Value Of Bulk Material Research Articles

Ellipsometry of very thin Al2O3-HfO2 stacks for nano-memory applications

Nowadays, the way towards manufacturing of advanced flash memory devices with conformal layers in stacks or laminates depends on their physical characterisation, i.e. the layer and interface thicknesses, density and composition. The transition dimension between thin and very thin stacks is in the range of few nanometres. The assumption that the oxide layer properties in the very thin stacks are constant in depth or are the same as for the bulk material values is not correct. We have applied ellipsometry (Variable Angle Spectral Ellipsometry, and Multiple Angle Incident Ellipsometry) with appropriate algorithms for data interpretation to investigate very thin Al2O3/HfO2 stacks (5 bioxide blocks) grown by ALD with a total thickness below 20 nm. Depth profiling was used in simulations as a complimentary tool. A quantitative determination of HfO2 volume fraction in the stack depth was obtained. An independent determination of the thicknesses and the composition of blocks in the stacks were achieved. Lorenz-Lorentz mixing model was applied for the estimation of dielectric properties of the different layers in the stack depth.

PREDICTING ELASTIC MODULUS OF THE BODY-CENTERED CUBIC METALLIC FILMS

The elastic modulus of the body-centered cubic (BCC) films is studied based on the moment method. For Fe, Ta, and W films a clear elastic modulus dependence of the thickness at ambient conditions and under temperatures up to 2000 K. The obtained results of the values of elastic modulus metallic films are smaller than the corresponding values of bulk material. Calculated results show the effects of temperature and thickness of elastic modulus for Fe, Ta, and W metallic films. On the other hand, when the thickness of thin films is about 60nm then the elastic modulus of the BCC films approaches the values of bulk material. Our results are compared with the other theoretical results and experimental values of bulk materials.

On the elastic tensors of ultra-thin films: A study of ruthenium

Critical Dimensions (CD) of electronic device patterns have been reduced to the order of a few nanometers due to the extreme miniaturization of devices, setting the thickness of some of its constituting materials at the (sub-)nanometer level. At these length scales, the mechanical integrity of the constituting films begin to deviate strongly from their bulk material values, introducing a set of undesired reliability side-effects such as mechanical failure, delamination, and strain enhanced diffusion. Understanding the fundamentals behind these aspects is critical to further sustain technology developments. We use Density Functional Theory (DFT) to quantify how the mechanical properties of sub-10 nm thick films depend on their thickness and surface roughness, specifically for Ru [001], which is currently being investigated for CMOS interconnects, an antiferromagnetic layer, and an etch stop layer in Magnetic Random Access Memories (MRAM). Our findings underline that overlooking the impact of film dimensions and surface roughness on the mechanical properties at these CDs, hampers the optimization of device performances and challenges the validity of many experimental and modeling techniques relying on the assumption that bulk mechanical properties are preserved.

Direct measurements of thermal transport in glass and ceramic microspheres embedded in an epoxy matrix

The time-domain thermoreflectance metrology is applied to evaluate the thermal conductivities of filler particles embedded in a composite matrix. Specifically, a system of glass and ceramic microspheres with a diameter of 100 to 150 μm embedded in an epoxy matrix was used as a representation of a typical composite thermal interface material (TIM) suitable for microelectronics applications. These measurements provide a direct characterization of the thermal properties of filler materials. The measured thermal conductivities of both borosilicate glass and yttria stabilized zirconia microspheres agree well with literature values for bulk materials, whereas the thermal conductivity of the alumina microspheres is nearly 50% lower than that of bulk crystals. The reduction in thermal conductivity of the alumina microspheres highlights how important this level of understanding is for TIM development and is attributed to enhanced phonon scattering due to structural heterogeneity, such as defects induced by phase mixing and microvoids. Combining sample preparation, structural characterization, and direct thermal measurements, our study reveals the structure–thermal property relationship for individual microspheres. The results of this work can facilitate the design and engineering of composite-based thermally conductive materials for thermal management applications.

