FacebookTwitterRssLinkedInEmail

Colossal shift current response in elemental two-dimensional ferroelectrics. (arXiv:2212.00326v1 [cond-mat.mtrl-sci])

2022-12-02T02:29:22+00:00December 2nd, 2022|Categories: Publications|Tags: |

A bulk material without inversion symmetry can generate a direct current under uniform illumination. This interface-free current generation mechanism, referred to as the bulk photovoltaic effect (BPVE), has the potential to overcome the Shockley-Queisser limit of traditional solar cells based on $p$-$n$ junctions. Here, we explore the shift current generation, a major mechanism responsible for the BPVE, in single-element two-dimensional ferroelectrics represented by phosphorene-like monolayers of As, Sb, and Bi. The strong covalency and large joint density of states afforded by these elemental 2D materials give rise to colossal shift currents, outperforming many state-of-the-art materials over a wide range of wavelengths including the visible light spectrum. For a given frequency and polarization of an incoming light, we find that the shift current, due to its topological nature, depends sensitively on the details of the Bloch wave functions. It is crucial to consider the electronic exchange-correlation potential beyond the generalized gradient approximation as well as the spin-orbit interaction in density functional theory calculations to obtain reliable photon frequency-dependent shift current responses.

Published in: "arXiv Material Science".

Room Temperature Optically and Magnetically Active Edges in Phosphorene Nanoribbons. (arXiv:2211.11374v1 [cond-mat.mes-hall])

2022-11-22T02:30:05+00:00November 22nd, 2022|Categories: Publications|Tags: , |

Nanoribbons – nanometer wide strips of a two-dimensional material – are a unique system in condensed matter physics. They combine the exotic electronic structures of low-dimensional materials with an enhanced number of exposed edges, where phenomena including ultralong spin coherence times, quantum confinement and topologically protected states can emerge. An exciting prospect for this new material concept is the potential for both a tunable semiconducting electronic structure and magnetism along the nanoribbon edge. This combination of magnetism and semiconducting properties is the first step in unlocking spin-based electronics such as non-volatile transistors, a route to low-energy computing, and has thus far typically only been observed in doped semiconductor systems and/or at low temperatures. Here, we report the magnetic and semiconducting properties of phosphorene nanoribbons (PNRs). Static (SQUID) and dynamic (EPR) magnetization probes demonstrate that at room temperature, films of PNRs exhibit macroscopic magnetic properties, arising from their edge, with internal fields of ~ 250 to 800 mT. In solution, a giant magnetic anisotropy enables the alignment of PNRs at modest sub-1T fields. By leveraging this alignment effect, we discover that upon photoexcitation, energy is rapidly funneled to a dark-exciton state that is localized to the magnetic edge and coupled to a symmetry-forbidden edge phonon mode. Our results establish PNRs as a unique candidate system for studying the interplay of magnetism and semiconducting ground states at room temperature and provide a stepping-stone towards using low-dimensional nanomaterials in quantum electronics.

Published in: "arXiv Material Science".

The overlooked role of band-gap parameter in characterization of Landau levels in a gapped phase semi-Dirac system: the monolayer phosphorene case. (arXiv:2211.04910v1 [cond-mat.mes-hall])

2022-11-10T04:30:14+00:00November 10th, 2022|Categories: Publications|Tags: , |

Two-dimensional gapped semi-Dirac (GSD) materials are systems with a finite band gap that their charge carriers behave relativistically in one direction and Schr”odinger-like in the other. In the present work, we show that besides the two well-known energy bands features (curvature and chirality), the band-gap parameter also play a crucial role in the index- and magnetic field-dependence of the Landau levels (LLs) in a GSD system. We take the monolayer phosphorene as a GSD representative example to explicitly provide physical insights into the role of this parameter in determining the index- and magnetic field-dependence of LLs. We derive an effective one-dimensional Schr”odinger equation for charge carriers in the presence of a perpendicular magnetic field and argue that the form of its effective potential is clearly sensitive to a dimensionless band-gap that is tunable by structural parameters. The theoretical magnitude of this effective gap and its interplay with oval shape $k$-space cyclotron orbits resolve the seeming contradiction in determining the type of the quantum Hall effect in the pristine monolayer phosphorene. Our results strongly confirm that the dependence of LLs on the magnetic field in this GSD material is as conventional two-dimensional semiconductor electron gases up to a very high field regime. Using the strain-induced gap modification scheme, we show the field dependence of the LLs continuously evolves into $B^{2/3}$ behavior, which holds for a gapless semi-Dirac system. The highlighted role of the band-gap parameter may affect the consequences of the band anisotropy in the physical properties of a GSD material,

Published : "arXiv Mesoscale and Nanoscale Physics".

