In-situ observation of non-hemispherical tip shape formation during laser-assisted atom probe tomography

Abstract

It is shown by SEM imaging of the tip and by observing the emission pattern of the evaporated atoms that laser assisted evaporation in an atom probe can lead to nonhemispherical tip shapes and time-dependent nonuniform emission. We have investigated this nonuniformity by observing the change in field of view when using laser wavelengths of 515 nm and 343 nm on silicon. The change is monitored in situ by 0.5 nm thick silicon oxide. We demonstrate that the field of view can easily be changed by more than 10 nm and that the apparent oxide layer thickness can deviate substantially from its correct value. The dependence of the tip shape deformations and the reconstruction artifacts on the laser wavelength are explained through simulations of the laser-tip interaction and nonhomogeneous heating effects.

Laser-induced asymmetric faceting and growth of a nano-protrusion on a tungsten tip

“…2(b). Note that some laser-induced surface modifications on tip apexes were observed in previous work, [21][22][23] but not the gradual growth of prominent features, which we observed in our experiments have been reported so far.…”

“…For instance, periodic nanostructures were formed on a surface through the excitation of surface plasmons following femtosecond laser ablation 20 and also asymmetric surface modification at an apex of a metal tip was formed by laser asymmetric heating. [21][22][23][24] In atom probe tomography experiments, atom migration followed by surface detachment due to bond-breaking and ionization by very high electric fields can be observed. [25][26][27] However, the formation of a stable surface nano-tip growing on the surface due to irradiation of laser has not been reported in these studies.…”

“…[25][26][27] However, the formation of a stable surface nano-tip growing on the surface due to irradiation of laser has not been reported in these studies. [20][21][22][23][24][25][26] On the other hand, applying strong electric fields on the metal surface by radio-frequency electromagnetic waves, strongly enhanced field emission currents often are measured from macroscopic surfaces, which implies a local electric field enhancement due to the formation of nanostructures. [28][29][30][31] A theoretical study suggests the formation of nano-protrusions, 32 but experimental efforts to identify the features responsible for enhanced field emission by using electron microscopy have been unsuccessful, given the inherent difficulty of identifying nano-scale features on centimeter-sized surfaces and correlating with field emission measured centimeters away.…”

Dopant/carrier profiling for 3D‐structures

“…For less conductive materials like semiconductors, it has been essential to add laser-assisted evaporation which does solve the conductivity problem but unfortunately creates at the same time a number of artifacts such as preferential adsorption and evaporation in heterogeneous systems, localised heating, etc. [15]. All these effects induce often a nonhemispherical tip formation causing a violation of the afore mentioned simplifications and thus lead to uncertainties in the reconstructed profiles [16].…”

Optical study of the band structure of wurtzite GaP nanowires

“…48,49 We mainly find carbon impurities, with a ratio in the concentration of C 2 complexes and single C atoms larger than 10:1, as listed in Table I (see also Fig. S5 in the supplementary material for more details).…”