Effect of build orientation on fracture behaviour of AlSi10Mg produced by selective laser melting

PurposeA key challenge found in additive manufacturing is the difficulty to produce components with replicable microstructure and mechanical performance in distinct orientations. This study aims to investigate the influence of build orientation on the fracture toughness of additively manufactured AlSi10Mg specimens.Design/methodology/approachThe AlSi10Mg specimens were manufactured using the selective laser melting (SLM) technology. The fracture toughness was experimentally determined (under ASTM E399-09) using C(T) specimens manufactured in different orientations. The microstructure of the specimens was examined using metallography to determine the effects of grain orientation on fracture toughness.FindingsThe fracture toughness magnitude of manufactured specimens ranged between 36 and 50 MPam, which closely matched conventional bulk material and literature values regarding AlSi10Mg components. The C(T) specimens printed in the T-L orientation yielded the highest fracture toughness. The grain orientation and fracture toughness values confirm the anisotropic nature of SLM parts where the T-L-oriented specimen obtained the highest KIC value. A clear interaction between the melt pool boundaries and micro-slipping during the loading application was observed.Originality/valueThe novelty of this paper consists in elucidating the relationship between grain orientation and fracture toughness of additively manufactured AlSi10Mg specimens because of the anisotropy generated by the different melting pool boundaries and orientations in SLM. The findings show that melt pool boundaries can behave as easier pathways for cracks to propagate and subsequently reduce the fracture toughness of specimens with cracks perpendicular to the build direction.

Enhancing the magnetic and inductive heating properties of Fe3O4 nanoparticles via morphology control

Fe3O4 nanoparticles (NPs) with different shapes have been prepared by a ‘solventless’ synthesis approach to probe shape anisotropy effects on the magnetic and inductive heating properties. Various shapes including spheres, octahedrons, cubes, rods, wires, and multipods are obtained through alterations in reaction conditions such as the ratio of precursor to surfactant content and heating rate. Magnetic and Mössbauer measurements reveal better stoichiometry in anisotropic-shaped Fe3O4 NPs than that in the spherical and multipod NPs. As a result, the magnetization value of the anisotropic-shaped NPs approaches the value for bulk material (∼86 emu g−1). More surprisingly, the Verwey transition, which is a characteristic phase transition of bulk magnetite structure, is observed near 120 K in the anisotropic-shaped NPs, which further corroborates the fact that these NPs possess better stoichiometry compared to the spherical and multipod-shaped NPs. Other than the improved magnetic properties, these anisotropic-shaped NPs are more effective for hyperthermia applications. For example, compared to the conventional spherical NPs, the nanowires show much higher SAR value up to 846 W g−1, making them a potential candidate for practical hyperthermia treatment. In particular, the octahedral NPs shows an SAR value higher than the same size spherical NPs, which demonstrates the importance of occurrence of the Verwey transition in Fe3O4 NPs for better stoichiometric and higher heating.

Thermal conduction in isotope diamond thin films studied by pump-probe laser reflectivity measurement

We study the thermal conductivity of isotope-controlled diamond thin films between 0.001% and 99% 13C contents using an ultrafast pump-probe laser experiment. We measure the surface temperature change through the reflectivity change of the probe light pulse after heating with the pump light pulse, compare it with a theoretical calculation, and estimate the thermal conductivity. The Brillouin-oscillation appears in the reflectivity change, which is used for determining the film thickness and then removed in determining the thermal conductivity. The theoretical calculation reveals that the diamond film should be thicker than 1 μm for obtaining appropriate thermal conductivity. Our results indicate that the thermal conductivity of the 50%-13C diamond thin film is much lower than the reported value, suggesting unavailability of reported values of bulk materials for thin films and necessity for measurement for the thermal conductivity of thin films.

Mechanical properties of REBaCuO single-grain bulk fabricated by the infiltration growth technique

In order to investigate the mechanical properties and fracture mechanisms of (Gd,Dy)BaCuO dense bulk material fabricated by the infiltration growth technique, tensile tests were carried out for specimens cut from the as-grown bulk material. The average tensile strength value of the (Gd,Dy)BaCuO dense bulk material fabricated by the infiltration growth technique was 44 MPa, which is superior to that of a porous bulk material fabricated through melt-processing in a 50% O2 atmosphere (37 MPa), and comparable to that of a dense bulk material fabricated through melt-processing in 100% O2 (45 MPa) that have been reported elsewhere. Through the observations of the flow-like patterns formed by the crack propagations on the fracture surfaces, the fatal crack initiation site was identified. One extraordinarily large pore, segregated secondary phase particles and some inclusion that mainly consists of Pt were observed around the crack initiation site on the fracture surfaces of the (Gd,Dy)BaCuO dense bulk material.

