Single Element Targets Research Articles

Effects of nitrogen flow ratio on the mechanical and anticorrosive properties of cosputtered (TiZrHfTa)Nx films

In this study, TiZrHfTa films were cosputtered through cyclical gradient composition deposition by using four single-element targets connected to direct-current power supplies. Multilayered and columnar structures formed at low and high rotation speeds of the substrate holder (RH), respectively. (TiZrHfTa)Nx thin films were then prepared through reactive cosputtering by using Ar/N2 mixed gas. A high RH value resulted in these films having homogeneous structures. Without the addition of reactive nitrogen gas, the fabricated metallic Ti0.24Zr0.23Hf0.27Ta0.26 film exhibited a valence electron concentration of 4.26, which resulted in the formation of a body-centered cubic (bcc) phase; a hardness of 4.7 GPa; and an elastic modulus of 104 GPa. (TiZrHfTa)Nx films with stoichiometric ratios (x) ranging from 0.59 to 0.97 were obtained by adjusting the reactive gas ratio fN2 (N2/(N2 + Ar)) from 0.1 to 0.7. The introduction of N into the TiZrHfTa crystallites caused the bcc phase to transform into a face-centered cubic phase and enhanced the mechanical properties of the films, with their hardness and elastic modulus increasing to 13.8–25.5 and 235–290 GPa, respectively. Nanoindentation, scratch, Rockwell-C adhesion, and potentiodynamic polarization tests indicated that among the prepared (TiZrHfTa)Nx films, the (Ti0.17Zr0.25Hf0.20Ta0.38)N0.75 film exhibited the best mechanical and anticorrosive properties. Target poisoning accompanied by defect formation affected the mechanical properties of the (TiZrHfTa)Nx films. The anticorrosive properties of the (TiZrHfTa)Nx films were dominated by the high-entropy effect through alloying with Ta and the adhesion strength between the films and substrates.

MOFs for Ultrahigh Efficiency Pulsed Laser Micropropulsion.

Conventional propellant materials, such as polymers and single metal elements, have long been investigated for their potential in pulsed laser micropropulsion (LMP) technology. However, achieving superior LMP efficiency through physical mixing of these materials remains a significant challenge. This study presents a paradigm shift by introducing porous crystalline polymers, known as metal-organic frameworks (MOFs), as novel propellants in pulsed LMP. MOFs are composed of metal cations and organic ligands that form ordered structures through coordination, eliminating the problem of local hot zones arising from uneven physical mixing encountered in LMP. In direct comparison to conventional polymers and single element targets, MOFs exhibit substantially higher LMP efficiency. By precisely tailoring the metal atom fraction within MOFs, an extraordinary ultrahigh efficiency of 51.15% is achieved in pulsed LMP, surpassing the performance of similar materials previously reported in the literature. This pioneering application of MOFs not only revolutionizes the field of LMP but also opens up new frontiers for MOF utilization in various energy applications.

Spectra of Multiply Charged Ions in Laser Plasma Formed from Gas-Containing Targets

The paper presents the results of a study of the charge and energy characteristics of multiply charged ions excited on the surface of a single-element and hydrogen-containing multi-component element targets under the influence of laser radiation with a power density (q=108-1012 W/cm2). It has been experimentally shown that, for all used values of q laser radiation, laser-induced plasma from gas-containing targets is characterized by a lower relative yield (dN/dE) of multi-charged ions with a charge number of Z>+3, compared to the plasma produced on the surface of the single element target. Moreover, the tendency to reduce dN/dE of multi-charged ions of the multi-element target, in comparison with the relative yield of ions from the plasma of the single-element target, is more significant and it depends on the charge of the excited ions. The increase in the charge and energy state, duration, and yield of ions of the heavy component, which occurs with an increase in the content of the light component in the target, has been established. This is explained by a decrease in the efficiency of recombination processes caused by an increase in the expansion velocity of a plasma plume due to a decrease in its average mass.

