Thermal Desorption Peak Research Articles

Deuterium retention and desorption behavior of W-Ta-Cr-V high entropy alloy

Deuterium retention and desorption behavior of W-Ta-Cr-V films under deuterium plasma irradiation were studied. The W-Ta-Cr-V films were prepared on the molybdenum (Mo) substrate by magnetron sputtering. Subsequently, all films annealed at 1000 °C were exposed to deuterium plasma at a flux of 8.13 × 1019 D/m2·s for 9 h to achieve an irradiation fluence of 2.63 ×1024 D/m2. Electron backscattered diffraction (EBSD) was used to characterize the texture and average grain size of films. Doppler broadening spectrometry of positron annihilation (DBS-PA) was carried out with an energy-variable slow positron beam to detect the concentration of vacancy-type defects in the films. The results suggest that there are fewer vacancy-type defects inside W-Ta-Cr-V grains. Deuterium retention and the desorption behavior of W-Ta-Cr-V were studied by compared to pure tungsten films. In the 300–800 K temperature range, the peaks of thermal desorption spectroscopy (TDS) of W-Ta-Cr-V films are substantially consistent with that of the W films. Notably, in the range of 800 K-1000 K, W-Ta-Cr-V film has no thermal desorption peak. We attribute this to the large lattice distortion and low vacancy formation energy, which inhibit the growth of voids inside the grains of W-Ta-Cr-V films. The total deuterium retention of W-Ta-Cr-V films is compared with that of W films. It is measured by TDS that the deuterium retention of W-Ta-Cr-V films is nearly 5 times that of W films. Based on the analysis of the TDS spectra, the higher deuterium retention in W-Ta-Cr-V films is due to the more grain boundary defects.

The erosion and retention properties of tungsten trioxide films exposed to low energy deuterium ions: Temperature dependence

The erosion behavior and retention properties of tungsten trioxide (WO3) and W films exposed to low energy (∼50 eV) deuterium (D) ions were studied at surface temperature from 403 K to 758 K. The initial thickness of WO3 and W films are approximately 7.0 × 1018 atoms cm−2 and 1.8 × 1018 atoms cm−2, respectively. The erosion rate of oxygen (O) by deuterium is thermally enhanced, and tungsten (W) atoms can be sputtered rapidly in the form of WxOy molecules and/or W atoms at higher temperatures due to the relatively weak binding energy between W and O, resulting on an increase in the W sputtering yield with temperature. Nano-sized pinholes appear on the surface at 403 K, however, pinholes with much smaller sizes and cracks appear on the surface at higher temperatures, and their density increases with increasing temperatures. The synergistic effects of ion irradiation and temperature cause the structure change of tungsten oxide films according to Raman spectra. X-ray photoelectron spectroscopy shows that after irradiation with D ions, metallic W appears on the surface, but the tungsten oxide is still present. Trapped D is almost uniformly distributed in WO3 and its concentration is much higher than that in W at lower irradiation temperature, which is mainly related to D atoms chemically bonded to O atoms with the formation of deuterium tungsten bronze. The thermal desorption peak temperatures of D2 (∼465 K or 500 K) and D2O (∼495 K, 730 K (or 790 K) and 825 K) are related to the heating rate (1 K s−1) and it implies that the deuterium tungsten bronze is decomposed under the low D ion irradiation temperatures.

Revealing Hydrogen States in Carbon Structures by Analyzing the Thermal Desorption Spectra

An effective methodology for the detailed analysis of thermal desorption spectra (TDS) of hydrogen in carbon structures at micro- and nanoscale was further developed and applied for a number of TDS data of one heating rate, in particular, for graphite materials irradiated with atomic hydrogen. The technique is based on a preliminary description of hydrogen desorption spectra by symmetric Gaussians with their special processing in the approximation of the first- and the second-order reactions. As a result, the activation energies and the pre-exponential factors of the rate constants of the hydrogen desorption processes are determined, analyzed and interpreted. Some final verification of the results was completed using methods of numerical simulation of thermal desorption peaks (non-Gaussians) corresponding to the first- and the second-order reactions. The main research finding of this work is a further refinement and/or disclosure of poorly studied characteristics and physics of various states of hydrogen in microscale graphite structures after irradiation with atomic hydrogen, and comparison with the related results for nanoscale carbon structures. This is important for understanding the behavior and relationship of hydrogen in a number of cases of high energy carbon-based materials and nanomaterials.

