Limiting Film Thickness Research Articles

All-Chemical YBCO-Based Architecture Using a Simplified Multilayer Buffer Deposition

Chemical solution deposition (CSD) is a versatile and cheap technique widely used for both buffer layer and YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7−<i>δ</i></sub> (YBCO) epitaxial film growth. One of the main limits hindering the widespread use of the CSD technique in the field of coated conductors is the limited film thickness that can be reached without degradation. Among the different strategies adopted to obtain thicker film by CSD, increase of precursor solution concentration and viscosity can be mentioned. Another interesting approach is the use of multilayer deposition in order to overcome the limits of CSD technique. Multilayer deposition has been so far realized by performing a complete heat treatment - or at least a pyrolysis step - after each deposited layer, resulting in increased processing time and overall cost. In this contribution, we show that an epitaxial multilayer buffer can be easily obtained by means of multiple successive depositions, in which after each layer only a fast drying step of the precursor solution is carried out. In this way, only a single conversion heat treatment can be used. This approach not only allows a significant reduction on the processing time but also it is more suitable for the growth on metallic template. The viability of this approach is shown by using multilayer Zr-doped CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer deposition on single crystalline YSZ substrate. It is shown that, up to 8 layers, no significant structural and morphological degradation of the buffer layer occurs. Further, YBCO film grown by CSD was used to test the suitability of multilayer buffer. YBCO film grown on multilayer buffer shows excellent superconducting properties, with zero-resistance critical temperature up to 92 K and a critical current density exceeding 1 MA/cm2 at 77 K in self field.

Parametric analysis on flooding limit and critical film thickness of a vertical two-phase closed thermosyphon

Flooding limit is the most severe limitation in the operation of a two-phase closed thermosyphon (TPCT). However, the effect of condenser length to the critical heat flux (CHF) and the influences of structural and operational parameters to the critical liquid film thickness (CFT) were not universally concerned. In the present study, a comprehensive model for TPCT is developed to predict the CHF and CFT. In particular, the proposed model is validated through three criterions. Based on the validated model, parametric analysis of the structural and operational parameters is comprehensively carried out, and variations in CHF and CFT are illustrated and discussed in detail. Simplified correlations for CHF are finally proposed based on the numerical modeling results. The results indicate that the CHF decreases with increasing absolute length and evaporator length, while increases with increasing vapor temperature, condenser length, and inner diameter. However, the increment due to the condenser length is limited. The CFT has different fluctuation trends in comparison with the CHF. It increases first and then decreases with increasing vapor temperature and inner diameter, while reverses with increasing absolute length and condenser length, and remains unchanged with increasing evaporator length. Meanwhile, the effect of working fluids to the CHF and the effect of aspect ratios to the CFT both indicate that much efforts need to be made to further understanding the TPCT. However, correlations of CHF can be obtained in a good agreement with the numerical modeling results within 30% deviation for the whole limited scope.

Strained ultra-thin films of BaO: a molecular dynamics investigation

A recent theoretical work by Bousquet and collaborators have predicted that ferroelectric ordering could be induced in the rocksalt oxides of alkaline earth metals (BaO, MgO, CaO and SrO) by strain. The expected functional properties present in these strained binary oxides, like polarization, dielectric constant and piezoelectric response, would be comparable to those of typical ferroelectric perovskites. Consequently, the strained binary oxides would be promising materials for fabrication of devices like ferroelectric memories and sensors. One possible way to explore the potential underlying these theoretical predictions is to grow thin and ultra-thin films of these binary oxides under epitaxial strain by choosing an adequate substrate. In such systems the interplay between epitaxial strain and the lack of translational symmetry (limited film thickness) may lead to the formation of interesting (anti)ferroelectric phases. Our goal in this work is to explore the potential structural and functional phase diagram of BaO ultra-thin films (thickness of only 8 BaO layers, ≈ 20 nm) obtained for different values of compressive epitaxial strain and temperature by performing a molecular dynamics investigation. A polarized phase (antipolar) is observed at a compressive strain of -9.0%, wich resists till a melting temperature around 1500 K, which is indeed high for such an ultra-thin film.

