We have studied the low-temperature (T=6K) optical properties of a series InGaN∕GaN single-quantum-well structures with varying indium fractions. With increasing fraction peak emission moves to lower energy and strength exciton–longitudinal-optical (LO)-phonon coupling increases. The Huang–Rhys factor extracted from Fabry–Pérot interference-free photoluminescence spectra has been compared results model calculation, yielding value approximately 2nm for in-plane localization length scale...

Spintronic terahertz (THz) emitters, consisting of ferromagnetic (FM)/non-magnetic (NM) thin films, have demonstrated remarkable potential for use in THz time-domain spectroscopy and its exploitation scientific industrial applications. Since the discovery that novel FM/NM heterostructures can be utilized as sources radiation, researchers endeavored to find optimum combination materials produce idealized spintronic emitters capable generating pulses radiation over a large spectral bandwidth....

Efficient carrier multiplication in InP nanoparticles is reported; ultrafast transient absorption measurements at the band edge were used to determine number of excitons per photoexcited nanoparticle for a range both excitation fluences and photon energies. At energies greater than $2.1\ifmmode\pm\else\textpm\fi{}0.2$ times gap, an average more 1 exciton was found even limit vanishing fluence. The generated by absorbed measured be $1.18\ifmmode\pm\else\textpm\fi{}0.03$ photons with 2.6 gap.

A cheap and more environmentally friendly method for the synthesis of high quality PbS nanoparticles in olive oil at 60 °C has been developed. Carefully controlling conditions reactions leads to with well-defined sizes, band gaps between 1.72 0.88 eV. The were characterized by XRD, HRTEM, NIR absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) a fluorescence lifetime experiment based on time-correlated single photon counting (TCSPC) technique. Photoelectrochemical study carried...

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Ultrafast transient absorption measurements have been used to study multiple exciton generation in solutions of PbS nanoparticles vigorously stirred avoid the effects photocharging. The threshold and slope efficiency are found be 2.5 ± 0.2 ×E(g) 0.34 0.08, respectively. Photoemission as a function nanoparticle size ageing show that position valence band maximum is pinned by surface effects, thick layer oxide rapidly formed at surfaces on exposure air.

We demonstrate a method to create arbitrary terahertz (THz) polarization profiles by exploiting the magnetic field-dependent emission process of spintronic source. As proof-of-concept, we show that applying specific field pattern source, it is possible generate quadrupole-like THz profile. Experimental measurements electric at focus beam revealed polarity flip in transverse profile mode with resulting strong, on-axis longitudinal component 17.7 kV cm−1. This represents an order magnitude...

The time-resolved change in the surface potential upon photoexcitation has been measured two $n$-type photovoltaics, Si (111) 7\ifmmode\times\else\texttimes\fi{}7 and ZnO ($10\overline{1}0$), using different laser pump-synchrotron x-ray probe methodologies. Taken together, these experiments allow dynamics of photovoltage (SPV) to be monitored over timescales subnanoseconds milliseconds. for photoinduced SPV are dramatically samples, with decay time constants 6.6 \ensuremath{\mu}s up 1.2 ms...

Truly alloyed PbS(x)Se(1-x) (x = 0-1) nanocrystals (∼5 nm in size) have been prepared, and their resulting optical properties are red-shifted systematically as the sulfur content of materials increases. Their discussed using a modified Vegard's approach bowing parameter for these nanoalloys is reported first time. The structure supported by energy-filtered transmission electron microscope images samples, which show homogeneous distribution selenium within nanocrystals. X-ray photoelectron...

We investigate the growth and physical optical properties of type-II heterostructured ZnTe/ZnSe colloidal nanocrystals, focusing on role 7% lattice mismatch between two materials in determining homogeneity band structure. find that places limitations range structures can be grown, for those which coherent is achieved we present clear evidence low bulk modulus ZnTe cores are compressed by higher ZnSe shells, accentuating red-shift excitonic state with increasing shell thickness. By employing...

Periodically-poled lithium niobate (PPLN) sources consisting of custom-built stacks large-area wafers provide a unique opportunity to systematically study the multi-cycle terahertz (THz) generation mechanism as they are assembled layer-by-layer. Here we investigate and optimize THz emission from PPLN wafer function number, pump fluence, pulse duration chirp, separation, focusing. Using 135 µm-thick, 2"-diameter generate high-energy, narrowband pulses with central frequencies up 0.39 THz,...

We investigate the use of tapered rectangular dielectric-lined waveguides (DLWs) for acceleration low-energy, subrelativistic, electron bunches by interaction with multicycle narrowband terahertz (THz) pulses. A key challenge exists in this subrelativistic regime; velocity changes significantly as energy is gained. To keep electrons accelerating phase, phase must also be increased to match. present simulations which demonstrate that dielectric thickness can kept constant and width lining...

