Pinching and Probing of Polygonal Grain Boundaries

In this study, sub-angstrom spatial resolution is achieved in mapping and spectroscopy of atoms and bonds within polygonal grain boundaries (GBs) of graphite using Scanning Tunneling Microscopy (STM). Robust van Hove singularities (VHS) are observed in addition to edge states under ambient conditions. The bias-dependent nature of these states reveals metallic traits of GB, through the charge accumulation and dissipation of localized electronic states. Utilizing a surface elastic deformation technique induced by STM tip allows pico-pinching of the GB, providing insights into its mechanical strength as well as in-situ strain-induced modification of their unique spectroscopy, revealing a tendency toward flattening of the electronic energy band dispersion. An initial atomic-level experimental technique of probing spin-polarized magnetic states is demonstrated, suggesting different densities for spin-up and spin-down states within a spin-degenerate band structure potentially applicable in spin transport or quantum spin sensing.Comment: Submitte

Characteristic nanoscale deformations on large area coherent graphite moir\'e

Highly oriented pyrolytic graphite (HoPG) may be the only known monatomic crystal with the ability to host naturally formed moire patterns on its cleaved surfaces, which are coherent over micrometer scales and with discrete sets of twist angles of fixed periodicity. Such an aspect is in marked contrast to twisted bilayer graphene (TBG) and other multilayered systems, where the long range coherence of the moire is not easily maintained due to twist angle disorder. We investigate the electronic and mechanical response of coherent graphite moire patterns through inducing external strain from STM tip-induced deformation. Consequently, unique anisotropic mechanical characteristics are revealed. For example, a lateral widening of one-dimensional (1D) domain walls (DWs) bridging Bernal (ABA) and rhombohedral (ABC) stacking domains (A, B and C refer to the atomic layer positioning), was indicated. Further, in situ tunneling spectroscopy as a function of the deformation indicated a tendency towards increased electrical conductance, which may be associated with a higher density of electronic states, and the consequent flattening of the electronic energy band dispersion. Such features were probed across the DWs, with implications for strain-induced electronic modulation of the moire characteristics

Strain Engineering of two dimensional materials by Scanning Tunneling Microscopy

Strain engineering on layered two dimensional materials has gained some interest for mod- ulating device electronics. This is done by twisting layered materials, stretching flexible substrates or applying hydro-static pressures. Our work offers to the straintronics and twistronics commu- nity, a new pathway of deforming individual atoms on surface controllably by tip-induced forces and probe in-situ the mechanical and electronic properties on surface under strain which can be exploited for innumerable applications.Tunneling gaps of interatomic distances can induce strain by individual atomic deformation controllably and elastically with an STM tip and while under strain probe in-situ their mechanical VDW strength or elasticity and electronic band structure. Such capabilities can be exploited in force microscopy studies of soft matter, biological, chemical and physical sensors or 2D materials based semiconductor nanoelectronics. We demonstrate that various weak forces only at small tip- surface gaps become strong enough to deform surfaces of graphite, monolayer graphene, Niobium diselenide and their step heights that reveals their dependence on their structural anisotropy. Addi- tionally we provide an application to our tip-induced deformative approach by locally deforming moiré patterns (partly shown in following figure) which not only reveals their mechanical prop- erties like interlayer VDWs strength of different moiré domains (including the domain walls) but also exhibits flattening of moire flat bands under strain. The flat bands aspect have helped understand the imaging issues of topologically protected grain boundaries. We reveal various experimental challenges and solutions to probing grain bound- aries that have distinct spectroscopic states on their surfaces. They play a role in charging or discharging effects on the grain boundary sensed by the STM. The origin of the flat band states around zero bias has been shown to be caused by the zigzag edges and the other VHS states could be caused the distinct topological arrangement of non-hexagons. Flat bands or VHS peaks also can be observed on moire patterns. We observe how mechan- ically the moire domains can be deformed and in-situ observe the deformation of electronic bands. Such band modulating approach by tip-induced forces have not been explored. We approach the strained moire patterns from the point of view of domain walls. Domain walls are confined 1D structures on 2D moire surfaces

Column study for the Cu(II) removal by the coconut shell from aqueous solution – MLR and GA modeling

Adsorption characteristics of locally available inexpensive natural adsorbent coconut shells were studied for Cu(II) removal. The present study adsorption process was carried through a fixed bed column to find out the breakthrough characteristics. The variation of operating variables is investigated, pH 6, influence Cu(II) concentration (10–30 mg·L–1), bed height (5–15 cm), the flow rate (10–30 ml·min–1). The suitability of various kinetic models has been tested. Maximum adsorption capacity, qe according to Thomas model, was 30.09 mg·g–1obtained at 20 ml/min, flow rate, 30 mg·L–1 metal solution, and 15 cm bed height. The correlation coefficient of the Thomas model ranges from 0.8260 to 0.9839. Besides this, according to the statistical parameters of the Yoon-Nelson and Yan et al. models, proving that the experimental data are suitable for this model. The statistical and GA modeling of the experimental data has also been performed successfully