Thursday, October 8, 2015

Imaging of Carrier Dynamics by Second-Generation 4D Scanning UEM enabled by Model IMPULSE from Clark-MXR. A new publication from Prof. Omar Abdelsaboor group at KAUST

Real-Space Imaging of Carrier Dynamics of Materials Surfaces by Second-Generation Four-Dimensional Scanning Ultrafast Electron Microscopy

Jingya Sun, Vasily A. Melnikov, Jafar I. Khan, and Omar F. Mohammed

Solar and Photovoltaics Engineering Research Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia

 Link to the Original Paper

Abstract
In the fields of photocatalysis and photovoltaics, ultrafast dynamical processes, including carrier trapping and recombination on material surfaces, are among the key factors that determine the overall energy conversion efficiency. A precise knowledge of these dynamical events on the nanometer (nm) and femtosecond (fs) scales was not accessible until recently. The only way to access such fundamental processes fully is to map the surface dynamics selectively in real space and time. In this study, we establish a second generation of four-dimensional scanning ultrafast electron microscopy (4D S-UEM) and demonstrate the ability to record time-resolved images (snapshots) of material surfaces with 650 fs and ∼5 nm temporal and spatial resolutions, respectively. In this method, the surface of a specimen is excited by a clocking optical pulse and imaged using a pulsed primary electron beam as a probe pulse, generating secondary electrons (SEs), which are emitted from the surface of the specimen in a manner that is sensitive to the local electron/hole density. This method provides direct and controllable information regarding surface dynamics. We clearly demonstrate how the surface morphology, grains, defects, and nanostructured features can significantly impact the overall dynamical processes on the surface of photoactive-materials. In addition, the ability to access two regimes of dynamical probing in a single experiment and the energy loss of SEs in semiconductor-nanoscale materials will also be discussed.

Tuesday, September 22, 2015

Another publication from Prof. Tony Heinz group with Clark-MXR's Model IMPULSE

Population inversion and giant bandgap renormalization in atomically thin WS2 layers

Alexey Chernikov, Claudia Ruppert, Heather M. Hill, Albert F. Rigosi & Tony F. Heinz

Nature Photonics 9, 466–470 doi:10.1038/nphoton.2015.104

Photoinduced optical response of WS2 monolayers.

Abstract

Control of the optical properties of matter on ultrashort timescales is of both fundamental interest and central importance for applications in photonics. It is desirable to achieve pronounced changes over a broad spectral range using the least possible amount of material. Here, we demonstrate a dramatic change over a spectral range of hundreds of meV on the femtosecond timescale in the optical response of atomically thin two-dimensional crystals of the transition-metal dichalcogenide WS2 following excitation by intense optical pump pulses. Our findings reveal the role of extremely strong Coulomb interactions. At the direct gap, we observe a Mott transition from excitonic states to free carriers, accompanied by a giant bandgap renormalization of approximately 500 meV and the development of population inversion.

Wednesday, September 9, 2015

A new publication from Prof. Tony Heinz group with Model IMPULSE from Clark-MXR. Please contact us for more information on Model IMPULSE and Model iNOPA. 

Observation of Rapid Exciton–Exciton Annihilation in Monolayer Molybdenum Disulfide

Dezheng Sun, Yi Rao, Georg A. Reider, Gugang Chen, Yumeng You, Louis Brézin, Avetik R. Harutyunyan, and Tony F. Heinz



Abstract Image

Monolayer MoS2 is a direct-gap two-dimensional semiconductor that exhibits strong electron–hole interactions, leading to the formation of stable excitons and trions. Here we report the existence of efficient exciton–exciton annihilation, a four-body interaction, in this material. Exciton–exciton annihilation was identified experimentally in ultrafast transient absorption measurements through the emergence of a decay channel varying quadratically with exciton density. The rate of exciton–exciton annihilation was determined to be (4.3 ± 1.1) × 10–2 cm2/s at room temperature.

Link to the original paper

Friday, August 28, 2015

Researchers at University of Bern and co-workers used Clark-MXR Model CPA-Series laser to carry out Laser Ablation/Ionization Mass Spectrometry in the quest to search for extraterrestrial life.

Chemical Composition of Micrometer-Sized Filaments in an Aragonite Host by a Miniature Laser Ablation/Ionization Mass Spectrometer

Marek Tulej, Anna Neubeck, Magnus Ivarsson, Andreas Riedo, Maike B. Neuland, Stefan Meyer, and Peter Wurz


ABSTRACT

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Detection of extraterrestrial life is an ongoing goal in space exploration, and there is a need for advanced instruments and methods for the detection of signatures of life based on chemical and isotopic composition. Here, we present the first investigation of chemical composition of putative microfossils in natural samples using a miniature laser ablation/ionization time-of-flight mass spectrometer (LMS). The studies were conducted with high lateral (∼15 μm) and vertical (∼20–200 nm) resolution. The primary aim of the study was to investigate the instrument performance on micrometer-sized samples both in terms of isotope abundance and element composition. The following objectives had to be achieved: (1) Consider the detection and calculation of single stable isotope ratios in natural rock samples with techniques compatible with their employment of space instrumentation for biomarker detection in future planetary missions. (2) Achieve a highly accurate chemical compositional map of rock samples with embedded structures at the micrometer scale in which the rock matrix is easily distinguished from the micrometer structures. Our results indicate that chemical mapping of strongly heterogeneous rock samples can be obtained with a high accuracy, whereas the requirements for isotope ratios need to be improved to reach sufficiently large signal-to-noise ratio

Link to the original paper 

Friday, June 12, 2015

Clark-MXR will be at LASER world of Photonics from June 22-25 in Munich, Germany.



 
Please meet our Director of Operations in Europe, Dr. Hans-Erik Swoboda at booth # B2.207 to discuss innovative ultrafast products and services that Clark-MXR has to offer.