High Ionization Rate Research Articles

MATHEMATICAL MODELING OF THE AEROION MODE IN A CAR

In this study, a mathematical method is proposed for calculating the concentration field of air ions of different polarities and dust levels in the passenger compartment, taking into account the geometry of the passenger compartment and seats, shelves, and other internal elements of the passenger compartment. The method also takes into account changes in the rate of the air flow ventilation, the location and number of ionizers, and sources of positive ions and dust, taking into account their different intensities and locations. On the basis of a numerical model for this method, software has been developed that allows users to carry out computational experiments without requiring much time for calculation. Based on the results, the optimal location of the ionizer in the passenger compartment of the car was determined to ensure comfortable conditions for the stay of passengers, which favorably affects their health. It has been found that the presence of two ionizers is optimal for creating comfort in the car with an ionization intensity of Q = n . 0 × 21 10 11 Q = n . 0 × 47 10 10 ions/s located at the top of the car. If there is one ionizer located on the dashboard or at the top of the car with a higher ionization rate than ions/s, it is not possible to simultaneously provide optimal ionization parameters for passengers in the front and rear seats of the car.

Effects of unsymmetrical magnetic field on discharge characteristics of Hall thruster with large height-radius ratio

The large height-radius ratio design of the Hall thruster increases the difference of radial distributions of magnetic field and plasma parameters in the channel, so that the optimal discharge effect of the thruster cannot be guaranteed under the symmetrical magnetic field configuration relative to the channel centerline. In this work, the effects of the unsymmetrical magnetic field on discharge characteristics of Hall thruster with large height-radius ratio were studied through experiments and PIC simulations. The results show that the thruster can realize stable discharge in a wide power range under unsymmetrical magnetic fields. Also, the unsymmetrical magnetic field plays a positive role in improving the discharge performance and prolonging the service life of the thruster. The inward-inclined magnetic field can effectively improve the discharge performance of the thruster, and the discharge efficiency can be increased by 1.5% under the rated working condition compared with the symmetrical magnetic field. The advantage in performance is mainly attributed to the improvement of ionization efficiency of propellant. The outward-inclined magnetic field is more conducive to prolong the service life of the thruster, and the peak value of ion power deposition on the inner wall can be reduced by 40% under the rated working condition due to the outward inclination of the ionization zone and the reduction of the radial electric field. However, under unsymmetrical magnetic field, the ionization zone deviates from the channel center, and the high ionization rate zone is more dispersed in distribution, thus leading to the increase in plume divergence angle. This study verifies that the unsymmetrical magnetic field has certain advantages under the structure of large height-radius ratio, which could be used as a guidance for the optimal design of Hall thruster with large height-radius ratio.

Suzaku observations of Fe K-shell lines in the supernova remnant W 51 C and hard X-ray sources in the proximity

Abstract In this paper, we investigate the Fe K-shell lines in the supernova remnant W 51 C and hard X-ray sources in the proximity. We measure the intensities of the Fe i Kα and Fe xxv Heα lines at 6.40 and 6.68 keV, respectively, and find that the intensity of the 6.68 keV line is consistent with the background level expected from previous studies, while that of the 6.40 keV line is higher at the significance level of 2.0σ. Given the presence of gamma-ray emission and high ionization rate point spatially coincident with the remnant, we conclude that the enhanced 6.40 keV line most likely originates from the interaction between low-energy cosmic rays and molecular clouds. Also, we discover an enhanced 6.68 keV line emission from the compact H ii region G49.0−0.3 at a significance level of 3.4σ. Spectral analysis reveals that the temperature and abundance of the thermal plasma with the 6.68 keV line is $kT=3.0^{+0.8}_{-0.7}$ keV and Z = 0.5 ± 0.2 solar, respectively. These values are explained by the thermal plasma generated by the stellar winds of O stars.