Young’s modulus and hardness of multiphase CaZrO3-MgO ceramics by micro and nanoindentation

The aim of this work is to determine the values of the hardness and elastic modulus of the phases present in CaZrO3-MgO-ZrO2 composites and to analyse their contribution to the composite properties. Two materials previously developed with the same major phases (CaZrO3, MgO and c-ZrO2) present in different volume fractions and grain size have been analysed. The hardness and Young’s modulus of each phase determined by nanoindentation are independent from the specific composite and coincident with nanoindentation values for single phase bulk materials. The contribution of the individual phases to Young’s modulus of the multiphase materials is in agreement with calculations using the nanoindentation values and the Voight upper limit of the “rule of mixtures”. Scale effect due to microcracking has been observed for micro-hardness values of the composites and differences between calculations and experimental values are related to this effect.

Thermal and Electrical Properties of 3.2 nm Thin Gold Films Coated on Alginate Fiber

The thermal transport in metallic thin films can be reduced by the electron scattering and there are very little available knowledge that can be used to explain the mechanism. In this work, we characterized the thermal and electron transport of 3.2 nm thin gold films coated on alginate fiber by the transient electrothermal (TET) technique. The results reveal that the thermal and electrical conductivities are reduced significantly from the respective values of bulk material by 76.2% and 93.9%. At the same time, the Lorenz number is calculated as 8.66 × 10−8 W Ω K−2 and it is almost three times increased from the value of bulk material. The intrinsic thermal diffusivity of alginate fiber is 3.25 × 10−7 m2 s−1 and the thermal conductivity is 0.51 W m−1 K−1.

Laser Ultrasonic Thin Film Characterization of Si-Cu-Al-Cu Multi-Layered Stacks

In this work, the step-wise determination of elastic properties of a Si-Cu-Al-Cu stack via laser induced ultrasonic measurements is presented. The analysed Si-Cu-Al-Cu system consists of a silicon (100) substrate, two copper layers and an aluminium layer embedded between the copper layers, with a thickness of about 1 µm of each layer. The obtained results for the Young’s moduli and Poisson’s ratios of the multi-layered system are compared to literature values for bulk materials. The presented non-contact method shows high potential regarding the non-destructive evaluation of elastic properties of thin films in multi-layered systems.

Effect of oxygen pressure on structure and ionic conductivity of epitaxial Li0.33La0.55TiO3 solid electrolyte thin films produced by pulsed laser deposition.

We report on the ionic conductivity of Li0.33La0.55TiO3 (LLTO) epitaxial films grown on the (100) and (111) surfaces of single crystal SrTiO3 (STO) substrates at different oxygen partial pressures (from 1.33 to 26.66 Pa). The films are intended for use as solid electrolytes for all-solid-state Li-ion batteries, and the epitaxial growth for modeling the electrolyte single crystal properties. The LLTO films overall exhibit formation of the perovskite-based orthorhombic structure with the epitaxial cube-on-cube orientation for both (100)STO and (111)STO substrates. Room temperature ionic conductivity of the LLTO films measured by impedance spectroscopy slightly decreases with the oxygen partial pressure changing from 1.33 to 26.66 Pa and is in the range of 10-4 to 10-5 S cm-1. Complex impedance plots at different temperatures indicate that the conductivity in these epitaxial films is predominantly an intrinsic bulk property and exhibits distribution of relaxation time. Activation energies (E a) for all the films were calculated employing the Arrhenius relationship and are between 0.30 eV and 0.40 eV, agreeing well with the reported values of bulk materials. Systematic difference in ionic conductivity between the (100)STO and (111)STO films is understood as being related to the difference in distribution of a "bottleneck" diffusion path. The measured conductivity of LLTO films indicates that these films can be used as a solid electrolyte in all-solid-state batteries.

