Mass Spectrometric Fragmentation of 1-(Benzyloxycarbonyl)amino-2-alkyl/cycloalkyl Thioacetates:a Thioester Pyrolysis-type Rearrangement under Electron Impact Ionization

The mass spectrometric fragmentation of 1-（benzyloxycarbonyl）amino-2-alkyl/cycloalkyl thioacetates has been studied with the aid of mass-analysed ion kinetic energy spectrometry under electron impact ionization. All compounds show a tendency to eliminate a ketene, thioacetic acid, and benzyl carbamate molecule, or an acetyl and benzyloxy radicals. A thioester pyrolysis-type rearrangement under electron impact ionizations was observed.

Laser Induced Photoelectron Impact Ionization In Multiphoton Ionization Process

Multiply charged ions of Ar and NO were observed in MPI experiment Of NO/Ar with TOF-MS. A delayable pulsed acceleration field wn applied tO investigate the effect of the photoelectrons on the formation of the multiply charged ions. The multiply charged ions were suggested to be produced by photoelectron impact ionization, in the region bentween the extractor grid and the repeller plate, step by step, from neutral species and lower charged ions. The 50-60ns of FWHM of the ion peaks implies that the pulse width of the photoelectrons should be shorter considering the broadening effect during the ionization process.

Dopingless impact ionization MOS(DL-IMOS)—a remedy for complex process flow

We propose a unique approach for realizing dopingless impact ionization MOS （DL-IMOS） based on the charge plasma concept as a remedy for complex process flow. It uses work-function engineering of electrodes to form charge plasma as surrogate doping. This charge plasma induces a uniform p-region in the source side and an n-region in the drain side on intrinsic silicon film with a thickness less than the intrinsic Debye length. DL-IMOS offers a simple fabrication process flow as it avoids the need of ion implantation, photo masking and complicated thermal budget via annealing devices. The lower thermal budget is required for DL-IMOS fabrication enables its fabrication on single crystal silicon-on-glass substrate realized by wafer scale epitaxial transfer. It is highly immune to process variations, doping control issues and random dopant fluctuations, while retaining the inherent advantages of conventional IMOS. To epitomize the fabrication process flow for the proposed device a virtual fabrication flow is also proposed here. Extensive device simulation of the major device performance metrics such as subthreshold slope, threshold voltage, drain induced current enhancement, and breakdown voltage have been done for a wide range of electrodes work-function. To evaluate the potential applications of the proposed device at circuit level, its mixed mode simulations are also carried out.

Intermolecular Phenolic Hydroxy Methylation Occurring between Chiral N,N'-Bis(2-hydroxyphenyl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamide and Co-crystallized Methanol under Electron Impact Ionization Conditions

An intermolecular phenolic hydroxy methylation occurring between chiral N,N'-bis(2-hydroxyphenyl)-2,2-di- methyl-1,3-dioxolane-4,5-dicarbamide and co-crystallized methanol under electron impact ionization conditions was observed. The result was confirmed by X-ray diffraction structural ananlysis of a co-crystalline of (R,R)-enantiomer and methanol.

Cluster-assisted generation of multi-charged ions in nanosecond laser ionization of pulsed hydrogen sulfide beam at 1064 and 532 nm

The multi-charged sulfur ions of Sq^＋ （q ≤ 6） have been generated when hydrogen sulfide cluster beams are irradiated by a nanosecond laser of 1064 and 532 nm with an intensity of 10^10- 10^12W.cm^-2. S^6＋ is the dominant multicharged species at 1064 nm, while S^4＋, S^3＋ and S^2＋ ions are the main multi-charged species at 532 nm. A three-step model （i.e., multiphoton ionization triggering, inverse bremsstrahlung heating, electron collision ionizing） is proposed to explain the generation of these multi-charged ions at the laser intensity stated above. The high ionization level of the clusters and the increasing charge state of the ion products with increasing laser wavelength are supposed mainly due to the rate-limiting step, i.e., electron heating by absorption energy from the laser field via inverse bremsstrahlung, which is proportional to λ2,λA being the laser wavelength.

Fully differential cross sections for C^(6+) single ionization of helium

The three-Coulomb-wave （3C） model is applied to study the single ionization of helium by 2 MeV/amu C6＋ impact. Fully differential cross sections （FDCS） are calculated in the scattering plane and the results are compared with experimental data and other theoretical predictions. It is shown that the 3C results of the recoil peak are in very good agreement with experimental observations, and variation of the position of the binary peak with increasing momentum transfer also conforms better to the experimental results. Furthermore, the contributions of different scat- tering amplitudes are discussed. It turns out that the cross sections are strongly influenced by the interference of these amplitudes.

A New Lifetime Prediction Model for pMOSFETs Under V_g=V_d/2 Mode with 2.5nm Oxide

Gate current for pMOSFETs is composed of direct tunneling current,channel hot hole,electron injection current,and highly energetic hot holes by secondary impact ionization.The device degradation under V g=V d/2 is mainly caused by the injection of hot electrons by primary impact ionization and hot holes by secondary impact ionization,and the device lifetime is assumed to be inversely proportional to the hot holes,which is able to surmount Si-SiO 2 barrier and be injected into the gate oxide.A new lifetime prediction model is proposed on the basis and validated to agree well with the experiment.