Improvement of microstructure and tribological properties of titanium nitride films by optimization of substrate bias current

Severe wear is a key factor affecting the work character and service life of the cutting tools used for dry cutting. The deposition of wear-resistant films on the cutting tools via magnetron sputtering is one of the most effective strategies, and the further improvement of the properties of the deposited films has attracted much attention. Plasma-enhanced magnetron sputtering possesses a much higher ionization rate than conventional magnetron sputtering and has been used to deposit dense hard wear-resistant film, but the influence of substrate bias current (Is) on the structure and properties of the films should be further studied. In this paper, plasma-enhanced magnetron sputtering technique was utilized to obtain an individually adjustable Is and TiN film was taken as an example to study the effects of Is on the properties of the films. It is found that the microstructure of the films is transformed from a loose columnar microstructure into a dense and featureless microstructure with increasing Is from 0.1 to 3.0 A, and the preferred growth orientation along TiN(111) is found at a high level of Is. As Is increases from 0.1 to 1.5 A, the grain size of the films is abruptly decreased, and the mechanical properties are significantly improved; but when Is further increases, the mechanical properties stay nearly unchanged. When Is is increased, the wear rate of TiN-coated samples is distinctly decreased at first, and then gradually increased. When Is is 3.0 A, the highest hardness of 38.7 GPa and lowest wear rate of 9.4 × 10–16 m3/(N•m) are obtained for the TiN-coated sample.

Low-Resistivity Cobalt and Ruthenium Ultra-Thin Film Deposition Using Bipolar HiPIMS Technique

Owing to the rapid growth of very large-scale integration technology at nanometer scales, cobalt and ruthenium interconnects are being used to solve the high-resistivity copper problem. However, with such interconnects, carbon contamination can occur during chemical vapor deposition and atomic layer deposition. Bipolar (BP) high-power impulse magnetron sputtering (HiPIMS) with a high ionization rate is an excellent vacuum process for depositing low-resistivity thin films. In this study, low-resistivity cobalt, ruthenium, and copper thin films were deposited using BP-HiPIMS, HiPIMS, and direct-current magnetron sputtering (DCMS). The resistivities of the cobalt, ruthenium, and copper thin films (<10 nm) deposited via BP-HiPIMS were 91.5, 75, and 35%, respectively, lower than the resistivities of the same film materials deposited using direct-current MS. To solve the low pass-through flux of cobalt, the target temperature was raised to the Curie temperature (approximately 1100 °C) using a thermal insulation backplate (Ti-6Al-4V), resulting in a resistivity reduction of about 73%. The study provides a novel method for the vacuum deposition of cobalt and ruthenium thin films.

Influence of Different Device Structures on the Degradation for Trench-Gate SiC MOSFETs: Taking Avalanche Stress as an Example.

The variations in the degradation of electrical characteristics resulting from different device structures for trench-gate SiC metal-oxide-semiconductor field effect transistors (MOSFETs) are investigated in this work. Two types of the most advanced commercial trench products, which are the asymmetric trench SiC MOSFET and the double-trench SiC MOSFET, are chosen as the targeted devices. The discrepant degradation trends caused by the repetitive avalanche stress are monitored. For the double-trench device, the conduction characteristic improves while the gate-drain capacitance (Cgd) increases seriously. It is because positive charges are injected into the bottom gate oxide during the avalanche process, which are driven by the high oxide electronic field (Eox) and the high impact ionization rate (I.I.) there. Meanwhile, for the asymmetric trench SiC MOSFET, the I–V curve under the high gate bias condition and the Cgd remain relatively stable, while the trench bottom is well protected by the deep P+ well. However, it’s threshold voltage (Vth) decreases more obviously when compared with that of the double-trench device and the inclined channel suffers from more serious stress than the vertical channel. Positive charges are more easily injected into the inclined channel. The phenomena and the corresponding mechanisms are analyzed and proved by experiments and technology computer-aided design (TCAD) simulations.

Mapping the high ionization rate of the GC starburst Sgr B2 through low HCO+ /N2H+ J=1-0 intensity ratios

