Photochemical Metal-organic Deposition Research Articles

Selector-less crossbar array resistive RAM based on TiO2 fabricated by photochemical metal-organic deposition

In this study, we demonstrated a TiO2-based 32 × 32 crossbar array resistive RAM (ReRAM), a promising candidate for next-generation non-volatile memory (NVM), by utilizing a photochemical metal-organic deposition (PMOD) process. We achieved an interface-type resistive switching device with rectifying characteristics by controlling the oxidation state of directly patterned TiOx films through post-heat treatment. The photochemical reaction induced by UV in the PMOD process and the anatase phase formation during the post-heat treatment were analyzed using Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). XPS analysis revealed the immediate formation of Ti peroxide post-PMOD process, underscoring the efficacy of post-heat treatments in controlling oxidation states. Employing 350 °C annealed TiOX as the active material, we successfully fabricated a high-yield (93%), selectorless 32 × 32 crossbar array architecture for ReRAM. Our findings highlight the PMOD process as a viable, cost-effective alternative for memory devices, offering optimized oxidation states crucial for the performance of redox-based ReRAM.

Engineering the NASICON electrolyte/Na anode interface with amorphous bismuth oxide for sodium batteries.

Amorphous BiOx, prepared on the surface of NASICON electrolyte by the photochemical metal-organic deposition method, can substantially improve the interfacial properties at the anode side. The Na symmetric cell delivers a critical current density of 1.2 mA cm-2 and cycles stably at 0.5 mA cm-2 for 1000 h at 30 °C.

Improved ORR/OER bifunctional catalytic performance of amorphous manganese oxides prepared by photochemical metal-organic deposition.

Transition metal oxide nanomaterials or nanocomposites containing transition metal oxides have the potential to replace traditional catalysts for electrochemical applications, photocatalysis, and energy storage. Amorphous manganese oxide catalysts were prepared via photochemical metal–organic deposition (PMOD). Through XRD, SEM-EDS, Raman spectroscopy, FTIR spectroscopy, HRTEM-EDS, and XPS, we confirmed that amorphous manganese oxide catalysts were successfully prepared. Amorphous catalysts prepared with different photolysis times were compared in terms of their performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and catalyst MnOx-PMOD48 showed the best performance because of its high Mn3+ proportion and electrochemically active surface area. MnOx-PMOD48 showed better ORR/OER performance than the crystalline MnOx and MnOx/Ti4O7 catalysts from our previous work. Following our previous work on crystalline manganese oxide catalysts, we added Ti4O7 during the PMOD process with 48 h of treatment and obtained the amorphous catalyst MnOx/Ti4O7-PMOD. MnOx/Ti4O7-PMOD was supported by Ti4O7 particles, which led to improved stability. The ORR/OER catalytic activity of MnOx/Ti4O7-PMOD was better than that of crystalline catalyst MnOx/Ti4O7-300, which was the best crystalline catalyst in our previous work. We also compared lithium-oxygen batteries assembled with MnOx/Ti4O7-PMOD and MnOx/Ti4O7-300. The battery performance tests confirmed that the amorphous manganese catalyst had better ORR/OER bifunctional catalytic performance than the crystalline manganese catalyst because of its high defect state with more abundant edge active sites and more surface-exposed catalytic active sites.

Highly efficient amorphous binary cobalt-cerium metal oxides for selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

This study reports for the first time the use of amorphous mixed cobalt-cerium metal oxides (Co10-aCeaOx), obtained by photochemical metal-organic deposition, for 5-hydroxymethylfurfural (HMF) oxidation. The optimized Co8Ce2Ox exhibites a good electrocatalytic activity toward HMF oxidation with a current density of 2.8 mA cm−2 at 1.60 V, which is 1.4 times higher than that of pure CoOx. Operando Raman spectra reveal that the incorporation of Ce alters the electronic structure of the composite by facilitating the formation of CoOOH/CoO2, thus promoting catalytic activity. Notably, it is found that the oxidation of HMF proceeds dominantly via the oxidation of the alcohol group, followed by its subsequent oxidation in both alkaline and neutral media. Due to the stability of the aldehyde group in neutral media, high valuable 2,5-diformylfuran (DFF) with the selectivity of 60%–92% is obtained, thus open the new route for electrocatalytic DFF production.

