Laser Deposition Parameters Research Articles

Relative effects of pulsed laser deposition parameters on the stoichiometry of thin films

Pulsed laser deposition has a reputation for maintaining the stoichiometry of the ablation target in the deposited film. Exceptions to this "rule" occur, however, for materials, such as multiferroic BixDy(1-x)FeO3 (BDFO), that contain elements with large differences in volatility, like Bi and Fe. The relative effect of various pulsed laser deposition processes on the resulting stoichiometry of BDFO films as a function of time (or number of laser pulses) has been examined using an interactive spreadsheet, as well as experimentally. The adjustable parameters within the spreadsheet include target composition, target element ablation yield, ablation plume spread, background gas pressure, ablated target atom kinetic energy, and ablated element sticking coefficient on the substrate. Examples of how the calculated film composition might evolve are given, along with experimental results showing how the deposition parameters individually affect BDFO film stoichiometry. Finally, the calculated relative contributions of the various deposition processes, in terms of how much they affect the deposited film stoichiometry, are compared.

Investigating the laser metal deposition of Inconel 718 superalloy using the numerical and experimental methods

In this research, a volume of fluid (VOF) model was developed to investigate the effect of laser deposition parameters on the geometry of molten pool and deposited layer in the Inconel 718 superalloy. For this purpose, the process parameters of laser power, laser beam diameter and scanning speed were considered to estimate the geometric characteristics of the molten pool and deposited layer. In the following, the laser deposition process of Inconel 718 superalloy was carried out experimentally to validate the results of simulation. It was observed that an increase in the laser power from 100 to 400 W resulted in an improvement in the length, width and depth of molten pool, while an increase in the values of laser beam diameter (from 1 to 2 mm) and scanning speed (from 2 to 10 mm s−1) was associated with a reduction in the length, width and depth of molten pool. From the results of both simulation and experiments, a reduction was observed in the wetting angle of deposited layer when the values of laser power and scanning speed increased up to 400 W and 10 mm s−1 respectively, while the increase of feeding rate from 48 to 62 mgr s−1 indicated an improvement in the wetting angle. It was also observed that the maximum penetration depth was obtained in the rear part of molten pool due to Marangoni convection currents that pushed the melt toward the end of molten pool. The comparison of the experimental results and those predicted by the VOF model indicated that the model is capable of predicting the shape of deposition layer with sensible error.

Characterization of microstructure and mechanical properties of titanium -based bioactive ceramics laser-deposited on titanium alloy

Titanium-Based Bioactive Ceramics (TBBC), obtained by laser deposition of Ti and hydroxyapatite (HAp) powders, are the preferred materials for the clinical application of mandibular implants which are beneficial for bone tissue regeneration. So far, the bonding strength of TBBC fabricated by traditional additive manufacturing techniques reported in literature is no more than 35 MPa. Therefore, the main problem that restricts the application of this material on the mandible is the low bonding strength with the matrix. Unfortunately, the effective method to improve the bonding strength of TBBC is rarely mentioned. Under this circumstance, TBBC fabricated on artificial mandible are prone to peeling off during the bite and chew. In order to improve the mechanical properties of materials without losing the biological activity, this paper firstly studied the interaction mechanism between laser beam and Ti-HAp mixed powders. Afterward, two major crack avoidance factors, dilution rate and overlap rate, were analyzed to determine the optimal laser deposition parameters for TBBC. Finally, the mechanical performances were comprehensively studied. Of course, the biological activity of the TBBC was also preliminarily evaluated in Simulated Body Fluid (SBF). The results show that the fabricated TBBC have a bonding strength of 177.3–338.6 MPa, at least 5 times higher than the traditional process of 35 MPa. Furthermore, the increase of the maximum mass ratio of HAp powders to 15% will generate the bio-phase of Ca3(PO4)2, which provides a better Ca/P environment with PO43− needed for bone tissue regeneration.

