Thermal Desorption Spectroscopy Measurements Research Articles

Influence of particle flux density and temperature on surface modifications of tungsten and deuterium retention

Systematic study of deuterium irradiation effects on tungsten was done under ITER – relevant high particle flux density, scanning a broad surface temperature range. Polycrystalline ITER – like grade tungsten samples were exposed in linear plasma devices to two different ranges of deuterium ion flux densities (high: 3.5–7·1023D+/m2s and low: 9·1021D+/m2s). Particle fluence and ion energy, respectively 1026D+/m2 and ∼38eV were kept constant in all cases.The experiments were performed at three different surface temperatures 530K, 630K and 870K. Experimental results concerning the deuterium retention and surface modifications of low flux exposure confirmed previous investigations. At temperatures 530K and 630K, deuterium retention was higher at lower flux density due to the longer exposure time (steady state plasma operation) and a consequently deeper diffusion range. At 870K, deuterium retention was found to be higher at high flux density according to the thermal desorption spectroscopy (TDS) measurements. While blisters were completely absent at low flux density, small blisters of about 40–50nm were formed at high flux density exposure. At the given conditions, a relation between deuterium retention and blister formation has been found which has to be considered in addition to deuterium trapping in defects populated by diffusion.

Oxygen and iodine adsorption on cesium-precovered Pt(111)

The adsorption behavior of oxygen and iodine on a Cs-precovered Pt(111) surface is studied with Low Energy Electron Diffraction (LEED), Thermal Desorption Spectroscopy (TDS) and work function measurements. TDS shows multiple oxygen desorption states that depend on Cs coverage, with both atomic and molecular oxygen desorbing from the surface. Cs is stabilized by oxygen relative to Cs on Pt(111), and most is retained on the surface until the last oxygen desorbs. Atomic arrangements are proposed for two (4×4)-Cs,O structures observed by LEED, and these are similar to Cs,I structures with ionic character. At the highest oxygen and Cs coverages, there is evidence for a molecular oxygen state above room temperature. Dosing iodine on Pt(111)-Cs,O results in substitution of O by I in Cs,O islands. Oxygen adsorption on a Cs-saturated Cs monolayer at 295K causes an initial work function decrease consistent with underlayer adsorption, i.e., with O adsorption below the plane of the Cs atoms. This feature is absent for adsorption on the lower-coverage Pt(111) (2×2)-Cs surface.

Desorption of oxygen from alloyed Ag/Pt(111).

We have investigated the interaction of oxygen with the Ag/Pt(111) surface alloy by thermal desorption spectroscopy (TDS). The surface alloy was formed during the deposition of sub-monolayer amounts of silver on Pt(111) at 800 K and subsequent cooling to 300 K. The low-temperature phase of the surface alloy is composed of nanometer-sized silver rich stripes, embedded within platinum-rich domains, which were characterized with spot profile analysis low energy electron diffraction. The TDS measurements show that oxygen adsorption is blocked on Ag sites: the saturation coverage of oxygen decreases with increasing Ag coverage. Also, the activation energy for desorption (Edes) decreases with Ag coverage. The analysis of the desorption spectra from clean Pt(111) shows a linear decay of Edes with oxygen coverage, which indicates repulsive interactions between the adsorbed oxygen atoms. In contrast, adsorption on alloyed Ag/Pt(111) leads to an attractive interaction between adsorbed oxygen atoms.

Measurement and Modeling of Hydrogen Environment-Assisted Cracking in Monel K-500

Hydrogen environment-assisted cracking (HEAC) of Monel K-500 is quantified using slow-rising stress intensity loading with electrical potential monitoring of small crack propagation and elastoplastic J-integral analysis. For this loading, with concurrent crack tip plastic strain and H accumulation, aged Monel K-500 is susceptible to intergranular HEAC in NaCl solution when cathodically polarized at −800 mVSCE (E A, vs saturated calomel) and lower. Intergranular cracking is eliminated by reduced cathodic polarization more positive than −750 mVSCE. Crack tip diffusible H concentration rises, from near 0 wppm at E A of −765 mVSCE, with increasing cathodic polarization. This behavior is quantified by thermal desorption spectroscopy and barnacle cell measurements of hydrogen solubility vs overpotential for planar electrodes, plus measured-local crevice potential, and pH scaled to the crack tip. Using crack tip H concentration, excellent agreement is demonstrated between measurements and decohesion-based model predictions of the E A dependencies of threshold stress intensity and Stage II growth rate. A critical level of cathodic polarization must be exceeded for HEAC to occur in aged Monel K-500. The damaging-cathodic potential regime likely shifts more negative for quasi-static loading or increasing metallurgical resistance to HEAC.

