Bio-inspired Materials Research for Improved 

Sensitivity Low-cost Uncooled Infrared (IR) 

Detector Focal-plane Arrays

by Wendy L. Sarney, John W. Little, Frank E. Livingston, Melanie W. Cole, 

Krisztian Niesz, Teyeb Ould-Ely, and Daniel E. Morse

ARL-TR-5172 April 2010

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Army Research Laboratory

Adelphi, MD 20783-1197

ARL-TR-5172 April 2010

Bio-inspired Materials Research for Improved 

Sensitivity Low-cost Uncooled Infrared (IR) 

Detector Focal-plan Arrays

Wendy L. Sarney and John W. Little

Sensors and Electron Devices Directorate, ARL

Frank E. Livingston

The Aerospace Corporation

El Segundo, CA 90345

Melanie W. Cole

Weapons and Materials Research Directorate, ARL

and

Daniel E. Morse, Krisztian Niesz, and Teyeb Ould-Ely

Institute for Collaborative Biotechnologies

University of California Santa Barbara

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Bio-inspired Materials Research for Improved Sensitivity Low-cost Uncooled 

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Wendy L. Sarney, John W. Little, Frank E. Livingston, Melanie W. Cole, 

Krisztian Niesz, Teyeb Ould-Ely, and Daniel E. Morse

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14. ABSTRACT

This report describes the highlights of progress made for the 6.2 project “Improved Sensitivity Low-Cost Uncooled IR Detector 

Focal-Plane Arrays” during the February–April 2009 time period. The program goals corresponded to the continued expansion 

of our BaTiO3 nanomaterial synthesis capabilities and deposition methods, laser-induced pyroelectric phase conversion studies 

and spectroscopic end-point control scheme, and comprehensive material characterization studies. The Aerospace Corporation

investigated the laser-induced phase conversion of functionalized thin-films from the pryoelectrically-inactive cubic polymorph 

to the pyroelectrically-active tetragonal polymorph. The Institute for Collaborative Biotechnologies (ICB) pursued further 

refinements in the vapor diffusion reactor design. Efforts also focused on the extension of the thin-film methods for the 

deposition of smooth, high quality functionalized nanoparticles over a range of thicknesses and nanoparticle densities. ARL 

investigated the application of various binders for the preparation of thin-films. Efforts also focused on the experimental design 

and instrumentation required for the pyroelectric capacitance measurements and electrical property analysis on both laseractivated and oven-processed thin-films.

15. SUBJECT TERMS

Biologically inspired, uncooled infrared, laser processing, low temperature growth

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Wendy L. Sarney

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iii

Contents 

List of Figures iv

List of Tables iv

Acknowledgments v

1. Introduction 1

2. Progress by The Aerospace Corporation 2

2.1 Analysis of Functionalized BaTiO3 Thin Films ..............................................................2

2.2 New Dual-beam SHG Experimental Setup and Methodology ........................................3

2.3 Piezoresponse Force Microscopy (PFM) Analysis of Ferroelectric Thin-films .............4

3. Progress by the Institute for Collaborative Biotechnologies (ICB) 5

3.1 Significantly Increased Throughput Synthesis of BaTiO3 Nanoparticles .......................5

3.2 Preparation and Characterization of Uniform BaTiO3 Nanoparticulate Thin-films, 

and Provision to Our Partners at ARL and The Aerospace Corporation ........................7

4. Progress by the U.S. Army Research Laboratory (ARL) 8

4.1 Preparation for Pyroelectric Parameter Measurements ...................................................8

4.2 Thin-film Studies ...........................................................................................................10

5. Plans and Goals for Year 2 Quarter 1 11

6. References 12

List of Symbols, Abbreviations, and Acronyms 13

Distribution List 14 
iv

List of Figures

Figure 1. Piezoelectric force microscopy results measured for a surface-modified lithium 

niobate single crystal. (a) Phase signal versus scanning distance. (b) 3-D map of 

piezoelectric moments that are aligned normal to the surface...................................................5

Figure 2. (a) Acceleration of synthesis throughput by sonication and vapor droplet collision. 

(b) XRD spectrum of the final product, showing high crystallinity of ca. 6 nm cubic 

barium titanate. (c) TEM image of the final product. (d) High resolution TEM image of 

the final product, showing crystallographic lattices. .................................................................7

Figure 3. Schematic representation of the test station that will be used for the pyroelectric 

coefficient measurements in pyroelectric thin-films.................................................................9

List of Tables

Table 1. Additional pyroelectric equipment to be procured. .........................................................10
v

Acknowledgments

We acknowledge support by the Institute for Collaborative Biotechnologies through grant 

DAAD19-03-D-0004 from the U.S. Army Research Office and The Aerospace Corporation 

Independent Research and Development (IR&D) Program and the Product and Development 

(PDP) Program.
vi

INTENTIONALLY LEFT BLANK.
1

1. Introduction

This report describes the highlights and summary of the year one, quarter four (Y1Q4) progress 

for the 6.2 project “Improved Sensitivity Low-Cost Uncooled IR Detector Focal-Plane Arrays.”

