scholarly journals Measurement of ultrafast hot‐carrier relaxation in silicon by thin‐film‐enhanced, time‐resolved reflectivity

1988 ◽  
Vol 52 (1) ◽  
pp. 36-38 ◽  
Author(s):  
F. E. Doany ◽  
D. Grischkowsky
Keyword(s):  
Thin Film ◽  
Time Resolved ◽  
Carrier Relaxation ◽  
Hot Carrier

Transient Reflectance Response to Hot Electron Relaxation in InP Based Films

2002 ◽  
Author(s):  
J. Michael Klopf ◽  
John L. Hostetler ◽  
Pamela M. Norris
Keyword(s):  
Thin Film ◽  
Transient Absorption ◽  
Film Growth ◽  
Laser Pulses ◽  
Ultrashort Laser Pulses ◽  
Photon Absorption ◽  
Hot Electron ◽  
Carrier Relaxation ◽  
Hot Carrier ◽  
Ultrashort Laser

Advancements in technologies related to thin film growth have led to astoundingly complex integrated photonic devices. The reliability of these devices relies upon the precise control of the band gap and absorption mechanisms in the thin film structures. Photon absorption in these devices can result in a reduction of laser efficiency as well as thermal runaway. To improve device performance prediction, an increased understanding of the localized absorption processes is paramount. A pump-probe technique is being developed to measure the transient absorption during hot carrier relaxation. This method relies upon the generation of hot carriers by the absorption of an intense ultrashort laser pulse. The change in reflectance due to hot carrier generation and relaxation is monitored using a probe pulse focused at the center of the excited region. The transient reflectance is measured as a function of the relative delay between the pump and probe pulses. Utilizing ultrashort laser pulses (τp ∼ 190 fs) it is possible to attain sub-picosecond resolution of the transient reflectance during hot carrier relaxation. Transient changes in the reflectance can then be related to transient changes in the absorption mechanisms of the film. Preliminary measurements made with this technique have shown clear differences in the transient reflectance of doped and undoped Indium Phosphide (InP) based films. This study will form the basis for development of a transient thermoreflectance model during hot carrier relaxation in III-V semiconductors.

scholarly journals Effects of Crystal Morphology on the Hot-Carrier Dynamics in Mixed-Cation Hybrid Lead Halide Perovskites

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 708
Author(s):  
Daniele Catone ◽  
Giuseppe Ammirati ◽  
Patrick O’Keeffe ◽  
Faustino Martelli ◽  
Lorenzo Di Mario ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Carrier Dynamics ◽  
Large Area ◽  
Photovoltaic Properties ◽  
Time Resolved ◽  
Hot Carrier ◽  
Mixed Cation ◽  
Small Crystals ◽  
Characterization Of Materials ◽  
Lead Halide

Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of charge carriers dynamics in perovskite materials providing crucial information on the dynamics of the excited carriers, and fundamental in the development of new devices with tailored photovoltaic properties. Fast transient absorbance spectroscopy on mixed-cation hybrid lead halide perovskite samples was used to investigate how the dimensions and the morphology of the perovskite crystals embedded in the capping (large crystals) and mesoporous (small crystals) layers affect the hot-carrier dynamics in the first hundreds of femtoseconds as a function of the excitation energy. The comparative study between samples with perovskite deposited on substrates with and without the mesoporous layer has shown how the small crystals preserve the temperature of the carriers for a longer period after the excitation than the large crystals. This study showed how the high sensitivity of the time-resolved spectroscopies in discriminating the transient response due to the different morphology of the crystals embedded in the layers of the same sample can be applied in the general characterization of materials to be used in solar cell devices and large area modules, providing further and valuable information for the optimization and enhancement of stability and efficiency in the power conversion of new perovskite-based devices.

Time resolved study of carrier relaxation dynamics in alpha-Al2O3.

2021 ◽  
Author(s):  
Allan Bildé ◽  
Kipras Redeckas ◽  
Andrius Melninkaitis ◽  
Mikas Vengris ◽  
S Guizard
Keyword(s):  
Relaxation Dynamics ◽  
Time Resolved ◽  
Carrier Relaxation ◽  
Carrier Relaxation Dynamics

A Comparison of Radiation Versus Convection Calibration of Thin-Film Heat Flux Gauges

1999 ◽  
Author(s):  
D. E. Smith ◽  
J. V. Bubb ◽  
O. Popp ◽  
T. E. Diller ◽  
Stephen J. Hevey
Keyword(s):  
Thin Film ◽  
Heat Flux ◽  
Surface Temperature ◽  
Temperature Response ◽  
Turbine Rotor ◽  
Separate Experiment ◽  
Measured Temperature ◽  
Conduction Model ◽  
Time Resolved ◽  
Turbine Rotor Blade

Abstract A transient, in-situ method was examined for calibrating thin-film heat flux gauges using experimental data generated from both convection and radiation tests. Also, a comparison is made between this transient method and the standard radiation substitution calibration technique. Six Vatell Corporation HFM-7 type heat flux gauges were mounted on the surface of a 2-D, first-stage turbine rotor blade. These gauges were subjected to radiation from a heat lamp and in a separate experiment to a convective heat flux generated by flow in a transonic cascade wind tunnel. A second set of convective tests were performed using jets of cooled air impinging on the surface of the gauges. Direct measurements were simultaneously taken of both the time-resolved heat flux and surface temperature on the blade. The heat flux input was used to predict a surface temperature response using a one-dimensional, semi-infinite conduction model into a substrate with known thermal properties. The sensitivities of the gauges were determined by correlating the semi-infinite predicted temperature response to the measured temperature response. A finite-difference code was used to model the penetration of the heat flux into the substrate in order to estimate the time for which the semi-infinite assumption was valid. The results from these tests showed that the gauges accurately record both the convection and radiation modes of heat transfer. The radiation and convection tests yielded gauge sensitivities which agreed to within ±11%.

Large scale alignment of a lamellar block copolymer thin film via electric fields: a time-resolved SFM study

Soft Matter ◽  
2006 ◽  
Vol 2 (12) ◽  
pp. 1089-1094 ◽  
Author(s):  
Violetta Olszowka ◽  
Markus Hund ◽  
Volker Kuntermann ◽  
Sabine Scherdel ◽  
Larisa Tsarkova ◽  
...  
Keyword(s):  
Thin Film ◽  
Block Copolymer ◽  
Electric Fields ◽  
Large Scale ◽  
Time Resolved ◽  
Large Scale Alignment
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