Thin Film Synthesis Technique Research Articles

High-pressure polycrystalline thin-film synthesis and semiconducting property of platinum pernitride

A polycrystalline platinum pernitride (PtN2) thin-film was successfully synthesized via nitridation of a platinum thin-film deposited on α-Al2O3 substrate at the pressure of ∼50 GPa by using the laser-heated diamond anvil cell. The current–voltage characteristic and optical reflectance of the synthesized PtN2 thin-film were measured under ambient conditions. Combined with first-principles calculations, these experimental results have revealed that PtN2 exhibits semiconducting property with a bandgap of ∼2 eV. This high-pressure thin-film synthesis technique could also be applied for revealing the physical properties of other novel pernitrides synthesized under ultra-high pressure, which can offer new insights into the physical properties and functionality of the pernitrides and related nitrides.

Synthesis and characterization of smart stimuli-responsive herbal drug-encapsulated nanoniosome particles for efficient treatment of breast cancer

Abstract Extraction from the herbs was performed using the Soxhlet method. Various formula was synthesized for niosomes containing the extracts through thin film synthesis technique, and the most efficient formulation was selected. Afterwards, physicochemical properties of niosomes, including size, polydispersity index (PDI), zeta potential, morphology, encapsulation efficacy (EE%), extract release rate, non-interactive action between the extracts and niosomes, antibacterial potential, and cellular uptake were assessed. Finally, the toxicity level of the niosomes to breast cancer cells was compared and their impact on the expression of p53 and MCL-1 was evaluated. Our data demonstrated that the synthesized niosomes were sensitive to the temperature and pH. Also, the niosomes containing Hedera Helix extract (Nio-HHE) sized 97.7 nm, with a zeta potential of −19.9 ± 6.7 mV, PDI of 0.35, and 58 ± 2.4% encapsulation efficacy showed more toxicity to the cancer cells than the niosomes of Glycyrrhiza glabra extract (Nio-GGE) with the size of 111 ± 8.5 nm, zeta potential of −23.5 ± 4.5 mV, PDI of 0.113, and 69 ± 1.2% encapsulation efficacy. The former system proved to have more antibacterial potential, and affect the expression of the oncogenes more than the latter. Meanwhile, both niosomal systems demonstrated an acceptable cellular uptake, and no chemical interaction with the extracts was observed. Furthermore, useful function of the synthesized niosomes was confirmed by morphological assessments. Our data confirmed that encapsulation of herbal extracts improves their anticancer and antibacterial potential. We concluded that Nio-HHE has more significant antitumor effects on breast cancer cells than Nio-GGE. Consequently, applying nano drug delivery systems based on herbal therapy could mitigate the side effects resulting from chemotherapy and radiotherapy, and offer promising perspectives for treatment of breast cancer.

Consistency and reproducibility in atomic layer deposition

Atomic layer deposition (ALD) is a thin film synthesis technique that can provide exquisite accuracy and precision in film thickness and composition even on complex, large area substrates. Based on self-limiting surface chemistry, ALD can be insensitive to process conditions and reactor designs, allowing an ALD process developed in one lab to be easily reproduced in other labs. In practice, however, ALD is sometimes difficult to reproduce or replicate, and the results can vary substantially between ALD reactors and between labs. This is exemplified by large deviations in reports on the growth of, e.g., Al2O3, FeOx, and TiO2 given the same precursors under similar conditions. Furthermore, the problem of irreproducibility seems to be growing as ALD is adopted by more researchers and integrated into new applications. In this article, the authors highlight some of the major sources of variations and errors and common misconceptions related to ALD. In particular, the authors focus on issues related to precursors, substrates, and deposition tools. The authors illustrate these problems through examples from the literature, and they present results from numerical simulations that describe how nonidealities would manifest in thickness profiles in a typical cross-flow reactor. They also describe how reproducibility in ALD is linked to consistent experimental practice and reporting between labs. The authors’ hope is that by educating newcomers to ALD and advocating for consistent reporting of deposition conditions, they can minimize irreproducibility and enable ALD practitioners to realize the full potential afforded by self-limiting surface chemistry.

