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Stanene‐Based Nanosheets for β‐Elemene Delivery and Ultrasound‐Mediated Combination Cancer Therapy

2021-01-13T13:07:48+00:00January 13th, 2021|Categories: Publications|Tags: |

Ultrasound (US)‐mediated sonodynamic therapy (SDT) has emerged as a superior modality for cancer treatment owing to the non‐invasiveness and high tissue‐penetrating depth. However, developing biocompatible nanomaterial‐based sonosensitizers with efficient SDT capability remains challenging. Here, we employed a liquid‐phase exfoliation strategy to obtain a new type of two‐dimensional (2D) stanene‐based nanosheets (SnNSs) with a band gap of 2.3 eV, which is narrower than those of the most extensively studied nano‐sonosensitizers, allowing a more efficient US‐triggered separation of electron (e − )−hole (h + ) pairs for reactive oxygen species (ROS) generation. In addition, we discovered that such SnNSs could also serve as robust near‐infrared (NIR)‐mediated photothermal therapy (PTT) agents owing to their efficient photothermal conversion, and serve as nanocarriers for anticancer drug delivery owing to the inherent 2D layered structure. This study not only presents general nanoplatforms for SDT‐enhanced combination cancer therapy, but also highlights the utility of 2D SnNSs to the field of nanomedicine.

Published in: "Angewandte Chemie International Edition".

Growth of germanium-silver surface alloys followed by in situ scanning tunneling microscopy: Absence of germanene formation. (arXiv:2011.12577v1 [cond-mat.mtrl-sci])

2020-11-26T02:29:48+00:00November 26th, 2020|Categories: Publications|Tags: , , |

Theoretical studies have shown that new physical properties such as tunable gap openings or quantum spinHall effects could be expected from group-IV graphene analogs (silicene, germanene, stanene). While therehave been numerous studies of growth of such Si, Ge, Sn monolayers, the demonstration of their hexagonalorganization has been often based on postgrowth characterization, and their analogy to graphene has remainedcontroversial. Our real-time scanning tunneling microscopy (STM) observation during Ge deposition on Ag(111)in the 380–430 K temperature range reveals that Ag atoms are involved in all the structures observed beforethe formation of a second layer, rejecting the possible formation of germanene on this substrate within theseexperimental conditions. The observation by STM of Ge atomic diffusion shows that easy exchange between Agand Ge atoms is responsible for the Ge-Ag surface alloying at such temperatures.

Published in: "arXiv Material Science".

Effects of parallel electric and magnetic fields on Rydberg excitons in buckled two-dimensional materials. (arXiv:2011.03093v1 [cond-mat.mes-hall])

2020-11-09T02:29:52+00:00November 9th, 2020|Categories: Publications|Tags: , , , |

We study direct and indirect magnetoexcitons in Rydberg states in monolayers and double-layer heterostructures of Xenes (silicene, germanene, and stanene) in external parallel electric and magnetic fields, applied perpendicular to the monolayer and heterostructure. We calculate binding energies of magnetoexcitons for the Rydberg states 1$s$, 2$s$, 3$s$, and 4$s$, by numerical integration of the Schr”{o}dinger equation using the Rytova-Keldysh potential for direct magnetoexciton and both the Rytova-Keldysh and Coulomb potentials for indirect excitons. Latter allows understanding a role of screening in Xenes. In the external perpendicular electric field, the buckled structure of the Xene monolayers leads to appearance of potential difference between sublattices allowing to tune electron and hole masses and, therefore, the binding energies and diamagnetic coefficients (DMCs) of magnetoexcitons. We report the energy contribution from electric and magnetic fields to the binding energies and DMCs. The tunability of the energy contribution of direct and indirect magnetoexcitons by electric and magnetic fields is demonstrated. It is also shown that DMCs of direct excitons can be tuned by the electric field, and the DMCs of indirect magnetoexcitons can be tuned by the electric field and manipulated by the number of h-BN layers. Therefore, these allowing the possibility of electronic devices design that can be controlled by external electric and magnetic fields and the number of h-BN layers. The calculations of the binding energies and DMCs of magnetoexcitons in Xenes monolayers and heterostructures are novel and can be compared with the experimental results when they will be available.