Visualization of Strain-Induced Landau Levels in a Graphene – Black Phosphorus Heterostructure. (arXiv:2211.04014v1 [cond-mat.mes-hall])

2022-11-09T04:30:23+00:00November 9th, 2022|Categories: Publications|Tags: , , , |

Strain-induced pseudo magnetic fields offer the possibility of realizing zero magnetic field Quantum Hall effect in graphene, possibly up to room temperature, representing a promising avenue for lossless charge transport applications. Strain engineering on graphene has been achieved via random nanobubbles or artificial nanostructures on the substrate, but the highly localized and non-uniform pseudomagnetic fields can make spectroscopic probes of electronic structure difficult. Heterostructure engineering offers an alternative approach: By stacking graphene on top of another van der Waals material with large lattice mismatch at a desired twist angle, it is possible to generate large strain-induced pseudo magnetic fields uniformly over the entire heterostructure. Here, we report using nano-angle resolved photoemission spectroscopy (nano-ARPES) to probe the electronic bandstructure of a graphene/black phosphorus heterostructure (G/BP). By directly measuring the iso-energy contours of graphene and black phosphorus we determine a twist angle of 20-degrees in our heterostructure. High-resolution nano-ARPES of the graphene bands near the Fermi level reveals the emergence of flat bands located within the Dirac cone. The spacing of the flat bands is consistent with Landau level formation in graphene, and corresponds to a pseudo-field of 11.36 T. Our work provides a new way to study quantum Hall phases induced by strain in 2D materials and heterostructures.

Published : "arXiv Mesoscale and Nanoscale Physics".

Visualization of Strain-Induced Landau Levels in a Graphene – Black Phosphorus Heterostructure. (arXiv:2211.04014v1 [cond-mat.mes-hall])

2022-11-09T02:29:13+00:00November 9th, 2022|Categories: Publications|Tags: , , , |

Strain-induced pseudo magnetic fields offer the possibility of realizing zero magnetic field Quantum Hall effect in graphene, possibly up to room temperature, representing a promising avenue for lossless charge transport applications. Strain engineering on graphene has been achieved via random nanobubbles or artificial nanostructures on the substrate, but the highly localized and non-uniform pseudomagnetic fields can make spectroscopic probes of electronic structure difficult. Heterostructure engineering offers an alternative approach: By stacking graphene on top of another van der Waals material with large lattice mismatch at a desired twist angle, it is possible to generate large strain-induced pseudo magnetic fields uniformly over the entire heterostructure. Here, we report using nano-angle resolved photoemission spectroscopy (nano-ARPES) to probe the electronic bandstructure of a graphene/black phosphorus heterostructure (G/BP). By directly measuring the iso-energy contours of graphene and black phosphorus we determine a twist angle of 20-degrees in our heterostructure. High-resolution nano-ARPES of the graphene bands near the Fermi level reveals the emergence of flat bands located within the Dirac cone. The spacing of the flat bands is consistent with Landau level formation in graphene, and corresponds to a pseudo-field of 11.36 T. Our work provides a new way to study quantum Hall phases induced by strain in 2D materials and heterostructures.

Published in: "arXiv Material Science".

Current-induced quasiparticle magnetic multipole moments. (arXiv:2210.15753v1 [cond-mat.mtrl-sci])

2022-10-31T02:29:15+00:00October 31st, 2022|Categories: Publications|Tags: , , |

Magnetic ordering beyond the standard dipolar order has attracted significant attention in recent years, but it remains an open question how to effectively manipulate such nontrivial order parameters using external perturbations. In this context, we present a theory for Cartesian magnetic multipole moments and their currents created by electric currents based on a general gauge-invariant formula for arbitrary-order spin magnetic multipole moments of Bloch wave packets. As a concrete example, we point out that the low-energy quasiparticles in phosphorene subject to a perpendicular electric field have a valley structure that hosts magnetic octupole moments. The quasiparticle magnetic octupole moments can be exhibited by an in-plane electric current and lead to accumulation of staggered spin densities at the corners of a rectangular-shaped sample. A current carrying the octupole moments can further be induced through nonlinear response. Our work paves the way to systematically searching for and utilizing quasiparticles with higher-order magnetic multipole moments in crystal materials.