Effects of heat treatment on electrical and electromechanical properties of hydrothermally synthesized epitaxial (K0.51Na0.49)NbO3 films

Effects of heat treatment on the electrical and electromechanical properties of hydrothermally synthesized epitaxial (K0.51Na0.49)NbO3 films were investigated. The film composition and crystal structure did not markedly change with heat treatment from 240 to 600 °C in O2 atmosphere. However, the leakage current density drastically decreased from the order of 101 to 10−5 A/cm2 at 50 kV/cm after heat treatment at 240 °C. The relative dielectric constant, remanent polarization, and transverse piezoelectric constant increased with increasing heat treatment temperature from 300 to 600 °C (from 330 to 750 in εr, from 5.4 to 14 µC/cm2 in remanent polarization, and from 41 to 56 pm/V in transverse piezoelectric response). H2O desorption of 12 ppm was detected in epitaxial (K0.51Na0.49)NbO3 films by thermal desorption spectroscopy measurement. Such H2O desorption can be related to the improvement of the electrical and electromechanical properties of the hydrothermally synthesized epitaxial (K0.51Na0.49)NbO3 films.

Thermal Desorption Spectroscopy Evaluation of the Hydrogen-Trapping Capacity of NbC and NbN Precipitates

In the current study, ferritic steels containing NbC or NbN precipitates were investigated. The materials were subjected to various heat treatments, giving rise to different precipitate size distributions as determined by transmission electron microscopy. Both NbC and NbN precipitates act as hydrogen traps. The steels were hydrogen charged both electrochemically and/or from the gaseous hydrogen source, followed by multiple thermal desorption spectroscopy (TDS) measurements. Electrochemical charging gave rise to a low-temperature peak [323 K to 523 K (50 °C to 250 °C)], originating from the hydrogen trapped near grain boundaries, with activation energy ranging between 24 and 33 kJ/mol, and at small NbC (39 to 48 kJ/mol) or NbN precipitates (23 to 24 kJ/mol). Gaseous charging caused a high-temperature TDS peak [723 K to 923 K (450 °C to 650 °C)], which was attributed to the presence of incoherent precipitates. The activation energy for NbC precipitates, charged in a hydrogen atmosphere, ranged between 63 and 68 kJ/mol and between 100 and 143 kJ/mol for NbN precipitates.

Influence of experimental parameters on thermal desorption spectroscopy measurements during evaluation of hydrogen trapping

Thermal desorption spectroscopy (TDS) was performed on two steels, (i) S550MC (an industrial, micro-alloyed high strength low alloy steel), and (ii) C075, a lab cast TiC containing steel. The influence of experimental parameters was studied which were related to hydrogen charging, sample features and the TDS measurement itself. It was found that the experimental conditions can significantly influence the TDS results. The results indicated that all experimental parameters are important in hydrogen related research and a reproducible experimental procedure is important in order to guarantee a reproducible analysis of the hydrogen trapping behavior by means of thermal desorption spectroscopy.

Thermally activated intermixture in pentacene-perfluoropentacene heterostructures

Using thermal desorption spectroscopy (TDS) the thermal stability of binary pentacene/perfluoropentacene (PEN/PFP) thin films has been investigated for various preparation protocols. Variation of stoichiometry ratio reveals a significantly enhanced thermal stability in comparison to the single compounds only for films with equimolar stoichiometry. The stabilization also depends on the preparation method and was found for co-deposition as well as for multi-stacks and subsequently grown PEN/PFP-stacks but not for stacks grown in the reversed order. By systemically varying the substrate temperature during deposition, we prove that the resulting intermixture is caused by a thermally activated diffusion during film growth and not due to post-deposition diffusion induced upon heating during TDS measurements. The different extents of thermal stabilization are discussed in the context of the film morphology studied by means of atomic force microscopy (AFM). For complementary information, optical absorption spectra of the heterostructures are analyzed, where the arisal of new absorption bands and the extinction of excitonic bands existing in the pure compounds are identified as decisive criteria to judge the efficiency of intermixture.