Chemical changes induced during heating of acetonitrile-rich ice pre-irradiated by X-rays and its implication in astrochemistry

In this work, we investigate the effects induced by the heating of acetonitrile-rich ice from 13 K to 350 K. Before the heating, the sample was irradiated at 13 K by broadband X-rays (6 eV to 2 keV), which trigger the production of new molecules, such as HCN, H2CCNH, CH4 and CH3NC (see Carvalho and Pilling, 2020) and also induced desorption of frozen species to gas-phase. New spectra were collected during heating to investigate whether new species, not present before at lower temperatures, appear due to thermal processing. New infrared bands were identified at temperatures around 120 K and 300 K, from which it was possible to notice the possible presence of HCN/CN radical, ammonia and C2N2. It was also verified that acetonitrile has a thermal desorption peak between 120 K and 200 K, which yields to the vanishing of acetonitrile within the sample for temperatures of 200 K and above. Some infrared features assigned before solely to acetonitrile remain for sample temperatures >200 K, which indicates the presence of blended species with similar infrared features. From analyzing those blended peaks, we also perceived the possible presence of aminoacetonitrile.

Peaks of Hydrogen Thermal Desorption: Simulation and Interpretation

Different models of hydrogen thermal desorption peaks have been analyzed. The model of volume-averaged concentration dynamics with a continuum parameter makes it possible to integrally take into consideration the dominance of limiting factors: diffusion and recombination of atoms into desorbing molecules. An analytical symmetry criterion for peaks versus the method of expanding a composed spectrum into a series of Gaussian curves is suggested. Modifications of (i) the Kissinger method to estimate the activation energy of desorption in experiments with several material heating rates and (ii) a procedure for solving the inverse problem of unimodal peak parametrical identification from one heat rate are presented. Comparison with the diffusion model with dynamic boundary conditions has been carried out. It has been shown that local peaks may arise not only because of release of hydrogen atoms with different binding energies captured by volume traps, but also because of interaction between volume and surface processes and heat-induced surface structure modifications. The parameters of deuterium thermal desorption from ISO-880U graphite have been estimated.

Investigation of the Laser Radiation Focusing Effect on the Sensitivity of Analysis of the Hydrogen Isotope Content in Plasma-Deposited Layers by Laser-Induced Desorption

The efficiency of the laser-induced desorption method as a detector of hydrogen isotopes under pulsed laser irradiation (wavelength 1064 nm, 100 mJ, duration 10 ns) for different power densities of incident radiation on deuterium-saturated thin titanium films was investigated. When the power flow density increases by 16 times, the intensity of the thermal desorption peak increases by more than 2 orders of magnitude. Long-term repeated irradiation of the surface does not lead to significant depletion of the content of hydrogen isotopes in the studied layers, allowing their further ex-situ analysis.

Пики термодесорбции водорода: моделирование и интерпретация

Various models of hydrogen thermal desorption peaks are analyzed. The dynamics model of the volume-averaged concentration with a continuum parameter allows integrally taking into account the degree of dominance of the limiting factors (diffusion and recombination of atoms into molecules during desorption). An analytical criterion for peaks symmetry is proposed in the context of comparison with the method of decomposing the component spectrum into the sum of Gaussian. Modifications of the Kissinger method for estimating the activation energy of desorption in experiments with several heating rates and procedures for solving the inverse problem of parametric identification of a unimodal peak using only one heating rate are presented. A comparative with a diffusion model with dynamic boundary conditions is performed. It is shown that the cause of local peaks can be not only capture with different binding energies but also the dynamics of interaction of bulk and surface processes, change in the surface structure during heating.

