Synthesis of water-stable and highly luminescent graphite quantum dots.

Highly stable and environmentally friendly nitrogen-doped graphite quantum dots consisting of ∼12 layers of graphene, average diameter of ∼7.3 nm, prepared by atmospheric pressure microplasma are reported to have blue emission due to surface states created by nitrogen doping (9 atomic%) and reaction with oxygen. The low-temperature synthesis method requires simple precursors in water, with no annealing or filtration, producing crystalline disc-shaped quantum dots with ∼68% photoluminescence emission quantum yield at 420 nm excitation and that have shown stability for more than one month after the synthesis. The nitrogen doping in the quantum dots mainly occurs in graphitic core as substituted type of doping (63-67 atomic%) and the amount of doping is sufficient to create emissive states without impacting the core structure. The optical and chemical properties do not undergo serious retardation even with re-dispersion suggesting easy applicability for cellular imaging or optoelectronics.

Surfactant-free synthesis of copper nanoparticles and gas phase integration in CNT-composite materials.

Copper nanoparticles (Cu-NPs) represent a viable low-cost alternative to replace bulk copper or other more expensive NPs (e.g. gold or silver) in various applications such as electronics for electrical contact materials or high conductivity materials. This study deals with the synthesis of well dispersed Cu-NPs by using an Ar + H2 microplasma using a solid copper precursor. The morphological analysis is carried out by electron microscopy showing particles with a mean diameter of 8 nm. Crystallinity and chemical analyses were also carried out by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. In the second step, the Cu-NPs were successfully deposited onto porous carbon nanotube ribbons; surface coverage and the penetration depth of the Cu-NPs inside the CNT ribbon structure were investigated as these can be beneficial for a number of applications. The oxidation state of the Cu-NPs was also studied in detail under different conditions.

Bridging energy bands to the crystalline and amorphous states of Si QDs.

The relationship between the crystallization process and opto-electronic properties of silicon quantum dots (Si QDs) synthesized by atmospheric pressure plasmas (APPs) is studied in this work. The synthesis of Si QDs is carried out by flowing silane as a gas precursor in a plasma confined to a submillimeter space. Experimental conditions are adjusted to propitiate the crystallization of the Si QDs and produce QDs with both amorphous and crystalline character. In all cases, the Si QDs present a well-defined mean particle size in the range of 1.5-5.5 nm. Si QDs present optical bandgaps between 2.3 eV and 2.5 eV, which are affected by quantum confinement. Plasma parameters evaluated using optical emission spectroscopy are then used as inputs for a collisional plasma model, whose calculations yield the surface temperature of the Si QDs within the plasma, justifying the crystallization behavior under certain experimental conditions. We measure the ultraviolet-visible optical properties and electronic properties through various techniques, build an energy level diagram for the valence electrons region as a function of the crystallinity of the QDs, and finally discuss the integration of these as active layers of all-inorganic solar cells.

Surface Functionalization of Grown-on-Tip ZnO Nanopyramids: From Fabrication to Light-Triggered Applications.

We report on a combined chemical vapor deposition (CVD)/radio frequency (RF) sputtering synthetic strategy for the controlled surface modification of ZnO nanostructures by Ti-containing species. Specifically, the proposed approach consists in the CVD of grown-on-tip ZnO nanopyramids, followed by titanium RF sputtering under mild conditions. The results obtained by a thorough characterization demonstrate the successful ZnO surface functionalization with dispersed Ti-containing species in low amounts. This phenomenon, in turn, yields a remarkable enhancement of photoactivated superhydrophilic behavior, self-cleaning ability, and photocatalytic performances in comparison to bare ZnO. The reasons accounting for such an improvement are unravelled by a multitechnique analysis, elucidating the interplay between material chemico-physical properties and the corresponding functional behavior. Overall, the proposed strategy stands as an amenable tool for the mastering of semiconductor-based functional nanoarchitectures through ad hoc engineering of the system surface.

Microplasma-synthesized ultra-small NiO nanocrystals, a ubiquitous hole transport material.

We report on a one-step hybrid atmospheric pressure plasma-liquid synthesis of ultra-small NiO nanocrystals (2 nm mean diameter), which exhibit strong quantum confinement. We show the versatility of the synthesis process and present the superior material characteristics of the nanocrystals (NCs). The band diagram of the NiO NCs, obtained experimentally, highlights ideal features for their implementation as a hole transport layer in a wide range of photovoltaic (PV) device architectures. As a proof of concept, we demonstrate the NiO NCs as a hole transport layer for three different PV device test architectures, which incorporate silicon quantum dots (Si-QDs), nitrogen-doped carbon quantum dots (N-CQDs) and perovskite as absorber layers. Our results clearly show ideal band alignment which could lead to improved carrier extraction into the metal contacts for all three solar cells. In addition, in the case of perovskite solar cells, the NiO NC hole transport layer acted as a protective layer preventing the degradation of halide perovskites from ambient moisture with a stable performance for >70 days. Our results also show unique characteristics that are highly suitable for future developments in all-inorganic 3rd generation solar cells (e.g. based on quantum dots) where quantum confinement can be used effectively to tune the band diagram to fit the energy level alignment requirements of different solar cell architectures.