Nanomechanical and electrical properties of Nb thin films deposited on Pb substrates by pulsed laser deposition as a new concept photocathode for superconductor cavities

We report a design of photocathode, which combines the good photoemissive properties of lead (Pb) and the advantages of superconducting performance of niobium (Nb) when installed into a superconducting radio-frequency gun. The new configuration is obtained by a coating of Nb thin film grown on a disk of Pb via pulsed laser deposition. The central emitting area of Pb is masked by a shield to avoid the Nb deposition. The nanomechanical properties of the Nb film, obtained through nanoindentation measurements, reveal a hardness of 2.8±0.3GPa, while the study of the electrical resistivity of the film shows the appearance of the superconducting transitions at 9.3K and 7.3K for Nb and Pb, respectively, very close to the bulk material values. Additionally, morphological, structural and contamination studies of Nb thin film expose a very low droplet density on the substrate surface, a small polycrystalline orientation of the films and a low contamination level. These results, together with the acceptable Pb quantum efficiency of 2×10−5 found at 266nm, demonstrate the potentiality of the new concept photocathode.

Modelling study of phase transitions in amorphous ultrathin films

The phase transition's critical temperature dependence of the thickness and critical magnetic concentration are studied using the method of configuration averaging over the interaction fields in the framework of the Ising model in amorphous ultrathin film to define the transition from ferromagnetic state to paramagnetic one. It is shown that the Curie temperature increases quickly with a rise in number of monolayers and critical magnetic concentration decreases to bulk material value.

Molecular beam epitaxy growth of superconducting LiFeAs film on SrTiO3(001) substrate

The stoichiometric “111” iron-based superconductor, LiFeAs, has attacted great research interest in recent years. For the first time, we have successfully grown a LiFeAs thin film by molecular beam epitaxy (MBE) on a SrTiO3(001) substrate, and studied the interfacial growth behavior by reflection high-energy electron diffraction (RHEED) and low-temperature scanning tunneling microscope (LT-STM). The effects of substrate temperature and Li/Fe flux ratio were investigated. A uniform LiFeAs film as thin as 3 quintuple layers (QL) is formed. A superconducting gap appears in LiFeAs films thicker than 4 QL at 4.7 K. When the film is thicker than 13 QL, the superconducting gap determined by the distance between the coherence peaks is about 7 meV, close to the value of bulk material. The ex situ transport measurement of a thick LiFeAs film shows a sharp superconducting transition around 16 K. The upper critical field, , is estimated from the temperature-dependent magnetoresistance. The precise thickness and quality control of the LiFeAs film paves the road for growing similar ultrathin iron arsenide films.

Effect of peak target power on the properties of Cr thin films sputtered by HiPIMS in deep oscillation magnetron sputtering (DOMS) mode

The advent of High-power Impulse Magnetron Sputtering (HiPIMS) and its variant Modulated Pulsed Power Magnetron Sputtering (MPPMS) allowed a new knob to control the flux of sputtered species, i.e., a new knob to control the kinetic effects of the growing film. Recently, a new design of the MPPMS pulses has been proposed to reduce arc generation. This form of high power pulses has been named deep oscillation magnetron sputtering (DOMS). In this work, the influence of the kinetic effects induced by a DOMS discharge on Cr sputtered thin films was studied and compared to direct current magnetron sputtering (DCMS) discharge. The Cr thin films were deposited with increasing peak power at the same average power (1.2kW) in order to minimize changes in the thermal effects that also influence film growth. The influence of the peak power on the morphology, structure and mechanical properties of Cr thin films was studied. The Cr films deposited by DCMS have a columnar morphology, a [110] preferential orientation, hardness between 7.2 and 8.5GPa and a maximum Young's modulus of 255GPa, value always lower than that for bulk material. Although substrate bias potential up to −110V was used, some porosity always remained in the DCMS films. The deposition rate of the Cr films deposited by DOMS with increasing peak power decreases from 60 to 30% of DCMS deposition rate. The films also have a [110] preferential orientation. Increasing the peak power changes the film morphology from columnar to dense, increases the hardness up to 17GPa, increases the lattice parameter and decreases the grain size. The Young's modulus of the films is always close to the bulk material value showing that all the films are porosity free.

