Increase In Electron Density Research Articles

The role of WO3 on the optical and radiation attenuation characteristics of ZnO–Na2O–B2O3 glasses

This works aims to investigate the role of the WO3 on the optical and radiation attenuation characteristics of ZnO–Na2O–B2O3 glasses which were called as ZNBW glasses using theoretical approach. The molar refractivity (Rmol), molar polarizability (αMol.), reflection loss (RLoss), static dielectric constant (εstatic), and optical dielectric constant (εoptical) of the ZNBW glasses enhance while optical transmission (TOpt.) and metallization criterion (M) of the ZNBW glasses reduce with enhancement of WO3 and decreasing of ZnO. The Rmol, αMol.,RLoss, εstatic and εoptical are the highest for ZNBW20 whereas they are the lowest for ZNBW0. The TOpt. and M are the highest for ZNBW0 while they are the smallest for ZNBW20. In terms of radiation attenuation characteristics, the linear attenuation coefficient, mass attenuation coefficient, effective atomic number, and effective electron density increase whereas half value layer, tenth value layer, mean free path and fast neutron removal cross section (FNRC) decline with the enhancement of WO3 and reducing of ZnO. The ZNBW20 which has the highest WO3 content possesses the greatest radiation attenuation properties and smallest FNRC whereas the ZNBW0 which has not WO3 content possesses the smallest radiation attenuation properties and the highest FNRC. Consequently, radiation attenuation characteristics of ZNBW glasses enhance whereas FNRC of ZNBW glasses decline with addition of WO3 and reducing of ZnO. The replacement of WO3 by ZnO has a positive effect on improving the radiation attenuation properties of the ZNBW glasses.

Imaging tunable Luttinger liquid systems in van der Waals heterostructures.

One-dimensional (1D) interacting electrons are often described as a Luttinger liquid1-4 having properties that are intrinsically different from those of Fermi liquids in higher dimensions5,6. In materials systems, 1D electrons exhibit exotic quantum phenomena that can be tuned by both intra- and inter-1D-chain electronic interactions, but their experimental characterization can be challenging. Here we demonstrate that layer-stacking domain walls (DWs) in van der Waals heterostructures form a broadly tunable Luttinger liquid system, including both isolated and coupled arrays. We have imaged the evolution of DW Luttinger liquids under different interaction regimes tuned by electron density using scanning tunnelling microscopy. Single DWs at low carrier density are highly susceptible to Wigner crystallization consistent with a spin-incoherent Luttinger liquid, whereas at intermediate densities dimerized Wigner crystals form because of an enhanced magneto-elastic coupling. Periodic arrays of DWs exhibit an interplay between intra- and inter-chain interactions that gives rise to new quantum phases. At low electron densities, inter-chain interactions are dominant and induce a 2D electron crystal composed of phased-locked 1D Wigner crystal in a staggered configuration. Increased electron density causes intra-chain fluctuation potentials to dominate, leading to an electronic smectic liquid crystal phase in which electrons are ordered with algebraical correlation decay along the chain direction but disordered between chains. Our work shows that layer-stacking DWs in 2D heterostructures provides opportunities to explore Luttinger liquid physics.

Discharge mode and particle transport in radio frequency capacitively coupled Ar/O2 plasma discharges

Abstract Simulations are conducted on capacitively coupled Ar/O2 mixed gas discharges employing a one-dimensional fluid coupled with an electron Monte Carlo (MC) model. The research explores the impact of different O2 ratio and pressures on the discharge characteristics of Ar/O2 plasma. At a fixed Ar/O2 gas ratio, with the increasing pressure, higher ion densities, as well as a slight increase in electron density in the bulk region can be observed. The discharge remains dominated by the drift–ambipolar (DA) mode, and the flux of O(3P) at the electrode increases with the increasing pressure due to higher background gas density, while the fluxes of O(1D) and Ar* decrease due to the pronounced loss rate. With the increasing proportion of O2, a change in the dominant discharge mode from α mode to DA mode can be detected, and the O2-associated charged particle densities are significantly increased. However, Ar+ density shows a trend of increasing and then decreasing, while for neutral fluxes at the electrode, Ar* flux decreases, and O(3P) flux increases with the reduced Ar gas proportion, while trends in O(1D) flux show slight differences. The evolution of the densities of the charged particle and the neutral fluxes under different discharge parameters are discussed in detail using the ionization characteristics as well as the transport properties. Hopefully, more comprehensive understanding of Ar/O2 discharge characteristics in this work will provide a valuable reference for the industry.

