Optical Emission Intensity Research Articles

Fabrication of high-performance nanostructured CsPbI3/Si perovskite photodetector by pulsed laser deposition: Challenges and prospects

The inorganic perovskite CsPbI3 is a promising material for optoelectronic applications like photodetectors and solar cells due to its suitable bandgap and excellent properties. In this work, nanostructured CsPbI3 thin films were deposited on glass and silicon substrates by pulsed laser deposition (PLD) at laser fluences ranging from 5.7 to 10 J/cm2. Systematic characterization revealed that increasing the laser fluence significantly enhances the crystallinity, phase purity, optical emission intensity, charge carrier concentration (up to 1.38 × 1012 cm−3), and mobility (up to 164.7 cm2/Vs) of the CsPbI3 films. An optimal laser fluence of 10 J/cm2 resulted in large, elongated grains over 280 nm, tightly packed films with minimal defects, and a suitable bandgap of 1.83 eV CsPbI3/Si heterojunction photodetectors were fabricated, with the device made at 8.5 J/cm2 exhibiting maximum responsivity of 8 A/W at 600 nm, detectivity exceeding 1014 Jones, external quantum efficiency up to 17.5 × 102 %, and a high ON/OFF ratio of 225 under illumination. The photodetector performance was strongly correlated with the optimized structural order, morphology, and optoelectronic quality achieved by careful control of the laser fluence during PLD. This work highlights PLD as an effective technique for realizing high-quality CsPbI3 films with tailored properties for advanced photodetection and photovoltaic applications.

Laser-induced breakdown spectroscopy (LIBS) of animal fat (lard): Efficient sample preparation for onsite analysis and influence of sample temperature on the signal intensity and plasma parameters

We report an efficient sample preparation method (freezing) for onsite fat and meat analysis via a specially designed thermoelectric cooling and temperature-controlling system. This investigation also focused on the effect of phase change on the sensitivity and reproducibility of LIBS emission signals and plasma parameters. The plasma emissions of animal fats (lard) were recorded when the sample was frozen (−2 °C), fluid (15 °C), and in a liquid state (37 °C) with a thermoelectric cooling system. At each temperature, the plasma emissions were acquired at laser pulse energy from 50 to 300 mJ and detector gate delay (DGD) from 0.5 to 5 μs. With increasing sample temperature, the DGD, where the optical emission intensity reached a maximum, decreased. At a laser pulse energy of 200 mJ and a sample temperature of −2 °C, the emission signals increased fourfold, the signal-to-noise ratio (SNR) improved tenfold, and the self-absorption in the emission lines decreased significantly. The repeatability of the emission signals and plasma parameters of frozen and liquid fat samples was determined using the relative standard deviation (RSD) of Se I (473.08 nm) and K I (766.48 nm) emission lines. The RSDs of the emission signals improved from 40 to 18 % and 37 to 16 %, whereas the shot-to-shot RSDs of the electron temperature and electron number density get improved from 11 to 6 % and 12 to 6.8 %, respectively.

Lattice Strain Enhanced Phase Transformation of NaYbF4: 2% Er3+ Upconverting Nanoparticles by Tuning the Molar Ratio of Na+/Yb3+

AbstractNaYbF4 upconverting nanoparticles (UCNPs) have enhanced optical properties compared to the NaYF4 UCNPs. However, synthesis of monodisperse NaYbF4 with controllable size and optical properties poses challenges, and the mechanism of phase transformation remains to be understood. Here, they report on the effect of Na+/Yb3+ molar ratio on the morphological and optical properties of upconverting NaYbF4: 2% Er3+ nanoparticles. Controllable transformation of cubic phase nanoparticles produced with [Na+]/[Yb3+] = 1 to hexagonal phase is achieved by increasing Na+ content. The hexagonal UCNPs produced with [Na+]/[Yb3+] = 4 have significantly enhanced intensity of optical emission of ≈600 times compared with the pure cubic phase crystal. The work reveals that the increasing dislocation of sodium and ytterbium distribution cause the accumulation of the lattice strain with increasing Na+ content, and triggers the lattice strain‐mediated phase transformation in cubic cell, as confirmed by the Density Function Theory simulations. These results provide new insights into the growth of UCNPs and pave the way for developing controlled synthesis of UCNPs for applications as bio‐probes and for energy harvesting.

