Injection Metal Organic Chemical Vapor Research Articles

Dimensionality Effect on Surface States and Piezoelectric Behavior in ZnO Nanowires Grown by Pulsed-Liquid Injection Metal–Organic Chemical Vapor Deposition

Dimensionality Effect on Surface States and Piezoelectric Behavior in ZnO Nanowires Grown by Pulsed-Liquid Injection Metal–Organic Chemical Vapor Deposition

Epitaxial LiNbO3 growth and layer transfer for thin-film electro-optic modulator realization

The aim of the PhD project is to develop a new trend in modulation system for Exail company: thin film (<1 μm) lithium niobate (LN) electro-optic modulator. It exhibits better performance in term of bandwidth, power consumption and footprint than legacy ones [1-3]. This PhD is a cooperation between Exail photonics which is world-renowned for the performances of their electro-optic modulators and FEMTO-ST institute which can offer the possibility to grow stoichiometric LN thin film by means of direct liquid injection metalorganic chemical vapor deposition (DLI-MOCVD). This cooperation opens the possibility to obtain industrialization of optical device based on CVD LN stoichiometric layers which allow to have enhanced performances such as higher electro-optic coefficient than that of congruent compositions of commercial single crystals. Thus, all steps from MOCVD layer deposition to modulator realization can be done here in Besançon.

Contribution of numerical modelling to design oxygen electrode for micro-solid oxide cells: A case study of high-performance nano-columnar La2NiO4 thin films

This article presents a numerical study that aims to guide the development of nano-columnar La2NiO4 thin films as high performing oxygen electrodes for micro-Solid Oxide Cell (μSOC). La2NiO4 thin films were deposited by Pulsed Injection Metal Organic Chemical Vapor Deposition (PI-MOCVD) and their performance is characterized by Electrochemical Impedance Spectroscopy (EIS) and Electrical Conductivity Relaxation (ECR). Excellent performance is obtained for 1 μm thick film with an Area Specific Resistance (ASR) of 0.12 Ω cm2 at 600 °C, making them suitable for low-temperature μSOCs. A Finite Element Method (FEM) model has been implemented and used to predict the ASR and impedance spectra in order to guide further optimization of the film thickness and morphology. After experimental validation of the model using various electrode thicknesses, the optimal value is estimated to be between 3 and 4 μm for the temperature range of 450–650 °C. For each temperature and thickness, the model can clearly predict whether the electrode is limited by the surface exchange reactions or the bulk diffusion. The simulations revealed that the gas diffusion process is not rate-limiting when the electrode thickness is below 5 μm and the temperature is below 650 °C. Furthermore, a geometrical parameters analysis study allowed to determine the ideal nano-columnar morphology for this promising electrode composition.

Correlation between the Dimensions and Piezoelectric Properties of ZnO Nanowires Grown by PLI-MOCVD with Different Flow Rates

Zinc oxide nanowires (ZnO NWs) have gained considerable attention in the field of piezoelectricity in the past two decades. However, the impact of growth-process conditions on their dimensions and polarity, as well as the piezoelectric properties, has not been fully explored, specifically when using pulsed-liquid injection metal–organic chemical vapor deposition (PLI-MOCVD). In this study, we investigate the influence of the O2 gas and DEZn solution flow rates on the formation process of ZnO NWs and their related piezoelectric properties. While the length and diameter of ZnO NWs were varied by adjusting the flow-rate conditions through different growth regimes limited either by the O2 gas or DEZn reactants, their polarity was consistently Zn-polar, as revealed by piezoresponse force microscopy. Moreover, the piezoelectric coefficient of ZnO NWs exhibits a strong correlation with their length and diameter. The highest mean piezoelectric coefficient of 3.7 pm/V was measured on the ZnO NW array with the length above 800 nm and the diameter below 65 nm. These results demonstrate the ability of the PLI-MOCVD system to modify the dimensions of ZnO NWs, as well as their piezoelectric properties.

