Ultrathin Slabs Research Articles

Study on Mechanical Properties and Safety of Ultra-Thin Reactive Powder Concrete Prefabricated Slabs Applied to I-Beam Joints of Bridges

Conventional methods for constructing bridge I-beam joints face several challenges, including heavy precast slabs, complicated transportation and lifting procedures, strict accuracy requirements, lengthy construction timelines, and increased safety risks. The use of ultra-thin, high-performance reactive powder concrete (RPC) prefabricated slabs can effectively resolve these issues. However, research in this area is limited, leaving our understanding of the strength and feasibility of ultra-thin RPC slabs for I-beam joints incomplete. Therefore, this study conducts a thorough examination of the strength and safety aspects of these slabs to assess their practical suitability. First, 11 numerical models are generated to evaluate the bearing capacity of ultra-thin RPC slabs, determining key factors such as cracking load, ultimate load, and safety factor according to relevant codes and standards. This establishes a theoretical foundation for practical engineering applications. Next, several sets of ultra-thin RPC slabs that meet material performance criteria are prefabricated to study the mechanical properties under equivalent concentrated load. Finally, two types of in situ temporary construction loads are encountered in the safety calculations of the RPC slabs. This study aims to provide a robust theoretical framework and technical support for the application and advancement of ultra-thin RPC prefabricated slabs in bridge I-beam joints.

Multiple absorption regimes in simple lithography-free structures leading to ultrathin slabs

Multiple absorption regimes in simple lithography-free structures leading to ultrathin slabs

Band Gap Engineering in Ultimately Thin Slabs of CdTe with Different Layer Stackings

Ultrathin solid slabs often have properties different from those of the bulk phase. This effect can be observed both in traditional three-dimensional materials and in van der Waals (vdW) solids in the few monolayer limit. In the present work, the band gap variation of the CdTe slabs, induced by their thickness, was studied by the density functional theory (DFT) method for the sphalerite (zinc-blende) phase and for the recently proposed inverted phase. The sphalerite phase has the Te–Cd–Te–Cd atomic plane sequence, while in the inverted phase Cd atoms are sandwiched by Te planes forming vdW blocks with the sequence Te–Cd–Cd–Te. Based on these building blocks, a bulk vdW CdTe crystal was built, whose thermodynamical stability was verified by DFT calculations. Band structures and partial densities of states for sphalerite and inverted phases were calculated. It was demonstrated for both phases that using slabs with a thickness of one to several monolayers for sphalerite phase (vdW blocks for inverted phase), structures with band gaps varying in a wide range can be obtained. The presented results allow us to argue that ultrathin CdTe can be a promising electronic material.

Self-healing in CdTe nanostructures: Insights into their structural stability and optical properties using first principles theory

Herein, we report a first-principle density functional theory-based study on CdTe nanostructures in 1D (nanorods and nanotubes) and 2D (ultra-thin slabs, monolayers) systems created within the top-down approach in terms of various properties, such as electronic structure, structural stability, and optical properties, and the effect of surface passivation on these properties. A substantial quantum confinement effect is observed with the increase in the energy band gap observed when the thickness or diameter of the nanostructure becomes less than the excitonic Bohr radius of CdTe. For all of the nanostructures studied, the structural stability improves upon surface passivation. The dielectric properties suggest that all of the passivated and specific unpassivated nanostructures are suitable for optoelectronic applications. Among the nanostructures studied, the 2D system prepared in the <110> orientation and the nanotube derived from the <111> monolayer are the most stable and show the least enhancement (0.1–0.2 eV) in the energy band gap upon passivation. This minimal change may be due to significant self-healing in the pristine structures. The charge density plots obtained for the relaxed and unrelaxed pristine structures show the surface had undergone reconstruction as a self-healing mechanism. The stability, self-healing ability, and energy bandgap of these nanostructures suggest their applicability in optoelectronic devices.

Anomalous transport in nodal ring semimetal slabs induced by vertical confinement

The nodal ring semimetal (NRSM) is a family member of gapless topological materials with the gap being closed at a nodal ring in momentum space. We partition the Fermi surface, a pipe ring, into two halves, so that the inter-half relaxation time is much longer than the in-half one. By calculating the parameter dependence of the relaxation times, we find that, the in-half relaxation results in the usual Drude conductance, and the inter-half relaxation, combined with the special energy bands of NRSM discretized by the vertical confinement, leads to an anomalous conductance that is inversely proportional to the slab thickness. The anomalous transport effect could be observed in ultra-thin NRSM slabs at low energies and can be regarded as the electronic transport signal of NRSMs.

Confinement-induced nonlocality and casimir force in transdimensional systems.