Surface sulfurization of amorphous carbon films in the chemistry of oxygen plasma added with SO2 or OCS for high-aspect-ratio etching

Etching of oxygen-based plasmas with sulfur dioxide (SO2) or carbonyl sulfide (OCS) can form high-aspect-ratio (HAR) features of amorphous carbon films as carbon hard masks (CHM). The etched profiles showing shapes such as bowing or tapering are essentially dependent on the partial pressures of SO2 or OCS in the O2 plasma. The surface treated after the OCS-added plasma exhibited strong sulfurization by S2 and CS species in S 2p of the X-ray photoelectron spectroscopy (XPS). The gas-phase interactions in the sulfur-oxygen-carbon system generated atoms and molecules, such as O, O+, and O2+, which etched at the bottom and, conversely, SO, CO, CS, CS2, and S2, which inhibited isotropic etching at the sidewalls of the HAR features. The chemical reactions of the CS sulfurizing precursors in the gas phase were monitored by comparing their optical emission intensities at a wavelength of 257 nm with those of SO2 at approximately 320 nm. The optimization of the HAR profiles of the CHM can be controlled by sidewall sulfurization of the CHM to obtain desirable profile shapes for the HAR features.

Electron characteristics and dynamics in sub-millimeter pulsed atmospheric dielectric barrier discharge

The discharge characteristics and mechanism of sub-millimeter pulsed dielectric barrier discharge in atmospheric-pressure helium are investigated experimentally and theoretically, demonstrating that when the discharge gap distance is reduced from 1.00 mm to 0.20 mm, the discharge ignition time is reduced to approximately 40 ns and discharge intensity is enhanced in terms of the discharge optical emission intensity and density of the plasma species, (energetic electrons with energy above 8.40 eV). The simulated results show that as the discharge gap distance is further reduced to 0.10 mm, the number of energetic electrons decreases, which is attributable to the contraction of plasma bulk regime and reduction of electron density in the discharge bulk. Conversely, the proportion of energetic electrons to the total electrons in the discharge monotonically increases as the discharge gap distance is reduced from 1.00 mm to 0.10 mm. It is proposed that a gap distance of 0.12 mm is optimal to achieve a high concentration and proportion of energetic electrons in sub-millimeter pulsed atmosphere dielectric barrier discharge.

Investigation of thermodynamic properties in picosecond laser-produced plasmas on silicon

The validity of local thermodynamic equilibrium (LTE) in plasma is a long-term concern for laser-induced breakdown spectroscopy applications. In this paper, the spatial and temporal dependence of LTE deviation in picosecond laser-induced plasmas has been proved. A picosecond (∼20 ps) laser operated at 532 nm was used to ablate a silicon target to produce plasma at a pressure of 10−5 mbar. A general electron energy distribution function was used to provide access to the insight into population ratios of different energy levels for the spatially and temporally resolved optical emission intensity of laser-induced plasma. A precise temporal and spatial LTE boundary of plasma generated in picosecond laser ablation was obtained, and the results showed that only at delay times of 180–300 ns, the plasma away from the surface (>4 mm) is in LTE.

Influence of sample temperature and ambient argon pressure on LIBS spectra of extracted animal fat

This work explores the influence of sample temperature, ambient gas pressure, laser energy, and detector gate delay (DGD) on the LIBS emissions of extracted animal fat. The emissions from laser-induced plasma of extracted animal fat were acquired with varying sample temperatures, ambient argon pressure, laser energy, and detector gate delay. A thermoelectric system fitted with a temperature-controlling sensor was used to control the sample temperature. For maximum optical emission intensity, the detector gate delay (DGD) shifted toward a lower value with the increase in sample temperature for all ambient argon pressures. The nine-fold signal enhancement, ten times improvement in signal-to-noise ratio (SNR), and significantly reduced self-absorption were observed in all detected emission lines recorded at 200 mJ laser energy –2 ºC sample temperature, 375 Torr ambient argon pressure, and 2 µs DGD. The repeatability of emission signals was evaluated by calculating the relative standard deviation (RSD) of the emission line (Zn I (636.23 nm)) at different sample temperatures, which improved from 35 % to 6 % when the sample changed from liquid to solid (frozen). During the semi-liquid form of fat, the decreasing ambient gas pressure did not significantly affect signal repeatability. In addition to diagnosing the fat plasma, the plasma temperature and electron number density have been evaluated as a function of sample temperature and ambient argon pressure.