We still do not understand which mechanisms dominate the heating and ionization of the extended molecular gas in galactic nuclei. The starburst Sgr B2, in the Galactic Center (GC), is an excellent template to spatially resolve the high-mass star-forming cores from the extended cloud environment, and to study the properties of the warm neutral gas in conditions likely prevalent in star-forming galaxies. We mapped ~1000 pc2 of Sgr B2 complex, using the IRAM 30m telescope, in the N2H+, HCO+ J=1-0 and SiO J=2-1 line emission. The extended nature of the N2H+ J=1-0 emission is remarkable. Compared to molecular clouds in the disk of the galaxy, the N2H+ J=1-0 emission is not confined to cold and dense cores and filaments. This can be explained by the high ionization rate (ζ ≳10−15 s−1), leading to overabundant H+3, He+, and N2H+. The enhanced ionization rate is likely responsible of the much lower line intensity ratio RI =HCO+/N2H+ J=1-0 observed in Sgr B2 (RI ≈ 2 ± 2), Arp 220 (RI ≈ 2), and NGC 253 (RI ≈ 5), compared to disk clouds such as Orion B (RI ≈ 24) and starburst galaxies such as M82 (RI ≈ 21).

SOLIS

Context. Isotopic fractionation is an important tool for investigating the chemical history of our Solar System. In particular, the isotopic fraction of nitrogen (14N/15N) is lower in comets and other pristine Solar System bodies with respect to the value measured for the protosolar nebula, suggesting a local chemical enrichment of 15N during the formation of the Solar System. Therefore, interferometric studies of nitrogen fractionation in Solar System precursors are needed for us to obtain clues about our astrochemical origins. Aims. In this work we have investigated the variation in the 14N/15N ratio in one of the closest analogues of the environment in which the Solar System was born: the protocluster OMC-2 FIR4. We present the first comparison at high angular resolution between HCN and N2H+ using interferometric data. Methods. We analysed observations of the HCN isotopologues H13CN and HC15N in the OMC-2 FIR4 protocluster. Specifically, we observed the transitions H13CN (1−0) and HC15N (1−0) with the NOrthern Extended Millimeter Array (NOEMA) within the context of the IRAM Seeds Of Life In Space (SOLIS) Large Program. We combined our results with analysis of archival data obtained with the Atacama Large Millimeter Array of N2H+ and its 15N isotopologues. Results. Our results show a small regional variation in the 14N/15N ratio for HCN, from ~250 to 500. The ratios in the central regions of FIR4, where the candidate protostars are located, are largely consistent with one another and within that range (~300). They also show little variation from the part of the protocluster known to harbour a high cosmic-ray ionisation rate to the portion with a lower rate. We also found a small variation in the 14N/15N ratio of N2H+ across different regions, from ~200 to ~400. Conclusions. These results suggest that local changes in the physical parameters occurring on the small linear scales probed by our observations in the protocluster do not seem to affect the 14N/15N ratio in either HCN or N2H+ and hence that this is independent of the molecule used. Moreover, the high level of irradiation due to cosmic rays does not affect the N fractionation either.

PDFCHEM: Fast simulations of the chemical ISM using probability distributions

We present PDFCHEM, a new numerical method able to compute the photodissociation region (PDR) chemistry of large-scale inhomogeneous ISM regions using probability distributions of physical parameters as an input. We distinguish between two visual extinctions, namely the ‘effective’ (AV,eff) referring to the local extinction and the ‘observed’ (AV,obs) referring to the extinction taken from observations. Using 1,200 pre-calculated PDR simulations, we apply PDFCHEM to two hypothetical AV,obs−PDFs, representing a diffuse region and a Giant Molecular Cloud. PDFchem is fast and can replace the computationally expensive hydrodynamical models in understanding the chemistry of the ISM in different environments, including at low metallicities and high cosmic-ray ionization rates.

Modelling cosmic masers in C-type shock waves – the coexistence of Class I CH3OH and 1720 MHz OH masers