Time-resolved analysis of Ar metastable and electron populations in low-pressure misty plasma processes using optical emission spectroscopy

Misty plasmas have recently emerged as a promising tool for nanocomposite thin films deposition. However, aerosol-plasma interactions remain poorly documented, especially at low working pressure. In this work, optical emission spectroscopy is used to probe the temporal evolution of three fundamental plasma parameters during pulsed liquid injection in an inductively coupled argon plasma at low-pressure. Time-resolved values of metastable argon density, electron temperature, and electron density are determined from radiation trapping analysis and particle balance equations of selected argon 1s and 2p levels. Pulsed liquid injection is found to induce a sudden drop in metastable density and electron temperature, and an increase in electron density. These results are attributed to the lower ionization thresholds of the injected molecular species compared to the one of argon. In addition, upstream liquid temperature is found to affect the transitory kinetics for non-volatile solvents more than volatile ones, in accordance with a previously reported flash boiling atomization mechanism.

Electron density in a non-thermal atmospheric discharge in contact with water and the effect of water temperature on plasma-water interactions

In this study the electron density of an atmospheric plasma generated between a pin electrode and a water surface is measured by determining the Stark broadening of H α and H β emission lines. Comparable values for the electron density are achieved using the H α and H β broadening obtained in separate measurements. During the temporally evolving system, increasing electron densities are measured of 0.5−3⋅1015 cm−3 during the plasma treatment of 5–10 min. The effect of the water temperature on plasma-water interaction is investigated by heating the water to ≈70∘ C prior to the measurements. This resulted in higher gas temperatures during the discharge up to 2500 K and 4000 K for positively and negatively pulsed discharge, respectively. Furthermore, an earlier increase of electron density and conductivity of the water is measured for the preheated experiments. The humidity of the gas is likely to be an important parameter causing the observed results.

Observations of ionospheric disturbances associated with the 2020 Beirut explosion by Defense Meteorological Satellite Program and ground-based ionosondes

Abstract. A major explosion that released a significant amount of energy into the atmosphere occurred in Beirut on 4 August 2020. The energy released may have reached the upper atmosphere and generated some traveling ionospheric disturbances (TIDs), which can affect radio wave propagation. In this study, we used data from the Defense Meteorological Satellite Program (DMSP) and ground-based ionosondes in the Mediterranean region to investigate the ionospheric response to this historic explosion event. Our DMSP data analysis revealed a noticeable increase in the ionospheric electron density near the Beirut area following the explosion, accompanied by some wavelike disturbances. Some characteristic TID signatures were also identified in the shape of ionogram traces at several locations in the Mediterranean. This event occurred during a period of relatively quiet geomagnetic conditions, making the observed TIDs likely to have originated from the Beirut explosion, not from other sources such as auroral activities. These observational findings demonstrate that TIDs from the Beirut explosion were able to propagate over longer distances, beyond the immediate areas of Lebanon and Israel–Palestine, reaching the Mediterranean and eastern Europe.

Numerical Analysis of the Breakdown Process of CF3I at Low Pressure

The breakdown of CF3I gas at low pressure is of significant importance for applications in fields such as aerospace and microelectronics. However, the DC low-pressure breakdown characteristics of CF3I remain underexplored. In this work, we utilize a one-dimensional implicit particle-in-cell/Monte Carlo collision (PIC/MCC) algorithm to investigate the complete DC breakdown process of low-pressure CF3I. Our model accounts for ion–molecule collisions, recombination reactions, and external circuit influences. The breakdown process is delineated into three stages: before breakdown, breakdown, and after breakdown. In the before-breakdown stage, both the density and energy of particles are low. In the breakdown stage, the rapid increase in electron density and energy accelerates ionization reactions, leading to successful breakdown. The circuit behavior transitions from capacitive to resistive, sharing voltage with the external resistance. In the after-breakdown stage, continued positive ion growth leads to the formation of a thin anode sheath and a negative plasma potential. Energy production, including heating power and secondary electron emission (SEE) power, balances with energy loss through collision and boundary absorption. Specifically, 62% of the total heating power comes from positive ions, 1.5% from negative ions, and approximately 85% of electron energy is lost via boundary absorption. Finally, we compare the Paschen curves of CF3I with those of SF6, providing insights that are beneficial for the application of CF3I as an SF6 alternative.

