Single-layer Sheets Research Articles

Single-layer honeycomb sheets of zinc selenide and beyond with superior electronic and optical properties

The freestanding four-atom-thick double-layer honeycomb sheets of zinc chalcogenides which were synthesized recently are outstanding two-dimensional (2D) materials for next-generation ultrathin optoelectronic nanodevice. In this work, we report a theoretical study on two different single-layer honeycomb sheets of MX (M = Zn, Cd; X = Se, S). The two kinds of single-layer sheets of MX would be thought by cutting along the zinc blende (ZB) bulk as well as wurtzite (WZ) bulk. By using state-of-the-art calculations based upon quasiparticle GW and Bethe–Salpeter equation (BSE), the single-layer sheets of MX possess wide band gaps and are capable of being used as photocatalysts for solar water splitting. The optical absorbance demonstrates that the single-layer sheets of CdSe and CdS have substantial absorption within the visible light region, and the optical absorption of the single-layer sheets of ZnSe can be easily modulated via strains. Furthermore, the electronic transport properties of the single-layer sheets of MX are investigated through the nonequilibrium Green’s function (NEGF) method combined with density functional theory (DFT). It is anticipated that these novel freestanding single-layer honeycomb sheets of MX would be great candidates for abundant potential applications in energy storage and conversion.

Frequency and In-Plane Vibration Analysis of Single-Layer Nano-Graphene Sheet by Scaled Boundary Finite Element Method

Frequency and In-Plane Vibration Analysis of Single-Layer Nano-Graphene Sheet by Scaled Boundary Finite Element Method

Self-assembly of colloidal single-layer carbon nitride.

We introduce a new concept of a "bottom-to-top" design of intercalate carbon nitride compounds based on the effects of self-assembly of colloidal single-layer carbon nitride (SLCN) sheets stabilized by tetraethylammonium hydroxide NEt4OH upon ambient drying of the water solvent. These effects include (i) formation of stage-1 intercalates of NEt4OH during the ambient drying of SLCN colloids on glass substrates and (ii) the spontaneous formation of layered hexagonally-shaped networks of SLCN sheets on freshly-cleaved mica surfaces. The dynamics of the intercalate formation was followed by in situ X-ray diffraction allowing different stages to be identified, including the deposition of a primary "wet" intercalate of hydrated NEt4OH and the gradual elimination of excessive water during its ambient drying. The intercalated NEt4+ cations show a specific "flattened" conformation allowing the dynamics of formation and structure of the intercalate to be probed by vibrational spectroscopies. The two-dimensional self-assembly on mica is assumed to be driven both by the internal hexagonal symmetry of heptazine units and by a templating effect of the mica surface.

3D printed geometrically tessellated sheets with origami-inspired patterns

This study demonstrates that the impact energy absorption capabilities of flexible sheets can be significantly enhanced by implementing tessellated designs into their structure. Configurations of three tessellated geometries were tested; they included a triangular-based, a rectangular-based, and a novel square-based pattern. Due to their geometrical complexity, multiple configurations of these tessellations were printed from a rubber-like material using an inkjet printer with two different thicknesses (2 and 4 mm), and their ability to absorb impact energy was compared to an unpatterned inkjet-printed sheet. In addition, the effect of multi-sheets stacking was also tested. Due to the tailored structure, the impact testing showed that the single-layer sheets were more effective at absorbing impact loads, and experience less deformation, than their two-layer counterparts. The 4 mm thick tessellated patterns were most effective at absorbing impact loads; all three thick patterns measured about 40% lower impact forces transferred to the base of the samples compared to the unpatterned counterparts.

Study of the Degradation of Biobased Plastic after Stress Tests in Water

Research on compostable bioplastics has recently obtained performances comparable to traditional plastics, like water vapor permeability, sealability, and UV transmission. Therefore, it is crucial to create new tools that help the developers of new polymeric composites study them quickly and cost-effectively. In this work, Raman spectroscopy (RS) was proposed as a versatile tool to investigate the degradation of biobased plastics after a stress test in water: this approach is a novelty for food packaging. Treatments at room temperature (RT) and 80 °C were selected, considering that these biopolymers can be used to packaging ready meals. The investigation was carried out on single-layer sheets of poly-lactic acid (PLA), cellulose ester (CE), poly-butylene succinate (PBS), poly-butylene adipate-co-terephthalate (PBAT), and a new composite material obtained by coupling CE and PBS (BB951) and PLA and CE (BB961). The vibrational modes of the water-treated materials at RT and 80 °C were compared to the Raman spectra of the pristine bioplastic, and the morphologies of the polymers were analyzed by scanning electron microscopy (SEM) and optical microscopy. Composite sheets were the plastics which were mostly affected by the 80 °C treatment in water, through changes in morphology (wrinkling with alternate white and transparent zones), as was especially the case for BB951. The Raman spectra acquired in different zones showed that the vibrations of BB951 were generally maintained in transparent zones but reduced or lacking in white zones. At the same time, the single-layer materials were almost unchanged. For BB961, the Raman vibrations were only slightly modified, in agreement with the visual inspection. The results suggest that RS detects the specific chemical bond that was modified, helping us understand the degradation process of biobased plastics after water treatment.

