High-pressure PLD

In this section advanced developments of the PLD technique are shortly described, e.g., the combinatorial approach and laser MBE. Because of the increasing research interest in ZnO-based nanostructures, the established PLD (at background gas pressure 10-4—3 mbar) was extended to much higher pressures of 50-200 mbar to grow arrays of free-standing ZnO nanowires. This unique high-pressure PLD process allows the growth of ZnO-based nanostructures with controlled shape and diameter and excellent optical properties. 

Fig. 7.32. Schematic illustration of the high-pressure PLD chamber for ZnO-based nano-heterostructures consisting of a T-shaped quartz tube with 30 mm outer diameter. Reprinted with permission from [140]...

First successful ZnO device demonstrations as for example stable homo-and heteroepitaxial pn-junctions and LED structures, thin film scintillators, and quantum well structures with optical confinement, and oxide-based Bragg reflectors, and high-quality Schottky contacts are based on PLD grown thin films. Several techniques as for example the PLD in UHV conditions (laser MBE), and gradient and combinatorial PLD, and high-pressure PLD for nano-heterostructures show the innovative potential of the advanced growth technique PLD. 

The hydrodynamic model is based on a sufficiently high collision probability under thermodynamic equilibrium. This condition is fulfilled only at p > 1 mbar, i.e., at high pressures above the typical PLD film deposition conditions, or at the beginning of plasma expansion, at high plasma density (small target to substrate distance). 

Figure 1 Changes of PLD activity during oil processing SI - S7 samples collected within 24 h in the intervals of four hours. I - seeds entering the process (15-25 °C), II -seeds after steaming (temperature increases by 10 - 15 °C), III - seeds are grinded -flakes (35 °C), IV - flakes after conditioning (85 - 90 °C), V - press cake (high pressure within hundreds of magnitude of atp.) VI - crush after extraction of the press cake by isohexane (110 - 130 C) VII - step VI. treated with lecithin slurry.

Fig. 7.25. CL intensity, Hall mobility, and carrier concentration at 300K of PLD ZnO thin films on a-plane sapphire show maxima around 1 mbar background gas pressure of O2, N2O, and N2 during growth at 100 mm target substrate distance, indicating the growth condition for ZnO thin film scintillators [89]. The average surface roughness is considerably increased at the high growth pressure of 1 mbar...

PLD in UHV (laser-MBE) MBE-like background pressure and in situ RHEED to ensure clean and controlled deposition of high-quality nucleation layers and films. For particular systems as SrTiC>3 and BaTiC>3, atomically smooth surface and interface were obtained [128,132]... 

The PLD activity was measured during the industrial oil processing at 7 stages of the process Figure 1). The serie of samples was collected within 24 hours in four hours intervals.The enzyme remains active up to fifth step of the process despite of the high temperature (approx. 100°C) and pressure treatment of the material. 

Matsubara et al. [126] used oxygen radical-assisted PLD to grow highly transparent and low-resistivity Al-doped ZnO films at room temperature. A KrF excimer laser (X = 248 nm, 30 ns pulse width, 10 Hz repetition rate) was used for ablation. The oxygen partial pressure during deposition was 0.7-1.4 x 10 Torr, and the applied RF power was 150W. The distance between the target and the substrate was approximately 6 cm. The minimum resistivity of the obtained transparent films was... 

The (100) orientation has been found to produce large dielectric constant and high tunability [44,56]. BST films have been successfully fabricated on Pt coated silicon substrates by sputtering [56], chemical vapor deposition (CVD) [57], and pulsed laser deposition (PLD) [58]. Compared to other deposition methods, the sputtering process offers some special characteristics, for example, controlling the Ar/02 ratio and the total (Ar + O2) pressure during the deposition could attain the (100) preferred orientation [56] and adjust the... 

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