Thermal Diffusivity of Carbon Materials as Candidate Reference Materials

Thermal-diffusivity measurements using the laser-flash method have been investigated in order to establish a thermal diffusivity standard. In many cases, thermal-conductivity values of bulk materials are calculated from the thermal diffusivity, specific heat capacity, and bulk density. The thermal diffusivity is one of the transport properties. It depends on the material and is sensitive to the structure. So, it is important to measure the thermal diffusivity of each material. The laser-flash method is one of the most popular methods for thermal-diffusivity measurements of bulk materials above room temperature. Because the method realizes a short-time method and is a non-contact method, it is very suitable for practical use. And it is known as a highly reliable measurement since one-dimensional heat diffusion phenomena observed in these measurements are simple. On the other hand, more reliable values measured by the method are important in the view of thermal design. According to the background, there is a need of a standard for thermal-diffusivity measurements using the laser-flash method to obtain reliable thermal diffusivities. The National Metrology Institute of Japan (NMIJ) in AIST has established reference materials for the laser-flash method and is supplying them. However, they are not sufficient to cover the whole range of thermal-diffusivity measurements. Thus, some candidate materials have been investigated to establish another reference material. Carbon materials are considered since it is preferable for the laser-flash method that the material is optically nontransparent and dark colored (ideally black). In this study, the thermal diffusivity of a pyrolytic graphite that is expected to be a candidate reference material for the laser-flash method is investigated. It was found that the intrinsic thermal diffusivities can be determined along the in-plane and cross-plane directions. The high thermal diffusivity of the in-plane direction, \(1.19 \times 10^{-3}\,\mathrm{m}^{2}\,{\cdot }\,\mathrm{s}^{-1}\), was successfully observed at room temperature. The thermal diffusivity along the cross-plane direction was determined to be \(4.8 \times 10^{-6}\,\mathrm{m}^{2}\,{\cdot }\, \mathrm{s}^{-1}\). It has indicated that the pyrolytic graphite has a large anisotropy from the view of the thermal diffusivity.

Formation energy of intrinsic point defects in nanometer‐thick Si and Ge foils and implications for Ge crystal growth from a melt

AbstractFormation energies of vacancies and self‐interstitials in nanometer‐thick Si and Ge foils are calculated by means of Density Functional Theory applying thin film models. Plate models consisting of six to sixteen atomic layers with c(4×2) dimer structures on both surfaces with a vacuum slab are used. The formation energies Ef of the intrinsic point defects of Si and Ge in the middle of the foil and obtained from the twelve layer models, are in good agreement with reported values for bulk material. In all cases, Ef in the middle of the foil decreases with decreasing foil thickness. Using the same twelve or more layers thin plate models for Si and Ge thus also allows comparing the formation energies of intrinsic point defects in the bulk. The thermal equilibrium concentration of Ge self‐interstitials near melt temperature is more than one order of magnitude lower than that of Si self‐interstitials while the vacancy concentrations are of same order of magnitude. Contrary to Si, the diffusivity of Ge self‐interstitials can therefore not recover the unbalance of the thermal equilibrium concentrations during crystal growth, even if the growth rate is reduced to very low values. This is the reason why Ge crystals grown from a melt are always vacancy‐rich which results in void formation in‐dependent of the crystal growth conditions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetostrictive thin films for microwave spintronics

Multiferroic composite materials, consisting of coupled ferromagnetic and piezoelectric phases, are of great importance in the drive towards creating faster, smaller and more energy efficient devices for information and communications technologies. Such devices require thin ferromagnetic films with large magnetostriction and narrow microwave resonance linewidths. Both properties are often degraded, compared to bulk materials, due to structural imperfections and interface effects in the thin films. We report the development of epitaxial thin films of Galfenol (Fe81Ga19) with magnetostriction as large as the best reported values for bulk material. This allows the magnetic anisotropy and microwave resonant frequency to be tuned by voltage-induced strain, with a larger magnetoelectric response and a narrower linewidth than any previously reported Galfenol thin films. The combination of these properties make epitaxial thin films excellent candidates for developing tunable devices for magnetic information storage, processing and microwave communications.

Experimental Investigation of the Thermal Conductivity of the Titanium Carbide Thin Films on Silicon Substrate

Thermal conductivities of the titanium carbide thin films with thickness ranging from 58 to 158 nm were measured at room temperature using the transient thermoreflectance technique. The results show that thermal conductivities of these films are lower than corresponding bulk material values. The reduction in the thermal conductivity can be attributed to the material microstructure brought by the thin film fabrication process. Both the film thickness and the atom ratio of Ti/C are the important factors. The thermal conductivity increases with the increasing film thickness and atom ratio of Ti/C. It also indicates that the material beneficial to thermal management and thermal design could be fabricated by improvement of the deposition techniques.