New article in Phys. Rev. Materials

Direct observation of large-area strain propagation on free-standing nanomembranes

Investigations on epitaxial nanostructures with size of tens of nanometers have been a challenging issue for techniques that present high strain sensitivity but restricted spatial resolution. This is the case of recently developed x-ray nanoprobe techniques. Despite its inherent nondestructive character, submicron x-ray spots have only been successfully applied to the study of individual nanostructures which are either strain free or present extremely mild spatial lattice parameter gradients. Such limitation, with an uttermost barrier given by the diffraction limit, leads to voxel or pixel sizes between 5 and 10 nm obtained in coherent diffraction imaging or ptychographic reconstructions of real-space objects. Whenever the strain field of a nanostructure is successfully reconstructed from reciprocal space measurements, it cannot vary considerably in short distances since this would induce diffraction peak broadening and cause abrupt phase variations, leading to convergence issues on reconstruction algorithms. Here we show how epitaxial systems with large lattice mismatch and appreciable interfacial strain can be identified and directly analyzed throughout their strain field propagation in nanometer-thin crystalline membrane platforms, using the InGaAs/GaAs Stranski-Krastanov system as a model. The strain-induced footprint becomes observable along a few microns if the membrane thickness is comparable to the nanostructure size. It is possible to retrieve both interfacial strain and nanostructure size by probing individual objects.

Yuri Bernardes, Lucas A. B. Marçal, Barbara L. T. Rosa, Ailton Garcia, Jr., Christoph Deneke, Tobias U. Schülli, Marie-Ingrid Richard, and Angelo Malachias

Phys. Rev. Materials 7, 026002

DOI: 10.1103/PhysRevMaterials.7.026002

New publication in “Journal of Physical Chemistry C” by group member

Strain Tuning in Graded SiGe on Insulator: Interplay between Local Concentration and Nonmonotonic Lattice Evolution after Ge Condensation

Germanium condensation has proven to be a reliable route for obtaining smoothly graded composition SiGe layers with good reproducibility and reduced defect density. The process is known as a crucial tool to induce well-defined strain on Si or SiGe layers with potential use in semiconductor devices. In this work, we show that starting from a low concentration Si0.92Ge0.08 layer grown on top of a crystalline Si(001) on SOI substrates, we can reach desirable concentration with a nonmonotonic interplay on in-plane and out-of-plane strain. The Ge concentration is evaluated by a combination of ultralow energy secondary ion mass spectroscopy (ULE-SIMS) and synchrotron X-ray measurements (diffraction and reflectivity). After the evaluation of Ge content, the strain-sensitive process of rolling up tubes from the flat layers is used and combined with X-ray diffraction to provide a concise scenario of the strain evolution along an in-growth oxidation series, pointing out the conditions that maximize strain, as well as its fading, as the Ge content rises.

Gilberto Rodrigues-Junior, Francesca Cavallo, Christoph Deneke, and Angelo Malachias

J. Phys. Chem. C 2022, xxxxx

DOI: 10.1021/acs.jpcc.2c05702

Master student for CNPq position

With the granting of the CNPq project (408219/2022-0) from call “Chamada CNPq/SEMPI/MCTI Nº 57/2022 – MESTRADO OU DOUTORADO EM COMPUTAÇÃO QUÂNTICA, FOTÔNICA INTEGRADA E INTELIGÊNCIA ARTIFICIAL”, Prof. Christoph Deneke has an open position for a master student to work in the area of photonics.

The position is available from now on to start in the next entrance to PostGraduation of the IFGW/Unicamp.

Fell free to contact Ch. Deneke.

Renovation of lab space

With the money from the FAEPEX project 2102/21, we could carry out some long needed renovation of the lab space. In January 2022, we renewed the chemical working places, created a common working space as well as improved the overall installations of the lab.

We will also clean out some old instruments to do a fresh restart of the area for everyone, now that we are back to the university.

Artigo em destaque

Sorry, this entry is only available in Português do Brasil.

Artigo de membros do grupo foi escolhido pelo SPBMat como artigo em destaque. Veja aqui o texto em português.

New article by group member

Strain-based band structure engineering is a powerful tool to tune the optical and electronic properties of semiconductor nanostructures. We show that we can tune the band structure of InGaAs semiconductor quantum wells and modify the helicity of the emitted light by integrating them into rolled-up heterostructures and changing their geometrical configuration. Experimental results from photoluminescence and photoluminescence excitation spectroscopy demonstrate a strong energy shift of the valence-band states in comparison to flat structures, as a consequence of an inversion of the heavy-hole with the light-hole states in a rolled-up InGaAs quantum well. The inversion and mixing of the band states lead to a strong change in the optical selection rules for the rolled-up quantum wells, which show vanishing spin polarization in the conduction band even under near-resonant excitation conditions. Band structure calculations are carried out to understand the changes in the electronic transitions and to predict the emission and absorption spectra for a given geometrical configuration. Comparison between experiment and theory shows an excellent agreement. These observed profound changes in the fundamental properties can be applied as a strategic route to develop novel optical devices for quantum information technology.

Leonarde N. Rodrigues, Diego Scolfaro, Lucas da Conceição, Angelo Malachias, Odilon D. D. Couto, Jr, Fernando Iikawa, and Christoph Deneke

ACS Appl. Nano Mater., online (2021)
DOI: 10.1021/acsanm.1c00354

Research was supported by FAPESP and CNPq.

The article was featured by the SPBMat – here the Portuguese post.

Presentation of PIBIC project – Pedro Carneiro

For the annual PIBIC congress, Pedro made a video poster of his work: “Desenvolvimento de um experimento de quantificação da concentração de elementos por fluorescência de raios X e aplicação para o estudo de modelos de epilepsia em roedores”.

Presentation of PIBIC project – Gabriel Gomes

For the annual PIBIC congress, Gabriel made a video poster of his work “Fabricação e caracterização de membranas baseadas em nanoestruturas semicondutoras”.

New article by group member: Band structure engineering in strain-free GaAs mesoscopic structures

We investigate the optical properties of strain-free mesoscopic GaAs/Al(x)Ga(1-x)As structures (MGS) coupled to thin GaAs/A(x)Ga(1-x)As quantum wells (QWs) with varying Al content (x). We demonstrate that quenching the QW emission by controlling the band crossover between AlGaAs X-point and GaAs Gamma-point gives rise to long carrier lifetimes and enhanced optical emission from the MGS. For x = 0.33, QW and MGS show typical type-I band alignment with strong QW photoluminescence emission and much weaker sharp recombination lines from the MGS localized exciton states. For x >= 0.50, the QW emission is considerably quenched due to the change from type-I to type-II structure while the MGS emission is enhanced due to carrier injection from the QW. For x >= 0.70, we observe PL quenching from the MGS higher energy states also due to the crossover of X and Gamma bands, demonstrating spectral filtering of the MGS emission. Time-resolved measurements reveal two recombination processes in the MGS emission dynamics. The fast component depends mainly on the X-Gamma mixing of the MGS states and can be increased from 0.3 to 2.5~ns by changing the Al content. The slower component, however, depends on the X-Gamma mixing of the QW states and is associated to the carrier injection rate from the QW reservoir into the MGS structure. In this way, the independent tuning of X-Gamma mixing in QW and MGS states allows us to manipulate recombination rates in the MGS as well as to make carrier injection and light extraction more efficient.

Vanessa Ors Gordo, Leonarde Nascimento Rodrigues, Floris Knopper, Ailton J Garcia, Fernando Iikawa, Odilon D. D. Couto Jr. and Christoph Deneke

Nanotechnology 31, 255202 (2020)