Corrosion barrier alumina/zirconia bilayer stack on low Cr steel by direct liquid injection metalorganic chemical vapor deposition

Numerous industrial fields necessitate the development of advanced metallic materials presenting high corrosion resistance in aqueous media and being less expensive than classical high chromium steels. In the present work, amorphous zirconia, alumina and alumina/zirconia coatings have been deposited on 2 wt% chromium steel coupons using an innovative direct liquid injection metal organic chemical vapor deposition process. Scanning electron microscopy and X-ray diffraction reveal that the alumina sublayer acts as an efficient barrier against steel oxidation occurring during the amorphous zirconia deposition performed under O2 at 400 °C. They also show that the steel oxidation occurring concomitantly to the zirconia coating modifies the film morphology by increasing its roughness and thickness, in comparison with the same zirconia coating on alumina. The anticorrosive properties of the thin films have been studied by an immersion test of the bare and coated coupons in deionized water at 80 °C during 6 days and by electrochemical impedance spectroscopy in aqueous sodium chloride solution for 48 h. They reveal that, in contrast to alumina and zirconia monolayers alone, the alumina/zirconia stack acts as a corrosion protection coating in pure water through a synergetic barrier effect against (i) oxidation by alumina and (ii) aqueous corrosion by zirconia.

Numerical Study of Growth Rate and Purge Time in the AlN Pulsed MOCVD Process

The relationship between the purge time and the overall growth rate in pulsed injection metal–organic chemical vapor deposition with different V/III ratios is studied by numerical analysis. The transport behavior of TMAl and TMAlNH3 during the process is studied to understand the effect of the adductive reaction. The results show that, as the V/III ratio increases, there is a significant reduction in the average growth rate per cycle, without the addition of a purging H2 pulse between the III and V pulses, due to stronger adductive reaction. The adductive reaction can be reduced by inserting a purging pulse of pure H2 between the III and V pulses, but there is a decrease in the overall growth rate due to the longer cycle time. At smaller V/III ratios, the growth rate decreases with increasing purge times, since the gain in reducing the adductive reaction is offset by the detrimental effect of extending the cycle time. The degree of reduction in the adductive reaction is higher for larger V/III ratios. When the benefit of reducing the adductive reaction overcomes the deficiency of the extending cycle time, a remarkable enhancement of the growth rate can be obtained at high V/III ratios by inserting a pure H2 purge pulse between the III and V pulses. A higher overall growth rate can be achieved at higher V/III ratios by choosing an appropriate purge time.

Tuneable polarity and enhanced piezoelectric response of ZnO thin films grown by metal–organic chemical vapour deposition through the flow rate adjustment

The formation process of ZnO thin films grown by pulsed-liquid injection metal–organic chemical vapour deposition (PLI-MOCVD) has a major impact on its morphological, structural, electrical and piezoelectric properties, but their correlation has not been elucidated yet nor decoupled from the thickness effects.

Low temperature Direct Liquid Injection MOCVD of amorphous CrCx coatings in large-scale reactors: An original route to nanostructured multilayer coatings

The effect of low temperature deposition on the quality and the microstructure of hard a -CrC x coatings grown by Direct Liquid Injection Metal-Organic Chemical Vapor Deposition (DLI-MOCVD) was investigated. At deposition temperatures higher than 525 °C, the coatings are bi-phased and polycrystalline , essentially composed of Cr 7 C 3 with Cr 3 C 2 as a minor phase. By decreasing the temperature in the 525–350 °C range, they are amorphous and exhibit a monolithic glassy-like microstructure without grain boundary. For temperatures lower than 350 °C, the uniform amorphous microstructure changes for a lamellar multilayer structure, while the composition of the gas phase was kept constant at the inlet of the reactor for all these CVD runs. The origin of this surprising lamellar structure has been investigated. After having discarded the idea of a self-organized multilayer growth, sometimes encountered in CVD processes, evidence was found for rapid changes in the deposition mechanism. They are induced by oscillations of the surface temperature around a critical value due to the regulation of the furnace used for such large-scale reactors. These almost periodic temperature changes lead to modulations in the surface composition of nutrient species, and subsequently, to the growth of multilayers. The individual composition of lamellae changes regularly, while the overall composition of the coatings remains identical to that of uniform monolithic coatings. For growth conditions leading to local temperature close to the critical value, a regular and controlled nanostructuring can be obtained with a period close to a hundred nanometers. Similar to monolithic a -CrC x coatings, these a -CrC x multilayer coatings exhibit a good barrier behavior against high temperature oxidation, according to the test performed. As future prospects, the main interest for these lamellar coatings could be their mechanical properties thanks to the numerous interfaces capable of deflecting and dissipating the propagation of cracks. • Chromium carbide coatings are deposited by DLI-MOCVD at very low temperatures. • A lamellar microstructure forms at temperatures as low as 325 °C. • Oxidation barrier behavior is fully conserved with the multilayer structure. • Changes in temperature and reaction mechanisms explain the lamellar growth.