Total and Differential Sputtering Yields Explored by SRIM Simulations

Total sputtering yield and spatial distributions of sputtered atoms are important for numerous deposition techniques. We performed SRIM (Stopping and Range of Ions in Matter) simulations to analyze the total sputtering yield and angular distribution of sputtered atoms for a range of single-element target materials. The simulations were conducted for normal argon ion incidence in the 300–1200 eV range and at an oblique angle for selected ion energies. We examined the total and differential sputtering yields for the transition metals in the periods 4–6 and groups 4–6 (Ti, V, Cr; Zr, Nb, Mo; Hf, Ta, and W) and group 11 (Cu, Ag, and Au) of the periodic table, and other materials that are relevant to sputtering (B and C; Al and Si). For the transition metals, the total sputtering yield increases with the group of the periodic table. The elements in group 4 (i.e., Ti, Zr, and Hf) have the lowest sputtering yield, while the elements in group 11 (i.e., Cu, Ag, and Au) exhibit the highest sputtering yield. The angular distribution of the sputtered atoms shows a cosine distribution for the transition metal atoms. The angular distribution of the sputtered atoms for the oblique ion incidence is more asymmetric for the lower ion energies, while for the higher ion energies, the atoms are sputtered more symmetrically. The symmetry also depends on the group of the periodic table and the atomic mass of the target material. The elements in group 11 show the most symmetric distribution, while the elements in group 4 experience the most asymmetric distribution. Furthermore, in an individual group, the distribution becomes more symmetric with heavier target elements. We also examined in detail the influence of the surface binding energy, atomic mass, and ion energy on the total sputtering yield. These parameters were analyzed with regard to the simplified analytical formula for the total sputtering yield, which was derived by Sigmund. This formula was modified by introducing a power fitting parameter, which accounts for the non-linear sputtering yield dependence on the ion energy. The equation provided good estimates for the total sputtering yield of the transition metals that were sputtered by argon ions with energies up to 1200 eV.

Suppression of pesting failure in MoSi2 film by doping of Si

MoSi2 usually suffers pesting failure at 400– 700 °C due to severe oxidation of Mo, which has been a great hindrance for industrial applications. To address this issue, this work grew MoSi2(Si) thin films via magnetron co-sputtering of a Si single element target and a MoSi2 compound target on Si wafer substrates at room temperature, followed by annealing at 950 °C in an argon atmosphere. The as-annealed thin films were heated in a muffle furnace at 700 °C in air to experience different duration of oxidation. After that, the oxidation resistance was evaluated by examining the thickness, morphology, structure and composition of the as-heated thin films using field emission scanning electron microscopy and X-ray diffraction, respectively. In comparison with the MoSi2 without doping of Si, the MoSi2(Si) film is denser and exhibits a C11b crystalline structure with a smaller crystal size of 30 nm. The oxidation of Mo is effectively inhibited. There is no big bulge on the film surface after 1 h oxidation. But the oxidation of Si is severe, resulting in the continuous growth of grey SiO2 layer which help preventing the further oxidation of Mo. SiO2 islands are observed after oxidation for 9 h. The early pesting sites gradually become healed by the grown SiO2 layer during oxidation for 60 h. The mechanism for suppressing the pesting failure of MoSi2 by Si doping is discussed in details. A model is developed to explain the process.

The flip-over effect in pulsed laser deposition: Is it relevant at high background gas pressures?

In pulsed laser deposition the use of a rectangular or elliptical beam spot with a non 1:1 aspect ratio leads to the so called flip-over effect. Here, the longest dimension of the laser spot results in the shortest direction of plasma plume expansion. This effect has been mainly reported for vacuum depositions of single element targets and is particularly noticeable when the aspect ratio of the beam spot is large.We investigate the flip-over effect in vacuum and at three relevant background-gas pressures for pulsed laser deposition using a La0.4Ca0.6MnO3 target by measuring the thickness dependence of the deposited material as a function of angle. The film thicknesses and compositions are determined by Rutherford backscattering and argon is used to reduce the influence of additional chemical reactions in the plasma. The results show the prevalence of the flip-over effect for all pressures except for the highest, i.e. 1×10−1mbar, where the film thickness is constant for all angles. The composition profiles show noticeable compositional variations of up to 30% with respect to the target material depending on the background gas pressure, the angular location, and the laser spot dimensions.

