*2.2.2.1. Cavities in Ta(99.9%)*

Porous tantalum is an alternative metal for the manufacture of total joint arthroplasty com‐ ponents that offer several unique properties since it has excellent biocompatibility and is safe to use in vivo [40]. Upon direct irradiation with several pulses impacting on the same area of a Ta(99.9%) sample, formation of air bubbles of sub-micrometric dimensions gives rise to a porous coating of tantalum and tantalum oxide of the surface. **Figure 8** shows cavities drilled on a Ta sample with 1, 500, and 1000 laser pulses of 200 mJ/cm2 .

**Figure 8.** SEM micrographies of cavities drilled on a Ta(99.9%) sample with (a) 1, (b) 500, and (c) 1000 laser pulses of 200 mJ/cm2 .

#### *2.2.2.2. Nanostructuring in Cu*

In the trepanning technique, a rotating movement is generated by applying sine wave voltages to the piezoelectric motors with coordinate phases associated to the XY axis of the positioning system. This circular nanometric movement produces a sand-down effect which decreases the drilled cavity walls' roughness. The misalignments of the laser beam focusing system as well as the beam's inhomogeneities are averaged and holes with controlled walls' shapes and roughness can be drilled. As a result, well-controlled circular holes with sub-micrometric

The SEM micrographies of **Figure 7** show cavities drilled on a sample of c-Si + Si2O(300) with

percussion method can be seen in **Figure 7a**. The grooves on the walls and the debris can be also observed. The debris tower several microns over the silicon surface. A cavity drilled by trepanning with 200 pulses is presented in **Figure 7b**. Marks left by single pulses can be also seen on the sides. In this case, the field of view of electronic microscope allows observing the cavity bottom. Micrography (**Figure 7c**) corresponds to a cavity drilled by trepanning with 2000 laser pulses, the bottom of which can no longer be seen due to its depth. The walls of the

**Figure 7.** SEM micrographies of (a) c-Si wafer drilled by percussion with 2400 pulses. The sample was inclined 45° to observe the cavity's walls were grooves of ~10 μm are seen. (b, c) Micrographies of cavities drilled by trepanning with 200 and 2000 pulses, respectively. The effect of increasing the laser pulse number for a fixed sample-lens distance and a

The micromachining experiments in metals were performed with the machining station of **Figure 1**. Nanostructuring on the surface of the devices machined on metallic substrates was observed by electronic microscopy [30]. In this section, the most relevant results obtained are

Porous tantalum is an alternative metal for the manufacture of total joint arthroplasty com‐ ponents that offer several unique properties since it has excellent biocompatibility and is safe to use in vivo [40]. Upon direct irradiation with several pulses impacting on the same area of

can be compared. A sine wave voltage of 10 V and 3 Hz was applied to the piezoelectric

cavities of **Figure 7b,c**, show the typical smoothness of the trepanning mode.

. A drilling performed with 2400 pulses with the

structures on the wall can be drilled.

442 Radiation Effects in Materials

laser fluence of 110 mJ/cm2

*2.2.2. Nanostructuring in metals*

*2.2.2.1. Cavities in Ta(99.9%)*

motors.

presented.

different number of laser pulses of 110 mJ/cm2

Micro-ionizer prototypes to be used in an ion mobility spectrometer [41] were machined on a printed circuit board (PCB). The thickness of the copper coating of these boards is about 300 μm. Direct irradiation of the Cu coating of the PCB was performed by the trepanning method with 200 mJ/cm2 . The SEM micrographies are shown in **Figure 9a**. It shows a sequence of contiguous cavities each drilled with 25 laser pulses each. **Figure 9b**,c shows the details of the cavities at different magnifications.

**Figure 9.** SEM micrographies (a) contiguous cavities machined on the copper coating of a PCB with 25 pulses each. (b, c) Micrographies at larger magnifications to show the porosity.

The appearance of a porous coating of copper and copper oxide is observed as the number of laser pulses impinging on the same sample area is increased. The lower density of porous copper makes it suitable to be used as a lighter material for electrodes and catalysis.

**Figure 10** shows the superficial modifications originated by laser irradiation of sub-micro‐ metric structures of copper oxide. **Figures 10a,b** are SEM micrographies of the surface before irradiation; **Figure 10c,d** after irradiation with one square laser shot.

**Figure 10.** SEM micrographies of a copper oxide surface: (a, b) before irradiation; (c, d) after irradiation with one square laser shot. Cu nanoparticles of lighter color than the rest of the surface due to their larger conductivity can be appreciated.