Understanding Molecular Layer Deposition Growth Mechanisms in Polyurea via Picosecond Acoustics Analysis

Molecular layer deposition (MLD) is an increasingly important thin film synthesis technique in areas such as sensors, microelectronics, protective coatings, and catalysis. However, new analytical a...

(Invited) Phonon Engineering for Improved Seebeck Coefficient and Thermal Conductivity of Thermoelectric Nanolaminate Films Synthesized on Porous Templates

Recently promising advances have been achieved with phononic crystal (PnC) nanostructures in thermoelectric materials, because the thermal conductivity of PnC samples is lower compared to non-patterned thermoelectric samples due to phonon-boundary scattering. In this study we report on the successful synthesis of PbTe and PbSe thermoelectric layers on patterned porous silicon substrates by a thermal ALD system. PbTe/PbSe nanolaminates grown on porous silicon membranes have higher Seebeck coefficients than the ones grown on regular planar silicon wafers. The higher Seebeck values result from the lower thermal conductivity k in porous structures, which in turn lead to a higher figure of merit ZT. We demonstrate the feasibility to enhance the figure of merit ZT further by modulating the size and periodicity of the pattern and the thickness of the thermoelectric film in relation to the mean free path (MFP) of the phonons of the thermoelectric material. In our study PbTe and PbSe thin films and nanolaminates were synthesized by Atomic Layer Deposition (ALD) technology on regular planar silicon wafers and on macro-porous silicon templates. ALD is a surface saturating, self-limiting, absolutely conformal thin film synthesis technique reacting two pulsed precursors that enable film growth of one atomic layer per growth cycle. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and (trimethylsilyl) selenide ((Me3Si)2Se) were employed as the chemical ALD precursors for lead, tellurium and selenium, respectively. The surface morphology observations indicate Volmer–Weber growth mechanism of PbTe/PbSe nanolaminates during the thermal ALD deposition process rather than classic layer-by-layer growth. The ALD PbTe/PbSe nanolaminates exhibited complete surface coverage on planar bulk silicon wafers and also inside the pores of microporous silicon membranes. For the case of porous Si templates, the Seebeck measurements in both the horizontal and vertical directions revealed significant enhancement in Seebeck coefficients for PbTe/PbSe nanolaminates synthesized inside strictly periodic lithographically defined porous silicon membranes.

A revisit to atomic layer deposition of zinc oxide using diethylzinc and water as precursors

Nanophase zinc oxide (ZnO) has been widely studied as an important multifunctional material in many applications. Atomic layer deposition (ALD) is a unique thin-film synthesis technique, featuring its extreme uniformity, unrivaled conformal coverage, low deposition temperature, and precise controllability. Using diethylzinc (DEZ) and water as precursors, ALD has been reported previously for growing nanophase ZnO thin films. However, the growth characteristics and the resultant ZnO crystallinity have not been well characterized and understood. To this end, we revisited the ALD process of ZnO using DEZ and water. Through employing a suite of advanced characterization techniques, we systematically addressed the growth characteristics, morphological changes, and the crystallinity evolution of ZnO along with growth temperature in the range of 30–250 °C. The growth characteristics of the ALD ZnO films were investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy, atomic force microscopy, and synchrotron-based X-ray reflectivity. The crystallinity of the ALD ZnO films was determined using synchrotron-based X-ray diffraction and high-resolution transmission electron microscopy. In addition, through further analyzing QCM data, we proposed the adsorption-limited surface reaction for ALD ZnO growth with the temperature-dependent number of –OH surface group reacting with one DEZ molecule. Thus, this study contributes to offer new and deep insights on the fundamental ALD process of ZnO.

Selectable phase formation in VAlN thin films by controlling Al+ subplantation depth

We report on a thin film synthesis technique which allows for unprecedented control over the crystalline phase formation in metastable transition metal nitride based layers. For the model material system of V0.26Al0.74N, a complete transition from hexagonal to supersaturated cubic structure is achieved by tuning the incident energy, hence subplantation depth, of Al+ metal ions during reactive hybrid high power impulse magnetron sputtering of Al target and direct current magnetron sputtering of V target in Ar/N2 gas mixture. These findings enable the phase selective synthesis of novel metastable materials that combine excellent mechanical properties, thermal stability, and oxidation resistance.

