Effect Of Thermal Vibrations Research Articles

Theoretical development and experimental validation on the measurement of temperature by extended X-ray absorption fine structure.

A systematic investigation on the theoretical framework of the ultra-fast measurement of temperature by extended X-ray absorption fine structure (EXAFS) applied in laser-driven-compression experiments has been carried out and a new temperature measurement scheme based on the EXAFS cumulant expansion analysis and anharmonic correlated Debye model has been advanced. By considering the anharmonic effect of thermal vibration and avoiding the employment of the empirical model as well as parameters which have large inherent uncertainties in the temperature determination, this new scheme is theoretically more accurate than traditional ones. Then the performance of the new measurement scheme and traditional methods were validated on a synchrotron radiation platform by temperature-dependent EXAFS (TDEXAFS) experiments on Au, Fe, V and Ti; the results showed that the new scheme could provide the most accurate measured temperatures with much lower uncertainties. This accurate scheme gives a firmer physical ground to the EXAFS temperature measurement technique and can expect to be applied in laser-driven compression experiments and promote the development of matter state research at extreme conditions.

Influence of a thin amorphous surface layer on de-channeling during aluminum implantation at different temperatures into 4H-SiC

Ion implantation is an important technique in semiconductor processing and has become a key technology for 4H-SiC devices. Today, aluminum (Al) implantations are routinely used for p-type contacts, p+-emitters, terminations and many other applications. However, in all crystalline materials, quite a few ions find a path along a crystal channel, so-called channeling, and these ions travel deep into the crystal. This paper reports on the channeling phenomenon during Al implantation into 4H-SiC, and in particular, the influence of a thin native oxide will be discussed in detail. The effects of thermal lattice vibrations for implantations performed at elevated temperatures will also be elucidated. 100 keV Al ions have been implanted along the [000-1] direction employing samples with 4° miscut. Before implantation, the samples have been aligned using the blocking pattern of backscattered protons. Secondary ion mass spectrometry has been used to record the Al depth distribution. To predict implantation profiles and improve understanding of the role of crystal structure, simulations were performed using the Monte-Carlo binary collision approximation code SIIMPL. Our results show that a thin surface layer of native oxide, less than 1 nm, has a decisive role for de-channeling of aligned implantations. Further, as expected, for implantations at elevated temperatures, a larger degree of de-channeling from major axes is present due to increased thermal vibrations and the penetration depth of channeled aluminum ions is reduced. The values for the mean-square atomic displacements at elevated temperatures have been extracted from experimental depth profiles in combination with simulations.

Study of Oxygen Vacancy Diffusion in Yttria-doped Ceria and Yttria-stabilized Zirconia by Statistical Moment Method

Oxygen vacancy diffusion in yttria-doped ceria (YDC) and yttria-stabilized zirconia(YSZ) are investigated using statistical moment method, including the anharmonicity effects of thermal lattice vibrations. The expressions of oxygen vacancy-dopant association energy and oxygen vacancy migration energy are derived in an explicit form. Calculation of the vacancy migration energy enable us to evaluate the important role of dopant cation on the oxygen vacancydiffusion. The dependences of the vacancy activation energies and diffusion coefficients in YDC and YSZ systems on dopant concentration are also discussed in detail. The calculated results are in good agreement with the other theoretical and experimental results.

Investigation of the Ionic Conductivities of Yttria-Doped Ceria and Yttria-Stabilized Zirconia by Using the Statistical Moment Method

The ionic conductivities of yttria-doped ceria (YDC) and yttria-stabilized zirconia (YSZ), are investigatied using statistical moment method including the anharmonicity effects of thermal lattice vibrations. The expressions for the lattice constant and the vacancy activation energy are derived in closed analytic forms in terms of the power moments of the atomic displacements. The distribution of oxygen vacancies around dopants and the important role of cation barriers on vacancy diffusion are evaluated in detail. The lattice constants, activation energies, ionic conductivities of YDC and YSZ are calculated as functions of the dopant concentration. Notably, the ionic conductivities depend linearly on dopant concentration. Our results are in good agreement with those of both previous experiments and several theoretical calculations.