Predicting the superconducting transition temperature and relative resistance ratio in YBa[formula omitted]Cu[formula omitted]O[formula omitted] films

The increase in critical temperature, Tc, of high-temperature superconductors fulfills the needs of practical applications with liquid-helium-free refrigeration and a delay in magnet failure. The YBa2Cu3O7 (YBCO) superconductor exhibits Tc of greater than 90 K and an upper critical field of greater than 100 T, which is a promising candidate in high-field magnet design. Due to their large anisotropy in current transportation, YBCO superconductors are usually processed as thin films by pulsed-laser deposition. But the research requires significant manpower for materials synthesis, analysis, and quench detection, as well as costly equipment and facilities. In this work, we develop the multiple linear regression model to shed light on the relationship between pulsed laser deposition parameters and the superconducting transition temperature (Tc) and relative resistance ratio (rR) in the laser deposition of YBa2Cu3O7 films. The model is straightforward and simple and demonstrates a high degree of accuracy and stability, contributing to fast low-cost estimations of Tc and rR.

Prediction of Geometric Characteristics of Melt Track Based on Direct Laser Deposition Using M-SVR Algorithm.

Geometric characteristics provide an important means for characterization of the quality of direct laser deposition. Therefore, improving the accuracy of a prediction model is helpful for improving deposition efficiency and quality. The three main input variables are laser power, scanning speed, and powder-feeding rate, while the width and height of the melt track are used as outputs. By applying a multi-output support vector regression (M-SVR) model based on a radial basis function (RBF), a non-linear model for predicting the geometric features of the melt track is developed. An orthogonal experimental design is used to conduct the experiments, the results of which are chosen randomly as training and testing data sets. On the one hand, compared with single-output support vector regression (S-SVR) modeling, this method reduces the root mean square error of height prediction by 22%, with faster training speed and higher prediction accuracy. On the other hand, compared with a backpropagation (BP) neural network, the average absolute error in width is reduced by 5.5%, with smaller average absolute error and better generalization performance. Therefore, the established model can provide a reference to select direct laser deposition parameters precisely and can improve the deposition efficiency and quality.

Effect of Pd/ZnO Morphology on Surface Acoustic Wave Sensor Response.

Laser deposition was used to obtain Pd/ZnO bilayers, which were used as sensing layers in surface acoustic wave (SAW) sensors. The effect of laser deposition parameters such as deposition pressure, laser energy per pulse, laser wavelength or pulse duration on the porosity of the Pd and ZnO films used in the sensors was studied. The effect of the morphology of the Pd and ZnO components on the sensor response to hydrogen was assessed. Deposition conditions producing more porous films lead to a larger sensor response. The morphology of the ZnO component of the bilayer is decisive and has an influence on the sensor properties in the same order of magnitude as the use of a bilayer instead of a single Pd or ZnO layer. The effect of the Pd film morphology is considerably smaller than that of ZnO, probably due to its smaller thickness. This has implications in other bilayer material combinations used in such sensors and for other types of analytes.

Surface Acoustic Wave Biosensor with Laser-Deposited Gold Layer Having Controlled Porosity

Laser-deposited gold immobilization layers having different porosities were incorporated into love wave surface acoustic wave sensors (LW-SAWs). Variation of pulsed laser deposition parameters allows good control of the gold film morphology. Biosensors with various gold film porosities were tested using the biotin–avidin reaction. Control of the Au layer morphology is important since the biotin and avidin layer morphologies closely follow that of the gold. The response of the sensors to biotin/avidin, which is a good indicator of biosensor performance, is improved when the gold layer has increased porosity. Given the sizes of the proteins, the laser-deposited porous gold interfaces have optimal pore dimensions to ensure protein stability.

Banding and microstructural features in laser cladding of a 304 substrate using 316 powder

The aim of the cladding process is to improve mechanical, chemical, and physical features of the surface of metals. This laser process is frequently used to promote such alterations via deposition of metals/alloys with mechanical behavior superior to that of the substrate. In this contribution, an AISI 304 austenitic stainless steel is covered with an AISI 316 as powder filler metal using multiple laser deposition parameters. In the produced samples, the effect of the studied parameters on the geometry, surface appearance, dilution, and microstructural features was evaluated. The authors focus on metallurgical characteristics of cladding, seeking to explain the formation of three attributes: banding, columnar structure, and equiaxial grains. It was determined that banding is composed of a cellular-dendritic structure and is generated by changes in the microstructure size, derived from local variations in the solidification rate. The same applies for the columnar and equiaxial zones, but the appearance of equiaxial geometry is due to the change of the growth direction of the aforementioned columns, in the middle of the fusion zone. All the samples confirmed the formation of F/MA-type solidification mode, which indicates that the cooling rate is low and similar to those recorded in conventional fusion welding.

