scholarly journals Effect of Ambient Gas Pressure on Pulsed Laser Ablation Plume Dynamics and Znte Film Growth

1995 ◽  
Vol 397 ◽  
Author(s):  
CM. Rouleau ◽  
D.H. Lowndes ◽  
M.A. Strauss ◽  
S. Cao ◽  
A.J. Pedraza ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
High Energy ◽  
Gas Pressure ◽  
Ex Situ ◽  
Extended Defect ◽  
Ion Probe ◽  
Ambient Gas ◽  
Probe Measurements

ABSTRACTEpitaxial thin films of nitrogen-doped p-ZnTe were grown on single-crystal, semi-insulating GaAs substrates via pulsed laser ablation of a stoichiometric ZnTe target. Both low pressure nitrogen ambients and high vacuum were used. Results of in situ reflection high energy electron diffraction (RHEED) and time-resolved ion probe measurements have been compared with ex situ Hall effect and transmission electron microscopy (TEM) measurements. A strong correlation was observed between the nature of the film's surface during growth (2-D vs. 3-D, assessed via RHEED) and the ambient gas pressures employed during deposition. The extended defect content (assessed via cross-sectional TEM) in the region >150 nm from the film/substrate interface was found to increase with the ambient gas pressure during deposition, which could not be explained by lattice mismatch alone. At sufficiently high pressures, misoriented, columnar grains developed which were not only consistent with the RHEED observations but also were correlated with a marked decrease in Hall mobility and a slight decrease in hole concentration. Ion probe measurements, which monitored the attenuation and slowing of the ion current arriving at the substrate surface, indicated that for increasing nitrogen pressure the fast (vacuum) velocity-distribution splits into a distinct fast and two collisionally-slowed components or modes. Gas-controlled variations in these components mirrored trends in electrical properties and microstructural measurements.

Silicon and zinc telluride nanoparticles synthesized by low energy density pulsed laser ablation into ambient gases

1999 ◽  
Vol 14 (2) ◽  
pp. 359-370 ◽  
Author(s):  
Douglas H. Lowndes ◽  
Christopher M. Rouleau ◽  
T.G. Thundat ◽  
G. Duscher ◽  
E.A. Kenik ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Energy Density ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Gas Pressure ◽  
Low Energy ◽  
Crystalline Core ◽  
Ambient Gases ◽  
The Mean ◽  
Ambient Gas

The size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure, P, and target-substrate separation, Dts. For both Si and ZnTe, the largest nanoparticles were found closest to the ablation target, and the mean nanoparticle size decreased with increasing Dts. For Si ablation into He, the mean nanoparticle diameter did not increase monotonically with gas pressure but reached a maximum near P = 6 Torr. High resolution Z-contrast transmission electron microscopy and energy loss spectroscopy revealed that ZnTe nanoparticles consist of a crystalline core surrounded by an amorphous ZnO shell; growth defects and surface steps are clearly visible in the crystalline core. A pronounced narrowing of the ZnTe nanocrystal size distribution with increasing Dts also was found. The results demonstrate that the size of laser-ablated nanoparticles can be controlled by varying the molecular weight and pressure of an ambient gas and that nanometer-scale particles can be synthesized. Larger aggregates of both ZnTe and Si having a “flakelike” or “weblike” structure were formed at the higher ambient gas pressures; for ZnTe these appear to be open agglomerates of much smaller (∼10 nm) particles.

scholarly journals Pulsed Laser Ablation Growth and Doping of Epitaxial Compound Semiconductor Films

1995 ◽  
Vol 397 ◽  
Author(s):  
Douglas H. Lowndes ◽  
Christopher M. Rouleau ◽  
D. B. Geohegan ◽  
A. A. Puretzky ◽  
M. A. Strauss ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Compound Semiconductors ◽  
Compound Semiconductor ◽  
Ex Situ ◽  
Semiconductor Films ◽  
Time Resolved ◽  
Control Film ◽  
Ion Probe

ABSTRACTPulsed laser ablation (PLA) has several characteristics that are potentially attractive for the growth and doping of chemically complex compound semiconductors including (1) stoichiometric (congruent) transfer of composition from target to film, (2) the use of reactive gases to control film composition and/or doping via energetic-beam-induced reactions, and (3) low-temperature nonequilibrium phase formation in the laser-generated plasma “plume.” However, the electrical properties of compound semiconductors are far more sensitive to low concentrations of defects than are the oxide metals/ceramics for which PLA has been so successful. Only recently have doped epitaxial compound semiconductor films been grown by PLA. Fundamental studies are being carried out to relate film electrical and microstructural properties to the energy distribution of ablated species, to the temporal evolution of the ablation pulse in ambient gases, and to beam-assisted surface and/or gas-phase reactions. In this paper we describe results of ex situ Hall effect, high-resolution x-ray diffraction, transmission electron microscopy, and Rutherford backscattering measurements that are being used in combination with in situ RHEED and time-resolved ion probe measurements to evaluate PLA for growth of doped epitaxial compound semiconductor films and heterostructures. Examples are presented and results analyzed for doped II–VI, I–III–VI, and column-Ill nitride materials grown recently in this and other laboratories.

