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GC-MS usually employs a 70 eV electron ionization (EI) ion source, which provides mass spectra with detailed fragment ion information that are amenable for library search and identification with names and structures at the isomer level. However, conventional EI often suffers from low intensity or the absence of molecular ions, which reduces detection and identification capabilities in analyses. In an attempt to enhance the molecular ions, several softer ion sources are being used to supplement standard EI, including chemical ionization (CI), atmospheric pressure chemical ionization (APCI), field ionization (FI), photoionization (PI), and low electron energy EI. However, the most advantageous way to enhance molecular ions is to use cold EI, which employs 70 eV EI of cold molecules in supersonic molecular beams. Cold EI yields classical EI mass spectra with highly enhanced molecular ions, which still provides high detectability and library-searchable mass spectra. In this paper, we explain and discuss why cold EI is not a supplementary ion source to standard EI, but rather it is a highly superior replacement to standard EI. With cold EI, there is no need for standard EI or any other supplemental ion source. We describe 16 benefits and unique features of cold EI that not only yield better results for existing applications but also significantly extend the range of compounds and applications amenable for GC-MS analysis.

Soft ionization by a chemical reaction in transfer (SICRIT) is applied to couple gas chromatography (GC) to a high-resolution atmospheric pressure inlet mass spectrometer. These instruments are generally used in combination with liquid chromatography systems (LC-MS). Ionization of alkanes is not possible here with conventional electrospray ionization. Alternatively, separate GC-electron ionization (EI)-MS is employed for the analysis of nonpolar substances like alkanes, however, with the inherent challenge of strong fragmentation. In the case of alkanes, the determination of molecular masses becomes nearly impossible in complex hydrocarbon mixtures because of the wealth of similar fragment ions and the absence of the molecular ion signal. SICRIT, a soft ionization technique based on dielectric barrier discharge (DBDI), produces characteristic oxidized cations from alkanes that can be directly correlated to their molecular mass. Isotope labeling experiments reveal an ionization mechanism via hydride abstraction and reaction with water. Soft ionization can be achieved for iso- and n-alkanes, with very little fragmentation, enabling the determination of their molecular mass. Calibrations for n-alkanes from C10 to C30 were performed exhibiting high linearity, reproducibility, and sensitivity with an average LOD of 69 pg (on column). Measurements of diesel fuel samples are compared to traditional GC-EI-MS. The presented method combines sensitivity and easy handling of a GC-EI-MS with the determination of molecular mass commonly only achieved with field ionization (FI)-MS, while using existing and highly optimized mass spectrometers commonly coupled with LC. Additionally, many other analytes such as (alkylated-) PAHs could be detected simultaneously in the diesel sample.

In this work, the influence of varying mixing ratios of O-2 on positive streamer initiation in supercritical (SC) CO2 at different applied voltages was investigated using a 3-D particle model. Zener's model was included in the 3-D particle model to calculate the field ionization rate during streamer formation and propagation. The evolution of positive streamer was classified into three main stages namely inception cloud, primary streamer channels, and successive streamer branching. The effect of O-2 with different mixing ratios (2%, 10%, and 20%) on the morphology, average electron density, electric field distribution, streamer length, and electron energy distribution function (EEDF) for positive streamer in SC-CO2 at four different voltages (12, 12.5, 13, and 13.5 kV) is then investigated. The 2-D cross sections of the initial stage of the streamer and the electric field distribution are presented in detail. At the same applied voltage, the size of inception cloud, average electron density, electric field, and streamer length with the maximum electric field decreased with increasing oxygen concentration in SC-CO2. With increasing applied voltage, the apparent size of inception cloud, primary streamer channels, successive streamer branching, average electron density, electric field, and streamer length increased. The simulation results showed that adding O-2 to SC-CO2 can significantly affect the streamer initiation and propagation.

