1 / 17

Miscut: progress report

This progress report outlines recent results and future directions in the study of micro-structured LCMO (lanthanum calcium manganese oxide) on strontium titanate (STO) substrates. The report discusses the metal-insulator transition and the effects of strain on the transition temperature. It also examines the growth inhomogeneities at step edges and the possibility of electroresistance. Additionally, it explores the recovery of the insulating state of STO and the potential for restoring anisotropy.

dpark
Download Presentation

Miscut: progress report

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Miscut: progress report Christianne 12-03-07

  2. Outline • Manganites (very quick reminder) • Brief history • Microstructured LCMO • Recent results • Conclusions & Future

  3. Manganites LCMO / STO: t = 50 nm polaron hopping DE model • Manganites have a metal-insulator transition at TC • TC(~ 150 K) reduced due to strain (bulk LCMO ~ 270 K)

  4. Micro-structured LCMO (1) Goal: control film properties on nanometer scale by inducing local strain variations through unit-cell sized steps on STO substrate. AFM picture of 1.0°miscut substrate terminate layer TiO2 Step height ~ 0.4 nm Terrace length: 24 nm E-beam lithography: Measured transport properties with strip || and ┴ to step edges Bridge: 5 μm x 20 μm

  5. Micro-structured LCMO (2) Sample : L410, 10 nm LCMO on 1.0° STO Growth inhomogenieties at step edges? PPMS not a constant current measurement!

  6. Micro-structured LCMO (3) Sample : L410, 10 nm LCMO on 1.0° STO Sun et al., APL 2005 4-point measurement! Current processing Ar-etched STO 2-point measurement Kan et al.

  7. Unstructured LCMO (1) Sample : L434, 8 nm LCMO on 1.0° STO unstructured (wiresaw) No anisotropy: smaller roughness and/or larger sample size

  8. Unstructured LCMO (2) Sample : L434, 8 nm LCMO on 1.0° STO unstructured (wiresaw) 2-point measurement Asymmetry caused by Ar-etching Electroresistance?? Percolation paths between metallic regions Growing FM regions through polarized current Zhao et al APL 2005: (show ER in mA range)

  9. Questions • Can we restore insulating state of STO after Ar-etching? • Was the anisotropy intrinsic and can we get it back? • Is the nonlinearity of IV, “Electroresistance”, intrinsic?

  10. STO problem solved? Sample: L438, 8 nm LCMO on 0.859° STO + Reference structure Bridge: 5 μm x 20 μm Spacing: ~ 100 μm Etching time 30 sec, only 4 sec over-etched. Only part of the STO substrate became conducting, thickness gradient? After etching, 4 runs of 15 sec in O2 plasma (resist MaN-2405). After every run checked resist and resistance. From reference structure measurement: STO fully recovered!

  11. Transport properties (4-point) Sample: L438, 8 nm LCMO on 0.859° STO Strip || step edges No “Electroresistance”! Some Joule heating at higher T

  12. Transport properties (4-point) Sample: L438, 8 nm LCMO on 0.859° STO Strip ┴ step edges No “Electroresistance”! Some Joule heating at higher T

  13. 2-point vs. 4-point Sample: L438, 8 nm LCMO on 0.859° STO Strip ┴ step edges Resistance of 2-pt. order of magnitude higher → high contact resistance Resistance switching at high current; low R → high R Joule heating? “Electroresistance” feature of 2-point measurement → barrier at interface?

  14. Joule heating (1) Padhan et al., PRB 70,134403 (2004) • Heat dissipation sample • Thermal conduction of substrate = transport current = resistivity = cross section of sample (5•10-6 x 8•10-9 m2) = thermal conductivity STO substrate (16 W m-1 K-1)

  15. Joule heating (2) Sample: L438, 8 nm LCMO on 0.859° STO Strip ┴ step edges; T = 50 K 4 point measurement

  16. Joule heating (3) Sample: L438, 8 nm LCMO on 0.859° STO Strip ┴ step edges; T = 50 K 2-point measurement Joule-heating raises sample temperature above transition

  17. Conclusions & Future • We can recover insulating state of STO with O2 treatment. • Electroresistance might not be intrinsic to LCMO thin films • Current processing has no influence on I-V, Sun et al. • Measure 5 nm LCMO to reproduce recovery STO and maybe get anisotropy back

More Related