Laser crystallization of germanium nanowires fabricated by electrochemical deposition

Abstract

Germanium (Ge) nanowires were fabricated by electrochemical deposition on titanium‐coated silicon substrate. Arrays of nanowires with different mean diameters were obtained using indium nanoparticles of various sizes as centers of nucleation. Raman spectroscopy was used to establish the structural properties of nanowires under different laser excitation intensities. Cycles of measurements with different intensities demonstrated irreversible changes in the structure. Initial study with minimal excitation intensity of 3 W/cm2 displayed that the spectra are descriptive of amorphous Ge. Further study at increased intensities led to the transformation of Raman spectra to the shapes that can be attributed to crystalline Ge. Detailed analysis of spectra shapes for samples with different mean diameters of Ge nanowires after exposure to high intensity laser radiation allows to estimate the fraction of the crystalline phase in Ge nanowires. The spectra of a sample irradiated by He–Ne laser were compared with thermally annealed sample in a vacuum at 150 °C. A similar shape of the obtained spectra indicates on the thermal nature of the effect, which leads to a change in the observed structural properties. This change under even slight heating can be explained by thermal isolation of nanowires from the substrate.

Investigation of the Stokes to anti‐Stokes ratio for germanium nanowires obtained by electrochemical deposition

“…Analyzing the shape of spectra, presented in Figure , we note, that in both cases ( λ exc = 532 nm and λ exc = 633 nm), the spectra obtained with maximum excitation power and attenuated by two times do not change their shape and peak position. This fact is a normal thing for the majority of cases in Raman studies of bulk materials, but as it was demonstrated earlier, GeNWs obtained by ec‐LLS method may easily change their spectrum shape under low excitation.…”

“…Our further measurements of Samples 2 and 3 confirmed the results demonstrated earlier . For more convenience, in Figure , we presented only the Stokes component that was registered with 532 nm excitation wavelength.…”

“…These dependencies demonstrate that Samples 2 and 3 may be easily heated to temperatures high enough for crystallization and even melting. Molten and crystallized areas of GeNW under laser beam may form agglomerates with characteristic dimensions of microns (see figures S7 and S8a,b in Gavrilov et al), which easily dissipate the heat.…”

“…Raman spectroscopy provides information locally that may be of great use while studying heating effects in nanostructures. Our recent study of GeNW by Raman spectroscopy demonstrated irreversible changes of the spectral lineshape, indicating a structural transformation due to intense exciting radiation . But irreversible changes in spectral lineshape may be caused by quantum confinement effect or mechanical stress induced in nanostructures.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIII

“…Gavrilov et al reported laser crystallization of germanium nanowires fabricated by electrochemical deposition. Detailed analysis of spectra shapes for samples with different mean diameters of Ge nanowires after exposure to high intensity laser radiation allows an estimation of the fraction of the crystalline phase in Ge nanowires . Grasseschi and co‐workers investigated the dynamics of dithiooxamide coordinated to gold NPs using SERS.…”