The study was devoted to the investigation of the place of modern mass spectrometric methods in the polymer research. The development of methods was investigated and it was shown that practically until the end of the 20th century, the use of mass spectrometry for investigation of polymers was extremely limited due to the non-volatility of polymers. The method of pyrolytic mass spectrometry is considered as the most common method for determining the molecular weight distribution, the determination of end groups, and other general problems. More modern methods of “soft” ionization, allowing ionizing polymers from a condensed state with simultaneous desorption into the gas phase were also described. A review of the literature has shown that such methods have almost completely replaced or significantly supplemented the tools of polymeric material researchers. Matrix-assisted laser desorption/ionization (MALDI), field desorption (FD), fast atom bombardment (SIMS), and electrospray ionization (ESI) are described in the literature. Also, pyrolytic mass spectrometry with direct injection and combined with gas chromatographic separation were described as being a more classical method. It was shown that mass spectrometry is the most versatile and sensitive method for any tasks related with the analysis and investigation of polymer materials.

Dissociation of water molecules after soft X-ray absorption can yield neutral fragments in high-Rydberg (HR) states. We have studied the production of such fragments by field ionization and ion time-of-flight (TOF) spectrometry. Neutral HR fragments are created at all resonances below the O 1s ionization potential (IP) and particularly within 1 eV above the O 1s IP. The latter effect is due to the recapture of the O 1s photoelectrons into HR orbitals of the molecular water ion after the emission of a fast Auger electron. H₂O+(HR) fragments subsequently dissociate, yielding neutral H(HR) and O(HR) fragments, as were found by measuring the TOF spectra by pulsed field ionization. Such measurements were carried out at the O 1s → 4a₁ and 2b₂ resonances as well as just above the O 1s IP. The TOF spectra also reveal two series of oscillatory structures that are attributed to quantum beats involving Lyman emission in one of the series and field ionization of H(HR) fragments in the other series.

A 3D particle‐in‐cell/Monte Carlo collision model is used to investigate the streamer discharge inception in CO2 at elevated pressures including gaseous, liquid and supercritical phases. Generation of free electrons is a prerequisite for initiation and development of positive streamers. Field ionization from impurity molecules of low density and low ionization energy is assumed as the source of primary ionization in the model. The field dependent generation rate of electrons is calculated by Zener's model. Tree‐like streamer with filamentary shape presents at the needle tip and propagates towards the plane electrode in all three phases of CO2, with differing in length and propagation speed. Furthermore, the influence of different parameters such as applied voltage, electrode tip size, and ionizable density and ionization potential of impurity molecules on the evolution of streamer discharge in supercritical CO2 are investigated. Simulation results obtained from the 3D model agree well with experimental observations in the literature, which show that field ionization might be one of possible ionization sources in pressurized CO2 in the presence of high electric field.

Capturing the dynamic fluctuations in structure and adsorbate coverage on catalytic surfaces under operating conditions is of critical importance to the identification of active sites and subsequent design of materials for targeted bond activation but remains challenging to achieve both experimentally and computationally. Field ion microscopy achieves such in situ reaction monitoring on single catalytic grains via applied electric fields which ionize atmospheric gases at the surface, providing images of the working catalyst surface. However, such images remain difficult to deconvolute without simplifying assumptions. Here, we use density functional theory to probe the mechanism for field ionization of a series of imaging gases (O2, N2, and NO) over oxygen, nitrogen, sulfur, and carbon covered Pd(331). From this dataset of field ionization systems, we determined that the primary factors affecting field ionization are the relative energy levels for the imaging gas’s occupied states and the surface’s unoccupied states, both of which are tunable through choice of imaging gas and the presence of adsorbates, respectively. Using such quantitative descriptors of the electronic accessibility of both the imaging gas and adsorbate covered surface, we develop a predictive tool for the rapid assessment of any system’s field ionization potential. Overall, this work provides fundamental insight into the field ionization mechanism and presents an easy-to-use predictive tool that can assist with both the analysis of existing field ion microscopy images and the design of future experiments.

We used field emission microscopy to study the field desorption of sodium and cesium atoms from a rhenium field emitter precarbonized in benzene vapor. The dependences of the ion currents of sodium and cesium on the voltage applied to the field emitter differ. The difference in the ion current dependences is explained by the formation of multilayer graphene on the crystalline surface of a rhenium field emitter in the regions of low-index faces and its intercalation by alkali metal atoms with different ionization potentials and different atomic and ionic radii.

