Combined AFM and STM measurements of a silicene sheet grown on Ag(111) surface
Zsolt Majzik, Mohamed Rachid Tchalala, Martin Švec, Prokop Hapala, Hanna Enriquez, Abdelkader Kara, Andrew J. Mayne, Gérald Dujardin, Pavel Jelínek, Hamid Oughaddou
In this Letter, we present the first non-contact atomic force microscopy (nc-AFM) of a silicene on silver (Ag) surface, obtained by combining non-contact atomic force microscopy (nc-AFM) and scanning tunneling microscopy (STM). STM images over large areas of silicene grown on Ag(111) surface show both (sqrt13xsqrt13)R13.9° and (4x4) superstructures. For the widely observed (4x4) structure, the nc-AFM topography shows an atomic-scale contrast inversion as the tip-surface distance is decreased. At the shortest tip-surface distance, the nc-AFM topography is very similar to the STM one. The observed structure in the nc-AFM topography is compatible with only one out of two silicon atoms being visible. This indicates unambiguously a strong buckling of the silicene honeycomb layer.
Point defects in epitaxial silicene on Ag(111) surface
硅烯是石墨烯的对应物,由于其奇异的电子性质和与成熟的硅基半导体技术的良好兼容性,获得了快速发展。然而,其约100 cm 2 V-1 s-1的低室温迁移率抑制了器件应用,例如场效应晶体管。一般来说,缺陷和晶界将作为散射中心,从而降低载流子迁移率。本文采用第一性原理计算结合扫描隧道显微镜(STM)的实验观测,系统地研究了Ag(111)表面外延硅烯中各种点缺陷的形貌。用扫描隧道显微镜(STM)对Ag(111)表面外延硅烯中的各种缺陷进行了表征。特别是,在Ag(111)支持的硅烯片的点缺陷的形成能显示出一个有趣的依赖于超结构,这反过来,可能有影响的缺陷密度控制在合成硅烯。通过对不同硅烯超结构中各种点缺陷浓度的估算,揭示了v13*v13硅烯在实验中出现缺陷的奥秘,并认为4*4硅烯片是未来器件应用的最佳结构。
Silicene, the two-dimensional (2D) allotrope of silicon has very recently attracted a lot of attention. It has a structure that is similar to graphene and it is theoretically predicted to show the same kind of electronic properties which has put graphene into the focus of large research and development projects world-wide. In particular, a 2D structure made from Si is of high interest because of the application potential in Si-based electronic devices. However, so far there is not much known about the silicene band structure from experimental studies. A comprehensive study is here presented of…
Highly oriented pyrolitic graphite (HOPG) is an inert substrate with a structural honeycomb lattice, well suited for the growth of two-dimensional (2D) silicene layer. It was reported that when Si atoms are deposited on HOPG surface at room temperature, they arrange in two configurations: silicene nanosheets and three dimensional clusters. In this work we demonstrate, by using scanning tunneling microscopy (STM) and Raman spectroscopy, that a third configuration stabilizes in the form of Si 2D nanosheets intercalated below the first top layer of carbon atoms. The Raman spectra reveal a structu…
Recently, silicene, the graphene equivalent of silicon, has attracted a lot of attention due to its compatibility with Si-based electronics. So far, silicene has been epitaxy grown on various crystalline surfaces such as Ag(110), Ag(111), Ir(111), ZrB2(0001) and Au(110) substrates. Here, we present a new method to grow silicene via high temperature surface reconstruction of hexagonal IrSi3 nanocrystals. The h-IrSi3 nanocrystals are formed by annealing thin Ir layers on Si(111) surface. A detailed analysis of the STM images shows the formation of silicene like domains on the surface of some of …
We report on the oxidation of self-assembled silicene nanoribbons grown on the Ag(110) surface using Scanning Tunneling Microscopy and High-Resolution Photoemission Spectroscopy. The results show that silicene nanoribbons present a strong resistance towards oxidation using molecular oxygen. This can be overcome by increasing the electric field in the STM tunnel junction above a threshold of +2.6 V to induce oxygen dissociation and reaction. The higher reactivity of the silicene nanoribbons towards atomic oxygen is observed as expected. The HR-PES confirm these observations: Even at high exposu…
The hydrogen-terminated Silicon(100)-2x1 surface (H-Si(100)-2x1) provides a promising platform for the development of atom scale devices, with recent work showing their creation through precise desorption of surface hydrogen atoms. While samples with relatively large areas of the hydrogen terminated 2x1 surface are routinely created using an in-situ methodology, surface defects are inevitably formed as well reducing the area available for patterning. Here, we present a catalog of several commonly found defects of the H-Si(100)-2x1 surface. By using a combination of scanning tunneling microscop…
