Solution Deposition Process Research Articles

Phase transition, leakage conduction mechanism evolution and enhanced ferroelectric properties in multiferroic Mn-doped BiFeO3 thin films

Pure and Mn-doped BiFeO3 thin films were prepared by a facile chemical solution deposition process. X-ray diffraction patterns and Raman spectra imply a phase transition from a rhombohedral structure in pure BiFeO3 film to a nearly tetragonal structure in Mn-doped BiFeO3 films. Moreover, it is found that doping of Mn could greatly modify the surface morphology, leakage current properties and ferroelectric properties of BiFeO3 films. Consequently, the lowest leakage current density and the largest remnant polarization are observed in BiFe0.925Mn0.075O3 film which could be well explained by the leakage conduction mechanism and its evolution from the space-charge-limited current behavior for BiFeO3 and BiFe0.95Mn0.05O3 films to the Poole–Frenkel emission for BiFe0.925Mn0.075O3 film, as well as completely an Ohmic behavior for BiFe0.90Mn0.10O3 film. Based on the X-ray photoelectron spectroscopy analysis of Mn ions, we argue that the varied valences of Mn ions such as Mn4+, Mn3+ and Mn2+ may play an important role in lowering leakage current density and enhancing the ferroelectric properties of BiFeO3 films.

Influence of Aliovalent Doping on Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Film for Voltage Tunable Applications

Ba0.6Sr0.4TiO3 thin film with aliovalent doping of acceptor nature at ‘A’ lattice sites of ABO3 structure were prepared by a metal organic solution deposition (MOSD) technique on low loss quartz substrate. Oxide thin film having perovskite structure, namely, lanthanum nicklate (LaNiO3), also deposited using chemical solution deposition technique (CSD), was used as conductive bottom electrode. Solution properties and deposition process parameters were optimized for crack-free, uniform and smooth, pure and doped BST films on LNO electrode. The structural and microstructural analyses of the film were done using X-ray diffraction (XRD) and atomic force microscopy (AFM). Dielectric properties of the deposited film were studied using C-V and C-F electrical characterizations. The results indicate high tunability of 46%, very low loss tangent of 0.0065 with corresponding figure of merits of 71 for 2% K doped BST films at 1 MHz. The considerable improvement of dielectric properties of doped films compare to pure BST film is due to combined effect of perovskite lattice matched conductive bottom electrode and optimum doping level. These films had moderate dielectric constant, very low loss with good tunability which is suitable for tunable microwave applications.

High reproducibility of perovskite solar cells via a complete spin-coating sequential solution deposition process

The controllability of conditions and parameters, in a certain procedure that adopted to prepare perovskite absorption layer, play a crucial role in morphology and crystallization of the resulting films, which is of great impact on the reproducibility of solar cells. Here we propose a complete spin-coating sequential solution deposition (spinning-SSD) process, in which a high concentration CH3NH3I precursor was spin-coated on PbI2-coated substrate insteading of immersing procedure; the pristine isopropanol was spin-coated to ameliorate the surface morphology and improve the quality of the resulting CH3NH3PbI3 films both before and after the spin-coating of CH3NH3I solution. Utilizing this spinning-SSD process, we fabricated meso-structured perovskite solar cells, and these devices exhibited decent performance and high reproducibility, achieving an average power conversion efficiency of 11.3% with the standard deviation as low as ±0.52. This optimized approach is expected to be used for fabricating high-performance perovskites solar cells with a full printable process.

Dielectric and Ferroelectric Performance of Pb(Zr(x)Ti(1-x))O3 Thin Films with Compositional Gradients.

A series of PZT thin films with compositional gradients were fabricated at ease by a combinatorial chemical solution deposition process. Their dielectric and ferroelectric properties are significantly different from uniform composition PZT films, depending on the composition, the span, and the direction of the compositional gradient. Among samples with the same average Zr content, the down-gradient thin films exhibit better dielectric and ferroelectric properties. PZT thin films with a narrow compositional gradient span favour better dielectric and ferroelectric properties. The down-gradient thin film PZT654 with a Zr-rich layer closest to the Pt substrate, in which the average composition is close to the morphotropic phase boundary (MPB, x = 0.52), shows the best dielectric and ferroelectric performance. These distinct thin films with different dielectric and ferroelectric properties could be designed by adjusting factors such as content, span and direction of the compositional gradient.

