Metal Targets Research Articles

Layer-by-layer structured nanocomposite deposits from plasma-synthesized organosilicon nanoparticles and organosilicon nanoparticles decorated with Ag nanoparticles by taking advantage of cyclic nanoparticle formation in Ar/HMDSO reactive plasmas

Rational engineering of thin nanocomposite layers, deposited in reactive plasmas, requires knowledge on the plasma behavior in order to produce multifunctional deposits with tailored properties (structural, optical, electrical, etc.) This work presents an experimental study of nanoparticles synthesized in the plasma gas-phase and their subsequent use as building-blocks to form layer-by-layer nanostructures. The experiment is performed in a plasma process that successfully combines plasma polymerization of an organosilicon molecular precursor (hexamethyldisiloxane, HMDSO) and sputtering of a metallic (silver) target. Pulsed injection of the precursor is found to promote cyclic nanoparticle formation in Ar/HMDSO reactive plasmas. The plasma electron temperature is found to vary in the range 1.6—2.2 eV as derived from time-resolved optical emission spectroscopy of the plasma energetic conditions. This diagnostic method is also shown to provide a reliable tool for online monitoring of the nanoparticle synthesis process. Two types of layer-by-layer structured nanocomposites can be obtained depending on the type of nanoparticles synthesized: (i) organosilicon nanoparticles of size less than 100 nm in all studied plasma conditions for a large quantity of injected HMDSO and (ii) raspberry-like nanoparticles of size less than 150 nm when the quantity of injected HMDSO is reduced. The organosilicon nanoparticle growth follows a polydimethylsiloxane (PDMS)-like oligomerization scheme in which the R2-Si(-O)2 silicon bond tends towards the formation of polymeric structure in a R3-Si(-O)1 silicon chemical environment, containing Si-(CH2)-Si type bridges that are involved in cross-linking. The elemental composition of the raspberry-like nanoparticles is similar to that of the organosilicon nanoparticles, supplemented by the Ag component. The decorating silver nanoparticles are ∼15 nm of size, round in shape and polycrystalline. There is no evidence for silver oxides in the nanostructures. The Si-O-Ag bridges, revealed by infrared spectroscopy, suggest the presence of junction sites between the metallic and the organosilicon parts of the raspberry-like nanoparticles. The silver nanoparticles are found to decorate the organosilicon nanoparticles to form the raspberry-like nanoparticles in the plasma gas-phase, before being deposited. This reveals a very interesting phenomenon of simultaneous growth of the silver- and organosilicon-parts in the plasma without mixing during the nucleation phase.

LIPSS formation on Ni surface using mixed near-infrared laser beam harmonics

Generation of laser-induced periodic surface structures (LIPSS) is investigated with femtosecond laser pulses with 1030nm wavelength and its second and its harmonics. The second (λ2ω = 515nm) and third harmonics (λ3ω = 343nm) beams in addition to their combination were utilized to control the period of the LIPSS on a Ni surface. The resulting periodicity of the formed structures was ∼ 0.42μm, 0.22μm, and 0.33μm respectively for the second harmonic beam, third harmonic beam, and their combination. This method demonstrates a direct way to control the periodicities on a metal target by employing an individual laser beam wavelength to induce a variable range of LIPSS periods.

Data-driven prediction of dimensionless quantities for semi-infinite target penetration by integrating machine-learning and feature selection methods

This study employs a data-driven methodology that embeds the principle of dimensional invariance into an artificial neural network to automatically identify dominant dimensionless quantities in the penetration of rod projectiles into semi-infinite metal targets from experimental measurements. The derived mathematical expressions of dimensionless quantities are simplified by the examination of the exponent matrix and coupling relationships between feature variables. As a physics-based dimension reduction methodology, this way reduces high-dimensional parameter spaces to descriptions involving only a few physically interpretable dimensionless quantities in penetrating cases. Then the relative importance of various dimensionless feature variables on the penetration efficiencies for four impacting conditions is evaluated through feature selection engineering. The results indicate that the selected critical dimensionless feature variables by this synergistic method, without referring to the complex theoretical equations and aiding in the detailed knowledge of penetration mechanics, are in accordance with those reported in the reference. Lastly, the determined dimensionless quantities can be efficiently applied to conduct semi-empirical analysis for the specific penetrating case, and the reliability of regression functions is validated.