Improved methods for signal processing in measurements of mercury by Tekran<sup>®</sup> 2537A and 2537B instruments

Abstract. Atmospheric Hg measurements are commonly carried out using Tekran® Instruments Corporation's model 2537 Hg vapor analyzers, which employ gold amalgamation preconcentration sampling and detection by thermal desorption (TD) and atomic fluorescence spectrometry (AFS). A generally overlooked and poorly characterized source of analytical uncertainty in those measurements is the method by which the raw Hg atomic fluorescence (AF) signal is processed. Here I describe new software-based methods for processing the raw signal from the Tekran® 2537 instruments, and I evaluate the performances of those methods together with the standard Tekran® internal signal processing method. For test datasets from two Tekran® instruments (one 2537A and one 2537B), I estimate that signal processing uncertainties in Hg loadings determined with the Tekran® method are within ±[1 % + 1.2 pg] and ±[6 % + 0.21 pg], respectively. I demonstrate that the Tekran® method can produce significant low biases (≥ 5 %) not only at low Hg sample loadings (< 5 pg) but also at tropospheric background concentrations of gaseous elemental mercury (GEM) and total mercury (THg) (∼ 1 to 2 ng m−3) under typical operating conditions (sample loadings of 5–10 pg). Signal processing uncertainties associated with the Tekran® method can therefore represent a significant unaccounted for addition to the overall ∼ 10 to 15 % uncertainty previously estimated for Tekran®-based GEM and THg measurements. Signal processing bias can also add significantly to uncertainties in Tekran®-based gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) measurements, which often derive from Hg sample loadings < 5 pg. In comparison, estimated signal processing uncertainties associated with the new methods described herein are low, ranging from within ±0.053 pg, when the Hg thermal desorption peaks are defined manually, to within ±[2 % + 0.080 pg] when peak definition is automated. Mercury limits of detection (LODs) decrease by 31 to 88 % when the new methods are used in place of the Tekran® method. I recommend that signal processing uncertainties be quantified in future applications of the Tekran® 2537 instruments.

D2 retention and microstructural evolution during He irradiation in candidate plasma facing material W-La2O3 alloy

A dispersion-strengthened W alloy, W-La2O3, was developed by spark plasma sintering (SPS). The D2 retention and microstructural evolution under 5-keV He irradiation at high temperatures were investigated. Although the density of the W-La2O3 alloy was lower than that of commercially available W, the D2 retention did not change significantly. In addition, the D2 thermal desorption peak, which did not appear in commercial W, appeared at ∼700 K due to the dissociation from D to vacancy clusters. In W-La2O3, the formation of He bubbles was observed at 773 K, 973 K and 1173 K. As the irradiation temperature was increased, void swelling also increased. For the same temperature, the formation of He bubbles was easier for W-La2O3 than for commercial W. This is considered to be the cause of low density of W-La2O3. W-La2O3 had a higher density of vacancies before He irradiation. The suppression of vacancy aggregation induced by the dispersion of La2O3 as the second phase appeared only at a high irradiation doses.

Characterization of thermal desorption with the Deans-switch technique in gas chromatographic analysis of volatile organic compounds