Towards the 3D Thin-Film Li-Ion Battery: A Novel Solution-Based Process for the Deposition of (Multi-)Metal Oxide Coatings on High Aspect Ratio Features

Many types of rechargeable batteries are on the market of which lithium ion chemistries capture the main part of the portable electronics. Conventional Li-ion battery technology typically uses slurries (based on powders) for the active electrode component in combination with a liquid electrolyte. In order to overcome the relatively high risk of shorts and hence thermal runaway or explosions, due to the high inflammability of the electrolyte, membrane separators and a bulky casing are necessary. As an alternative, all-solid-state Li-ion batteries and in particular thin film based battery technology is being explored. It is obvious that the use of compact thin films as components in these commercially available devices has advantages regarding safety, especially when it comes to the electrolyte. Furthermore, they are characterized by a higher resistivity against (electro)chemical degradation, resulting in a longer cycle life. The typical lower conductivity of solid electrolytes, compared to liquid electrolytes, is compensated by the thinness of the films. However, planar thin film electrodes limit the maximum energy density of these devices. Therefore, 3D thin-film batteries, consisting of electrode and electrolyte thin films, coated on 3D structured surfaces, creating a large surface area and thus an higher energy density, are proposed. One can understand that for this new type of batteries, which are currently in an exploratory stage, there is a strong need for coating of various oxides (electrodes and electrolyte) on 3D surfaces.[1] Conformal coverage of high surface area 3D substrates is typically done via atomic layer deposition (ALD). However, ALD suffers from high running and equipment costs, low throughput (especially for substrates with a strongly increased surface area) and a limited applicability towards complex, multi-metal oxides.[2] In view of commercial 3D battery applications and upscaling, there is a strong need to overcome these disadvantages. We present a novel chemical solution deposition (CSD) process for the deposition of (multi-)metal oxide coatings on 3D substrates, i.e. silicon micropillars coated with 20 nm TiN.[3] The CSD method has been developed first for TiO2, a candidate anode material. As starting point, an aqueous citrate-peroxo Ti precursor, which had been successfully applied for the deposition of uniform, good quality TiO2on planar substrates via spin coating [4], was used. This precursor system was optimized, in particular by adding an additive, to allow coating on high aspect ratio features. The whole was spray coated at 180°C and by controlling all levels of the process, complete coverage of the silicon pillars with the Ti precursor was obtained. Since the deposition was performed at elevated temperature, the solution was instantly transformed into a gel, consisting of coordinated complexes in which Ti ions were immobilized. The deposited gel, which was already partly decomposed due to the elevated deposition temperature, is shown in the SEM images in Figure 1. Further heat treatment of the pillars lead to the complete combustion of the gel and thus to titanium oxide formation, it also triggered the crystallization of the deposited layer. A thorough crystallization study indicated that phase-pure TiO2 anatase films could be obtained by a well-defined post deposition anneal at 500°C. Lithium-ion insertion and extraction behavior was observed for the anatase film deposited on TiN-coated silicon pillars, indicating its application potential for 3D Li-ion batteries. The presented technique was also successfully applied to deposit Li4Ti5O12 on the microstructured substrate. Because of its negligible volume change upon charge/discharge, this anode material seems best suited for thin-film applications.[1] On-going research further shows that the reported novel method, which implies operational simplicity, low cost and relatively short deposition times, can be applied to achieve a series of multi-metal oxide coatings (e.g. LLTO) on 3D substrates, bringing commercial thin-film 3D Li-ion batteries one step closer to reality. [1] P. M. Vereecken et al., ECS Transactions, 58(10), 111-118 (2013). [2] (a) T. R. B. Foong et al., Adv. Funct. Mat., 20, 1390-1396 (2010) / (b) S. M. George, Chem. Rev., 110, 111-131 (2010). [3] S. Gielis et al., EP/PCT patent, submitted. [4] (a) A. Hardy et al., J. Sol-Gel Sci. Technol., 44, 65-74 (2007) / (b) I. Truijen et al., J. Sol-Gel Sci. Technol., 41, 43-48 (2007). Figure 1

Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices.

