Local Potential at Atomically Abrupt Oxide Interfaces by Scanning Probe Microscopy
- PDF / 1,075,188 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 39 Downloads / 215 Views
ABSTRACT Electrostatic force microscopy and scanning surface potential microscopy are combined to quantify nanometer scale field variations in the vicinity of grain boundaries in donor doped 15 SrTiO 3 bicrystals. An analytical electrostatic model is used to develop a procedure for determining interface potential from measurements made above the surface. Grain boundary potentials and depletion widths determined by both techniques are in excellent agreement despite the fundamental difference in imaging mechanisms. The comparison confirms the analytical approach and illustrates use of scanning probes to image interface properties.
I. INTRODUCTION Perovskite-based oxide materials are widely used for many technical applications in conjunction with semiconductivel, ferroelectric2'3, superconductive , magnetoresistive 5 and other properties. The macroscopic properties of polycrystalline perovskite are largely determined by the microstructure, particularly by the grain boundary structure and topology; consequently, electro active grain boundaries in SrTiO 3 based oxides are the focus of much research. In the present paper the application of scanning probe microscopy techniques such as electrostatic force microscopy (EFM) and scanning surface potential microscopy (SSPM) to
quantification of grain boundary potential is described. First an analytical approach to SSPM and EFM contrast interpretation is described. The subsequent analysis of a SrTiO 3 X5 bicrystal grain boundary quantifies local interface potential and lateral depletion depth. II. THEORETICAL ANALYSIS OF IMAGE DATA The fact that scanning probes operate above a surface necessitates a correlation between the measurement and actualproperty at the surface. Extrapolations have been done based on assumptions of tip geometry ' and uniform surface properties or with numerical calculations Incorporating the actual tip shape and lateral property inhomogeneity is done here in two steps: the potential above the surface is calculated with the method of image chargesl' and an isopotential surface for the tip is determined with the line charge model. The grain boundary is characterized by an interface charge density, 07, an adjacent space charge layer of width d, and a volume charge density, Po. The potential above the surfaceinterface junction, i.e. the amplitude of potential profile is: 2 (1) + 21n(z)- ln(dk2 + Z2 Pre q'(z) = 0 +[1)[2(d - z arctan
j+dscZ(l
where 4o is the dielectric permittivity of vacuum, e is the dielectric constant of material, and z is the distance from surface. The potential amplitude at the grain boundary-surface junction 15
Mat. Res. Soc. Symp. Proc. Vol. 586 © 2000 Materials Research Society
(po = (p(O) = pod' /2eo(e + 1) is related to potential in the bulk as Oga
= 0o (e + 1)/e = 00 for
large e. Quantification of EFM force gradient data requires analysis of the grain boundary contribution to the EFM signal. The total electrostatic force between the biased tip and the surface, F(z), can be written as a sum of capacitive and Coulombic compon
Data Loading...