The Effect of Growth Parameters on Electrophysical and Memristive Properties of Vanadium Oxide Thin Films.

We have experimentally studied the influence of pulsed laser deposition parameters on the morphological and electrophysical parameters of vanadium oxide films. It is shown that an increase in the number of laser pulses from 10,000 to 60,000 and an oxygen pressure from 3 × 10−4 Torr to 3 × 10−2 Torr makes it possible to form vanadium oxide films with a thickness from 22.3 ± 4.4 nm to 131.7 ± 14.4 nm, a surface roughness from 7.8 ± 1.1 nm to 37.1 ± 11.2 nm, electron concentration from (0.32 ± 0.07) × 1017 cm−3 to (42.64 ± 4.46) × 1017 cm−3, electron mobility from 0.25 ± 0.03 cm2/(V·s) to 7.12 ± 1.32 cm2/(V·s), and resistivity from 6.32 ± 2.21 Ω·cm to 723.74 ± 89.21 Ω·cm. The regimes at which vanadium oxide films with a thickness of 22.3 ± 4.4 nm, a roughness of 7.8 ± 1.1 nm, and a resistivity of 6.32 ± 2.21 Ω·cm are obtained for their potential use in the fabrication of ReRAM neuromorphic systems. It is shown that a 22.3 ± 4.4 nm thick vanadium oxide film has the bipolar effect of resistive switching. The resistance in the high state was (89.42 ± 32.37) × 106 Ω, the resistance in the low state was equal to (6.34 ± 2.34) × 103 Ω, and the ratio RHRS/RLRS was about 14,104. The results can be used in the manufacture of a new generation of micro- and nanoelectronics elements to create ReRAM of neuromorphic systems based on vanadium oxide thin films.

Tetragonal tungsten bronze phase thin films in the K–Na–Nb–O system: Pulsed laser deposition, structural and dielectric characterizations

Pulsed laser deposition parameters have been determined to synthesize pure Tetragonal Tungsten Bronze (TTB) phase thin films in the (K,Na)–Nb–O system (KNN). In relation to the high volatility of alkaline elements, it was found that the target composition and the target-substrate distance are of first importance. The TTB phase was identified by X-ray and electron diffraction and the surface microstructure consisting mainly of nanorods supports the formation of hallmark of the TTB phase. Poly-oriented nanorods have been obtained on both C-plane sapphire and (111)Pt/TiO2/SiO2/(001)Si substrates whereas horizontal nanorods oriented along the (hk0) planes have been grown on (100) and (110) SrTiO3. All the nanorods are parallel together when grown on (110) SrTiO3 and they present two in-plane orientations rotated of 90° from each other on (100) SrTiO3. Dielectric characteristics (dielectric permittivity εr, and loss tangent tanδ) have been measured at low (1 kHz - 1 MHz) and high (1 GHz–40 GHz) frequencies, on films deposited on Pt coated silicon and sapphire, respectively. A value of εr = 200 at 1 kHz with tanδ = 0.015 were measured in a parallel plate capacitor configuration, whereas εr = 130 and tanδ = 0.20 at 10 GHz were retrieved from transmission lines printed on the KNN TTB thin film grown on C-plane sapphire. Raman investigations of the TTB films were performed in the temperature range 77–873 K, confirming the TTB phase formation and the absence of structural transition. Piezoelectric Force Microscopy measurements evidenced a piezoelectric signal although no switching could be performed. However the dielectric measurements, complicated by high leakage currents when a DC voltage was applied, did not evidence any proof of ferroelectricity for the undoped KNN TTB films whereas results reported on other niobates (A,A′)6Nb10O30 (with A: K, Na and A’: Sr, Ba, Ca) have shown Curie temperatures, lying between 156 °C and 560 °C, separating the paraelectric phase (space group: P4/mbm N°127) and the ferroelectric one (space group: P4bm N°100).

Confinement-Induced Giant Spin-Orbit-Coupled Magnetic Moment of Co Nanoclusters in TiO2 Films.