Simultaneous Separation of Protactinium-230 and Uranium-230 Isotopes from a Proton-Irradiated Thorium Matrix.

The use of radioisotopes in cancer therapy is becoming increasingly important. As a potential candidate for targeted alpha therapy, 230U (t1/2 = 20.8 d), the decay daughter of 230Pa (t1/2 = 17.4 d) is currently being investigated for cancer treatment. For radioisotopes to be used in biomedicine, they must be radiochemically pure and free from carrier interference. This can be challenging given their short half-life. Thus, radiological separation methods for harvesting isotopes for use in biomedicine must be simple, fast, and capable of obtaining the required purity levels. Herein, we demonstrate a new rapid method for the separation of 230U and 230Pa from a proton-irradiated 232Th metal target and from coproduced fission products with high recovery and purity. A dual-column approach was used, in which the first column was an anion exchange (AX) column and the second column was a DGA column. The MP-1 AX resin was used for the primary separation of the three major components (U, Pa, and Th, as well as fission products), and the DGA column was used for further purification of the separated 230U. The method is simple and allows for straightforward separation of U, Pa, Th, and fission products; also, the entire process from target dissolution to shipment of 230U could be completed in 3 days with an overall 230U recovery yield of 96 ± 3%. Additionally, separated 230Pa fractions can be used to harvest ingrown 230U after initial separation.

NbC thin films via reactive DC sputtering in a CH4/Ar atmosphere

We have demonstrated the growth of NbC-Amorphous C films that manifest a well-known nanocomposite structure (Klages and Memming, 1990; Nedfors et al., 2011; Sala et al., 2021). The films were deposited using reactive DC sputtering in a CH4/Ar atmosphere using an insulating substrate near room temperature. A metallic Nb sputtering target was sputtered in an argon/CH4 atmosphere with a pressure range of 5.9 to 8.5 mTorr as the CH4 flow was also varied. Crystalline NbC films were deposited at room temperature at the lowest CH4 flow rate. The films exhibited ohmic electrical response at room temperature. The DC electrical resistivity scaled almost 4 orders of magnitude from 4.39 × 10−4 Ω-cm to 1.08 × 10−1 Ω-cm through changes in CH4 flow rates and the resultant C content of the films. The large variation in resistivity cannot be attributed to the changes in sample composition, e.g. volumetric mixing. It is postulated from XRD and TEM results that the large change in resistivity is due to the decreasing NbC crystallite size with increasing CH4. This leads to additional three-dimensional nanoscale intragranular interfaces and results in increased resistivity. X-ray reflectivity measurements were conducted, and the modelled film density was found to match the expected density for the film compositions as measured using X-ray photoelectron spectroscopy. Elastic recoil detection analysis (ERDA) was used to quantify H content of the films. The H content increased from 5.5 to 22 atomic percent with corresponding increase in CH4 flow. Transmission electron microscopy utilizing precession electron diffraction (PED) was conducted and showed a strong dependence of crystallinity on CH4 flow. A multilayer layer sample with varying CH4 flowrates was examined with TEM and showed that films were amorphous in nature for flow rates above 10 SCCM CH4; in agreement with XRD results.

