Publication

Ion implantation in Ni-Ti shape memory alloy thin films

Thomas La Grange
2005
Theses

Abstract

The present thesis focuses on the effect of 5 MeV Ni ion irradiation on the microstructure and the thermomechanical behavior in prestrained (ε∼4%) martensitic Ti-rich NiTi thin films. At this ion energy, damage is limited to a depth of approximately 2 µm (the ion projected range predicted the Transport and Range of Ions in Matter (TRIM) code). When applied to a pre-deformed 6µm thick film, this technique may be used to excite reversible out-of-plane bending which can perform useful work as an actuator in microdevices. Conceptually, the frustration of the martensitic transformation by ion beam damage creates a differential latent strain between the beam-damaged and undamaged layer upon reverse transformation. Furthermore, the beam-damaged layer acts as an intrinsic bias spring that allows a reversible bending motion during thermal cycling. Thus, the actuator and bias spring can be realized in a single thin film element, using a single and simple planar processing. Due to the potential complexity of the thermomechanical response of the bimorph, it is obvious that detailed information about the effects of high-energy heavy-ion irradiation on microstructure and transformation characteristics are needed if the performance of these ion-biased bimorphs is to be optimized. Thus, the present thesis work has been undertaken to develop a better understanding of the influence of ion irradiation parameters on thermally-induced cyclic deflection, with a strong emphasis on the development of the ion damaged microstructure. Cross-sectional transmission electron microscopy (TEM) investigations and X-ray diffraction (XRD) studies of the irradiated microstructure showed that both NiTi and Ti2Ni precipitates were readily amorphized with 5 MeV Ni ions at doses above 5×1013 ions/cm2, especially at lower irradiation temperatures, i.e.

Official source

Thomas La Grange
2005
Theses

Abstract

Official source

Related concepts (32)

Ion implantation

Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the physical, chemical, or electrical properties of the target. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as in materials science research. The ions can alter the elemental composition of the target (if the ions differ in composition from the target) if they stop and remain in the target.

Collision cascade

In condensed-matter physics, a collision cascade (also known as a displacement cascade or a displacement spike) is a set of nearby adjacent energetic (much higher than ordinary thermal energies) collisions of atoms induced by an energetic particle in a solid or liquid. If the maximum atom or ion energies in a collision cascade are higher than the threshold displacement energy of the material (tens of eVs or more), the collisions can permanently displace atoms from their lattice sites and produce defects.

Stopping power (particle radiation)

In nuclear and materials physics, stopping power is the retarding force acting on charged particles, typically alpha and beta particles, due to interaction with matter, resulting in loss of particle kinetic energy. Its application is important in areas such as radiation protection, ion implantation and nuclear medicine. Both charged and uncharged particles lose energy while passing through matter. Positive ions are considered in most cases below. The stopping power depends on the type and energy of the radiation and on the properties of the material it passes.

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