Electrochemical formation of oxide films on Ti6Al4V alloy

The results of the study of the process of electrochemical oxidation of Ti6Al4V titanium alloy in solutions of tartaric, citric and oxalic acids are presented. It is shown that the nature of the forming dependencies of the alloy depends on the magnitude of the current density. When ja&lt;0,5 A∙dm–2, a continuous oxide film does not form on the alloy surface and the specified voltage value is not reached. At ja&gt;0,5 A∙dm–2, a continuous oxide film forms on the surface of the alloy and linear dependences are observed. Films produced under these conditions are interference colored. The maximum thickness of the film is determined by the specified value of the forming voltage U and does not depend on other parameters of electrolysis. For a number of identical values of U, the dependence of the limiting film thickness has a linear form. The color of the oxide film is determined by the voltage value and does not depend on the current density and electrolyte concentration. It is established that the color of the film corresponds to the magnitude of the forming voltage in the range of 10–100 V. The effect is due to the fact that film formation during anodic polarization occurs under the presence of a potential gradient, the magnitude of which is constant for titanium. An increase in a given value of U leads to a proportional increase in the limiting thickness of the oxide, which determines the color of its color. The research results to determine the effect of electrolysis parameters on the characteristics of oxide films make it possible to substantiate the regime for producing TiO2 films on the surface of the Ti6Al4V alloy. The obtained data are the basis for the development of technology for the electrochemical oxidation of titanium alloys to give their surface functional properties

Coherent piezoelectric strain transfer to thick epitaxial ferromagnetic films with large lattice mismatch

Strain control of epitaxial films using piezoelectric substrates has recently attracted significant scientific interest. Despite its potential as a powerful test bed for strain-related physical phenomena and strain-driven electronic, magnetic, and optical technologies, detailed studies on the efficiency and uniformity of piezoelectric strain transfer are scarce. Here, we demonstrate that full and uniform piezoelectric strain transfer to epitaxial films is not limited to systems with small lattice mismatch or limited film thickness. Detailed transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements of 100 nm thick CoFe2O4 and La2/3Sr1/3MnO3 epitaxial films on piezoelectric 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 substrates (+4.3% and −3.8% lattice mismatch) indicate that misfit dislocations near the interface do not hamper the transfer of piezoelectric strain. Instead, the epitaxial magnetic oxide films and PMN-PT substrates are strained coherently and their lattice parameters change linearly as a function of applied electric field when their remnant growth-induced strain state is negligible. As a result, ferromagnetic properties such as the coercive field, saturation magnetization, and Curie temperature can be reversibly tuned by electrical means. The observation of efficient piezoelectric strain transfer in large-mismatch heteroepitaxial structures opens up new possibilities for the engineering of strain-controlled physical properties in a broad class of hybrid material systems.

Phonon transport in two-dimensional silicon thin film: influence of film width and boundary conditions on temperature distribution

Radiative phonon transport in two-dimensional silicon thin film is considered and equivalent equilibrium temperature is analyzed for different boundary conditions at the film faces. The influence of the film thickness on phonon transport is also examined and limiting film thickness for two-dimensional phonon transport is demonstrated. It is found that the two-dimensional phonon transport reduces to one-dimensional transport for the film width more than or equal to the twice of the thickness of the silicon film. Equivalent equilibrium temperature predicted, agrees well with the previous findings.

아스팔트 피막두께 변화에 따른 중온 아스팔트의 접착성질에 관한 연구

Warm-Mix Asphalt(WMA) technologies have been developed since 15 years ago, which are internationally and domestically concerned with energy-saving and environmental-friendly technologies in public and private sectors of highway engineering. The performance of asphalt mass is traditionally evaluated by the penetration, viscosity, or Superpave tests. This research, however, is focused more on the properties depending on asphalt film thicknesses instead of evaluating asphalt mass behaviors by those tests. For this approach, a new testing protocol and analysis method are described by the bonding properties on each film thickness. This testing method and analysis tool are borrowed from those of DSR Moisture Damage test and applied by using ARES. The analysis results indicate that there is a limit film thickness between and , which causes significant changes of the properties. In addition, the results show that the property changes of Hot-Mix Asphalt(HMA) and WMA on the limit film thickness are also different. Therefore, it is suggested that the properties on thin film thicknesses between and should be considered in order to evaluate WMA properly.

