RESUMO
Se presentan propiedades eléctricas y de transporte en películas nanocristalinas del compuesto cuaternario Cu2ZnSnSe4 (CZTSe) por método de co-evaporación física. Las muestras fueron crecidas sobre sustratos de vidrio soda-lime y variando en rango los parámetros de síntesis: masa de Cu y temperatura de sustrato. A partir de termopotencia a temperatura ambiente y de transmitancia espectral, se encontró que el material está caracterizado por conductividad tipo n y ancho de banda de energía prohibida de 1.7 eV, respectivamente. Las medias de conductividad eléctrica (región de bajas temperaturas; 90-200 K) mostraron que los procesos de conducción se realizan vía hopping de rango de variable entre estados extendidos. Los parámetros que caracterizaron éste mecanismo, energía de activación (Whopp) y rango hopping (Rhopp), fueron obtenidos mediante teoría de percolación y modelo difusional. Se obtuvo, que para las muestras CZTSe la densidad de estados de defecto cerca del nivel de Fermi del material, N(Ef), está alrededor de 3,403x10(18) cm-3 eV-1. Se presentó correlación entre parámetros de depósito y propiedades eléctricas. Se observó influencia de parámetros sobre formación de fases adicionales en el compuesto.
Here, we present electronic and transport properties of quaternary Cu2ZnSnSe4 (CZTSe) nanocrystalline films fabricated by physical co-evaporation. The samples were grown on soda-lime glass substrates and synthesis parameter ranges, Cu mass and substrate temperature were varied. Using thermopower at room temperature and spectral transmittance we found that the material is characterized by n-type conductivity and forbidden energy bandwidth of 1.7 eV, respectively. Electrical conductivity means (low temperature region; 90-200 K) showed that conductivity processes occur via variable range hopping between extended states. We obtained the parameters characterizing this mechanism, activation energy (Whopp), and range hopping (Rhopp), by employing the percolation theory and diffusion model. The density of defect states near the Fermi level of the material, N (Ef) of the CZTSe samples is about 3,403x10(18) cm-3 eV-1. We found a correlation between deposition parameters and electrical properties and observed a parameter influence on the formation of additional phases in the compound.
Apresentam-se propriedades elétricas e de transporte em películas nano-cristalinas do composto quaternário Cu2ZnSnSe4 (CZTSe) pelo método de co-evaporação física. As amostras foram crescidas sobre substratos de vidro soda-lime e variando a amplitude dos parâmetros de síntese: massa de Cu e temperatura do substrato. A partir de termo-potência a temperatura ambiente e de transmissão espectral, encontrou-se que o material está caracterizado pela condutividade tipo n e largura de banda de energia proibida de 1.7 eV, respetivamente. As medidas de condutividade elétrica (regiões de baixas temperaturas; 90-200 K) mostraram que os processos de condução se realizam via hopping de amplitude variável entre estados estendidos. Os parâmetros que caracterizaram este mecanismo, energia de ativação (Whopp) e amplitude hopping (Rhopp), foram obtidos mediante a teoria de percolação e o modelo de difusão. Obteve-se que, para as amostras CZTSe, a densidade de estados de defeito próximos do nível de Fermi do material, N(EF), está ao redor de, 3,403x10(18) cm-3 eV-1. Apresentou-se correlação entre parâmetros de depósito e propriedades elétricas. Observou-se influencia de parâmetros sobre a formação de fases no composto.
