Decrease In Linewidth Research Articles

Influence of Ge4+ doping on photo- and electroluminescence properties of ZnGa2O4

Nanocrystalline ZnGa2O4 samples doped with varying concentrations of Ge4+ ions were prepared and their photo- and electroluminescence properties were investigated in detail before and after annealing at 900 °C. X-ray diffraction (XRD) studies confirmed that Ge4+ doping even to a level of 0.5 at.% at the expense of Ga3+ in ZnGa2O4, leads to incorporation of significant extent Ga3+ ions (∼29%) at Zn2+ site (tetrahedral site) in ZnGa2O4 lattice thereby increasing relative extent of distorted gallium-oxygen (GaOx) structural units. XRD, UV-Visible optical reflectance and lifetime measurements confirmed that a maximum of 0.65 at.% Ge4+ is doped in nanocrystalline ZnGa2O4. Observed blue shift in photoluminescence maximum and decrease in line width with Ge4+ doping is explained based on increased electro-negativity of Ge4+ compared to Ga3+ and lack of formation of oxygen vacancies particularly for 900 °C annealed samples. Lack of oxygen vacancies in Ge4+ doped annealed samples facilitates selective excitation of regular GaO6 and GaOx structural units, upon application of AC voltages, leading to around 50% reduction in line width of electroluminescence peak from doped sample compared to undoped one. Observed variation in electroluminescence properties between doped and undoped samples have been understood based on difference in nature of defects generated in the lattice.

Gold nano-urchins for plasmonic enhancement of random lasing in a dye-doped polymer

We report our results on a plasmonic random laser with three-dimensional (3D) gold nano-urchins as scatterers distributed in rhodamine 6G dye-doped polymer film. The performance of anisotropic urchin scatterers is first studied using electromagnetic simulations for absorption/scattering cross-section and local field enhancement. This is compared to gold nanospheres of similar size. The simulation results indicate a two-fold local field enhancement, a higher scattering cross-section, and a low absorption cross-section in the 400 nm–570 nm spectral region of interest for nano-urchins. The effective scattering mean free path for urchins is calculated to be 90 µm less than nanoparticles. This suggests nano-urchins are efficient scatterers over conventional nanospheres for random lasing. A random laser is then experimentally demonstrated using gold nano-urchin scatterers, and incoherent lasing emission is observed for very low urchin number density of order ∼108 cm−3. A three-fold increase in scatterer concentration is shown to reduce the threshold energy from 0.8 mJ to 0.28 mJ per pulse. This is accompanied by a linewidth decrease from the rhodamine 6G emission bandwidth of 58 nm to up to 3 nm. Along with particle scattering, the waveguiding mechanism is identified to provide additional feedback for the lasing. This has been validated by the angular measurement of emission and by using spot pumping scheme. With low gold nano-urchin concentration, being incoherent and in film form, this plasmonic random laser could be an economical solution for speckle-free imaging applications.

Control of the coupling strength and linewidth of a cavity magnon-polariton

The full coherent control of hybridized systems such as strongly coupled cavity photon-magnon states is a crucial step to enable future information processing technologies. Thus, it is particularly interesting to engineer deliberate control mechanisms such as the full control of the coupling strength as a measure for coherent information exchange. In this work, we employ cavity resonator spectroscopy to demonstrate the complete control of the coupling strength of hybridized cavity photon-magnon states. For this, we use two driving microwave inputs which can be tuned at will. Here, only the first input couples directly to the cavity resonator photons, whilst the second tone exclusively acts as a direct input for the magnons. For these inputs, both the relative phase $\phi$ and amplitude $\delta_0$ can be independently controlled. We demonstrate that for specific quadratures between both tones, we can increase the coupling strength, close the anticrossing gap, and enter a regime of level merging. At the transition, the total amplitude is enhanced by a factor of 1000 and we observe an additional linewidth decrease of $13\%$ at resonance due to level merging. Such control of the coupling, and hence linewidth, open up an avenue to enable or suppress an exchange of information and bridging the gap between quantum information and spintronics applications.