Recent Advances in the Doping of 4H-SiC by Channeled Ion Implantation

The effect of lattice thermal vibrations on the channeling of 100 keV Al ions in 4H-SiC is investigated. By implanting at room temperature in the direction, the depth distribution of the incident ions is shown to be about 7 times deeper than for random implantations. At higher implantation temperatures, the channeling is reduced by the lattice vibrations and, for instance, at 600 °C implantation the distribution is about 3-4 times deeper than for a RT random implantation. The results are of technological interest for further development of implantation technology for 4H-SiC device manufacturing.

A mechanistic model of damage evolution in lead free solder joints under combinations of vibration and thermal cycling with varying amplitudes

A broad range of electronics applications involve the long-term exposure to combinations of thermal excursions and vibration with constantly varying amplitudes, and the ultimate life is very often limited by fatigue of the solder joints. The assessment of this is usually based on a combination of simplified accelerated tests and the assumption of simple acceleration factor expressions or models. Neither of the latter can, however, even account for observed effects of accelerated test parameters. To make matters worse common constitutive relations may be strongly misleading. Also, current damage accumulation rules cannot account for major interactions between thermal cycling and vibration or even just for ongoing variations in vibration amplitudes or thermal cycling parameters, respectively. Even if we are ‘just’ aiming to decide between alternative material, design, or process parameters, or to compare a new product to a previous (supposedly similar) one, we should be concerned with the relative performance in service and not just in accelerated tests.The main objective of the present work is to combine two recent mechanistic models into a more comprehensive one that includes interactions between effects of thermal cycling and vibration with varying amplitudes. Important parameters in the resulting model still remain to be determined but a detailed understanding of the underlying mechanisms and the consequences of their interactions for realistic Tin-Silver-Copper (SnAgCu) joints allows for the prevention of surprises, the definition of appropriate test protocols, and the proper interpretation of results. This includes the identification of ‘worst case’ real life scenarios to test for, as well as justification for the use of shear testing in thermal cycling when event detection is not an option. Extension of the model to new alloys is briefly discussed as well.

Superfocusing and zero-degree focusing in planar channeling of protons in a thin silicon crystal

This is a theoretical study of the superfocusing and zero-degree focusing effects appearing in channeling of protons of energy of 2 MeV in the {1 1 0} channel of a thin silicon crystal. We prove that the ultimate origin of these effects is the crystal rainbow effect, which has been discovered and explored in ion transmission through axial crystal channels, nanotubes and graphene. Moreover, the effect is the origin of the shapes of the whole spatial and angular distributions of channeled protons. The incident proton velocity vector is taken to be parallel to the channel midplane. We use the Molière's approximation of the Thomas-Fermi proton-atom interaction potential and the continuum approximation. The effect of thermal vibrations of the crystal's atoms is included. We solve numerically the proton equation of motion and analyze the spatial and angular proton transmission functions. The extrema of these functions are the spatial and angular rainbow points, respectively. When the whole proton beam is taken into account, a spatial rainbow pattern, composed of the lines emerging from the superfocusing points, and an angular rainbow pattern, consisting of the lines emerging from the origin and the zero-degree focusing points, appear along the channel. We consider the region of crystal thickness comprising the first, second and third superfocusing and zero-degree focusing points. When the effect of thermal vibrations is neglected, each of these rainbow lines look like the bifurcation set of the cusp catastrophe, and when the effect is included, the line resembles the bifurcation set of the butterfly catastrophe. We demonstrate that the spatial and angular distributions of transmitted protons are fully determined by the spatial and angular rainbow lines, respectively. The superfocusing and zero-degree focusing effects weaken with the increase of the crystal thickness. This is a consequence of the anharmonicity of the continuum proton-crystal interaction potential, which makes the proton beam propagation through the channel incoherent. We also explore the influence of the effect of proton collisions with the crystal's electrons on the beam dynamics in the channel. This effect additionally contributes to the incoherence of the beam motion along the channel. Our opinion is that the peaks of the spatial and angular distributions of ions transmitted through the planar channels lying off the origin registered before were in fact the rainbow peaks.