Enhanced Li-O2 battery performance using NiS/MoS2 heterostructure by building internal electric field to promote the one-electron oxygen reduction/oxidation

Electrocatalysts with appropriate electron coupling toward LiO2 intermediates can exhibit superior oxygen reduction/evolution reaction kinetics in Li-O2 batteries (LOBs). In this work, a charge redistribution strategy has been developed by constructing NiS/MoS2 heterostructure nanosheet self-assembled hollow microspheres with an internal electric field to regulate the interaction with LiO2 and then improve the electrochemical performance of LOBs. Density functional theory calculations and physicochemical characterizations reveal that the difference of work functions between NiS and MoS2 promotes the electron redistribution in heterointerface via built-in electrical field, leading to increased electron density of interfacial Ni atom, thereby enhancing its electron coupling toward LiO2 intermediates and promoting one-electron oxygen reduction/oxidation reaction kinetics. As a result, the NiS/MoS2-based LOBs exhibit evidently higher discharge capacity and much better cycling performance than the batteries using NiS and MoS2. This work provides a reliable charge redistribution strategy induced by build-in electric field to design efficient catalysts for LOBs.

Experimental and molecular insights on the regulatory effects of solvent on CaC2 reaction activity

AbstractCalcium carbide (CaC2) is a valuable carbanion resource, but the reactivity is highly restricted by its insolubility and super‐basicity. For this, the effect of solvent and mechanical forces on its reactivity is investigated extensively here via quantum chemistry calculation, molecular dynamic simulation, and experiments. The dissolution free energy of CaC2 in over 100 solvents has been evaluated. DMSO, CH3CN, and DMF can enhance the negative potential and reactivity of CaC2, especially DMSO. The electrostatic interaction of CaC2‐solvent mainly originates from the interaction between Ca2+ and O or N atom. The increased electron density around is mainly ascribed to the electron transfer from solvent. DMSO can change the ionic orientation of CaC2 interface. The solvent may be deprotonated by , compromising the solvent stability. The interface interaction of CaC2 with DMF and DMSO is verified through FT‐IR, and the lattice structure of CaC2 is lost virtually after 0.5 h mechanical milling.

Regulating Reactive Oxygen Intermediates of Fe–N–C SAzyme via Second‐Shell Coordination for Selective Aerobic Oxidation Reactions

Reactive oxygen species (ROS) regulation for single‐atom nanozymes (SAzymes), e.g., Fe–N–C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe–N–C containing the same FeN4 but with tunable second‐shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe–N–C sample, the second‐shell sulfur functionalized Fe–N–C delivered a·2.4‐fold increase of oxidase‐like activity via the bound Fe=O intermediate. Conversely, free ROS (•O2‐) release was significantly reduced after functionalization, down to only 17% of that observed for Fe–N–C. The detailed characterizations and theoretical calculations revealed that the second‐shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe–N–Cs with different second‐shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

Regulating Reactive Oxygen Intermediates of Fe-N-C SAzyme via Second-Shell Coordination for Selective Aerobic Oxidation Reactions.

Reactive oxygen species (ROS) regulation for single-atom nanozymes (SAzymes), e.g., Fe-N-C, is a key scientific issue that determines the activity, selectivity, and stability of aerobic reaction. However, the poor understanding of ROS formation mechanism on SAzymes greatly hampers their wider deployment. Herein, inspired by cytochromes P450 affording bound ROS intermediates in O2 activation, we report Fe-N-C containing the same FeN4 but with tunable second-shell coordination can effectively regulate ROS production pathways. Remarkably, compared to the control Fe-N-C sample, the second-shell sulfur functionalized Fe-N-C delivered a 2.4-fold increase of oxidase-like activity via the bound Fe=O intermediate. Conversely, free ROS (⋅O2 -) release was significantly reduced after functionalization, down to only 17 % of that observed for Fe-N-C. The detailed characterizations and theoretical calculations revealed that the second-shell sulfur functionalization significantly altered the electronic structure of FeN4 sites, leading to an increase of electron density at Fermi level. It enhanced the electron transfer from active sites to the key intermediate *OOH, thereby ultimately determining the type of ROS in aerobic oxidation process. The proposed Fe-N-Cs with different second-shell anion were further applied to three aerobic oxidation reactions with enhanced activity, selectivity, and stability.