We study within the framework of the Lifshitz theory the long-range Casimir force for in-plane isotropic and anisotropic free-standing transdimensional material slabs. In the former case, we show that the confinement-induced nonlocality not only weakens the attraction of ultrathin slabs but also changes the distance dependence of the material-dependent correction to the Casimir force to go as contrary to the ∼1/l dependence of that of the local Lifshitz force. In the latter case, we use closely packed array of parallel aligned single-wall carbon nanotubes in a dielectric layer of finite thickness to demonstrate strong orientational anisotropy and crossover behavior for the inter-slab attractive force in addition to its reduction with decreasing slab thickness. We give physical insight as to why such a pair of ultrathin slabs prefers to stick together in the perpendicularly oriented manner, rather than in the parallel relative orientation as one would customarily expect.

Surface and Optoelectronic Properties of Ultrathin Trigonal Selenium: A Density Functional Theory Study with van der Waals Correction.

Selenium is an important earth-abundant and nontoxic semiconductor with numerous applications across semiconductor industries. Selenium has drawn attention from scientific communities for photovoltaics and imaging devices. Its usage as a photosensitive material largely involves the synthesis of the amorphous phase (a-Se) via various experimental techniques. However, the ground state crystalline phase of this material, the trigonal selenium (t-Se), a layered van der Waals solid, has not been extensively studied for its optimum electronic and optical properties. In this work, we present systematic studies based on density functional theory (DFT) for ultrathin (101̅0) surface slabs of t-Se. We report the surface energy as well as work function and electronic and optical properties as a function of number of layers for (101̅0) surface slabs to access its suitability for applications as a photosensitive material and compare these calculations to historical data.

Spectroscopic signature of surface states and bunching of bulk subbands in topological insulator ( Bi0.4Sb0.6)2Te3 thin films

High quality thin films of the topological insulator (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ have been deposited on SrTiO$_3$ (111) by molecular beam epitaxy. Their electronic structure was investigated by in situ angle-resolved photoemission spectroscopy and in situ scanning tunneling spectroscopy. The experimental results reveal striking similarities with relativistic ab-initio tight binding calculations. We find that ultrathin slabs of the three-dimensional topological insulator (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ display topological surface states, surface states with large weight on the outermost Te atomic layer, and dispersive bulk energy levels that are quantized. We observe that the bandwidth of the bulk levels is strongly reduced. These bunched bulk states as well as the surface states give rise to strong peaks in the local density of states.

Development and study of the properties of a ceramic-matrix composite material for the production of ultra-thin large-format ceramic granite slabs

The article analyzes the advantages and disadvantages of large-format ultra-thin ceramic granite slabs, shows the need and identifies ways to increase their strength. The composition of the ceramic matrix has been developed, provides the maximum level of sintering (W ≤ 0.5 %) in accordance with the requirements for ceramic plates of class ВІа, and the choice of the reinforcing filler has also been substantiated. It has been experimentally established that mullite-silica fibers have a positive effect on the physical and mechanical properties of the slabs, which makes it possible to reduce their thickness by three times, and therefore significantly reduce the weight of products. The fractional composition of the grinding products of mullitesilica fibers was determined depending on the grinding conditions, and the influence of the quantitative and qualitative characteristics of the reinforcing filler on the main properties that determine the quality of ceramic granite slabs was investigated. The conditions for the formation of densely sintered composite materials with a complex of high-performance properties have been determined. It was shown the possibility of increasing the samples bending strength up to 57 MPa by introducing 4 wt. % of finely dispersed mullitesilica fibers, most of which (~ 60 %) have a length up to 45 microns, which is achieved by 3 min grinding in a planetary mill at a speed of 300 rpm. The structural-phase features of the samples obtained under the high-speed firing conditions, which consist in the increased amount of the mullite phase formation in the presence of mullite-silica fibers, have been established. The latter not only reinforce the ceramic matrix, but also act as a precursor of new mullite formations, the crystals of which, in the presence of a melt, acquire an isometric shape and contribute to an increase in the products strength. The research results indicate the promising obtain large-format ultra-thin ceramic granite slabs using composite materials technology. The combination of excellent technical qualities, large dimensions, and reduced slabs thickness opens up the new possibilities for using composite ceramic granite in design of furniture and large rooms due to the possibility of creating a continuous seamless coating and a significant reduction in the products weight.

Impact of Transduction Scaling Laws on Nanoelectromechanical Systems.

We study the electromechanical transduction in nanoelectromechanical actuators and show that the differences in scaling laws for electrical and mechanical effects lead to an overall nontrivial miniaturization behavior. In particular, the previously neglected fringing fields considerably increase electrical forces and improve the stability of nanoscale actuators. This shows that electrostatics does not pose any limitations to the miniaturization of electromechanical systems; in fact, in several respects, nanosystems outperform their microscale counterparts. As a specific example, we consider in-plane actuation of ultrathin slabs and show that devices consisting of a few layers of graphene are feasible, implying that electromechanical resonators operating beyond 40GHz are possible with currently available technology.