This work occurred during the February–April 2009 time period. A description of the 

background technical information and earlier progress is discussed in prior technical reports (1–

2).

The program goals for Y1Q4 corresponded to the continued expansion of our Barium Titanium 

Oxide (BaTiO3) nanomaterial synthesis capabilities and deposition methods, laser-induced 

pyroelectric phase conversion studies and spectroscopic end-point control scheme, and 

comprehensive material characterization studies. The respective team tasks included:

Aerospace: Conducted further investigations into the laser-induced phase conversion of Institute 

for Collaborative Biotechnology (ICB)-provided functionalized BaTiO3 thin-films from the 

pryoelectrically-inactive cubic polymorph to the pyroelectrically-active tetragonal polymorph. 

Efforts also focused on the development of a new dual-beam second harmonic generation (SHG) 

setup that permits phase conversion analysis during both static laser exposures and laser raster 

patterning, along with the continued implementation of piezoelectric force microscopy (PFM) 

techniques for pyroelectric/ferroelectric phase contrast studies.

ICB: Pursued further refinements in the vapor diffusion reactor design to permit the more rapid 

and large-scale synthesis of 100-g batches of BaTiO3 nanoparticles with high quality and 

crystallinity in 24–48 h. Efforts also focused on the extension of the thin-film methods for the 

deposition of smooth, high quality functionalized BaTiO3 nanoparticles over a range of 

thicknesses from the monolayer to several microns, and over a range of nanoparticle densities. 

ARL: Investigated the application of various binders such as polyvinyl alcohol (PVA) for the 

preparation of high quality BaTiO3 thin-films using the bio-inspired perovskite nanoparticles 

synthesized by the ICB. Efforts also focused on the experimental design and instrumentation 

required for the pyroelectric capacitance measurements and electrical property analysis on both 

laser-activated and oven-processed BaTiO3 thin-films.

All project teams have accomplished their respective planned milestones for Y1Q4, and 

highlights of the major activities are provided in this report.
2

2. Progress by The Aerospace Corporation

2.1 Analysis of functionalized BaTiO3 thin films

During the fourth quarter, The Aerospace Corporation received two sets of functionalized 

BaTiO3 thin films from our ICB collaborators that were prepared via layer-by-layer spin coating. 

The BaTiO3 nanoparticles were pre-functionalized with oleic acid and dispersed in a hexane 

colloidal solution for eventual spin coating on optical quality quartz substrates. One set of 

samples remained un-annealed, while the companion sample set underwent annealing at 400 °C 

for 1 h as described in section 3.2. The as-received BaTiO3 thin-films were of impressive and 

uniform quality, and profilometry measurements by the ICB team revealed film thicknesses of 

approximately 330 nm and 380 nm for the un-annealed and annealed samples, respectively. Our 

optical transmission measurements revealed that the fluctuations in the band gap energies that 

were observed previously with unfunctionalized BaTiO3 nanoparticle thin films have been 

notably reduced, and light scattering during laser processing has been decreased as well. X-ray 

diffraction (XRD) measurements indicated that the films comprised amorphous barium titanate 

with no evidence of crystalline cubic domains. The complementary Raman spectra, however,

were essentially featureless and were consistent with cubic phase BaTiO3 as expected. While the 

band gap energy fluctuations have been reduced, the absolute band gap energy for the 

functionalized BaTiO3 thin-films is appreciably blue-shifted compared with the band gap energy 

for the unfunctionalized BaTiO3 thin-films; first-derivative analysis of the absorption spectra for 

the functionalized thin-films yielded band gap energies that ranged from E=4.02 eV to |E=4.15 

eV (300-309 nm), while for the unfunctionalized thin-films the band gap energies ranged from 

E=3.82 eV to E=4.03 eV (308–325 nm). Interband transitions in the functionalized BaTiO3 thinfilms now occur at wavelengths of less than 360 nm, and the percent transmission remains quite 

high (approximately 90%) at our current laser processing wavelength of λ = 355 nm. 