Temperature Dependence of Raman and Photoluminescence Spectra of Ternary Alloyed CdSe0.3Te0.7 Quantum Dots

The Raman and photoluminescence spectra of ternary alloyed CdSe0.3Te0.7 quantum dots (QDs) have been studied at temperatures between 84 K and 293 K. The average diameter of QDs is about 5.1 nm. The temperature dependence of the longitudinal optical (LO) phonon frequencies and the phonon band width was analyzed and the anharmonic constants relating to various high-order phonon processes was determined. While the three-phonon processes plays a dominant role in the temperature-dependent shift of the LO-phonon frequencies, the four-phonon processes contribute to the increase of the phonon linewidth with increasing temperature. The photoluminescence (PL) spectra were used to study the temperature dependence of the bandgap, the linewidth and the integrated PL intensity. At low temperatures below about 120 K, the PL linewidth decreases and the PL intensity increases as temperature increases. This temperature behavior can be ascribed to the exciton fine structure.

Study on Electromigration of Nano-Silver Paste with Different Hot Pressing Sintering Conditions

Silver is suitable for use as a interconnect material due to its good thermal conductivity and electrical conductivity. Additionally, nano-sized silver particles (or pastes) can be rapidly sintered at related low temperatures (<250°C ) due to their high surface to volume ratio. The nano-sized silver particle paste developed in this study can be hot-pressed at 250°C and 10 Mpa to form a low porosity (6.2%) and low-resistivity (2.9*10-8 Ω-m) interconnect, which is comparable to that of commercial available products. With the demand for higher packing density of integrated circuit, the interconnect line width decreases and the current density increases. In general, if the current density is increased to higher than 105 A/cm2, electro-migration phenomenon would become more serious and could cause unpredictable failure of interconnect. In order to understand the electro-migration mechanism of silver interconnect made by nano-paste followed by hot pressing sintering, the porosity of samples with different hot-pressing parameters was measured. Subsequently, current-stressing tests (at 250°C and 105 A/cm2 ) of interconnects were carried out. Through observations of changes in the surface morphology and cross-sectional microstructures during current-stressing tests, the failure mechanism and electro-migration phenomenon are investigated in detail. It is observed as shown in the figure that the electro-migration occurred in early stage (within about 1 day) that resulted in the decrease of porosity near cathode and increase of porosity near anode respectively. Figure 1 Figure 1

Carrier escape mechanism in laterally correlated InAs sub-monolayer quantum dots using temperature dependent photoluminescence

We have quantitatively investigated relative effects of photo-carrier escape mechanism upon the quenching of photoluminescence with temperature in an ensemble of embedded InAs sub-monolayer (SML) quantum dots by varying InAs SML coverage from 0.4 ML to 0.8 ML. The mutual interplay of carrier recombination and tunneling throughout the laterally coupled quantum dots for different InAs coverage have been established to determine the temperature dependent photoluminescence (TDPL) spectra. The respective characteristic life times were extracted from the individual TDPL spectra by fitting them with model carrier rate equation. The consequent enhancement of inter-dot tunnel strength with respect to the carrier recombination rate with increasing InAs coverage has been marked out to be responsible for sustainable photoluminescence efficiency at higher temperature. Enhancement of tunneling rate with increasing InAs SML coverage has been physically described as consequence of reduced average inter-dot lateral separation as estimated from grazing incidence small angle x-ray scattering (GISAXS) measurement. Moreover, we have observed the anomalous decrease of spectral linewidth with temperature which can also be described as a consequence of the tunnel induced faster inter-dot carrier transfer at higher sub-monolayer coverage. The absence of any wetting layer in SML QD resulted in speeding up of carrier transfer through inter-dot tunneling pathways with tunnel time as low as 350 ps. This is significantly faster than the conventional InAs/GaAs SK QDs with tunnel time of 1328 ps.

Droplet sliding behaviour on textured and fluorinated surface

Engineered surfaces have the potential to control droplet movement phenomena on the surface. Many products that contact liquids, such as wet production processes or their machines have design parameters that include droplet movement phenomena such as sliding, rolling, slopping, coalescing and separation. This study investigated the sliding behaviour of water droplets depending on an anisotropic surface pattern. On a line-and-space patterned surface, smaller and larger droplets start sliding faster than on a flat surface in directions parallel and perpendicular to the pattern, respectively. Additionally, a decrease in line width, i.e., the ratio of contact area is an important factor in enhancing droplet sliding. The rotational and translational movement are dominant on flat and textured surfaces, respectively.