An electric field-assisted photochemical metal–organic deposition allowing control of oxygen content for resistive switching in directly patterned TiOx films

An electric field-assisted photochemical metal–organic deposition allowing control of oxygen content for resistive switching in directly patterned TiOx films

Amorphous Nickel Oxide as Efficient Electrocatalyst for Urea Oxidation Reaction

Amorphous nickel oxide loaded on nickel foam (a-NiOx/NF) is synthesized via a facile photochemical metal-organic deposition (PMOD) approach and evaluated as catalyst for urea oxidation reaction (UOR). It exhibits superior activity with current density of 1 and 10 mA cm−2 at 1.240 (0.002) and 1.256 (0.001) V vs. RHE in 1.0 M KOH and 0.5 M urea solution, surpassing most of reported UOR catalysts. It also shows decent durability at 100 mA cm−2. The UOR mechanism exploration reveals that the rate-determining step is the removal of the last proton from the amino-group. This work demonstrates that amorphous materials can be efficient electrocatalysts for UOR which enables efficient H2 production.

Directly-Patternable Bi2O3 Nanoparticle for Polymer Nanocomposite Capacitor

A polyvinylidene fluoride (PVDF) film incorporating size-controlled, uniformly dispersed, directly patterned Bi2O3 nanoparticles was developed to achieve a high-k polymer nanocomposite capacitor. The photochemical metal-organic deposition (PMOD) method was employed to form uniformly dispersed and directly patterned nanoparticles on the substrate. Bi nanoparticles were produced by spin coating a Bismuth 2-ethylhexanoate solution on a Pt substrate with UV irradiation for 1, 4, 7, and 10 min. The average diameter of nanoparticles and the number of nanoparticles per unit area (μm2) were about 30, 70, and 120 nm and 30, 30, and 31 particles/μm2 for UV irradiation times of 4, 7, and 10 min, respectively. In addition, the capacitance of PVDF nanocomposite film could be controlled by the Bi2O3 nanoparticle size. The PVDF nanocomposite film containing Bi2O3 nanoparticles with 1, 4, 7, and 10 min UV irradiation were able to improve capacitance by about 1.4, 2.0, 2.7, and 3.4 times compared with an as-prepared PVDF film. By using a mask aligner, directly pattered Bi nanoparticles on the substrate, which had a 5 μm line width pattern, were successfully defined and demonstrated.

Direct Photolithographic Deposition of Color‐Coded Anti‐Counterfeit Patterns with Titania Encapsulated Upconverting Nanoparticles

AbstractCreating security labels as anti‐counterfeit measures can require multi‐step methods, clean room processing, and high‐cost equipment. Some labels also have a limited applicability due to the ease of creating a counterfeit. Herein, a photochemical metal‐organic deposition (PMOD) based approach that enables creation of high‐resolution luminescent patterns that retain nanoparticles in transparent metal oxide films is reported. This low‐cost, photoresist‐free process creates high‐resolution patterns of metal oxides without requiring processes such as etching or lift‐off. Upconverting nanoparticles (UCNPs) with tunable red/green or blue emission are prepared by doping Yb3+/Er3+ and Yb3+/Tm3+ into β‐NaYF4 hosts, respectively. Luminescent inks are prepared by suspending UCNPs in solutions with titanium di‐n‐butoxide bis(2‐ethylhexanoate). Customizable luminescent patterns are prepared by casting inks onto substrates, followed by exposure to ultraviolet light through photomasks. Photodecomposition of the titanium precursor yields amorphous oxide films encapsulating the UCNPs. Security labels are prepared by selectively patterning luminescent inks using PMOD. Distinct patterns of red‐green‐blue (RGB) luminescence are discernible only upon excitation with a near‐infrared (NIR) laser. These customizable, anti‐counterfeit labels exhibit the merits of low‐cost, high‐throughput, and simple manufacturing techniques. Yet, the versatility of customizing their emissive properties suggests a practical application as an anti‐counterfeiting measure.

Resistive switching characteristics of directly patterned Y-doped CeO2 by photochemical organic-metal deposition

Resistive RAM (ReRAM), which uses the anion-based resistive switching characteristic of transition metal oxide, is one of the strong candidates for next-generation non-volatile memory. The resistance switching characteristics depend on oxygen defects and their electrochemical migration. This study systematically investigated the Y3+ doping effect in CeO2 resistive switching behavior to control oxygen vacancy. The resistive switching devices of Ce1-xYxO2-y (CYO) (x = 0, 0.05, 0.1, 0.15, and 0.2) were fabricated by the photochemical metal-organic deposition method, which could successfully obtain directly patterned CYO films. The XRD pattern and Raman spectrum confirmed that the lattice shrink and structural distortion was induced and increased gradually by increasing the oxygen vacancy concentration with yttrium content. All the CYO devices showed bipolar filament-type resistive switching, and both resistance of the pristine state and forming voltage decreased with increasing Y content from an increase in oxygen vacancy concentration. And the on/off ratio decreased with increasing Y content because of reduced HRS resistance, even after the recovered insulation oxide region by HRS switching, due to fixed defect sites with trapped electrons formed by yttrium. And with a SPEM experiment, we found that ceria loses 24% oxygen for LRS resistive switching, which induced a resistance change of about five orders of magnitude.