Strain Effects in Heterogeneous Oxide Electrolyte Films

A number of opportunities exist to use thin film deposition methods to nanoengineer materials so that we can understand and improve their ion transport behavior and other electrochemical properties. Here, we describe experiments on sputter-deposited ceramic films with controlled, heterogeneous chemical composition. Films are created using a technique developed in our lab where pure, single-element targets are reactively co-sputtered to create ceria-zirconia films where both the host and dopant atom concentrations can be controlled at the nanometer scale through the film thickness. The ionic conductivity of all samples was determined using impedance spectroscopy in the temperature range 573 K to 1073 K and over a range of oxygen partial pressures.Two sets of results using this system will be presented. First, we will discuss films made to have heterogeneous dopant content. By placing the dopants in 2-D atomic planes, defects are trapped in engineered space charge zones surrounding the interface, and vacancy-dopant associations can be studied. Specifically, by comparing samples using heterogeneous La, Gd, or Y dopants, the role of strain in the mobility and concentration of defects in the space charge region is examined, with larger dopant ion correlated to increased space charge conductivity. A second system to be presented will involve modulation of the Ce/Zr ratio through the thickness. Since the lattice parameter is a linear function of Ce/Zr ratio, these samples can be used to smoothly and systematically control lattice strain. Strain was determined by x-ray diffraction and microscopy, including selected area electron diffraction. Clear differences in interfacial structure are found as the lattice parameter differential between the layers is adjusted. The strained multilayers indicate both a strain-based change in vacancy mobility and a general reduction in conductivity as the interfacial density increases.

Effects of Ta on the Microstructure and Magnetic Properties of FePt Thin Films

ABSTRACTWe have studied the effect of Ta on the structure, magnetic properties and the ordering temperature of FePt(Ta) thin films. The samples are prepared by the dc and rf magnetron cosputtering method with 3 single element targets. After a deposition, the samples are annealed in a vacuum at various temperatures. The XRD patterns show strong (111) peaks at all annealing temperatures, but the change in the d-spacings reveals a disorder-order transformation. The more Ta is added to the FePt, the larger the coercivity becomes. The coercivity of the FePtTa40W film annealed at 700°C reaches about two times as large as the value of the pure FePt film. The delta m curves imply that Ta atoms diffuse into the grain boundary to reduce inter-granular exchange coupling, which leads the enhancement of coercivity

Lanthanum aluminate by atomic layer deposition and molecular beam epitaxy

A comparison of physical and electrical characteristics of lanthanum aluminate (LAO) dielectrics formed by atomic layer deposition (ALD) and molecular beam epitaxy (MBE) is investigated in this study. Physical characteristics of LAO deposited with these two deposition methods are compared using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). Capacitors with TaN and TaSiN gate electrodes were fabricated to assess electrical properties of these LAO films. ALD LAO was deposited using La[N(SiMe3)2]3,Al(CH3)3 and water at 225–275 °C. ALD LAO is stable against Pt and TiN∕W metal gates up to 800 °C. After annealing at 900 °C, interactions between metal gates and dielectrics are observed resulting in nonfunctional devices. MBE LAO film was deposited at room temperature or 200–400 °C in two ways: Using single element targets (La, Al) or a compound target. The LAO∕TaN stack deposited with single element targets showed significant Si up diffusion from the substrate to the dielectric and the metal gate electrode. In addition, nitrogen diffusion from the metal gate into the dielectric was detected. The LAO∕TaN stack deposited with a compound target showed improved thermal stability. No metal out-diffusion and only very slight Si out diffusion was detected after a 900 °C anneal. LAO capacitors show well-behaved capacitance-voltage and leakage current density-voltage characteristics. These results indicate that the method by which lanthanum aluminate films are deposited strongly influenced their thermal stability. Of all the films examined, the most stable films are deposited by MBE using a compound target.

Simulation of the interaction of galactic cosmic ray protons with meteoroids: On the production of 3H and light noble gas isotopes in isotropically irradiated thick gabbro and iron targets

