Emission Theory Research Articles

Richardson constant and characteristics of pentacene organic planar Schottky diode

Planar organic Schottky diodes were fabricated using undoped pentacene as an active layer with both palladium and aluminum as contacts. Pentacene organic thin films were deposited on n-type silicon substrates with 100 (n-Si<100>) and 111 (n-Si<111>) orientations. X-ray diffraction (XRD) measurements revealed that the pentacene films’ XRD patterns exhibit several peaks with various orientations. The energy-dispersive X-ray technique was used for chemical analysis of the pentacene, and scanning electron microscopy was used to characterize the surface morphology. A structural and morphological study of the deposited pentacene indicates a polycrystalline triclinic (anorthic) nature. A current–voltage curve was experimentally constructed at temperatures (T) ranging from 300 K to 360 K with a step of 15 K. The diode parameters, such as saturation current, ideality factor (n), and barrier height (ΦB), were systematically analyzed using thermionic emission theory. The fabricated devices exhibit decreasing n and increasing ΦB values with increasing T. Richardson's constant for pentacene was calculated, which indicated that the conventionally calculated value from the temperature-dependent characteristic curve is much lower than the calculated theoretical value. It was also observed that the device deposited over the n-Si<111> substrate exhibited larger forward and lower reverse currents than the n-Si<100> substrate device.

General form of the tunneling barrier for nanometrically sharp electron emitters

Field electron emission from nanometer-scale objects deviates from the predictions of the classical emission theory as both the electrostatic potential curves within the tunneling region and the image potential deviates from the planar one. This impels the inclusion of additional correction terms in the potential barrier. At the apex of a tip-like rotationally symmetric surface, these terms are proportional to the (single) local emitter curvature. The present paper generalizes this relation, showing that for any emitter geometry, the coefficient of the correction terms is given by the mean curvature, i.e., the average of the two principal curvatures.

Temporal Coupled-Mode Theory for Thermal Emission from Multiple Arbitrarily Coupled Resonators

Controlling the spectral response of thermal emitters has become increasingly relevant for a range of energy and sensing applications. Conventional approaches to achieving arbitrary spectrum selectivity in photonic systems have entailed combining multiple resonantly emissive elements together to achieve a range of spectral profiles through numerical optimization, with a universal theoretical framework lacking. Here, we develop a temporal coupled-mode theory for thermal emission from multiple, arbtirarily coupled resonators. We validate our theory against numerical simulations of complex two- and three-dimensional nanophotonic thermal emitters, highlighting the anomalous thermal emission spectra that can emerge when multiple resonators with arbitrary properties couple to each other with varying strengths.

Mass-energy equation and the theory of photon emission derived from Bohr's theory

The Einstein's relativistic mass-energy equation ε = mc2 is also obtained from Bohr's theory. The Schrödinger equation (SE) is modified using this equation. In the hydrogenlike atom, the modified SE is solved for consistency with the eigenvalues of electron's energy derived from the Dirac equation. Based on the consistency of their eigenvalues, the theory of photon emission is expressed. From this theory, an emission process different from bremsstrahlung is expressed. X-ray and gamma-ray bursts associated with thunderclouds and lightning are discussed by this process.

Staggered heterojunction Pentacene/ZnO based organic–inorganic flexible photodetector

This article describes the performance analysis of the fabricated visible photodetector based on the Pd/pentacene/ZnO/ITO/PET structure. Hydrothermal and thermal vacuum deposition techniques deposited the ZnO and pentacene films, and FESEM images examined the topology of the deposited films. The I-V characteristics of a device were assessed in both dark and light environments throughout a voltage range of −5 to 5 V. With the help of Cheung's method and the standard thermionic emission theory, electrical performance parameters in the dark mode were extracted. The barrier height and ideality factor for the thermionic emission test were 0.784 eV and 2.19, respectively. In contrast, the barrier height and ideality factor for the Cheung technique was found to be 0.77 eV and 1.4, respectively. This research demonstrates Cheung's approach, which accounts for series resistance 692.46 Ω. The proposed photodetector exhibits a high gain of 579 and responsivity of 279 A/W.