Amorphous cobalt-cerium binary metal oxides as high performance electrocatalyst for oxygen evolution reaction

The amorphous Co-Ce binary metal oxides Co1-yCeyOx prepared by the photochemical metal–organic deposition (PMOD) method is developed as high performance electrocatalysts for oxygen evolution reaction (OER). The influence of Ce content on the OER activity is investigated in terms of geometric and electronic factors. Ce can remarkably enhance the OER activity of CoOx due to the synergistic effect of surface area, Co3+ content, and metal-OH bond strength when the content of Ce is less than 60%. Co0.9Ce0.1Ox supported on fluorine-doped tin oxide (FTO) coated glass substrate shows overpotential of 320 (2) mV at 10 mA cm−2 in 1 M KOH solution. The OER mechanism exploration reveals that the rate determining step changes with the Ce content due to the variation of metal-OH bond strength. This work sheds light on the design of high-performance yet cost-effective OER catalysts.

Resistive switching characteristic of Ce0.9Y0.1O2/TiO2 bi-layer structure by photochemical metal-organic deposition

Sneak current is one of the main bottlenecks for dense crossbar array resistive random access memory. This study reports highly non-linear resistive switching characteristic from Ce0.9Y0.1O2/TiO2 bi-layer (1S/1R device) structure, fabricated by photochemical metal-organic deposition, as a solution for sneak current issue. Ce0.9Y0.1O2 material, possessing oxygen vacancies, was used as a potential barrier as well as oxygen reservoir which rectified the current of low resistance state without an electrical breakdown in 1S/1R device. TiO2 was adopted for resistive switching property, and TiO2 layer having mixed phase (anatase and brookite) showed typical diode switching behavior. The photochemical reaction of photochemical metal-organic deposition process and phase formation were monitored and established using by Fourier-transform infrared spectroscopy and X-ray diffraction, respectively. The 1S/1R device showed highly non-linear resistive switching characteristic, large on/off ratio of above three orders of magnitude with low operating current.

Effect of annealing temperature on the structural, morphological and optical properties of ThO2 thin films grown by photochemical metal–organic deposition

In this work, we report the influence of annealing temperature on the structural, morphological and optical properties of ThO2 thin films deposited on fused quartz and (100) silicon substrates by photochemical metal–organic deposition (PMOD) using hinokitiolate thorium (IV) complex as the precursor. X-ray photoelectron spectroscopy (XPS) confirmed the deposition of the ThO2 films. The effect of thermal annealing (from 300 °C to 1100 °C) on the structural properties of the ThO2 films was evaluated with X-ray diffraction (XRD), UV–Vis transmittance spectroscopy, spectroscopic ellipsometry and atomic force microscopy (AFM). XRD patterns of the films annealed above 300 °C revealed that all diffraction peaks belong to a cubic ThO2 structure without preferential orientation. The average crystallite size increased from 2.3 nm to 3.7 nm as the annealing temperature increased from 300 °C to 750 °C. Annealing at 1100 °C promoted the formation of huttonite (β-ThSiO4) in the ThO2 layer. Films deposited on fused quartz showed 80% transmittance in the visible range, and the annealing temperature did not impact the band gap energy. The AFM studies revealed that as the annealing temperature increased, the film surface roughness decreased. Between 750 °C and 950 °C, the film surface was relatively smooth with an of RMS surface roughness in the range 2.3–5.0 nm. The values of the refractive index of the films were in the range of n = 1.6 for the as-deposited film to n = 2.1 for the films annealed at 750 °C. This result suggests the potential use of ThO2 films as a transparent reflector material for short wavelengths.

Understanding the Roles of NiOx in Enhancing the Photoelectrochemical Performance of BiVO4 Photoanodes for Solar Water Splitting.