The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5-15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln2O2CO3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 μC/cm(2), and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices.

Enhanced performance of layer-evolved bulk-heterojunction solar cells with Ag nanoparticles by sequential deposition

Organic photovoltaic devices based on layer-evolved bulk-heterojunction (LE-BHJ) from poly{[4,4′-bis(2-ethylhexyl) dithieno(3,2-b:2′,3′-d)silole]-2,6-diyl-alt-[4,7-bis(2-thienyl)-2,1,3-benzothiadiazole]-5,5′-diyl} (Si-PCPDTBT)/[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) are successfully fabricated by a sequential solution deposition process. During the process of a top layer being deposited from an appropriate cosolvent ratio control, the top layer of PC71BM vertically penetrates a pre-coated layer of Si-PCPDTBT, resulting in an inter-diffused nanostructure with an LE-BHJ surface morphology. The LE-BHJ cells exhibit improved nanoscale phase separation and comparable performance, in comparison with the conventional BHJ device. Furthermore, Ag nanoparticles (NPs) with optimized ratio embedded LE-BHJ exhibit significant enhanced efficiency in comparison with the conventional BHJ and pristine LE-BHJ devices, because the multiple scattering from the Ag NPs leads to longer optical paths, which give rise to effective absorptivity and reduced leakage current within the BHJ active film.

Fluorene copolymer bilayers for emission colour tuning in inverted hybrid light emitting diodes

We report a novel solution deposition process for TFB in inverted OLEDs and demonstrate tuneable emission.

Mössbauer spectra and electric properties of 57Fe-enriched BiFeO3 thin films

57Fe-enriched BiFeO3 (BFO) thin films are fabricated on Pt/Ti/SiO2/Si substrates from a stoichiometric precursor solution by chemical solution deposition process. The microstructure of the thin films is controlled by a changing the sintering time at 550 °C. The polycrystalline thin film fabricated at 550 °C for 5 min shows well-saturated polarization–electric field (P–E) hysteresis loops and the remnant polarization Pr and coercive field Ec at room temperature are 52 µC/cm2 and 365 kV/cm, respectively, at an applied electric field of 1200 kV/cm. The Mössbauer spectra show that the BFO thin film has the valence state of Fe3+ only, consisting of antiferromagnetic and paramagnetic components. The paramagnetic component with an area fraction from 11 to 18%, which is not amorphous or Bi2Fe4O9, seems to distribute in the surface shell of the grains and the grain boundaries. This component must strongly influence the ferroelectric properties at room temperature.

Investigation of Photovoltaic and Optical Properties of Self-Organized Organic-Inorganic Hybrids Using Aromatic Drugs and Patterned Silicon

The effect of incorporation of the functional groups of aromatic moleculas onto the Si surface has been investigated by photovoltaic (PV) and photoluminescence (PL) characteristics, infrared (IR) spectroscopy, scanning electron microscopy (SEM), and optical microscopy (OM). To realize the organic-inorganic hybrids, the thin (10–100 nm) layers of heteroatom aromatic pharmaceutical drugs (APD) such as clonidine hydrochloride (CLON), procainamide hydrochloride (PRO), and сyanocobalamin (CYCAM – B12 vitamin) were formed by the chemical solution deposition process on the Si patterned surface at room temperature under laboratory ambient conditions. The hybrids have shown: (i) the solar energy conversation with an efficiency up to 6–7% in dependence on the chemical solution media and the surface and interface morphologies; (ii) the highest efficiency of 8.4% in CLON–Si hybrids produced in a mixed solution with a layer 30 nm in thickness and a self-organized net-like surface morphology; (iii) the intense photoluminescence in the waverange of 400–900 nm, luminescence profile, and peak position suggest the vibronic origin of this band; (iv) the presence of characteristic bands associated to the functional groups containing nitrogen (amines NHx (x = 0, 1, 2), amides OCN, cyanonitrile CN), carbon and/or hydrogen-hydrocarbons (CHx (x = 1, 2, 3)), oxygen (hydroxyl OH, peptide CO), halogene (chloroalkane) and phosphorus (phosphate OPO(OH)2). Possible principles of operation of APD–Si hybrids are discussed.

