21 research outputs found
Quantum Transport Characteristics of Lateral pn-Junction of Single Layer TiS3
Using density functional theory and nonequilibrium Greens functions-based
methods we investigated the electronic and transport properties of monolayer
TiS3 pn-junction. We constructed a lateral pn-junction in monolayer TiS3 by
using Li and F adatoms. An applied bias voltage caused significant variability
in the electronic and transport properties of the TiS3 pn-junction. In
addition, spin dependent current-voltage characteristics of the constructed
TiS3 pn-junction were analyzed. Important device characteristics were found
such as negative differential resistance and rectifying diode behaviors for
spin-polarized currents in the TiS3 pn-junction. These prominent conduction
properties of TiS3 pn-junction offer remarkable opportunities for the design of
nanoelectronic devices based on a recently synthesized single-layered material
Ag and Au Atoms Intercalated in Bilayer Heterostructures of Transition Metal Dichalcogenides and Graphene
The diffusive motion of metal nanoparticles Au and Ag on monolayer and
between bilayer heterostructures of transition metal dichalcogenides and
graphene are investigated in the framework of density functional theory. We
found that the minimum energy barriers for diffusion and the possibility of
cluster formation depend strongly on both the type of nanoparticle and the type
of monolayers and bilayers. Moreover, the tendency to form clusters of Ag and
Au can be tuned by creating various bilayers. Tunability of the diffusion
characteristics of adatoms in van der Waals heterostructures holds promise for
controllable growth of nanostructures.Comment: accepted, APL Ma
Nonlinear photoluminescence in gold thin films
Promising applications in photonics are driven by the ability to fabricate
crystal-quality metal thin films of controlled thickness down to a few
nanometers. In particular, these materials exhibit a highly nonlinear response
to optical fields owing to the induced ultrafast electron dynamics, which is
however poorly understood on such mesoscopic length scales. Here, we reveal a
new mechanism that controls the nonlinear optical response of thin metallic
films, dominated by ultrafast electronic heat transport when the thickness is
sufficiently small. By experimentally and theoretically studying electronic
transport in such materials, we explain the observed temporal evolution of
photoluminescence in pump-probe measurements that we report for crystalline
gold flakes. Incorporating a first-principles description of the electronic
band structures, we model electronic transport and find that ultrafast thermal
dynamics plays a pivotal role in determining the strength and time-dependent
characteristics of the nonlinear photoluminescence signal, which is largely
influenced by the distribution of hot electrons and holes, subject to diffusion
across the film as well as relaxation to lattice modes. Our findings introduce
conceptually novel elements triggering the nonlinear optical response of
nanoscale materials while suggesting additional ways to control and leverage
hot carrier distributions in metallic films.Comment: 20 pages, 6 figures, 64 reference
Kagome silicene: a novel exotic form of two-dimensional epitaxial silicon
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.Comment: 13 pages, 6 figure
Giant All-Optical Modulation of Second-Harmonic Generation Mediated by Dark Excitons.
All-optical control of nonlinear photonic processes in nanomaterials is of significant interest from a fundamental viewpoint and with regard to applications ranging from ultrafast data processing to spectroscopy and quantum technology. However, these applications rely on a high degree of control over the nonlinear response, which still remains elusive. Here, we demonstrate giant and broadband all-optical ultrafast modulation of second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides mediated by the modified excitonic oscillation strength produced upon optical pumping. We reveal a dominant role of dark excitons to enhance SHG by up to a factor of ∼386 at room temperature, 2 orders of magnitude larger than the current state-of-the-art all-optical modulation results. The amplitude and sign of the observed SHG modulation can be adjusted over a broad spectral range spanning a few electronvolts with ultrafast response down to the sub-picosecond scale via different carrier dynamics. Our results not only introduce an efficient method to study intriguing exciton dynamics, but also reveal a new mechanism involving dark excitons to regulate all-optical nonlinear photonics
Hydrogenated derivatives of hexacoordinated metallic Cu2Si monolayer
Sahin, Hasan/0000-0002-6189-6707; Senger, R. Tugrul/0000-0003-0800-1924; Sahin, Hasan/0000-0002-6189-6707; Iyikanat, Fadil/0000-0003-1786-3235; unsal, elif/0000-0001-6419-384XWOS: 000452778800023Herein, we carried out first-principles calculations based on density functional theory to investigate the effects of surface functionalization with hydrogen atoms on structural, dynamical and electronic properties of Cu2Si monolayer. Pristine Cu2Si, a metallic monolayer, has a planar hexacoordinate structure. Calculations revealed that the most favorable position of a single H atom on the Cu2Si monolayer is at the top of a Si site. Derivatives of Cu2Si monolayer with various H concentrations were investigated, and by performing phonon calculations, it was found that there are three stable hydrogenated structures. Specific heat of these monolayers was found to increase with the hydrogen concentration at temperatures higher than 100 K. Electronically, the hydrogenated derivatives of Cu2Si monolayer preserve the metallic character