The discovery of the ionizing effect of strong electric fields in the order of volts per Ångstrom in the early 1950s eventually led to the development of field ionization-mass spectrometry (FI-MS). Due to the very low ion currents, and thus, limited by the instrumentation of the 1960s, it took some time for the, by then, new technique to become adopted for analytical applications. In FI-MS, volatile or at least vaporizable samples mainly deliver molecular ions, and consequently, mass spectra showing no or at least minor numbers of fragment ion signals. The next major breakthrough was achieved by overcoming the need to evaporate the analyte prior to ionization. This was accomplished in the early 1970s by simply depositing the samples onto the field emitter and led to field desorption-mass spectrometry (FD-MS). With FD-MS, a desorption ionization method had become available that paved the road to the mass spectral analysis of larger molecules of low to high polarity and even of organic salts. In FD-MS, all of these analytes deliver spectra with no or at least few fragment ion peaks. The last milestone was the development of liquid injection field desorption/ionization (LIFDI) in the early 2000s that allows for sample deposition under the exclusion of atmospheric oxygen and water. In addition to sampling under inert conditions, LIFDI also enables more robust and quicker operation than classical FI-MS and FD-MS procedures. The development and applications of FI, FD, and LIFDI had mutual interference with the mass analyzers that were used in combination with these methods. Vice versa, the demand for using these techniques on other than magnetic sector instruments has effectuated their adaptation to different types of modern mass analyzers. The journey started with magnetic sector instruments, almost skipped quadrupole analyzers, encompassed Fourier transform ion cyclotron resonance (FT-ICR) and orthogonal acceleration time-of-flight (oaTOF) analyzers, and finally arrived at Orbitraps. Even interfaces for continuous-flow LIFDI have been realized. Even though being niche techniques to some degree, one may be confident that FI, FD, and LIFDI have a promising future ahead of them. This Account takes you on the journey from principles and applications of the title methods to a glimpse into the future.

International audience; A new experimental method has been developed to record photoelectron spectra based on the well-established pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy technique and inspired by the data treatment employed in slow photoelectron spectroscopy. This method has been successfully applied to two well-known systems: the X+2Pg,1/2(v+=0) X1S+g (v=0)and the X+1S+(v+=2) X2P1/2(v=0)ionizing transitions of CO2 and NO, respectively. The first results highlight several advantages of our technique such as an improved signal-to-noise ratio without degrading the spectral resolution and a direct field-free energy determination. The data obtained for NO indicate that this method might be useful for studying field-induced autoionization processes.

In atom probe tomography of molecular organic materials, field ionization of either entire molecules or molecular fragments can occur, but the mechanism governing this behavior was not previously understood. This work explains when a doubly ionized small molecule organic material is expected to undergo fragmentation. We find that multiple detection events arising from post-ionization fragmentation of a parent molecular dication into two daughter ions is well explained by the free energy and geometries of the molecules computed using density functional theory. Of the systems studied, exergonic free energies for formation of the daughter ions, smaller activation energies for dissociation, and increases in bond length are all found to be quantitative predictors for ion fragmentation. This work expands the applicability of atom probe tomography to organic materials by increasing the fundamental understanding of processes occurring during this analysis technique.

A gas field ion source (GFIS) has several advantages such as high current density, low energy spread, and high brightness. In this study, Helium gas was used in a GFIS, generated using the field ionization and field evaporation processes. The (110) oriented three adatoms tip (TAT) and single atom tip (SAT) were prepared with its ion emission stability 9.8% and 10.1% by the nitrogen field-assisted etching, respectively. The TAT and SAT were reproduced throughout the field evaporation and nitrogen field-assisted etching along the same crystal axis with its brightness 2.6 × 107 A/(m2 sr) and 1.6 × 108 A/(m2 sr), respectively. The field emission electron beam effective radii for three adatoms and single atom were calculated to be 2.90 A and 1.47 A, respectively, by Fowler-Nordheim plot, in which the single atom size was especially shown to be quite in good consistency with an atomic radius of tungsten.

