Implications for Ultrafast Reflection Electron Diffraction from Temporal and Spatial Evolution of Transient Electric Fields

2009 ◽  
Vol 1230 ◽  
Author(s):  
Hyuk Park ◽  
J.M. Zuo
Keyword(s):  
Electron Diffraction ◽  
Electric Fields ◽  
Materials Science ◽  
Thermionic Emission ◽  
Sample Surface ◽  
High Energy ◽  
Intense Laser ◽  
Hot Electron ◽  
Time Resolved ◽  
Reflection Electron Diffraction

AbstractUnderstanding interaction of ultrafast pulsed laser with matter is critical for probing ultrafast processes in materials science, understanding the physics of laser ablation and the laser induced non-equilibrium carrier dynamics in metals and semiconductors, including plasmonics. When an intense laser pulse of femtoseconds (fs) in duration hits the surface of a targeted matter, it excites a hot electron gas. Part of the hot electrons is emitted from the surface in a way similar to thermionic emission. Electrons can also be emitted through multiphoton photoemission (MPPE) or thermally assisted MPPE. The emitted electrons travel at speeds that create transient electric fields (TEFs). To detect TEFs and study the dynamics of emitted electrons, we have developed a time resolved electron beam imaging technique that allows us to measure TEFs above a sample surface at picoseconds time resolution. We have also developed a model of the TEFs based on the propagation of emitted electrons and the percentage of electrons escaping from the surface. We examine the significance of TEFs for ultrafast reflection electron diffraction by examining anomalous effects in ultrafast reflection high energy electron diffraction (RHEED) of silicon surfaces.

Detector commissioning and development for PETRA-III

2010 ◽  
Vol 1 (SRMS-7) ◽  
Author(s):  
David Pennicard ◽  
Heinz Graafsma ◽  
Michael Lohmann
Keyword(s):  
High Speed ◽  
Materials Science ◽  
Dynamic Range ◽  
Photon Counting ◽  
High Energy ◽  
X Rays ◽  
Silicon Detectors ◽  
Time Resolved ◽  
Wide Range ◽  
Synchrotron Light

The new synchrotron light source PETRA-III produced its first beam last year. The extremely high brilliance of PETRA-III and the large energy range of many of its beamlines make it useful for a wide range of experiments, particularly in materials science. The detectors at PETRA-III will need to meet several requirements, such as operation across a wide dynamic range, high-speed readout and good quantum efficiency even at high photon energies. PETRA-III beamlines with lower photon energies will typically be equipped with photon-counting silicon detectors for two-dimensional detection and silicon drift detectors for spectroscopy and higher-energy beamlines will use scintillators coupled to cameras or photomultiplier tubes. Longer-term developments include ‘high-Z’ semiconductors for detecting high-energy X-rays, photon-counting readout chips with smaller pixels and higher frame rates and pixellated avalanche photodiodes for time-resolved experiments.

Calculation of Reflected Intensities for Medium and High Energy Electron Diffraction

1972 ◽  
Vol 27 (3) ◽  
pp. 390-395 ◽  
Author(s):  
A.R. Moon
Keyword(s):  
Electron Diffraction ◽  
Surface Structure ◽  
Incident Angle ◽  
High Energy ◽  
Numerical Calculations ◽  
High Energy Electron ◽  
Matrix Eigenvalue ◽  
High Energy Electrons ◽  
Experimental Values ◽  
Reflection Electron Diffraction

Abstract The Bethe theory of electron diffraction is used to calculate reflection electron diffraction intensities for medium and high energy electrons. A generalized Hill's determinant method is used for the numerical calculations instead of the more common but slower matrix-eigenvalue technique. Results of a "systematics" calculation of the specular intensity as a function of incident angle are compared with some experimental values for the Si (111) surface. The application of the Bethe theory to crystals where the surface structure differs from the bulk is also considered.