Metal–Insulator Phase Transition in Iron-Doped Vanadium Dioxide Thin Films

The electrical conductivity of polycrystalline V(1 – x)FexO2 films has been investigated in a wide temperature range, which covers both the metal and insulator phase regions. It is shown that with an increase in the iron concentration the metal–insulator phase transition shifts toward lower temperatures, while the temperature range of the transition in doped samples additionally broadens as compared with pure VO2. To explain the temperature dependence of the electrical conductivity of the V(1 – x)FexO2 insulator phase, a hopping conductivity model has been used, which takes into account the effect of thermal vibrations of atoms on the resonance integral. The values of parameter e have been calculated as a function of the degree of VO2 doping.

Passive Thermal Management of Launch Vehicle Systems using Phase Changing Materials

<p>Electronic systems in expendable launch vehicles and missiles rely on their own thermal inertia to operate for the stipulated time, without overheating, owing to absence of active cooling systems and natural convection at elevated altitude. Traditionally, this inertia is built-into the electronics by increasing its chassis (support structure) mass, proportional to the associated thermal load. For power intensive systems, especially in vehicle upper stages where mass is at premium, this approach results in reduction in payload capability. In the proposed paper, a Heat Sink based on Neopentyl Glycol (NPG) with solid-to-solid phase change (crystalline transformation) is explored as a mass effective alternative due to the material’s capability to absorb a significant amount of energy during phase change. However, due to its lower thermal conductivity, a Thermal Conductivity Enhancer (TCE) to maximize heat transfer had to be employed. The resulting heat sink, utilizing TCE for heat transfer capability and NPG for heat storage capability is called as Hybrid Heat Sink. A heat sink with plate type fins as TCE is realized and a mass reduction factor of 1.4 is achieved against traditional approach. This is followed by a heat sink with pin type fins as TCE where mass reduction factor is increased to 2.6. Effect of thermal cycling and vibration on its performance is also studied.</p>

High microwave absorption characteristic nanomaterial preparation and mechanism analysis

Due to the excellent microwave absorption characteristics, YIG has a broad prospect in microwave application. This paper successfully synthesized YIG nanoparticles with the average size of 68.2 nm. The size uniformity of nanoparticles was verified and calculated by TEM and XRD. Microwave absorption value reached up to -34.5 dB, which was far more than microwave absorption threshold value (−10 dB). The mechanism of high microwave absorption characteristics discovered in the study is derived from four aspects: (a) Multiple scattering and interfacial polarization of YIG nanoparticles on surfaces. (b) High coercivity and high magnetic loss parameters of YIG nanoparticles in the high frequency region. (c) Magnetic loss mechanism and ferromagnetic resonance of YIG. (d) The influence of lesser pinning site caused by smaller grain size. The study found that the fundamental reasons of FMR spectrum asymmetric behavior come from three factors: (І) Nanoparticles random orientation. (П) Different easy axis. (Ш) Non-uniform resonance modes in the process of YIG synthesis. It was observed that microwave absorption markedly reduced due to the influence of skin effect and temperature. The effects of temperature on skin depth and microwave absorption are because of different amounts of excited electrons from the valence band and different magnetic spin configurations. The mechanism of the effect of temperature on the resistance of YIG was discovered, which is derived from electron hoping mechanism, remnant phases influence, the effect of the lattice atoms thermal vibration and skin effect.

Фазовый переход металл-диэлектрик в тонких пленках диоксида ванадия, легированного железом

AbstractThe electrical conductivity of polycrystalline V_(1 – _ x )Fe_ x O_2 films has been investigated in a wide temperature range, which covers both the metal and insulator phase regions. It is shown that with an increase in the iron concentration the metal–insulator phase transition shifts toward lower temperatures, while the temperature range of the transition in doped samples additionally broadens as compared with pure VO_2. To explain the temperature dependence of the electrical conductivity of the V_(1 – _ x )Fe_ x O_2 insulator phase, a hopping conductivity model has been used, which takes into account the effect of thermal vibrations of atoms on the resonance integral. The values of parameter ε have been calculated as a function of the degree of VO_2 doping.