A novel electrochemical sensor based on Pb0.95Ti0.05O-decorated nitrogen self-doped biochar for highly sensitive and selective detection of carvacrol

Carvacrol has widely used in the field of medicine and sterilization. Thus, developing reliable, efficient, and rapid method for the carvacrol detection is meaningful. In this study, we fabricated a carvacrol sensor based on Pb0.95Ti0.05O decorated with nitrogen self-doped biochar (Pb0.95Ti0.05O/NC), which was synthesized by hydrothermal and carbonization of soybean root nodules, respectively. The prepared sensor exhibited better electrochemical performances than that of PbO, Pb0.95Ti0.05O, NC. The fabricated Pb0.95Ti0.05O/NC sensor exhibited a wide detection range from 0.1 to 190 µM and a low detection limit of 0.054 µM. The excellent electrochemical performances were attributed to the increased electron density and electron mobility after the introduction of Ti doping and nitrogen doped carbon. Mechanistic studies revealed that the electrochemical oxidation of carvacrol involves one electron and was limited by adsorption process. The sensor demonstrated good stability, anti-interference, reproducibility, and good repeatability. Moreover, the sensor displayed excellent recovery rates ranging from 92.7% to 102.9% when applied to the detection of carvacrol in real samples, making it a promising candidate for practical applications in the sensitive detection of carvacrol.

The promoting role of framework Ti(IV) in enhancing the hydrodeoxygenation performance of palmitic acid over a mesoporous TS-1 supported Ni catalyst

Developing a highly efficient Ni-based hydrodeoxygenation catalyst is crucial for the production of renewable biodiesel. Herein, a mesoporous TS-1 zeolite supported Ni catalyst (Ni/TS-1-M) exhibited exceptional hydrodeoxygenation (HDO) activity and achieved 100 % yield of deoxygenated hydrocarbons (97.3 % pentadecane vs 2.7 % hexadecane), outperforming other catalysts such as Ni on mesoporous ZSM-5 (Ni/ZSM-5-M), mesoporous Silicalite-1 (Ni/Silicalite-1-M) and TiO2 (Ni/TiO2). The Ti(IV) atoms in the form of TiO4 and TiO6 can transfer its electron to nearby metal Ni, leading to the increase in electron density of metal Ni, which enhanced the hydrogenation activity and facilitated the C–C bond cleavage of the hexadecanal to produce pentadecane. Furthermore, the framework Ti(IV) species accelerated the esterification process to generate palmityl palmitate, which was easily hydrogenolyzed to the main intermediate of hexadecanol under the synergistic effect of metal Ni and Ti(IV) on Ni/TS-1-M catalyst. The formed hexadecanol mainly underwent successive dehydrogenation/decarbonylation process to transform into pentadecane.

Customized modulation on plasma uniformity by non-uniform magnetic field in capacitively coupled plasma

A two-dimensional fluid model based on COMSOL Multiphysics is developed to investigate the modulation of static magnetic field on plasma homogeneity in a capacitively coupled plasma (CCP) chamber. To generate a static magnetic field, direct current is applied to a circular coil located at the top of the chamber. By adjusting the magnetic field’s configuration, which is done by altering the coil current and position, both the plasma uniformity and density can be significantly modulated. In the absence of the magnetic field, the plasma density exhibits an inhomogeneous distribution characterized by higher values at the plasma edge and lower values at the center. The introduction of a magnetic field generated by coils results in a significant increase in electron density near the coils. Furthermore, an increase in the sets of coils improves the uniformity of the plasma. By flexibly adjusting the positions of the coils and the applied current, a substantial enhancement in overall uniformity can be achieved. These findings demonstrate the feasibility of using this method for achieving uniform plasma densities in industrial applications.

Unveiling Sub-60 mV/decade Subthreshold Swing in The Oxide Local Thinning (OLT) Gated MIS Tunnel Diodes by TCAD Simulations

In this study, we unveil the sub-60 mV/decade subthreshold swing (SS) characteristics observed in the oxide local thinning (OLT) gated p-type metal-insulator-semiconductor (MIS) tunnel diodes (TD) utilizing TCAD simulations. Through our simulations, we successfully replicate the sub-60 mV/decade SS behavior and attribute this remarkable characteristic to the rapid increase in electron density near the gate edge. This phenomenon arises from electron injection through the gate OLT region under a negative gate voltage, leading to a significant elevation in electron density near the gate edge. Armed with this insight, we design scaled devices to assess the feasibility of achieving sub-60 mV/decade SS behavior. By modulating the substrate thickness, we effectively simulate devices with SS lower than 60 mV/decade across a current range spanning 8 orders of magnitude.