scholarly journals Effect of ambient gas pressure on pulsed laser ablation plume dynamics and ZnTe film growth

1995 ◽  
Author(s):  
C.M. Rouleau ◽  
D.H. Lowndes ◽  
D.B. Geohegan ◽  
L.F. Allard ◽  
M.A. Strauss ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Film Growth ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Gas Pressure ◽  
Ablation Plume ◽  
Plume Dynamics ◽  
Ambient Gas ◽  
Znte Film

Effect of Non-equilibrium Pulsed Ejection of Si Species into Background Gas on the Formation of Si Nanocrystallite and Nanocrystal-film

2011 ◽  
Vol 1305 ◽  
Author(s):  
Ikurou Umezu ◽  
Shunto Okubo ◽  
Akira Sugimura
Keyword(s):  
Laser Ablation ◽  
Film Growth ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Hydrogen Gas ◽  
Gas Pressure ◽  
Spatial Confinement ◽  
The Individual ◽  
Background Gas ◽  
Non Equilibrium

ABSTRACTThe Si nanocrystal-films are prepared by pulsed laser ablation of Si target in a mixture of helium and hydrogen gas. The total gas pressure and hydrogen partial gas pressure were varied to control structure of nanocrystal-film. The surface of Si nanocrystallite was hydrogenated and degree of hydrogenation increased with increasing hydrogen partial gas pressure. The aggregate structure of nanocrystal-film depended on both the total gas pressure and the hydrogen partial gas pressure. The former and the latter alter spatial confinement of Si species during deposition and the surface hydrogenation of individual nanocrystal, respectively. Spatial confinement increases probability of collision between nanocrystals in the plume. While, surface hydrogenation prevents coalescence of nanocrystals. The individual or aggregated nanocrystals formed in the plume reach the substrate and the nanocrystal-film is deposited on the substrate. The non-equilibrium growth processes during pulsed laser ablation are essential for the formation of the surface structure and the subsequent nanocrystal-film growth. Our results indicate that the structure of nanocrystal-film depends on the probabilities of collision and coalescence between nanocrystals in the plume. These probabilities can be varied by controlling the total gas pressure and the hydrogen partial gas pressure.

Non-equilibrium Growth Processes of Porous TiO2 Nanocrystal-films during Pulsed Laser Ablation

2013 ◽  
Vol 1497 ◽  
Author(s):  
Ikurou Umezu ◽  
Nobuyasu Yagi ◽  
Akira Sugimura ◽  
Takehito Yoshida
Keyword(s):  
Laser Ablation ◽  
Pulsed Laser ◽  
Hierarchical Structures ◽  
Pulsed Laser Ablation ◽  
Rutile Phase ◽  
Gas Pressure ◽  
Target Distance ◽  
Structural Formation ◽  
Background Gas ◽  
Non Equilibrium

ABSTRACTWe performed pulsed laser ablation of titanium dioxide (TiO2) target in O2 background gas. Effects of background gas pressure and substrate target distance on the structure of deposited films are clarified. The hierarchical structures are observed when we change scale of observation. The film deposited on the substrate is composed of primary nanocrystal and secondary porous-aggregated-nanostructures. The primary nanocrystal changes from anatase to rutile phase with increasing background gas pressure or substrate target distance. The porosity of secondary aggregated structure increases with increasing background gas pressure or substrate target distance. The similarity between the effects of background gas and substrate target distance indicates that confinement of the plume between target and substrate is important for structural formation. The non-equilibrium aggregation processes of nanocrystals in the plume and on the substrate are essential for the hierarchical structure of the nanocrystal film.

Ion Probe Diagnostics of Laser Ablated Plumes for Thin Carbon Films Deposition

1998 ◽  
Vol 12 (25) ◽  
pp. 2619-2633 ◽  
Author(s):  
R. K. Dwivedi ◽  
S. P. Singh ◽  
R. K. Thareja
Keyword(s):  
Film Growth ◽  
Pulsed Laser ◽  
Target Surface ◽  
Carbon Films ◽  
Gas Pressure ◽  
Plasma Parameters ◽  
Ion Probe ◽  
Thin Carbon ◽  
Ambient Gas ◽  
Deposited Film

The propagation of the carbon plumes in argon atmosphere used for film growth by pulsed laser ablation deposition (PLAD) is studied using ion probe. Spatial and angle resolved analysis of plasma parameters as a function of argon gas pressure is presented. The electron temperature is strongly dependent on the angle with target surface normal as well as the distance from the target surface. The forward directed nature of the PLAD process is strongly influenced by the pressure of the ambient gas. The plasma parameters are used to explain the effect of ambient gas pressure on the characteristics of the deposited film.

In-situ and ex-situ investigations of pulsed laser ablation of Y target

2011 ◽  
Vol 520 (1) ◽  
pp. 117-120 ◽  
Author(s):  
A. Lorusso ◽  
F. Gontad ◽  
A. Perrone
Keyword(s):  
Laser Ablation ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Ex Situ
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