ABSTRACT The collisional pumping of CH3OH and OH masers in non-dissociative C-type shock waves is studied. The chemical processes responsible for the evolution of molecule abundances in the shock wave are considered in detail. The large velocity gradient approximation is used to model radiative transfer in molecular lines. We present calculations of the optical depth in maser transitions of CH3OH and OH for a grid of C-type shock models that vary in cosmic ray ionization rate, gas density, and shock speed. We show that pre-shock gas densities nH, tot = 2 × 104–2 × 105 cm−3 are optimal for the pumping of methanol maser transitions. A complete collisional dissociation of methanol at the shock front takes place for shock speeds us ≳ 25 km s−1. At high pre-shock gas density nH, tot = 2 × 106 cm−3, the collisional dissociation of methanol takes place at shock speeds just above the threshold speed us ≈ 15–17.5 km s−1, corresponding to sputtering of icy mantles of dust grains. We show that the methanol maser transition E 4−1 → 30 at 36.2 GHz has an optical depth |τ| higher than that of the transition A+ 70 → 61 at 44.1 GHz at high cosmic ray ionization rate $\zeta _\mathrm{H_2} \gtrsim 10^{-15}$ s−1 and pre-shock gas density nH, tot = 2 × 104 cm−3. These results can be applied to the interpretation of observational data on methanol masers near supernova remnants and in molecular clouds of the Central Molecular Zone. At the same time, a necessary condition for the operation of 1720 MHz OH masers is a high ionization rate of molecular gas, $\zeta _\mathrm{H_2} \gtrsim 10^{-15}$ s−1. We find that physical conditions conducive to the operation of both hydroxyl and methanol masers are cosmic ray ionization rate $\zeta _\mathrm{H_2} \approx 10^{-15}$–3 × 10−15 s−1 and a narrow range of shock speeds 15 ≲ us ≲ 20 km s−1. The simultaneous observations of OH and CH3OH masers may provide restrictions on the physical parameters of the interstellar medium in the vicinity of supernova remnants.

High power impulse magnetron sputtering growth processes for copper nitride thin film and its highly enhanced UV - visible photodetection properties

Copper Nitride (Cu3N) thin films exhibit promising optoelectronic properties and are favourable for further applications in the field of photodetection, lithium-ion batteries etc. In this work, Cu3N thin film deposited by reactive High-Power Impulse Magnetron Sputtering (HiPIMS) and used for photodetection application for the first time. The microstructure of Cu3N nanocrystal shows the uniform crystalline morphology and less defects due to high target species ionization rate. The phase structure analysis results confirmed the presence of nitrogen within Cu3N thin film that is composed of Cu3N crystallites with anti-ReO3 structure. Remarkably, optical properties reveal significant absorbance and enhancement in ultraviolet (UV) and visible (Viz) range, which strongly affect the photodetection properties of fabricated ITO/Cu3N/ITO device. Excellent photosensitivity of 3792% was attained with a fixed light intensity. Furthermore, the photosensitivity was increased to 7443% with increased light intensity. It was perceived that the enhanced surface properties and perfect formation of ITO/Cu3N/ITO resulted in beneficial pn junction thus exhibits high performance and ultrafast electron-hole recombination. Also, the HiPIMS technique offers high-quality films with a dense and smooth surface that helped in enhancing photodetection. These outstanding results emanate Cu3N films could be potential candidate for future optoelectronic devices fabrication that can be applied in smart thin-film gadgets.

Effects of structured electrodes on electron power absorption and plasma uniformity in capacitive RF discharges

The electron power absorption dynamics and plasma uniformity in low pressure capacitively coupled RF discharges with structured electrodes are investigated by graphics processing unit-based 2d3v particle-in-cell/Monte Carlo simulations in argon gas. In the presence of planar electrodes, the plasma is radially nonuniform due to strong electron density peaks close to the reactor sidewall, which are caused by edge effects that locally enhance the electron power absorption and ionization. Such a local enhancement of these characteristics can also be achieved in a controllable manner by using a single ring-shaped rectangular trench embedded in the powered electrode close to the reactor center. This effect is understood by analyzing the trajectories of selected electrons as well as the time evolution of their energy and velocity inside and above such trenches. Electrons are found to gain high energies inside the trench by bouncing between the sheaths at the trench walls during the sheath expansion phase. Combined with the cross-firing of energetic electrons at the trench orifice, this leads to high local ionization rates. Using these trench effects, the plasma uniformity above the wafer placed on a planar powered electrode can be remarkably improved by including multiple trenches in the opposing grounded electrode, which enhance the ionization and plasma density at their respective radial positions. Meanwhile, the ion flux-energy distribution function at the wafer is found to be almost unaffected.

