Hot Electron Capture Research Articles

Achieving Electron Capture Dissociation in the Radio Frequency Linear Ion Trap without the Assistance of a Magnetic Field─A Simulation Study.

It is extremely difficult to inject a low-energy electron beam into a conventional radiofrequency (RF) linear ion trap for electron capture dissociation (ECD) without using a magnetic field to focus the electrons. In this study, the dynamic process of electrons in an RF field during their injection and transmission through a linear ion trap was simulated to determine the range of the RF phase where the electrons can be decelerated to meet the energy requirement for ECD. The ECD time window was expanded by applying a time-dependent compensation voltage to the cathode. The relationship between the cathode voltage and the phase of the RF voltage was determined. The ECD time window was increased to 49.4% of the total RF cycle after applying a compensation voltage. Between the phases of RF voltage of 0 and 0.975 π, at least 98.7% of electrons can be injected into the ECD reaction zone, and 94% of them had an energy less than 3 eV. The range of electron energy can also easily be shifted upward to enable hot electron capture dissociation.

Plasmonic Pt-PPCN/TiN Ohmic Junction for Photo-Thermo Catalytic Hydrogen Production.

The rational design of photocatalysts for improving the conversion of solar energy into hydrogen is a promising route for achieving carbon neutrality. Herein, we couple plasmonic titanium nitride (TiN) with highly crystalline potassium-doped polymeric carbon nitride (PPCN) to construct a PPCN/TiN ohmic junction. Such an ohmic junction not only broadens the absorption spectrum but also inhibits the recombination of electrons and holes. In addition, Pt nanoparticles are introduced into this ohmic junction to form plasmonic Pt-PPCN/TiN, improving the capture of hot electrons generated by TiN and thereby promoting the dissociation of the O-H bond in H2O. The energy barrier decreases from 0.7 to 0.2 eV. Enhanced separation of carrier, activation of water molecules, and capture of hot electrons are jointly promoting photo-thermo catalytic hydrogen production. Therefore, under full-spectrum irradiation, the hydrogen production rate of Pt-PPCN/TiN reaches 19 085 μmol g-1 h-1. This novel plasmonic photocatalyst is promising for full-spectrum photo-thermo catalytic hydrogen production.

Analysis of Sialic Acid Linkage in N-Linked Glycopeptides Using Liquid Chromatography-Electron-Activated Dissociation Time-of-Flight Mass Spectrometry.

Herein, we report a novel liquid chromatography coupled with tandem mass spectrometry method to characterize N-acetylneuraminic acid (Neu5Ac, Sa) linkage in N-linked glycans in glycopeptides with no sialic acid derivatization. First, we established a separation in reversed-phase high-performance liquid chromatography (HPLC) using a higher formic acid concentration in the mobile phases, which separated the N-glycopeptides depending on the Sa linkage. We also demonstrated a novel characterization method of Sa linkages in N-glycopeptides using electron-activated dissociation. We found that hot electron capture dissociation using an electron beam energy higher than 5 eV cleaved glycosidic bonds in glycopeptides, resulting in each glycosidic bond in the antennas being broken on both sides of the oxygen atom. Such glycosidic bond cleavage at the reducing end (C-type ion) showed the difference in Sa linkages between Sa-Gal, Gal-GlcNAc, and GlcNAc-Man. We proposed a rule to characterize the Sa linkages using the Sa-Gal products. This method was applied to N-glycopeptides in tryptic fetuin digest separated by an optimized reversed-phase HPLC. We successfully identified a number of isomeric glycoforms in the glycopeptides with different Sa links, whose peptide backbones were also simultaneously sequenced by hot ECD.

