Negative capacitance (NC) in a planar W-doped VO2 micro-switch was observed at room temperature in the low-frequency range 1 kHz-10 MHz. The capacitance changed from positive to negative values as the W-doped VO2 active layer switched from semiconducting to metallic state under applied voltage. In addition, a capacitance-voltage hysteresis was observed as the applied voltage was cycled from -35...

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Optical excitation typically enhances electrical conduction and low-frequency radiation absorption in semiconductors. We, however, observe a pronounced transient decrease of conductivity in doped monolayer molybdenum disulfide (MoS(2)), a two-dimensional (2D) semiconductor, using ultrafast optical-pump terahertz-probe spectroscopy. In particular, the conductivity is reduced to only 30% of its e...

The measurement of short time intervals during the first half of 20 century was limited to intervals longer than one nanosecond. The advent of lasers in 1960 revolutionized the field of time-resolved spectroscopy. The time interval is shortened from 10 to 10 seconds, which made ultrafast experiment grows rapidly. New subfields of science, including femtochemistry and femtobiology, have been cre...

Ultrafast imaging has been a key enabler to many novel imaging modalities, including looking behind corners and imaging behind scattering layers. With picosecond time resolution and unconventional sensing geometries, ultrafast imaging can fundamentally impact sensing capabilities in industrial and biomedical applications. This paper reviews the fundamentals, recent advances, and the future pros...

We investigate the ultrafast optoelectronic properties of single Al0.3Ga0.7As/GaAs core-shell nanowires. The nanowires contain GaAs-based quantum wells. For a resonant excitation of the quantum wells, we find a picosecond photocurrent which is consistent with an ultrafast lateral expansion of the photogenerated charge carriers. This Dember-effect does not occur for an excitation of the GaAs-bas...

Due to the high-index contrast between the silicon core and silica cladding, the silicon waveguide allows strong optical confinement and large effective nonlinearity, which facilitates low cost chip scale demonstration of all-optical nonlinear functional devices at relatively low pump powers. One of the challenges in ultrafast science is the full characterization of optical pulses in real time....

Polymer solar cells are attracting attention as next-generation energy sources. Scalable deposition techniques of high-quality organic films should be guaranteed to realize highly efficient polymer solar cells in large areas for commercial viability. Herein, we introduce an ultrafast, scalable, and versatile process for forming high-quality organic films on an aqueous substrate by utilizing the...

The influence of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of excited donor-acceptor complexes has been explored both theoretically and experimentally. The theoretical description involves the explicit treatment of both the optical formation of the nuclear wave packet on the excited free energy surface and its ensuing dynamics. The wave packet motion ...

The photodynamics in symmetric and unsymmetric β-diketones are studied with transient absorption in the deep-UV. Excitation leads to ultrafast ESIPT while further relaxation and isomerization processes depend on the molecular symmetry and solvent environment. OCIS codes: (320.7150) Ultrafast spectroscopy; (300.6540) Spectroscopy, ultraviolet; (190.7110) Ultrafast nonlinear optics