Boridene: Two-dimensional Mo4/3B2-x with ordered metal vacancies obtained by chemical exfoliation.

Extensive research has been invested in two-dimensional (2D) materials, typically synthesized by exfoliation of van der Waals solids. One exception is MXenes, derived from the etching of constituent layers in transition metal carbides and nitrides. We report the experimental realization of boridene in the form of single-layer 2D molybdenum boride sheets with ordered metal vacancies, Mo4/3B2-xTz (where Tz is fluorine, oxygen, or hydroxide surface terminations), produced by selective etching of aluminum and yttrium or scandium atoms from 3D in-plane chemically ordered (Mo2/3Y1/3)2AlB2 and (Mo2/3Sc1/3)2AlB2 in aqueous hydrofluoric acid. The discovery of a 2D transition metal boride suggests a wealth of future 2D materials that can be obtained through the chemical exfoliation of laminated compounds.

High Performance Hybrid Graphene Nano Filters as a Total dissolved solid remover

Graphene, a single-layer carbon sheet with its distinctive two-dimensional (2D) single-atomic-thick sp2 hybridized hexagonal packed lattice structure which is nearly friction less with high chemical inertness, and pliability which can be manufactured sustainably in great amounts with less expense, has shown many unique properties, Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (GO), offers a wide range of possibilities to produce nano-filters containing graphene membrane which is capable to remove ninety percent of the heavy contaminants from different sources of water and to reduce the level of total dissolved solids, salinity, and neutralizes the pH level further inorganic membrane used in synergism with graphene oxide shows improved efficiency and reduction in cost of production of separation membranes. In this review, we demonstrated real world application of graphene, Fabricated with Several Metal Oxides in synergism to illustrate enhanced photocatalysis properties, Flexural strength and anti-fouling characteristics of the material in comparisons to conventional membrane, photocatalytic metal oxides nanoparticles such as Titania TiO2, Zirconia ZrO2, Alumina Al2O3, and Silica SiO2 functions in the presence of Multiple Spectrums of Light by absorbing photons and releasing Oxygen Radical which degrades harmful water pollutants into less harmful substances.

Eigenmodes and resonance vibrations of graphene nanomembranes

Natural and resonant oscillations of suspended circular graphene and hexagonal boron nitride (h-BN) membranes (single-layer sheets lying on a flat substrate having a circular hole of radius $R$) have been simulated using full-atomic models. Substrates formed by flat surfaces of graphite and h-BN crystal, hexagonal ice, silicon carbide 6H-SiC and nickel surface (111) have been used. The presence of the substrate leads to the forming of a gap at the bottom of the frequency spectrum of transversal vibrations of the sheet. The frequencies of natural oscillations of the membrane (oscillations localized on the suspended section of the sheet) always lie in this gap, and the frequencies of oscillations decrease by increasing radius of the membrane as $(R+R_i)^{-2}$ with nonezero effective increase of radius $R_i>0$. The modeling of the sheet dynamics has shown that small periodic transversal displacements of the substrate lead to resonant vibrations of the membranes at frequencies close to eigenfrequencies of nodeless vibrations of membranes with a circular symmetry. The energy distribution of resonant vibrations of the membrane has a circular symmetry and several nodal circles, whose number $i$ coincides with the number of the resonant frequency. The frequencies of the resonances decrease by increasing the radius of the membrane as $(R+R_i)^{\alpha_i}$ with exponent $\alpha_i<2$. The lower rate of resonance frequency decrease is caused by the anharmonicity of membrane vibrations.