Abstract— Thick spherical targets, one made of gabbro (R = 25 cm) and one made of iron (R = 10 cm), were irradiated isotropically with 1.6 GeV protons at Laboratoire National Saturne (LNS)/Saclay to simulate the interactions of galactic cosmic ray protons with meteoroids in space. At various depths, both artificial meteoroids contained a large number of high‐purity, single‐element target foils and chemical compounds of up to 28 target elements. In these individual target foils, the elemental production rates of radionuclides and noble gas isotopes were measured. Here, we report the results for the light noble gas isotopes 3,4He, 20,21,22Ne, and 36,38,39Ar for the most cosmochemically relevant target elements as well as for some meteoritic material from Jilin, Farmington, and Cape York. From 3He analyses done several years apart, 3H diffusive losses during sample storage have been obtained, and direct as well as cumulative 3He production rates for O, Mg, Al, Si, Fe, Ni, and the meteoritic material are given. Losses by diffusion of tritium from metallic Mg and Fe are found to occur on time scales of months, while metallic Al, Si, and stone meteorites are much more retentive. The production rate ratios P(3H)/P(3He)d obtained in the simulation experiments are 0.73, 1.28, and 1.16 for O, Al, and Si, respectively. These rates are based on our best knowledge about the 3H and 3He production rates and should, therefore, replace data published earlier (Leya et al. 2000a). The earlier calculations for 4He, 20,21,22Ne, and 36,38,39Ar remain valid.The new modeled correlation 3Hecum/21Ne versus 22Ne/21Ne for chondrites exposed to cosmic rays with an energy spectrum characterized by a modulation parameter of φ = 650 MeV is in fair agreement with the empirical relationship (“Berne plot”). However, for small meteorites and little shielding in larger ones, there are systematic differences that most likely are due to an underestimation of the spallogenic 22Ne/21Ne ratio by ˜2%.

Homogenized penetration calculations

A model was developed which describes the penetration of a target composed of multiple discrete elements in terms of the penetration of an equivalent single-element target of identical thickness. To achieve this aim, the effective density and target resistance terms for the equivalent target have been homogenized from the densities and target resistances of the individual discrete elements composing the original target. Though the current model may be employed to treat a target's internal air gaps in the homogenization process, the current model does nothing special to address target considerations, such as obliquity, confinement, length-to-diameter (L/D) effects, etc. Rather, the model was intentionally restricted to flat-plate-type target elements being impacted at normal incidence, to focus upon the homogenization technique itself. To avoid the need to transform the shape or velocities of the bodies in question, only techniques which strictly preserved length and time dimensions were considered. Several homogenization schemes were examined and compared to the corresponding multi-element penetration calculation. It was determined that a straightforward volume averaging of target properties is usually not sufficient to effectively simulate a multi-element target. Other techniques presented here seem to do a better job at predicting residual penetrator length and velocity, respectively.

Measurements of extreme UV yields from Nd-YAG plasmas using a multilayer monochromator

A multilayer monochromator is used to measure the radiative emission from laser produced plasmas of single element targets in the region of 125 eV (99 Å). The characteristics and performance of the instrument are described. A study is then presented of the relative yield variations as the target atomic number is changed. An interpretation of the observed trend is proposed based on high resolution spectra of the same target element in the same spectral window.

Collisional Effects of Background Gases on Pulsed Laser Deposition Plasma Beams

AbstractThe penetration of energetic pulsed ablation plumes through ambient gases is experimentally characterized to investigate a general phenomenon believed to be important to film growth by pulsed laser deposition (PLD). Under typical PLD conditions involving background gases, the ion flux in the ablation plume is observed to split into distinct fast and slow components over a limited range of distances1,2 the fast component is transmitted with near-initial velocities and high kinetic energies, potentially damaging to growing films at these distances. Formation of the second, significantly-slowed component correlates with the bright contact front3 formation observed1,4 in fast ICCD imaging studies. This general effect is explored in detail for the case of yttrium ablation into argon, a single-element target into an inert gas.5 Time-resolved optical absorption spectroscopy and optical emission spectroscopy are employed to simultaneously view the populations of both excited and ground states of Y and Y+ for comparison with quantitative intensified-CCD photography of the visible plume luminescence and ion flux measurements made with fast ion probes during this phenomenon. these measurements confirm that, in addition to the bright significantly-slowed front which has been described by shock or drag propagation models1, a fast-component of target material is transmitted to extended distances for some ambient pressures with near-initial velocities.