The distribution and origin of C2H in NGC 253 from ALCHEMI

Context. Observations of chemical species can provide insights into the physical conditions of the emitting gas however it is important to understand how their abundances and excitation vary within different heating environments. C2H is a molecule typically found in PDR regions of our own Galaxy but there is evidence to suggest it also traces other regions undergoing energetic processing in extragalactic environments. Aims. As part of the ALCHEMI ALMA large program, we map the emission of C2H in the central molecular zone of the nearby starburst galaxy NGC 253 at 1.6″ (28 pc) resolution and characterize it to understand its chemical origins. Methods. We used spectral modeling of the N = 1−0 through N = 4−3 rotational transitions of C2H to derive the C2H column densities towards the dense clouds in NGC 253. We then use chemical modeling, including photodissociation region (PDR), dense cloud, and shock models to investigate the chemical processes and physical conditions that are producing the molecular emission. Results. We find high C2H column densities of ∼1015 cm−2 detected towards the dense regions of NGC 253. We further find that these column densities cannot be reproduced if it is assumed that the emission arises from the PDR regions at the edge of the clouds. Instead, we find that the C2H abundance remains high even in the high visual extinction interior of these clouds and that this is most likely caused by a high cosmic-ray ionization rate.

The low temperature growth of stable p-type ZnO films in HiPIMS

In this study, the influence of substrate temperature on properties of Al-N co-doped p-type ZnO films is explored. Benefitting from the high ionization rate in high-power impulsed magnetron sputtering, the concentration of ionized nitrogen N+ and ionized zinc Zn+ were increased, which promoted the formation of ZnO films and lowered the necessary substrate temperature. After optimization, a co-doped p-type ZnO thin film with a resistivity lower than 0.35 Ω cm and a hole concentration higher than 5.34 × 1018 cm−3 is grown at 280 °C. X-ray diffraction results confirm that Al-N co-doping does not destruct the ZnO wurtzite structure. X-ray photoelectron spectroscopy demonstrates that the presence of Al promotes the formation of acceptor (No) defects in ZnO films, and ensures the role of Al in stabilizing p-type ZnO.

Characterisation of density linear control in a helicon plasma source with tunable antenna wavenumber spectra

The helicon plasma source is widely used in various fields due to its high ionisation rate. The helicon wave dispersion relationship indicates that the density is proportional to axial wavenumbers. In this study, we systematically investigated how the plasma density varies with the axial wavenumber by employing several phased antenna systems. The antenna comprised different numbers of loops, and each loop was connected to an individual radio frequency power source. We adjusted the plasma density from approximately 1011 to 1013 cm−3. Such two orders of magnitude adjustments may provide a novel operation mode for helicon applications. The density was linearly proportional to the axial wavenumber, when the axial wavenumber was not exceptionally large. In addition, in a low magnetic field, density peaks were observed in all three antenna configurations. The density peak appears irrespective of whether the Landau damping frequency is higher than collision frequency. This finding suggested that Landau damping and other mechanisms can lead to such a phenomenon of low field density peak.

Influence of neutral depletion on blue core in argon helicon plasma

Blue core (BC) is a special spectral phenomenon in argon helicon plasma, with intense blue lights from ion emission around the radial center of discharge tube. In this paper, the characteristics of BC in argon (Ar) helicon plasma were investigated experimentally from aspects of discharge mode transitions, plasma spatial distributions, and spectral features. It is found that the BC generally appears at strong magnetic field (480 G or above in this work) with high plasma density in wave mode, accompanied by exponentially rising of ion line intensity. The electron density and temperature, the neutral density and temperature, and the line emission intensity show a radial profile with a central peak in BC mode. The steep gradient of ion line intensity (corresponding to the ion density) defines a clear boundary of the core. Further, a pressure balance model was developed to investigate the influence of neutral depletion on BC formation. The neutral density is depleted significantly from 7.24×1013 to 0.38 × 1013 cm−3 at magnetic field of 600 G in BC mode, while to 3.13 × 1013 cm−3 at magnetic field of 250 G in normal wave (NW) mode. The ionization rate in BC reaches as high as 70% compared with 9.6% of that in NW mode. The ionization rate and the ion line intensity show similar radial profiles, indicating the BC phenomenon is closely related to the distribution of peaked ion density and hollowed neutral density. Fundamentally, the central electron heating and strong magnetic field contribute to the centrally local high ionization rate and strong neutral heating. The severe neutral depletion with prominent central heating is considered to be the immediate cause of appearance of blue core.