Suppression of hot electron effect in AlGaN/GaN HEMT with multi-grooves barrier-etched structure

A multi-grooves barrier-etched structure between barrier layer and passivation layer is proposed in this paper to suppress the hot electron effect at the gate edge on the drain side in the p-GaN gate AlGaN/GaN high-electron-mobility transistor. In the TCAD simulations, the groove structure induces extra electric field concentration region and AlGaN/SiN interface area, which can lower the high electric field peak and electron temperature in the channel at the gate edge, leading to the alleviated capture and release of hot electrons. The static I–V characteristic and dynamic switching performance and breakdown characteristic show that the multi-grooves barrier-etched structure improves the current collapse and switching time and breakdown voltage. Our work exhibits the great potential of multi-grooves barrier-etched structure on the stability and reliability of the AlGaN/GaN HEMT.

Efficient Hot Electron Capture in CuPc/MoSe2 Heterostructure Assisted by Intersystem Crossing.

Efficient hot electron extraction is a promising approach to develop photovoltaic devices that exceed the Shockley-Queisser limit. However, experimental evidence of hot electron harvesting employing an organic-inorganic interface is still elusive. Here, we reveal the hot electron dynamics at a CuPc/MoSe2 interface using steady-state spectroscopy and transient absorption spectroscopy. A hot electron transfer efficiency of greater than 78% from MoSe2 to CuPc is observed, comparable to that achieved in quantum dot hybrid systems. The mechanism is proposed as follows: the photogenerated hot electrons in MoSe2 transfer to CuPc and form singlet charge transfer states, which subsequently transform into triplet charge transfer states assisted by the rapid intersystem crossing, inhibiting back-donation of electrons and facilitating exciton dissociation into CuPc polarons with a nanosecond lifetime. Our results demonstrate that the intersystem crossing of the hybrid electronic state at organic-inorganic interfaces may serve as a scheme to enable efficient hot electron extraction in photovoltaic devices.

Localization of Multiple O-Linked Glycans Exhibited in Isomeric Glycopeptides by Hot Electron Capture Dissociation.

We describe a method to obtain a comprehensive profile of multiple glycosylations in glycopeptide isoforms. We detected a wide range of abundances of various O-glycoforms in isomeric glycopeptides using hot electron capture dissociation (hot ECD) in liquid chromatography-tandem mass spectrometry. To capture low abundant glycosylated species, a prototype of a ZenoTOF 7600 system incorporating an efficient electron-activated dissociation device to perform hot ECD was operated in targeted or scheduled high-resolution multiple reaction monitoring workflows. In addition, Zeno trap pulsing was activated to enhance the sensitivity of the time-of-flight mass spectrometer. Sixty-nine O-glycopeptides of the long O-glycopeptides in tryptic bovine fetuin digest were obtained with a relative abundance range from 100 to 0.2%, which included sialylated glycans with Neu5Ac and Neu5Gc.

Plasmonic Hot‐Electron‐Induced Control of Emission Intensity and Dynamics of Visible and Infrared Semiconductor Quantum Dots

AbstractPlasmonic hot‐electron‐assisted control of emission intensities and dynamics of CdSe/ZnS and infrared PbS quantum dots are studied. This is done by exploring the impact of Au/Si and Ag/Si Schottky junctions on the decay rates of such quantum dots when these junctions are placed in close vicinity of a Si/Al oxide charge barrier, forming metal‐oxide plasmonic metafilms. Such structures are used to investigate how metal‐dependent distributions of hot electrons and their capture via Schottky junctions can lead to suppression of the defect environments of quantum dots, offering a novel platform wherein off‐resonant (non‐Purcell) plasmonic processes are used to control exciton dynamics. These results show that Ag metafilms can enhance the emission of CdSe/ZnS quantum dots and elongate their lifetimes more than Au metafilms. This highlights the more efficient nature of Ag/Si Schottky junctions for hot electron excitation and capture. These results also show that such junctions can significantly suppress the nonradiative decay rates of PbS quantum dots at frequencies far from the plasmon resonances. These results demonstrate a field‐effect passivation of quantum dot defects via entrapment of hot electrons and control of emission intensities and dynamics of quantum dots via the nearly frequency‐independent electrostatic field of such electrons.