Mechanism analysis of field electron emission of titanium

Field electron emission (FEE) is generally considered to be closely correlated with radio frequency (RF) breakdown in accelerating structures and high-power microwave (HPM) devices. In this study, the field emission characteristics of titanium are investigated by using a field emission test system. With the increase of the number of field emission tests and stability tests, the repeatability of the field emission characteristic curve of titanium tends to be better, and the amplitude of the current oscillation in the stability tests gradually decreases, indicating that the field emission performance of titanium gradually becomes stable. Subsequently, the field emission characteristic curve of titanium is analyzed by adopting the field emission theory of metal microprotrusions. Combined with the analysis of the electric field enhancement effects caused by the surface morphology, the dominant effect of the metal microprotrusions on the FEE of titanium is excluded from the two aspects of the electric field enhancement factor and local maximum emission current density. At last, the field emission theory of dielectric micropoints is introduced to analyze the field emission characteristics of titanium. The electric field enhancement factor of 102 ∼ 103 are explained theoretically. Simultaneously, the reasonable effective emission area and local emission current density are given, which can better explain the field emission phenomena of titanium, such as the sharp decrease in emission current and repeatability of the field emission curve. Hence, it is revealed that the key factor that dominates the FEE of titanium is the dielectric impurities on the surface, rather than the metal microprotrusions.

The Double Gaussian Distribution of Inhomogeneous Barrier Heights in Au/NAMA/n-Si Schottky Diodes

In this work, we report the results of temperature dependent barrier properties of Au/NAMA/n-Si Schottky diode in the low temperature range of 80–330 K. The analysis results of according to thermionic emission theory showed that the barrier height decreases, and the ideality factor increases towards low temperatures, depend on the barrier height inhomogeneities. The obtained results show the presence of a double Gaussian distributions with standard deviations (σ 0) of 0.073 V and 0.18 V and mean barrier height () values of 0.595 and 1.427 eV in the change of 80–140 K and 160–330 K, respectively. Moreover, evaluation of the modified Richardson curve, the values of Richardson constant (A*) of 321.805 and 110.935 A K−2 cm−2, and mean barrier height of 0.606 and 1.422 eV were found for the low- and high-temperature regions, respectively. The A* value of 110.935 A K−2 cm−2 is close to the theoretical value of 112 A K−2 cm−2 for n-Si. These results proved that there is barrier inhomogeneity.

Coupled macro–meso damage constitutive model for fractured rocks based on logistic growth theory

Rock mass is a complex system contains large amounts of macroscopic and mesoscopic damage. The evolution of this internal macroscopic and mesoscopic damage under stress conditions has a significant impact on the stability of rock masses. However, most of the current damage constitutive models do not consider the coupled effects of damage at different scales, including mesoscopic and macroscopic damage in fractured rock masses, also unable to reflect the nonlinear characteristics shown in the process of rock damage. In order to investigate the effect of the nonlinear process of the macro- and mesoscopic damage evolution on the mechanical behavior of fractured rock masses, this study first divided the deformation and damage processes of fractured sandstone under uniaxial compression into three phases based on acoustic emission test data: the compaction phase, elastic phase, and damage phase. Subsequently, the mesoscopic damage variables for fractured sandstone in the compaction phase were derived from damage mechanics and nonlinear dynamics; the mesoscopic damage variables for fractured sandstone in the damage phase were derived from acoustic emission theory, micro-unit strength theory, and nonlinear dynamics; and the macroscale damage variables for fractured sandstone were derived from damage mechanics and fracture mechanics. The Lemaitre strain equivalence hypothesis was used to couple the mesoscopic and macroscopic damage variables, thereby constructing a coupled macro–meso formulation for the damage variables and a constitutive model for fractured sandstone under uniaxial compression. The results of comparisons with several sets of experimental data indicated that the damage constitutive model proposed in this study could accurately reflect the stress–strain relationship and damage evolution of fractured sandstone during uniaxial compression.