Consequently, the laser phase conversion efficiency at our current exposure wavelength of λ = 

355 nm will be significantly diminished and more of the incident energy will be lost to the 

underlying substrate due to transmission; this effect depends greatly on whether the phase 

conversion process retains a single- or multiple-photon dependence, and we are currently 

exploring the linear and non-linear behavior of the photo-induced phase conversion process. To 

enhance the laser-induced conversion efficiency and help mitigate any potential problems 

associated with the increased transparency of the functionalized BaTiO3 films, we intend to 

investigate and implement several strategies:

• Examine the laser-induced direct-write phase conversion using laser irradiation at 

wavelengths of λ=250–290 nm, where the percent transmission is only approximately 30–

35%. With adaptations to our current laser systems and optical configurations, we can 

examine laser phase conversion under a wide range of wavelengths (250–1100 nm), along 
3

with variations in pulse length (100 fs–5 ns) and pulse repetition rate conditions (5 kHz–

80 MHz).

• Explore the use of photosensitizers and dopants to red-shift the band gap energy and 

enhance photo-absorption in select wavelength regions that correspond to practical 

harmonic wavelengths and common commercial laser systems. The ICB team has had prior 

success in doping metal oxide nanoparticles (e.g., lanthanum, samarium, bismuth and 

manganese), and together we will work closely to establish the doping protocol and 

spectral characteristics required to optimize the pyroelectric phase conversion efficiency. 

We will also consult with our U.S. Army Research Laboratory (ARL) collaborators to 

ensure that the doped thin-films retain the appropriate infrared (IR) responsiveness and 

electrical properties.

• Investigate the capability of using the IR absorbing overlayer on the BaTiO3 thin-film to 

resonantly capture the laser energy for pyroelectric phase transformation. This capability 

may facilitate enhancements to the IR photosensitizer layer, and permit the formation of IR 

absorbing layer patterns and pyroelectric phase domains that are in-registry for improved 

resolution.

• Other plans include the use of thicker, micron-sized BaTiO3 thin-films to exploit the 1/e 

fall-off in the optical penetration depth of the laser irradiation, along with the potential 

implementation of a non-intrusive, benign reflective interlayer located between the BaTiO3

nanoparticle thin-film and silicon substrate to improve localization of laser energy in the 

perovskite thin-film and further protect the underlying substrate.

2.2 New Dual-beam SHG Experimental Setup and Methodology

Our fourth quarter efforts have also focused on a new experimental design and setup for 

additional SHG studies of the laser-induced pyroelectric phase transformation process. During 

past quarters, we have designed and developed an in situ pump-probe SHG spectroscopic 

detection scheme for dynamic, real time monitoring of the pyroelectric phase conversion during 

laser patterning. The intent is to use the SHG activity associated with the non-centrosymmetric 

tetragonal polymorph to assess the extent of phase conversion from the SHG-inactive 

centrosymmetric cubic polymorph.

The new dual-beam experimental design permits additional and complementary SHG analysis 

under static laser exposure conditions. The ultraviolet (UV) laser processing beam (e.g. λ =355 

nm) and IR SHG pump-beam (e.g., λ = 1064 nm) are concurrently delivered to the BaTiO3 thinfilm. The laser processing and pump beams are aligned in a collinear fashion, and the BaTiO3

sample is positioned in a vertical manner. Consequently, the SHG signal (λ=532 nm) can be 

measured in a transmission mode configuration, where the pump laser beam and the SHG light 

are propagating in the same direction; this feature is particularly useful for SHG analysis on ultra 

thin films where high transparency and minimal surface scattering exist. If desired, the UV laser 
4

processing beam and IR SHG pump-beam can be simultaneously delivered to a substrate under 

dynamic patterning conditions and a substrate under static exposure conditions. These 

modifications to the optical configuration allow the UV laser processing beam to be derived from 

either the electro-optic modulator or directly from the laser cavity. The incident IR pump-beam 

power is modulated using a zero-order half-wave plate in combination with a Glan-Taylor 

polarizer. This design facilitates examination of the polarization-dependent behavior of the SHG 

process. The emitted SHG light is focused into a polarization maintaining fiber bundle, guided 

into a custom-designed in-line filter assembly for laserline extraction and subsequently delivered 

to the entrance slit of an ultra fast gated charge-coupled device (CCD) coupled to an Acton 300i 

spectrometer for spectroscopic analysis. In addition, under static exposure conditions, we can 

more easily measure the time dependent evolution of the SHG signal on a pulse-by-pulse and 

dose-by-dose basis using uniform intensity modulation or genotype-scripted modulation. The 

static exposure-SHG detection capability will help to determine the absolute total energy that is 

required for laser-induced pyroelectric phase conversion, and permit more rapid assessment of 

whether certain laser pulse scripts can successfully induce phase transformation. These laser 

pulse scripts correspond to “locally” optimized pulse scripts that can be used as first-generation 

scripts for future incorporation into the evolutionary algorithm approach to laser-induced 

transformation control and the eventual determination of the “globally” optimized pulse script.