The double signature of local cosmic-ray acceleration in star-forming regions

Context.Recently, there has been an increased interest in the study of the generation of low-energy cosmic rays (&lt; 1 TeV) in shocks situated on the surface of a protostar or along protostellar jets. These locally accelerated cosmic rays offer an attractive explanation for the high levels of non-thermal emission and ionisation rates observed close to these sources.Aims.The high ionisation rate observed in some protostellar sources is generally attributed to shock-generated UV photons. The aim of this article is to show that when synchrotron emission and a high ionisation rate are measured in the same spatial region, a locally shock-accelerated cosmic-ray flux is sufficient to explain both phenomena.Methods.We assume that relativistic protons and electrons are accelerated according to the first-order Fermi acceleration mechanism, and we calculate their emerging fluxes at the shock surface. These fluxes are used to compute the ionisation rate and the non-thermal emission at centimetre wavelengths. We then apply our model to the star-forming region OMC-2 FIR 3/FIR 4. Using a Bayesian analysis, we constrain the parameters of the model and estimate the spectral indices of the non-thermal radio emission, the intensity of the magnetic field, and its degree of turbulence.Results.We demonstrate that the local cosmic-ray acceleration model makes it possible to simultaneously explain the synchrotron emission along the HOPS 370 jet within the FIR 3 region and the ionisation rate observed near the FIR 4 protocluster. In particular, our model constrains the magnetic field strength (∼250−450 μG), its turbulent component (∼20−40 μG), and the jet velocity in the shock reference frame for the three non-thermal sources of the HOPS 370 jet (between 350 km s−1and 1000 km s−1).Conclusions.Beyond the modelling of the OMC-2 FIR 3/FIR 4 system, we show how the combination of continuum observations at centimetre wavelengths and molecular transitions is a powerful new tool for the analysis of star-forming regions: These two types of observations can be simultaneously interpreted by invoking only the presence of locally accelerated cosmic rays, without having to resort to shock-generated UV photons.

Submillimeter imaging of the Galactic Center starburst Sgr B2

Context. Star-forming galaxies emit bright molecular and atomic lines in the submillimeter and far-infrared (FIR) domains. However, it is not always clear which gas heating mechanisms dominate and which feedback processes drive their excitation. Aims. The Sgr B2 complex is an excellent template to spatially resolve the main OB-type star-forming cores from the extended cloud environment and to study the properties of the warm molecular gas in conditions likely prevailing in distant extragalactic nuclei. Methods. We present 168 arcmin2 spectral images of Sgr B2 taken with Herschel/SPIRE-FTS in the complete ~450−1545 GHz band. We detect ubiquitous emission from mid-J CO (up to J = 12−11), H2O 21,1−20,2, [C I] 492, 809 GHz, and [N II] 205 μm lines. We also present velocity-resolved maps of the SiO (2−1), N2H+, HCN, and HCO+ (1−0) emission obtained with the IRAM 30 m telescope. Results. The cloud environment (~1000 pc2 around the main cores) dominates the emitted FIR (~80%), H2O 752 GHz (~60%) mid-J CO (~91%), [C I] (~93%), and [N II] 205 μm (~95%) luminosity. The region shows very extended [N II] 205 μm emission (spatially correlated with the 24 and 70 μm dust emission) that traces an extended component of diffuse ionized gas of low ionization parameter (U ≃ 10−3) and low LFIR / MH2 ≃ 4−11 L⊙M⊙−1 ratios (scaling as ∝Tdust6). The observed FIR luminosities imply a flux of nonionizing photons equivalent to G0 ≈ 103. All these diagnostics suggest that the complex is clumpy and this allows UV photons from young massive stars to escape from their natal molecular cores. The extended [C I] emission arises from a pervasive component of neutral gas with nH ≃ 103 cm−3. The high ionization rates in the region, produced by enhanced cosmic-ray (CR) fluxes, drive the gas heating in this component to Tk ≃ 40−60 K. The mid-J CO emission arises from a similarly extended but more pressurized gas component (Pth / k ≃ 107 K cm−3): spatially unresolved clumps, thin sheets, or filaments of UV-illuminated compressed gas (nH ≃ 106 cm−3). Specific regions of enhanced SiO emission and high CO-to-FIR intensity ratios (ICO / IFIR ≳ 10−3) show mid-J CO emission compatible with C-type shock models. A major difference compared to more quiescent star-forming clouds in the disk of our Galaxy is the extended nature of the SiO and N2H+ emission in Sgr B2. This can be explained by the presence of cloud-scale shocks, induced by cloud-cloud collisions and stellar feedback, and the much higher CR ionization rate (&gt;10−15 s−1) leading to overabundant H3+ and N2H+. Conclusions. Sgr B2 hosts a more extreme environment than star-forming regions in the disk of the Galaxy. As a usual template for extragalactic comparisons, Sgr B2 shows more similarities to nearby ultra luminous infrared galaxies such as Arp 220, including a “deficit” in the [C I] / FIR and [N II] / FIR intensity ratios, than to pure starburst galaxies such as M 82. However, it is the extended cloud environment, rather than the cores, that serves as a useful template when telescopes do not resolve such extended regions in galaxies.