Effects of thermal annealing on the structural and electrical properties of ZnO thin films for boosting their piezoelectric response

The growth process and post-deposition treatment have strong effects on the structure of ZnO thin films, which can also affect significantly their electrical and piezoelectric properties. In this report, the effect of high temperature annealing under oxygen atmosphere on ZnO stacked thin films grown on silicon by pulsed-liquid injection metal-organic chemical vapor deposition is investigated in detail. By varying the annealing temperature from 600 to 1000 °C, the structural analysis reveals the occurrence of c-axis oriented grain coarsening and growth processes associated with the improvement of crystallinity and removal of carbon impurities. The electrical resistivity also varies strongly with thermal annealing. Those variations are accompanied by an enhancement of the piezoelectric amplitude measured by piezo-response force microscopy (PFM). Interestingly, the PFM measurements reveal the predominant development of O- and Zn-polar domains at low and high temperature annealing, respectively, originating from the anisotropic grain boundary velocity. The present findings show that the high temperature annealing under oxygen atmosphere in ZnO thin films can enhance not only its piezoelectric amplitude but also its Zn-polarity uniformity, which unambiguously leads to the improvement of its piezoelectric performance.

Superconducting protector against electromagnetic pulses based on YBCO film prepared on an Al2O3 substrate with a CeO2 sublayer

The electric and magnetic properties of microbridges made from 440 nm thick Y–Ba–Cu–O films prepared on Al2O3 substrates with CeO2 sublayers by the pulsed injection metal organic chemical vapor deposition (MOCVD) method were studied in temperatures ranging from 20 K to 300 K in order to investigate the possibilities of using these microbridges as fast fault current limiters. The application of an external magnetic field () causes the flux flow induced magneto-resistive effect, which is proportional to and to at low and high temperatures, respectively. The experimentally obtained S-shaped I–V characteristic and the change of the microbridge resistance over time when affected by a step-like magnetic field can be well explained using a thermo-electrical model based on Joule heating and the flux flow nature of the resistive state (RS). The transition from the superconducting to the RS, studied using ns duration rectangular waveform electrical pulses able to create up to ≈2106 A cm−2 current densities without rises of microbridge temperatures, demonstrated that the I–V characteristics of the RSs consisting of an assembly of straight lines corresponding to the different pinning centers. At temperatures close to the critical temperature of superconductivity, the number of these lines increases, and the I–V characteristics can be described with high accuracy by a power law. It was concluded that microbridges made from these films can be used as protectors against complicated waveform electromagnetic pulses having short rise times, high voltage peak amplitudes and long low-value over-current ‘tails’.

