Elevated Substrate Temperatures Research Articles

Rapid Prototyping for Accelerated Establishment of Film Processing‐Performance Relationships in Silicon Phthalocyanine OFETs

AbstractUnderstanding the complex relationships underlying the performance of organic electronic devices, such as organic field‐effect transistors (OFETs), requires researchers to navigate a multi‐dimensional parameter space that includes material design, solution formulation, fabrication parameters, and device geometry. Herein, a recently developed materials acceleration platform is demonstrated, named the RoboMapper, to perform direct on‐chip fabrication of OFETs by ultrasonic meniscus printing using silicon phthalocyanine (SiPc) derivatives as the semiconductor. OFETs using bis(tri‐n‐butylsilyl oxide) SiPc ((3BS)2‐SiPc) exhibited the best device performance characterized by the highest electron field‐effect mobility (µe). Through optical microscopy and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), the favorable performance of (3BS)2‐SiPc is attributed to the specific film morphology and molecular packing achieved with optimal print conditions. Investigating the impact of deposition parameters reveals the crucial role of solvent evaporation rate and print speed in achieving high‐quality film formation. Overall, optimal fabrication conditions for (3BS)2‐SiPc devices include slow print speeds and fast evaporating solutions achieved by using a mixture of co‐solvents and an elevated substrate temperature. The results of this work reveal distinct relationships between deposition conditions, film properties, and device performance for each SiPc derivative and emphasize the necessity of high throughput experimentation to comprehensively understand process‐performance relationships in organic semiconductors.

Effect of substrate temperature on the structural properties of Tungsten Carbide and Tungsten-rich Tungsten Carbide films

ABSTRACT The unique mechanical properties of Tungsten Carbide (WC), such as fracture toughness, exceptional hardness, high melting temperature, outstanding thermal stability, anti-oxidation qualities fatigue and creep resistance, have made it a suitable industrial material for different applications. It is also considered to be a promising material for coating on plasma-facing walls in a Tokamak reactor. The aim of the present work is to study the effect of varying substrate temperature, concentration of tungsten (W) and annealing in the structural properties of WC films. The WC films are deposited on a silicon substrate at different substrate temperatures viz. RT (300 K), 400, 500, 600 and 700 K using DC magnetron sputtering. W-rich WC films were deposited keeping the power of WC constant (100 Watt) and varying W powers (10 Watt, 20 Watt, 30 Watt, 40 Watt) at room temperature. Later, these W-rich WC films were annealed at 800°C in a reducing atmosphere. Glancing incidence X-ray diffraction (GIXRD) and Raman spectroscopy of the films are performed for structural analysis. GIXRD of the WC films reveals that as-deposited RT films are amorphous. However, films which are either deposited at elevated substrate temperature or are annealed are crystalline. This is confirmed by Raman’s measurements. It also indicates the presence of disorder and nanocrystalline phases due to temperature variations.

Numerical investigation of evaporation-induced flow around sessile droplets using a sharp-interface algebraic VOF approach

In this study, we numerically investigate the external gaseous flow around an evaporating sessile droplet, especially the interaction between different transport mechanisms of the evaporation-induced flow and evaporation dynamics. A sharp-interface algebraic volume-of-fluid (SA-VOF) solver which incorporates the Boussinesq approximation to deal with thermal and solutal buoyancy has been developed for direct numerical simulation of evaporating droplets in natural convection. Evaporation of a heptane droplet is first simulated to validate the developed solver, and the predicted evaporation rates show good agreement with experimental data. An evaporating sessile droplet on a heated substrate is then simulated through three distinct models to account for contributions from different transport mechanisms of the evaporation-induced flow, i.e. diffusion, the Stefan flow and natural convection. Extensive cases have been simulated at different gravity levels and environmental conditions to clarify the separate role of each mechanism. Results show that the convective flow can enhance evaporation of sessile droplets considerably at elevated substrate temperatures, accounting for up to 40.4% of total evaporation at the substrate temperature of 60 °C and the humidity of 36%. The contribution of the Stefan flow or natural convection in the evaporation process increases with the substrate temperature while stays almost independent of the environmental humidity. Additionally, minute details of the evaporation-induced flow at zero and normal gravity, including flow field, gas mixture density, vapor fraction and temperature distribution, are comparatively studied to reveal the complex characteristics of momentum, mass and heat transfer associated with droplet evaporation in natural convection.