High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our material engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at % Co-TiO2 film. The presence of these nanoclusters was confirmed using transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray absorption fine structure. The film exhibits a very high saturation magnetization of 99 emu/cm3. Detailed studies using X-ray magnetic circular dichroism confirm that Co has an enhanced magnetic moment of 3.5 μB/atom, while the Ti and O also contribute to the magnetic moments. First-principles calculations supported our hypothesis that the metallic Co nanoclusters surrounded by a TiO2 matrix can exhibit both large spin and orbital moments. Moreover, a quantum confinement effect results in a high Curie temperature for the embedded Co nanoclusters. These findings reveal that 1-2 nm nanoclusters that are quantum confined can exhibit very large magnetic moments above room temperature, representing a promising advance for the design of new high magnetization materials.

Plasmonic carbon nanohybrids from laser-induced deposition: controlled synthesis and SERS properties

A novel single-step, laser-induced and solution-based process is presented for synthesizing complex hybrid metal/carbon nanostructures. The process relies on simply illuminating the interface between a substrate and a liquid solution of the supramolecular complex [Au13Ag12(C2Ph)20(PPh2(C6H4)3PPh2)3][PF6]5 (hereinafter abbreviated as SMC) with an unfocussed He–Cd laser having a wavelength of 325 nm and an intensity of I = 0.5 W/cm2. The process results in hybrid nanostructures of well-controlled morphology: nanoparticles (NP) and 2D flakes, which may also grow jointly to form 3D morphologically complex multipetal ‘flower-like’ structures. At the atomic scale, the obtained metamaterials are complex in composition and structure, i.e., they contain bimetallic Au–Ag nanoclusters of diameter 3–5 nm incorporated inside a carbonaceous matrix. This matrix can be amorphous or crystalline, and the details of the compositional outcome can be controlled and steered by the laser deposition parameters. Au–Ag nanoclusters show plasmonic behavior including the enhancement of electromagnetic fields of visible light. This leads to the enhancement of Raman scattering by the Au–Ag nanoparticle ensemble within the carbonaceous matrix. This enables a 3D architecture for stimulating surface-enhanced Raman scattering (SERS).

Selective brookite polymorph formation related to the amorphous precursor state in TiO2 thin films

A wide variety of brookite TiO2 synthesis methods have been published over the past several decades, but few studies discuss the underlying mechanism that stabilizes brookite over its stable counterparts, rutile and anatase. Here, we investigate of the effect of pulsed laser deposition parameters on the as-deposited amorphous precursor titania thin films, which subsequently crystallize into stable and metastable TiO2 polymorphs upon annealing. We find that oxygen pressure in the deposition chamber strongly influences the non-equilibrium state of the amorphous precursor, which ultimately allows for selective polymorph formation. Rutile forms as the dominant phase at low pO2 < 0.1 mTorr, while anatase is favored at high pO2 > 5 mTorr. Brookite forms primarily at intermediate pO2 (0.5–1.0 mTorr). Controlling the amorphous structure (i.e. Ti—O bonding and polyhedral arrangement) of the precursors via oxygen deficiency is therefore likely for the selective formation of crystalline TiO2 polymorphs from sub-stoichiometric amorphous precursors. Directing phase selectivity by manipulating the structure and internal energy of the precursor amorphous state may have tremendous potential for synthesis of metastable crystalline phases that exhibit more desirable properties in comparison to their stable counterparts.

Controlling the phase composition of cadmium sulfide films during pulsed laser deposition

Thin cadmium sulfide films grown by pulsed laser deposition on crystalline and amorphous substrates have been shown to consist of a mixture of a cubic (sphalerite structure) and a hexagonal (wurtzite structure) phase. We have demonstrated the possibility of controlling the percentages of the hexagonal and cubic phases in cadmium sulfide films by varying pulsed laser deposition parameters. Varying the deposition parameters allows one to control the optical and structural parameters and surface morphology of thin cadmium sulfide films.

Laser additive processing of Fe-Si-B-Cu-Nb magnetic alloys

The magnetic alloy of nominal composition, Fe73.5Si13.5B9Nb3Cu1, has been successfully processed using the laser engineered net shaping (LENS™) process, from a feedstock of elemental powders. The microstructure consists of dendritic α-Fe3Si grains, with B and Nb partitioning to the inter-dendritic regions, resulting in the formation of Fe3B grains. Additionally, Fe23B6 grains are visible at the α-Fe3Si/Fe3B interface. The scale of this microstructure can be varied via the laser deposition parameters and this, in turn, influences coercivity (Hc) and saturation magnetization (Ms) of these laser-deposited magnetic alloys. This work shows the feasibility of creating novel geometries of magnetic materials by the laser engineered net shaping process.

