Magnesium Target Research Articles

A time-resolved Langmuir double-probe method for the investigation of pulsed magnetron discharges

Langmuir probes are important means for the characterization of plasma discharges. For measurements in plasmas used for the deposition of thin films, the Langmuir double probe is especially suited. With the increasing popularity of pulsed deposition discharges, there is also an increasing need for time-resolved characterization methods. For Langmuir probes, several single-probe approaches to time-resolved measurements are reported but very few for the double probe. We present a time-resolved Langmuir double-probe technique, which is applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The investigations show that a proper treatment of the current measurement is necessary to obtain reliable results. In doing so, a characteristic time dependence of the charge-carrier density during the “pulse on” time containing maximum values of almost 2∙1011cm−3 was found. This characteristic time dependence varies with the pulse frequency and the duty cycle. A similar time dependence of the electron temperature is only observed when the probe is placed near the magnesium target.

Amorphous magnesium nitride films produced by reactive pulsed laser deposition

Amorphous magnesium nitride films were prepared on silicon substrates by reactive laser ablation using a magnesium target in a molecular nitrogen environment. These films were studied in situ using Auger, electron energy loss and X-ray photoelectron spectroscopies. The nitrogen content, x=[N]/[Mg], changes between 0 and 0.73 for a corresponding variation in nitrogen pressure of 4×10−10 Torr to 60 mTorr. By this method it is possible to achieve sub-, over- and stoichiometric films at different nitrogen pressures. The results show that the amorphous matrix keeps its metallic character for x⩽0.45; x=0.4 is a critical composition at which the material starts developing ionic characteristics; at x=0.66 the solid is totally ionic.

Time Resolved Langmuir Probe Characterisation of Reactive Pulse Magnetron Sputtering of MgO Thin Films

A time resolved Langmuir double probe technique is presented, which is applied to a pulsed magnetron discharge at several hundred kilohertz used for MgO deposition. The probe was positioned on the symmetry axis of the circular magnetron. The time resolved measurement was done by fixing the probe voltage and recording the probe current as a function of time. This was repeated for different voltages. Then, the matrix of the IU(t) curves was transposed with a computer to yield the usual I(U) characteristic for each time step, from which the plasma density and electron temperature were determined. After proper correction of the measured IU(t) curves, consistent results are obtained. In particular, a characteristic time dependence of the charge carrier density during the 'pulse on' time including a sequence of maximum and minimum values was found. This characteristic temporal evolution of the charge carrier density depends on the pulse frequency and duty cycle. Similar structures in the electron temperature are only observed when the probe is placed near the magnesium target. SE/510

P‐66: High Deposition Rate Technique of Magnesium Oxide Thin Film in Oxide Mode for Plasma Display Panel Applications

AbstractA high rate deposition sputtering process of magnesium oxide thin film in oxide mode has been developed using a 20 kW unipolar pulsed power supply. The power supply was operated at a maximum constant voltage of 500 V and a constant current of 40 A. The pulse repetition rate and the duty were changed in the ranges of 10 ∼ 50 kHz and 10 ∼ 60 %, respectively. The deposition rate increased with increasing incident power to the target. Maximum incident power to the magnesium target was obtained by the control of frequency, duty and current. The deposition rate of a moving state was 9 nm m/min at the average power of 1.5 kW. This result shows higher deposition rate than any other previous work of reactive sputtering at the oxide mode. The thickness uniformities over the whole substrate area of 982 mm × 563 mm were observed at the processing pressure of 2.8 ∼ 9.5 mTorr. The thickness distribution was improved at lower pressure. This technique is proposed to apply high through‐put sputtering system for plasma display panel.