In this article we present the three-body fragmentation dynamics of ${\mathrm{C}}_{2}{{\mathrm{H}}_{4}}^{3+}$ caused by $18\text{\ensuremath{-}}\mathrm{keV}/\mathrm{u}\phantom{\rule{0.16em}{0ex}}{\mathrm{Ne}}^{8+}$ ion impact. Utilizing the cold target recoil ion momentum spectroscopy, the complete kinematical information of three fragmentation channels, i.e., ${\mathrm{C}}_{2}{{\mathrm{H}}_{4}}^{3+}\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{H}}^{+}+{\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{+}, {\mathrm{H}}^{+}+\mathrm{C}{\mathrm{H}}^{+}+\mathrm{C}{{\mathrm{H}}_{2}}^{+}$, and ${\mathrm{H}}^{+}+{{\mathrm{H}}_{2}}^{+}+{\mathrm{C}}_{2}{\mathrm{H}}^{+}$ is obtained. For each channel, both concerted and sequential fragmentation mechanisms are observed and differentiated through the momentum correlation of resultant fragments visualized by the Dalitz plot and the Newton diagram. In particular, for the channel ${\mathrm{C}}_{2}{{\mathrm{H}}_{4}}^{3+}\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{H}}^{+}+{\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{+}$, it is found in addition to the sequential pathway that the two protons can be emitted concertedly in two ways, i.e., from the same carbon atom or from the two carbon atoms. The present results show a more diverse molecular fragmentation triggered by ion collisions in contrast to a previous study using intense laser field ionization.

The use of autoionization as a tool to quantitatively analyze transitions between high-n strontium Rydberg states with low-to-intermediate values of L is described and is demonstrated through observations of Rabi oscillations when driving 5snf 1F3 → 5s(n + 1)g 1G4, 5snf 1F3 → 5s(n + 2)h 1H5, and 5snp 1P1 → 5s(n + 1)d 1D2 transitions using microwave fields. The technique is shown to offer advantages when compared to selective field ionization and can be used with other alkaline-earth and alkaline-earth-like metals.

Experimental and theoretical studies of laser-induced breakdown in dielectrics provide conflicting conclusions about the possibility to trigger ionization avalanche on the sub-picosecond time scale and the relative importance of carrier-impact ionization over field ionization. On the one hand, current models based on single ionization-rate equations do not account for the gradual heating of the charge carriers which, for short laser pulses, might not be sufficient to start an avalanche. On the other hand, models based on multiple rate equations that track the carriers kinetics rely on several free parameters, which limits the physical insight that we can gain from them. In this paper, we develop a model that overcomes these issues by tracking both the plasma density and carriers' mean kinetic energy as a function of time, forming a set of delayed rate equations that we use to match the laser-induced damage threshold of several dielectric materials. In particular, we show that this simplified model reproduces the predictions from the multiple rate equations, with a limited number of free parameters determined unambiguously by fitting experimental data. A side benefit of the delayed rate equations model is its computational efficiency, opening the possibility for large-scale, three-dimensional modelling of laser-induced breakdown of transparent media., Comment: 11 pages, 7 figures

Desorption of cesium atoms in an electric field from the carbonized rhenium field emitter was investigated by the field desorption microscopy. The effect of the concentration of cesium atoms on the voltage and on the distribution of emission centers on the surface of the emitter is studied. It is shown that rhenium carburization can lead to a surface modification with the formation of carbon nanostructures.