Engineering Copper Adhesion on Poly-Epoxy Surfaces Allows One-Pot Metallization of Polymer Composite Telecommunication Waveguides

Mass gain in the aerospace sector is highly demandable for energy savings and operational efficiency. Replacement of metal parts by polymer composites meets this prerequisite, provided the targeted functional properties are recovered. In the present contribution, we propose two innovative and scalable processes for the metallization of the internal faces of carbon fiber reinforced polymer radiofrequency waveguides foreseen for implementation in telecommunications satellites. They involve sequential direct liquid injection metalorganic chemical vapor deposition of copper and cobalt. The use of ozone pretreatment of the polymer surface prior deposition, or of cost effective anhydrous dimethoxyethane as solvent for the injection of the copper precursor, yield strongly adherent, 5 µm Cu films on the polymer composite. Their electrical resistivity is in the 4.1–5.0 μΩ·cm range, and they sustain thermal cycling between −175 °C and +170 °C. Such homogeneous and conformal films can be obtained at temperatures as low as 115 °C. Demonstration is achieved on a polymer composite waveguide, composed of metallized 60-mm long straight sections and of E-plane and H-plane elbows, that paves the way towards the metallization of scale one devices.

Interface structure and strain relaxation in Nd0.96MnO3 epilayers grown on (001) SrTiO3 substrates

In this work we focus on the growth of highly oriented Nd0.96MnO3 (NMO) perovskite epilayers of different thickness on single-crystalline (001)SrTiO3 (STO) template, using an injection metal-organic chemical vapor deposition process. X-ray diffraction revealed that the epilayers have an orthorhombic Pnma structure and were purely ((1¯01) oriented parallel to the (001) plane of the substrates. The orientation relationships between the film and substrate are rather well defined in the vicinity of the interface as 1¯01NMO//[001]STO (out-of-plane), 101NMO//[100]STO and [010]NMO//[010]STO (in plane). It can be concluded that the film thickness significantly influences the strain state of the NMO epilayers deposited on STO. There was a contraction of out-of-plane layer network spacing leading to a progressive relaxation in the growth direction. The out-of-plane lattice parameter is lower than the bulk value. As the film thickness increases, the NMO epilayer strain reduces so that out-of-plane lattice parameters tend towards their bulk values. The calculated strain goes from −0.4%(thickness of 150 nm) to 0% (thickness of 600 nm). These epilayers are therefore strained at the interface and relax with the thickness. The out-of-plane lattice parameter observed for the 600 nm thick epilayer relaxed toward the bulk NMO. No traces of extra phases are detected. An atomic model of interfaces has been built using cross-sectional transmission electron microscopy image, as well as a crystallographic simulation software CrystalMaker.

Alumina layer using low-cost direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD) on AISI 1018 steel

Amorphous alumina layers were deposited on low carbon steel (AISI 1018) substrates by the direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD) technique. For the DLI- MOCVD technique, two temperatures were used: a vaporization chamber temperature of 180 °C and a reaction chamber temperature of 370 °C. Liquid precursor aluminum tri-sec-butoxide was introduced in form of atomized liquid, each pulse of 1 Hz frequency and 3 ms opening time, the solution was pressurized at 40 psi under inert Argon atmosphere. 200 sccm of Argon were used as continuous carrier gas during all the deposition process. Microscopy and XRD techniques were used to characterize the deposited material. The thickness of the alumina coatings was of 100 μm, approximately.

Morphology Transition of ZnO from Thin Film to Nanowires on Silicon and its Correlated Enhanced Zinc Polarity Uniformity and Piezoelectric Responses.

ZnO thin films and nanostructures have received increasing interest in the field of piezoelectricity over the last decade, but their formation mechanisms on silicon when using pulsed-liquid injection metal-organic chemical vapor deposition (PLI-MOCVD) are still open to a large extent. Also, the effects of their morphology, dimensions, polarity, and electrical properties on their piezoelectric properties have not been completely decoupled yet. By only tuning the growth temperature from 400 to 750 °C while fixing the other growth conditions, the morphology transition of ZnO deposits on silicon from stacked thin films to nanowires through columnar thin films is shown. A detailed analysis of their formation mechanisms is further provided. The present transition is associated with strong enhancement of their crystallinity and growth texture along the c-axis together with a massive relaxation of the strain in nanowires. It is also related to a prevailed zinc polarity, for which its uniformity is strongly improved in nanowires. The nucleation of basal-plane stacking faults of I1-type in nanowires is also revealed and related to an emission line at about 3.326 eV in cathodoluminescence spectra, further exhibiting fairly low phonon coupling. Interestingly, the transition is additionally associated with a significant improvement of the piezoelectric amplitude, as determined by piezoresponse force microscopy measurements. The Zn-polar domains exhibit a larger piezoelectric amplitude than the O-polar domains, showing the importance of controlling the polarity in these deposits as a prerequisite to enhance the performances of piezoelectric devices. The present findings demonstrate the high potential in using the PLI-MOCVD system to form ZnO with different morphologies and polarity uniformity on silicon. They further reveal unambiguously the superiority of nanowires over thin films for piezoelectric devices.