Ultra-fast Time-Resolved Electron Diffraction of Strongly Driven Phase Transitions on Silicon Surfaces

2009 ◽  
Vol 1230 ◽  
Author(s):  
Simone Möllenbeck ◽  
Anja Hanisch-Blicharski ◽  
Paul Schneider ◽  
Manuel Ligges ◽  
Ping Zhou ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Electron Diffraction ◽  
Structural Phase ◽  
High Energy ◽  
Silicon Surfaces ◽  
Fast Time ◽  
Time Resolved ◽  
Disorder Phase Transition ◽  
Pulse Pump

AbstractThe dynamics of strongly driven phase transitions at surfaces are studied by ultra-fast time-resolved reflection high energy electron diffraction. The surfaces are excited by an intense fs-laser pulse (pump) and probed by an ultra-short electron pulse with variable time delay. The order-disorder phase transition from a c(4×2) to a (2×1) of the bare Si(001) surface shows a transient decrease of the intensity of the c(4×2) spots which recovers on a time scale of a few hundred picoseconds indicating the excitation of the phase transition. On Si(111) a monolayer of Indium induces a (4×1) reconstruction which undergoes a Peierls like phase transition to a (8ד2”) reconstruction below 100 K. Upon laser excitation at a temperature of 40 K the phase transition was strongly driven. The (8ד2”)-diffraction spots instantaneously disappears, while the intensity of the (4×1)-spots increases. This increase of the (4×1) spot intensity excludes an explanation by the Debye-Waller-Effect and is evidence for a true structural phase transition at a surface.

An advanced three-dimensional RHEED mapping approach to the diffraction study of Co/MnF2/CaF2/Si(001) epitaxial heterostructures

2016 ◽  
Vol 49 (5) ◽  
pp. 1532-1543 ◽  
Author(s):  
S. M. Suturin ◽  
A. M. Korovin ◽  
V. V. Fedorov ◽  
G. A. Valkovsky ◽  
M. Tabuchi ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Cross Sections ◽  
Three Dimensional ◽  
Sample Surface ◽  
High Energy ◽  
Mapping Technique ◽  
Plan View ◽  
Mapping Approach ◽  
Three Dimensional Mapping ◽  
Dimensional Mapping

An advanced three-dimensional mapping approach utilizing reflection high-energy electron diffraction (RHEED) is introduced. The application of the method is demonstrated in detail by resolving the crystal structure and epitaxial relations of individual components within epitaxially grown magnetically ordered Co/MnF2/CaF2/Si(001) heterostructures. The electron diffraction results are cross-checked using synchrotron X-ray diffraction measurements. A number of advantages of the three-dimensional mapping technique as compared to conventional electron diffraction are demonstrated. Not least amongst these is the possibility to build arbitrary planar cross sections and projections through reciprocal space, including the plan-view projection onto the plane parallel to the sample surface, which is otherwise impossible to obtain.

Reflection Electron Diffraction and Structural Behavior of Gaas / Gaas (111)B Grown Via Mbe

1990 ◽  
Vol 208 ◽  
Author(s):  
K. C. Rajkumar ◽  
P. Chen ◽  
A. Madhukar
Keyword(s):  
Electron Diffraction ◽  
Surface Morphology ◽  
High Energy ◽  
In Situ Monitoring ◽  
Spot Intensity ◽  
High Energy Electron ◽  
Surface Phase ◽  
Gaas Films ◽  
Reflection Electron Diffraction

Homoepitaxy on the {111} face of GaAs has been long known to give films with surfaces marred with macroscopic features. We have identified this problem to be tied to the surface phase regime. We have used Reflection High Energy Electron Diffraction (RHEED) to identify a phase regime wherein specular-surfaced GaAs films can be grown. We have found that it is possible to glean information regarding the macroscopic surface morphology by monitoring the variation in the RHEED specular spot intensity during growth. This has allowed in situ monitoring of the macroscopic surface morphology of a growing film in real time which has made it possible to grow specular-surfaced films reproducibly.

Sign in / Sign up

Export Citation Format

Share Document