Enhanced photovoltaic performance of dye sensitized solar cells using cesium bromide modified TiO2 electron transport layer

TiO2 is one of the most widely explored materials as an electron transport layer (ETL) in dye sensitized solar cells (DSSCs) due to its excellent physical and chemical properties. However, recombination at the device's interface slackens the charge carrier movement, adversely affecting their device performance. Rapid extraction of photogenerated charge carriers plays a vital role in developing high efficiency DSSCs. The conduction band alignment of TiO2 ETL and N719 dye light absorber plays a crucial role in charge carrier dynamics of DSSCs. Herein, the band structure of TiO2 ETL is finely tuned by the incorporation of cesium bromide (CsBr). At the optimal concentration (0.4 Wt. %), DSSCs achieved the best power conversion efficiency (PCE) of 9.28 % compared to 7.61 % for pristine TiO2. The modified TiO2–CsBr ETL induced a negative shift in flat band potential (Vfb) from −0.46 to −0.50 V, which improved the open circuit voltage (VOC), its work function (ɸ) from −4.71 to −3.75 eV and increased conduction band minimum (CBM) from −3.58 to −2.42 eV. CsBr incorporation increased electron density in TiO2 matrix, indicating the suppression of trap state and significantly improved the overall photovoltaic performance of DSSCs.

Cell-Free Hemoglobin Induces Vascular and Mitochondrial Dysfunction in the Pulmonary Endothelium in an Oxidation-State Dependent Manner

Background: Sepsis results in significant organ damage due in part to a breakdown in endothelial vascular function. Elevated levels of cell-free hemoglobin (CFH) drive endothelial dysfunction in the lungs. CFH generates reactive oxygen species (ROS) via the iron present in the heme moiety, which can be oxidized from ferrous (CFH2+) to ferric (CFH3+). Recent studies suggest mitochondrial dysfunction may be a key pathway leading to microvascular dysfunction. We hypothesize that CFH induces mitochondrial dysfunction and microvascular endothelial barrier disruption in the lung in an oxidative-state dependent manner. Methods: CFH was converted from CFH2+ to CFH3+ by UV irradiation (validated by spectrophotometry). Primary human lung microvascular endothelial cells (HLMVECs) were treated with 1.0 mg/mL CFH2+, CFH3+, or vehicle control. Barrier dysfunction was measured via electric cell-substrate impedance sensing (ECIS) and express permeability test (XPerT) at 24h. We quantified mitochondrial superoxide (MitoSOX Red; 5 uM) by flow cytometry (1, 6, 24h) and total cellular ROS production (CellROX Deep Red; 5 uM) by fluorescence microscopy (6 and 24 h). Mitochondrial morphology (electron density, roundness, area, circularity, and aspect ratio) was assessed by transmission electron micrographs at 6h and quantified by a blinded reviewer (ImageJ). Activation of the mitochondrial permeability transition pore (mPTP) was assessed by flow cytometry using calcein-AM with cobalt chloride. DNA was purified from patient plasma and the copy number of mitochondrial genes ND4L and CYB was quantified by digital droplet PCR. Results: In HLMVECs, CFH generated excess ROS (CellROX and MitoSOX) at 6h compared to vehicle (522 vs 265 MFI, p < 0.01). Morphology analysis demonstrated increased electron density and aspect ratio and decreased circularity and roundness. mPTP activity was increased by CFH3+ (1295 vs 2197 MFI, p < 0.01) compared to vehicle or CFH2+. Barrier dysfunction caused by CFH3+ measured by ECIS peaked at 6h (-1270 vs 262 max TER drop, p < 0.0001), while XPerT confirmed dysfunction at 24h (9.41e+06 vs 6.53e+05 total fluorescent area, p < 0.01). Quantification of mtDNA copy number in patient plasma revealed that circulating mt-ND4L copies correlate with CFH (r = 0.44, p < 0.01). Conclusions: The results demonstrate significant perturbations to mitochondrial function and network dynamics caused by oxidized CFH (3+). The novel findings point towards the ferric (3+) form of hemoglobin as the primary driver of endothelial dysfunction, and the underlying mechanism is directly related to disruption of the mitochondrial network. The association of mitochondrial and vascular biomarkers demonstrates an urgent need to better understand how mitochondrial dysfunction can be prevented to limit vascular damage. This work was funded by the National Institutes of Health NHLBI 5R35HL150783 and 1F31HL167471. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Photoluminescence Emission Efficiency Analysis Methodology by Integrating Raman Spectroscopy of the A1(LO) and E2(high) Phonons in a GaInN/GaN Heterostructure

