Pyroelectric Electron Emission from Nanometer-Thick
Films of PbZrxTi1-xO3
Patrick C. Fletcher1, Vengadesh Kumara R. Mangalam2, Lane
W. Martin2, and William P. King1,2,a)
1
Department of Mechanical Science and Engineering, University of Illinois at UrbanaChampaign, Urbana, Illinois, 61801, USA
2
Department of Materials Science and Engineering and Materials Research Laboratory,
University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA
SUPPLEMENTARY INFORMATION
I. Steady State Temperature Dependence
We measured field emission current from nanometer-sharp tip arrays coated with 30 nm
thick films of epitaxial PbZr0.2Ti0.8O3 at elevated steady state temperatures. Figure S1 shows the
field emission current, IM, as a function of the anode voltage, VM, where the separation between
the anode and emitter cathode was 150 μm. A closed-loop electrical heater mounted beneath the
emitter cathode maintained thermal equilibrium during field emission experiments at
temperatures of 25 °C, 100 °C, 150 °C, 200 °C, and 250 °C. The good agreement between I–V
curves despite varying the temperature indicates that emission in the presence of an electric field
from pyroelectric PZT is not dependent on the absolute temperature of the film between
temperatures of 25–250 °C.
a)
Author to whom correspondence should be addressed. Electronic mail: wpk@illinois.edu; Telephone: +1-217-
244-3864
1
FIG. S1. Measured field emission current from tip emitters coated with a 30 nm PbZr0.2Ti0.8O3
film. The emitter chip temperature was constant during field emission testing.
II. Field Enhancement Factor
We experimentally determined the field enhancement factor for the nanometer-sharp tip
arrays coated with 30 nm thick PbZrxTi1-xO3 (PZT) by analyzing Fowler-Nordheim (F-N) type
plots of field emission current. The elementary F-N equation for large-area field emitters
(LAFEs) is

I M  aAM  1 2VM 2 d M  2 exp  b 3 / 2 d M / VM

(1)
where IM is the field emission current, a = 1.541×10-6 A eV V-2 and b = 6.831×109 eV-3/2 V m-1
are universal F-N constants, AM = 23.76 mm2 is the macroscopic emission area, ϕ is the emitter
work function, γ is the field enhancement factor, VM is the anode voltage, and dM = 150 μm is the
anode-cathode separation distance.1-3 This equation is commonly used to make comparisons
between LAFEs.
2
Figure S2 shows F-N plots of the field emission data, measured at room temperature,
from PbZr0.2Ti0.8O3 and PbZr0.8Ti0.2O3 emitters. The linear relationship between ln(IM/VM2) and
1000/VM for data at low electric field strengths confirms that electron emission is via field
emission. The slope (FNSL) and intercept (FNINT) of the F-N linear fits are given in Table S1
and are used to calculate the field enhancement factor. Using Eq. (1), the geometric field
enhancement factor for all the PZT emitters is
  (b 3 / 2 d M ) /( FNSL 103 )
(2)
where the FNSL is in units reported by Table S1. We calculated the work function of the PZT
films using Eq. (1) and emission data from a control sample of uncoated silicon emitter tips.
Details on this calculation can be found elsewhere.4 Since all the tip emitters have about the
same height and tip sharpness, we made the assumption that all the emitters have an identical
field enhancement factor. The field enhancement factor, γ, is calculated to be about 1526 from
the experimental field emission data. This is a large improvement over a flat surface of the same
material without tips, and is about 50 times larger than the theoretically calculated γ of 30.1. We
attribute this large field enhancement to the uniform tip morphology, uniform emitter spacing,
and 10–30 nm radius of the nanometer-sharp tips.
Table S1. Experimental field enhancement factor from Fowler-Nordheim analysis.
a
Tip
material
FNSL
(ln(A/V2)·V/1000)
FNINT
(ln(A/V2))
Field enhancement
factora , γ
PZT (20:80)
PZT (80:20)
-0.67
-9.5
-27.72
-25.02
1526.0
1526.0
γ = (-6.83089×109 V eV-3/2 m-1 × ϕ3/2 × dM) / (FNSL×103)
3
FIG. S2. Fowler-Nordheim (F-N) type plots of measured emission data taken at room
temperature. The F-N linear behavior at low electric field strengths confirms field emission.
Slopes of the linear fits are given in Table S1 and are used to calculate the field enhancement
factor, γ.
REFERENCES
1
R. H. Fowler and L. Nordheim, P. R. Soc. Lond. A-Conta. 119, 173 (1928).
2
E. L. Murphy and R. H. Good, Jr., Phys. Rev. 102, 1464 (1956).
3
K. L. Jensen, Advances in Imaging and Electron Physics, (Elsevier, 2007), pp. 1-46.
4
P. C. Fletcher, V. K. R. Mangalam, L. W. Martin, and W. P. King, J. Vac. Sci. Technol. B 31, 021805
(2013).
4