resumo
Diphenylalanine (FF) peptide nanotubes (PNTs) represent a unique class of self-assembled functional biomaterials owing to a wide range of useful properties including nanostructural variability, mechanical rigidity and chemical stability. In addition, strong piezoelectric activity has recently been observed paving the way to their use as nanoscale sensors and actuators. In this work, we fabricated both horizontal and vertical FF PNTs and examined their optical second harmonic generation and local piezoresponse as a function of temperature. The measurements show a gradual decrease in polarization with increasing temperature accompanied by an irreversible phase transition into another crystalline phase at about 140-150 degrees C. The results are corroborated by the molecular dynamic simulations predicting an order-disorder phase transition into a centrosymmetric (possibly, orthorhombic) phase with antiparallel polarization orientation in neighbouring FF rings. Partial piezoresponse hysteresis indicates incomplete polarization switching due to the high coercive field in FF PNTs.
palavras-chave
2ND-HARMONIC GENERATION; MICROSCOPY; TRANSITION; POLYMORPHISM; PROBE
categoria
Physics
autores
Heredia, A; Bdikin, I; Kopyl, S; Mishina, E; Semin, S; Sigov, A; German, K; Bystrov, V; Gracio, J; Kholkin, AL
nossos autores
Andrei Kholkin
Investigador Principal
Svitlana Kopyl
Investigador
Vladimir Bystrov
Bolseiro de pós-Doutoramentoagradecimentos
The work is supported by the Ministry of Science and Education (Federal Special-Purpose Programme 'Cadres', contract No 02.740.11.560). IB would like to thank the Programme Ciencia, 2008 of the Portuguese Science and Technology Foundation (FCT). We are also grateful to FCT project REDE/1509/RME/2005 for use of the RNME facility.