Approaching the high intrinsic electrical resistivity of NbO2 in epitaxially grown films

Abstract

NbO2 is a promising candidate for resistive switching devices due to an insulator-metal transition above room temperature, which is related to a phase transition from a distorted rutile structure to undistorted one. However, the electrical resistivity of the NbO2 thin-films produced so far has been too low to achieve high on-off switching ratios. Here we report on the structural, electrical and optical characterization of single-crystalline NbO2 (001) thin-films grown by pulsed laser deposition on MgF2 (001) substrates. An annealing step reduced the full width at half maximum of the NbO2 (004) X-ray Bragg reflection by one order of magnitude, while the electrical resistivity of the films increased by two orders of magnitude to about 1 kΩcm at room-temperature. Temperature dependent resistivity measurements of an annealed sample revealed that below 650 K two deep-level defects with activation energies of 0.25 eV and 0.37 eV dominate the conduction, while above 650 K intrinsic conduction prevails. Optical characterization by spectroscopic ellipsometry and by absorption measurements with the electric field vector of the incident light perpendicular to the c-axis of the distorted rutile structure indicates the onset of fundamental absorption at about 0.76 eV at room temperature, while at 4 K the onset shifts to 0.85 eV. These optical transitions are interpreted to take place across the theoretically predicted indirect band gap of distorted rutile NbO2.

Morphological Control: Properties and Applications of Metal Nanostructures

“…Anodic aluminum oxide porous membranes with regular hexagonal pores have higher chemical and thermal stability and are therefore commonly used as a hard mold for the synthesis of metal nanowires [84,85]. Also, the porosity density in these structures reaches 10 11 holes per square centimeter [12,13].…”

“…ese plasmatic interactions can be controlled by changing the morphology and dimensions of metal nanostructures [8][9][10]. Applications related to the field of nanoplasmatic include super lenses, Raman-enhanced surface spectroscopy (SERS), molecular spectroscopy, plasmonic-enhanced fluorescence, quantum computing, energy-dependent photochemical lithography, energy-assisted plasma ionization [11][12][13][14][15]. Silver is more than 50 times cheaper than gold, and because of its unique physicochemical properties, it is a good choice for use in plasmatic applications [16][17][18].…”

Reciprocal space slicing: A time-efficient approach to femtosecond x-ray diffraction

“…AFM measurements of the surface support this interpretation by revealing domains at the nanometer length scale. 20 Since the x-ray probe spot on the specimen measures tens to hundreds of micrometers in both directions, the signal of the diffracted intensity is a lateral average of the domains and thus, contains both contributions.…”

“…With both setups, we demonstrate the slicing by examination of a sample fabricated by pulsed laser deposition a thin layer of NbO 2 on top of a TiO 2 substrate. 20 NbO 2 exhibits an insulator-metal phase transition, accompanied by a transition in the crystalline ordering at 1070 K. 21 This renders NbO 2 and its alloys a promising material class for electrical switching and even memory applications at high temperatures. 22–24 Future ultrafast strain assessment during the phase transition using UXRD may reveal novel insight into the transition and promote application development in electronics, complementing all-optical studies.…”

Optical Properties of Porous Alumina Assisted Niobia Nanostructured Films–Designing 2-D Photonic Crystals Based on Hexagonally Arranged Nanocolumns

“…The optical, structural, and electrochromic properties of the different crystalline polymorphic forms of the niobia films make them attractive for optical applications [ 19 , 20 ]. There are various methods for the oxide materials synthesis, in particular, alumina and niobia: the metal thermal oxidation with oxygen to obtain an oxide in the highest oxidation state [ 18 , 21 ] and metal subsequent sintering (sinter) with higher oxide in vacuum in required proportion to obtain oxides in an intermediate oxidation state [ 20 ], spray pyrolysis deposition [ 22 , 23 ], atomic-layer deposition [ 24 , 25 ], and plasma-enhanced atomic layer deposition [ 26 ], magnetron sputtering technique [ 18 , 27 , 28 , 29 ], and reactive magnetron sputter process [ 30 ], chemical precipitation from solution [ 18 , 31 ], the controlled precipitation method [ 16 ], sol-gel method [ 4 , 10 , 18 , 32 , 33 ], polymeric precursors (Pechini) method [ 32 ], hydro-thermal (in water) and solvothermal (in other solvents such as acetone and isopropyl alcohol) synthesis techniques [ 18 ], extraction from natural minerals [ 4 ], chemical vapor deposition [ 19 , 34 ], and plasma-enhanced chemical vapor deposition [ 35 ], pulsed laser deposition [ 36 , 37 , 38 ], electron beam evaporation [ 22 ], molecular beam epitaxy [ 39 ], electrodeposition [ 18 ].…”