Plasmons in ultra-thin gold slabs with quantum spill-out: Fourier modal method, perturbative approach, and analytical model

We numerically study the effect of the quantum spill-out (QSO) on the plasmon mode indices of an ultra-thin metallic slab, using the Fourier modal method (FMM). To improve the convergence of the FMM results, a novel nonlinear coordinate transformation is suggested and employed. Furthermore, we present a perturbative approach for incorporating the effects of QSO on the plasmon mode indices, which agrees very well with the full numerical results. The perturbative approach also provides additional physical insight, and is used to derive analytical expressions for the mode indices using a simple model for the dielectric function. The analytical expressions reproduce the results obtained from the numerically-challenging spill-out problem with much less effort and may be used for understanding the effects of QSO on other plasmonic structures.

Light-field enhancement on thin and ultra-thin high-index dielectric slabs with rectangular nano-pits

We closely study the local amplifications of visible light on a thin dielectric slab presenting a sub-wavelength array of small, rectangular, bottom-closed holes. The high-quality Fabry-Perot resonances of eigen modes which vertically oscillate, and their corresponding near-field maps, especially inside the voids, are numerically quantified with RCWA and analytically interpreted through a quasi-exact modal expansion. This last method gives explicit opto-geometrical rules allowing to finely understand the general trends in 1D and 2D. In more advanced examples, we show that multi-cavity and/or slightly thicker two-dimensional gratings may generate anomalously frequency-susceptible surfaces over a broad spectral range. Also, dielectric membranes a few nanometers thick only, can catch light, with tremendous enhancements of the electric field intensity ($>10^6$) that largely extends in the surrounding space.

II-VI Based Inorganic-Organic Hybrid Quantum Structures with High Degree of Structural Ordering, Long-Term Stability, and Novel Properties

Translational symmetry ensures phase coherency of a physical process among different units of a crystal, and thus produces collective quantum effects beyond the sum of the units. Any significant physical and/or chemical fluctuation, which typically exists in a semiconductor alloy or self-assembled or artificially grown nanostructure array, would hinder our ability to study and use the collective behavior relying on this coherency. Man-made structures remain as one of the central interests since semiconductor superlattices were proposed by Esaki and Tsu in 1970. Unfortunately, man-made structures with both genuine long- and short-range order are rare. Here a new family of inorganic-organic hybrid quantum structures provides us a unique opportunity to explore coherency quantum phenomena in man-made structures. These self-assembled hybrid structures are ultra-thin slabs or atomic chains of II-VI semiconductors interconnected or coordinated by small organic molecules, exhibiting very high degree of structural perfectness comparable to a typical binary semiconductor, as manifested in a very small XRD and Raman linewidth. They exhibit several extraordinary properties, for instance, exceedingly strong excitonic absorption, large exciton binding energies, and zero thermal expansion. By varying either the inorganic or organic component, one can tune the coupling between the inorganic units to achieve quasi-1-D, quasi-2-D, and 3-D super-structures with tailored material properties for different basic research interests and potential applications (e.g., room temperature exciton-polariton condensation, high efficiency UV emission and detection, p-type transparent conducting material). Furthermore, some hybrid structures, such as β-ZnTe(en)0.5, have been found to retain the same structural perfectness after being stored under ambient condition over a decade, despite others show varying degrees of structural degradation. This finding indicates that the long-term stability of the material depends on both the intrinsic effect, the strength of chemical bonding, and the extrinsic effect, such as the presence of defects in the initial structure.

Strain Engineered Band Gaps and Electronic Properties in PbPdO₂ and PbPd0.75Co0.25O₂ Slabs.

Electronic structure and corresponding electrical properties of PbPdO2 and PbPd0.75Co0.25O2 ultrathin slabs with (002) preferred orientation were systematically investigated using first-principles calculations. The calculated results revealed the strain induced evidently the changes of band structure and carrier concentration in both slabs. It was also found that PbPdO2 and PbPd0.75Co0.25O2 ultrathin slabs exhibited evident differences in the external strain dependence of the band gap and charge carrier concentration, which was strongly dependent on bond angle and bond length induced by in-plane anisotropy strain. Interestingly, the carrier concentration of the PbPd0.75Co0.25O2 slab could increase up to 5–6 orders of magnitude with the help of external strain, which could explain the potential mechanism behind the observed colossal strain-induced electrical behaviors. This work demonstrated that the influence of the doping effect in the case of PbPdO2 could be a potentially fruitful approach for the development of promising piezoresistive materials.