This study presents a novel application based on the Deans-switch cutting technique to characterize the thermal-desorption (TD) properties for gas chromatographic (GC) analysis of ambient volatile organic compounds (VOCs). Flash-heating of the sorbent bed at high temperatures to desorb trapped VOCs to GC may easily produce severe asymmetric or tailing GC peaks affecting resolution and sensitivity if care is not taken to optimize the TD conditions. The TD peak without GC separation was first examined for the quality of the TD peak by analyzing a standard gas mixture from C2 to C12 at ppb level. The Deans switch was later applied in two different stages. First, it was used to cut the trailing tail of the TD peak, which, although significantly improved the GC peak symmetry, led to more loss of the higher boiling compounds than the low boiling ones, thus suggesting compound discrimination. Subsequently, the Deans switch was used to dissect the TD peak into six 30s slices in series, and an uneven distribution in composition between the slices were found. A progressive decrease in low boiling compounds and increase in higher boiling ones across the slices indicated severe inhomogeneity in the TD profile. This finding provided a clear evidence to answer the discrimination problem found with the tail cutting approach to improve peak symmetry.Through the use of the innovated slicing method based on the Deans-switch cutting technique, optimization of TD injection for highly resolved, symmetric and non-discriminated GC peaks can now be more quantitatively assessed and guided.

On the annealing of radiation-induced point defects in tungsten

The interaction between deuterium and radiation-induced point defects in tungsten and the stages of their transformation and annealing are investigated by means of thermal-desorption spectroscopy. Primary defects, mainly vacancies, are created using 10-keV D+ ions at room temperature. In investigating the evolution of radiation-induced defects, irradiated samples are annealed at temperatures of 550–1400 K and the subsequent filling of defects is carried out by deuterium after sample irradiation with D3+ ions with an energy of 0.67 keV/deuteron at room temperature. The characteristic positions of thermal desorption peaks, as well as the temperatures of vacancy clusterization and annealing of defects, are determined.

Solvation of 3-Methylpentane in Nanoconfined Water and Methanol at Cryogenic Temperatures

The solvation of 3-methylpentane (3MP) in thin films of water and methanol, as well as the effect of a graphite substrate, has been investigated based on a multiplicity of thermal desorption peaks. The 3MP molecules desorbed from the free surface, film interior, and substrate interface are clearly distinguishable; the distribution of molecules in these three configurations depends on the thickness and thermal history of the films. The 3MP adspecies is incorporated in the methanol monolayer due to surface diffusion of methanol and the attractive interaction of the graphite substrate irrespective of methanol’s thermal history. In contrast, when 3MP is adsorbed on methanol multilayers, a porous structure is required for 3MP to be solvated. The solvation force overcomes the attractive force of 3MP on graphite when the multilayer of methanol is present. The water multilayer has fundamentally no effects on the solvation of 3MP when 3MP is in direct contact with graphite. However, the 3MP molecules detach from t...

Tritium release experiments on Li4SiO4 pebbles from TRINPC-I experiments: Effects of water adsorption and hydrogen gas

Out-of-pile tritium release experiments under different water uptake contents and purge gas chemistry were performed on Li4SiO4. Water measurement was performed on samples under different experimental procedures. It was found that water was adsorbed on the sample during its transferring and storage process. A strong dependence of tritium release behavior on water uptake was determined. By doping H2 in the sweep gas, the formation of water in orthosilicate was observed in addition to the isotope exchange reaction with H2 gas. Thermal desorption peaks of the water formation reaction and H2 isotope exchange reaction appeared at 668°C and 463°C, respectively, at ramping rate of 5°C/min.

Adsorption and dissociation kinetics of alkanes on CaO(100)

The adsorption kinetics of ethane, butane, pentane, and hexane on CaO(100) have been studied by multi-mass thermal desorption (TDS) spectroscopy. The sample cleanliness was checked by Auger electron spectroscopy. A molecular and dissociative adsorption pathway was evident for the alkanes, except for ethane, which does not undergo bond activation. Two TDS peaks appeared when recording the parent mass, which are assigned to different adsorption sites/configurations of the molecularly adsorbed alkanes. Bond activation leads to desorption of hydrogen and several alkane fragments assigned to methane and ethylene formation. Only one TDS feature is seen in this case. Formation of carbon residuals was absent.

