Loading...
Please wait, while we are loading the content...
Similar Documents
Enhancement of thickness uniformity of thin films grown by pulsed laser deposition
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Fernandez, Felix E. |
| Copyright Year | 1995 |
| Description | A peculiarity of the pulsed laser deposition technique of thin-film growth which limits its applicability is the very rapid drop of resulting film thickness as a function of distance from the deposition axis. This is due to the narrow forward peaking of the emission plume characteristic of the laser ablation process. The plume is usually modeled by a cos(sup n) theta function with n greater, and in some cases, much higher, than 1. Based on this behavior, a method is presented to substantially enhance coverage uniformity in substrate zones of the order of the target-substrate distance h, and to within a specified thickness tolerance. Essentially, target irradiation is caused to form an annular emission source instead of the usual spot. By calculating the resulting thickness profiles, an optimum radius s is found for the annular source, corresponding to a given power in the emission characteristic and a given value of h. The radius of this annulus scales with h. Calculated numerical results for optimal s/h ratios corresponding to a wide range of values for n are provided for the case of +/- 1% tolerance in deviation from the thickness at deposition axis. Manners of producing annular illumination of the target by means of conic optics are presented for the case of a laser beam with radially symmetric profile. The region of uniform coverage at the substrate can be further augmented by extension of the method to multiple concentric annular sources. By using a conic optic of novel design, it is shown also how a single-laser beam can be focused onto a target in the required manner. Applicability of the method would be limited in practice by the available laser power. On the other hand, the effective emitting area can be large, which favors extremely high growth rates, and since growth can occur uniformly over the whole substrate for each laser pulse, single-shot depositions with substantial thicknesses are possible. In addition, the simultaneity of growth over the complete substrate is desirable when monitoring the growth in situ. |
| File Size | 728440 |
| Page Count | 9 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19950019661 |
| Archival Resource Key | ark:/13960/t0ht7jw14 |
| Language | English |
| Publisher Date | 1995-04-01 |
| Access Restriction | Open |
| Subject Keyword | Nonmetallic Materials Augmentation Thin Films Crystal Growth Laser Outputs Conics Radiation Distribution Radii Pulsed Laser Deposition Laser Beams Film Thickness Pulsed Lasers Plumes Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