Modeling of multicomponent reactive sputtering

Computer process modeling has become an important tool in the development of new thin-film processes. Previously, we presented a model that successfully describes the complex behavior of the reactive sputtering of a single-element target. The model enables one to predict, e.g., the hysteresis effect and the composition of the deposited film. There exists, however, a demand for developing reliable reactive-sputtering processes for more complicated materials. This calls for an extended reactive-sputtering model including more than one target element. In this article, we will for the first time present an extension of our previous model now taking the effect of multicomponent targets into consideration. The transition from metallic- to compound-sputtering mode normally occurs at different levels for different single-element targets. The new extended reactive-sputtering model predicts the transition from metallic to compound mode during multicomponent reactive sputtering of thin films. The results indicate that under normal operating conditions, only one transition region exists irrespective of the number of target elements involved in the process. This is experimentally verified for the process of reactive cosputtering of Al+Ti in an Ar/O2 atmosphere. We will also point out the complex composition behavior of the reactive-cosputtering process as compared with reactive sputtering from an alloy target.

IMPLNT — A fortran program to calculate the distribution of implanted ions which includes the effects due to sputtering

The computer program IMPLNT has been written to study what happens as an ion beam is incident on a target. The target is divided into layers, and as each layer is sputtered away, the fraction of beam atoms to target atoms in the surface layer, as well as the distribution off the beam atoms within the target are calculated. At present the program considers the beam ion incident onto a single element target. It takes account of the dilation of the target as beam atoms are added to it, and also the change in range with the increase of beam atoms. A Gaussian distribution is used to distribute the beam atoms within the target. Some samples of the curves plotted by the program are given. Comparison with experiment has indicated that, besides sputtering, diffusion must also be considered.

Elastic and inelastic surface effects on ion penetration and the resulting sputtering and backscattering

The computer code ITMC (Ion Transport in Materials and Compounds) has been developed to study in detail the transport of charged particles in solid materials and surface related phenomena such as sputtered atoms and backscattered ions. The code is based on Monte Carlo methods to follow the path and the damage produced by the charged particles in three dimensions as they slow down in target materials. Single-element targets as well as alloys with possible different surface and bulk compositions or with layered structures of different materials can be used. Various models developed to calculate the inelastic energy losses in collisions with target electrons can be used in the code. Most known interatomic potentials can also be used to calculate the elastic energy losses. The major advantages of the code are its ability and flexibility to use and compare various models of elastic and inelastic energy losses in any target with different compounds and different surface and bulk composition.

Choosing a therapy electron accelerator target

Angular distributions of photon depth dose produced by 25-MeV electrons incident on several fully stopping single-element targets (C, Al, Cu, Mo, Ta, Pb) and two composite layered targets (Ni-Al, W-Al) were studied. Depth-dose curves measured using TLD-700 (thermoluminescent dosimeter) chips embedded in lucite phantoms. Several useful therapy electron accelerator design curves were determined, including relative flattener thickness as a function of target atomic number, "effective" bremsstrahlung endpoint energy or beam "hardness" as a function of target atomic number and photon emission angle, and estimates of shielding thickness as a function of angle required to reduce the radiation outside the treatment cone to required levels.

X-Ray-Emission Microanalysis of Rock-Forming Minerals I. Experimental Techniques

In order to provide a basis for calibration of X-ray-emission analyses, existing theories and experimental measurements on the generation, absorption, and fluorescence of X-rays produced by electron bombardment of mixed targets are reviewed and compared with new measurements for a variety of targets, principally common silicates. Theoretically, the efficiency of X-ray generation should depend strongly on the mean atomic number of a mixed target, and its variation is commonly described by a so-called atomic-number factor. Using hard radiation for which the absorption is trivial, measurements have shown that the Philibert factor (1 + h) varies too little with mean atomic number. A new empirical factor, fits the data to within 2 per cent, except for close to (is incident electron accelerating voltage in kilovolts, is ionization voltage for K-electrons, {\langle}Z{\rangle} is mean atomic number of target weighted according to mass concentration, {\langle}Z/A{\rangle} is a similar average for ratio of atomic number to atomic weight, R is Green's backscatter coefficient to express proportion of potential ionization energy retained in target). For soft radiation, empirical absorption curves have been derived for simple and complex oxides on the assumption that the above efficiency-of-generation factor is valid. These curves differ markedly from those suggested by measurements on single-element targets, and it is recommended that the new curves be used for analyses in which the same experimental conditions are used. It is concluded that analyses of major elements in common minerals can be carried out to a relative accuracy of 1-5 per cent by suitable choice of standards and experimental conditions; such conditions are described.