Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userUltra-low power threshold for laser induced changes in optical properties of 2D Molybdenum dichalcogenides
80
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The optical response of traditional semiconductors depends on the laser excitation power used in experiments. For two-dimensional (2D) semiconductors, laser excitation effects are anticipated to be vastly different due to complexity added by their ultimate thinness, high surface to volume ratio, and laser-membrane interaction effects. We show in this article that under laser excitation the optical properties of 2D materials undergo irreversible changes. Most surprisingly these effects take place even at low steady state excitation, which is commonly thought to be non-intrusive. In low temperature photoluminescence (PL) we show for monolayer (ML) MoSe2 samples grown by different techniques that laser treatment increases significantly the trion (i.e. charged exciton) contribution to the emission compared to the neutral exciton emission. Comparison between samples exfoliated onto different substrates shows that laser induced doping is more efficient for ML MoSe2 on SiO2/Si compared to h-BN and gold. For ML MoS2 we show that exposure to laser radiation with an average power in the $mu$W/$mu$m$^2$ range does not just increase the trion-to-exciton PL emission ratio, but may result in the irreversible disappearance of the neutral exciton PL emission and a shift of the main PL peak to lower energy.
rate research
Read More
Transition metal dichalcogenides (TMDs) are interesting for understanding fundamental physics of two-dimensional materials (2D) as well as for many emerging technologies, including spin electronics. Here, we report the discovery of long-range magnetic order below TM = 40 K and 100 K in bulk semiconducting TMDs 2H-MoTe2 and 2H-MoSe2, respectively, by means of muon spin-rotation (muSR), scanning tunneling microscopy (STM), as well as density functional theory (DFT) calculations. The muon spin rotation measurements show the presence of a large and homogeneous internal magnetic fields at low temperatures in both compounds indicative of long-range magnetic order. DFT calculations show that this magnetism is promoted by the presence of defects in the crystal. The STM measurements show that the vast majority of defects in these materials are metal vacancies and chalcogen-metal antisites which are randomly distributed in the lattice at the sub-percent level. DFT indicates that the antisite defects are magnetic with a magnetic moment in the range of 0.9-2.8 mu_B. Further, we find that the magnetic order stabilized in 2H-MoTe2 and 2H-MoSe2 is highly sensitive to hydrostatic pressure. These observations establish 2H-MoTe2 and 2H-MoSe2 as a new class of magnetic semiconductors and opens a path to studying the interplay of 2D physics and magnetism in these interesting semiconductors.
Optical interconnect has emerged as the front-runner to replace electrical interconnect especially for off-chip communication. However, a major drawback with optical interconnects is the need for photodetectors and amplifiers at the receiver, implemented usually by direct bandgap semiconductors and analog CMOS circuits, leading to large energy consumption and slow operating time. In this article, we propose a new optical interconnect architecture that uses a magnetic tunnel junction (MTJ) at the receiver side that is switched by femtosecond laser pulses. The state of the MTJ can be sensed using simple digital CMOS latches, resulting in significant improvement in energy consumption. Moreover, magnetization in the MTJ can be switched on the picoseconds time-scale and our design can operate at a speed of 5 Gbits/sec for a single link.
Impurities play an important role during recombination processes in semiconductors. Their important role is sharpened in atomically-thin transition-metal dichalcogenides whose two-dimensional character renders electrons and holes highly susceptible to localization caused by remote charged impurities. We study a multitude of phenomena that arise from the interaction of localized electrons with excitonic complexes. Emphasis is given to the amplification of the phonon-assisted recombination of biexcitons when it is mediated by localized electrons, showing that this mechanism can explain recent photoluminescence experiments in ML-WSe$_2$. In addition, the magnetic-field dependence of this mechanism is analyzed. The results of this work point to (i) an intriguing coupling between the longitudinal-optical and homopolar phonon modes that can further elucidate various experimental results, (ii) the physics behind a series of localization-induced optical transitions in tungsten-based materials, and (iii) the importance of localization centers in facilitating the creation of biexcitons and exciton-exciton annihilation processes.
Hybrid nanophotonics based on metal-dielectric nanostructures unifies the advantages of plasmonics and all-dielectric nanophotonics providing strong localization of light, magnetic optical response and specifically designed scattering properties. Here we demonstrate a novel approach for fabrication of ordered hybrid nanostructures via femtosecond laser melting of asymmetrical metal-dielectric (Au-Si) nanoparticles created by lithographical methods. The approach allows selective reshaping of the metal components of the hybrid nanoparticles without affecting dielectric ones. We apply the developed approach for tuning of the hybrid nanostructures scattering properties in the visible range. The experimental results are supported by molecular dynamics simulation and numerical solving of Maxwell equations.
Titanium doped sapphire (Ti:sapphire) is a laser gain material with broad gain bandwidth benefiting from the material stability of sapphire. These favorable characteristics of Ti:sapphire have given rise to femtosecond lasers and optical frequency combs. Shaping a single Ti:sapphire crystal into a millimeter sized high quality whispering gallery mode resonator ($Qsim10^8$) reduces the lasing threshold to 14.2 mW and increases the laser slope efficiency to 34%. The observed lasing can be both multi-mode and single-mode. This is the first demonstration of a Ti:sapphire whispering-gallery laser. Furthermore, a novel method of evaluating the gain in Ti:sapphire in the near infrared region is demonstrated by introducing a probe laser with a central wavelength of 795 nm. This method results in decreasing linewidth of the modes excited with the probe laser, consequently increasing their $Q$. These findings open avenues for the usage of whispering gallery mode resonators as cavities for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire can also be utilized as an amplifier inside its gain bandwidth by implementing a pump-probe configuration.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