The photovoltaic and photodiode properties of Au/Carmine/n-Si/Ag diode

In this study, carmine films were deposited on glass slides and n-Si substrates using a spin coater. The scanning electron microscope (SEM) and absorbance analyses of the deposited carmine film on glass were performed. Twenty-four (24) Au/Carmine/n-Si/Ag dots were identically fabricated, and their current–voltage (I–V) characteristics were taken at room temperature, both in the dark and under daylight. It was seen that all diodes exhibited a rectifying behavior. The ideality factor (n, IF), barrier height (Φb, BH), rectification ratio (RR), and series resistance (Rs) of each dot were determined using the thermionic emission (TE) theory and modified Norde’s functions, respectively. Although the dots were prepared on the same substrate, there was a difference from one dot to the next. The n and Φb values of the 24 dots were found in the range of 1.52–2.72 and 0.76–0.85 eV in the dark, respectively. Furthermore, a high current rectification ratio of 104 was achieved for the 11 dots in the dark. The photovoltaic and photodiode properties of one (labeled as D18) of the Au/Carmine/n-Si/Ag dots under the different light intensities varied from 30 to 100 mW/cm2 at room temperature, and its capacitance–voltage (C–V) characteristics were investigated only in the dark. The D18 dot exhibited typical photodiode behavior with a fill factor (FF) value of 36.2 % and an experimental efficiency (ŋ) of 2.45 % under 30 mW/cm2 light intensity, respectively. It also has a high ON/OFF current (Ion/Ioff) ratio of 7.45x103. Because the maximum current value of the Au/Carmine/n-Si/Ag photodiode has not changed, it exhibits good stability for 12 on/off cycles.According to these experimental findings, the high-performing Au/Carmine/n-Si/Ag diode displays good photodiode behavior, and photodiodes based on the carmine thin film can be used to develop future optoelectronic devices.

Current transport characterization and photovoltaic performance of Si nanopencil-based Schottky junction assisted with VOx as a hole-injection layer

Pencil-shaped silicon nanowires (SiNPs) were utilized in Schottky junction solar cells covered by sub-stoichiometric vanadium dioxide (VO2-x) to work as a hole injection layer. The asymmetry of nanopencils is responsible for their many useful properties, such as their ability to absorb and trap light over a wide spectrum. Dark current-voltage (I–V) curves for an Ag/VO2-x/SiNPs/Ti/Ag Schottky junction device were measured and analyzed across a temperature range of 298–358 K. The junction parameters were calculated in terms of thermionic emission theory at different temperatures from the (I–V) curves, including the ideality factor (n) and the barrier height (φb), and were found to be 1.73 and 0.78 eV, respectively, at room temperature. In the forward bias regime, we found that thermionic emissions dominate at low voltages (V ≤ 0.12 V), space-charge-limited current controlled by a single trap state dominates at middle voltages (0.12 < V < 0.3 V), and space-charge-limited current regulated by a distribution of trap levels dominates at high voltages (V ≥ 0.3 V). The (C–V) measurements were used to calculate the built-in potential, which was discovered to be 0.62 eV. Unless encapsulation is provided, PEDOT:PSS/SiNPs hybrid solar cells rapidly degrade under ambient conditions, whereas VO2-x/SiNPs solar cells are far more stable.

A novel simplified ballistic impact theory for woven composites

Composite behaviour under ballistic impact is a challenging engineering problem due to its nonlinear nature, besides the ballistic impact itself is a dynamic and complex phenomenon. This study presents a novel analytical formulation for the speed reduction of impacts of bullet-type projectiles based on in-plane tensile failure energy absorption, including a new approach representing the energy absorption due to friction. Since for low-velocity impacts, energy absorption mechanisms are drastically different from high-velocity impacts, limitation algorithms are developed to accommodate for low-velocity impact cases. The developed formulations are applied to real and virtual ballistic impact test cases to predict the residual velocities. A satisfying correlation between results is observed.

Exploring the absolute yield curve of secondary electrons using machine learning methods.

Knowledge of absolute secondary electron yield (δ) is important for various applications of electron emission materials. Besides, it is also crucial to know the dependence of δ on primary electron energy Ep and material properties like atomic number Z. The available experimental database of δ reveals a large discrepancy among the measurement data, while the oversimplified semi-empirical theories of secondary electron emission can only present the general shape of the yield curve but not the absolute yield value. This limits not only the validation of a Monte Carlo model for theoretical simulations but also presents large uncertainties in the applications of different materials for various purposes. In applications, it is highly desirable to have the knowledge of the absolute yield of a material. Therefore, it is highly desirable to establish the relationship of the absolute yield with material and electron energy based on the available experimental data. Recently, machine learning (ML) methods have been increasingly used for the prediction of material properties mainly based on the atomistic calculations with the first-principles theory. We propose here the application of ML models to a material property study, starting with experimental observations and unfolding the relationship of δ with basic material properties and primary electron energy. Our ML models are able to predict δ(Ep)-curve covering a wide energy range of 10 eV-30 keV for unknown elements within the uncertainty range of the experimental data and can suggest more reliable data among the scattered experimental data.