Published in: "arXiv Material Science".

Spin splitting and spin Hall conductivity in buckled monolayers of the group 14: first-principles calculations. (arXiv:2009.13753v1 [cond-mat.mtrl-sci])

2020-09-30T02:30:21+00:00September 30th, 2020|Categories: Publications|Tags: , |

Elemental monolayers of the group 14 with a buckled honeycomb structure, namely silicene, germanene, stanene, and plumbene, are known to demonstrate a spin splitting as a result of an electric field parallel to their high symmetry axis which is capable of tuning their topological phase between a quantum spin Hall insulator and an ordinary band insulator. We perform first-principles calculations based on the density functional theory to quantify the spin-dependent band gaps and the spin splitting as a function of the applied electric field and extract the main coefficients of the invariant Hamiltonian. Using the linear response theory and the Wannier interpolation method, we calculate the spin Hall conductivity in the monolayers and study its sensitivity to an external electric field. Our results show that the spin Hall conductivity is not quantized and in the case of silicene, germanene, and stanene degrades significantly as the electric field inverts the band gap and brings the monolayer into the trivial phase. The electric field induced band gap does not close in the case of plumbene which shows a spin Hall conductivity that is robust to the external electric field.

Published in: "arXiv Material Science".

Structure and binding of stanene on the Al$_{2}$O$_{3}$(0001) surface. (arXiv:2009.00684v1 [cond-mat.mtrl-sci])

2020-09-03T02:29:30+00:00September 3rd, 2020|Categories: Publications|Tags: , |

Stanene, the two-dimensional monolayer form of tin, has been predicted to be a 2D topological insulator due to its large spin-orbit interaction. However, a clear experimental demonstration of stanene’s topological properties has eluded observation, in part because of the difficulty of choosing a substrate on which stanene will remain topologically nontrivial. In this paper, we present first-principles density functional theory (DFT) calculations of epitaxial monolayer stanene grown on the (0001) surface of alumina, Al$_{2}$O$_{3}$. We perform a detailed analysis of the binding energy and electronic structure of stanene on Al$_{2}$O$_{3}$, and demonstrate that it is a quantum spin Hall insulator. In addition, we discuss the relevance of decorated stanene and dumbbell stanene on the alumina surface.

Published in: "arXiv Material Science".

Chemical functionalization, electronic and dielectric properties of hybrid organic-tin layers. (arXiv:2008.13630v1 [cond-mat.mtrl-sci])

2020-09-01T02:29:32+00:00September 1st, 2020|Categories: Publications|Tags: |

Band gap tuning and dielectric properties of small organic ligands adsorbed on tin monolayers (stanene) have been investigated using first-principles calculations. Charge density analysis using density-functional theory shows that the ligands are chemisorbed on stanene and some of the groups can open a band gap in the originally metallic statene. Furthermore many-body GW calculations demonstrate that the dielectric properties of bare and ligand adsorbed stanene have a large anisotropy. Our findings of a finite gap opens a path for rational theoretical design of functionalized two-dimensional stanene.

Published in: "arXiv Material Science".

Fast Bayesian Force Fields from Active Learning: Study of Inter-Dimensional Transformation of Stanene. (arXiv:2008.11796v1 [physics.comp-ph])

2020-08-28T02:29:18+00:00August 28th, 2020|Categories: Publications|Tags: |

We present a way to dramatically accelerate Gaussian process models for interatomic force fields based on many-body kernels by mapping both forces and uncertainties onto functions of low-dimensional features. This allows for automated active learning of models combining near-quantum accuracy, built-in uncertainty, and constant cost of evaluation that is comparable to classical analytical models, capable of simulating millions of atoms. Using this approach, we perform large scale molecular dynamics simulations of the stability of the stanene monolayer. We discover an unusual phase transformation mechanism of 2D stanene, where ripples lead to nucleation of bilayer defects, densification into a disordered multilayer structure, followed by formation of bulk liquid at high temperature or nucleation and growth of the 3D bcc crystal at low temperature. The presented method opens possibilities for rapid development of fast accurate uncertainty-aware models for simulating long-time large-scale dynamics of complex materials.