Effect of an additional floating electrode on radio frequency cross-field atmospheric pressure plasma jet

Atmospheric pressure plasma jets with cross-field electrode configuration are a potential jet design for gases with high breakdown fields. This study focuses on the effect of an additional floating electrode on the cross-field plasma jet properties. Detailed experiments are done with the additional floating electrodes of different widths introduced below the ground electrode in a plasma jet with a cross-field electrode configuration. It is observed that in the presence of an additional floating electrode in the jet propagation path, less applied power is needed for the plasma jet to cross the nozzle and jet length increases. This threshold power, as well as the maximum jet length, depends on the electrode widths. A detailed analysis of charge dynamics in the presence of an additional floating electrode shows decrement in the net charge transferred radially to the external circuit through the ground electrode, and an increment in the net charge transferred axially. Increment in the optical emission intensity of reactive oxygen and nitrogen species, as well as the relative yield of ions like N^{+}, O^{+}, OH^{+}, NO^{+}, O^{-}, and OH^{-} in the plasma plume, that are crucial for biomedical applications suggest an improvement in the reactivity of plasma plume in the presence of additional floating electrode.

Surface plasmon resonance (SPR) in nanofibers of cesium titanium bromide CsTiBr3 synthesized by two-stage deposition technique

The optical phenomenon of surface plasmon resonance (SPR) finds applications in bio-imaging, photocatalysis, biosensors, LED, and solar cells. In the present study, the SPR property of lead-free nanofibers of cesium titanium bromide (CsTiBr3) synthesized by a two-stage deposition technique is reported for the first time. The optical properties and SPR in CsTiBr3 are mainly promoted by the spherical-shaped metal cluster and concave-shaped metal neck formation of cesium bromide crystal. The spherical-shaped metal cluster formation is confirmed by SEM and HRTEM analysis. The intensity of optical absorption and emission of CsTiBr3 are amplified by SPR. The intensified absorption and emission of photons make CsTiBr3 a promising candidate for solar cells, bioimaging, biosensors, and photocatalysis.

Rational design of compact ceramic coating on SiCp/Al composites by tailoring soft sparking discharge of plasma electrolytic oxidation

The characteristics of PEO processes on SiCp/Al composite in aluminate electrolyte under the influence of negative pulse were comparatively investigated, aiming to tailor the soft sparking discharge states, thus achieving the compact ceramic coating and providing a deep understanding of the mechanisms involved. Tracking the variation trend of element optical emission intensity by OES technology reflects the influence of negative voltage on the evolution of the spark state, and the results show that large negative voltage accelerates the transition from arc sparking discharge to soft sparking discharge. When the PEO process completely enters the soft spark discharge state, the lowest electron density can also be kept at 1.06 × 1022 m−3, reaching the local thermodynamic equilibrium condition. At this time, the electron temperature in the plasma discharge zone is about 4000 K. In addition, the coating surface roughness value decreases with the increase of negative voltage, and the introduction of negative voltage effectively reduces the irregular convex structures and the macropores in the coating, due to inhibiting destructive high-intensity spark discharge by the soft sparking discharge.

Temperature Dependent Hydrogen Bond Toward High Emission in an Emerging Indium-Based Perovskite.