Influence of the mobility of oxygen on the reactivity of La1 − x Sr x MnO3 perovskites in methane oxidation

Radically different dependences of the activity of La1 − xSrxMnO3 (x = 0−0.5) perovskites in methane oxidation on the degree of substitution of strontium for lanthanum are observed for low and high temperatures. Unsubstituted LaMnO3 exhibits the highest activity in the temperature range from 300 to 500°C, while the sample with the maximum degree of substitution (La0.5Sr0.5MnO3) shows the highest activity at higher temperatures of 700–900°C. In the low temperature region, the activity of La1t - xSrxMnO3 is determined by the amount of weakly bound (overstoichiometric) oxygen, which is formed in cation-deficient lattices and is characterized by a thermal desorption peak with Tmax = 705°C. At higher temperatures (800–900°C), the strongly bound oxygen of the catalyst lattice is involved in the formation of the reaction products under both unsteady- and steady-state conditions. As a consequence, the catalytic activity in methane oxidation correlates with the apparent rate constant of oxygen diffusion in the oxide bulk.

Oxygen desorption from polycrystalline palladium: Thermal desorption of O2 from a chemisorbed layer of Oads in the course of the decomposition of PdO surface oxide and in the release of oxygen from the bulk of palladium

The desorption of oxygen from polycrystalline palladium (Pd(poly)) was studied using temperature-programmed desorption (TPD) at 500–1300 K and the amounts of oxygen absorbed by palladium (n) from 0.05 to 50 monolayers. It was found that the desorption of O2 from Pd(poly), which occurred from a chemisorbed oxygen layer (Oads), in the release of oxygen from a near-surface metal layer in the course of the decomposition of PdO surface oxide, and in the release of oxygen from the bulk of palladium (Oabs), was governed by repulsive interactions between Oads atoms and the formation and decomposition of Oads-Pd*-Oabs structures (Pd* is a surface palladium atom). At θ ≤ 0.5, the repulsive interactions between Oads atoms (ɛaa = 10 kJ/mol) resulted in the desorption of O2 from Pd(poly) at 650–950 K. At 0.5 ≤ n ≤ 1.0, the release of inserted oxygen from a near-surface palladium layer occurred during TPD in the course of the migration of Oabs atoms to the surface and the formation-decomposition of Oads-Pd*-Oabs structures. As a result, the desorption of O2 occurred in accordance with a first-order reaction with a thermal desorption (TD) peak at Tmax ∼ 700 K. At 1.0 ≤ n ≤ 2.0, the decomposition of PdO surface oxide occurred at a constant surface cover-age with oxygen during TPD in the course of the formation-decomposition of Oads-Pd*-Oabs structures. Because of this, the desorption of O2 occurred in accordance with a zero-order reaction at low temperatures with a TD peak at Tmax ∼ 675 K. At 1.0 ≤ n ≤ 50, oxygen atoms diffused from deep palladium layers in the course of TPD and arrived at the surface at high temperatures. As a result, O2 was desorbed with a high-temperature TD peak at T > 750 K.

Effect of Cr and Zr Dopes on Hydrogen Behaviour in Rapidly Solidified Aluminium Foils

Hydrogen (H) behaviour in materials was investigated in rapidly solidified (RS) foils of pure aluminium (Al), Al-0.4 Cr and Al-0.25 Zr alloys (at %) by means of thermal desorption spectroscopy (TDS). In addition, Al-0.25; 0.3 Zr alloys were examined with respect to microstructure and its instability during the thermal process using SEM and microhardness measurements. The effect of dopes and heating rate on H desorption was summarized. The lowest energy desorption is attributed with significant thermal desorption peak which temperature was found is correlated with sample composition.