Published in: "arXiv Material Science".

Stanene: A Good Platform for Topological Insulator and Topological Superconductor. (arXiv:2007.05465v1 [cond-mat.mtrl-sci])

2020-07-13T02:29:25+00:00July 13th, 2020|Categories: Publications|Tags: , |

Two dimensional (2D) topological insulators (TIs) and topological superconductors (TSCs) have been intensively studied for recent years due to its great potential for dissipationless electron transportation and fault-tolerant quantum computing, respectively. Here we focus on stanene, the tin analogue of graphene, to give a brief review of its development as a candidate for both 2D TI and TSC. Stanene is proposed to be a TI with a large gap of 0.3 eV, and its topological properties are sensitive to various factors, e.g., the lattice constants, chemical functionalization and layer thickness, which offer various methods for phase tunning. Experimentally, the inverted gap and edge states are observed recently, which are strong evidence for TI. In addition, stanene is also predicted to be a time reversal invariant TSC by breaking inversion symmetry, supporting helical Majorana edge modes. The layer-dependent superconductivity of stanene is recently confirmed by both transport and scanning tunneling microscopy measurements. This review gives a detailed introduction to stanene and its topological properties and some prospects are also discussed.

Published in: "arXiv Material Science".

Combining quantum spin hall effect and superconductivity in few-layer stanene. (arXiv:2006.09834v1 [cond-mat.mes-hall])

2020-06-18T02:30:07+00:00June 18th, 2020|Categories: Publications|Tags: |

Stanene was proposed to be a quantum spin hall insulator containing topological edges states and a time reversal invariant topological superconductor hosting helical Majorana edge mode. Recently, experimental evidences of existence of topological edge states have been found in monolayer stanene films and superconductivity has been observed in few-layer stanene films excluding single layer. An integrated system with both topological edge states and superconductivity are higly pursued as a possible platform to realize topological superconductivity. Few-layer stanene show great potential to meet this requirement and is highly desired in experiment. Here we successfully grow few-layer stanene on bismuth (111) substrate. Both topological edge states and superconducting gaps are observed by in-situ scanning tunneling microscopy/spectroscopy (STM/STS). Our results take a further step towards topological superconductivity by stanene films.

Published in: "arXiv Material Science".

Type-II Ising pairing in few-layer stanene

2020-03-26T19:09:00+00:00March 26th, 2020|Categories: Publications|Tags: |

Spin-orbit coupling has proven indispensable in the realization of topological materials and, more recently, Ising pairing in two-dimensional superconductors. This pairing mechanism relies on inversion symmetry–breaking and sustains anomalously large in-plane polarizing magnetic fields whose upper limit is predicted to diverge at low temperatures. Here, we show that the recently discovered superconductor few-layer stanene, epitaxially strained gray tin (α-Sn), exhibits a distinct type of Ising pairing between carriers residing in bands with different orbital indices near the -point. The bands are split as a result of spin-orbit locking without the participation of inversion symmetry–breaking. The in-plane upper critical field is strongly enhanced at ultralow temperature and reveals the predicted upturn.

Published in: "Science".

Kagome silicene: a novel exotic form of two-dimensional epitaxial silicon. (arXiv:2001.11241v1 [cond-mat.mtrl-sci])

2020-01-31T02:29:26+00:00January 31st, 2020|Categories: Publications|Tags: , , |

Since the discovery of graphene, intensive efforts have been made in search of novel two-dimensional (2D) materials. Decreasing the materials dimensionality to their ultimate thinness is a promising route to unveil new physical phenomena, and potentially improve the performance of devices. Among recent 2D materials, analogs of graphene, the group IV elements have attracted much attention for their unexpected and tunable physical properties. Depending on the growth conditions and substrates, several structures of silicene, germanene, and stanene can be formed. Here, we report the synthesis of a Kagome lattice of silicene on aluminum (111) substrates. We provide evidence of such an exotic 2D Si allotrope through scanning tunneling microscopy (STM) observations, high-resolution core-level (CL) and angle-resolved photoelectron spectroscopy (ARPES) measurements, along with Density Functional Theory calculations.