Multi-functional MnO2 nanomaterials for photo-activated applications by a plasma-assisted fabrication route.

Supported MnO2-based nanomaterials were fabricated on fluorine-doped tin oxide substrates using plasma enhanced-chemical vapor deposition (PE-CVD) between 100 °C and 400 °C, starting from a fluorinated Mn(ii) diamine diketonate precursor. Growth experiments yielded ß-MnO2 with a hierarchical morphology tuneable from dendritic structures to quasi-1D nanosystems as a function of growth temperature, whose variation also enabled a concomitant tailoring of the system fluorine content, and of the optical absorption and band gap. Preliminary photocatalytic tests were aimed at the investigation of photoinduced hydrophilic (PH) and solid phase photocatalytic (PC) performances of the present nanomaterials, as well as at the photodegradation of Plasmocorinth B azo-dye aqueous solutions. The obtained findings highlighted an attractive system photoactivity even under visible light, finely tailored by fluorine content, morphological organization and optical properties of the prepared nanostructures. The results indicate that the synthesized MnO2 nanosystems have potential applications as advanced smart materials for anti-fogging/self-cleaning end uses and water purification.

Perception of dentists, dental students, and patients on dentogingival aesthetics / Percepção de dentistas, estudantes de odontologia e pacientes sobre a estética dentogengival

Abstract Introduction Patients' demand for dentogingival aesthetics has increased significantly in recent years, and this is a complex concept due to numerous factors involved in obtaining patient/professional satisfaction. Some dentogingival features may alter smile harmony, such as excessive gingival display. Objective To evaluate whether the presence of gingival display has a negative influence on the perception of dentogingival aesthetics. Material and method 180 individuals (60 dentists, 60 dental students, and 60 patients) evaluated images of volunteer smiles. These images were digitally altered by the Adobe Photoshop™ software, creating different situations of gingival display (4 mm, 2 mm, 0 mm, -2 mm, -4 mm), and graded by the evaluators with the following scores: (01) very pleasant smile, (02) pleasant smile, and 03) unpleasant smile. The scores assigned were analyzed using ANOVA (α=0.05). Result Gingival displays between 0 and 2 mm were considered aesthetically pleasing. Changes of -4 and +4 mm were defined as the most disharmonious smiles. The 0-mm female smile was considered the most harmonious for dentists (1.51) and dental students (1.77), by Student's t test (p<0.05). In the opinion of patients, the smile of +2 mm was considered the most aesthetic. In the image evaluations of men, the 0-mm smile was considered the most aesthetic (p <0.05) for dentists (1.85) and dental students (1.62). The patients considered +2 mm of gingival display the most harmonious smile. Conclusion The aesthetic perception of dental students and dentists was different when compared to the group of patients.

Resumo Introdução A procura dos pacientes pela estética dentogengival tem aumentado significativamente nos últimos anos, sendo um conceito complexo devido aos inúmeros fatores envolvidos para a obtenção da satisfação paciente/profissional. Algumas características dentogengivais podem alterar a harmonia do sorriso como por exemplo o excesso de exposição gengival. Objetivo Avaliar se a presença da exposição gengival tem uma influência negativa na percepção da estética dentogengival. Material e método 180 indivíduos (60 dentistas, 60 acadêmicos de odontologia e 60 pacientes) avaliaram imagens de sorrisos de voluntários. Essas imagens foram alteradas digitalmente pelo software Adobe Photoshop™, criando diferentes situações de exposições gengivais (4 mm, 2 mm, 0 mm, -2 mm, -4 mm), e classificados pelos avaliadores através dos escores: (01) sorriso muito agradável, (02) agradável e (03) desagradável. Os escores atribuídos foram analisados por meio da ANOVA (α=0,05). Resultado Exposições gengivais entre 0 e 2 mm foram consideradas esteticamente agradáveis. Alterações de -4 e +4 mm foram definidas como as mais desarmônicas. O sorriso de 0 mm no sexo feminino foi considerado mais harmônico para os dentistas (1,51) e estudantes de odontologia (1,77), pelo teste t de Student (p<0.05). Na opinião dos pacientes o sorriso de +2 mm foi considerado o mais estético. Na avaliação das imagens do sexo masculino, o sorriso de 0 mm foi considerado o mais estético (p<0,05), para dentistas (1,85) e estudantes de odontologia (1,62). Os pacientes consideraram +2 mm de exposição gengival como o sorriso mais harmônico. Conclusão A percepção estética de estudantes de odontologia e cirurgiões dentistas foram diferentes quando comparado ao grupo dos pacientes.