Metalorganic chemical vapor deposition and investigation of nonstoichiometry of undoped BaSnO3 and La-doped BaSnO3 thin films

Wide bandgap (~3 eV) perovskite transparent conductive oxide material exhibiting superior electric properties is highly desired in today's optoelectronics. Just recently La-doped barium stannate (LBSO) bulk n-type semiconductor with outstanding carrier mobility (~320 cm2 V−1 s−1) at high carrier density (1020 cm−3) has been discovered. Highly conductive thin LBSO film synthesis has been challenging due to large lattice mismatch and nonstoichiometry as being the least investigated. Therefore, in this work, the Pulsed injection metalorganic chemical vapor deposition method was used for the growth of undoped BaSnO3 (BSO) and La-doped BaSnO3 thin films. Film depositions were carried out on monocrystalline LaAlO3, SrTiO3, Al2O3 substrates in wide stoichiometric range. Deviation from stoichiometric composition in BSO (Sn/Ba) and LBSO (Sn/(Ba + La)) had a significant impact on microstructure, optical, and electric properties while maintaining cubic symmetry. Near-stoichiometric films even grown at a high rate of ~10 nm/min showed sufficient electric properties.

Integration of LaMnO3+δ films on platinized silicon substrates for resistive switching applications by PI-MOCVD.

The next generation of electronic devices requires faster operation velocity, higher storage capacity and reduction of the power consumption. In this context, resistive switching memory chips emerge as promising candidates for developing new non-volatile memory modules. Manganites have received increasing interest as memristive material as they exhibit a remarkable switching response. Nevertheless, their integration in CMOS-compatible substrates, such as silicon wafers, requires further effort. Here the integration of LaMnO3+δ as memristive material in a metal–insulator–metal structure is presented using a silicon-based substrate and the pulsed injection metal organic chemical vapour deposition technique. We have developed three different growth strategies with which we are able to tune the oxygen content and Mn oxidation state moving from an orthorhombic to a rhombohedral structure for the active LaMnO3+δ material. Furthermore, a good resistive switching response has been obtained for LaMnO3+δ-based devices fabricated using optimized growth strategies.

Black Co oxides coatings for thermosensitive polymer surfaces by low-temperature DLI-MOCVD

Black coatings are deposited at low temperature in order to enable the functionalization of thermosensitive substrates, such as epoxy-based carbon fiber reinforced polymers (CFRP). The direct liquid injection metalorganic chemical vapor deposition of Co oxide films is performed with the dicobalt octacarbonyl precursor, Co2(CO)8, in the temperature range 50°C–160°C, on Si substrates, first. Films morphology can be described by a dense sublayer on which the typical “cauliflower” microstructure grows, with a large amount of voids and open porosity. We obtain nanocrystalline CoO in the deposition temperature range 50°C–125°C, and nanocrystalline (CoO+Co3O4) above 125°C. The bulk composition of the films is Co(45)O(45)C(10). Over the deposition temperatures tested, films processed at 125°C repetitively show the lowest reflectivity in the visible range. An important role in the optical reflectivity is attributed to the carbon content, although it is not possible to decorrelate microstructural changes from the carbon elimination in calcination experiments. Finally, we reproduce the above-mentioned results with success on CFRP substrates, and demonstrate the applicability of the process on thermosensitive composite parts with results comparable to the state-of-the-art in the visible range.