Elongated Lifetime and Enhanced Flux of Hot Electrons on a Perovskite Plasmonic Nanodiode.

A fundamental understanding of hot electron transport is critical for developing efficient hot-carrier-based solar cells. There have been significant efforts to enhance hot electron flux, and it has been found that a key factor affecting the hot electron flux is the lifetime of the hot electrons. Here, we report a combined study of hot electron flux and the lifetime of hot carriers using a perovskite-modified plasmonic nanodiode. We found that perovskite deposition on a plasmonic nanodiode can considerably improve hot electron generation induced by photon absorption. The perovskite plasmonic nanodiode consists of MAPbI3 layers covering a plasmonic-Au/TiO2 Schottky junction that is composed of randomly connected Au nanoislands deposited on a TiO2 layer. The measured incident photon-to-electron conversion efficiency and the short-circuit photocurrent show a significantly improved solar-to-electrical conversion performance of this nanodiode. Such an improvement is ascribed to the improved hot electron flux in MAPbI3 caused by effective light absorption from near-field enhancement of plasmonic Au and the efficient capture of hot electrons from Au nanoislands via the formation of a three-dimensional Schottky interface. The relation between the lifetime and flux of hot electrons was confirmed by femtosecond transient absorption spectroscopy that showed considerably longer hot electron lifetimes in MAPbI3 combined with the plasmonic Au structure. These findings can provide a fundamental understanding of hot electron generation and transport in perovskite, which can provide helpful guidance to designing efficient hot carrier photovoltaics.

Peptide Sequence Influence on the Differentiation of Valine and Norvaline by Hot Electron Capture Dissociation.

Isomeric amino acid residues such as valine (Val) and norvaline (Nva) are common in recombinant proteins. The mis-incorporation of Nva for leucine (Leu) causes heterogeneity and in some cases even toxicity. Previous studies have shown that hot electron capture dissociation (HECD) is able to differentiate Val from Nva by producing diagnostic w ions on custom designed synthetic model peptides. To broaden the utilization of HECD in proteomic studies and to define the critical structural features, a thorough investigation was performed on representative peptides including specifically designed synthetic peptides as well as biological peptides bearing tryptic digest-like features and peptides with post-translational modifications. Experimental evidence confirmed that the formation of a w ion is directly dependent upon the presence of the corresponding z ion. The results suggested that a charge carrier residue at the C-terminus is promoting the formation of diagnostic w ions for Nva. Thus, peptides resulting from trypsin digestion, with arginine (Arg) or lysine (Lys) at the C-terminus, can be analyzed using the HECD method. Post-translational modification (PTM) such as phosphorylation did not prevent the generation of the requisite side chain fragmentation w ions. These results suggest the general applicability of HECD for unambiguous identification of Val and Nva especially in structure characterization of therapeutic proteins.

Differentiation of Norvaline and Valine in Peptides by Hot Electron Capture Dissociation.

During the production of recombinant proteins, misincorporation of Nva (norvaline) is common and causes heterogeneity or even toxicity. To characterize Nva and differentiate it from Val (Valine), a systematic study was conducted using hot electron capture dissociation (HECD) and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The thorough investigation of the fragmentation behaviors of a set of model peptides led us to reveal the characteristic/diagnostic fragment ions, w ions, which can be used to differentiate Val and Nva. However, when both Nva and Val were present in one peptide, the observation of interfering ions may mislead the interpretation. Interestingly, HECD also produced v ions, which have the same nominal mass as the M+1 isotope of the w ion and can only be determined by MS with ultrahigh mass resolution and high mass accuracy. The energy-dependent study of the v ion provided an unambiguous identification of Nva and Val since the v ion was generated only when Val was present, not Nva within the electron energy range we studied. In addition, an electron energy-dependent curve provided an overall picture on how w ions and v ions, as well as interfering ions, behaved as the electron energy increased from 1.5 to 14 eV. The results suggest that careful selection of electron energy during a HECD experiment is crucial for the unambiguous differentiation of Val and Nva.