Solar water oxidation is considered as a promising method for efficient utilization of solar energy and bismuth vanadate (BiVO4 ) is a potential photoanode. Catalyst loading on BiVO4 is often used to tackle the limitations of charge recombination and sluggish kinetics. In this study, amorphous nickel oxide (NiOx ) is loaded onto Mo-doped BiVO4 by photochemical metal-organic deposition method. The resulting NiOx /Mo:BiVO4 photoanodes demonstrate a two-fold improvement in photocurrent density (2.44 mA cm-2 ) at 1.23 V versus reversible hydrogen electrode (RHE) compared with the uncatalyzed samples. After NiOx modification the charge-separation and charge-transfer efficiencies improve significantly across the entire potential range. It is further elucidated by open-circuit photovoltage (OCP), time-resolved-microwave conductivity (TRMC), and rapid-scan voltammetry (RSV) measurements that NiOx modification induces larger band bending and promotes efficient charge transfer on the surface of BiVO4 . This work provides insight into designing BiVO4 -catalyst assemblies by using a simple surface-modification route for efficient solar water oxidation.

Molybdenum-containing amorphous metal oxide catalysts for oxygen evolution reaction

Amorphous mixed metal oxide oxygen evolution reaction catalysts containing Mo, Co, and Fe were synthesized by a low energy required photochemical metal-organic deposition (PMOD) process. The composition of the ternary amorphous metal oxide catalyst film can be precisely controlled as to its precursor solution, and there was no phase segregation observed. The electrocatalytic activity of this ternary catalyst system was carefully mapped out as contour plots to illustrate the kinetics parameters such as onset potential, Tafel slope as well as the overall performance, i.e. the potential required to reach the benchmark current density. In this study, adding higher valence state material, Mo, into catalytic active metal oxides, such as CoOx and FeOx, to form Co50Mo50Ox and Fe50Mo50Ox could highly increase the catalyst stability. More importantly, the ternary metal oxide Fe10Co25Mo65Ox showed the advantage of the relatively low onset potential (1.52 V), low Tafel slope (∼31 mV/dec), lowest potential to reach the benchmark 1 mA/cm2 and a better stability for the oxygen evolution reaction in Mo/Co/Fe system.

Photochemical metal organic deposition of FeO x catalyst on BiVO 4 for improving solar-driven water oxidation efficiency

Abstract Scheelite-monoclinic BiVO4 serving as a photoanode for photoelectrochemical water oxidation is known for its fast electron–hole recombination and slow kinetics, thus limiting its efficiency. In this study, a highly active oxygen evolution reaction catalyst, FeOx, is successfully deposited on BiVO4 by a simple and low energy needed photochemical metal organic deposition (PMOD) process under ambient environment. During the PMOD process, metal organic precursor goes through ligand-to-metal charge transfer, triggers by UV irradiation, and then reacts with oxygen to form a thin amorphous FeOx catalyst layer. This FeOx coated BiVO4 photoanode boosts the hole injection efficiency to ∼100% which is almost triple comparing to the bare BiVO4. Furthermore, with FeOx layer, the onset potential shifts cathodically for about 0.4 V and the photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) reaches 1.1 mA/cm2 which is 2.5 times of a bare BiVO4 photoanode. The stability of the photoanode is also improved. The FeOx coated BiVO4 demonstrates a substantial enhancement of the incident photon to current efficiency (IPCE) and the absorbed photon to current efficiency (APCE) due to its ability in increasing the hole injection efficiency and oxygen evolution reaction (OER) kinetics.

Electrical properties of UV-irradiated thick film piezo-sensors on superalloy IN718 using photochemical metal organic deposition

Lead zirconate-titanate thick films of perovskite structure Pb(Zr0.52Ti0.48)O3 were fabricated on the curved surface of IN718 superalloy substrate using photochemical metal organic deposition technique. The films were heated at 200°C, irradiated by UV lamp (365nm, 6W) for 10min, pyrolyzed at 400°C, and subsequently annealed at 700°C for 1h after successive multi-step coating with 10wt.% excess PbO. Fairly smooth, dense, and crack-free polycrystalline thick films of Au/PZT/Au structure were deposited on IN718. The films were characterized to investigate the effect of photochemical deposition process and substrate on the crystalline, morphological, dielectric, ferroelectric and piezoelectric properties. Remanent polarization (Pr=20.2μC/cm2), coercive field (Ec=−10kV/cm), permittivity (εr=324@1kHz), dielectric loss (tanδ≈3%), and piezoelectric charge coefficient (d33=113.4pm/V) of the PZT thick film transducers were measured and interpreted as regards domain wall motions. Consequently, the photochemical grown lead zirconate-titanate thick film on the superalloy substrate IN718 was confirmed to be consistent to structural health monitoring due to its acceptable electrical response.