Magnetoresistance anisotropy of ultrathin epitaxial La0.83Sr0.17MnO3 films

We present the study of temperature dependence of resistivity (ρ), magnetoresistance (MR), and magnetoresistance anisotropy (AMR) of thin epitaxial La0.83Sr0.17MnO3 films. The films with thickness from 4 nm to 140 nm were grown on an NdGaO3 (001) substrate by a pulsed injection metal organic chemical vapor deposition technique. We demonstrate that the resistivity of these films significantly increases and the temperature Tm of the resistivity maximum in ρ(T) dependence decreases with the decrease of film thickness. The anisotropy of ρ(T) dependence with respect to the electrical current direction along the [100] or [010] crystallographic axis of the film is found for ultrathin films (4–8 nm) at temperatures close to Tm. Both MR and AMR, measured in magnetic fields up to 0.7 T applied in the film plane parallel and perpendicular to the current direction, have shown strong dependence on the film thickness. It was also found that the anisotropy of magnetoresistance could change its sign from positive (thicker films) to negative (ultrathin films) and obtain very small values at a certain intermediate thickness (20 nm) when the current is flowing perpendicular to the easy magnetization axis [010]. While the positive AMR effect was assigned to the conventional magnetic ordering of manganites, the AMR of ultrathin films was influenced by the pinning of magnetization to the easy axis. The temperature dependence and change of the AMR sign with film thickness is shown to be well described by the two-region model (more strained closer to the film substrate and more relaxed further from it) assuming that the relative concentration of both regions changes with the film thickness. The possibility to use the effect of the AMR compensation for the development of scalar in-plane magnetic field sensors is discussed.

Magnetoresistance Relaxation Anisotropy of Nanostructured La-Sr(Ca)-Mn-O Films Induced by High-Pulsed Magnetic Fields

The results of investigation of colossal magnetoresistance relaxation in nanostructured La-Sr(Ca)-Mn-O films upon removal of magnetic field pulse are presented. Thin films having thicknesses of 75-350 nm grown by pulsed injection metal-organic chemical vapor deposition technique were studied in pulsed magnetic fields having duration of 0.9 ms and amplitudes of 2-12 T. It was obtained that “fast” relaxation process occurring in hundred microseconds time scale exhibits anisotropy: the magnitude of remnant resistivity is approximately three times smaller and the process is faster when magnetic field is applied perpendicular to the film plane in comparison with in-plane direction. The dynamics of this relaxation process was analyzed using Kolmogorov-Avrami-Fatuzzo model, taking into account nucleation and reorientation of magnetic domains into equilibrium state. The “fast” remnant relaxation was not observed after the application of longer pulses (20 ms) having amplitude of 60 T. Influence of remnant relaxation on operation of B-scalar magnetic field sensors based on nanostructured manganite films is discussed.

Up-conversion luminescence in Er/Yb-doped YF3 thin films deposited by PLI-MOCVD

We have studied the NIR (near infrared) to visible up-conversion of Er/Yb co-doped YF3 thin films prepared by PLI-MOCVD (pulsed liquid injection metal-organic chemical vapor deposition). Violet, strong green, as well as red emission bands corresponding to intra-4f transitions in Er3+ were observed under 972nm excitation. The up-converted emission was studied as a function of the Yb concentration and in doing so, a change in the red/green emission intensity ratio was observed. We attributed this, on one hand, to an Er-to-Yb back transfer corresponding to 4S3/2 → 4I13/2:2F7/2 → 2F5/2, which starts to occur at increasing Yb concentrations. As a consequence, the red emission is shown to be enhanced through an upward energy transfer 4I13/2 → 4F9/2. On the other hand the depopulation of 4S3/2 is also related to an upward transfer from Yb to Er corresponding to transition 2F5/2 → 2F7/2 :4S3/2 → 4G9/2 which is enhanced by an increasing Yb concentration. We performed power-dependent up-conversion luminescence measurements to confirm the proposed excitation mechanisms. Finally, lifetimes of the intermediate states 4S3/2 and 4F9/2 were determined, to show the influence of the Yb concentration on the relaxation processes in Er3+.