Research

Deterministic release and rearrangement of nanomembranes or thin films

In the last years, freestanding membranes were established as a building block for nanotechnology. Investigated structures include stretchable electronics, free-standing solar cells, free-standing Si membranes for high mobility, wrinkled semiconductor membranes as well as rolled-up and folded three-dimensional micro- and nano-objects.

Rolled-up tubes as building blocks for nanotechnology

Rolled-up tube with integated QW and its PL spectra

We are working on emerging device structures based on rolled-up membranes. Such structures are fabricated by defining an pattern by optical lithography followed by selective underetching of an strain engineered heterostructure. These structures are currently grown in the molecular beam epitaxy facility of the LNNano/CNPEM. Optical characterization is carried out at the IFGW in collaboration with other members of the department.

Semiconductor membranes as virtual substrates for epitaxy

Currently, we overgrow of freestanding structures to investigate the influence of compliant substrates to the formation of self-assembled nanostructures (supported by FAPESP and CNPq). We are interested to understand the growth dynamics during material deposition by molecular beam epitaxy using the facilities of the LNNano/CNPEM. We investigate the surface diffusion and the preferred accumulation by ex-situ methods like scanning electron microscopy and atomic force microscopy. We carry out x-ray diffraction to quantivy the strain transfer from deposited material to the underlying substrate.

The image above depicts an AFM study of a overgrown, wrinkled InGaAs nanomembrane with InAs islands formed in the released areas of the sample (Nanotechnolgy 25, 455603 (2014)).

Growth of semiconductor hetero- and nanostructures

I am responsible for the molecular beam epitaxy facilities of the LNNano/CNPEM. We have an ongoing collaboration and research line for growing various kinds of III-V heterostructures. These include standard samples like GaAs quantum wells, InAs dots, and more advanced structures like Bragg reflectors provided for external collaborators. Furthermore, we fabricate heterostructures for our own research, and study - besides the membrane overgrowth - the fabrication of unstrained quantum emitters for optical applications.

The AFM images above depict structures made by Ga assisted deoxidation and local hole etching followed by the overgrowth with AlGaAs/GaAs/AlGaAs to develop unstrained mesoscopic GaAs structures (Nanoscale Research Letters 12, 61 (2017)).