Finite size and volume effects in line node semimetals: A first-principles investigation

We systematically study the bulk and finite size effects on the band structure of prototypical line node materials using density functional theory based computations. For the bulk system, we analyze quantum oscillations with changes in the Fermi surface topology. We show that ultra thin slabs are gapped, with the first signatures of the line node appearing beyond a critical thickness. Further, motivated by possibility of tuning the bulk line node, we find that the line node radius is rather sensitive to bulk volume change. Based on this observation, we propose that application of pressure or suitable substrate engineering can be used as an effective means to control and tune the line node and the accompanying surface drumhead states.

Electronic structure and its external electric field modulation of PbPdO2 ultrathin slabs with (002) and (211) preferred orientations

The Electronic structure of PbPdO2 with (002) and (211) preferred orientations were investigated using first-principles calculation. The calculated results indicate that, (002) and (211) orientations exhibit different electric field dependence of band-gap and carrier concentration. The small band gap and more sensitive electric field modulation of band gap were found in (002) orientation. Moreover, the electric field modulation of the resistivity up to 3–4 orders of magnitude is also observed in (002) slab, which reveals that origin of colossal electroresistance. Lastly, electric field modulation of band gap is well explained. This work should be significant for repeating the colossal electroresistance.

Surface termination dependent atomic relaxation of RT5 ultra-thin slabs (R = Y, Ce, Sm and T = Fe, Co, Ni) and their electronic and magnetic properties

Investigations on two different surface terminated (0001) slabs of RT5 (R=Y, Ce, Sm and T=Fe, Co, Ni) compounds are performed by first principles calculations, in order to compare their structural stability, magnetic, and electronic properties. In bulk RT5 compounds, atomic sub-layers – RT2 (R-rich) and T3 (T-rich) – are alternatively stacked along z-axis. Therefore, two different RT5 (0001) slabs are constructed with terminating R-rich and T-rich sub-layers at both top and bottom of surfaces. Our calculations show that T-rich slabs are having higher structural stability owing to charge smoothing and inward relaxations of atoms at the surface, whereas R-atoms presented in the surface of slabs, particularly 4f elements experience outward relaxation as a consequence of corrugated surface charge density. The reason for inward and outward relaxations of respective atoms is quantitatively understood by the Bader charge analysis. Our results suggest that as the Co and Fe-rich surface slabs possess high structural stability and enhanced spin moment when compared to respective R-rich slabs, they can be potentially used for fabricating the multilayered exchange spring magnet.

Optical properties of magnetically doped ultrathin topological insulator slabs

Starting from a three dimensional Hamiltonian, we study the optical properties of ultra-thin topological insulator slabs for which the coupling between Dirac fermions on opposite surfaces results in two degenerated gapped hyperbolic bands. The gap is a threshold for the optical absorption and translates in a peak in the imaginary part of the optical conductivity. An exchange field applied perpendicular to the slab splits the degenerated hyperbolic bands and a double step structure come out in the optical absorption, whereas a double peak structure appears in the imaginary part of the longitudinal optical conductivity. The exchange field breaks time-reversal symmetry and for exchange fields larger than the surfaces coupling gap, the zero frequency Hall conductivity is quantized to $e^2/h$. This result implies large values of the Kerr and Faraday rotation angles. In ultra-thin slabs, the absence of light multiple scattering and bulk conductivity, makes the Kerr and Faradays angles to remain rather large in a wide range of frequencies.

Electronic effects of isolated halogen atoms on the Ge(001) surface

The asymmetric slab approach and density functional theory (DFT) are used to discuss the interaction of isolated halogen atoms (F, Cl, Br and I) with the Ge(001)c(4×2) surface. For each adsorbate on thick slabs we find two stable adatom configurations separated by ~0.1eV. In both configurations, the unsaturated dangling bonds (DB) of the chemisorbed dimers are fully charged due to the interaction of the DB-derived surface states with the bulk states. This behavior is found to be insensitive to whether the calculations are performed using standard ground-state DFT, or DFT supplemented by MBJLDA and spin-orbit corrections to produce an accurate surface electronic structure and energy gap. On chemisorbed ultrathin Ge slabs, however, these unsaturated DB's are empty for the lowest energy configurations. This results in different geometries and energetics for the chemisorbed dimers. A detailed analysis of the predicted scanning tunneling microscopy images of halogen-chemisorbed surfaces is also presented. It is predicted that the halogen atoms may image darkly, yielding filled-state images similar to that of the clean surface, while the empty-state images should be noticeably different.

An ultrathin directional carpet cloak based on generalized Snell's law

Based on generalized Snell's law, we propose an ultrathin directional carpet cloak operating in the reflection geometry. The cloak is constructed by two identical ultrathin metal-backed dielectric slabs with metallic “H” patterns on the other sides to form a triangular region. When put on an infinite ground plane and illuminated by electromagnetic waves from overhead, it can manipulate the reflected wavefronts to mimic the infinite ground plane. We fabricate a microwave sample and perform near-field scanning experiments to verify the cloaking effect. The measurement results are in good agreement with full-wave simulations and theoretical analysis.