Study on the ablative characteristics of steel target irradiated by nanosecond pulsed pseudo spark electron beams: Experiment and molecular dynamics simulation

A combination of simulation and experimentation is employed to explore the influence of the non-uniformity of energy distribution in nanosecond PSEB on the target ablation. Firstly, A spatiotemporally distributed heat source model is built using Monte Carlo computational method and an ablation phase transition model is established using molecular dynamics method. The results reveal the time evolution of multiple cavities in the sub-surface region, as well as the temperature and stress field distributions with electron beam irradiation. Phase explosion formation and lattice structure changes in the steel target during the ablation process is found for the first time. The PSEB modified AISI1045 steel samples is experimentally conducted. The characterization results show the changes in the crystal structure within AISI1045 steel, which is attributed to the formation of an amorphous layer resulting from grain refinement and structural defects, as well as the combined effects of thermal elastic stress waves, shock thermal stress waves and temperature gradient distribution. The experimentally obtained crystal phase changes are consistent with the simulation results, confirming the accuracy and validity of the modelling. The findings of this study provide a molecular-scale explanation for the formation of unique morphology and micro-structures during the PSEB ablated metal target.

Deposition rate and optical emissions in niobium oxide processes by reactive sputtering

Niobium oxide films find various applications, such as antireflective optical layers, gas sensors, and solar cells. They also show promise for emerging applications such as electrochromic and photocatalytic devices. In order to optimize the deposition of niobium oxide films by RF reactive sputtering, a detailed investigation of the plasma parameters was performed. A pure metallic target and a mixture of Ar and O2 in different proportions were used in the experiments. The deposition power was varied between 120 and 260 W, while the total pressure was kept at 0.67 Pa throughout. Deposition rates, discharge self-bias voltage, and plasma optical emissions were monitored and analyzed. Additionally, computer simulations of the process utilizing existing models were conducted and a comparative analysis with the experimental results was performed. The main findings include mapping the deposition conditions as functions of oxygen flow rate. The flow ranges in which the deposition regime changes from metallic to oxygen contaminated target conditions were identified. The narrow O2 flow range associated with the regime changes was characterized by significant changes in the self-bias voltages and plasma emissions from oxygen, argon, and niobium. The observations evidence the importance of the detailed analysis of the deposition process to get the desired stoichiometry and optimized film properties.

Penetration mechanics of rigid projectiles impacting metallic and concrete targets—A summary of our work

The physical mechanisms operating during the penetration and perforation of metallic and concrete targets by rigid projectiles are reviewed in this paper. The review covers our approach to these phenomena, as detailed in several papers that were published during the last decade. This approach is based on experimental data and their numerical simulations, through which we constructed analytical expressions for the penetration depths and the ballistic limit velocities of the corresponding projectile/target pairs. This review article will benefit researchers in the terminal ballistics community because it presents a full picture of our approach to the subject, and it also outlines the development in our thinking over the years.

Critical pulse in multi-shot femtosecond laser ablation on metallic surfaces

Thermal effect remains a thorny issue for femtosecond-laser surface engineering and nanostructuring on metallic targets with high pulse energies or high repetition rates, which needs to be paid adequate attentions. Herein, we have experimentally investigated the heat diffusion and accumulations during single-shot and multi-shot femtosecond laser ablation on metallic surfaces. We have for the first time observed a novel phenomenon that the thermal effect was intensified abruptly when the laser-pulse number goes over a threshold (approximately between 10 and 20 for aluminum alloy with laser fluence of 6 J cm−2), accompanied with a dramatic reduction of ablated depth and complicated plasma dynamics. Based on both optical and thermodynamic analysis, we introduced a defocusing-dominated plasma-assistant model for this abnormal thermal effect. This work explored the critical experimental parameters for femtosecond-laser surface modification and processing in micro-scale engineering applications.

Effect of Laser Shock Peening on Electrochemistry and Wettability of Additively Manufactured Stainless Steel