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Influence of process parameters on the properties of pulsed laser deposited CuIn0.7Ga0.3Se2 thin films

This work reports on the influence of pulsed laser deposition growth parameters on the properties of CuIn0.7Ga0.3Se2 thin films. Polycrystalline CuIn0.7Ga0.3Se2 thin films were grown on soda-lime glass substrates under various growth conditions. Morphological, compositional, structural, electrical and optical properties of CuIn0.7Ga0.3Se2 thin films were investigated as a function of laser fluence, background gas and substrate temperature. A threshold of laser fluence, 0.8 J/cm2, and background pressure, 0.01 mbar, determined through a systematic parametric investigation, for obtaining stoichiometric films. A minor secondary phase of Cu2−xSe was observed by X-ray diffraction, and found to gradually diminish with increasing deposition temperature. The film grown at 500 °C shows the purest CuIn0.7Ga0.3Se2 chalcopyrite phase. The electrical properties of the films, i.e., dark resistivity, carrier concentration and mobility, are shown to be mostly affected by the Cu2−xSe phase and the crystal quality of the films. All films exhibit high absorption coefficients of ∼2–3 ∗ 104 cm−1 in the vicinity of the band-edge; a blue shift of the energy gap with deposition temperature is attributed to the relaxation of the lattice strain, as corroborated by the respective shift of (1 1 2) peak of the XRD patterns. The monotonic increase of the photoluminescence intensity accompanied by the concomitant decrease of the emission linewidth and Stokes shift indicate an improvement in the material quality and uniformity as deposition temperature increases in accordance with the structural and electrical measurement findings. Long PL lifetime of ∼50 ns is measured in the band-edge region for the film grown at 500 °C, suggestive of a single phase material with low defect density. Our results overall indicate that high-quality, stoichiometric CuIn0.7Ga0.3Se2 thin films can be obtained using pulsed laser deposition, a rapid single-step growth method that eliminates the need for post-selenization.

Strain tuning of excitons in monolayer WSe2

The authors investigate the influence of strain on the electronic properties of monolayer WSe${}_{2}$ using optical absorption and photoluminescence spectroscopy. The linewidth of the $A$ exciton exhibits a significant and unexpected decrease, from 42 to 24 meV at room temperature. A slightly different behavior is observed for WS${}_{2}$; its linewidth decreases from 30 to 24 meV. They provide a model that explains both the decrease in linewidth and differences in the magnitude of the effect in these two similar material systems. Their findings reveal the utility of strain tuning for probing subtle aspects of 2D materials.

Narrowing of Plasmon Resonance Peaks as an Ensemble Effect

The frequency of localized surface plasmon resonance (LSPR) displayed by gold nanoparticles (AuNPs) redshifts as a function of their local refractive index, which renders them valuable transducers for sensing applications. An ensemble hypothesis is presented herein, along with spectroscopic evidence, using the biotin–streptavidin system on immobilized AuNPs to interpret the decrease in ensemble line width (ELW) consistently observed upon functionalization of plasmonic nanoparticles and the subsequent analyte binding. These results demonstrate that ELW can be used to monitor recognition reactions, providing spectral details and a possible sensitivity enhancement to the conventional wavelength sensing. A novel sensing platform allowing the simultaneous measurement of both LSPR wavelength and ELW is proposed, which not only combines the advantages of both parameters but also permits real-time measurement and miniaturization.

Simple model of saturable localised surface plasmon

Localised surface plasmons (LSPs) are now applied to various fields, such as bio-sensing, solar cell, molecular fluorescence enhancement and quantum-controlled devices at nanometre scale. Recent experiments show that LSPs are optically saturated by high-intensity light. Absorption saturation arises as a result of strong optical nonlinearity and cannot be explained by the conventional boson model of LSPs. Here, we propose a simple model of saturable LSPs using an effective dipole approximation. The strategy is to directly compare the classical linear optical response of an LSP with that obtained from a saturable quantum two-level system in the limit of weak excitation. The second quantization can then be performed by replacing a classical polarizability with a quantum dipole operator. Taking an ellipsoidal nanometal as an example, we analyse in detail the optical response of a single ellipsoidal nanometal to validate our model. Our numerical results show that the plasmon resonance frequency and spectral linewidth decrease as the aspect ratio of the ellipsoid increases, which is similar to the size dependence observed in early experiments.