Microreactor-Assisted Solution Deposition for Compound Semiconductor Thin Films

State-of-the-art techniques for the fabrication of compound semiconductors are mostly vacuum-based physical vapor or chemical vapor deposition processes. These vacuum-based techniques typically operate at high temperatures and normally require higher capital costs. Solution-based techniques offer opportunities to fabricate compound semiconductors at lower temperatures and lower capital costs. Among many solution-based deposition processes, chemical bath deposition is an attractive technique for depositing semiconductor films, owing to its low temperature, low cost and large area deposition capability. Chemical bath deposition processes are mainly performed using batch reactors, where all reactants are fed into the reactor simultaneously and products are removed after the processing is finished. Consequently, reaction selectivity is difficult, which can lead to unwanted secondary reactions. Microreactor-assisted solution deposition processes can overcome this limitation by producing short-life molecular intermediates used for heterogeneous thin film synthesis and quenching the reaction prior to homogeneous reactions. In this paper, we present progress in the synthesis and deposition of semiconductor thin films with a focus on CdS using microreactor-assisted solution deposition and provide an overview of its prospect for scale-up.

Effect of internal and external constraints on sintering behavior of thin film electrolytes for solid oxide fuel cells (SOFCs)

The effect of internal and external constraints on the sintering behavior of yttria-stabilized zirconia (YSZ) thin film electrolytes is investigated for intermediate-temperature solid oxide fuel cells (SOFCs). The external constraints imposed by rigid substrates result in major process flaws, such as vertical and delamination cracks during film densification, in a chemical solution deposition (CSD) process. In this study, YSZ nanoparticles are incorporated into the precursor solution to impose internal constraints and control the shrinkage rate of the sol–gel matrix. Because the structural stability of the thin film is determined by the grain size distribution, it is critical to optimize the content and dispersion structure of the nanoparticles and the sintering temperature to obtain a gas-tight thin film electrolyte for SOFCs. A clustering model is proposed to obtain a comprehensive understanding of the sintering behavior of the YSZ thin-film electrolyte containing the nanoparticles in the CSD process.

ChemInform Abstract: UV‐Assisted Nucleation and Growth of Oxide Films from Chemical Solutions

AbstractReview: 50 refs.

Fabrication of high-performance graphene field-effect transistor with solution-processed Al2O3 sensing membrane

High performance graphene field-effect transistors (FETs) with a solution-processed Al2O3 sensing membrane were fabricated. The solution-processed deposition technique offers a lot of advantages in terms of low cost, simplicity, high throughput, and large-area devices. Especially, the solution-deposition process is well-suited for membrane formation of graphene FETs, which is vulnerable to plasma or thermal processes for insulator growth on surface. The graphene FETs with a solution-deposited Al2O3 sensing membrane exhibited a higher pH sensitivity as well as good chemical stability. Therefore, the graphene FETs with solution-deposited Al2O3 sensing membrane are very promising to biological sensors application.

Photoelectric properties of BiVO4 thin films deposited on fluorine doped tin oxide substrates by a modified chemical solution deposition process

BiVO4 films deposited on Fluorine doped tin oxide glass substrates were successfully prepared by a modified chemical solution deposition process. Structure and optical spectrum analysis show that the resultant BiVO4 films consist entirely of monoclinic scheelite structure and have a narrow band gap of ～2.66 eV. The films were investigated by photoelectrochemical and photovoltaic measurements with regard to hydrogen production and solar energy conversion under visible light. The BiVO4 photoanodes show significantly higher visible light induced photoelectrochemical performance (～1.1 mA/cm2 at 1.0 V vs. Ag/AgCl) than those reported ones, which is very promising for splitting water to H2 and O2. A Schottky BiVO4 solar cell was also investigated for comparison with photoelectrochemical measurements. The correlation between the photoelectrochemical and photovoltaic behavior for BiVO4 was explained. Our research should provide important support for the applications of BiVO4 films or its modified forms such as doping and nanocomposite in heterojunction photoelectrochemical cells and solar cells with suitable energy level alignment at the interface.