Microstructure and Unusual Ferromagnetism of Epitaxial SnO2 Films Heavily Implanted with Co Ions

In this work, we have studied the microstructure and unusual ferromagnetic behavior in epitaxial tin dioxide (SnO2) films implanted with 40 keV Co+ ions to a high fluence of 1.0 × 1017 ions/cm2 at room or elevated substrate temperatures. The aim was to comprehensively understand the interplay between cobalt implant distribution, crystal defects (such as oxygen vacancies), and magnetic properties of Co-implanted SnO2 films, which have potential applications in spintronics. We have utilized scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), differential thermomagnetic analysis (DTMA), and ferromagnetic resonance (FMR) to investigate Co-implanted epitaxial SnO2 films. The comprehensive experimental investigation shows that the Co ion implantation with high cobalt concentration induces significant changes in the microstructure of SnO2 films, leading to the appearance of ferromagnetism with the Curie temperature significantly above the room temperature. We also established a strong influence of implantation temperature and subsequent high-temperature annealing in air or under vacuum on the magnetic properties of Co-implanted SnO2 films. In addition, we report a strong chemical effect of ethanol on the FMR spectra. The obtained results are discussed within the model of two magnetic layers, with different concentrations and valence states of the implanted cobalt, and with a high content of oxygen vacancies.

Numerical investigation of laser powder bed fusion of glass

Additive manufacturing of glass using laser powder bed fusion has been recently developed, demonstrating its potential to be applied in small scale applications such as flow reactors for the chemical engineering and pharmaceutical manufacturing industries. While previous research demonstrated that complex 3-dimensional shapes can be manufactured, built parts are often brittle, exhibit high porosity and lack transparency. This study employs a transient, heat transfer finite element analysis to shed light on the thermal response of laser—glass powder bed interaction and the impact of processing parameters. Through this understanding, the research seeks to identify practical strategies that can be employed to improve the quality and properties of the built parts. Bulk solid and powder soda lime silica glass properties are used as input in the model, while the laser heat flux and scan strategy, conversion of powder feedstock to bulk solid glass and heat losses from convection and radiation effects are introduced in the model through Fortran coding. The study showed that effective powder consolidation, resulting in well-defined geometrical features, is achieved for temperatures near the glass melting point. Additionally, uniform consolidation depths and widths can be achieved by increasing laser power, elevating substrate temperature and reducing scan speed within certain limits, whilst ensuring hatch spacing is below the corresponding single scan track width for unidirectional adjacent laser trajectories.

Mechanical responses and plastic rheological behavior of Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films deposited with different substrate temperatures during nanoindentation and nanoscratch process

Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films were deposited by magnetron sputtering at different substrate temperatures of 293 K, 373 K, and 473 K. All the thin films were indicated to be amorphous. The roughness was decreased from 0.71 ± 0.02 nm (293 K) to 0.65 ± 0.01 nm (473 K) and the thin film became more densified with fewer voids and defects. Consequently, the mechanical properties, plastic rheological behavior, and nanoscratch properties varied regularly with the microstructure at different substrate temperatures. The hardness and elastic modulus showed increasing trends with the elevated substrate temperature. The strain-rate strengthening effect occurred, causing the gradual disappearance of the pop-in event with the increasing strain rate. The cut-off value of strain burst size showed an increasing trend with the elevating strain rate. This trend was weakened with the elevated substrate temperature due to the decreased chaos of the interaction between atoms. The cut-off value also increased with the elevating substrate temperature. During the nanoscratch measurement, the elastic recovery ratio increased with the elevating substrate temperature. The critical stress for interface separation of the Ti–Zr-Hf-Co-Ni-Cu metallic glass thin film was improved from 1.9 N to 2.7 N with the substrate temperature rising from 293 K to 473 K.

