Centrum pre Nanodiagnostiku Materiálov

MOTOLA, Martin – ČAPLOVIČOVÁ, Mária – KRBAL, Miloš – SOPHA, Hannah – THIRUNAVUKKARASU,  Guru Karthikeyan – GREGOR, Maroš – PLESCH, Gustáv – MACAK, Jan M.

In Electrochimica Acta. Vol. 331, (2020)

https://doi.org/10.1016/j.electacta.2019.135374

Abstract

In this work, a two-step treatment of TiO₂ nanotube (TNT) layers towards enhanced photocatalytic performance is presented. TNT layers with a thickness of ∼7 μm and an average inner diameter of ∼190 nm were prepared via electrochemical anodization of Ti foil in a fluoride containing ethylene glycol-based electrolyte. To improve the photocatalytic activity of the produced TNT layers a two-step post-treatment was conducted. First, the inner shell of the native double-wall TNT layers was removed via a mild pre-annealing followed by a selective etching treatment of the inner shell in piranha solution yielding single-wall TNT layers. Second, reduction via annealing in H₂/Ar atmosphere was performed. The resulting Ti³⁺ doped single-wall TNT layers possess 100% enhancement of photocatalytic activity compared to their non-treated counterparts.

CHAUHAN, Prerna – HASENÖHRL, Stanislav – VANČO, Ľubomír – ŠIFFALOVIČ, Peter – DOBROČKA, Edmund – MACHAJDÍK, Daniel – ROSOVÁ, Alica – GUCMANN, Filip – KOVÁČ, Jaroslav jr. – MATKO, Igor – KUBALL, Martin – KUZMÍK, Ján

In CrystEngComm. Vol. 22, iss. 1 (2020)

https://doi.org/10.1039/C9CE01549C

Abstract

Thick InAlN layers (In-molar fraction >0.37) on GaN buffer layers were prepared using a close-coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor. This work provides a discussion of the dependence of reactor parameters (pressure, ammonia flow and temperature) and unintentional Ga-incorporation on structural, optical and chemical properties of those layers down to the nanoscale. Rutherford back-scattering spectrometry, Auger electron spectroscopy, and transmission electron microscopy with the energy dispersive X-ray analysis were used for in-depth chemical analysis of layers. A diminishing Ga-auto-incorporation in thick InAlN layer creates a chemically graded InAl(Ga)N interlayer that assists in releasing of interfacial strain and paves the way toward In-rich InAlN layer. The rate of unintentional Ga-auto-incorporation in InAlN layers increases with decreasing of growth temperature, and increasing of reactor pressure and ammonia flow during growth. Raman and photoluminescence spectroscopy were used to get the crystal structural fingerprint influenced by Ga-incorporation. We suggested that Ga could incorporate at nitrogen vacancies at high reactor pressures (≥200 mbar). Screw dislocations and/or N-vacancies in InAl(Ga)N layers may be energetically favorable sites for In-incorporation and lead to compositional fluctuation and local In-rich InAl(Ga)N phase.