Energy level control: toward an efficient hot electron transport.

Highly efficient hot electron transport represents one of the most important properties required for applications in photovoltaic devices. Whereas the fabrication of efficient hot electron capture and lost-cost devices remains a technological challenge, regulating the energy level of acceptor-donor system through the incorporation of foreign ions using the solution-processed technique is one of the most promising strategies to overcome this obstacle. Here we present a versatile acceptor-donor system by incorporating MoO3:Eu nanophosphors, which reduces both the ‘excess' energy offset between the conduction band of acceptor and the lowest unoccupied molecular orbital of donor, and that between the valence band and highest occupied molecular orbital. Strikingly, the hot electron transfer time has been shortened. This work demonstrates that suitable energy level alignment can be tuned to gain the higher hot electron/hole transport efficiency in a simple approach without the need for complicated architectures. This work builds up the foundation of engineering building blocks for third-generation solar cells.

Elucidating the sequence of intact bioactive peptides by using electron capture dissociation and hot electron capture dissociation in a linear radio‐frequency quadrupole ion trap

Electron capture dissociation (ECD) is useful tool for sequencing of peptides and proteins with post-translational modifications. To increase the sequence coverage for peptides and proteins, it is important to develop ECD device with high fragmentation efficiency. Sequence analysis of intact undigested bioactive peptides (3000-5000 Da) was performed by use of electron capture dissociation (rf-ECD) and collision-induced dissociation (CID) in a linear radio-frequency quadrupole ion trap that was coupled to a time-of-flight mass spectrometer. We applied rf-ECD, hot rf-ECD (rf-ECD with high electron energy), and CID for intact bioactive peptide ions of various charge states and evaluated the sequence coverage of their fragment spectra. Hot rf-ECD produced a higher number of c- and z-type fragment ions of modified peptide ions as electron energy increased in lower charged peptide ions, and sequence coverage greater than 80% was obtained compared with the CID case (40-80%). The result indicates that intact bioactive modified peptides (Ghrelin, ANP) were correctly identified by use of hot rf-ECD.

The effect of hot captured electrons on dust particle charge in a dusty plasma

We consider the effect of allowing the capture of hot electrons by a dust particle in a dusty plasma by considering the temperature gradient created between these and the ambient plasma and by calculating the contribution to the electron current which results. A graph of the curve for the contribution from the temperature gradient to the electron current at the dust particle and the curve for the function without the temperature gradient included for a variety of values of the effective reduced potential of the dust particle shows a significant reduction in the charge on the dust particle when the temperature gradient is included. We present results for the percentage differences between the function with and without the temperature gradient included for a range of values of the reduced potential. These show that the effect of hot electrons can reduce the electron current contribution to the dust charge by up to 38% when the ion temperature is equal to the ambient electron temperature and that it can increase the electron current contribution to the dust charge by up to 33% when the ion temperature is a tenth of the ambient electron temperature.

Hot Electron Capture Dissociation Distinguishes Leucine from Isoleucine in a Novel Hemoglobin Variant, Hb Askew, β54(D5)Val→Ile

Population migration has led to the global dispersion of human hemoglobinopathies and has precipitated a need for their identification. An effective mass spectrometry-based procedure involves analysis of the intact alpha- and beta-globin chains to determine their mass, followed by location of the variant amino acid residue by direct analysis of the enzymatically digested chains and low-energy collision induced dissociation of the variant peptide. Using this procedure, a variant was identified as either beta54Val-->Leu or beta54Val-->Ile, since the amino acids leucine and isoleucine cannot be distinguished using low-energy collisions. Here, we describe how hot electron capture dissociation on a Fourier transform-ion cyclotron resonance mass spectrometer was used to distinguish isoleucine from leucine and identify the mutation as beta54(D5)Val-->Ile. This is a novel variant, and we have named it Hb Askew.

