to match chemically feasible degradation pathways. Simple dissolution and in vitro tests allow grouping of nanosheet materials into four classes: A, potentially biopersistent; B, slowly degradable (>24–48 hours); C, biosoluble with potentially hazardous degradation products; and D, biosoluble with low-hazard degradation products. The proposed framework is demonstrated through an experimental case study on MoO3 nanoribbons, which have a dual 2D/1D morphology and have been reported to be stable in aqueous stock solutions. The nanoribbons are shown to undergo rapid dissolution in biological simulant fluids and in cell culture, where they elicit no adverse responses up to 100 μg ml?1 dose. These results place MoO3 nanoribbons in Class D, and assigns them a low priority for further nanotoxicology testing. We anticipate use of this framework could accelerate the risk assessment for the large set of new powdered 2D nanosheet materials, and promote their safe design and commercialization.
关键词： 2D materials,nanosheets,cytotoxicity,hazard screening,biodissolution,MoO3 nanoribbons
更新于2025-09-04 15:30:14
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Distinguishing Zigzag and Armchair Edges on Graphene Nanoribbons by X-ray Photoelectron and Raman Spectroscopies
摘要： Graphene nanoribbons (GNRs) have recently emerged as alternative 2D semiconductors owing to their fascinating electronic properties that include tunable band gaps and high charge-carrier mobilities. Identifying the atomic-scale edge structures of GNRs through structural investigations is very important to fully understand the electronic properties of these materials. Herein, we report an atomic-scale analysis of GNRs using simulated X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Tetracene with zigzag edges and chrysene with armchair edges were selected as initial model structures, and their XPS and Raman spectra were analyzed. Structurally expanded nanoribbons based on tetracene and chrysene, in which zigzag and armchair edges were combined in various ratios, were then simulated. The edge structures of chain-shaped nanoribbons composed only of either zigzag edges or armchair edges were distinguishable by XPS and Raman spectroscopy, depending on the edge type. It was also possible to distinguish planar nanoribbons consisting of both zigzag and armchair edges with zigzag/armchair ratios of 4:1 or 1:4, indicating that it is possible to analyze normally synthesized GNRs because their zigzag to armchair edge ratios are usually greater than 4 or less than 0.25. Our study on the precise identification of GNR edge structures by XPS and Raman spectroscopy provides the groundwork for the analysis of GNRs.
关键词： X-ray photoelectron spectroscopy,Graphene nanoribbons,armchair edges,zigzag edges,Raman spectroscopy
更新于2025-09-04 15:30:14
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Detachment Dynamics of Graphene Nanoribbons on Gold
摘要： Metal-surface physisorbed graphene nanoribbons (GNRs) constitute mobile nanocontacts whose interest is simultaneously mechanical, electronic, and tribological. Previous work showed that GNRs adsorbed on Au(111) generally slide smoothly and superlubrically owing to incommensurability of their structures. We address here the nanomechanics of detachment, such as realized when one end is picked up and lifted by an AFM cantilever. AFM nanomanipulations and molecular-dynamics (MD) simulations identify two successive regimes, characterized by (i) a progressively increasing local bending, accompanied by the smooth sliding of the adhered part, followed by (ii) a stick-slip dynamics involving sudden bending relaxation associated to intermittent jumps of the remaining adhered GNR segment and tail end. AFM measurements of the vertical force exhibit oscillations which, compared with MD simulations, can be associated to the successive detachment of individual GNR unit cells of length 0.42 nm. Extra modulations within one single period are caused by step-like advancements of the still-physisorbed part of the GNR. The sliding of the incommensurate moir′e pattern that accompanies the GNR lifting generally yields an additional long-period oscillation: while almost undetectable when the GNR is aligned in the standard “R30” orientation on Au(111), we predict that such feature should become prominent in the alternative rotated “R0” orientation on the same surface, or on a different surface, such as perhaps Ag(111).
关键词： molecular-dynamics simulations,gold,AFM,graphene nanoribbons,detachment dynamics
更新于2025-09-04 15:30:14