Dynamic Theory of Electric Breakdown for Oxides

The dynamic aspects of dielectric breakdown (DB) is studied in this article. A quantitative model based on impact ionization is presented. The formulae of microdefect growth rate and lifetime prediction are derived and show fair agreement with experimental data in SiO2. All the fitting parameters have definite physical meanings.

Temperature Dependence of Performance of 6H-SiC Unipolar Power Devices

The temperature dependence of some performance of 6H SiC unipolar power devices is analyzed theoretically.By employing the temperature dependent ionization coefficient and mobility of a silicon carbide,the analytical expressions of the temperature dependent performance,such as breakdown characteristics and on resistance of 6H SiC unipolar power devices are derived in a closed form.The analytical results are compared with the experimental results,with good accordance found in the breakdown characteristics.

Degradation mechanism of enhancement-mode AlGaN/GaN HEMTs using fluorine ion implantation under the on-state gate overdrive stress

The degradation mechanism of enhancement-mode Al Ga N/Ga N high electron mobility transistors（HEMTs） fabricated by fluorine plasma ion implantation technology is one major concern of HEMT＇s reliability. It is observed that the threshold voltage shows a significant negative shift during the typical long-term on-state gate overdrive stress. The degradation does not originate from the presence of as-grown traps in the Al Ga N barrier layer or the generated traps during fluorine ion implantation process. By comparing the relationships between the shift of threshold voltage and the cumulative injected electrons under different stress conditions, a good agreement is observed. It provides direct experimental evidence to support the impact ionization physical model, in which the degradation of E-mode HEMTs under gate overdrive stress can be explained by the ionization of fluorine ions in the Al Ga N barrier layer by electrons injected from 2DEG channel.Furthermore, our results show that there are few new traps generated in the Al Ga N barrier layer during the gate overdrive stress, and the ionized fluorine ions cannot recapture the electrons.

Nonlinear radiation response of n-doped indium antimonide and indium arsenide in intense terahertz field

The nonlinear radiation responses of two different n-doped bulk semiconductors: indium antimonide(In Sb) and indium arsenide(In As) in an intense terahertz(THz) field are studied by using the method of ensemble Monte Carlo(EMC)at room temperature. The results show that the radiations of two materials generate about 2-THz periodic regular spectrum distributions under a high field of 100 k V/cm at 1-THz center frequency. The center frequencies are enhanced to about 7 THz in In Sb, and only 5 THz in In As, respectively. The electron valley occupancy and the percentage of new electrons excited by impact ionization are also calculated. We find that the band nonparabolicity and impact ionization promote the generation of nonlinear high frequency radiation, while intervalley scattering has the opposite effect. Moreover, the impact ionization dominates in In Sb, while impact ionization and intervalley scattering work together in In As. These characteristics have potential applications in up-convension of THz wave and THz nonlinear frequency multiplication field.

Comparative Studies on Mass Spectrometric Fragmentation of Linear Chiral Secondary Alcohols (R)-1-(4-Alkylphenyl) and (R)-1-(4-Alkoxyphenyl/Alkylthiophenyl) Alcohols

Mass spectrometric behaviour of （R） -1- （ 4-alkylphenyl ） alcohols, 1- （4-alkoxylphenyl） alcohols, and 1- （4-alkylthiophenyl） alcohols were studied with the aid of mass-analyzed ion kinetic energy spectrometry under electron impact ionization. All the title compounds show a tendency to eliminate a water molecule to form alkene ions and undergo an a-cleavago to produce protonated aldehyde ions by the loss of alkyl radicals. Except these two common fragment ions, they also show some different fragmentations due to with or without oxy/thioether-linkage.

Exploiting Quantum Confinement for Future Solar Cell Application

Present solar cells are expensive making photovoitaic electricity only attractive whenever there is government incentive. This paper highlights the cost of photovoltaic classified according to first, second and third generations. The first and second generations make up the current photovoltaic. The reasons for the efficiency limitation of the first and second generation photovoltaic are given. Nanoparticles such as quantum dots have confinement properties that can be exploited to improve solar cell efficiency and help reduce the cost. Quantum effect that support hot electron collection and multiple exciton generation through impact ionization are discussed. These form the basis of the future generation quantum dot solar cell.

Quantum Transport Theory for Fusion Plasmas

Fundamental quantum transport equation for impact-ionization processes in fusion plasmas is formulated in the actor-spectator description. The density-matrix formulism is adopted to treat both coherent and incoherent effects in a unified fashion. Quantum electrodynamic effects are also considered for high-temperature scenarios. Electron-impact ionization of uranium ion U91＋ and proton-impact ionization of hydrogen are given as examples.

