Modelling of laser ablation and reactive oxygen plasmas for pulsed laser deposition of zinc oxide

Self Cite

The spatial and temporal evolution of the absolute electron densities and temperatures in plasmas formed by nanosecond pulsed laser ablation of silicon in vacuum at two wavelengths (1064 and 532 nm), at similar irradiances, have been explored by complementary simulation (using combined hydrodynamic and adiabatic models) and experiment. Modelling the laser-target and laser-plume interactions with the POLLUX code reveals the evolving composition and dynamics of the laser induced plasma (LIP) during the incident laser pulse: 532 nm irradiation causes more ablation, but the LIP formed by 1064 nm excitation has a higher average charge state and expands faster. The experimental data, from the analysis of Stark broadened line shapes of SiIII and SiIV cations in time-gated, position- and wavelength-resolved images of the plume emission, allow characterisation of the plume dynamics at later times. These dynamics are compared with predictions from two forms of adiabatic expansion model. Both take as input parameters the plume properties returned by the POLLUX simulations for the end of the laser pulse, but differ according to whether the initial plasma is assumed isothermal or isentropic. The study illustrates the important λ-dependences of the target absorption coefficient (in establishing the ablated material density) and of electron–ion inverse bremsstrahlung absorption (in coupling laser radiation into the emergent plasma); the extents to which these interactions, the relative ablation yields, and the plume expansion dynamics depend on λ; and the importance of identifying appropriate initial conditions for adiabatic expansion modelling of LIP in vacuum.

Section: Experimental and Modellingmentioning

confidence: 99%

Section: Experimental and Modellingmentioning

confidence: 99%

Wavelength-dependent variations of the electron characteristics in laser-induced plasmas: A combined hydrodynamic and adiabatic expansion modelling and time-gated, optical emission imaging study

Liu

Ashfold

Meehan

et al. 2019

Self Cite

“…[1][2][3][4][5] To realize a process where these modifications are reproducible and uniform over a large area, plasma control techniques capable of tailoring the properties of the plasma, including the mean electron energy and reactive species densities, are crucial. [6][7][8][9][10][11] Of particular importance in this context are the radial distributions of both quantities. Furthermore, the wafer material itself and the condition of the other wall materials in the reactor affect the absolute number densities of reactive species due to wall loss processes, the probability for which is dependent on many factors.…”

mentioning

confidence: 99%

Investigation of the radially resolved oxygen dissociation degree and local mean electron energy in oxygen plasmas in contact with different surface materials

Tsutsumi

Greb

Gibson

et al. 2017

Energy Resolved Actinometry is applied to simultaneously measure the radially resolved oxygen dissociation degree and local mean electron energy in a low-pressure capacitively coupled radio-frequency oxygen plasma with an argon tracer gas admixture. For this purpose, the excitation dynamics of three excited states, namely, Ar(2p1), O(3p3P), and O(3p5P), were determined from their optical emission at 750.46 nm, 777.4 nm, and 844.6 nm using Phase Resolved Optical Emission Spectroscopy (PROES). Both copper and silicon dioxide surfaces are studied with respect to their influence on the oxygen dissociation degree, local mean electron energy, and the radial distributions of both quantities and the variation of the two quantities with discharge pressure and driving voltage are detailed. The differences in the measured dissociation degree between different materials are related back to atomic oxygen surface recombination probabilities.

“…The leading edge electron densities in laser ablated plasma can be as high as 10 20 electrons/cm 3 , which can be greater than the density very close to the target during ablation. 24 After the leading edge excitation occurs in the background gas at around 400 ns, the main plasma plume flux causes ionization just before 1000 ns. The intensity of ionized molecular nitrogen increases as the gas pressure within the deposition chamber increases and reaches a maximum at values greater than 30 mTorr and at a time of 1600 ns.…”

Section: Resultsmentioning

confidence: 99%

Temporally and spatially resolved plasma spectroscopy in pulsed laser deposition of ultra-thin boron nitride films

Glavin

Muratore

Jespersen

et al. 2015

Physical vapor deposition (PVD) has recently been investigated as a viable, alternative growth technique for two-dimensional materials with multiple benefits over other vapor deposition synthesis methods. The high kinetic energies and chemical reactivities of the condensing species formed from PVD processes can facilitate growth over large areas and at reduced substrate temperatures. In this study, chemistry, kinetic energies, time of flight data, and spatial distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas were investigated. Time resolved spectroscopy and wavelength specific imaging were used to identify and track atomic neutral and ionized species including B þ , B*, N þ , N*, and molecular species including N 2 *, N 2 þ , and BN. Formation and decay of these species formed both from ablation of the target and from interactions with the background gas were investigated and provided insights into fundamental growth mechanisms of continuous, amorphous boron nitride thin films. The correlation of the plasma diagnostic results with film chemical composition and thickness uniformity studies helped to identify that a predominant mechanism for BN film formation is condensation surface recombination of boron ions and neutral atomic nitrogen species. These species arrive nearly simultaneously to the substrate location, and BN formation occurs microseconds before arrival of majority of N þ ions generated by plume collisions with background molecular nitrogen. The energetic nature and extended dwelling time of incident N þ ions at the substrate location was found to negatively impact resulting BN film stoichiometry and thickness. Growth of stoichiometric films was optimized at enriched concentrations of ionized boron and neutral atomic nitrogen in plasma near the condensation surface, providing few nanometer thick films with 1:1 BN stoichiometry and good thicknesses uniformity over macroscopic areas. V C 2015 AIP Publishing LLC. [http://dx.