Structural, surface, and thermomechanical properties of intrinsic and argon implanted tetrahedral amorphous carbon

The structural, surface, and thermomechanical properties of intrinsic and argon incorporated tetrahedral amorphous carbon films deposited using the filtered cathodic vacuum arc process are reported. Argon atoms were simultaneously incorporated during the deposition of the films using an argon ion gun in the energy range of 0–180 eV. Contact angle measurements revealed that all of the deposited films are hydrophobic, regardless of the substrate bias voltage that was applied during the depositions. Thermal desorption spectroscopy measurements revealed that high argon bombarding energy favors films that are structurally more compact and thermally more stable. An investigation unbinding the mechanism of argon effusion and intrinsic stress relief is presented.

Growth, solvent effects, and thermal desorption behavior of octylthiocyanate self-assembled monolayers on Au(111)

The growth process, solvent effects, and thermal desorption behavior of octylthiocyanate [OTC, CH(3)(CH(2))(7)S-CN] self-assembled monolayers (SAMs) on Au(111) were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). To investigate their growth processes, octanethiol [OT, CH(3)(CH(2))(7)S-H] and OTC SAMs were prepared in 0.5 μM ethanol solution at room temperature as a function of immersion time: 10 min, 1 h, 2 h, and 24 h. STM imaging revealed that OT SAMs underwent a phase transition from the liquid phase containing striped-phase domains to the closely packed c(4 × 2) phase. OTC SAMs underwent a different phase transition from the liquid phase containing aggregated molecules to the disordered phase containing striped-phase domains. The adsorption amounts of OTC SAMs formed after immersion for 10 min and 24 h were measured to be 16% and 30% smaller than those of OT SAMs under the same conditions. STM and XPS results show that the growth kinetics of OTC SAMs on Au(111) are much slower than those of OT SAMs. Hexane resulted in OTC SAMs of higher structural quality than ethanol, DMF, or toluene. TDS measurements revealed that the relative desorption intensities of octanethiolate (C8S(+), monomer) and dioctyl disulfide (C8SSC8(+), dimer) to octanethiol (C8SH(+)) fragments for OTC SAMs were much weaker than those of OT SAMs. This is because desorption of monomers and dimers is strongly suppressed by low surface coverage of OTC SAMs, as revealed by STM observations.

Influence of Surface Morphology and Substrate on Thermal Stability and Desorption Behavior of Octanethiol Self-Assembled Monolayers: Cu, Ag, and Au

The formation and thermal desorption behaviors of octanethiol (OT) SAMs on single crystalline Au(111) and polycrystalline Au, Ag, and Cu substrates were examined by X-ray photoelectron microscopy (XPS), thermal desorption spectroscopy (TDS), and contact angle (CA) measurements. XPS and CA measurements revealed that the adsorption of OT molecules on these metals led to the formation of chemisorbed self-assembled monolayers (SAMs). Three main desorption fragments for dioctyl disulfide (C8SSC8+, dimer), octanethiolate (C8S+), and octanethiol (C8SH+) were monitored using TDS to understand the effects of surface morphology and the nature of metal substrates on the thermal desorption behavior of alkanethiols. TDS measurements showed that a sharp dimer peak with a very strong intensity on single crystalline Au(111) surface was dominantly observed at 370 K, whereas a broad peak on the polycrystalline Au surface was observed at 405 K. On the other hand, desorption behaviors of octanethiolates and octanethiols were quite similar. We concluded that substrate morphology strongly affects the dimerization process of alkanethiolates on Au surfaces. We also found that desorption intensity of the dimer is in the order of Au ≫ Ag > Cu, suggesting that the dimerization process occurs efficiently when the sulfur–metal bond has a more covalent character (Au) rather than an ionic character (Ag and Cu). The relative desorption intensity of the octanethiolates to the octanethiols follows the order of bond strength, Cu > Au > Ag. Alkanethiolates may be a dominant desorption product as metal–sulfur bonds become stronger. In this study, we clearly demonstrate that the thermal stability and desorption behaviors of alkanethiol SAMs are strongly influenced by the surface morphologies of metal substrates, bonding character of the sulfurs, the bond strength of metal–sulfur, and van der Waals interactions. Our results provide new insights into understanding the thermal stability and desorption behaviors of alkanethiols on Au, Ag, and Cu surfaces.