Electron hybridization and anharmonic thermal vibration effect on structure transition of SrTiO3 at high-pressure and low-temperature

Abstract We execute electron density analysis of SrTiO3 at low temperatures up 80 K and high pressures up to 11.88 GPa using X-ray single-crystal diffraction and ab initio quantum chemical molecular orbital (MO) calculation. By changing pressures, the cubic SrTiO3 with perovskite structure goes through a antiferroelastic distortion to tetragonal symmetry above the critical pressure Pc=7 GPa with c/a 1 and increasing with lowering temperature. Difference Fourier (D-F) synthesis experimentally proves the residual electron densities Δρ(xyz) are associated with two different effects: electron hybridization bonding electron and anharmonic thermal vibration atoms. The d–p–π hybridization between Ti(3d) and O(2p) orbitals is confirmed in the residual electron density, which is deformed from the ideal spherical density conducted by the atomic scattering factor fi using Hartree–Fock (HF) approximation. MO calculation also reveals the electron hybridization. Anharmonic thermal vibration of atoms yields a large effect to the structure transition. Mulliken charges analysis of MO calculation indicates much smaller charges than their formal ionic charges. Their ionicity increases from cubic to tetragonal above Pc and below Tc.

Hexagonal structure of phase III of solid hydrogen

A hexagonal structure of solid molecular hydrogen with $P6_122$ symmetry is calculated to be more stable below about 200 GPa than the monoclinic $C2/c$ structure identified previously as the best candidate for phase III. We find that the effects of nuclear quantum and thermal vibrations play a central role in the stabilization of $P6_122$. The $P6_122$ and $C2/c$ structures are very similar and their Raman and infra-red data are in good agreement with experiment. However, our calculations show that the hexagonal $P6_122$ structure provides better agreement with the available x-ray diffraction data than the $C2/c$ structure at pressures below about 200 GPa. We suggest that two phase-III-like structures may be formed at high pressures, hexagonal $P6_122$ below about 200 GPa and monoclinic $C2/c$ at higher pressures.

Local Structural Distortion Induced Uniaxial Negative Thermal Expansion in Nanosized Semimetal Bismuth.

The corrugated layer structure bismuth has been successfully tailored into negative thermal expansion along c axis by size effect. Pair distribution function and extended X-ray absorption fine structure are combined to reveal the local structural distortion for nanosized bismuth. The comprehensive method to identify the local structure of nanomaterials can benefit the regulating and controlling of thermal expansion in nanodivices.

Homogeneous and inhomogeneous spectrum broadening in Nd3+-doped mixed vanadate crystals

Homogeneous and inhomogeneous spectrum broadening in Nd:LuxGd1−xVO4 series crystals were directly measured for the first time, and compared with that in the Nd:LuxY1−xVO4 and Nd:GdxY1−xVO4 crystals. Spectroscopic properties including fluorescence lifetime, spectral line width, emission peak, and stimulated emission cross section had obvious changes with the temperature increased from 77 K to 300 K, owing to the thermal phonon vibration. Compared to the pure vanadate crystals, we found these changes were more sensitive to temperature in the case of mixed crystals, in which cations (Lu, Y, and Gd) are random replaced by each other at the same lattice site. At 77 K, the thermal phonon vibration effect can be ignored and the inhomogeneous spectrum broadening that caused by disordered structure in all samplers can be calculated with the line-width of pure vanadate crystals as reference point, the corresponding values (ΔΓ(T)′) were 2.2 nm–3.8 nm in 4F3/2 → 4I11/2 transition and 1.7 nm–2.8 nm in 4F3/2 → 4I13/2 transition. Compared to Nd:LuxY1−xVO4 and Nd:GdxY1−xVO4 series mixed crystals, the change in spectral line width with x is most obvious in the case of Nd:LuxGd1−xVO4 series crystals, which may be attributed to the larger ionic radius difference between Gd and Lu (RLu < RY < RGd).