Abstract Laser shock peening (LSP) is investigated for its use in altering the electrochemical and wetting behavior of 316L stainless steel made with laser powder bed fusion (LPBF). The corrosion performance of LPBF stainless steel varies between studies and build parameters, thus motivating the search for postprocessing methods that enable wetted surface applications. Compressive surface stress has been demonstrated to reduce corrosion rate in additively manufactured metal and LSP is known to impart compressive residual stress into metal targets. Wettability also affects corrosion behavior and LSP induces hydrophobicity. LSP is therefore a promising tool for improving corrosion behavior of LPBF stainless steel. This paper examines the electrochemical properties of LPBF stainless steel before and after LSP with electrochemical impedance spectroscopy and potentiokinetic measurements. Contact angle, surface free energy, and surface finish are studied with dynamic contact angle measurements and profilometry. X-ray diffraction and energy-dispersive X-ray spectroscopy measures residual stress and surface chemistry. The top surface perpendicular to the build direction (XY) and the wall surface parallel with the build direction (XZ) are studied for all measurements due to the large differences in roughness and mechanical properties between these surfaces. LSP increases pitting potential for both XY and XZ surfaces and causes an increase to the surface electrochemical impedance. LSP also increases the contact angle of liquids on both surfaces. These changes to electrochemistry and wettability are attributed in part to surface morphology and surface chemistry alterations as well as the inducement of compressive residual stress.

Support Reconstruction of Dielectric and Metallic Targets via the Contraction Integral Equation

Support Reconstruction of Dielectric and Metallic Targets via the Contraction Integral Equation

Experimental design using the Taguchi method for the development of conductive textiles used in flexible thermoelectric generators

This paper presents several aspects of the robust experimental design methodology using the Taguchi method to develop electrically conductive textiles. These conductive textiles will be used to make thermoelectric generators based on the Seebeck effect. Since the experimental development involves the use of the magnetron sputtering method with more than three variables, the Taguchi method was selected to observe how different parameters (5 independent variables such as argon flow, power, pressure, deposition surface area and metal type used for solid targets) influence the mean and variance of the process performance defined by the thickness of the metal film deposited (dependent variable). In the experimental design framework, the analysis using the Taguchi method, followed by optimisation, helped select the optimal experiments from the set of possible experiments. This methodology reduced the number of experiments by 21–42% and minimised resource consumption (e.g., metal targets, argon, energy).

Scattering Field Intensity and Orbital Angular Momentum Spectral Distribution of Vortex Electromagnetic Beams Scattered by Electrically Large Targets Comprising Different Materials

In this study, we obtained the intensity and orbital angular momentum (OAM) spectral distribution of the scattering fields of vortex electromagnetic beams illuminating electrically large targets composed of different materials. We used the angular spectral decomposition method to decompose a vortex beam into plane waves in the spectral domain at different elevations and azimuths. We combined this method with the physical optics algorithm to calculate the scattering field distribution. The OAM spectra of the scattering field along different observation radii were analyzed using the spiral spectrum expansion method. The numerical results indicate that for beams with different parameters (such as polarization, topological charge, half-cone angle, and frequency) and targets with different characteristics (such as composition), the scattering field intensity distribution and OAM spectral characteristics varied considerably. When the beam parameters change, the results of scattering from different materials show similar changing trends. Compared with beams scattered by uncoated metal and dielectric targets, the scattering field of the coating target can better maintain the shape and OAM mode of beams from the incident field. The scattering characteristics of metal targets were the most sensitive to beam-parameter changes. The relationship between the beam parameters, target parameters, the scattering field intensity, and the OAM spectra of the scattering field was constructed, confirming that the spiral spectrum of the scattering field carries the target information. These findings can be used in remote sensing engineering to supplement existing radar imaging, laying the foundation for further identification of beam or target parameters.

In Situ Metallic Coating of Atom Probe Specimen for Enhanced Yield, Performance, and Increased Field-of-View.

Atom probe tomography requires needle-shaped specimens with a diameter typically below 100 nm, making them both very fragile and reactive, and defects (notches at grain boundaries or precipitates) are known to affect the yield and data quality. The use of a conformal coating directly on the sharpened specimen has been proposed to increase yield and reduce background. However, to date, these coatings have been applied ex situ and mostly are not uniform. Here, we report on the controlled focused-ion beam in situ deposition of a thin metal film on specimens immediately after specimen preparation. Different metallic targets e.g. Cr were attached to a micromanipulator via a conventional lift-out method and sputtered using Ga or Xe ions. We showcase the many advantages of coating specimens from metallic to nonmetallic materials. We have identified an increase in data quality and yield, an improvement of the mass resolution, as well as an increase in the effective field-of-view. This wider field-of-view enables visualization of the entire original specimen, allowing to detect the complete surface oxide layer around the specimen. The ease of implementation of the approach makes it very attractive for generalizing its use across a very wide range of atom probe analyses.