Copper tantalum nitride (CuTaN2) thin films prepared by reactive radio-frequency magnetron sputtering

RF reactive sputtering was used to deposit copper tantalum nitride (CuTaN2) films from a Cu/Ta target in an environment containing a mixture of argon and nitrogen at two different substrate temperatures: room temperature and 200 °C. The films were studied by SEM, EDS, XRD, Raman spectroscopy, spectrophotometry, and resistivity measurements. The deposition conditions significantly impacted the morphology of the films, which varied from smooth, void-free films at high nitrogen concentrations and at room temperature substrates to cauliflower-like grains with voids at low nitrogen contents and elevated substrate temperatures. Despite the target’s 1:1 Cu: Ta ratio, the stoichiometric analysis showed a lower Ta content in the deposited film. The films produced on silicon substrates were polycrystalline, whereas those deposited on glass substrates were amorphous. The band gap (0.9 eV to 1.55 eV) and film resistivity (20 kΩ-cm to 76 kΩ-cm) are strongly affected by the nitrogen fraction in the sputtering gas. Increasing the nitrogen percentage in semiconductor films results in smoother films with larger bandgaps (approximately 1.5 eV), higher resistivity, and compositions closest to those of stoichiometric CuTaN2.

Effect of zirconia coating on Ti6Al4V at elevated substrate temperature on its wear, corrosion and hemocompatibility properties

Titanium and its alloys have been recognized as biocompatible materials since decades although these materials can at times show wear, corrosion and thrombosis leading to various health complications. Surface coating has been found to be one of the effective techniques to overcome this issue in-vitro as well as in-vivo. In this paper, thin film coating of zirconia (ZrO2) on Ti6Al4V is reported using pulsed laser deposition (PLD) technique at elevated substrate temperatures ranging from room temperature to 800 °C (TiZr800). The morphology, composition, wettability and average surface roughness of the samples were analyzed by scanning electron microscope, Raman spectrometer, water contact angle (WCA) and profilometer, respectively. Adhesion between film and substrate was qualified using Elcometer. The tribological studies were performed in ball-on-disc against ZrO2 counterpart, the electrochemical potential analysis was done in simulated body fluid to replicate body environment and the hemocompatibility test was evaluated on the basis of human whole blood adsorption and distribution of Red Blood Cells (RBCs) on the samples. The results revealed an increase in WCA and film adhesion with increased substrate temperature. At 800 °C, formation of zirconium carbide, a relatively harder material, was observed due to diffusion of substrate carbon into ZrO2 film, as confirmed by the Raman analysis. In comparison to pristine, TiZr800 sample showed a reduction in wear rate from 3.5 × 10−3 mm3/Nm to 1.1 × 10−3 mm3/Nm indicating improved resistance of the sample against abrasive wear. Further, drop in Icorr from 4.96 × 10−7 A/cm2 to 2.75 × 10−7 A/cm2 resulted in a 44 % increase in corrosion protective efficiency of the sample coated at 800 °C. Additionally, a 4.5 fold increase in RBC counts was observed on TiZr800 sample. Therefore, it is inferred that while ZrO2 coating can improve overall surface properties of Ti–6Al–4V, additional benefits can be obtained by performing PLD at higher substrate temperatures, more so when the temperature is such as to promote formation of ZrC in the coating.

Nanomechanical and Microstructural Characterization of Biocompatible Ti3Au Thin Films Grown on Glass and Ti6Al4V Substrates.

