Abstract: A gallium nitride structure that includes: a substrate; a gallium nitride layer opposed to the substrate and containing gallium nitride as a main component thereof; and a first electrode between the gallium nitride layer and the substrate. The first electrode includes at least one hafnium layer containing a single metal of hafnium as a main component thereof, and the at least one hafnium layer is in contact with the gallium nitride layer.

Abstract: A piezoelectric thin film composed of aluminum nitride and which contains magnesium and 31 to 120 atomic percent of niobium relative to 100 atomic percent of the magnesium, and the total content of the magnesium and the niobium relative to the total sum of contents of the magnesium, the niobium and the aluminum nitride falls within the range of 10 to 67 atomic percent.

Abstract: A germanium-containing aluminum nitride piezoelectric film and a method for manufacturing an aluminum nitride piezoelectric film in which a germanium-containing aluminum nitride piezoelectric film is grown on a substrate by sputtering.

Abstract: A gallium nitride structure that includes: a substrate; a gallium nitride layer opposed to the substrate and containing gallium nitride as a main component thereof; and a first electrode between the gallium nitride layer and the substrate. The first electrode includes at least one hafnium layer containing a single metal of hafnium as a main component thereof, and the at least one hafnium layer is in contact with the gallium nitride layer.

Abstract: A piezoelectric thin film comprising aluminum nitride containing magnesium and hafnium, wherein a content of the hafnium based on 100 atomic % of the magnesium is 8 atomic % or more and less than 100 atomic %, and a total content of the magnesium and hafnium based on a sum of a content of the magnesium, hafnium, and aluminum is in a range of 47 atomic % or less.

Abstract: A germanium-containing aluminum nitride piezoelectric film and a method for manufacturing an aluminum nitride piezoelectric film in which a germanium-containing aluminum nitride piezoelectric film is grown on a substrate by sputtering.

Abstract: A piezoelectric thin film composed of aluminum nitride and which contains magnesium and 31 to 120 atomic percent of niobium relative to 100 atomic percent of the magnesium, and the total content of the magnesium and the niobium relative to the total sum of contents of the magnesium, the niobium and the aluminum nitride falls within the range of 10 to 67 atomic percent.

Abstract: A piezoelectric thin film comprising aluminum nitride containing magnesium and hafnium, wherein a content of the hafnium based on 100 atomic % of the magnesium is 8 atomic % or more and less than 100 atomic %, and a total content of the magnesium and hafnium based on a sum of a content of the magnesium, hafnium, and aluminum is in a range of 47 atomic % or less.

Abstract: An exhaust gas purification device for purifying exhaust gas of an engine, having an absorbent trapper absorptive of hydrocarbons in the exhaust gas up to a first gas temperature such as 200.degree. C. while releasing the absorbed hydrocarbons in the exhaust gas above a second gas temperature such as 400.degree. C., and a passage system responsive to the gas temperature for conducting the exhaust gas from the engine to pass through the absorbent trapper until the gas temperature rises up to the first gas temperate, to bypass the absorbent trapper when the gas temperature exceeds the first gas temperature, and to pass through the absorbent trapper and the catalytic converter in this order when the gas temperature exceeds the second gas temperature.