Electric field strength and temperature dependence of conduction relaxation in AlGaN/AlN/GaN 2D electron gas

Electrical pulses of ns duration were applied parallel to the interfaces of AlGaN/AlN/GaN samples with a two-dimensional gas channel and an ultra-thin AlN spacer to create electric elds with strength up to 80 kV=cm. Conduction relaxation of the two-dimensional electron gas was measured after the high voltage pulses in temperature range from 86 to 293 K. Results of the conduction relaxation obtained in ns time scale were approximated by an expression containing two exponential components with different time constants. The time constants were chosen to correspond to the relaxation process in the eld range from 40 to 60 kV=cm at various temperatures. Analysis of obtained expressions showed that the smaller constant ?1 slightly depended on temperature and the applied electric eld and this was attributed to the electron release after the capture of hot electrons into shallow traps located in the AlN spacer or the AlGaN/AlN interface. The greater constant ?2, which appreciably depends both on electric eld and temperature, we attribute to electron thermal release after the capture of hot electrons in the GaN layer. Also, the electrons can be thermally released from the centres in GaN present due to uctuations of the bottom of the conduction band. The activation energy associated with the thermal processes is evaluated.

Relaxation of parameters of thin-film electroluminescent ZnS:Mn-based structures when turned off

Results of experimental study of decay of the current flowing through a thin-film electroluminescent MISIM structure indicate a bimolecular process of electron capture by the surface states of the anode interface. A two-stage model of the process is suggested. At the first stage, the impact Auger capture of hot electrons takes place. At the second stage, upon varying the field direction, the holes of the valence band generated due to tunnel emission from deep centers drift to this interface, where they recombine with electrons of deepest occupied surface states. The electron lifetime and rate of the surface capture of electrons as well as their dependences on excitation parameters are determined. The behavior of the time dependence of the instant internal quantum yield at the decay portion is interpreted.

The Electric Field and Temperature Dependence of Conductance of Two-Dimensional Electron Gas in AlGaN/AlN/GaN

The two-dimensional gas in AlGaN/AlN/GaN heterostucture with a very thin (0.6 nm) AlN spacer was investigated by conductivity relaxation measurements in 86–300 K temperature range. The results show the presence of two exponential relaxation processes characterized by different characteristic time constants. Parameters of the fast and slow components of the processes differently depend on the electric field and temperature. The fast process is attributed to influence of the electric field on the barrier formed by the spacer, while the slow process is attributed to the hot-electron capture out of the channel followed by electron thermal release.

Magnetic field tuning of hot electron resonant capture in a semiconductor device

We study hot-electron capture on resonant N-impurities in the dilute nitride Ga(AsN) alloy under high magnetic fields up to 23T. We show that when the ratio of electric and magnetic fields reaches a critical value, the trajectory of conduction electrons becomes fully localized in real space; this leads to a negative differential conductance and current instabilities tuneable by magnetic field.

Thermal-collisional mechanism of hot electron capture in strong crossed electromagnetic fields

The subject of investigation is the thermal-collisional mechanism of electron capture in crossed electromagnetic fields (E ⊥ H) and the ranges of electric and magnetic fields where this mechanism works. The ratio between recombination coefficients corresponding to the thermal-collisional and Lax capture mechanisms is calculated at different degrees of compensation at a cryogen temperature (T = 4.2 K) for n-type semiconductors.

Rapid hot-electron capture in self-assembled quantum dots via phonon processes

Electron capture induced by carrier heating in InAs∕GaAs quantum dots is studied theoretically. Room temperature capture rates due to single longitudinal-optical (LO) phonons, LO phonons plus acoustic phonons, and two LO phonons are compared. Due to energy broadening from carrier-carrier scattering, single LO-phonon processes are the fastest capture channel. Screening from wetting-layer (WL) carriers is studied comprehensively using a number of screening models. Due to the dispersion of the WL electron-hole plasma and dynamic effects of screening, antiscreening occurs expediting rather than slowing down electron capture, with capture times of several picoseconds when the carrier temperature is 100–200K above room temperature.