Fabrication of thin-film gadolinia-doped ceria (GDC) interdiffusion barrier layers for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by chemical solution deposition (CSD)

A dense gadolinia-doped ceria (GDC) interdiffusion barrier layer as thin as 300nm was successfully fabricated on a rigid anode/electrolyte bilayer substrate using the chemical solution deposition (CSD) process for intermediate temperature solid oxide fuel cells (SOFCs). Drying-related macro-defects were removed by employing drying control chemical additives (DCCA), which effectively relieved drying stresses. The major process flaws caused by the constraining effects of the rigid substrate were completely eliminated by the addition of GDC nanoparticles into the chemical solution, which suppressed the generation of microstructural anisotropy by mitigating the predominant bi-axial substrate constraints. As a consequence, a thin film GDC interlayer was successfully deposited with a high volumetric density, effectively preventing the chemical interaction between the electrolyte and cathode during the fabrication process and subsequent operation. The cell test and microstructural analysis confirmed excellent electrochemical performance and structural and chemical stability. The CSD process presented in this paper is considered to be a promising technology for the practical preparation of GDC thin film barrier layers for intermediate temperature SOFCs based on the film quality, processing costs and potential for large-scale production.

UV-assisted nucleation and growth of oxide films from chemical solutions

The fabrication of thin oxide films at low temperatures using simple processes has been a significant challenge associated with expanding the potential applications of these materials. Recent developments have demonstrated that the photo-assisted chemical solution deposition (PACSD) process offers a promising means of solving these difficulties, allowing high volume, on-demand production of variable sample sizes using an advantageous wet process. A better understanding of the crystal growth phenomena associated with this process, however, is required to enable various oxide thin films to be prepared using this new concept. Under pulsed ultraviolet (UV) laser irradiation, crystal growth has been confirmed to proceed by near-instantaneous photothermal heating and photochemical effects at the reaction interface. Vacuum UV lamp irradiation is also a useful means of generating oxide nuclei, since it results in effective chemical bond cleavage and simultaneously produces reactive oxidant (O3/O((1)D)) species. In this review, the nucleation and growth mechanisms which occur during the PACSD process are introduced and discussed and we examine the future possible applications of this process.

Observation of high dielectric constant of Bi-Nb-O<sub>x</sub> thin-film capacitors fabricated by chemical solution deposition process

Observation of high dielectric constant of Bi-Nb-O<sub>x</sub> thin-film capacitors fabricated by chemical solution deposition process

A simple one-step solution deposition process for constructing high-performance amorphous zirconium oxide thin film

Based on the magic substance dopamine (DA), a simple and effective one-step solution deposition strategy has been developed for constructing high-performance amorphous zirconium oxide (ZrO2) nanocomposite thin film. DA can be auto-polymerized to form a polydopamine (PDA) coating, which adheres strongly to the silicon substrate and serves as an active platform to induce the subsequent deposition of ZrO2. The obtained ZrO2 nanocomposite thin films with the thickness of about one hundred nanometers presents outstanding mechanical and tribological performances even without a subsequent high-temperature annealing process. More importantly, the preparation process is definitely low-consumption and environmentally friendly. This work overcomes the claim that ZrO2 films obtained by aqueous solution deposition process generally possess low mechanical properties and thus avoid the defects of focusing mainly on nature and performances of heat-treated and crystalline ZrO2. Based on this work, it is believed that the as-deposited ZrO2 nanocomposite film can be widely used as a protecting coating and lubricating material for micro- and nano-electromechanical systems (MEMS/NEMS) and many other systems working in similar conditions.

Fabrication of YBCO/CeO2/YBCO multilayer films through an all chemical solution deposition approach

In this paper, the growth characteristics and superconducting properties of YBCO/CeO2/YBCO multilayer films derived from an all chemical solution deposition process layer by layer are investigated. X-ray diffraction results show that the c-axis epitaxial growth feature of the bottom YBa2Cu3O7-δ (YBCO) film was perfectly inherited. Alternating epitaxial growth of YBCO/CeO2/YBCO multilayer films was confirmed by high resolution transmission electron microscopy in combination with selected area electron diffraction, which will lay the groundwork for preparation of SIS-type Josephson junctions. In addition, nanosized BaCeO3 particle rather than BaCeO3 transition layer was observed in the interface between YBCO and CeO2. The superconductivity measurement results show that the proposal method gives better superconducting properties only for high magnetic field and at low magnetic field it deteriorates the superconducting properties.