Modeling chemistry during star formation: water deuteration in dynamic star-forming regions

Context. Recent observations of the HDO/H2O ratio toward protostars in isolated and clustered environments show an apparent dichotomy, where isolated sources show higher D/H ratios than clustered counterparts. Establishing which physical and chemical processes create this differentiation can provide new insights into the chemical evolution of water during star formation and the chemical diversity during the star formation process and in young planetary systems. Aims. We seek to determine to what degree the local cloud environment influences the D/H ratio of water in the hot corinos toward low-mass protostars and establish which physical and chemical conditions can reproduce the observed HDO/H2O and D2O/HDO ratios in hot corinos. Methods. The evolution of water during star formation is modeled using 3D physicochemical models of a dynamic star-forming environment. The physical evolution during the protostellar collapse is described by tracer particles from a 3D MHD simulation of a molecular cloud region. Each particle trajectory is post-processed using RADMC-3D to calculate the temperature and radiation field. The chemical evolution is simulated using a three-phase grain-surface chemistry model and the results are compared with interferometric observations of H2O, HDO, and D2O in hot corinos toward low-mass protostars. Results. The physicochemical model reproduces the observed HDO/H2O and D2O/HDO ratios in hot corinos, but shows no correlation with cloud environment when similar initial conditions are tested. The observed dichotomy in water D/H ratios requires variation in the initial conditions, for example the duration and temperature of the prestellar phase. Reproducing the observed D/H ratios in hot corinos requires a prestellar phase duration t ~ 1−3 Myr and temperatures in the range T ~ 10−20 K prior to collapse. Furthermore, high cosmic-ray ionization rates (ξH2 ~ 10−15 s−1) appear to be incompatible with the observed D/H ratios toward low-mass protostars. Conclusions. This work demonstrates that the observed differentiation between clustered and isolated protostars stems from differences in the molecular cloud or prestellar core conditions and does not arise during the protostellar collapse itself. The observed D/H ratios for water in hot corinos are consistent with chemical inheritance of water, and no resetting during the protostellar collapse, providing a direct link between the prestellar chemistry and the hot corino.

Raised Source/Drain (RSD) and Vertical Lightly Doped Drain (LDD) Poly-Si Thin-Film Transistor

The raised source/drain (RSD) structure is one of thin film transistor designs that is often used to improve device characteristics. Many studies have mentioned that the high impact ionization rate occurring at a drain side can be reduced, owing to a raised source/drain area that can disperse the drain electric field. In this study, we will discuss how the electric field at the drain side of an RSD device is reduced by a vertical lightly doped drain (LDD) scheme rather than a RSD structure. We used different raised source/drain forms to simulate the drain side electric field for each device, as well as their output characteristics, using Integrated Systems Engineering (ISE-TCAD) simulators. Different source and drain thicknesses and doping profiles were applied to verify the RSD mechanism. We found that the electric fields of a traditional device and uniform doping RSD structures are almost the same (~2.9 × 105 V/cm). The maximum drain electric field could be reduced to ~2 × 105 V/cm if a vertical lightly doped drain RSD scheme was adopted. A pure raised source/drain structure did not benefit the device characteristics if a vertical lightly doped drain design was not included in the raised source/drain areas.