Hypersonic impact properties of pristine and hybrid single and multi-layer C3N and BC3 nanosheets

Carbon, nitrogen, and boron nanostructures are promising ballistic protection materials due to their low density and excellent mechanical properties. In this study, the ballistic properties of C3N and BC3 nanosheets against hypersonic bullets with Mach numbers greater than 6 were studied. The critical perforation conditions, and thus, the intrinsic impact strength of these 2D materials were determined by simulating ballistic curves of C3N and BC3 monolayers. Furthermore, the energy absorption scaling law with different numbers of layers and interlayer spacing was investigated, for homogeneous or hybrid configurations (alternated stacking of C3N and the BC3). Besides, we created a hybrid sheet using van der Waals bonds between two adjacent sheets based on the hypervelocity impacts of fullerene (C60) molecules utilizing molecular dynamics simulation. As a result, since the higher bond energy between N–C compared to B-C, it was shown that C3N nanosheets have higher absorption energy than BC3. In contrast, in lower impact speeds and before penetration, single-layer sheets exhibited almost similar behavior. Our findings also reveal that in hybrid structures, the C3N layers will improve the ballistic properties of BC3. The energy absorption values with a variable number of layers and variable interlayer distance (X = 3.4 Å and 4X = 13.6 Å) are investigated, for homogeneous or hybrid configurations. These results provide a fundamental understanding of ultra-light multilayered armors' design using nanocomposites based on advanced 2D materials. The results can also be used to select and make 2D membranes and allotropes for DNA sequencing and filtration.

2D MoS2 Encapsulated Silicon Nanopillar Array with High-Performance Light Trapping Obtained by Direct CVD Process

Weak absorption remains a vital factor that limits the application of two-dimensional (2D) materials due to the atomic thickness of those materials. In this work, a direct chemical vapor deposition (CVD) process was applied to achieve 2D MoS2 encapsulation onto the silicon nanopillar array substrate (NPAS). Single-layer 2D MoS2 monocrystal sheets were obtained, and the percentage of the encapsulated surface of NPAS was up to 80%. The reflection and transmittance of incident light of our 2D MoS2-encapsulated silicon substrate within visible to shortwave infrared were significantly reduced compared with the counterpart planar silicon substrate, leading to effective light trapping in NPAS. The proposed method provides a method of conformal deposition upon NPAS that combines the advantages of both 2D MoS2 and its substrate. Furthermore, the method is feasible and low-cost, providing a promising process for high-performance optoelectronic device development.

Ultrahigh hydrogen storage capacity of holey graphyne

Holey graphyne (HGY), a novel two-dimensional (2D) single-crystalline carbon allotrope, was recently synthesized by Castro–Stephens coupling reaction. The naturally existing uniform periodic holes in the 2D carbon–carbon network demonstrate its promising potential in energy storage. Herein, we conduct density functional theory (DFT) calculation and ab initio molecular dynamics simulations (AIMD) to predict the H storage properties of a single-layer HGY sheet modified by Li metal atoms. The DFT calculations demonstrate that Li atoms can bind strongly to the HGY sheet without forming clusters, and each Li atom can anchor four H2 molecules with an average adsorption energy of about −0.22 eV/H2. The largest H storage capacity of the doped HGY sheet can reach as high as 12.8 wt%, showing that the Li/HGY complex is an ideal H storage material at ambient conditions. In addition, we investigate the polarization mechanism of the storage media and find that the polarization originates from the electric field induced by both the ionic Li atoms and the weak polarized H2 molecules. Finally, the desorption mechanism of the adsorbed H2 molecules is thoroughly investigated using a kinetic AIMD method.

The buckling behavior of single-layer MoS2 sheets on silica substrates

The buckling of a single-layer molybdenum disulfide (SLMoS2) sheet can strongly influence its stability and reliability of MoS2-based nanodevices. In the study, the buckling behavior of SLMoS2 sheets on the silica substrate is investigated by theoretical modeling and molecular dynamics simulation. The difference between the suspended and substrate-supported SLMoS2 sheets is compared. The effect of substrate surface morphology, including the groove and periodic surface microstructure substrate, on the buckling behavior is mainly focused. It is found that the critical strain increases significantly compared with the suspended SLMoS2 sheets due to the introduction of the underlying substrate. The evolution of SLMoS2 sheets on substrates with grooves contains two different paths depending on the groove height and the width. Additionally, both the period and effective contact area of the surface microstructure have direct impacts on the critical strain. The finding of buckling behavior of SLMoS2 sheets on substrates should be helpful for the design of MoS2-based flexible electronic devices.