Published in: "arXiv Material Science".

Van der Waals heterostructure mid-infrared emitters with electrically controllable polarization states and spectral characteristics. (arXiv:2210.14098v1 [physics.optics])

2022-10-26T02:29:36+00:00October 26th, 2022|Categories: Publications|Tags: , , |

Modern infrared (IR) microscopy, communication, and sensing systems demand control of the spectral characteristics and polarization states of light. Typically, these systems require the cascading of multiple filters, polarization optics and rotating components to manipulate light, inevitably increasing their sizes and complexities. Here, we report two-terminal mid-infrared (mid-IR) emitters with electrically controllable spectral and polarization properties. Our devices are composed of two back-to-back p-n junctions formed by stacking anisotropic light-emitting materials, black phosphorus and black arsenic-phosphorus with MoS2. By controlling the crystallographic orientations and engineering the band profile of heterostructures, the emissions of two junctions exhibit distinct spectral ranges and polarization directions; more importantly, these two electroluminescence (EL) units can be independently activated, depending on the polarity of the applied bias. Furthermore, we show that when operating our emitter under the polarity-switched pulse mode, its EL exhibits the characteristics of broad spectral coverage, encompassing the entire first mid-IR atmospheric window, and electrically tunable spectral shapes. Our results provide the basis for developing groundbreaking technology in the field of light emitters.

Published in: "arXiv Material Science".

Highly Modulated Dual Semimetal and Semiconducting Gamma-GeSe with Strain Engineering. (arXiv:2210.08704v1 [cond-mat.mtrl-sci])

2022-10-18T02:29:45+00:00October 18th, 2022|Categories: Publications|Tags: , , , |

Layered hexagonal Gamma–GeSe, a new polymorph of GeSe synthesized recently, shows strikingly high electronic conductivity in its bulk form (even higher than graphite) while semiconducting in the case of monolayer (1L). In this work, by using first-principles calculations, we demonstrate that, different from its orthorhombic phases of GeSe, the Gamma–GeSe shows a small spatial anisotropic dependence and a strikingly thickness-dependent behavior with transition from semimetal (bulk, 0.04 eV) to semiconductor (1L, 0.99 eV), and this dual conducting characteristic realized simply with thickness control in Gamma-GeSe has not been found in other 2D materials before. The lacking of d-orbital allows charge carrier with small effective mass (0.16 m0 for electron and 0.23 m0 for hole) which is comparable to phosphorene. Meanwhile, 1L Gamma–GeSe shows a superior flexibility with Young’s modulus of 86.59 N/m, only one-quarter of that of graphene and three-quarters of that of MoS2, and Poisson’s ratio of 0.26, suggesting a highly flexible lattice. Interestingly, 1L Gamma-GeSe shows an in-plane isotropic elastic modulus inherent with hexagonal symmetry while an anisotropic in-plane effective mass owing to shifted valleys around the band edges. We demonstrate the feasibility of strain engineering in inducing indirect-direct and semiconductor-metal transitions resulting from competing bands at the band edges. Our work shows that the free 1L Gamma-GeSe shows a strong light absorption (~106 cm-1) and an indirect bandgap with rich valleys at band edges, enabling high carrier concentration and a low rate of direct electron-hole recombination which would be promising for nanoelectronics and solar cell applications.

Published in: "arXiv Material Science".

Biological Effects of Black Phosphorus Nanomaterials on Mammalian Cells and Animals

2022-10-12T13:07:28+00:00October 12th, 2022|Categories: Publications|Tags: |

The remarkable progress of applied black phosphorus nanomaterials (BPNMs) is attributed to its outstanding properties. Due to its potential for applications, environmental release and subsequent human exposure are virtually inevitable. Therefore, how BPNMs impact biological systems and human health needs to be considered. In this comprehensive review, the most recent advancements in understanding the mechanisms and regulation factors of BPNMs endogenous toxicity to mammalian systems are presented. These achievements lay the ground work for an understanding of its biological effects, aimed towards establishing regulatory principles to minimize the adverse health impacts.

