Evidence for a different dispersion of the topological edge state of germanene at armchair and zigzag edges

Utilizing a tunneling spectroscopy approach based on the energy-dependent inverse decay length, our research unveils distinct dispersion characteristics of germanene's topological edge states. We observe a pronounced variance in Fermi velocity, with armchair edges exhibiting a velocity higher than zigzag edges by about an order of magnitude. This difference highlights the influence of edge termination on the energy-momentum dispersion relation of one-dimensional topological edge states in two-dimensional topological insulators, aligning with the theoretical framework of a Kane-Mele topological insulator.</p

Nanoscale Investigation of Defects and Oxidation of HfSe₂

HfSe2 is a very good candidate for a transition metal dichalcogenide-based field-effect transistor owing to its moderate band gap of about 1 eV and its high-κ dielectric native oxide. Unfortunately, the experimentally determined charge carrier mobility is about 3 orders of magnitude lower than the theoretically predicted value. This strong deviation calls for a detailed investigation of the physical and electronic properties of HfSe2. Here, we have studied the structure, density, and density of states of several types of defects that are abundant on the HfSe2 surface using scanning tunneling microscopy and spectroscopy. Compared to MoS2 and WSe2, HfSe2 exhibits similar type of defects, albeit with a substantially higher density of 9 × 1011 cm-2. The most abundant defect is a subsurface defect, which shows up as a dim feature in scanning tunneling microscopy images. These dim dark defects have a substantially larger band gap (1.25 eV) than the pristine surface (1 eV), suggesting a substitution of the Hf atom by another atom. The high density of defects on the HfSe2 surface leads to very low Schottky barrier heights. Conductive atomic force microscopy measurements reveal a very small dependence of the Schottky barrier height on the work function of the metals, suggesting a strong Fermi-level pinning. We attribute the observed Fermi-level pinning (pinning factor ∼0.1) to surface distortions and Se/Hf defects. In addition, we have also studied the HfSe2 surface after the exposure to air by scanning tunneling microscopy and conductive atomic force microscopy. Partly oxidized layers with band gaps of 2 eV and Schottky barrier heights of ∼0.6 eV were readily found on the surface. Our experiments reveal that HfSe2 is very air-sensitive, implying that capping or encapsulating of HfSe2, in order to protect it against oxidation, is a necessity for technological applications

Impact of TCO Microstructure on the Electronic Properties of Carbazole-based Self-Assembled Monolayers

Carbazole-based self-assembled monolayers (PACz-SAMs), anchored via their phosphonic acid group on a transparent conductive oxide (TCO) have demonstrated excellent performance as hole-selective layers in inverted perovskite solar cells. However, the influence of the TCO microstructure on the work function (WF) shift after SAM anchoring as well as the WF variations at the micro/nanoscale have not been extensively studied yet. Herein, we investigate the effect of the Sn-doped In2O3 (ITO) microstructure on the WF distribution upon 2PACz-SAMs and NiOx/2PACz-SAMs application. For this, ITO substrates with amorphous and polycrystalline (featuring either nanoscale or microscale-sized grains) microstructures are studied. A correlation between the ITO grain orientation and 2PACz-SAMs local potential distribution was found via Kelvin probe force microscopy and electron backscatter diffraction. These variations vanish for amorphous ITO or when adding an amorphous NiOx buffer layer, where a homogeneous surface potential distribution is mapped. Ultraviolet photoelectron spectroscopy confirmed the ITO WF increase after 2PACz-SAMs deposition. Considering the importance of polycrystalline TCOs as high mobility and broadband transparent electrodes, we provide insights to ensure uniform WF distribution upon application of hole transport SAMs, which is critical towards enhanced device performance.Comment: 18 pages, 5 figure

Spatially resolved electronic structure of twisted graphene

We have used scanning tunneling microscopy and spectroscopy to resolve the spatial variation of the density of states of twisted graphene layers on top of a highly oriented pyrolytic graphite substrate. Owing to the twist a moire pattern develops with a periodicity that is substantially larger than the periodicity of a single layer graphene. The twisted graphene layer has electronic properties that are distinctly different from that of a single layer graphene due to the nonzero interlayer coupling. For small twist angles (about 1-3.5 degree) the integrated differential conductivity spectrum exhibits two well-defined Van Hove singularities. Spatial maps of the differential conductivity that are recorded at energies near the Fermi level exhibit a honeycomb structure that is comprised of two inequivalent hexagonal sub-lattices. For energies |E-E_F|>0.3 eV the hexagonal structure in the differential conductivity maps vanishes. We have performed tight-binding calculations of the twisted graphene system using the propagation method, in which a third graphene layer is added to mimic the substrate. This third layer lowers the symmetry and explains the development of the two hexagonal sub-lattices in the moire pattern. Our experimental results are in excellent agreement with the tight-binding calculations.Comment: To appear in Phys. Rev.

Rio Verde Foothills area plan

abstract: It is important to note that the Rio Verde Foothills Area Plan is not a document that represents ultimate buildout as many municipal general plans typically do. Rather, it prepares for and accommodates growth over the next ten to fifteen years, but will be reexamined and updated periodically to reflect current conditions and changes. While not a complete solution, the Rio Verde Foothills Area Plan helps address the effects of growth and development by enhancing cooperation between government agencies, citizens, and other affected interests, and by considering regional implications.Issued as part of Maricopa County 2020 Eye to the Future, the Maricopa County General Plan

Charge transport modulation by a redox supramolecular spin-filtering chiral crystal

The chirality induced spin selectivity (CISS) effect is a fascinating phenomena correlating molecular structure with electron spin-polarisation in excited state measurements. Experimental procedures to quantify the spin-filtering magnitude relies generally on averaging data sets, especially those from magnetic field dependent conductive-AFM. We investigate the underlying observed disorder in the IV spectra and the origin of spikes superimposed. We demonstrate and explain that a dynamic, voltage sweep rate dependent, phenomena can give rise to complex IV curves for chiral crystals of coronene bisimide. The redox group, able to capture localized charge states, acts as an impurity state interfering with a continuum, giving rise to Fano resonances. We introduce a novel mechanism for the dynamic transport which might also provide insight into the role of spin-polarization. Crucially, interference between charge localisation and delocalisation during transport may be important properties into understanding the CISS phenomena

Structure and dynamics of two-dimensional confined water

The structure and dynamics of water under a geometric confinement is of great significance due to its importance in water flow, surface chemistry and environmental sciences. The physical properties of water at an interface or in a nanopore are often different than its bulk counterpart and can strongly depend on the fine details of the confinement. A systematic understanding of the influence of the confinement on this rich behavior was, until recently poor, because of experimental limitations to access interfacial water structures. The discovery that graphene is stable in its two dimensional form has opened new research possibilities and it has proved to be an instrumental tool for the investigation of confined water structures. Its remarkable mechanical and electronic properties combined with scanning probe techniques allowed us to directly visualize and measure water structures that are confined between graphene and a variety of supporting substrates. Information regarding the influence of the interface structure and wettability, environmental humidity, temperature, pressure and the presence of foreign species on the structure and dynamics of confined water were experimentally accessed in situ and real time with scanning probe microscopies. The observed phase behavior, phase transitions and dynamics of the confined water structures underline the complexity of the governing physical mechanisms. We found that the behavior of the water molecules heavily depends on the confinement characteristics as well as temperature and pressure, which indicates the significance of the interface in defining the geometry of the ice phase. We conclude that a general picture of the state of water under confinement cannot be drawn without considering the exact confinement details and conditions