Morphology of Semicrystalline Diblock Copolymer Thin Films upon Directional Solvent Vapor Flow

AbstractThe possibility of achieving templates of highly ordered nanostructures with crystalline nano‐objects embedded inside an amorphous matrix is addressed. Atomic force microscopy and grazing incidence small‐angle X‐ray scattering (GISAXS) are used to probe the morphology at the surface and inside thin films of the diblock copolymer polystyrene‐block‐poly(ethylene oxide) P(S‐b‐EO). Directional benzene vapor flow introduces the orientation of poly(ethylene oxide) (PEO) cylinders inside the PS matrix. Within a limited film thickness regime, the cylinders are oriented parallel to the sample surface in domains of several micrometers due to shearing effects caused by the flow of benzene vapor parallel to the polymer surface. The crystallization of the PEO block by the benzene vapor treatment is also observed and crystals with sizes that approach that of the confined PEO domains are formed. Perpendicular orientation of the PEO crystalline stems with respect to the PEO cylindrical nanodomains is deduced from grazing incidence X‐ray diffraction. X‐ray reflectometry and scanning electron microscopy complement the investigation. magnified image

Fabrication of desired three-dimensional structures by holographic assembly technique

We demonstrate a novel technique to fabricate desired three-dimensional (3D) periodic structures by holographically assembling multiple one-dimensional (1D) or multiple two-dimensional (2D) structures. Thanks to the high-absorption effect of the used material, we fabricated for each time, by employing a two-beam interference technique, a 1D or a 2D structure with very limited film thickness. By using the same sample and repeating the same fabrication process, i.e., (i) spin coating, (ii) exposure, and (iii) post-exposure bake, we created, layer-by-layer, a 3D structure as desired, without the limitation of the number of layers. This technique allows rapid fabrication of very large and thick 3D photonic crystal template with variable period, flexible design, low cost, and possible introduction of arbitrary defects inside a 3D structure.

Luminescent Properties of Eu-Doped Lanthanum Oxyfluoride Sol−Gel Thin Films

Highly luminescent Eu3+-doped LaOF thin films have been prepared by a sol−gel procedure using La(hfa)3 diglyme (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = bis(2-metoxyethyl)ether) as a single-source precursor for lanthanum and fluorine. Europium doping (Eu/La = 3 and 10 atom %) has been achieved by adding the proper amount of europium acetate hydrate (Eu(CH3CO2)3·xH2O, x ≤ 4) to the precursor solution. After single-layer deposition, the obtained coatings were heat treated in air up to 700 °C. All the samples, under UV irradiation, presented a bright red luminescence clearly visible to the naked eye notwithstanding the low europium content and the limited film thickness (≤50 nm). The microstructure, composition, and morphology of the samples and their interplay with the synthesis conditions were investigated by glancing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and field emission scanning electron microscopy (FE-SEM)....

Highly Photoluminescent Silica Layers Doped with Efficient Eu(III) and Tb(III) Antenna Complexes

Eu(III) and Tb(III) antenna complexes employing different units−phenanthroline and acetophenone derivatives−for light absorption and sensitization of the lanthanide (Ln) emitting states, have been synthesized and successively anchored in silica layers by the sol−gel technique. The luminescence properties of the complexes, preliminarily studied in H2O and D2O solutions, were improved in the oxide host matrix, showing the effectiveness of the employed synthesis route for the preparation of efficient molecular-based light-emitting materials. All the prepared films were highly transparent and homogeneous and displayed a bright red (Eu3+) or green (Tb3+) luminescence notwithstanding the low luminophore content (Ln/Si = 1/400 or 1/100 molar ratios) and limited film thickness (≤140 nm). It is worth highlighting that the silica layers containing the Tb3+ complex bearing an acetophenone derivative as an antenna are characterized by photoluminescence quantum yields as high as 45%.