Interlayer-decoupled BiOX (X=Cl, Br, and I) sheets for photocatalytic water splitting: a computational study

In this work, we comprehensively study the electronic and photocatalytic properties of single-layer and multilayer bismuth oxyhalides BiOX (X=Cl, Br, and I) sheets by means of extensive density functional theory, which have been successfully synthesized in the previous experimental studies. Our computational simulations show that single-layer BiOX sheets possess indirect band gap, suitable band edge alignments, and pronounced optical properties, suggesting that they can be utilized as photocatalysts for splitting H2O into H2 and O2 from theoretical aspects. In the case of multilayer BiOX sheets, some primary physical properties determined the photocatalytic performance are rather robust, almost independent of the layer number. According to these calculated results, we are optimistic that BiOX sheets, especially for single-layer BiOI, have great chances to be used for photocatalytic water splitting.

The dome of gold nanolized for catalysis.

Gold is noble in bulk but turns out to be a superior catalyst at the nanoscale when supported on oxides, in particular titania. The critical thickness for activity, namely two-layer gold particles on titania, observed two decades ago represents one of the most influential mysteries in the recent history of heterogeneous catalysis. By developing a Bayesian optimization controlled global potential energy surface exploration tool with machine learning potential, here we determine the atomic structures of gold particles within ∼2 nm on a TiO2 surface. We show that the smallest stable Au nanoparticle is Au24 which is pinned on the oxygen-rich TiO2 and exhibits an unprecedented dome architecture made by a single-layer Au sheet but with an apparent two-atomic-layer height. Importantly, this has the highest activity for CO oxidation at room temperature. The physical origin of the high activity is the outstanding electron storage ability of the nano-dome, which activates the lattice oxygen of the oxide. The determined CO oxidation mechanism, the simulated rate and the fitted apparent energy barrier are consistent with known experimental facts, providing key evidence for the presence of both the high-activity Au dome and the low-activity close-packed Au particles in real catalysts. The future direction for the preparation of active and stable Au-based catalysts is thus outlined.

Towards One-Dollar Robots: An Integrated Design and Fabrication Strategy for Electromechanical Systems

SUMMARYTo improve the accessibility of robotics, we propose a design and fabrication strategy to build low-cost electromechanical systems for robotic devices. Our method, based on origami-inspired cut-and-fold and E-textiles techniques, aims at minimizing the resources for robot creation. Specifically, we explore techniques to create robots with the resources restricted to single-layer sheets (e.g., polyester film) and conductive sewing threads. To demonstrate our strategy’s feasibility, these techniques are successfully integrated into an electromechanical oscillator (about 0.40 USD), which can generate electrical oscillation under constant-current power and potentially be used as a simple robot controller in lieu of additional external electronics.

Two-Point Incremental Forming of Metal–Polymer Three-Layer Sheets

Incremental forming process is a manufacturing process with many advantages, so it has received attention by many researchers, while further investigation is required for incremental forming of sandwich panels. In this study, the response surface method is employed to perform a series of experiments, and the effects of parameters, including vertical step down size, tool diameter, tool rotation speed and polymer type (as the core material) on incremental forming of metal–polymer three-layer sheets are studied. The results are used to evaluate the average tool force and uniformity of sheet thickness distribution. The results of variance analysis of the average tool force show that the vertical step size, tool diameter, polymer type and tool rotation speed have, respectively, the greatest effects on the average tool force. Moreover, the interactions between the pairs of vertical step size/tool rotation speed, vertical step size/tool diameter, vertical step size/polymer type and the tool rotational speed/tool diameter affect the average tool force. From the results of variance analysis of maximum thickness variation, it can be concluded that the vertical step size, polymer type, tool rotation speed and tool diameter have, respectively, the greatest effects on the maximum thickness variation; moreover, the interaction between vertical step size and polymer type also affects the maximum thickness variation. It is shown that the vertical tool force in incremental forming of a metal–polymer three-layer sheets is approximately 50% that of a single-layer aluminum sheet with similar bending moment.

The buckling behavior of single-layer MoS2 sheets with kirigami-inspired structures under compression

The buckling behavior of single-layer MoS2 sheets under both uniaxial and biaxial compression is studied in the present paper. The critical strain, critical stress, equivalent elastic modulus as well as post-buckling morphologies are comprehensively studied. It is found that both the critical stress and equivalent elastic modulus of SLMoS2 sheets with kirigami-inspired structures are reduced significantly compared with perfect ones. The geometric parameters of kirigami-inspired structures in armchair and zigzag directions have different effects on the compressive behavior of SLMoS2 sheets. SLMoS2 sheets that sustain more strain could be realized by introducing kirigami-inspired structures. What is more, a desired post-bulking morphology can be obtained by properly tuning kirigami-inspired structures. The results should be helpful for various practical and potential applications of the new 2D material.

