Search

It was discovered in 2010 that Croconic Acid, in its crystal form, has the highest polarization among organic ferroelectrics. In the context of eliminating toxic substances from electronic devices, Croconic Acid has a great potential as a sublimable lead-free ferroelectric. However, studies on ferroelectric properties of its thin films are only in their early stages and its capability to be incorporated in nanoscale devices is unknown. In this work, we demonstrate, upon ferroelectric switching at the nanoscale, stable and enduring room temperature polarization with no leakage current in Croconic Acid thin films. We thus show that it is a promising lead-free organic ferroelectric toward integration in nanoscale devices. The challenging switching current and polarization reversal characterization at the nanoscale was done using a unique combination of piezoresponse force microscopy, polarization switching current spectroscopy and the concurrent electromechanical strain response. Indeed, this combination can help to rationalize otherwise asymmetric polarization-voltage data and distorted hysteresis due to current jumps below the background noise, which are statistically washed away in macrojunctions but become prevalent at the nanoscale. These results are valid irrespective of the ferroelectrics' nature, organic or inorganic. Beyond the potential of Croconic Acid as an ecological ferroelectric material in devices, our detection of a clear nanoscopic polarization switching current thus paves the way for a fundamental understanding and technological applications of the polarization reversal mechanism at the nanoscale.

Desde a divulgação do laser de rubi em 1960, os lasers têm sido utilizados em diversos campos da medicina, e o seu uso na medicina dentária foi introduzido em 1964. Hoje, vários sistemas a laser são discutidos para possível uso na medicina dentária. Desde então, o laser desenvolveu-se para diferentes funções no ambiente odontológico: cuidados conservadores, endodontia, cirurgia oral ... A extensão das aplicações desta nova ferramenta inclui naturalmente a área da periodontologia. Os lasers Nd: YAG (dopados com neodímio: ítrio, alumínio e granada) e o CO2 (dióxido de carbono) são de interesse limitados devido aos seus efeitos colaterais térmicos, enquanto os lasers Er: YAG (dopados com érbio: ítrio, alumínio e granada) tornam-se cada vez mais populares no tratamento não cirúrgico da periodontite crónica. Um dos principais objetivos no tratamento da periodontite é a eliminação de depósitos bacterianos e a interrupção da progressão da doença. Para atingir esse objetivo, é necessário a remoção completa da placa aderida, tártaro e cemento infetado, embora a remoção completa seja difícil. O objetivo desta revisão integrativa é avaliar e comparar eficácia clínica do laser Er: YAG na raspagem e alisamento radicular e descontaminação de bolsas periodontais, relativamente ao tratamento mecânico convencional não cirúrgico de raspagem e alisamento radicular.

Realization of spin crossover (SCO) based applications requires studying of spin state switching characteristics of SCO complex molecules at nanostructured environments especially on-surface. Except for a very few cases, the SCO of a surface bound thin molecular film is either quenched or heavily altered due to (i) strong molecule-surface interactions and (ii) differing intermolecular interactions in films relative to the bulk. By fabricating SCO complexes on a weakly interacting surface such as highly oriented pyrolytic graphite (HOPG) and copper nitride (CuN), the interfacial quenching problem has been tackled. However, engineering intermolecular interactions in thin SCO active films is rather difficult. This work proposes a molecular self-assembly strategy to fabricate thin spin switchable surface bound films with programmable intermolecular interactions. Molecular engineering of the parent complex system [Fe(H$_{2}$B(pz)$_{2}$)$_{2}$(bpy)] (pz = pyrazole, bpy = 2,2'-bipyridine) with a dodecyl (C$_{12}$) alkyl chain yielded a classical amphiphile-like functional and vacuum sublimable charge neutral Fe$^{\rm II}$ complex, [Fe(H$_{2}$B(pz)$_{2}$)$_{2}$(C$_{12}$-bpy)] (C$_{12}$-bpy = dodecyl[2,2'-bipyridine]-5-carboxylate). The bulk powder and 10 nm thin film, on quartz glass/SiO$_{\rm x}$ surface, of the complex showed comparable spin state switching characteristics mediated by similar lamellar bilayer like self-assembly/molecular interactions in both bulk and thin film states. This unprecedented observation augurs well for the development of SCO based applications, especially in molecular spintronics.