From Low-k to Ultralow-k Thin-Film Deposition by Organosilicon Glow Discharges

Continuous and modulated discharges, fed with divinyltetramethyldisiloxane mixed with oxygen and argon, were used to deposit carbon-doped silica-like (SiCOH) low- to ultralow- films. The effect of various process parameters on the dielectrical and thermal properties of films as well as on their chemical composition were investigated. As deposited, the SiCOH films exhibited dielectric constants from 4.45 to 2.70. Thermal annealing in the temperature range was found to be necessary to reach ultralow-permittivity values, but the temperature must be controlled in order to prevent an excessive collapse of the silicate matrix, which leads to poor thermal stability and mechanical properties. Lowering the oxygen content in the discharge allowed for a continuous decrease in values down to 2.32 when low radio frequency power was used, with a limited film thickness loss upon annealing of 11%. Fourier transform infrared spectra of ultralow- film exhibited intense absorptions from C-containing moieties, like and . Upon annealing at , the organic content considerably decreases, though the loss of groups is quite limited. Thermogravimetric analysis coupled with mass spectrometry revealed that during thermal treatment, silicon-containing fragments were lost from the matrix along with hydrocarbon ones.

Interfacial Interaction Dependence of Microdomain Orientation in Diblock Copolymer Thin Films

The dependence of the orientation of lamellar microdomains in thin films of symmetric diblock copolymers of polystyrene-b-polymethyl methacrylate was quantitatively investigated by small angle neutron scattering, transmission electron microscopy (TEM), and reflectance optical microscopy. A mixed orientation of the lamellar microdomains was found when the difference in the interfacial energies between each block and the substrate was not strong enough to force the orientation of the lamellae parallel to the substrate throughout the film. A limiting film thickness was found, below which a parallel alignment of the lamellar microdomains was seen throughout the film. This film thickness was found to depend on the strength of the interfacial interactions of each block with the substrate. TEM images indicate that the surface field suppresses the fluctuations in the microdomain, reduces defects, and consequently, propagates the orientation of the domains parallel to the surface into the film.

Efficient Detection of Oxygen Vacancy Double Donors in Capacitors with Ultra-thin Ta2O5 Films for DRAM Applications by Zero-bias Thermally Stimulated Current Spectroscopy

Efficient Detection of Oxygen Vacancy Double Donors in Capacitors with Ultra-thin Ta₂O₅ Films for DRAM Applications by Zero-bias Thermally Stimulated Current Spectroscopy

Growth of Passivating CuBTA Films on Copper in Aqueous Chloride/Benzotriazole Solutions

The growth of cuprous benzotriazole films (CuBTA), formed on Cu monocrystals and vapor deposited films under controlled potential conditions (+0.040 vSHE.) in I M NaCI + 5.6 X 10 M 1-H benzotriazole, has been studied by measurement of electrical charge. Film growth follows a direct logarithmic relationship to 25 nm thickness and effects of crystallographic orientation are insignificant. Variations in film growth under similar test conditions are attributed to variations in the randomness of CuBTA polymers in the film. A limiting film thickness is predicted, after which slow dissolution occurs without further thickening.

Early Stages of Film Creation in Thin Diblock Copolymer Films

Thin poly(styrene-block-p-methylstyrene) diblock copolymer films on top of silicon substrates were examined right after preparation and during the early stages of annealing. Using specular and off-specular X-ray scattering as well as scanning force microscopy, the film morphology is determined. With the spin-coating technique films are prepared which exhibit a roughness correlation between the substrate and the copolymer surface within a limited film thickness and molecular weight range right after preparation. The transferred part of the roughness spectrum of the substrate is probed and explained as a morphology of a frozen liquid with a surface bending rigidity. During annealing the energetically unfavorable roughness replication decays, and an internal ordering is formed. The decay of long-range correlation is explained by a surface diffusion where diffusion is slowed down as compared to bulk behavior.

Multi-layer structure for chemical vapor deposition diamond on electroplated diamond tools

In this work we established a process to overcome the deposition difficulty on electroplated diamond tools by a multi-layer structure. The process consists of the following steps: (1) diamond powder aggregation with nickel (this step is the conventional method for the production of electroplated tools); (2) electrochemical deposition of a chromium layer, but leaving the diamond grains partially uncovered; (3) nitridation of the chromium layer; and (4) deposition of the chemical vapor deposition (CVD) diamond layer. This method uses the advantages and overcome the disadvantages of each step. Electroplating with nickel is conventionally used due to its relatively good wettability to diamond. The direct aggregation of the diamond powder with a chromium layer results in looser grains and is not usable. The nickel layer is inadequate for diamond deposition; even after treatment in hydrogen atmosphere, diamond does not grow on it. The chromium nitride layer is well known to be very suitable for diamond growth, however, the thermal stress between these layers is very high limiting film thickness and its applicability. With the multi-layer structure obtained the CVD diamond film is deeply anchored by the diamond grains into the metal matrix and helps considerably to decrease the stress. The process has been developed on flat surfaces and tested on small conventional diamond burrs. The diamond films have been characterized by scanning electron microscopy (SEM), energy dispersive X-rays (EDS) and Raman spectroscopy (RS).