Low-dimensional organic-inorganic hybrid perovskites (OIHPs) with broadband emission attract immense scientific interest due to their potential application for the next generation of solid-state lighting. However, due to low exciton utilization, organic cations generally adjust structure rather than contribute the band edge to affect optical properties. Based on this, OIHPs are usually allowed to obtain a low photoluminescence quantum yield (PLQY). Herein, a good charge transfer carrier (p-phenylenediamine, PPDA) as organic cation is rationally employed and a novel indium-based perovskite is synthesized. By coupling with H2 O molecules, a strong interaction between organic and inorganic components is realized by hydrogen bonding, which has good transportability and greatly improves the exciton utilization. The regions of hydrogen bonding show high electron mobility, combined with the induced recombination center, improving the progress of charge relaxation. As a result, the regulation of hydrogen bond strength based on the microstructure optimization directly determines the optical emission intensity, realizing nearly 100% PLQY. Further, the polyhydrogen bond structure makes each component a stronger interaction, showing high stability in polar, organic, and acidic solvent, as well as long-term storing, which represents one of the highest overall performances for lighting in OIHPs.

Experimental investigation of the radially-dependent ignition process in a pulsed capacitively coupled RF discharge: Effects of pressure, voltage and afterglow duration

The effects of the gas pressure, the voltage amplitude and the afterglow duration on the ignition process over 300 mm-diameter in a pulse-modulated capacitively coupled radio-frequency argon discharge are experimentally investigated. A home-made optical probe is used to measure the optical emission intensity (OEI) as a function of time since the beginning of each pulse at various radial positions. A voltage and a current probe are used to measure the voltage and current waveforms at the power feeding point and then the time-dependent power deposition is also obtained. It was found that the radial profile of the OEI exhibits complex evolution when changing these external conditions. At lower pressures, the ignition occurs earlier, and the radial-integral OEI and the power deposition overshoot more slightly during the ignition. By increasing the pressure, these two quantities overshoot more significantly, and the OEI gradually evolves from an edge-peaked radial profile to a center-high radial profile for a given time when the OEI increases rapidly during the ignition. When increasing the voltage amplitude, the ignition tends to occur earlier, featuring a more significant overshoot of the OEI and power deposition at a higher voltage. Compared to that at high voltage, the OEI exhibits a significant center-high radial profile at low voltage amplitude during the ignition. By increasing the afterglow duration, T off, the ignition is delayed and the overshoot becomes more significant, due to a lower initial electron density when each pulse is turned on. During the phase when the growth rate of the OEI versus time is maximum, the OEI exhibits different radial distributions, i.e., it appears a center-high profile at short T off, an edge-peaked profile at intermediate T off, and a center-high profile at relatively long T off.

Real-time monitoring of plasma synthesis of functional materials by high power impulse magnetron sputtering and other PVD processes: towards a physics-constrained digital twin

Plasma synthesis of thin films by physical vapour deposition (PVD) enables the creation of materials that drive significant innovations in modern life. High value manufacturing demand for tighter quality control and better resource utilisation can be met by a digital twin capable of modelling the deposition process in real time. Optical emission spectroscopy (OES) was combined with process parameters to monitor all stages of both high power impulse magnetron sputtering and conventional magnetron sputtering processes to provide a robust method of determining process repeatability and a reliable means of process control for quality assurance purposes. Strategies and physics-based models for the in-situ real-time monitoring of coating thickness, composition, crystallographic and morphological development for a CrAlYN/CrN nanoscale multilayer film were developed. Equivalents to the ion-to-neutral ratio and metal-to-nitrogen ratios at the substrates were derived from readily available parameters including the optical emission intensities of Cr I, N2 (C–B) and Ar I lines in combination with the plasma diffusivity coefficient obtained from the ratio of substrate and cathode current densities. These optically-derived equivalent parameters identified the deposition flux conditions which trigger the switch of dominant crystallographic texture from (111) to (220) observed in XRD pole figures and the development of coating morphology from faceted to dense for a range of magnetron magnetic field configurations. OES-based strategies were developed to monitor the progress of chamber evacuation, substrate cleaning and preventative chamber wall cleaning to support process optimisation and equipment utilisation. The work paves the way to implementation of machine learning protocols for monitoring and control of these and other processing activities, including coatings development and the use of alternative deposition techniques. The work provides essential elements for the creation of a digital twin of the PVD process to both monitor and predict process outcomes such as film thickness, texture and morphology in real time.