In this review article collection of summary of research works related to gas ionization sensors based on nanostructured materials is attempted. Among physical gas sensors, gas ionization sensor is used to identify gases based on breakdown of ionized gases as each gas has a unique breakdown voltage. The sensor is generally, made of two parallel electrodes separated by a narrow gap. Nanostructures, usually metallic or semiconducting, in from of nanowires/nanorods are places between the two plates. These structures act as electric field amplifiers to enhance the electric field intensity to reduce the breakdown voltages of the gases. Numerous investigations revealed that type of materials and their physical properties play important roles in the sensor characteristics and their operations. Identifying materials to optimize the strength of electric field and generate large field enhancement is a crucial step towards this application. Carbon nanotubes were among the first candidates to utilize in these structures and in fact, they were used to prove the principle of the device. The very first developed sensor showed that using carbon nanotubes between the two parallel plates of the sensor reduces the required applied voltages to ionize gases up to one order of magnitude. Since 2003 many studies are done to improve the performance and physical properties like sensitivity, selectivity, durability and stability of the device by incorporating various materials in form of nanowires/nanorods inside the device structure. In this work, first the fundamental structure of gas ionization sensor and the theory of their operations like field emission, field ionization and quantum tunneling phenomena are presented. Then, related research works reported in the literature are summarized. This review article is partitioned based on the materials used in the structure of the device as they play the most effective role in their performances. It is started with studies on devices based on carbon nanotubes, and then those used metallic nanowires followed by works done using semiconductor nanostructure to develop the device. The review started from the oldest articles in each category carried on to the most recent published works. All essential parameters effecting the structures and operations of the reported devices including their pros and cons are discussed.

The conductivity of epitaxial diamond films lightly doped with boron has been studied at strong electric fields up to ~5 × 105 V/ cm. It is shown that field ionization of boron acceptors in diamond at room temperature, because of the low concentration of free holes and the high binding energy of boron, occurs due to the Frenkel–Poole effect.

Field ionization is adopted as a streamer initiation mechanism in highly pressurized CO 2 , using a 3D particle model. The field ionization is implemented into the 3D model through Zener’s model. Streamer evolution is classified into three stages; inception cloud formation, main streamer channels, and subsequent streamer branching independent of the medium state. The comparison of average electron density, electric field, and the length of streamer in three thermodynamic states of CO 2 is presented. Box counting method is used to calculate the fractal value (D) for positive streamer pattern in gaseous, liquid, and supercritical (SC) CO 2 . The figures of streamer discharge obtained from the 3D simulation model are fractal with fractal dimension for gaseous, liquid phase, and SC- CO 2 as 1.577, 1.578, and 1.587. The results of fractal analysis of positive streamer branching in this paper are consistent with the fractal values of streamer in the SC-CO 2 through experiments in literature.

Simulation concerning the field ionization and streamer propagation processes in liquid nitrogen under pulsed voltage is performed to investigate the discharging characteristics and the factors that may influence the discharging process. In order to have a better description of field ionization in liquid nitrogen, a computational quantum chemistry method is utilized for obtaining the relations between the ionization potential of nitrogen molecule and the electric field. Results indicate that the pre-breakdown process could be divided into four stages which are initiation, propagation, re-ignition and annealing. In addition, the temperature in liquid nitrogen during the discharging process is investigated which shows that the temperature of liquid nitrogen in a small region near the needle electrode would reach the global maximum close to 120 K whereas along the discharge path there exists an area where the temperature of liquid nitrogen would exceed 85 K after 250 ns under 200 kV pulsed voltage with a 2 mm needle-sphere gap. Finally, several factors that would impact the streamer propagation are discussed.

A new setup combining a ThermoFisher Exactive Plus Orbitrap Mass Spectrometer with a liquid injection field desorption ionization (LIFDI) source directly connected to an inert atmosphere glovebox is presented. The described setup allows for the analysis of very air- and moisture sensitive samples. Furthermore, the soft nature of LIFDI ionization gives access to the molecular ions of fragile molecules. This new setup is therefore especially useful for sensitive organometallic complexes. The functionality of the new setup is tested against [(Cp)2TiCl]˙, which is known for its notorious sensitivity to air and moisture. Its drastic colour change from green to orange upon exposure to air further supports the easy detection of traces of oxygen during the experiment. In addition, we applied this setup to the mass spectrometric analysis of the qualitative composition of a Cu/Al cluster mixture, which is not accessible by other analytical methods.