Mechanical properties of multilayer pvd Ti/TiB2 coatings

To obtain from a tribological perspective acceptable PVD coatings of covalently bonded materials, such as borides and oxides, it is essential to control and often reduce the very high compressive stresses which develop during coating growth, since such stresses not only reduce coating adhesion but also limit film thickness. A possible way to obtain lower stress levels could be to utilise multilayer coatings, that is to combine the stressed material with a more ductile material in a layered structure. In the present study a highly stressed PVD TiB2 material was layered with ductile Ti. The multilayer period, i.e. the combined thickness of one Ti lamella and one TiB2 lamella, and the lamellar thickness ratio of the two phases were varied in order to evaluate their influences on some important mechanical properties and on the abrasive wear resistance of the Ti/TiB2 coatings. The coatings were deposited using magnetron sputtering of TiB2 and electron beam gun evaporation of Ti. To evaluate the coating phase composition X-ray diffraction was used. Mechanical and tribological properties were examined by nanoindentation (hardness and modulus), beam deflection (residual stress), scratch testing (cohesion and adhesion), and dimple grinding (abrasive wear resistance). Hardness, Young’s modulus, compressive residual stress, and abrasive wear resistance were found to increase with the fraction of TiB2 in the coatings, and an inverse relation was found for the critical normal load obtained in scratch tests, i.e. cohesion/adhesion decreased with increasing TiB2 fraction. The investigation showed that a hybrid PVD technique combining electron beam evaporation of Ti and magnetron sputtering of TiB2 can be used to produce coatings with increased fracture toughness, decreased residual stress, and relatively high hardness as compared to homogeneous PVD TiB2 . It was also found that the yield/fracture strength of Ti was insufficient, i.e. it could not accommodate the level of stress generated in the TiB2 phase. Therefore, by choosing another material with higher yield/fracture strength than Ti it is believed that the properties of the multilayer coating could be improved even further.

General stress reduction mechanisms for the deposition of cubic boron nitride thin films

Intense ion bombardment has been necessary so far to produce cubic boron nitride thin films independent of the deposition technique used. Unfortunately, residual stress is one of the consequences of ion–surface interactions, leading to low adhesion and limited film thickness. In this study, boron nitride thin films were deposited by r.f.magnetron sputtering of a hexagonal boron nitride target combined with r.f. argon ion bombardment. The films were characterized by X-ray reflectivity analysis, X-ray Auger electron and infra-red spectroscopy as well as stress analysis. Stress reduction mechanisms are discussed: (1) deposition at higher substrate temperatures, (2) post-annealing, (3) post-ion implantation, (4) addition of a third alloying component, (5) multilayer concept, and (6) optimization of the deposition parameters.

Tensile and fracture behavior of free-standing copper films

We have studied tensile deformation and crack growth behavior of free-standing, electron beam evaporated copper films suspended over windows etched in a silicon substrate. In-situ straining experiments were performed on these films using a transmission electron microscope. External tests were conducted on a piezoelectric-driven microtensile system. Macroscopically, these copper films exhibited very low ductility ( < 1%). Dislocation activity was limited in regions far from propagating cracks. We discuss this in terms of how limited film thickness and fine grain size restrict dislocation glide distances and source operation during uniform loading. Near stable growing cracks, we observed considerable local plasticity. We saw evidence of slip activity both within grain interiors and in grain boundaries near such cracks. Although some dislocations moved very fast, others showed rates much lower than those typically measured for bulk copper. Fracture was both intergranular and transgranular, and occurred by linking of microcracks. Microcracks formed within one grain diameter or so of the main crack, usually within a grain boundary. Linking then took place by the easiest available path. A thickness-limited fracture toughness relation adequately describes the observed behavior.