Crecimiento y caracterización de películas delgadas de V6 O13 por Sputtering Magnetron dc

Se reporta el crecimiento de películas delgadas de óxido de vanadio V6 O13 en fase pura sobre substratos amorfos, por la técnica de deposición sputtering reactivo con magnetrón dc. El estudio a partir de películas delgadas de este material ha tomado mucha importancia por sus propiedades electrocrómicas y su potencial uso como interruptores ópticos. Estudios de difracción de rayos x demostraron que las películas de V6O13 están altamente orientadas en la dirección (00l) . Las películas se lograron crecer bajo una atmósfera de oxígeno y argón con presión parcial de 0.8mTorr y 5.1mTorr respectivamente, y a una temperatura de substrato de 400ºC. Las películas fueron caracterizadas por sus propiedades ópticas a partir de medidas de transmitancia en el rango de luz visible y ultravioleta, así como por sus propiedades eléctricas midiéndose el cambio de resistencia en función de la temperatura. Reportamos el comportamiento que exhiben las películas de V6 O13 en radiación de largo de onda del IR. Las medidas de transmisión se hicieron en un rango de temperatura de 4 K a 180 K, rango en el cual el material experimenta cambio de fases de metálico. El estudio topográfico se hizo con microscopio fuerza atómica (AFM). A partir de los espectros de transmitancia en el rango de luz visible y ultravioleta se estimó en 2.75eV el ancho de banda prohibida del V6 O13, resultado que está dentro del rango de valores estimado para este material.Abstract: We report the growing of thin films of pure vanadium oxide V6 O13 on amorphous substrates, using the reactive sputtering technique with dc magnetron. The study of these thin films has become relevant due to their electrocromic properties and their potential to be used as optical switches. X rays diffraction studies showed that the thin films are highly oriented in the direction. They were grown under an oxygen and argon atmosphere and with a partial pressure of 0.8 mTorr and 5.1 mTorr respectively while the temperature was kept at 400 ºC. Optical properties of the thin films were studied measuring transmission in the visible light and ultraviolet ranges. Additional, electrical measurements of the resistance as a function of the temperature were obtained. We report the behavior that this films exhibit in the IR wavelength range. The transmission data was gathered in the temperature range of 4 to 180K, values within the material experiences a phase change. The topographic study was done with atomic force microscope (AFM). From the transmission spectra in the visible Light and ultraviolet range a energy gap of 2.75 eV was determined for the films, result that is in agreement with the known values for this material

Large non-thermal contribution to picosecond strain pulse generation using the photo-induced phase transition in VO2

Picosecond strain pulses are a versatile tool for investigation of mechanical properties of meso-and nano-scale objects with high temporal and spatial resolutions. Generation of such pulses is traditionally realized via ultrafast laser excitation of a light-to-strain transducer involving thermoelastic, deformation potential, or inverse piezoelectric effects. These approaches unavoidably lead to heat dissipation and a temperature rise, which can modify delicate specimens, like biological tissues, and ultimately destroy the transducer itself limiting the amplitude of generated picosecond strain. Here we propose a novel non-thermal mechanism for generating picosecond strain pulses via ultrafast photo-induced first-order phase transitions (PIPTs). We perform experiments on vanadium dioxide VO2 films, which exhibit a first-order PIPT accompanied by a lattice change. We demonstrate that during femtosecond optical excitation of VO2 the PIPT alone contributes to ultrafast expansion of this material as large as 0.45%, which is not accompanied by heat dissipation, and, for excitation density of 8 mJ cm-2 , exceeds the contribution from thermoelastic effect by the factor of five.