Power transformer is the key equipment for power transmission and transformation. However, the operating accidents caused by the insulation fault lead to huge economic loss. In order to reveal the mechanism of surface discharge in oil-paper insulation under various temperature, a numerical simulation model based on hydrodynamic equation for three kinds of charge carriers, coupled with current field equation, is proposed. The streamer inception and propagation along the oil-paper interface are simulated. According to the results, the effect of temperature on inception voltage, flashover voltage and streamer propagating velocity in oil-paper insulation are acquired and analyzed. According to the simulating results, the inception of streamer takes approximately $80 \mu\mathrm{s}$ for charge carriers accumulation and only when the electric field intensity reaches a specific value can the streamer propagate along the oil-paper interface within about $3 \mu\mathrm{s}$ . What's more, with the increase of temperature, the field ionization and the movement of charge carrier become more active, leading to the decrease of inception voltage and flashover voltage of surface discharge in oil-paper insulation. Last but not least, with the increase of temperature, the average velocity of surface discharge increases. When the temperature reaches 85 °C, the average velocity of streamer propagation increases sharply, with the value of 4790.1 m/s.

We present a full quantal study on the dissociation of a weakly bound molecular ion in the presence of an external time-dependent electric field. We focus on the dissociation dynamics of a molecular ion in a Paul trap relevant for atom-ion hybrid traps. Our results show that a weakly bound molecular ion survives in a Paul trap giving a theoretical ground to previous experimental findings [A. Kr\"ukow et al. Phys. Rev. Lett. 116, 193201 (2016) and A. Mohammadi et al. Phys. Rev. Research 3, 013196 (2021)]. In particular, we find that weakly bound molecular ions are more likely to survive in traps with large RF frequency. Similarly, we show that applying an electric field ramp is an efficient method to state-selectively detect weakly bound molecular ions, analogous to the well-known selective field ionization technique applied in Rydberg atoms, that it may also be used to detect these species in atom-ion hybrid traps., Comment: 4 pages, 4 figures

GaN nanowires grown by molecular beam epitaxy generally suffer from dominant nonradiative recombination, which is believed to originate from point defects. To suppress the formation of these defects, we explore the synthesis of GaN nanowires at temperatures up to 915 °C enabled by the use of thermally stable TiNx/Al2O3 substrates. These samples exhibit indeed bound exciton decay times approaching those measured for state-of-the-art bulk GaN. However, the decay time is not correlated with the growth temperature, but rather with the nanowire diameter. The inverse dependence of the decay time on diameter suggests that the nonradiative process in GaN nanowires is not controlled by the defect density, but by the field ionization of excitons in the radial electric field caused by surface band bending. We propose a unified mechanism accounting for nonradiative recombination in GaN nanowires of arbitrary diameter.

Nanosecond plasmas in liquids are being used for water treatment, electrolysis, or biomedical applications. The exact nature of these very dynamic plasmas and, most importantly, their ignition physics are strongly debated. The ignition itself may be explained by two competing hypotheses: ignition in water may occur (i) via field effects at the tip of the electrode followed by tunneling of electrons in between water molecules causing field ionization or (ii) via gaseous processes of electron multiplication in nanovoids that are created from liquid ruptures due to the strong electric field gradients. Both hypotheses are supported by theory, but experimental data are very sparse due to the difficulty in monitoring the very fast processes in space and time. In this paper, we analyze nanosecond plasmas in water that are created by applying a positive and a negative polarity to a sharp tungsten electrode. The main diagnostics are fast camera measurements and fast emission spectroscopy. It is shown that plasma ignition is dominated by field effects at the electrode–liquid interface either as field ionization for positive polarity or as field emission for negative polarity. This leads to a hot tungsten surface at a temperature of 7000 K for positive polarity, whereas the surface temperature is much lower for negative polarity. At ignition, the electron density reaches 4 × 10 25 m − 3 for the positive and 2 × 10 25 m − 3 for the negative polarity. At the same time, the emission of the H α light for the positive polarity is four times higher than that for the negative polarity. During plasma propagation, the electron densities are almost identical of the order of 1– 2 × 10 25 m − 3 followed by a decay after the end of the pulse over 15 ns. It is concluded that plasma propagation is governed by field effects in a low density region that is created either by nanovoids or by density fluctuations in supercritical water surrounding the electrode that is created by the pressure and temperature at the moment of plasma ignition.