Mechanical properties of metallic thin films: theoretical approach

The statistical moment method in statistical mechanics was developed to investigate the mechanical properties of free-standing metallic thin films at ambient conditions including the anharmonicity effects of thermal lattice vibrations. Analytical expressions of isothermal areal modulus BT, Young’s modulus E and shear modulus G were derived in terms of the power moments of the atomic displacements. Numerical calculations have been performed for metallic Ni, Au and Al thin films, and compared with those of bulk metals. This method is physically transparent and it successfully described the temperature effects on mechanical properties of metallic thin films.

Specific features of electrical conductivity of the insulating phase of vanadium dioxide doped with niobium

The electrical conductivity of V1 – xNbxO2 single crystals have been investigated over a wide temperature range covering regions of the existence of the metallic and insulating phases. It has been shown that, with an increase in the niobium concentration, the electrical conductivity of the metallic phase becomes below the Mott limit for the minimum metallic conductivity. Immediately after the metal–insulator transition, the electrical conductivity is determined by a large amount of free electrons that gradually localized with a decrease in the temperature. The temperature dependence of the electrical conductivity in the insulating phase of V1 – xNbxO2 has been explained in the framework of the hopping conductivity model that takes into account the effect of thermal vibrations of atoms on the resonance integral.

Atomic disorder of Li0.5Ni0.5O thin films caused by Li doping: estimation from X-ray Debye-Waller factors.

Cubic type room-temperature (RT) epitaxial Li0.5Ni0.5O and NiO thin films with [111] orientation grown on ultra-smooth sapphire (0001) substrates were examined using synchrotron-based thin-film X-ray diffraction. The 1[Formula: see text]1 and 2[Formula: see text]2 rocking curves including six respective equivalent reflections of the Li0.5Ni0.5O and NiO thin films were recorded. The RT B1 factor, which appears in the Debye-Waller factor, of a cubic Li0.5Ni0.5O thin film was estimated to be 1.8 (4) Å2 from its 1[Formula: see text]1 and 2[Formula: see text]2 reflections, even though the Debye model was originally derived on the basis of one cubic element. The corresponding Debye temperature is 281 (39) K. Furthermore, the B2 factor in the pseudo-Debye-Waller factor is proposed. This parameter, which is evaluated using one reflection, was also determined for the Li0.5Ni0.5O thin film by treating Li0.5Ni0.5O and NiO as ideal NaCl crystal structures. A structural parameter for the atomic disorder is introduced and evaluated. This parameter includes the combined effects of thermal vibration, interstitial atoms and defects caused by Li doping using the two Debye-Waller factors.

Effect of thermal vibrations on interference effects at the reemission of attosecond electromagnetic pulses by regular multiatomic systems

The theory of reemission of attosecond electromagnetic pulses by regular multiatomic systems of identical complex atoms has been developed with allowance for thermal vibrations. It has been shown that thermal vibrations result in noticeable changes in the “diffraction” maxima characteristic of regular targets with atoms at rest. A one-dimensional lattice has been considered as an example. Generalization to two- and three-dimensional lattices has been given.

Theoretical investigation of the thermodynamic properties of metallic thin films

Abstract The thermodynamic properties of metallic thin films with face-centered cubic structure at ambient conditions were investigated using the statistical moment method including the anharmonicity effects of thermal lattice vibrations. The analytical expressions of Helmholtz free energy, lattice parameter, linear thermal expansion coefficient, specific heats at the constant volume and constant pressure were derived in terms of the power moments of the atomic displacements. Numerical calculations of thermodynamic properties have been performed for Au and Al thin films and compared with those of bulk metals. This research proposes that thermodynamic quantities of thin films approach the values of bulk when the thickness of thin film is about 70 nm.