Microscopic lattice vibration images of the E2(high) mode (E2H) and another mode of A1(LO) (A1L) or the higher energy branch of LO‐phonon−plasmon coupling mode (LOPC+) in a Ga0.95In0.05N film on a GaN template are obtained by Raman scattering spectroscopy using a 325 nm laser. The increase in temperature by increasing the laser power is obtained from the decrease in the energy of E2H and the theoretical formula comprising two terms based on the mode energy variation of the bulk material and the thermal strain effect. Using the obtained temperature and the energy shift of the LOPC+, the mapping images of the temperature and electron density in the x–y plane are simultaneously obtained. This image provides the spatial variation of photoluminescence (PL) emission efficiency, given as PL intensity per electron. This method enables the quantitative discussion on photo‐emission efficiency even in the regions of low or high carrier density affected by carrier transport. In the investigated area, a region with a lower PL efficiency is found despite a higher electron density and lower temperature increase than the surrounding region. This imaging analysis is feasible in integrating the carrier and thermal energy transports and recombination processes in carrier dynamics study.

Effect of protonation and deprotonation on oxygen-containing groups functionalized graphene for boron adsorption removal

This study investigated the adsorption mechanisms of boron on protonated and deprotonated graphene with oxygen-containing functional groups. Six representative adsorption conformations of boron predominant species (B(OH)3 (B3) and B(OH)4− (B4)) on graphene were proposed. Protonation and deprotonation of graphene had significant effects on boron adsorption. Deprotonation of hydroxyl-modified (G20-OH) and carboxyl-modified graphene (G20-COOH) with 20 carbon rings decreased B3 and B4 adsorption. Protonation of G20-OH enhanced B3 adsorption. The adsorption interface, mainly around hydrogen atoms associated with protonated groups, exhibited a sharp gradient, due to the increased electron density from OH bond formation. B3 showed stronger electron sharing, emphasizing robust interactions. Hydrogen bonding dominated G20-OH2-B3, while G20-O-B4 exhibited more substantial hydrogen bond interactions. In summary, hydrogen bond strength was crucial in B3 adsorption, while electrostatic repulsion hindered B4 adsorption on deprotonated graphene. These findings highlight the importance of graphene protonated and deprotonated states in effectively removing various pKa contaminants.

Effect of desorbed gas on microwave breakdown on vacuum side of dielectric window

The gas desorbed from the dielectric surface has a great influence on the characteristics of microwave breakdown on the vacuum side of the dielectric window. In this paper, the dielectric surface breakdown is described by using the electromagnetic particle-in-cell-Monte Carlo collision (PIC-MCC) model. The process of desorption of gas and its influence on the breakdown characteristics are studied. The simulation results show that, due to the accumulation of desorbed gas, the pressure near the dielectric surface increases in time, and the breakdown mechanism transitions from secondary electron multipactor to collision ionization. More and more electrons generated by collision ionization drift to the dielectric surface, so that the amplitude of self-organized normal electric field increases in time and sometimes points to the dielectric surface. Nevertheless, the number of secondary electrons emitted in each microwave cycle is approximately equal to the number of primary electrons. In the early and middle stages of breakdown, the attenuation of the microwave electric field near the dielectric surface is very small. However, the collision ionization causes a sharp increase in the number density of electrons, and the microwave electric field decays rapidly in the later stage of breakdown. Compared with the electromagnetic PIC-MCC simulation results, the mean energy and number of electrons obtained by the electrostatic PIC-MCC model are overestimated in the later stage of breakdown because it does not take into account the attenuation of microwave electric field. The pressure of the desorbed gas predicted by the electromagnetic PIC-MCC model is close to the measured value, when the number of gas atoms desorbed by an incident electron is taken as 0.4.