Two-dimensional electron temperature and density profiles of Hall thruster plume plasmas using tomographically reconstructed optical emission spectroscopy

Two-dimensional electron temperature and density profiles in the plume region of 300 W-class Hall thruster Ar plasmas were obtained using tomographically reconstructed optical emission intensity profiles combined with a collisional-radiative (CR) model. A total of 1242 lines of sight were used by rotating the thruster to apply inverse Radon transform-based tomographic reconstructions and Abel inversion. The reconstruction accuracy of the developed diagnostic system was evaluated using a priori images derived from plasma pictures, and the reconstruction error was less than 1% in the region of interest, exhibiting higher accuracy than the Abel inversion. From the Ar Hall thruster plasma, more than 12 different two-dimensional profiles of Ar I emission intensity within a spectral range of 600–1000 nm were obtained 6 mm from the exit plane of the thruster. A CR model using 31 allowed transitions at 15 different states from the ground state to the 2p i states was incorporated with the tomographically reconstructed emission intensity sets. Consequently, two-dimensional electron temperature and density profiles in the range of 5–18 eV and 2.0 × 1016–4.7 × 1017 m−3 were obtained, respectively, exhibiting reasonable agreement with the double Langmuir probe measurements.

Effects of ‘step-like’ amplitude-modulation on a pulsed capacitively coupled RF discharge: an experimental investigation

We present measurements of the time evolution of plasma and electrical parameters in a pulsed capacitively coupled argon discharge operated at a radio frequency of 12.5 MHz, whose amplitude is ‘step-up’ and ‘step-down’ modulated. The ‘step-up (-down)’ amplitude-modulated waveform consists of three segments, i.e., a low (high)-voltage, a high (low)-voltage, and a zero-voltage stage. Here, we focus on the effect of the ratio (ζ = V L/V H ⩽ 1) of the low-(V L) to high-voltage (V H) amplitude (measured at the end of the respective segment) on the time evolution of discharge parameters. We monitor the behavior of the discharge by measuring (i) the optical emission intensity (OEI) of a selected Ar-I spectral line, (ii) the electron density at the center of the plasma (using a hairpin probe) as well as (iii) the electrical characteristics (by voltage and current probes). It is found that at relatively large ζ (i.e., at low disparity between the two voltage amplitudes), for both the ‘step-up’ and ‘step-down’ cases, these parameters evolve relatively smoothly with time upon changing the voltage amplitude, and the ignition process strongly depends on the duration of the zero-voltage period. At low ζ (i.e., at high disparity between the voltage amplitudes), an abnormal evolution of the parameters can be observed during the low-voltage period for both cases. Specifically, the voltage amplitude and the modulus of the system impedance increase to a higher value, while the relative phase, φ vi, between the voltage and the current approaches 90°, resulting in a reduction of the power deposition and the OEI. The enhanced voltage amplitude decreases to a steady-state value, accompanied by a decline of φ vi, and an abnormal increase of the current amplitude and the electron density after some time, of which the duration increases with the decrease of ζ. The ζ-dependent evolution of the electron density during the low-voltage period was found to significantly affect the subsequent ignition process and electron power absorption mode at the beginning of the high-voltage period.

Deep-ultraviolet plasmon resonance of Ni nanoparticles embedded in BaTiO3 matrix

A tunable nanocomposite structure, consisting of Ni nanoparticles (NPs) with various morphologies and controllable BaTiO3 (BTO) films, was designed using a pulse laser deposition method. The morphological transformation of NPs and the crystal structure of BTO could be modulated by the Ni NP concentration. The experimental demonstration of absorption and photoluminescence enhancement using surface plasmon resonance (SPR) excitation in the deep-ultraviolet (DUV) region was investigated. The splitting of the Ni SPR peak was found in the DUV region, accompanied by decreased band gaps as the Ni NP concentration increased. By photoluminescence analysis, more Ni NPs embedding could provide more electron-hole recombination possibilities, enhancing the optical emission intensity and widening the emission range from red to ultraviolet luminescence. The DUV optical response of Ni NPs with various morphologies was further verified by finite-difference time-domain calculations. Compared with the reported metal NPs using the DUV SPR effect, the smaller Ni NPs provide a new non-noble metal NPs alternative with a high performance SPR excitation in the DUV region beyond the previous Al-based materials, giving new opportunities for manipulating high-energy photons.