Published in: "Angewandte Chemie International Edition".

Wigner molecules in phosphorene quantum dots. (arXiv:2210.02705v1 [cond-mat.mes-hall])

2022-10-07T04:30:22+00:00October 7th, 2022|Categories: Publications|Tags: |

We study Wigner crystallization of electron systems in phosphorene quantum dots with confinement of an electrostatic origin with both circular and elongated geometry. The anisotropy of the effective mass allows for the formation of Wigner molecules in the laboratory frame with a confined charge density that has lower symmetry than the confinement potential. We find that in circular quantum dots separate single-electron islands are formed for two and four confined electrons but not for three trapped carriers. The spectral signatures of the Wigner crystallization to be resolved by transport spectroscopy are discussed. Systems with Wigner molecule states are characterized by a nearly degenerate ground state at $B=0$ and are easily spin-polarized by the external magnetic field. In electron systems for which the single-electron islands are not formed, a more even distribution of excited states at $B=0$ is observed, and the confined system undergoes ground state symmetry transitions at magnetic fields of the order of 1 Tesla. The system of five electrons in a circular quantum dot is indicated as a special case with two charge configurations that appear in the ground-state as the magnetic field is changed: one with the single electron islands formed in the laboratory frame and the other where only the pair-correlation function in the inner coordinates of the system has a molecular form as for three electrons. The formation of Wigner molecules of quasi-1D form is easier for the orientation of elongated quantum dots along the zigzag direction with heavier electron mass. The smaller electron effective

Published : "arXiv Mesoscale and Nanoscale Physics".

Superconducting properties of doped blue phosphorene: Effects of non-adiabatic approach. (arXiv:2210.01151v1 [cond-mat.supr-con])

2022-10-05T04:30:31+00:00October 5th, 2022|Categories: Publications|Tags: |

We study the effects of Kohn anomalies on the superconducting properties in electron- and hole-doped cases of monolayer blue phosphorene, considering both adiabatic and non-adiabatic phonon dispersions using first-principles calculations. We show that the topology of the Fermi surface is crucial for the formation of Kohn anomalies of doped blue phosphorene. By using the anisotropic Eliashberg formalism, we further carefully consider the temperature dependence of the non-adiabatic phonon dispersions. In cases of low hole densities, strong electron-phonon coupling leads to a maximum critical temperature of $T_c=97$ K for superconductivity. In electron-doped regimes, on the other hand, a maximum superconducting critical temperature of $T_c=38$ K is reached at a doping level that includes a Lifshitz transition point. Furthermore, our results indicate that the most prominent component of electron-phonon coupling arises from the coupling between an in-plane (out-of-plane) deformation and in-plane (out-of-plane) electronic states of the electron (hole) type doping.

Published : "arXiv Mesoscale and Nanoscale Physics".

Superconducting properties of doped blue phosphorene: Effects of non-adiabatic approach. (arXiv:2210.01151v1 [cond-mat.supr-con])

2022-10-05T02:29:18+00:00October 5th, 2022|Categories: Publications|Tags: |

We study the effects of Kohn anomalies on the superconducting properties in electron- and hole-doped cases of monolayer blue phosphorene, considering both adiabatic and non-adiabatic phonon dispersions using first-principles calculations. We show that the topology of the Fermi surface is crucial for the formation of Kohn anomalies of doped blue phosphorene. By using the anisotropic Eliashberg formalism, we further carefully consider the temperature dependence of the non-adiabatic phonon dispersions. In cases of low hole densities, strong electron-phonon coupling leads to a maximum critical temperature of $T_c=97$ K for superconductivity. In electron-doped regimes, on the other hand, a maximum superconducting critical temperature of $T_c=38$ K is reached at a doping level that includes a Lifshitz transition point. Furthermore, our results indicate that the most prominent component of electron-phonon coupling arises from the coupling between an in-plane (out-of-plane) deformation and in-plane (out-of-plane) electronic states of the electron (hole) type doping.

Published in: "arXiv Material Science".

