Navy

Surface adhesion improvement via pulsed laser nanostructuring

Better adhesion characteristics by controlled formation of surface structures at the nano or micrometer scale

Photonics Materials

The system for modifying the surface chemistry of a material 102, includes a pulsed laser 104 emitting a pulse 106 and an enclosure 108 that includes an aperture 110 and a gaseous mixture 112. The energy irradiance of the laser pulse is sufficient to convert the surface portion 114 to a plasma state. While the surface portion is in a plasma state, it interacts with the gaseous mixture. Upon turning off the laser, altered surface chemistry remains.

Patterning the surface of a material can significantly improve its mechanical, chemical, or electro-optical qualities.

Conventional patterning techniques suffer from one or more of the following deficiencies: removal of desirable material from a surface, time/labor intensive, requiring costly and hazardous chemicals, difficult to control and possible damage to the treated surface. Additionally, conventional techniques, such as mechanical abrasion, acid etching, plasma etching, and chemical bonding, are somewhat limited in the precision, scale, and accuracy that they can be performed.

As an alternative to commonly used patterning techniques, Navy scientists have developed a patterning process with precision control and which does not require hazardous chemicals. The method is ideally suited to imparting a pattern for adhesion purposes.

The method relies on laser alteration of the substrate material by high energy laser pulses. The laser pulse is directed within a gaseous closed environment onto the surface to be patterned. The energy irradiance of the laser pulse converts the surface portion to a plasma state. While the surface portion is in a plasma state, it interacts with the gas portion. After the laser pulse no longer irradiates the surface the interaction results in altered surface chemistry.

Liquids or solids placed on the substrate may take the place of gas in the enclosed atmosphere and in one example, a liquid hydrocarbon is placed on the surface of titanium, tantalum, hafnium, zirconium, silicon, aluminum, etc. As such, after the laser pulse no longer irradiates the surface the altered surface chemistry may be one or more metal carbides, for example, TiC, TaC, HfC, ZrC, SiC or the like.

Patterning in this manner increases the surface area and the adhesion and mechanical interlocking characteristics of the surface. Tests show that the surface adhesion increased by approximately 29% over average unprimed samples, by approximately 19% over the best performing unprimed samples, and by approximately 11% over primed samples. Primed samples are that have been treated using a convention technique such as mechanically abraded, plasma etched, acid etched, or treated with a chemical bonding agent.

Optimization of the process to accommodate for different surfaces and reactants (gasses, liquids, solids) is done by changing the parameters of the laser such as pulse duration, wavelength, the angle of incidence, spot size, and frequency of pulses.

Businesses and entrepreneurs interested in developing this exciting technology for commercial applications should contact TechLink for more information.

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