RESUMO
AIM: To investigate the antimicrobial activity of 2.5% and 5.25% sodium hypochlorite and 2.0% chlorhexidine gel and liquid as endodontic-irrigating substances against selected single-species biofilms. METHODS: Single-species biofilms of Enterococcus faecalis, Staphylococcus aureus, Candida albicans, Prevotella intermedia, Porphyromonas gingivalis, Porphyromonas endodontalis and Fusobacterium nucleatum were generated on a cellulose nitrate membrane placed on agar medium. The biofilms were then immersed in the endodontic-irrigating substances for 30 s and also for 5, 10, 15, 30 and 60 min, with and without mechanical agitation. Sterile saline was used as control. After each time period, the membrane filters were then transferred to tubes containing 2 mL of fresh broth medium plus neutralizers (in order to prevent the residual action of the tested substances). The micro-organisms were suspended using a vortex, and the inoculum was serially diluted 10-fold. Aliquots of the dilutions were plated on 5% sheep blood agar medium, and incubated under adequate gaseous conditions. Colony-forming units were calculated. The samples were compared using the Friedman and Tukey test, when necessary, at a significance level of P < 0.05. RESULTS: Mechanical agitation promoted the effectiveness of the antimicrobial agents, resulting in less time to eliminate the same micro-organisms, except for S. aureus with 2.5% NaOCl. Antimicrobial agents in liquid presentation, especially 5.25% NaOCl and 2% chlorhexidine, killed the tested micro-organisms more rapidly. Saline did not inhibit the growth of any of the tested micro-organisms, with or without agitation, being statistically different (P < 0.05) from NaOCl and chlorhexidine. P. intermedia, P. gingivalis, P. endodontalis and F. nucleatum were eliminated in 30 s by all antimicrobial agents, with our without agitation, in contrast with the facultative and aerobe strains. CONCLUSIONS: Mechanical agitation improved the antimicrobial properties of the chemical substances tested using a biofilm model, favouring the agents in liquid presentation, especially 5.25% NaOCl and 2% chlorhexidine.
Assuntos
Anti-Infecciosos Locais/farmacologia , Biofilmes/efeitos dos fármacos , Clorexidina/farmacologia , Desinfetantes/farmacologia , Irrigantes do Canal Radicular/farmacologia , Hipoclorito de Sódio/farmacologia , Anti-Infecciosos Locais/administração & dosagem , Técnicas Bacteriológicas , Candida albicans/efeitos dos fármacos , Clorexidina/administração & dosagem , Contagem de Colônia Microbiana , Desinfetantes/administração & dosagem , Relação Dose-Resposta a Droga , Enterococcus faecalis/efeitos dos fármacos , Fusobacterium nucleatum/efeitos dos fármacos , Humanos , Teste de Materiais , Porphyromonas endodontalis/efeitos dos fármacos , Porphyromonas gingivalis/efeitos dos fármacos , Prevotella intermedia/efeitos dos fármacos , Irrigantes do Canal Radicular/administração & dosagem , Hipoclorito de Sódio/administração & dosagem , Staphylococcus aureus/efeitos dos fármacos , Fatores de TempoRESUMO
AIM: To evaluate the efficacy of 0.5%, 2.5% and 5.25% sodium hypochlorite (NaOCl) as intracanal irrigants associated with hand and rotary instrumentation techniques against Enterococcus faecalis within root canals and dentinal tubules. METHODOLOGY: A total of 180 extracted human premolar teeth were infected for 21 days with E. faecalis. The specimens were divided into 12 groups, as follows: group 1: 5.25% NaOCl + Hybrid technique (Valdrighi et al. 1998); group 2: 5.25% NaOCl + nickel-titanium (NiTi) rotary technique 4 mm shorter than the apex (by FOP-UNICAMP); group 3: 5, 25% NaOCl + NiTi rotary technique (Hero 642); group 4: 2.5% NaOCl +Hybrid technique; group 5: 2.5% NaOCl + NiTi rotary technique 4 mm shorter than the apex; group 6: 2.5% NaOCl + NiTi rotary technique (Hero 642); group 7: 0.5% NaOCl + Hybrid technique; group 8: 0.5% NaOCl + NiTi rotary technique 4 mm shorter than the apex; group 9: 0.5% NaOCl + NiTi rotary technique (Hero 642); group 10: sterile saline solution + Hybrid technique; group 11: sterile saline solution + NiTi rotary technique 4 mm shorter than the apex; group 12: sterile saline solution + NiTi rotary technique (Hero 642). Canals were sampled before and after preparation. After serial dilution, samples were plated onto brain heart infusion (BHI) agar, and the colony forming units (CFU) that were grown were counted. The teeth were sectioned into three thirds and dentine chips were removed from the canals with conical burs. The samples obtained with each bur were immediately collected into test tubes containing BHI broth, and were incubated at 37 degrees C and plated onto BHI agar. The CFU were counted and analysed. RESULTS: At all depths and thirds of the root canals and for all techniques used, 5.25% NaOCl was shown to be the most effective irrigant solution tested when dentinal tubules were analysed, followed by 2.5% NaOCl. No differences among concentrations in cleaning the canals were found. CONCLUSIONS: Especially at higher concentrations, NaOCl, was able to disinfect the dentinal tubules, independent of the canal preparation technique used.