Ti-Au intermetallic-based material systems are being extensively studied as next-generation thin film coatings to extend the lifetime of implant devices. These coatings are being developed for application to the articulating surfaces of total joint implants and, therefore, must have excellent biocompatibility combined with superior mechanical hardness and wear resistance. However, these key characteristics of Ti-Au coatings are heavily dependent upon factors such as the surface properties and temperature of the underlying substrate during thin film deposition. In this work, Ti3Au thin films were deposited by magnetron sputtering on both glass and Ti6Al4V substrates at an ambient and elevated substrate temperature of 275 °C. These films were studied for their mechanical properties by the nanoindentation technique in both variable load and fixed load mode using a Berkovich tip. XRD patterns and cross-sectional SEM images detail the microstructure, while AFM images present the surface morphologies of these Ti3Au thin films. The biocompatibility potential of the films is assessed by cytotoxicity tests in L929 mouse fibroblast cells using Alamar blue assay, while leached ion concentrations in the film extracts are quantified using ICPOEMS. The standard deviation for hardness of films deposited on glass substrates is ∼4 times lower than that on Ti6Al4V substrates and is correlated with a corresponding increase in surface roughness from 2 nm for glass to 40 nm for Ti6Al4V substrates. Elevating substrate temperature leads to an increase in film hardness from 5.1 to 8.9 GPa and is related to the development of a superhard β phase of the Ti3Au intermetallic. The standard deviation of this peak mechanical hardness value is reduced by ∼3 times when measured in fixed load mode compared to the variable load mode due to the effect of nanoindentation tip penetration depth. All tested Ti-Au thin films also exhibit excellent biocompatibility against L929 fibroblast cells, as viability levels are above 95% and leached Ti, Al, V, and Au ion concentrations are below 0.1 ppm. Overall, this work demonstrates a novel Ti3Au thin film system with a unique combination of high hardness and excellent biocompatibility with potential to be developed into a new wear-resistant coating to extend the lifetime of articulating total joint implants.

Thermal-based efficient modeling for mechanical properties of thermoplastic polymers in material extrusion

The process-induced void defects play an important role in the mechanical properties of thermoplastic polymers fabricated by material extrusion (ME). Thus, it is meaningful to accurately and efficiently determine the impact of void defects on the ultimate mechanical properties of ME-printed parts. However, the straightforward relation between process parameters, void density, and mechanical properties remains unclear. In this paper, semi-analytical modeling is presented to efficiently predict the effective properties of ME-printed thermoplastic polymers. The void density related to process variables in the ME process is numerically determined based on a thermal sintering model. Subsequently, the effective properties of as-printed thermoplastic polymers are analytically predicted using the unit-cell-based homogenization method. The predicted results by the proposed semi-analytical model are validated by the comparison with experiments and finite element analysis. Furthermore, the effect of primary printing parameters on the degree of fusion, void density, and effective properties is examined. The results show that the elevated extrusion and substrate temperatures, as well as the decreased printing speed, layer height, and nozzle radius, contribute to the higher degree of fusion, leading to lower void density and superior elastic properties. In addition, moderate feeding speed and environmental temperature can enhance the elastic properties of ME-printed thermoplastic parts. These results offer useful guidelines for the design and manufacturing of thermoplastic parts with high performance.

Stability of inkjet printed lines at elevated substrate temperature

Precise manipulation of line morphologies is crucial for optimizing the performance of inkjet printing. Among various techniques, the utilization of heated substrates as an active control approach stands out due to its good controllability and precision. Thus, this study experimentally investigated the characteristics of inkjet-printed lines with high-temperature substrate, employing high-concentration indium tin oxide nano-ink. The phase diagrams of line patterns were plotted in the space of dimensionless droplet spacing and printing velocity. The transition boundaries between different line modes were obtained in the cases of different substrate temperatures. Two theoretical models have been developed. First, a new printing stability model was developed, which works well for high-temperature substrates. Second, for the newly observed overlapping deposition line pattern on higher temperature substrates, a theoretical model was developed to predict the pattern transition boundaries based on the timescale of droplet interval and evaporation time of each droplet. The findings could be useful for the inkjet printing optimization by means of substrate heating techniques.