On the linewidth in photoelectron spectra of size-selected clusters.

A systematic analysis of the average linewidth of features in the photoelectron spectra of size-selected elemental clusters consisting of up to 10 atoms is presented. With increasing atomic weight, the average linewidth decreases. Several possible reasons for this trend are discussed. Obvious effects such as experimental resolution, vibrational temperature, and lifetime broadening can be excluded. The only remaining explanation is a mass-dependence of the Franck-Condon envelope. Each photoelectron peak corresponds to an electronic transition, which exhibits a Frank-Condon envelope. Its full width of half maximum depends on the spatial expansion of the nuclear wave functions in the initial state. With increasing atomic mass, the nuclear wave functions narrow down.

High figure of merit hydrogen sensor using multipolar plasmon resonance modes

Fabrication of long Au nanorods (AuNRs) has resulted in the appearance of higher order plasmon resonance modes, or multipoles, in the absorbance spectrum that can be monitored as a function of time and gas exposure. Due to the proximity of the multipolar mode to the transverse dipole mode of the AuNRs, both modes were monitored as the sample was exposed to hydrogen in an air background. These results were also compared to a shorter AuNR sample where the longitudinal dipole peak position matched the multipolar peak position. Polarization dependence of the higher order resonance as well as boundary element method (BEM) simulations confirm that the mode order is n=3. Due to the 36% decrease in linewidth of the multipolar peak compared to the dipole, the figure of merit (FoM) of the multipolar resonance is calculated to be 22% higher than the longitudinal dipole resonance for the shown gas sensing results and is promising for high temperature gas sensing applications.

Design and Fabrication of Anisotropic Conductive Film for Application of Probe Card

AbstractPrior to integrated circuit (IC) packaging, die performance must be verified using probe cards to screen for defective products. With the decrease in IC line width, the dimensions of the pads used for performance verification and the spacing between adjacent pads have also decreased. However, when the pad pitch is reduced to less than 30 μm, commonly used probe cards will face manufacturing problems in miniaturization. To resolve probe card manufacturing problems caused by the miniaturization of IC components, the use of an anisotropic conductive film (ACF) in probe cards was proposed in this study. Theoretical calculations and experimental testing of this probe structure were conducted to demonstrate the feasibility of this concept.In theoretical calculations, composite material and buckling theory were utilized to evaluate the buckling behavior of the ACF. In experimental testing, photolithography and electroplating techniques were used to control the line width and spacing intervals of the micron-scale metal wires in the ACF. After the ACF was fabricated, the mechanical properties of the ACF during wafer testing were assessed. Theoretical analyses and experimental testing verified that ACFs can potentially be applied to the performance verification of IC products. In the ACF structure, multiple probes came into contact with each pad. Therefore, ACFs can potentially be applied to the performance verification of IC components with pad diameters of less than 20 μm. The results of this study directly benefit the miniaturization of ICs.

Flash light sintering of ag mesh films for printed transparent conducting electrode

Transparent conducting electrodes (TCEs) are fabricated through the flash light sintering of reverse-offset printed Ag mesh patterns. Interestingly, the narrower printing lines require a higher flash light energy to obtain an equivalent sheet resistance even if the same Ag nanoparticle ink is used. The microstructural development of sintered Ag nanoparticles is also retarded with the decrease of line width after the same flash light sintering. The temperature calculation in the Ag mesh patterns clearly reveals that heat dissipation is affected by the print dimension. To improve the performance of Ag mesh TCEs with 3μm wide lines, a preheating step comprised of multi-pulses is inserted before a main flash light sintering. The multi-pulsed flash light sintering is effective in decreasing the sample temperature and in removing the substrate damages or microstructural defects. As a result, the flash light-sintered Ag mesh TCEs shows a sheet resistance of 27Ω/□ and an optical transmittance of 84.7% including an optical transmittance of substrate.