Electronic structure ofLa2CuO4in theTandT′crystal structures using dynamical mean field theory

Using $N\text{th}$ order muffin-tin-orbital-based downfolding technique in combination with dynamical mean field theory, we investigate the correlated electronic structure of ${\text{La}}_{2}{\text{CuO}}_{4}$ in the so-called ``$T$'' and ``${T}^{\ensuremath{'}}$'' crystal structure which serve as the parent compounds for the hole-doped and electron-doped high ${T}_{c}$ compounds. ${\text{La}}_{2}{\text{CuO}}_{4}$, which naturally forms in $T$ structure, has been reported to made to form in ${T}^{\ensuremath{'}}$ structure by means of special thin-film synthesis technique of replacing La by isovalent $RE$ $(RE=\text{Y},\text{Lu},\text{Sm},\text{Gd}\dots{})$ ions [A. Tsukada et al., Solid State Commun. 133, 427 (2005)]. The experimental studies on ${T}^{\ensuremath{'}}$-structured ${\text{La}}_{2}{\text{CuO}}_{4}$ reveal contrasting properties to that in $T$ structure, which we examine by means of electronic structure calculations. Our dynamical mean field calculations show introduction of correlation effect to the one-electron band structure of ${T}^{\ensuremath{'}}$- and $T$-structured ${\text{La}}_{2}{\text{CuO}}_{4}$, providing metallic solution in one case $({T}^{\ensuremath{'}})$ and insulating solution to another $(T)$.

Combinatorial Thin Film Synthesis of Cerium Doped Scintillation Materials in the Lutetium Oxide—Silicon Oxide System

The search for new scintillator crystals can be limited by the time consuming nature of the crystal growth process. In this paper, we demonstrate the use of a combinatorial thin film synthesis technique that is being used to explore new scintillator materials. The combinatorial synthesis process utilizes up to four individual R.F. magnetron sputtering sources which can be simultaneously powered to generate a wide composition space of binary, ternary, or quaternary material systems. In this work, we have investigated the lutetium oxide (Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> )-silicon oxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) material system doped with cerium. Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5-</sub> doped with cerium has been thoroughly characterized due to its use in PET imaging and provides a good benchmark for our proposed approach. Thin film, cerium doped lutetium oxide-silicon oxide gradients were synthesized to investigate the phases of the material system that exhibit scintillation properties and the results were compared to the results of bulk crystal samples. We have found that the emission spectra of the thin film materials have similar characteristics compared to the bulk crystals. Additionally, X-ray diffraction measurements have been correlated to the anticipated phases of the equilibrium phase diagram, and the intensity of the luminescence emission spectra have been correlated with the corresponding phases of the system.

Fourier transform approach for thickness estimation of reflecting interference filters

An empirical procedure based on optical-density-bandwidth products was recently proposed for thickness estimation of dielectric thin film reflectors. A parallel is established with new results derived from the Fourier transform thin film synthesis technique. Two Fourier-transform approaches are proposed and justified by numerical examples.

Ultraviolet emitting (Y 1− xGd x) 2O 3− δ thin films deposited by radio frequency magnetron sputtering: Combinatorial modeling, synthesis, and rapid characterization

Gadolinium-doped, yttrium oxide thin films have been deposited on silicon (001) substrates by radio-frequency (RF) magnetron reactive sputtering that exhibit cathodoluminescence (CL) at ultraviolet frequencies. The maximum CL brightness occurred at λ∼314–315 nm characteristic of the 6P 3 / 2 → 8S ( λ = 314 nm) transition observed in Gd-doped, yttrium oxide powders. The radiative recombination takes place at the rare earth activator Gd 3+ site embedded in the Y 2O 3− δ host; the optical transition resides within the band gap of the Y 2O 3− δ host and the transition observed is characteristic of atomic gadolinium. A combinatorial approach to sputtering was used to deposit a film of variable composition from 1 to 23 at.% Gd in Y 2O 3− δ in order to rapidly discern the composition node of optimal CL brightness. A simulation was created for the purpose of predicting the film combinatorial composition for binary and ternary alloys prior to sputtering experiments in order to facilitate our combinatorial thin film synthesis technique. The model prediction varied from the real experimental composition profile by only 2.2 at.% Gd ± 1.6 at.% proving the predictor as a useful aide to complement combinatorial thin film experiments. A film of composition Y 1.56Gd 0.44O 3.25 (8.3 at.% Gd) yielded the maximum CL brightness. CL brightness increased continuously up to the 8.3 at.% Gd composition due to the increased number of activators present in the host. Beyond this composition the brightness drastically decreased. The oxygen composition in the combinatorial film was strongly dependent on the Gd composition; films were sub-stoichiometric δ > 0 below ∼6 at.% Gd and was over-stoichiometric δ < 0 beyond this composition.