Study of nanoindentation behavior of NiCrCoAl medium entropy alloys under indentation process using molecular dynamics

Abstract The mechanical properties and deformation behavior of CoCrNiAl medium entropy alloy (MEA) subjected to indentation by an indenter tooltip on the substrate are explored using molecular dynamics (MD) simulation. The study investigates the effects of alloy compositions, temperature variations, and ultra vibration (UV) on parameters, such as total force, shear strain, shear stress, hardness, reduced modulus, substrate temperature, phase transformation, dislocation length, and elastic recovery. The findings indicate that higher alloy compositions result in increased total force, hardness, and reduced modulus, with Ni-rich compositions demonstrating superior mechanical strength. Conversely, increasing alloy compositions lead to reduced von Mises stress (VMS), phase transformation, dislocation distribution, and dislocation length due to the larger atomic size of Ni compared to other primary elements. At elevated substrate temperatures, atoms exhibit larger vibration amplitudes and interatomic separations, leading to weaker atomic bonding and decreased contact force, rendering the substrate softer at higher temperatures. Additionally, higher initial substrate temperatures enhance atom kinetic energy and thermal vibrations, leading to reduced material hardness and increased VMS levels. Increasing vibration frequency enlarges the indentation area on the substrate’s surface, concentrating shear strain and VMS with vibration frequency. Higher vibration amplitude and frequency amplify force, shear strain, VMS, substrate temperature, and dislocation distribution. Conversely, lower vibration amplitude and frequency result in a smaller average elastic recovery ratio. Moreover, increased amplitude and frequency values yield an amorphous-dominated indentation region and increased proportions of hexagonal close-packed and body-centered cubic structures. Furthermore, this study also takes into account the evaluation of a material’s ability to recover elastically during the indentation process, which is a fundamental material property.

Synthesis of Erbium Deuterides via Deuterium Ion Implantation into Erbium Thin Films

An experimental study of a synthesis technique in which deuterium ions are implanted into thin films of erbium to form erbium deuterides is presented. Results from thermal desorption spectroscopy indicate the synthesis of multiple hydride phases has occurred, including ErD3 and ErD2. The findings also indicate that, for erbium deuteride synthesis via ion beam bombardment, elevated substrate temperatures are not required to promote deuterium uptake in the film. Stoichiometries of up to ErD0.21 were achieved for a 400-nm film exposed to a 1000-eV ion beam for 5 h at a deuterium ion fluence of 3.6 × 1022 m−2. Over the tested experimental conditions, deuterium uptake was found to scale proportionally with deuterium ion fluence and ion energy. The presence of deuterium in the film was confirmed by secondary ion mass spectrometry.

Anisotropic assembly and reorganization of noble metals on black phosphorus van der Waals template

Black phosphorus (BP), an emerging layered semiconducting crystal, exhibits intriguing properties associated with its puckered in-plane structure. In particular, BP can serve as a template with remarkable van der Waals epitaxial effect owing to its strong anisotropic template effect. Herein, we investigated the assembly behavior of Au and Ag physically deposited on a BP template via transmission electron microscopy techniques. The results show that the orientation, assembly morphology, and crystallinity of metals can be tuned by controlling the BP substrate temperature during deposition. Electron diffraction analysis confirmed that elevated substrate temperature aids the selective formation of [110] oriented Ag and Au films by suppressing the [111] orientation. Moreover, the morphological shape and crystallinity of metals in the initial assembly mode showed temperature-dependent anisotropic effect. This study aids in understanding mechanisms of oriented metal epitaxy on anisotropic two-dimensional crystals, leading to the formation of high-quality metal-semiconductor van der Waals heterojunctions.