Investigation on role of corrosion generated hydrogen in process of stress corrosion cracking of austenitic stainless steel in marine atmospheric environment

Evidence on the role of corrosion generated hydrogen in stress corrosion cracking of austenitic stainless steel in marine atmospheric environment is provided. The formation of corrosive solution film on the surface of steel was observed. Hydrogen permeation through the stainless steel membrane was measured. Slow strain rate tests showed that anodic and cathodic polarisations around the free corrosion potential can both increase the elongation. Thermal desorption spectroscopy measurement showed hydrogen concentration increase under cathodic potentials. The hydrogen concentration increase under deformation conditions was also confirmed. However, hydrogen accumulation at the tip of the prenotched specimens was not detected.

Correlation between oxygen stoichiometry, structure, and opto-electrical properties in amorphous In2O3:H films

We have characterized amorphous In2O3:H (H : ∼4 at.%) transparent conducting films by Rutherford backscattering spectrometry (RBS), thermal desorption spectroscopy, spectroscopic ellipsometry, and Hall measurements. The amorphous In2O3:H films have been fabricated at room temperature by sputtering of an In2O3 ceramic target under Ar, O2, and H2O vapor with variation of a flow ratio r(O2) = O2/(O2+Ar). We observe (i) signals originating from Ar in RBS spectra for all the films and (ii) desorption of H2O and Ar gases during post thermal annealing of the films. Furthermore, O2 desorption together with H2O and Ar is observed for the films grown at r(O2) > 0.375%, whereas In desorption together with H2O and Ar is observed for the films grown at r(O2) < 0.375%. These results suggest that the films have void and/or multi-vacancy rich structures inside the amorphous network, and the variety of atoms, such as Ar, H2O, and weakly bonded O and In, is present in the void structures for the films grown at O2-rich and O2-poor conditions, respectively. Corresponding to the structural changes, optical and electrical properties also change at r(O2) = 0.375%. For the films grown at r(O2) < 0.375%, we observe a broad absorption in the visible wavelengths that cannot be explained by free carrier absorption. In this film, the carrier mobility reduces rapidly with increasing carrier density. Analysis of spectroscopic ellipsometry and Hall measurements reveals that a large decrease in mobility is due to a large increase in carrier effective mass, in addition to the effect of ionized impurity scattering. In this article, we discuss the optical and transport properties with the variation of oxygen stoichiometry and microscopic structures in the amorphous In2O3:H films.

Hydrogen adsorption on electron-dopedC60monolayer on Cu(111) studied by He atom scattering

Hydrogen adsorption onto an electron-doped C${}_{60}$ monolayer on Cu(111) was examined at room temperature by means of highly surface-sensitive He atom scattering measurements. The electron-doped C${}_{60}$ was modeled utilizing the self doping of the C${}_{60}$ monolayer on the Cu(111) substrate. Hydrogen was found to adsorb randomly on the surface area of the electron-doped C${}_{60}$ monolayer, while the ordered structure of the C${}_{60}$ monolayer remained unchanged. The surface hydrogen layer desorbed completely below 420 K. Thermal desorption spectroscopy measurements suggested the dissociative adsorption of hydrogen. The driving mechanism to facilitate the adsorption in this system should be in agreement with recent theoretical predictions concerning the enhanced hydrogen storage ability of the doped carbon nanomaterials.