Performance assessment of a perovskite solar cell-driven thermionic refrigerator hybrid system

To develop a high-performance solar refrigeration technology, a novel refrigeration system composed of a perovskite solar cell (PSC) and a thermionic refrigerator (TIR) is constructed. Based on theories of photovoltaic effect, thermionic emission and non-equilibrium thermodynamics, the coefficient of performance (COP) and refrigerating capacity of the integrated system are mathematically expressed, in which the various irreversible losses are taken into consideration. The integration characteristics and coupling relationships between the PSC and TIR are investigated, and the working voltage regions for the combined operation of the subsystems are determined. Furthermore, the impacts of the area ratio, the work function, the environment temperature, the cold reservoir temperature and the heat transfer coefficient on systemic performance are evaluated in detail. Numerical calculation examples illustrate that the maximum COP and maximum refrigerating capacity of the integrated system are 0.81 and 81.2 W, respectively. Analysis results show that there exist optimal area ratio and work function to optimize the system performance. The present study may offer some fresh perspectives on the evolution of the solar refrigeration system.

Investigation of the Electrical Properties of PAN-GO/p-Si Schottky Diode

In this article, the electrical properties of PAN-GO/p-Si Schottky diode were investigated in the dark at room temperature. Field-emission scanning electron microscopy (FE-SEM) was utilized to study the structure of the PAN:GO interfacial layer. Diode parameters were calculated according to thermionic emission theory. By using the I-V characteristic of the prepared PAN-GO diode, the ideality factor (n), barrier height (ФB) and series resistance (Rs) values were evaluated with the I-V method and Norde functions. The barrier height values calculated with the I-V and Norde function were found to be 0.767 eV and 0.761 eV, respectively. The ideality factor was found to be 2.078 from the I-V method. The series resistance value of the diode was calculated as 42 kΩ using Norde functions. Energy-dependence profile of interface state density was determined from the current-voltage characteristics by considering the voltage-dependence of barrier height and ideality factor The interface state density (Nss) values of the PAN-GO/p-Si Schottky diode are 9.5x1011 eV-1cm-2 for 0.35-Ev eV and 1.03x1011 eV-1cm-2 for 0.74-Ev eV. Experimental results approved that the PAN-GO interfacial layer improved the performance of metal-semiconductor Schottky diode in respect of low ideality factor, interface state density, and high barrier height and rectification rate.

Dynamic Simulation and Parameter Analysis of Harpoon Capturing Space Debris

This paper aims to study the penetration effect of harpoons on space debris to ensure the sustainable development of the space environment and solve the increasingly serious space debris problem. Firstly, a harpoon system was designed to capture space debris. Secondly, based on the Johnson-Cook dynamic constitutive model and fracture failure criterion, the finite element models of aluminum alloy plates were established. Then, the ballistic limit theory for the aluminum alloy target predicted the minimum launch velocity of the harpoon. Finally, the validation experiment was set up to verify the correctness of the model. The results show that the error between the simulation results of the speed for the harpoon embedded in the target and the theoretical results of the ballistic limit is 9.1%, which provides guidance for active space debris removal technology.

Dark conduction mechanisms of PTQBDT based heterojunction diode

Al:LiF/PTQBT:PCBM/PEDOT:PSS/ITO/glass organic-based diode is fabricated with different weight ratios in PTQBT:PCBM active layer. The diodes D1, D2 and D3 are prepared using the precursor solution for spin coating process as 1:2, 1:3 and 1:4, respectively. Under dark, main diode parameters are extracted by conventional thermionic emission theory using the results of measurements. Parasitic resistance contribution, non-ideal barrier height formation and high values of ideality factor indicate possible effects of space charge limited current flow mechanism on forward biased characteristics. At saturated voltage region, series resistances are calculated and the results are evaluated according to Cheung’s method. The possible voltage sharing between interface layer and depletion region are also investigated by analysis of density of interface states. In addition, field effect is found in a major role on the reverse current flow and the mechanism is evaluated according to Schottky-Richardson model.