Generation of ArnH3+ cluster ions by laser vaporization and their black-body radiation induced dissociation

Arn+H3 ions are produced in a laser vaporization source, and their stability against black-body radiation is tested in an FT-ICR mass spectrometer. Using a magnesium target and hydrogen doped argon as carrier gas, Arn+H3 are formed with n = 1–3 in large quantities and traces of n = 4. Arn+H, n = 1–3 are also present. Both Ar3+H3 and Ar2+H3 are heated by room temperature black-body radiation and decay on a timescale of seconds. The observed rate constants are compared with recently calculated IR spectra. The results are in agreement with the presence of strong IR absorptions around 350 cm−1, which may serve as a fingerprint for the identification of H3+ in solid argon.

On the role of prepulses during solid target heating by picosecond laser pulses

X-ray emission spectra of the plasma created at the surface of magnesium, aluminum, copper, and zinc targets heated by 1-ps laser pulses with a peak power density of up to 1016 W/cm2 were measured. The effect of a picosecond prepulse on the spectra was studied for various power densities and intensity contrasts of the main laser pulse. It is established that the emission spectra of laser plasmas are weakly affected by a change from 105 to 107 in the main pulse contrast relative to the first prepulse. Variations in the parameters of emission from aluminum and magnesium plasmas were calculated using relative intensities and widths of the resonance lines of H-and He-like ions and their two-electron satellite peaks.

Formation mechanism of new corrosion resistance magnesium thin films by PVD method

Magnesium thin films were deposited on cold-rolled steel by physical vapor deposition sputtering technique. The crystal orientation and morphology of the deposited films were investigated by using XRD and scanning electron microscopy, respectively. The effect of crystal orientation and morphology of magnesium films on corrosion behaviors was estimated by measuring anodic polarization curves in deaerated 3% NaCl solution. With the increase of argon gas pressure, the morphology of the deposited magnesium films changed from columnar to granular structure and the diffraction peaks of the film became little sharp and broad. And all the sputtered magnesium films obviously showed good corrosion resistance compared with 99.99% magnesium target metal. Formation mechanism on the crystal orientation and morphology of magnesium films can be explained by applying the effects of adsorption and occlusion of argon gas.

Mixed metal films with switchable optical properties

Thin, Pd-capped metallic films containing magnesium and first-row transition metals (Mn, Fe, Co) switch reversibly from their initial reflecting state to visually transparent states when exposed to gaseous hydrogen or following cathodic polarization in an alkaline electrolyte. Reversion to the reflecting state is achieved by exposure to air or by anodic polarization. The films were prepared by cosputtering from one magnesium target and one manganese, iron, or cobalt target. Both the dynamic optical switching range and the speed of the transition depend on the magnesium-transition metal ratio. Infrared spectra of films in the transparent, hydrided (deuterided) states support the presence of the intermetallic hydride phases Mg3MnH7, Mg2FeH6, and Mg2CoH5.

Energy distributions of secondary ions sputtered from aluminium and magnesium by Ne +, Ar + and O 2+: a comprehensive study

The energy distributions of positive and negative secondary ion species produced by 5 keV Ne +, Ar + and O 2 + ion bombardment at 30° to polycrystalline aluminium and magnesium targets have been studied. The measurements were carried out in a small solid angle along the surface normal, without extracting ions into the mass–energy analyser. The most probable and average energies along with the widths of the distributions were tabulated; essential features of the spectra were interpreted in the terms of a linear collision cascade model with a knock-on contribution. Three energy sub-ranges with appreciable different energy power dependence E − s , which could approximate the experimental curves, were revealed for both Al + and Mg + atomic ions within a wide energy range E mp< E<1000 eV. Nearly all the energy spectra of negative secondary ions demonstrated complex structure, with two distinct peaks, caused by impurity species with different binding energies.