Published in: "arXiv Material Science".

Spin-dependent Dirac electrons and valley polarization in the ferromagnetic stanene/$mathrm{Cr}{mathrm{I}}_{3}$ van der Waals heterostructure

2019-11-21T16:33:04+00:00November 21st, 2019|Categories: Publications|Tags: , |

Author(s): Baoxing Zhai, Juan Du, Chenhai Shen, Tianxing Wang, Yuting Peng, Qiming Zhang, and Congxin XiaRealization and regulation of valley polarization is a core issue in the valleytronics fields. Here, through first-principles calculations, we find that the valley polarization (up to 39.6 meV) can be realized in stanene, by stacking it on a monolayer ferromagnetic insulator CrI3, forming the ferrom…[Phys. Rev. B 100, 195307] Published Thu Nov 21, 2019

Published in: "Physical Review B".

Selected graphenelike zigzag nanoribbons with chemically functionalized edges: Implications for electronic and magnetic properties. (arXiv:1910.00301v1 [cond-mat.mes-hall])

2019-10-02T02:29:21+00:00October 2nd, 2019|Categories: Publications|Tags: , , |

It is known that there is a wide class of quasi-two-dimensional graphenelike nanomaterials which in many respects can outperform graphene. So, here in addition to graphene, the attention is directed to stanene (buckled honeycomb structure) and phosphorene (puckered honeycomb structure). It is shown that, depending on the doping, these materials can have magnetically ordered edges. Computed diagrams of magnetic phases illustrate that, on the one hand, n-type doped narrow zigzag nanoribbons of graphene and stanene have antiferromagnetically aligned magnetic moments between the edges. On the other hand, however, in the case of phosphorene nanoribbons the zigzag edges can have ferromagnetically aligned magnetic moments for the p-type doping. The edge magnetism critically influences transport properties of the nanoribbons, and if adequately controlled can make them attractive for spintronics.

Published in: "arXiv Material Science".

Epitaxial growth and electronic properties of few-layer stanene on InSb (1 1 1)

2019-10-01T10:34:56+00:00October 1st, 2019|Categories: Publications|Tags: |

Stanene has been theoretically predicted to be a 2D topological insulator with a large band gap, potentially hosting quantum spin Hall effect at room temperature. Here, few-layer stanene films have been epitaxially grown on Sb-terminated InSb (1 1 1) surface and their structural and electrical properties are characterized. Scanning tunneling spectrum results reveal a large bulk bandgap in single-layer stanene (over 0.2 eV). Moreover, spectroscopy evidence for a filled edge state near the steps was observed. The gap decreases dramatically with increasing number of layers, and multilayer stanene should become a Dirac semimetal in the bulk limit. The changeover may involve nontrivial topological phase transitions. Clear and reproducible Shubnikov–de Haas oscillations were observed on the single-layer stanene films that were exposed to atmospheric conditions for an extended period of time, showing the possibility for device experiments using nanofabrication and magneto-transport. Ou…

Published in: "2DMaterials".

Quantum Spin Hall Insulators in Tin Films: Beyond Stanene. (arXiv:1909.09326v1 [cond-mat.mtrl-sci])

2019-09-23T02:29:36+00:00September 23rd, 2019|Categories: Publications|Tags: , |

Large-gap quantum spin Hall (QSH) insulators were previously predicted in stanene and its derivatives. Beyond stanene that is the thinnest $alpha$-Sn(111) film, we propose to explore QSH insulators in $alpha$-Sn films with different crystallographic orientations. Our first-principles calculations reveal that the thickness-dependent band gap of $alpha$-Sn (100) and (110) films does not show a monotonic decrease as typically expected by quantum confinement, but displays an oscillating change behavior, an indicative of topological quantum phase transition. While these films are normal insulators in the ultrathin limit, the QSH phase emerges above a critical film thickness of around 10 layers. Remarkably, the QSH insulators are obtainable within a wide thickness range and their energy gaps are sizable (even $>$0.1 eV), which facilitates experimental realization of the high-temperature QSH effect.