New insights into thermal processes of metal deposits on h-BN/Rh(1 1 1): A comparison of Au and Rh

In this paper the thermal properties of Au and Rh deposits are compared on hexagonal boron nitride (h-BN) “nanomesh” prepared on Rh(111), applying STM, XPS, low energy ion scattering (LEIS), LEED, and DFT. At room temperature, both metals essentially follow Volmer-Weber (3D) growth. Upon subsequent annealing, agglomeration (sintering), intercalation, and desorption are competing surface processes for both metals. For the more reactive Rh, we suggest an additional encapsulation mechanism: between 600 K and 750 K, fragments of decomposed h-BN diffuse locally from the bottom onto the metal clusters covering them partially. STM data indicates that agglomeration of gold nanoparticles proceeds faster compared to rhodium. At higher temperatures (∼1050 K–1100 K), all non-desorbing gold atoms diffuse below h-BN, even for large initial coverages. On the other hand, for larger Rh deposits (≥5 ML), the outermost layer always contains Rh. Accumulation of gold at the interface between h-BN and Rh(111) significantly enhances the thermal stability of h-BN, attributed to the lower reactivity of Au in the decomposition of h-BN compared to Rh(111). At elevated substrate temperatures, intercalation of individual adatoms takes place during deposition, which requires higher temperatures for rhodium due to its slower diffusion and higher probability of nucleation.

Electrical and Optical properties of ITO Films Prepared by Ion-Assisted Deposition at Ambient Substrate Temperatures

Traditionally, to achieve low resistivity and high transmission indium-tin oxide (ITO) films were deposited at elevated substrate temperatures about 400o C. In some cases, films deposited at low substrate temperatures can then annealed at higher temperature to achieve lower resistivity. In this paper thin films of ITO with various oxygen flow rates were prepared by ion-assisted electron beam evaporation at ambient substrate temperature. The electrical and optical properties of ITO thin films have been investigated as a function of oxygen flow rate, rate of deposition and the layer thickness. The transmittance and optical band-gap energy were measured by spectrophotometer, whereas the sheet resistance was measured using four-point probe method. It has been found that at 25 sccm oxygen flow, 0.4 nm/sec rate of deposition and 140 nm layer thickness were suitable for improving the properties of ITO films. The optical transmittance, optical band-gap and the resistivity were 92%, 4.2 eV and 175x10-4Ω-cm, respectively.

Shape‐Controlled Solution‐Epitaxial Perovskite Micro‐Crystal Lasers Rivaling Vapor Deposited Ones

AbstractEpitaxial growth methods usually need dedicated equipment, high energy consumption to maintain pure vacuum conditions and evaporation of source materials, and elevated substrate temperatures. Solution epitaxial growth requires nothing of that but is rarely used because the achieved microstructures are of low quality, not homogeneous, and finally exhibit worse performances in devices. Here, an antisolvent‐vapor‐assisted‐crystallization of metal‐halide‐perovskites as a method overcoming these disadvantages is demonstrated. The methylammonium lead tribromide exhibits van‐der‐Waals type of epitaxial growth on mica substrates, resulting in micro‐crystallites whose shape can be controlled to be either triangular micro‐prism or micro‐cuboid. These micro‐crystallites act as optical resonators supporting various optical modes and lasing is achieved under optical excitation with low thresholds and record high environmental stability. Selecting suitable resonators from a large variety of sizes allows control of mode spacing and finally mono‐mode operation, considered to be an important feature of semiconductor laser devices. The achieved results are essentially competitive to those obtained by vapor phase epitaxial microstructures, highlighting that epitaxy of high‐quality optoelectronic device structures is feasible by minimum technological efforts and energy consumption, which are of increasing importance considering issues such as global warming and the current energy crisis.