MOLYBDENUM TRIOXIDE THIN FILMS DOPED WITH GOLD NANOPARTICLES GROWN BY A SEQUENTIAL METHODOLOGY: PHOTOCHEMICAL METAL-ORGANIC DEPOSITION (PMOD) AND DC-MAGNETRON SPUTTERING

Gold nanoparticles (AuNPs) were deposited by DC-magnetron sputtering onto molybdenum trioxide (MoO3) thin films grown by Photochemical Metal- Organic Deposition (PMOD) on Si(100) and borosilicate glass substrates. The chemical, optical and morphology properties of the films were studied by UV/ Vis Spectroscopy, Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and X-Ray Diffraction (XRD). SEM revealed that AuNPs formed after 5 s of sputtering. AuNPs are spherical and have both an average diameter of 18 nm and a relatively narrow size distribution. As the deposition time increases, larger structures are formed by an aggregation of AuNPs. XPS studies of the AuNP/MoO3 films on Si(100) showed the presence of Mo(VI) and Mo(V), which indicated that the films were primarily non-stoichiometric molybdenum oxides. The occurrence of oxygen vacancies in the substrate play an important role to stabilize the AuNPs.

Structural, Electrical, and Optical Properties of Photochemical Metal-Organic-Deposited ZnO Thin Films Incorporated with Ag Nanoparticles and Graphene

Ag nanoparticles (NPs) and/or graphene were incorporated into a zinc oxide (ZnO) photosensitive precursor solution. Then, direct-patternable ZnO nanocomposite thin films were fabricated via photochemical metal-organic deposition. The transmittance and crystallinity of ZnO films were not almost changed but the resistivity of ZnO thin films was decreased by after incorporation of Ag NPs and/or graphene. Especially a double incorporation (Ag NPs and graphene) led to a greater decrease in the resistivity of the films more than the single incorporation (Ag NPs or graphene). This difference in resistivities was due to the combined enhancement of both the carrier concentration and mobility. The improvements in the electron concentration and mobility of ZnO composite films were largely dependent upon the introduction of Ag NPs and graphene, respectively. ZnO composite films could be direct-patterned without a photoresist and/or dry etching. Therefore, our results show that the cost of fabrication can be reduced by using a direct micro-patterning system and that the electrical properties of ZnO thin films can be improved by the incorporation of Ag NPs and graphene, while maintaining the structural and optical properties of the films.

Piezoelectric Transducers on Curved Dispersive Bending Wave and Poke-Charged Touch Screens

Ferroelectric thin films of lead zirconate titanate Pb(Zr0.52,Ti0.48)O3(PZT) and bismuth titanate Bi4Ti3O12(BiT) were prepared by photochemical metal-organic deposition as electromechanical transducers used in optoelectronic devices. Both solutions were deposited on flat and convex amorphous glass substrates to poke-charge the device or detect the touch point coordinate on new generation of free-shaped screens. The effects of optimization on UV exposure, precursor type and annealing temperature (600–800 °C) were investigated on microstructural, optical and ferroelectric properties of deposited thin films. Suppressing the non-uniformity of the film thicknesses due to repetitive deposition, actually there is no structural difference between the two types of substrates and their effects on the film properties. Polarization-voltage hysteresis loops showed relatively larger remnant polarization of P r = 9.3 µC/cm2 and 6.1 µC/cm2 for optimized UV-irradiated PZT and BiT thin films, respectively, than uncured samples.

Compositional Study of Surface, Film, and Interface of Photoresist-Free Patternable SnO2Thin Film on Si Substrate Prepared by Photochemical Metal-Organic Deposition

The direct-patternable <TEX>$SnO_2$</TEX> thin film was successfully fabricated by photochemical metal-organic deposition. The composition and chemical bonding state of <TEX>$SnO_2$</TEX> thin film were analyzed by using X-ray photoelectron spectroscopy (XPS) from the surface to the interface with Si substrate. XPS depth profiling analysis allowed the determination of the atomic composition in <TEX>$SnO_2$</TEX> film as a function of depth through the evolution of four elements of C 1s, Si 2p, Sn 3d, and O 1s core level peaks. At the top surface, nearly stoichiometric <TEX>$SnO_2$</TEX> composition (O/Sn ratio is 1.92.) was observed due to surface oxidation but deficiency of oxygen was increased to the interface of patterned <TEX>$SnO_2/Si$</TEX> substrate where the O/Sn ratio was about 1.73~1.75 at the films. This O deficient state of the film may act as an n-type semiconductor and allow <TEX>$SnO_2$</TEX> to be applied as a transparent electrode in optoelectronic applications.