Hydrogen outgassing mechanism in titanium materials

This paper addresses a hydrogen outgassing mechanism in titanium materials with extremely low outgassing property by investigating the distribution of hydrogen atoms concentration in depth below the surface, and the activation energy for desorption of dissolved hydrogen atoms into the boundary region between the surface oxide layer and the bulk titanium and that of adsorbed hydrogen atoms on the surface. The distribution of hydrogen atoms concentration in depth below the surface was analyzed by a time-of-flight secondary ion mass spectrometry (TOF-SIMS). The activation energy for desorption of dissolved hydrogen atoms was estimated by the thermal desorption spectroscopy (TDS) measurement with various heating rates. The activation energy for desorption of adsorbed hydrogen atoms was estimated by the temperature dependence of the outgassing rate in titanium material. In the titanium material, hydrogen atoms show maximum concentration at the boundary between the surface oxide layer and the bulk titanium. Concentration of hydrogen atoms decreases rapidly at the surface oxide layer, while it decreases slowly in the deep region below the surface layer–bulk boundary by the vacuum evacuation without/with the baking process. The activation energy for desorption of 1.02eV of dissolved hydrogen atoms into the surface layer–bulk boundary is about three times as large as that of 0.38eV of the adsorbed hydrogen atoms on the surface. These results suggest that the hydrogen outgassing mechanism in the titanium material is composed the follows processes, i.e. the slow hydrogen atoms diffusion at the surface layer–bulk boundary, quick hydrogen atoms diffusion at the surface oxide layer and rapid desorption of adsorbed hydrogen atoms on the surface. This outgassing mechanism gives very low hydrogen concentration near the surface, which results in the extremely low outgassing rate in titanium materials.

Decomposition of lithium magnesium aluminum hydride

The quaternary aluminum hydride LiMg(AlH 4) 3 contains 9.7 wt% hydrogen, of which 7.2 wt% can be released in a two-step decomposition reaction via first formation of LiMgAlH 6 and then the binary hydrides MgH 2 and LiH. In-situ synchrotron radiation powder X–ray diffraction and thermal desorption spectroscopy measurements were performed to analyze the product distributions formed during the thermal decomposition of LiMg(AlD 4) 3. The first decomposition step occurs at about 120 °C and the second at about 160 °C for the as-milled sample, while for a purified sample of LiMg(AlD 4) 3, the decomposition temperatures involving release of hydrogen increase to 140 and 190 °C, respectively, suggesting that pure samples of LiMg(AlD 4) 3 are kinetically stabilized. Studies of the purified LiMg(AlD 4) 3 also showed that the second decomposition step can be divided into two reactions: 3LiMgAlD 6 → Li 3AlD 6 + 3MgD 2 + 2Al + 3D 2 and Li 3AlD 6 → 3LiD + Al + 3/2D 2. Addition of TiCl 3 to LiMg(AlD 4) 3 under a variety of ball milling conditions consistently led to decomposition of LiMg(AlD 4) 3 during milling. Correspondingly, all attempts to rehydrogenate the (completely or partially) decomposed samples at up to 200 bar hydrogen pressure failed. Decomposition of MgD 2 was observed at relatively low temperatures. This is ascribed to thermodynamic destabilization due to the formation of different Al xMg y phases, and to kinetic destabilization by addition of TiCl 3. A thermodynamic assessment was established for the calculation of phase stability and decomposition reaction relationships within the Li–Mg–Al−H system. The calculations confirmed the metastability of the LiMg(AlH 4) 3 phase and the irreversibility of the Li–Mg alanate phase decomposition reactions. The Li–Mg alanate decomposition pathways followed experimentally could be explained by the endothermicity of the calculated decomposition enthalpies, in that an impure or catalyzed LiMgAlH 6 intermediate phase could more directly access an endothermic decomposition reaction at lower temperatures, while a kinetically-hindered, purified LiMgAlH 6 would require higher temperatures to initiate the two-step decomposition through an exothermic reaction.

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

The surface structures, adsorption conditions, and thermal desorption behaviors of cyclopentanethiol (CPT) self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). STM imaging revealed that although the adsorption of CPT on Au(111) at room temperature generates disordered SAMs, CPT molecules at <TEX>$50^{\circ}C$</TEX> formed well-ordered SAMs with a <TEX>$(2{\surd}3{\times}{\surd}5)R41^{\circ}$</TEX> packing structure. XPS measurements showed that CPT SAMs at room temperature were formed via chemical reactions between the sulfur atoms and gold surfaces. TDS measurements showed two dominant TD peaks for the decomposed fragments (<TEX>$C_5H_9^+$</TEX>, m/e = 69) generated via C-S bond cleavage and the parent molecular species (<TEX>$C_5H_9SH^+$</TEX>, m/e = 102) derived from a recombination of the chemisorbed thiolates and hydrogen atoms near 440 K. Interestingly, dimerization of sulfur atoms in n-alkanethiol SAMs usually occurs during thermal desorption and the same reaction did not happen for CPT SAMs, which may be due to the steric hindrance of cyclic rings of the CPT molecules. In this study, we demonstrated that the alicyclic ring of organic thiols strongly affected the surface structure and thermal desorption behavior of SAMs, thus providing a good method for controlling chemical and physical properties of organic thiol SAMs.