Tailored nanoparticle films from monosized tin oxide nanocrystals: Particle synthesis, film formation, and size-dependent gas-sensing properties

In order to investigate the change of gas-sensitive properties of undoped tin oxide nanoparticle films depending on particle size, a thin film synthesis technique has been developed. Well-defined tin oxide nanoparticles have been prepared using a gas-phase condensation method. Pure SnO was used as starting material and was evaporated at T=820 °C. The resulting particles were sintered and crystallized in-flight at T=650 °C. Size-selected nanoparticles ranging from 10 to 35 nm were produced to form a nanoparticle film by means of electrostatic precipitation or low pressure impaction. The effect of in-flight oxidation, sintering, and crystallization on the structure, size, and size distribution of nanoparticles have been studied in detail. The samples show n-type semiconductors’ behavior like bulk SnO2. The influence of particle size on gas sensitivity and response behavior is investigated for C2H5OH at operating temperatures 200–300 °C using silicon substrates having an interdigitated contact pattern and an integrated heating system. In the range of 10–35 nm it has been shown unambiguously that decreasing the particle size of tin oxide particles leads to an increase of the sensitivity and a more rapid response on changing gas conditions. The effect is especially clear for films with a particle size of 20 nm or smaller.

Modified needle method with simultaneous thickness and refractive-index refinement for the synthesis of inhomogeneous and multilayer optical thin films

Useful features of an efficient thin-film synthesis technique based on the refinement of inhomogeneous films are adapted to the needle method. As in the former approach, all the layer refractive indices and thicknesses are refined simultaneously, and special attention is given to computation speed and accuracy. In particular, key parameters are calculated from analytical formulas, namely, the gradients used in the optimization routines and the optimum needle positions and refractive indices. Inhomogeneous as well as multilayer solutions are possible. The efficiency of the modified approach is demonstrated by the solution of a complex nonpolarizing, wide-angle antireflection coating problem. The results are compared with those obtained in the past by the conventional needle method and by refinement of inhomogeneous films.

Optical coating synthesis by simultaneous refractive-index and thickness refinement of inhomogeneous films

A fast, efficient thin-film synthesis technique is described. Dielectric films are subdivided into thin layers whose refractive indices and thicknesses are varied simultaneously. Because of the large number of optimized parameters, speed and accuracy are given special attention. The efficiency of the method is demonstrated by the successful reproduction of several complex nonpolarizing filters synthesized in the past with the needle method, one of the best approaches currently available.

Fourier transform technique with refinement in the frequency domain for the synthesis of optical thin films

An optical thin-film synthesis technique combining a Fourier transform approach with the refinement of design parameters in the Fourier space is proposed. The theory and numerical examples are described.

Synthesis and Characterization of ( CeO2 ) 0.8 ( SmO1.5 ) 0.2 Thin Films from Polymeric Precursors

(CSO) has been suggested for solid oxide fuel cell (SOFC) applications, because of its higher electrical conductivity and chemical stability, compared to other ceria‐based materials. However, CSO is difficult to densify under conditions compatible with other SOFC components. A thin film synthesis technique has been developed for the fabrication of dense CSO films from precursor solutions at relatively low temperatures. Dense, smooth, and homogeneous films were obtained on Pt, single‐crystal Si, and (LSCF) substrates by spin‐coating a polymeric precursor and subsequent heat‐treatment. Crystallization of the film occurred at temperatures as low as 320°C. The developed oxide film did not react with , LSCF, or (YSZ) at temperatures up to 1200°C. When a CSO layer was applied between LSCF and YSZ, a significant improvement in the interfacial resistance was observed. The results suggest that CSO can be used as a buffer layer on YSZ electrolytes for improved performance of high temperature SOFCs.