Numerical and experimental study on formability of TC4 alloy in a novel multi-layer sheet hot stamping process

In this study, a novel modified hot stamping process is proposed to prevent the heat loss of titanium alloy sheet during transferring and stamping. A technology which is two steel sheets clamping one titanium alloy sheet (the sandwich structure) to transfer and deform was used in the multi-layer sheet hot stamping process. The formability of TC4 alloy under the triple-layer sheet hot stamping condition was studied by means of experiment and numerical simulation. The influence of sheet temperature, stamping speed, and blank holder force on the depth and thickness uniformity of parts was analyzed. The results show that the deep-drawing depth of titanium alloy parts is improved and the thickness uniformity of parts is better by using the triple-layer sheet hot stamping process proposed in this paper. On the one hand, the flow stress of the TC4 alloy is low because of the less heat loss in the triple-layer sheet hot stamping process. On the other hand, the TC4 alloy sheet can be deformed better because of the changing of the friction situation of the titanium alloy sheet. And the contact force between titanium alloy sheet and steel sheet is less because of the protection of two steel sheet under the triple-layer sheet hot stamping condition. With the sheet temperature increasing, the deep-drawing depth of titanium alloy parts increases by 22.2% from 27 mm of 750 °C to 33 mm of 900 °C. Compared with the single-layer sheet hot stamping process, the stamping depth of titanium alloy parts obtained by the triple-layer sheet hot stamping process increases by 135.7% at 900 °C, and the local thinning of titanium alloy sheet is improved. Due to strain rate strengthen and the uniform distribution of sheet temperature, the thickness uniformity of parts is improved with the increase of stamping speed. Based on the microstructure observation tests, it is can be seen that more equiaxed α phase of TC4 alloy parts can be obtained by the triple-layer sheet hot stamping process.

Structure and Property Evolution of Graphene Oxide Sheets during Low-Temperature Reduction on a Solid Substrate

The structure and property evolution of graphene oxide (GO) during low-temperature (≤200 °C) reduction is related to the economically effective production and many behaviors of graphene-based materials, such as property tuning and long-term stability at high working temperatures. The interfacial effects on the physiochemical processes are yet to be quantified experimentally. Here, combining scanning polarization force microscopy with UV–vis absorption spectra, the formation and expansion of sp2 domains on individual single-layered GO sheets and the opto-electronic behaviors of GO films on average at low temperatures are in situ monitored. Kinetics of the interfacial evolutions are examined. Surprisingly, unexpected faster evolution of GO sheets at interfaces than that in bulk water is observed. We find this discrepancy can be addressed if the water atmosphere is taken into account and the humidity dependence of evolution is verified. Environmental water and asymmetric moisturizing of GO are believed to play important roles in the process. Based on this, the evolution rate is modulated via adjusting the humidity. The findings shed light on the interfacial structure and property evolution processes of GO and open a new avenue to manipulate the evolution rates at low temperatures.

An Ultra-Wideband Terahertz Metamaterial Absorber Utilizing Sinusoidal-Patterned Dielectric Loaded Graphene

In this paper, a non-structured graphene sheet loaded with a sinusoidal-patterned dielectric is introduced as an ultra-wideband metamaterial absorber in terahertz regime. Regardless of conventional structures with multilayered-graphene, a single layer sheet of non-structured graphene is used whereas the proposed structure benefits from dielectric width modulation and cavity method in order to excite continuous graphene plasmon resonances. The structure comprises four layers that two Fabry-Perot cavity mirrors are constructed by upper sinusoidal-patterned dielectric and a gold film. Full wave simulation results demonstrate that a broadband over 90% absorption with absolute bandwidth of 6.58 THz and central frequency of 3.97 THz is achieved under normal TE/TM incident plane wave. The designed structure yields 166% relative bandwidth. According to the symmetric configuration, the absorption spectra of mentioned polarizations are thoroughly close to each other resulting to a polarization insensitive structure. The stability of bandwidth and absorbance of the structure versus angle of incidence, θ, up to 35°/65° for TM/TE polarizations, respectively, and azimuth angle, φ, shows an interesting capability for utilization as detectors and sensors. The simple geometry of utilized graphene layer results in easy fabrication. The designed structure has wideband absorption in THz regime. Moreover, it is more compact than conventional broadband THz absorbers.