Chemisorption of water and carbon dioxide on nanostructured BaTiO3–SrTiO3(001) surfaces

The interaction of water and carbon dioxide with nanostructured epitaxial (Ba,Sr)TiO3(001) thin film and bulk single crystal SrTiO3(001) surfaces was studied using x-ray photoemission spectroscopy (XPS), thermal desorption spectroscopy (TDS), and density functional theory (DFT). On both surfaces, XPS and TDS indicate D2O and CO2 chemisorb at room temperature with broad thermal desorption peaks (423–723 K) and a peak desorption temperature near 573 K. A comparison of thermal desorption Redhead activation energies to adsorption energies calculated using DFT indicates that defect surface sites are important for the observed strong adsorbate-surface reactivity. Numerical calculations of the competetive adsorption/desorption equilibria for H2O and CO2 on SrTiO3(001) surfaces show that for typical atmospheric concentrations of 0.038% carbon dioxide and 0.247% water vapor the surfaces are covered to a large extent with both adsorbates. The high desorption temperature indicates that these adsorbates have the potential to impact measurements of the electronic structure of BaTiO3–SrTiO3(001) surfaces exposed to air, or prepared in high vacuum deposition systems, as well as the electrical properties of thin film ATiO3-based devices.

Interaction between oxygen and polycrystalline palladium at O2 pressures of 10−6–10 Pa

The interaction between oxygen and polycrystalline palladium (Pd(poly)) at \( P_{O_2 } \) = 2.6 × 10−6–10 Pa and T = 300–1300 K was studied by the thermal desorption (TD) method. The interaction between O2 and Pd(poly) is governed by the O2 pressure and the sample temperature. At low pressures of \( P_{O_2 } \) (≤1.3 × 10−5 Pa), O2 is chemisorbed dissociatively on the Pd(poly) surface. During chemisorption, the Oads-surface bond energy and the O2 sticking coefficient gradually decrease as the surface coverage θ increases. At \( P_{O_2 } \) ≥ 10−2 Pa and T ≤ 500 K, after the saturation of the Oads layer (θ ∼ 0.5), Oads atoms penetrate under the surface layer of the metal to form surface palladium oxide. At \( P_{O_2 } \) ≥ 1 Pa and T > 500 K, after the saturation of the surface oxide film 2 ML in thickness (n ∼ 2), Oads atoms penetrate into the oxide film and then into the subsurface palladium layer and diffuse deep into the metal bulk. As a result, the oxygen uptake at 700 K is n ∼ 50. Upon heating, the surface oxides decompose, desorbing O2, which gives rise to a low-temperature TD peak with Tmax = 715 K. The release of oxygen inserted in the subsurface layers of palladium shows itself as a distinct high-temperature TD peak with Tmax ≥ 750 K.

D2 desorption kinetics on amorphous solid water: from compact to porous ice films

The desorption kinetics of D(2) from amorphous solid water (ASW) films have been studied by the temperature-programmed desorption (TPD) technique in the 10-30 K temperature range. Compact (and nonporous) films were grown at 120 K over a copper substrate. Ultra-thin porous films were additionally grown at 10 K over the compact base. The TPD spectra from compact and from up to 20 monolayers (ML) porous films were compared. The simulation of the TPD experimental traces provides the corresponding D(2) binding-energy distributions. As compared to the compact case, the binding-energy distribution found for the 10 ML porous film clearly extends to higher energies. To study the transition from compact to porous ice, porous films of intermediate thicknesses (<10 ML), including ultra-thin films (<1 ML), were grown over the compact substrate. The thermal D(2) desorption peak was found to shift to higher temperatures as the porous ice network was progressively formed. This behavior can be explained by the formation of more energetic binding sites related to porous films. TPD spectra were also modelled by using a combination of the two energy distributions, one associated to a bare compact ice and the other associated to a 10 ML porous ice film. This analysis reveals a very fast evolution of the binding-energy distribution towards that of porous ice. Our results show that few ML of additional porous film are sufficient to produce a sample for which the D(2) adsorption can be described by the energy distribution found for the 10 ML porous film. These experiments then provide evidence that the binding energy of D(2) on ASW ice is primarily governed by the topological and morphological disorder of the surface at molecular scale.