Photoluminescence of combinatorically sputtered Al2O3–Y2O3 thin films with a Cr3+ and Nd3+ co-doping concentration gradient

The characterization of a wide range of luminescent thin films can be a long and tedious endeavor. With reactive combinatorial sputtering of multiple metal targets, it possible to fabricate thin films with a gradient in composition simply by not rotating the substrate. In this work, combinatorically sputtered thin films of Cr3+ and Nd3+ doped in the Al2O3–Y2O3 system (YAlO) are studied for thin film based luminescent solar concentrators (TFLSCs) application. Contrary to mm's thick plate type LSC's, TFLSCs of just several 100 nm thick require much higher Cr3+ concentration to achieve 40% absorption which can enable several 10's of W/m2 LSC power efficiencies. Our transmission measurements on a Cr2O3 film with a thickness gradient result in an absorption cross section at 460 nm of 1.3 ± 0.7 × 10−19 cm2 showing that the TFLSC absorption requirement can be fulfilled provided that the Cr3+ concentration is in the order of 1022 ions/cm3. The Y:Al ratio of the YAlO host in our films ranged between 0.5 and 3.5, thereby including the monoclinic (Y4Al2O9), perovskite (YAlO3) and garnet (Y3Al5O12) stoichiometry's on a single film. Position dependent XRD, EDX, excitation, emission and lifetime measurements of Cr3+ and Nd3+ show that the unique gradient film sputtering method is able to characterize thin films as a function of host composition and doping concentration. Energy transfer between Cr3+ and Nd3+ in co-doped YAlO films is concluded from Cr3+ excitation bands observed while monitoring Nd3+ emission and from the matching of the rise-time of Nd3+ 1340 nm emission (4F3/2 ->4I11/2) and the decay time of Cr3+ 840 nm emission (4T2 ->4A2). Nd3+ lifetime systematically decreases from 0.24 to 0.05 ms with increasing Cr3+ concentration in Y3Al5-xCrxO12:Nd (0.05 < x < 2). The constraints of heavily doped Cr3+ thin films for enabling adequate absorption and energy transfer to Nd3+ in TFLSC applications are the subjects of the discussion.

Impact of Synthesis Parameters upon the Electronic Structure in PVD-Deposited CdxZn1-xO Composite Thin Films: An XPS-XANES Investigation.

The impact of different synthesis parameters, such as thickness, postsynthesis annealing temperature, and oxygen gas flow rate, upon the electronic structure is discussed in detail in the present experimental investigation. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectroscopy techniques are used to evaluate the surface electronic properties along with the presence and stability of the CdO2 surface oxide in CdxZn1-xO (x = 0.4) composite thin films. The thin films were synthesized with varying thicknesses using a Cd0.4Zn0.6O (CZO) ceramic and Cd0.4Zn0.6 (CZ) metallic targets and oxygen gas flow rates during magnetron sputtering. The Zn L3,2 edge and O K edge XANES spectra are affected by the oxygen gas flow rate. For the zero rate, an increase in intensity is observed in the Zn L3,2 edge, and notable changes occur in the overall spectral features of the O K edge. In the films synthesized in the presence of oxygen, highly probable O 2p → antibonding Zn 3d electronic transitions decrease the probability of the Zn 2p1/2 → antibonding Zn 3d electronic transition by filling the vacant antibonding Zn 3d states, leading to the reduction in overall intensity in the Zn L3,2 edge. Scanning electron microscopy reveals grain growth with increasing annealing temperature. The annealing induces orbital hybridization, generating new electronic states with higher transition probabilities and intensity enhancement in both Zn L3,2 and O K edges. The presence of the CdO2 surface phase is confirmed by analyzing the Cd 3d5/2 and O 1s XPS core levels. The CdO2 surface phase is observed in the films synthesized using the CZO target for all thicknesses, while the CZ target is only observed for higher thicknesses. Further postsynthesis annealing treatment results in the disappearance of the CdO2 phase. The CdO2 surface phase can be controlled by varying the film thickness and postsynthesis annealing temperature.