Published in: "arXiv Material Science".

Microscopic theory of in-plane critical field in two-dimensional Ising superconducting systems. (arXiv:1909.08819v1 [cond-mat.supr-con])

2019-09-20T02:29:33+00:00September 20th, 2019|Categories: Publications|Tags: |

We study the in-plane critical magnetic field of two-dimensional Ising superconducting systems, and propose the microscopic theory for these systems with or without inversion symmetry. Protected by certain specific spin-orbit interaction which polarizes the electron spin to the out-of-plane direction, the in-plane critical fields largely surpass the Pauli limit and show remarkable upturn in the zero temperature limit. The impurity scattering and Rashba spin-orbit coupling, treated on equal-footing in the microscopic framework, both weaken the critical field but in qualitatively different manners. The microscopic theory is consistent with recent experimental results in stanene and Pb superconducting ultra-thin films.

Published in: "arXiv Material Science".

Formation of a Te-Ag Honeycomb Alloy: A New Type of Two-Dimensional Material. (arXiv:1909.09008v1 [cond-mat.mtrl-sci])

2019-09-20T02:29:27+00:00September 20th, 2019|Categories: Publications|Tags: , , |

Inspired by the unique properties of graphene, the focus in the literature is now on investigations of various two-dimensional (2D) materials with the aim to explore their properties for future applications. The group IV analogues of graphene, i.e., silicene, germanene and stanene have been intensively studied in recent years. However, their semi-metallic band structures hamper their use in electronic applications. Hence, the synthesis of 2D materials with band gaps of various sizes has attracted a large interest. Here, we report a successful preparation of a 2D Te-Ag binary alloy with a honeycomb structure. Angle-resolved photoelectron spectroscopy (ARPES) in combination with first-principles calculations using density functional theory (DFT) confirmed the formation of this binary alloy. The semiconducting property is verified by the ARPES data and a direct gap of ~0.7 eV is predicted by the DFT calculations.

Published in: "arXiv Material Science".

Selected graphenelike zigzag nanoribbons with chemically functionalized edges: Implications for electronic and magnetic properties

2019-09-16T16:37:53+00:00September 16th, 2019|Categories: Publications|Tags: , , |

Author(s): S. KrompiewskiIt is known that there is a wide class of quasi-two-dimensional graphenelike nanomaterials which in many respects can outperform graphene. So, here in addition to graphene, the attention is directed to stanene (buckled honeycomb structure) and phosphorene (puckered honeycomb structure). It is shown …[Phys. Rev. B 100, 125421] Published Mon Sep 16, 2019

Published in: "Physical Review B".

Spin-orbit coupling in elemental two-dimensional materials

2019-09-16T14:38:07+00:00September 16th, 2019|Categories: Publications|Tags: , , , , , |

Author(s): Marcin Kurpas, Paulo E. Faria Junior, Martin Gmitra, and Jaroslav FabianThe fundamental spin-orbit coupling and spin mixing in graphene and rippled honeycomb lattice materials silicene, germanene, stanene, blue phosphorene, arsenene, antimonene, and bismuthene is investigated from first principles. The intrinsic spin-orbit coupling in graphene is revisited using multiba…[Phys. Rev. B 100, 125422] Published Mon Sep 16, 2019

Published in: "Physical Review B".

Wave mixing and high harmonic generation at two-color multiphoton excitation in two-dimensional hexagonal nanostructures

2019-07-25T14:41:54+00:00July 25th, 2019|Categories: Publications|Tags: , , |

Author(s): H. K. Avetissian, A. K. Avetissian, B. R. Avchyan, and G. F. MkrtchianThe high-order wave mixing by two-color multiphoton excitation in nonlinear regime along with the harmonics generation in two-dimensional (2D) nanostructures such as graphene, silicene, germanene, and stanene is investigated. We consider the coherent part of the spectra corresponding to high harmoni…[Phys. Rev. B 100, 035434] Published Thu Jul 25, 2019

Published in: "Physical Review B".

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