Unexpected Persistent Production of Reactive Oxygen Species during the Degradation of Black Phosphorous in the Darkness

2022-10-01T13:07:44+00:00October 1st, 2022|Categories: Publications|Tags: |

Few-layer black phosphorus (FLBP) is easily degraded under ambient condition which is an important barrier that plagues the application of FLBP, but its degradation mechanism is not yet well understood. In this work, we surprisingly found the persistent reactive oxygen species (ROS) generation was involved with FLBP degradation process even in the dark, and ROS generation patterns and mechanism was revealed by chemiluminescence (CL) and density functional theory (DFT) . Meanwhile, rhodamine B (RhB) and methyl orange (MO) can also be removed by FLBP under dark conditions, which further evidence the ROS generation during FLBP self-degradation. This work provides new insights into FLBP self-degradation mechanism and opens opportunities to practically implement FLBP for green catalytic application.

Published in: "Angewandte Chemie International Edition".

Effect of excess charge carriers and fluid medium on the magnitude and the sign of the Casimir-Lifshitz torqueP. Thiyam. (arXiv:2209.08846v1 [cond-mat.mes-hall])

2022-09-20T04:30:41+00:00September 20th, 2022|Categories: Publications|Tags: |

Last year, we reported a perturbative theory of the Casimir-Lifshitz torque between planar biaxially anisotropic materials in the retarded limit [Phys. Rev. Lett. {bf 120}, 131601 (2018)], which is applied here to study the change of sign and magnitude of the torque with separation distance in biaxial black phosphorus having excess charge carriers. The study is carried out both in vacuum as well as in a background fluid medium. The presence of extra charge carriers and that of an intervening fluid medium are both found to promote enhancement of the magnitude of the torque between identical slabs. The degree of enhancement of the magnitude of torque increases not only with an increased carrier concentration but also with separation distance. In the non-identical case when different planes of anisotropic black phosphorus face each other, owing to the non-monotonic characteristic of the sign-reversal effect of the torque, the enhancement by carrier addition and intervening medium also becomes non-monotonic with distance. In the presence of a background medium, the non-monotonic degree of enhancement of the torque with distance is observed even between identical slabs.

Published : "arXiv Mesoscale and Nanoscale Physics".

Diatomic Pd‐Cu Metal‐Phosphorus Sites for Complete N≡N Bond Formation in Photoelectrochemical Nitrate Reduction

2022-08-31T13:07:45+00:00August 31st, 2022|Categories: Publications|Tags: , |

The synergistic effect of bimetallic heterogeneous catalysis in the reaction of nitrate reduction to nitrogen has been widely discussed, but it is still not clear how this effect works at the atomic scale, hindering the rational design of high-performance catalysts. Here, for the first time, 2D phosphorene was used as a giant P ligand to confine high-density PdCu dual-atom to form a unique PdCuP 4 coordination structure, and this catalyst achieves 96.3% NO 3 − removal rate and 95.2% N 2 selectivity. In-situ characterization combined with density functional theory (DFT) calculations show that the PdCu dual-atom form covalent-like bonds with adjacent P atoms, reducing the adsorption energy of the reactants. The synergistic effect of PdCu dual-atom promotes the breaking of N-O bond, and the short bond distance of ~ 3Å between PdCu atoms accelerates the transfer of NO 2 − , and eventually the two Pd-N adjacent to the surface of Pd rapidly combine to form N 2 .

Published in: "Angewandte Chemie International Edition".

Transmission gaps in phosphorene superlattice. (arXiv:2208.13067v1 [cond-mat.mes-hall])

2022-08-30T04:30:17+00:00August 30th, 2022|Categories: Publications|Tags: , , |

Our research focuses on the transmission gaps of charge carriers passing through phosphorene superlattice, which are made up of a series of barriers and wells generating $n$ identical cells. We determine the solutions of the energy spectrum and then transmission using Bloch’s theorem and the transfer-matrix approach. The analysis will be done on the impact of incident energy, barrier height, potential widths, period number, and transverse wave vector on transmission. We show that pseudo-gaps appear and turn into real transmission gaps by increasing the number of cells. Their number, width, and position can be tuned by changing the physical parameters of the structure. At normal incidence, a forbidden gap is found, meaning that there is no Klein tunneling effect, in contrast to the case of graphene. Our findings can be used to create a variety of phosphorene-based electronic devices.

Published : "arXiv Mesoscale and Nanoscale Physics".