Study on microstructures, properties and mechanisms of sinter-joining refractory metal W[sbnd]30Si powders and sputtering targets by spark plasma sintering technique

The development of semiconductor integrated circuits has been limited by the low utilization rate of refractory metal sputtering targets. Spark plasma sintering (SPS) technology has shown great superiority in the sintering and joining of materials, which can be applied to the repair of waste targets and improve the utilization rate. In this study, SPS technology was used to sinter-join the high-purity refractory metal W30Si sputtering powder and the target for integrated circuits to determine the optimal repair process and repair mechanism. The morphological characteristics, grain size, relative density, and Vickers hardness of the repair layer (powder-sintered body) and the target under different joining times were analyzed, and the interface structure and properties of the W30Si joint were also studied. It was found that the W30Si joint was composed of WSi2 and Si phases. The grain size, relative density, and Vickers hardness of the W30Si powder-sintered body and targets increased with the joining time. When the joining time was 10 min (1200 °C), the W30Si joint formed a “zigzag” joining interface, and the bending strength, relative density, grain size, Vickers hardness, and thermal conductivity of the joint were similar to those of the pristine target. In addition, the physical model of SPS sintered and joined refractory metal powders and targets was constructed. Studies have shown that the sinter-joining consists of three stages: early stage, middle stage, and late stage. Among them, the middle stage included two steps that may occur simultaneously, namely the sintering of refractory metal powders and the joining of refractory metal powders with the target, involving pressure welding, micro-arc welding, resistance welding, and diffusion welding mechanisms. This work can provide theoretical guidance for the optimal design of the SPS repair process for refractory metal W30Si sputtering targets.

Gradual weakening down to complete disappearance of the velocity correlated cluster emission effect in keV collisions of C60 with light metallic targets: Microscopic insights via molecular dynamics simulations

The so-called velocity correlated cluster emission (VCCE) effect is the recently reported emission of large clusters with nearly the same velocity from an atomically heavy target (such as coinage metals) following a single C60− impact at the keV kinetic energy range. The effect was observed to get weaker for a meaningfully lighter target (Al) down to its complete disappearance for C60–Be impact. Microscopic insight into the subpicosecond evolution and thermalization of the impact induced energy spike (driving the effect) is achieved using molecular dynamics simulations. It is shown that the weakening of the VCCE effect for aluminum (toward its complete disappearance for Be) is due to ultrafast decay of the atomic number density within the spike nanovolume, thus not enabling the buildup of sufficient subsurface pressure as required for driving the correlated emission. For the Be target, an extremely rapid decay of nearly 90% of the initial density within 200 fs from impact is observed. This finding provides further support for the conclusion that the emission of the velocity correlated clusters as observed for the heavier targets takes place within an ultra-short time window of only a few hundreds of femtoseconds, roughly extending from 200 to 500 fs from impact. The lower bound is dictated by the requirement for a relatively slow rate of decay of number density, enabling the buildup of a sufficiently intense pressure spike. The upper bound is dictated by the cooling rate of the spike (still maintaining an extremely high temperature of kT ≥ 1 eV, as experimentally observed) and the onset of the evolution of the impact crater.

Heavy Metal Levels and Target Hazard Quotients of Ipomoea aquatica Grown in Soils Applied with Stabilized Biosolids

Heavy Metal Levels and Target Hazard Quotients of Ipomoea aquatica Grown in Soils Applied with Stabilized Biosolids

Impact of high-power impulse magnetron sputtering pulse width on the nucleation, crystallization, microstructure, and ferroelectric properties of hafnium oxide thin films

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO2 films is investigated. HfO2 films were sputtered from a hafnium metal target in an Ar/O2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μs stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. These results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material.