Quantitative modeling of reactive sputtering process for MgO thin film deposition

Reactive sputtering process of magnesium target in d.c. planar magnetron discharge using argon and oxygen gases as buffer and reactive gases, respectively, has been investigated. A drastic mode transition between metallic and oxide modes has been observed due to a large difference in the secondary electron emission coefficients of magnesium and magnesium oxide. To describe the experimental results quantitatively, a new reactive sputtering model has been developed. The model is fundamentally based on a simple reactive gas balance model proposed by Berg et al. in 1988, but includes the change in the secondary electron emission coefficient of target. The modified model can deal with the change of plasma properties through the change of ion to electron current ratio at the target, and can quantitatively describe experimental results such as oxygen flow rate dependence of deposition rate and discharge voltage, which were obtained at a constant discharge current.

Theoretical sputtering yields of Al and Mg targets in physical vapor deposition processes

Calculations of sputtering yields are performed for aluminum and magnesium target materials with the use of a homemade software based on the analytical expression of Garcia-Rosalès. The theoretical yield of magnesium is about twice the value related to aluminum in accordance with the experimental ratio of the Mg/Al deposition rates. We show that the deposits of the same materials must be subjected to densification followed by resputtering phenomena when a bias voltage is set to the substrates. These predictions are confirmed by atomic force microscopy observations, especially for magnesium deposits owing to their texture and the high sputtering yield of this material.

Depth of origin of sputtered atoms for elemental Al and Mg targets in physical vapor deposition processes

The TRIM.SP Monte Carlo type program is used to calculate the escape depths for sputtered aluminum and magnesium target materials in physical vapor deposition processes involving argon plasma. Escape distributions are established for all sputtered atoms, as well as for sputtered atoms at several energies, in the case of normal impinging Ar ions. Distributions are also performed for several incidence angles up to 80°, in connection with recoils in collision cascades at a given energy. Mean escape depth calculations show that sputtered Mg atoms originate deeper underneath the surface compared to Al atoms, in accordance with their total stopping powers and sputtering yields. But, as a whole, the majority of sputtered Al and Mg atoms would come from the first two top layers.

Angular distribution of X-ray line radiation from laser-irradiated planar targets

A study of angular distribution of X-ray line radiation emitted from a laser-produced plasma is presented. Plasma was produced by irradiating a planar magnesium target using single laser pulses of 6 J, 4.5 ns (FWHM) from an Nd:glass laser system. Angular distribution of X-ray emission in the spectral range of 7–10 Å was recorded using a single X-ray crystal spectrograph. X-ray emission intensity for different resonance lines is observed to decrease up to an angle of ∼45° with respect to target normal, followed by a significant increase at higher angles. The observed departure of angular distribution from a monotonically decreasing behavior is broadly in agreement with the calculations of the escape factor of the radiation at different angles from a thick disk-shaped plasma using a spectroscopic code RATION.

Numerical modelling of low-temperature laser-produced magnesium plasma

The two-dimensional laser-plasma-interaction hydrodynamic code POLLUX has been used to simulate the ablation of a magnesium target by a 30-ns, 248-nm KrF excimer laser at low laser fluences of ≤10 J cm2. This code, originally written for much higher laser intensities, has been recently extended to include a detailed description of the equation of state in order to treat changes of phase within the target material, and also includes a Thomas Fermi description of the electrons. The simulated temporal and spatial evolution of the plasma plume in the early phase of the expansion (≤100 ns) is compared with experimental interferometric measurements of electron density. The expansion dynamics are in good agreement, although the simulated electron number density is about 2.5 times higher than the experimental values.