Anisotropy of the Optical Properties of Pentacene:Black Phosphorus Interfaces. (arXiv:2208.07780v1 [cond-mat.mtrl-sci])

2022-08-17T02:29:32+00:00August 17th, 2022|Categories: Publications|Tags: |

Black phosphorus (BP) is a layered material with anisotropic properties. We study interfaces formed by a pentacene monolayer adsorbed on monolayer BP, a prototypical system for BP surface passivation. We place the pentacene monolayer along the zigzag and armchair directions of the BP substrate, respectively, to examine the anisotropy of the heterogeneous interfaces. We perform first-principles $GW$ plus Bethe-Salpeter equation ($GW$-BSE) calculations to determine the quasiparticle and optical properties. To quantitatively analyze the anisotropy of the optical properties, we develop a general computational scheme to decompose the interface excitons into different contributions. We find a distinct charge-transfer exciton formed when the monolayer pentacene is placed along the armchair direction, and discuss how the anisotropy of each component is modulated by the interface. Our results shine a light on the understanding of the BP surface passivation via molecular adsorption and provide a benchmark for future experimental and computational studies.

Published in: "arXiv Material Science".

Nanomechanical Resonators: Toward Atomic Scale. (arXiv:2208.07164v1 [cond-mat.mes-hall])

2022-08-16T04:30:23+00:00August 16th, 2022|Categories: Publications|Tags: , |

The quest for realizing and manipulating ever smaller man-made movable structures and dynamical machines has spurred tremendous endeavors, led to important discoveries, and inspired researchers to venture to new grounds. Scientific feats and technological milestones of miniaturization of mechanical structures have been widely accomplished by advances in machining and sculpturing ever shrinking features out of bulk materials such as silicon. With the flourishing multidisciplinary field of low-dimensional nanomaterials, including one-dimensional (1D) nanowires/nanotubes, and two-dimensional (2D) atomic layers such as graphene/phosphorene, growing interests and sustained efforts have been devoted to creating mechanical devices toward the ultimate limit of miniaturization–genuinely down to the molecular or even atomic scale. These ultrasmall movable structures, particularly nanomechanical resonators that exploit the vibratory motion in these 1D and 2D nano-to-atomic-scale structures, offer exceptional device-level attributes, such as ultralow mass, ultrawide frequency tuning range, broad dynamic range, and ultralow power consumption, thus holding strong promises for both fundamental studies and engineering applications. In this Review, we offer a comprehensive overview and summary of this vibrant field, present the state-of-the-art devices and evaluate their specifications and performance, outline important achievements, and postulate future directions for studying these miniscule yet intriguing molecular-scale machines.

Published : "arXiv Mesoscale and Nanoscale Physics".

Atomically Sharp, Closed Bilayer Phosphorene Edges by Self-Passivation. (arXiv:2208.01288v1 [cond-mat.mes-hall])

2022-08-03T04:30:15+00:00August 3rd, 2022|Categories: Publications|Tags: , , |

Two-dimensional (2D) crystals’ edge structures not only influence their overall properties but also dictate their formation due to edge-mediated synthesis and etching processes. Edges must be carefully examined because they often display complex, unexpected features at the atomic scale, such as reconstruction, functionalization, and uncontrolled contamination. Here, we examine atomic-scale edge structures and uncover reconstruction behavior in bilayer phosphorene. We use in situ transmission electron microscopy (TEM) of phosphorene/graphene specimens at elevated temperatures to minimize surface contamination and reduce e-beam damage, allowing us to observe intrinsic edge configurations. Bilayer zigzag (ZZ) edge was found the most stable edge configuration under e-beam irradiation. Through first-principles calculations and TEM image analysis under various tilting and defocus conditions, we find that bilayer ZZ edges undergo edge reconstruction and so acquire closed, self-passivated edge configurations. The extremely low formation energy of the closed bilayer ZZ edge and its high stability against e-beam irradiation are confirmed by first-principles calculations. Moreover, we fabricate bilayer phosphorene nanoribbons with atomically-sharp closed ZZ edges. The identified bilayer ZZ edges will aid in the fundamental understanding of the synthesis, degradation, reconstruction, and applications of phosphorene and related structures.

Published : "arXiv Mesoscale and Nanoscale Physics".

Graphene publications, patents and news are copyrighted by their respective owner. Editorial posts and everything else, copyright 2012-2017 2D Research.
FacebookTwitterRssLinkedInEmail
Toggle Sliding Bar Area
Some say, that 2D Research is the best website in the world.