Structural characterizations and photoelectric performance of non-crystalline boron subphthalocyanine chloride films/FTO for photodiode applications

A thin film of Boron subphthalocyanine chloride (B-subPcCl) has been deposited with different thicknesses, up to 300 nm, on the conductive fluorine-doped tin oxide (FTO) substrates using an evaporating coating unit. The structure of the fabricated film has been studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD confirmed that B-subPcCl films are an amorphous material, and AFM showed that the fabricated thin films' grain sizes increased from 123.5 to 206.5 nm as the film thickness from 76 to 300 nm. The optical properties such as reflectance, transmission, absorption index, and refractive index have been characterized by the analysis of the spectrophotometric measurements. As a result of the thin film thickness increase up to 300 nm, the energy bandgap was decreased by about 10%. The refractive index shows the lowest value at 1680 nm due to the polarization decrease. The I–V characteristics of the FTO/B-subPcCl/Au photodiode were investigated in the dark and under various light illumination intensities. The rectification ratio of our diode was 199 and 59 in dark and light, respectively. The thermionic emission theory was used to calculate the main diode parameters. The current architecture, FTO/B-subPcCl/Au, demonstrated a good light response, with estimated values of responsivity of about 4.2 × 10−6 A/W at -1 V and illumination intensity of 80 mW/cm2.

Electrical characteristics of (AgNPs-PVA)-based Schottky diode and its application as a low-voltage varistor devices

In this report, we studied the influence of silver nanoparticles (AgNPs) on the electrical conductivity of Polyvinyl Alcohol (PVA) as a semiconductor nanocomposites active layer. Here, the Schottky junction is constructed by mechanically pressing a copper (Cu) electrode onto a AgNPs-PVA nanocomposite, which shows rectification behavior at room temperature. The synthesis of silver nanoparticles (AgNPs) was achieved by the physical reduction of silver nitrate using an ultraviolet lamp. The nanocomposite films were created using a casting technique. An ultraviolet spectrophotometer (UV–vis), which displayed maximum absorbance at 430 nm, was used to confirm the synthesis of AgNPs and carry out the optical band gap. The charge carrier transport properties of AgNPs-PVA film were investigated by using impedance spectroscopy and I–V measurements. Then, AC impedance analysis was used to determine grain and grain boundary resistances; current-voltage analysis enabled the barrier height (Φ) to be determined. Moreover, the metal/semiconductor (Cu/AgNPs-PVA) Schottky barrier was confirmed as an equivalent circuit model via the Nyquist plot. Based on thermoionic emission theory, the characteristic I–V induced rectifying Schottky behavior can be understood. Moreover, the AgNPs-PVA nanocomposite exhibited hysteresis behavior under multiple repetitive measurements. For low voltage varistor devices, the nonlinear behavior may be completely utilized.

Improved Tunneling Property of p+Si Nanomembrane/n+GaAs Heterostructures through Ultraviolet/Ozone Interface Treatment

Here, heterostructures composed of p+Si nanomembranes (NM)/n+GaAs were fabricated by ultraviolet/ozone (UV/O3, UVO) treatment, and their tunneling properties were investigated. The hydrogen (H)-terminated Si NM was bonded to the oxygen (O)-terminated GaAs substrate, leading to Si/GaAs tunnel junctions (TJs). The atomic-scale features of the H-O-terminated Si/GaAs TJ were analyzed and compared to those of Si/GaAs heterojunctions with no UVO treatment. The electrical characteristics demonstrated the emergence of negative differential resistance, with an average peak-to-valley current ratio of 3.49, which was examined based on the band-to-band tunneling and thermionic emission theories.

Theory and experiments of pressure-tunable broadband light emission from self-trapped excitons in metal halide crystals

Hydrostatic pressure has been commonly applied to tune broadband light emissions from self-trapped excitons (STE) in perovskites for producing white light and study of basic electron-phonon interactions. However, a general theory is still lacking to understand pressure-driven evolution of STE emissions. In this work we first identify a theoretical model that predicts the effect of hydrostatic pressure on STE emission spectrum, we then report the observation of extremely broadband photoluminescence emission and its wide pressure spectral tuning in 2D indirect bandgap CsPb2Br5 crystals. An excellent agreement is found between the theory and experiment on the peculiar experimental observation of STE emission with a nearly constant spectral bandwidth but linearly increasing energy with pressure below 2 GPa. Further analysis by the theory and experiment under higher pressure reveals that two types of STE are involved and respond differently to external pressure. We subsequently survey published STE emissions and discovered that most of them show a spectral blue-shift under pressure, as predicted by the theory. The identification of an appropriate theoretical model and its application to STE emission through the coordinate configuration diagram paves the way for engineering the STE emission and basic understanding of electron-phonon interaction.