All‐Oxide Crystalline Microelectromechanical Systems: Bending the Functionalities of Transition‐Metal Oxide Thin Films

Abstract

Transition-Metal Oxides (TMO) are of great technological impact due to the numerous properties they exhibit, like superconductivity, ferroelectricity and piezoelectricity, dielectricity, semiconductivity, orbital and spin ordered phases, and fully spin-polarized current. Their rich phase diagrams are determined by coupling of spin, charge, and lattice degrees of freedom, whose interplay can be modified by doping, external fields and lattice strain. In TMO, the transition-metal d-orbitals play the game; as a consequence of the strong local interactions, the phase diagrams strongly depend on the overlapping, the occupancy, and the fluctuations of the atomic orbitals.[1] In this scenario, lattice strain is one of the most powerful parameters to achieve control of TMO functionalities. Biaxial strains up to a few percent have been achieved on TMO thin films by changing the substrate lattice constant or by chemical doping, triggering phase transitions and modulating transition temperatures. [2][3][4][5][6][7][8][9] The real contribution of strain is often hindered by spurious effects arising from the growth mechanisms, and is not reversible. [10,11] In order to clarify these issues and move toward applications, active modulation of strain in crystalline TMOs thin films has been achieved by mechanical apparata [12] or by epitaxial locking with ferropiezoelectric substrates [13][14][15][16][17][18] or thin films. [19,20] The maximum attained voltage-assisted biaxial in-plane strain modulation, mainly compressive, is currently limited to about À0.25%. [21] Different approaches for strain manipulation of oxides also exploit the mechanical coupling between oxide nanocomposites [22,23] or the bending of oxide nanobeams and nanowires. [24,25] Nevertheless, bending of thin epitaxial TMO films is still an unexplored terrain. The objective of this work is to produce strain on TMO films by combining crystalline TMO thin films with microelectromechanical systems (MEMS) concepts. In particular, we show a MEMS device that employs mechanical deformations to induce tensile strain on a functional oxide film. So far, despite the enormous strategic interest of smart devices, few works on functional oxide MEMS and free-standing oxide structures have been reported, [26][27][28][29][30] mainly for applications as bolometers, mostly grown on buffer silicon substrates. Employment of piezoelectric ZnO or ferroelectric Pb(Zr 1 Ti)O 3 films for sensing or actuation of silicon cantilevers for atomic force microscopy (AFM) [31] and resistive strain gauges based on polycrystalline binary oxide films have been also reported.[32]Here, we show micro-electromechanical structures entirely based on crystalline perovskites that can be employed as ''strain-generator devices'' for a wide class of epitaxial oxide films. A crystalline suspended bridge of the most common substrate for TMOs deposition, SrTiO 3 (STO), is used as flexible substrate for the deposition of functional epitaxial TMO thin films. This element is bent both mechanically by an AFM tip and...

Ramp‐Reversal Memory and Phase‐Boundary Scarring in Transition Metal Oxides

“…The effect of strain fields can result in an increased TC of the boundaries. [24,38,39] The width of the scarred phaseboundary must be smaller than the size of the phase-separated regions, which may be a number of nanometers in our TMOs. [8,11] In principle the scarred phase boundaries may be only a few unit-cells wide.…”

Nanopatterning of carbonaceous structures by field-induced carbon dioxide splitting with a force microscope

“…[1][2][3][4] This method is based on the field-induced activation of molecules within a water meniscus and the subsequent oxidation of the sample surface. [5][6][7] Local oxidation nanolithography has been applied to fabricate nanoscale electronic devices, 8,9 microelectromechanical systems 10 or templates for the direct growth of single-molecule magnets 11 or metallic nanoparticles. 12,13 Local oxidation is compatible with imprinting techniques, thus enables the patterning of large areas has been demonstrated.…”

Nanoscale space charge generation in local oxidation nanolithography

“…Thus, templates to build molecular architectures, 6,7 resist masks, 8 nanomechanical resonators, 9,10 or several nanoelectronic devices and transistors [11][12][13][14] have been fabricated by local oxidation. In AFM oxidation, the tip is used as a cathode and the water meniscus formed between the tip and the surface is the source of the oxyanions species.…”