Deuterium retention in tungsten exposed to low-energy pure and helium-seeded deuterium plasmas

Influence of helium (He) on the deuterium (D) retention in tungsten (W) under simultaneous He-D plasma exposure was investigated. Bulk polycrystalline tungsten and two W coatings on carbon substrate, namely, plasma-sprayed tungsten and combined magnetron-sputtered and ion implanted tungsten (CMSII-W) were exposed to pure and He-seeded D plasmas generated by electron-cyclotron-resonance plasma source. The D retention in each sample was subsequently analyzed by various methods such as nuclear reaction analysis for the D depth profiling up to 6 μm and thermal desorption spectroscopy for the determination of total amount of D retention. It is shown that seeding of helium into D plasma with helium ion flux fraction of 10% reduces the deuterium retention for all tungsten grades but more significant reduction was observed for polycrystalline W and less significant effect was found for W coatings. From the thermal desorption spectroscopy measurements, we conclude that the presence of He modifies the density of existing traps for D but does not modify the nature of traps. Maximum effect of a reduction in the deuterium retention due to helium seeding was observed at around 500 K for bulk polycrystalline W. Mechanisms of deuterium retention and He effect in different W materials are discussed.

Hydrogen Retention Properties of SiC/SiC Composites as Plasma Facing Material of Fusion Reactor

In order to examine the deuterium retention properties of SiC/SiC compositess, the deuterium ion irradiation was conducted followed by a thermal desorption spectroscopymeasurement. The deuterium retained was desorbed in forms of HD, D2, HDO, CD4 and C2D4. The ratio of the amount of desorbed hydrocarbons to the total amount of retained deuterium was approximately 6%, which is much smaller, compared with the case of carbon material. Namely, we confirmed that the chemical erosion of SiC/SiC composites isquite small. In the D2 desorption spectra, two desorption peaks appeared. The lower and higher temperatures peaks were regarded to be due to detrappings of Si-D and C-D bonds, respectively. The ratio of deuterium amount desorbed at highertemperature decreased with increase of the deuterium fluence.This behavior could be explained that the carbon content at thesurface is reduced by the selective sputtering due to deuteriumions.

Desorption kinetics of GeO from GeO2/Ge structure

High-κ dielectrics on Ge have recently attracted much attention as a potential candidate to replace planar silicon transistors for sub-32-nm generations. However, the instability of the high-κ/Ge interface, especially the desorption of germanium monoxide (GeO), hampers the development of Ge-based devices. Therefore, the typical GeO2/Ge structure was chosen to investigate GeO desorption. In this contribution, we describe the desorption kinetics of GeO, including Ge/GeO2 interface reaction, the diffusion process during GeO desorption, the desorption activation energy of GeO, the different mechanisms of GeO desorption, and the active oxidation of Ge. Through annealing GeO2/Ge in an ultrahigh vacuum (UHV), direct evidence for the consumption of Ge substrate has been shown by atomic force microscopy (AFM) measurements of the consumption depth. By using thermal desorption spectroscopy (TDS) measurements and studying oxygen-18 isotope tracing, we have clarified that the GeO desorption is not caused by the GeO direct-diffusion process. Isothermal TDS measurements and morphology investigation have revealed a transition from a uniform desorption mechanism to a nonuniform one as GeO2 thickness was reduced. On the basis of the experimental results in this study, a GeO desorption model has been developed. For GeO desorption, about 2 eV of activation energy has been obtained from kinetic calculation on the basis of TDS analysis. Different from the UHV annealing, the active oxidation of Ge has been observed by AFM measurements under low oxygen partial pressures.