Effect of oxygen fraction in nitrogen/oxygen mixtures on primary and secondary streamers in atmospheric-pressure barrier discharge

Two-dimensional simulation of an atmospheric-pressure dielectric barrier discharge (DBD) was performed with different oxygen fractions, [O2]f, of 20%, 40%, 60%, 80%, and 99% in N2/O2 gas to investigate their effects on the primary and secondary streamers. We simulated the optical emission intensity at different [O2]f and compared them with the experimental values. The simulation results indicate that [O2]f affects the ratio of the amount of the electron production from electron impact ionizations and a photoionization, resulting in the changes in the electric field at the tip of the streamer and that in the streamer channel.

Ignition dynamics of radio frequency discharge in atmospheric pressure cascade glow discharge

A cascade glow discharge in atmospheric helium was excited by a microsecond voltage pulse and a pulse-modulated radio frequency (RF) voltage, in which the discharge ignition dynamics of the RF discharge burst was investigated experimentally. The spatio-temporal evolution of the discharge, the ignition time and optical emission intensities of plasma species of the RF discharge burst were investigated under different time intervals between the pulsed voltage and RF voltage in the experiment. The results show that by increasing the time interval between the pulsed discharge and RF discharge burst from 5 μs to 20 μs, the ignition time of the RF discharge burst is increased from 1.6 μs to 2.0 μs, and the discharge spatial profile of RF discharge in the ignition phase changes from a double-hump shape to a bell-shape. The light emission intensity at 706 nm and 777 nm at different time intervals indicates that the RF discharge burst ignition of the depends on the number of residual plasma species generated in the pulsed discharges.

Various concentric-ring patterns formed in a water-anode glow discharge operated at atmospheric pressure

Pattern formation is a very interesting phenomenon formed above a water anode in atmospheric pressure glow discharge. Up to now, concentric-ring patterns only less than four rings have been observed in experiments. In this work, atmospheric pressure glow discharge above a water anode is conducted to produce diversified concentric-ring patterns. Results indicate that as time elapses, the number of concentric rings increases continuously and up to five rings have been found in the concentric-ring patterns. Moreover, the ring number increases continuously with increasing discharge current. The electrical conductivity of the anode plays an important role in the transition of the concentric patterns due to its positive relation with ionic strength. Hence, the electrical conductivity of the water anode is investigated as a function of time and discharge current. From optical emission spectrum, gas temperature and intensity ratio related with density and temperature of electron have been calculated. The various concentric-ring patterns mentioned above have been simulated at last with an autocatalytic reaction model.

N-polar InGaN/GaN nanowires: overcoming the efficiency cliff of red-emitting micro-LEDs

A high efficiency, high brightness, and robust micro or sub-microscale red light emitting diode (LED) is an essential, yet missing, component of the emerging virtual reality and future ultrahigh resolution mobile displays. We report, for the first time, to our knowledge, the demonstration of an N-polar InGaN/GaN nanowire sub-microscale LED emitting in the red spectrum that can overcome the efficiency cliff of conventional red-emitting micro-LEDs. We show that the emission wavelengths of N-polar InGaN/GaN nanowires can be progressively shifted from yellow to orange and red, which is difficult to achieve for conventional InGaN quantum wells or Ga-polar nanowires. Significantly, the optical emission intensity can be enhanced by more than one order of magnitude by employing an in situ annealing process of the InGaN active region, suggesting significantly reduced defect formation. LEDs with lateral dimensions as small as ∼ 0.75 μm , consisting of approximately five nanowires, were fabricated and characterized, which are the smallest red-emitting LEDs ever reported, to our knowledge. A maximum external quantum efficiency ∼ 1.2 % was measured, which is comparable to previously reported conventional quantum well micro-LEDs operating in this wavelength range, while our device sizes are nearly three to five orders of magnitude smaller in surface area.