We review our effective potential approach based on the multiconfiguration time-dependent (TD) Hartree–Fock (MCTDHF) method to simulate the multielectron dynamics of molecules. According to the formulation of MCTDHF, we introduce the equations of motion for TD natural orbitals \(\{ \phi_{j} (t)\}\) and TD effective potentials \(v_{j}^{{{\text{eff}}}} (t)\) that determine the fate of the dynamics of \(\phi_{j} (t)\). \(v_{j}^{{{\text{eff}}}} (t)\) is separated into the one-body part \(v_{1} (t)\) including the interaction with the laser electric field \({\varvec{\varepsilon}}\left( t \right)\) and the two-body part \(v_{2,\,j} (t)\) originating from electron–electron interaction. The estimated ionization rate for a CO molecule in an intense near-IR field is higher when \({\varvec{\varepsilon}}\left( t \right)\) turns to the direction from C to O than when \({\varvec{\varepsilon}}\left( t \right)\) is reversed, which is in agreement with experimentally observed preferential ionization from the C side. The mechanism of the directional anisotropy in tunnel ionization of CO is attributed to a narrow hump near the C nucleus formed in \(v_{5\sigma }^{{{\text{eff}}}} (t)\) of the 5σ HOMO which results from the field-induced change in \(v_{{2{,}\,5\sigma }} (t).\) Analysis of effective potentials reveals that the suppression of 5σ ionization when \({\varvec{\varepsilon}}\left( t \right)\) points from O to C is correlated with the enhancement in high-order harmonic generation from 4σ HOMO-2. A hump structure is also found in \(v_{{{\text{HOMO}}}}^{{{\text{eff}}}} (t)\) of LiH interacting with an intense near-IR pulse, which identifies the ionization mechanism as “asymmetric charge-resonance enhanced ionization.”

It has been found that the optical properties and characteristics of exciton photoluminescence in thin organometallic perovskite layers, which are promising for application in high-efficiency solar cells, change when these layers are deposited on a crystalline silicon (c-Si) substrate. The observed shift of the photoluminescence band toward higher photon energies and a decrease in the lifetime of photoluminescence compared to layers deposited on a glass substrate with conducting metal oxide coating have been explained by the effect of an electric field that is formed in an organometallic perovskite/c-Si heterostructure and leads to the field ionization and the decay of excitons in the organometallic perovskite layer.

In this study, a novel planar MEMS-based gas ionization sensor based on the field ionization of zinc oxide nanowires is reported. Selective and seedless ZnO nanowires have been grown directly on gold electrodes by low-cost and low-temperature hydrothermal method. Low operating voltage with fast response and recovery times have been achieved for detecting Argon, Helium, Air + %32 RH, Nitrogen, Dry Air, Oxygen, and Carbon dioxide at ambient temperature in atmospheric pressure. Sharp tips of ZnO nanowires reduce the gas breakdown voltage of different gases as shown for Helium and Argon to about 115 V, 85 V respectively due to their local electric field enhancement characteristic. Furthermore, an excellent semi linear response (about 80 V decrease in breakdown voltage) was observed by introducing 250 ppm of NH3 to pure N2 in 4 stages from 0 ppm to 1000 ppm as ammonia gas sensor. In addition, ZnO nanowires protect high conductive Au cathode and anode against sputtering and deformation due to their superior physical, chemical and mechanical properties.

Laser-driven ion acceleration is often analyzed assuming that ionization reaches a steady state early in the interaction of the laser pulse with the target. This assumption breaks down for materials of high atomic number for which the ionization occurs concurrently with the acceleration process. Using particle-in-cell simulations, we have examined acceleration and simultaneous field ionization of copper ions in ultra-thin targets (20–150 nm thick) irradiated by a laser pulse with intensity 1 × 1021 W/cm2. At this intensity, the laser pulse drives strong electric fields at the rear side of the target that can ionize Cu to charge states with valence L-shell or full K-shell. The highly-charged ions are produced only in a very localized region due to a significant gap between the M- and L-shells’ ionization potentials and can be accelerated by strong, forward-directed sections of the field. Such an “ionization injection” leads to well-pronounced bunches of energetic, highly-charged ions. We also find that for the thinnest target (20 nm) a push by the laser further increases the ion energy gain. Thus, the field ionization, concurrent with the acceleration, offers a promising mechanism for the production of energetic, high-charge ion bunches.