Abstract Strain relaxation has been studied for the 10‐period quantum well (QW) heterostructures grown by MOVPE, In 0.16 Ga 0.84 N/GaN and 0.2 0.8 N/GaN, both emitting with high efficiency in blue green regions, respectively. Additionally, a set of high‐In content InGaN/GaN QW structures, where growth parameters were kept constant but numbers varied between 1 10, also analysed TEM, XRD PL. For highly‐efficient variable samples, TEM structural studies identified large well‐width fluctuations...

We report on the characterization of intrinsic, anisotropic, dielectric properties wurtzite gallium nitride in spectral range 0.5–11 THz, using terahertz time-domain spectroscopy. The ordinary (ε˜⊥) and extraordinary (ε˜∥) components complex function were determined experimentally for a semi-insulating, m-plane single crystal, providing measurements refractive indices (n⊥,∥) absorption coefficients (α⊥,∥). These material parameters successfully modeled by considering contribution optical...

The sub-luminal phase velocity of electromagnetic waves in free space is generally unobtainable, being closely linked to forbidden faster than light group velocities. requirement effective phase-velocity laser-driven particle acceleration schemes imposes a fundamental limit on the total achievable free-space, and necessitates use dielectric structures waveguides for extending field-particle interaction. Here we demonstrate new travelling-source propagation approach overcoming limits....

We demonstrate the generation of near-single cycle longitudinally polarized terahertz radiation using a large-area radially biased photoconductive antenna with longitudinal field amplitude in excess 2 kV/cm. The 76 mm diameter was photo-excited by 0.5 mJ amplified near-infrared femtosecond laser system and voltage up to 100 kV applied over concentric electrodes. Amplitudes for both transverse components source were measured calibrated electro-optic detection scheme. By tightly focusing...

The charge dynamics at the surface of transparent conducting oxide and photoanode material ZnO are investigated in presence absence light-harvesting colloidal quantum dots (QDs). time-resolved change potential upon photoexcitation has been measured the<italic>m</italic>-plane (101̄0) using a laser pump-synchrotron X-ray probe methodology. By varying oxygen annealing conditions, hence vacancy concentration sample, we find that dark carrier lifetimes vary from hundreds μs to ms...

We explore the terahertz (THz) emission from CoFeB/Pt spintronic structures in below-magnetic-saturation regime and reveal an orientation dependence emission, arising in-plane uniaxial magnetic anisotropy (UMA) ferromagnetic layer. Maximizing UMA during film deposition process aligning applied field with easy axis of structure allow THz to reach saturation under weaker fields. In addition, amplitude remains at levels when is removed. The development that can emit broadband pulses without...

A novel fluoride-centered triangular-bridged carboxylate complex, [Ni2Cr(μ3-F)(O2C(t)Bu)6(HO2C(t)Bu)3] (1), is reported. Simple postsynthetic substitution of the terminal pivalic acids in 1 with pyridine and 4-methylpyridine led to isolation [Ni2Cr(μ3-F)(O2C(t)Bu)6(C5H5N)3] (2) [Ni2Cr(μ3-F)(O2C(t)Bu)6((4-CH3)C5H4N)3] (3). Structural magnetic characterizations carried out on series reveal a dominating antiferromagnetic interaction between nickel chromium centers leading an S = (1)/2 ground...

We demonstrate the generation of single-cycle longitudinally polarized terahertz pulses with field amplitudes in excess 11 kV/cm using interferometric recombination two linearly beams. High strength transversely were generated by optical rectification a matched pair magnesium-oxide doped stoichiometric lithium niobate (MgO:SLN) crystals reversal χ333(2) orientation. The discontinuity produces polarity flip transverse field; longitudinal produced as consequence was measured far-field. Both...

Abstract We report on a combined theoretical and experimental study of the impact alloy fluctuations Coulomb effects electronic optical properties $$c$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>c</mml:mi></mml:math> -plane GaN/AlGaN multi-quantum well systems. The presence carrier localization in this system was demonstrated by observations, such as “S-shape” temperature dependence photoluminescence (PL) peak energy, non-exponential PL decay curves that varied across...

We have investigated the relative quantum efficiency in a series of InGaN∕GaN single wells with differing indium concentration. The results measurements involving direct detection phonons emitted as result nonradiative recombination and carrier energy relaxation are compared time-resolved photoluminescence studies. Using these complementary techniques we extracted low-temperature internal observed effect free-carrier screening on radiative processes well samples. All samples exhibit high...

The adsorption of malonic acid on rutile TiO2 (110) has been studied using photoelectron spectroscopy and C K-edge, near edge X-ray fine structure (NEXAFS). Analysis the O 1s Ti 2p spectra suggest that molecule adsorbs dissociatively in a doubly-bidentate geometry as malonate. data are unable to distinguish between chelating bonding mode with backbone lying along [001] azimuth or bridging direction. Work carried out wiggler beamline suggests is unstable under irradiation by high-flux...