Graphene, consisting of an inert, thermally stable material with an atomically flat, dangling bond-free surface is by essence an ideal template layer for van der Waals heteroepitaxy of two-dimensional materials such as silicene. However, depending on the synthesis method and growth parameters, graphene (Gr) substrates could exhibit, on a single sample, various surface structures, thicknesses, defects, and step heights. These structures noticeably affect the growth mode of epitaxial layers, e.g. turning the layer-by-layer growth into the Volmer-Weber growth promoted by defect-assisted nucleatio…
The contrast obtained in scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images is determined by the tip termination and symmetry. Functionalizing the tip with a single metal atom, CO molecule or organic species has been shown to provide high spatial resolution and insights into tip-surface interactions. A topic where this concept is utilized is the adsorption of organic molecules at surfaces. With this work we aim to contribute to the growing database of organic molecules that allow assignment by intra-molecular imaging. We investigated the organic molecule para-sexiphen…
Photoexcited Hole States at the SrTiO3(001) Surface Imaged with Noncontact AFM
TU Wien(维也纳工业大学);University of Vienna(维也纳大学);Charles University(查理大学);Jagiellonian University(雅盖隆大学);CNR-SPIN, c/o Department of Physical and Chemical Sciences, University of L’Aquila(拉奎拉大学物理与化学科学系附属意大利国家研究委员会自旋中心)
Tuning the magnetism of the top-layer FeAs on BaFe$_{2}$As$_{2}$(001): First-principles study
用第一性原理电子结构计算方法研究了BaFe $_{2}$ As $_{2}$(001)表面的磁性.我们发现,对于As终止表面的磁性基态的顶层FeAs是在交错的二聚体反铁磁(AFM)秩序,而Ba终止表面的共线(单条纹)AFM秩序是最稳定的。当Ba或K原子覆盖到As表面时,计算得到的BaFe $_{2}$ As $_{2}$(001)上顶层FeAs的原子力显微镜能级差减小,表明自旋涨落增强.为了确定新的交错的二聚体AFM秩序的终止,我们模拟了扫描隧道显微镜(STM)图像为这个状态,它显示了不同的$\sqrt{2}\times\sqrt{2}$图案的情况下,半钡覆盖。我们的研究结果表明:(1)表面掺杂可以有效地调节BaFe $_{2}$ As $_{2}$(001)上顶层FeAs的磁性;(2)表面终止和顶层FeAs中的原子力显微镜有序度都可以影响BaFe $_{2}$ As $_{2}$(001)的STM图像。
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 …
Atomic-scale characteristics of surfaces dictate the principles governing numerous scientific phenomena ranging from catalysis to friction. Despite this fact, our ability to visualize and alter surfaces on the atomic scale is severely hampered by the strict conditions under which the related methods are operated to achieve high spatial resolution. In particular, the two prominent methods utilized to achieve atomic-resolution imaging - scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) - are typically performed under ultrahigh vacuum (UHV) and often at low tempe…
We combined in-situ scanning tunneling microscopy (STM) with the conventional growth characterization methods of atomic force microscopy (AFM) and reflection high energy electron diffraction (RHEED) to simultaneously assess atomic-scale impurities and the larger-scale surface morphology of molecular beam epitaxy (MBE) grown homoepitaxial InAs(111)A. By keeping a constant substrate temperature and indium flux while increasing the As$_2$ flux, we find two differing MBE growth parameter regions for optimized surface roughness on the macro and atomic scale. In particular, we show that a pure step-…
Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of K$_x$Fe$_{2-y}$Se$_2$
最近发现的K-Fe-Se高温超导体引起了关于其母体化合物性质的激烈争论。输运、角分辨光电子能谱和STM测量表明,它的母体化合物可能是绝缘的、半导体的甚至是金属的[M. H.方,H.- D.王角H.董志J. Li,C.- M. Feng,J. Chen,and H. Q.袁,欧罗巴。Lett. 94,27009(2011); F. Chen等人Phys.Rev.X1,021020(2011);和W. Li等人,物理修订信函109,057003(2012)]。由于与这些不同相关联的磁性基态尚未被识别,磁性和超导性之间的关系也没有完全理解,因此该系统的真正母体化合物仍然难以捉摸。在这里,我们报告的中子衍射实验,揭示了一个半导体反铁磁(AFM)阶段与菱形铁空位秩序。半导体相的磁性顺序与铁磷属元素化物母体化合物的条纹AFM顺序相同。此外,当root 5 * root 5块AFM相与超导性共存时,条纹AFM有序被抑制,这使我们推测新的半导体磁性有序相是该超导体的真正母相。
Based on first-principles calculations and symmetry analysis, we propose that EuIn$_2$As$_2$ is a long awaited axion insulator with antiferromagnetic (AFM) long range order. Characterized by the parity-based invariant $\mathbb Z_4=2$, the topological magneto-electric effect is quantized with $θ=π$ in the bulk, with a band gap as large as 0.1 eV. When the staggered magnetic moment of the AFM phase is along $a/b$ axis, it's also a TCI phase. Gapless surface states emerge on (100), (010) and (001) surfaces, protected by mirror symmetries (nonzero mirror Chern numbers). When the magnetic moment is…
The interplay between magnetism and non-trivial topology in magnetic topological insulators (MTI) is expected to give rise to a variety of exotic topological quantum phenomena, such as the quantum anomalous Hall (QAH) effect and the topological axion states. A key to assessing these novel properties is to tune the Fermi level in the exchange gap of the Dirac surface band. MnBi$_2$Te$_4$ possesses non-trivial band topology with intrinsic antiferromagnetic (AFM) state that can enable all of these quantum states, however, highly electron-doped nature of the MnBi$_2$Te$_4$ crystals obstructs the e…