Laser in situ synthesis of gradient aluminides in metal matrix composite during DMD process

The suitability of direct metal deposition process of exothermic powders (Ni-Al, Ti-Al, Fe-Al systems), traditionally used in the self-propagating high-temperature synthesis technology, is described. Owing to the synthesis of new intermetallic phases, the overlapping of laser in situ synthesis and layerwise deposition processes makes it possible both to obtain more durable parts of complex shape, and to enlarge the functional resource of these functional-graded structures. Besides, relationships between the main laser deposition parameters and the intermetallic phase structures of the built-up objects were studied. In our research we applied optical microscopy, X-ray analysis, microhardness measurement and SEM with EDX analysis of the laser-fabricated intermetallics.

The Relevance of Different Oxygen Reduction Pathways of La0.8Sr0.2MnO3 (LSM) Thin Film Model Electrodes

Sr-doped lanthanum manganite (LSM) is a widely used cathode material in solid oxide fuel cells (SOFC). Despite being a poor ion conductor, LSM electrodes can reduce oxygen via two pathways: a “3PB surface path” which includes surface diffusion of oxygen species and oxide ion incorporation at the three phase boundary (3PB), and a “bulk path” based on oxygen diffusion in LSM. In this work, the kinetics of both paths and their dependence on temperature and electrode geometry is investigated by impedance spectroscopy on micropatterned LSM thin film electrodes. Differently shaped and sized macroscopic and microscopic LSM electrodes as well as LSM electrodes with oxygen blocking Pt capping layers are employed to identify two parallel reaction pathways of oxygen reduction. On circular microelectrodes the 3PB surface path carries most of the current in the lower temperature region (below ca. 700°C), while at high temperatures (above ca. 700°C) the bulk path is dominating. The significance of each reduction path also depends on the microstructure of the columnar LSM films which can be changed by varying pulsed laser deposition (PLD) parameters or by annealing. Moreover, relevance of a pseudo-3PB path across edges of the LSM electrodes is discussed.

An investigation of the effect of laser deposition parameters on characteristics of multilayered 316 L deposits

A potential problem in applying the direct laser deposition (DLD) technique to material fabrication is the effect that subsequent deposited layers have on reheating previous laser deposition layers. Most of the previous investigations examined the effect of the laser deposition parameters on the microstructure and mechanical properties of a single layer. This work focused on the effect of the laser parameters of subsequent layers on the microstructure and mechanical properties of the deposited layers to select proper parameters and characterize the effect. The microstructure morphology and property values are affected by the varied parameters. This leads to some tempering and aging effects in the steels. The microstructure of the top layer was equiaxed, while the near substrate region was fine dendritic. Typically, both of the travel speed and power of the laser show the significant effects on microstructure and hardness.

Structural and electrical properties of sodium bismuth titanate (Na0.5Bi0.5TiO3) thin films optimized using the Taguchi approach

Controllable Pulsed Laser Deposition (PLD) parameters have been optimized to grow sodium bismuth titanate (Na0.5Bi0.5TiO3) (NBT) thin films. Target to substrate distance, background gas pressure, substrate temperature, laser fluence, laser rate of repetition, annealing time and NBT targets with and without excess Bi have been chosen as the parameters using a Taguchi L18 orthogonal array. Taguchi's Signal-to-Noise (S/N) ratios and analysis of variance (ANOVA) tools highlight the relevance of each parameter, and also yield the optimal setting of the parameters. The dominant parameters affecting dielectric properties are oxygen gas pressure and substrate temperature, whereas the distance between target to substrate and laser fluence appear as significant parameters. Fine tuning experiments and a subsequent verification experiment using the dominant and significant parameters result in the best values for the dielectric constant of 735, dielectric loss of 0.07 at 1kHz and remnant polarization of 21.42µC/cm2.

Femtosecond pulsed laser deposition of silicon thin films

Optimisation of femtosecond pulsed laser deposition parameters for the fabrication of silicon thin films is discussed. Substrate temperature, gas pressure and gas type are used to better understand the deposition process and optimise it for the fabrication of high-quality thin films designed for optical and optoelectronic applications.