Potential tribological and antibacterial benefits of pulsed laser-deposited zirconia thin film on Ti6Al4V bio-alloy

Demand for artificial body implants has been on the rise over the years. However, wear and bacterial infection are identified as two major reasons that can lead to inflammation and implant failure. In this communication, the advantages of pulsed laser deposited zirconia thin film on Ti6Al4V bio-alloy at room temperature and at an elevated substrate temperature are discussed wherein a comparison of the change in surface roughness, wettability, surface free energy, tribological and antibacterial properties of uncoated and zirconia coated Ti6Al4V samples is presented. The results of tribological analysis carried out using a standard ball-on-disc tribometer at different loads (2N, 5N and 7N) exhibited advantageous effects of zirconia coating on Ti6Al4V. Prominently, the sample coated at 200 C substrate temperature maintained very low coefficient of friction up to hundreds of sliding cycles and showed a notable reduction in the wear rate by 49% at 5N load. The in vitro bacterial retention test showed a clear inhibition in growth of Staphylococcus aureus and Klebsiella pneumonia bacteria on the surface of the coated samples indicating the possibility of prevention of biofilm formation. More than 50% reduction in density of Staphylococcus aureus was observed on coated sample in comparison to pristine Ti6Al4V and this can be attributed to reduction in surface energy of the sample after coating. Additionally, the observation of a larger number of decimated bacteria on coated samples by fluorescence microscopy revealed superior antibacterial properties of zirconia coating. The novelty of this work is the use of pulsed laser deposition technique for zirconia coating which dearly improves tribological and antibacterial properties of Ti6Al4V simultaneously; this shows prospects of increasing durability of artificial implant in the human body.

From impact to solidification in drop-on-demand metal additive manufacturing using MetalJet

Drop-on-demand metal jetting is a promising additive manufacturing (AM) technology that is gaining interest due to its capability to directly print complex single and multi-material components at high resolutions. It also has key advantages over other metal AM techniques, such as avoiding powder handling and extensive post-processing. In this method, parts are built via spatially controlled deposition of individual molten droplets onto a substrate. Therefore, the success of the process entirely depends on the behaviour of these single droplets from deposition to solidification including their interactions with the substrate, which is scarcely investigated to date. To fill this research gap, the in-house MetalJet platform was used to investigate the spreading and solidification of metallic micro-droplets at low Weber numbers. This was undertaken onto various substrates using a range of jetting and substrate temperatures through an integrated experimental, analytical, and computational approach. This study reports that increasing the substrate temperature enhanced the diffusion between the droplet and substrate, hence improving the bonding. Moreover, ripples forming on a droplet’s periphery during solidification disappeared at elevated substrate temperatures, resulting in improved inter-droplet bonding. Furthermore, the significant role of the substrate wettability and thermal properties, which control the droplet’s dynamics and solidification behaviour, respectively, is elucidated. This highlights the importance of substrate material selection using this technology. The results presented in this article underpin the optimal process conditions under which the 3D structures produced with this technology can exhibit reliable integrity and consistency. This represents a step forward in the direct metal printing of high resolution functional multi-material components.

Tailoring of rhenium oxidation state in ReOx thin films during reactive HiPIMS deposition process and following annealing

Bulk rhenium trioxide (ReO3) has an unusually high electrical conductivity and, being nanosized, has promising catalytic properties. However, the production of pure ReO3 thin films is challenging due to the difficulty to stabilize rhenium in a 6+ oxidation state. Here we present a novel approach for the deposition of ReOx (x ≈ 1.6–2.9) thin films using reactive high power impulse magnetron sputtering (r-HiPIMS) from a metallic rhenium target in a mixed Ar/O2 atmosphere. The thin films were deposited in the gas-sustained self-sputtering regime, observed during r-HiPIMS process according to current waveforms. The influence of the substrate temperature, the oxygen-to-argon flow ratio and post-annealing at 250 °C in the air for 3 h on the properties of the films were studied. The as-deposited films have an X-ray amorphous structure (a-ReOx) when deposited at room temperature while a nano-crystalline β-ReO2 phase when deposited at elevated temperatures (150 or 250 °C). The amorphous a-ReOx can be converted into the crystalline ReO3 with a lattice parameter of 3.75 Å upon annealing in the air. The surface morphology of the films is dense without detectable voids when elevated substrate temperatures are used. Various Re oxidation states are observed on the surface of the films in different ratios depending on the deposition parameters. All samples exhibit electrical resistivity on the order of 10−3 Ωcm and optical properties typical for thin metallic films.