Hot electron effects on the satellite spectrum of laser-produced plasmas

In laser-produced plasmas, the interaction of the intense laser light with plasma electrons can produce high-energy superthermal electrons with energies in the keV range. These hot electrons can influence the level populations which determine spectral line structure. In the present paper, the effect of hot electrons on the X-ray satellite spectrum of laser-produced plasmas is studied. Calculated spectra are compared with experimental observations. Magnesium targets irradiated by three different types of laser pulses are considered. These include, a high-intensity 600 fs Nd-glass laser, a 1 ns Nd-glass laser, and a 2 ns CO 2 laser. The Nd-glass laser experiments were conducted recently at the Los Alamos Trident Facility and the CO 2 data were recorded by MISDC. High-resolution spectra were measured near the He-like resonance line of magnesium. The calculations employ an electron energy distribution which includes a thermal and a hot electron component, as part of a detailed collisional-radiative model. Plasma parameters including electron temperature, density, and hot electron fraction are estimated by choosing best fits to the experimental measurements. The calculations show that hot electrons can cause several anomalous effects. The Li-like jkl, abcd , and qr satellites can show intensities which are generally attributed to electron densities in excess of 10 23 cm -3. In addition, the relative amplitude of the intercombination line can be unusually large even at high electron densities due to enhanced collisional excitation of the 1 s2p 3 P state by hot electrons.

Electron number density measurements in magnesium laser produced plumes

Interferometry has been used to investigate the spatio-temporal evolution of electron number density following 248 nm laser ablation of a magnesium target. Fringe shifts were measured as a function of laser power density for a circular spot obtained using a random phase plate. Line averaged electron number densities were obtained at delay times up to ∼100 ns after the laser pulse. Density profiles normal to the target surface were recorded for power densities on target in the range 125–300 MW cm −2.

Pion production in nuclear charge exchange reactions A(t, 3He)

Abstract The charge exchange reaction (t, 3 He) on carbon and magnesium targets is investigated in experiments using a streamer chamber. The experimental pion longitudinal momentum spectrum is compared with the calculated one for events with a single secondary pion. From this comparison it follows that the contribution from quasi-free Δ − excitation in the target nucleus in a single pion channel is only 60–70%. The momentum of the pions in the remaining fraction of events is significantly higher than that of the pions produced in delta de-excitation. The contribution from several possible processes is analyzed. The data indicate a significant role of coherent pion production via N(1440) or/and N(1520) in the target nucleus while part of the pion spectrum can be explained by projectile excitation.

α-particle induced high-energy γ-ray yields from light elements

Alpha-induced thick-target γ-ray yields from light elements have been measured in the energy range 5.6 MeV ≤ E a ≤ 10 MeV. The γ-ray yields above 2 MeV from thick targets of beryllium, boron nitride, sodium fluoride, magnesium, and aluminum were measured, and the results of this experiment were used to construct tables suitable for calculating the α-induced direct production γ-ray intensity distributions from materials. These results show a significant reduction compared with previous estimates of the distribution.

X-ray spectral investigations of a high irradiance picosecond laser produced plasma

A 1.5 picosecond laser pulse with an intensity of more than 10 18 W/cm 2 was used to heat solid state magnesium targets. The unique characteristics of this plasma source together with a high resolution recording system ( λ Δλ = 10 4 ) allowed us to study multicharged ions with L- and M-shell dielectronic satellite structures in the wavelength range of 9.2–9.5 Å. Ten spectral lines determined by 1 s2 p4 l–1 s 24 l and 1 s2 p3 l–1 s 23 l transitions in Mg X and of 43 spectral lines of Mg IX were identified and measured. Parameters of the plasma in the process of its evolution were deduced.

The Auger (autoionization) spectra excited by argon and neon ion bombardment of a magnesium surface

The Auger (autoionization) spectra produced by bombarding a magnesium target with argon and neon ions of energy in the range 200 eV-5 keV are reported. The observed spectra of both gases contained considerable fine structure broadly similar to that observed in spectra from aluminium and silicon targets. The Mg spectra contained structure not previously reported, which could be indexed as part of a series of transitions from an excited state in MgO to states at and above the ground state in Mg+. The variation of the heights of the main peaks was examined as a function of incident ion energy. The graph of peak height against incidence energy showed a sharp maximum for Ar while this was not the case for either Ne or Mg. The rare gas Auger peaks increased in energy with increasing incident ion energy and the shift could be explained in terms of a simple Doppler model appropriate to the strongly forward scattered experimental conditions used here. No systematic variation in the energies of the Mg peaks was observed.