Avalanche photodetectors based on two-dimensional layered materials

The past decade has witnessed a dramatic increase in interest in emerging photodetectors built from two-dimensional(2D)layered materials.A major driver of this trend is the growing demands for lightweight,uncooled,and even flexible photodetection technology.However,2D layered materials always suffer from low light absorption coefficients due to their atomically thin nature.Impact ionization,which can achieve carrier multiplication,is a promising strategy to design 2D photodetectors with high detection efficiency.In this review,typical types of photodetection mechanisms in 2D photodetectors are first summarized.We then discuss the avalanche mechanism induced by impact ionization and avalanche photodetectors based on conventional silicon and III–V compound semiconductors.Finally,a host of emerging avalanche photodetectors based on 2D materials and their van der Waals heterostructures,and their potential applications in the field of photon-counting technologies are detailed.By reviewing the recent progress and discussing challenges faced by 2D avalanche photodetectors,this review aims to provide perspectives on future research directions of 2D material-based ultrasensitive photodetectors such as single-photon detectors.

Intrinsic carrier multiplication in layered Bi_(2)O_(2)Se avalanche photodiodes with gain bandwidth product exceeding 1 GHz

Emerging layered semiconductors present multiple advantages for optoelectronic technologies including high carrier mobilities,strong light-matter interactions,and tunable optical absorption and emission.Here,metal-semiconductor-metal avalanche photodiodes(APDs)are fabricated from Bi2O2Se crystals,which consist of electrostatically bound[Bi2O2]2+and[Se]2−layers.The resulting APDs possess an intrinsic carrier multiplication factor up to 400 at 7 K with a responsivity gain exceeding 3,000 A/W and bandwidth of~400 kHz at a visible wavelength of 515.6 nm,ultimately resulting in a gain bandwidth product exceeding 1 GHz.Due to exceptionally low dark currents,Bi2O2Se APDs also yield high detectivities up to 4.6×1014 Jones.A systematic analysis of the photocurrent temperature and bias dependence reveals that the carrier multiplication process in Bi2O2Se APDs is consistent with a reverse biased Schottky diode model with a barrier height of~44 meV,in contrast to the charge trapping extrinsic gain mechanism that dominates most layered semiconductor phototransistors.In this manner,layered Bi2O2Se APDs provide a unique platform that can be exploited in a diverse range of high-performance photodetector applications.

Motion of current filaments in avalanching PIN diodes

The motion of current filaments in avalanching PIN diodes has been investigated in this paper by 2D transient numerical simulations. The simulation results show that the filament can move along the length of the PIN diode back and forth when the self-heating effect is considered. The voltage waveform varies periodically due to the motion of the filament. The filament motion is driven by the temperature gradient in the filament due to the negative temperature dependence of the impact ionization rates. Contrary to the traditional understanding that current filamentation is a potential cause of thermal destruction, it is shown in this paper that the thermally-driven motion of current filaments leads to the homogenization of temperature in the diode and is expected to have a positive influence on the failure threshold of the PIN diode.

New expressions for non-punch-through and punch-through abrupt parallel-plane junctions based on Chynoweth law

The relations among the breakdown voltage,the width and the concentration of the voltage-sustaining layer for the non-punch-through（NPT） and punch-through（PT） abrupt parallel-plane junctions have been reestablished based on the ionization integral by the Chynoweth model,distinguished from the conventional results obtained by the Fulop model.The numerical calculation results indicate that the new expressions are more accurate than those in previous literature.While the breakdown voltage of the NPT case varied from 400 to 1600 V using the Chynoweth model,the value using the Fulop model is overestimated by 12%（478 V） to 18%（1895 V）.For the PT case with optimum design of the specific on-resistance,when the breakdown voltage is varied from 400 to 1600 V,the width and concentration are from 81.0168%to 80.2416%and from 91.4341%to 91.6941%of those of the NPT cases,respectively.The relations between the specific on-resistance and the breakdown voltage for both the NPT and PT structures are also established.Simulation results by MEDICI show good agreement with the proposed expressions.

Single- and multi-shot laser-induced damages of Ta_2O_5/SiO_2 dielectric mirrors at 1064 nm

Ta2O5/SiO2 dielectric mirrors deposited by ion beam sputtering （IBS） are studied. The multi-shot laserinduced damage threshold （LIDT） and its dependence on the number of shots are investigated, after which we find that the multi-shot LIDT is lower than that of single-shot. The accumulation effects of defects play an important role in the multi-shot laser damage. A simple model, which includes the conduction band electron production vsa multiphoton and impact ionizations, is presented to explain the experimental phenomena.

Noise performance in AlGaN/GaN HEMTs under high drain bias

The advent of fully integrated GaN PA-LNA circuits makes it meaningful to investigate the noise performance under high drain bias. However, noise performance of AlGaN/GaN HEMTs under high bias has not received worldwide attention in theoretical studies due to its complicated mechanisms. The noise value is moderately higher and its rate of increase is fast with increasing high voltage. In this paper, several possible mechanisms are proposed to be responsible for it. Impact ionization under high electric field incurs great fluctuation of carrier density, which increases the drain diffusion noise. Besides, higher gate leakage current related shot noise and a more severe self-heating effect are also contributors to the noise increase at high bias. Analysis from macroscopic and microscopic perspectives can help us to design new device structures to improve noise performance of AlGaN/GaN HEMTs under high bias.