Influence of Substrates on the Long-Range Order of Photoelectrodeposited Se-Te Nanostructures

Considering the rapid development and advancement in optical devices, effective design and synthesis of adaptive nanostructured materials with excellent properties is highly desirable. For instance, phototropic growth has recently attracted significant attention among researchers by offering a platform for controlling the morphologies of the designed complex three-dimensional nanostructures.

Presently, Se-Te alloys films exhibit phototropic growth and thus have been electrodeposited on various substrates. Even though the structural properties of the substrates exhibit negligible influence on the morphology of the resulting photo electrodeposited Se-Ti films, the influence of the nanoscale lamellar patterns during the synthesis process has not been fully explored. Recent studies have shown that the difference in the distribution and behavior of charge carriers in either illuminated or dark conditions adversely affect the electrochemical reactions of semiconductors as well as the metal deposition. Alternatively, absorption of light energy above the Se-Te band gap contributes to the phototropic growth of the Se-Te films. This results in an electron-hole pair that has potential influence on the growth and morphology of the phototropic films attributed to the energetics between the interface of the electrodeposit and the substrate.

Recently, California Institute of Technology researchers: Ethan Simonoff, Ph.D. candidate Michael Lichterman, Kimberly Papadantonakis and led by Professor Nathan Lewis explored the long-range order of the photo-electrodeposited Si-Te nanostructures. In particular, they investigated the influence of the substrates on the development of the lamellar patterns on the Se-Te films as well as its corresponding electrical effects induced by the energetics between the semiconducting film and the substrate. Their work is currently published in the journal, Nano Letters.

In brief, the initiated their experiments by electrochemically growing Se-Te films at room temperature under controlled conditions i.e. polarized near infrared illumination with uniform intensity. Next, both p-and n-doped crystalline (111)-oriented Si substrates were used to investigate the long-range order of the grown films. Additionally, the scanning electron microscope was used to obtain large scale images for analysis using the Fourier Transform method.

The authors observed that the p-doped silicon substrates produced phototropic films with significantly perfect pattern period and high anisotropy degree as compared to their n-doped silicon substrate counterpart. This was attributed to dynamic behavior at the Se-Te interface during the phototropic growth induced by the electrical effects due to the difference interfacial junction energetics.

In summary, Caltech scientists demonstrated the influence of substrates on the long-range order of photoelectrochemically grown Si-Te nanofilms. To actualize their study, the illumination and deposition parameters were adjusted. However, similar aforementioned differences in the pattern fidelity and phototropic Se-Te films were recorded. Altogether, the study by Professor Nathan Lewis and his research team will advance the design and synthesis of advanced materials for numerous applications.