Refinement of solid layers via wetting on homogeneous lyophilic surfaces

Surface control additives (SCAs), or surfactants, can obstruct the wetting of liquid films on lyophilic surfaces even though they lower surface tension. In this work, this unusual behavior was used to decrease the widths of printed organic and nanoparticle lines on different homogeneous surfaces. A decrease in line width accompanied a change in its cross section. The ability of a SCA to decrease the line width was correlated with contact angle but not the surface tension of the solution. Line refinement was consequently attributed to an increase in contact angle. Because there were no reports that surfactants increased contact angles, the mechanisms to increase contact angle were discussed in static and dynamic terms. First, Owens and Wendt’s theory revealed that contact angle changes depended on SCA-induced modification of polar and dispersive interfacial components. However, a definitive increase in contact angle could not be deduced from this theory alone. Second, the effect of solutal Marangoni forces induced by the SCAs on contact angle was discussed by considering the wetting behaviors of binary solvents. SCA concentration dependence of surface tension at higher than the initial SCA concentration correlated well with the ability of the SCA to decrease line width.

Mechanically induced defects in milled CdZnSe nanocrystal: A low-temperature electron spin resonance spectroscopy analysis

The electron spin resonance (ESR) linewidth of the milled powder decreases as a function of increasing temperature. On the other hand, the intensity of the signal increases with increasing temperature from 108K to 243K and subsequently approaches Curie-like temperature behavior above 245K. These behaviors were understood in terms of the orbital degeneracy of fast-relaxing impurities, such as Fe3+ ion debris, from the grinding media that was embedded in the atomic structure of the milled powder and are not completely quenched. At lower temperature, only ±1/2 is occupied and the excited energy state is less likely effective in dipolar broadening compared with lower energy states of ±5/2 and ±3/2. In this regard, decrease in linewidth should be expected with increasing temperature.

Amplitude and Phase Noise of Frequency Combs Generated by Single-Section InAs/InP Quantum-Dash-Based Passively and Actively Mode-Locked Lasers

We investigate the amplitude and phase noise of an optical frequency comb based on InAs/InP quantum-dash mode-locked laser. The laser demonstrates low relative intensity noise (< −125 dB/Hz) and phase noise in the passive mode-locking regime. By actively mode-locking the laser, we observe a reduction in the flicker FM noise and timing jitter, as a result of which the optical linewidth decreases, and hence the effective bandwidth compatible with optical coherent systems increases by more than 50% to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.1$ </tex-math></inline-formula> THz.

Physical properties optimization of polycrystalline LiFeAs

We present a study of parameter optimization for synthesizing truly stoichiometric polycrystalline LiFeAs. Stoichiometric LiFeAs has been prepared in a very broad range of synthesis temperature (200–900°C) under otherwise exactly the same conditions, and has been characterized by structural, magnetic, transport, nuclear quadrupole resonance (NQR), and specific heat measurements. Our study showed that the LiFeAs phase is formed at 200°C with a large amount of impurity phases. The amount of these impurity phases reduces with increasing synthesis temperature and the clean LiFeAs phase is obtained at a synthesis temperature of 600°C. Magnetic susceptibility and resistivity measurements confirmed that the superconducting properties such as the critical temperature Tc, and the upper critical field Hc2 do not depend on the synthesis temperature (≤700°C), remaining at almost the same value of ∼19K and ∼40T, respectively. However, the width ΔTc of the transition and the NQR line width decrease with increasing the synthesis temperature and reached to minimum value for the synthesis temperature of 600°C. Our careful analysis suggests that the best sample obtained at 600°C is optimal concerning the low resistivity, high residual resistivity ratio (RRR), low ΔTc, high Tc and Hc2, and a small NQR line width with values which are comparable to that reported for LiFeAs single crystals. Specific heat measurements confirmed the bulk superconducting nature of the samples. The Hc2 value estimated from the specific heat is consistent with that of the resistivity measurements. Concisely, 600°C synthesis temperature yields optimal high quality polycrystalline LiFeAs bulk samples. Further improvement of the quality of the sample prepared at 600°C could be obtained by a controlled slow cooling process. Microstructural analysis reveals that the abundance of micro-cracks becomes strongly reduced by the slow cooling process, resulting in an increase in clean and well-connected grain boundaries.