2.3 Piezoresponse Force Microscopy (PFM) Analysis of Ferroelectric Thin-films

We are continuing to explore and develop the use of scanning PFM techniques for 

complementary nanoscale analysis of the laser-induced BaTiO3 phase conversion. PFM permits 

direct imaging of ferroelectric domain structures with nanometer-scale resolution (~3–10 nm), 

and is ideally suited for post-processing examination of the BaTiO3 thin-films due to its relative 

insensitivity to topography and ease of implementation. Traditional atomic force microscopy 

(AFM) instruments can be augmented and tailored for specific operational modes like PFM, 

where the mechanical response of the sample is measured during local electrical excitation by the 

AFM probe tip. A modulated ac voltage is applied between the underlying substrate and

conductive AFM/PFM tip during contact mode scanning. Using lock-in amplifier techniques, the 

local electromechanical displacement can be decoupled from the topographical displacement via 

the phase shift between the rapidly oscillating ac field and the slow cantilever displacement 

feedback. The static cantilever deflection corresponds to the surface profile variations and 

topography, while the modulated cantilever oscillations are related to the piezoelectric response 

of the sample.

As discussed in our prior report (2), we intend to develop several new PFM and laser processing 

approaches to facilitate ferroelectric phase contrast detection in nanostructured perovskite thinfilms, including spectroscopy mode operation, localized poling of BaTiO3 nanoparticles and 

dynamic polarization control during laser irradiation. During the fourth quarter, we have 

specifically developed and tested a dual lock-in amplifier mode PFM approach on several model 

pyroelectric and ferroelectric materials. We have successfully implemented dual lock-in 
5

amplifier assemblies to acquire simultaneous phase-difference (i.e., tip vibration signal vs. 

reference ac modulation signal) data corresponding to out-of-plane distortions where the 

polarization is normal to the surface, and in-plane lateral distortions where the polarization is 

parallel to the surface.

Figure 1 shows PFM piezoelectric phase contrast results measured for a Lithium Niobate 

(LiNbO3) sample. The example shown here corresponds to single crystal LiNbO3 that has 

undergone recrystallization and hexagonal-to-trigonal phase conversion in the surface layer via 

chemical-induced surface restructuring. The phase signal profile is displayed in the left panel in 

figure 1a and reveals that the PFM phase contrast is increased as the probe tip comes into contact 

with piezoelectric domains on the LiNbO3 surface. By scanning the sample surface and 

measuring the amplitude and phase signals, a 3-D map can be generated which corresponds to 

the piezoelectric moments that are oriented normal to the surface. The piezoelectric domains are 

readily identified by the bright field contrast in the right panel in figure 1a, where the 

piezoelectric regions correspond to the gold color and the non-piezoelectric domains appear as a 

dark brown color.

In the coming quarters we will examine the pyroelectric/ferroelectric phase contrast in 

standardized sets of nanostructured barium titanate thin-films under a wide range of preparation 

(film thickness and functionalization) and processing (as-prepared, furnace heated and laserexposed) conditions.

Figure 1. Piezoelectric force microscopy results measured for a surface-modified 

lithium niobate single crystal. (a) Phase signal versus scanning distance. 

(b) 3-D map of piezoelectric moments that are aligned normal to the surface.

3. Progress by the Institute for Collaborative Biotechnologies (ICB)

3.1 Significantly Increased Throughput Synthesis of BaTiO3 Nanoparticles

By the end of the third quarter of year 1, we had successfully designed, optimized and used 

reactors to increase the scale of synthesis of BaTiO3 nanoparticles to the 100-gram scale. This 

represented a 100-fold increase in the scale of synthesis from the start of the project, using a 

single-source bimetallic alkoxide with our bio-inspired, vapor diffusion catalysis method to 
6

produce 6-nm single-crystal BaTiO3 nanoparticles at very low temperatures and in virtually 

quantitative yield. However, throughput was still relatively low, as the total synthesis time 

required was several days. In this final quarter of year 1, we report a breakthrough in which 

sonication and reaction by vapor-droplet collision are used to accelerate synthesis kinetics to 

permit significant increase in throughput.

We found that we can significantly accelerate the kinetics and throughput of synthesis by a 

combination of sonication and vapor-droplet collision, as described here: concentrations of 

catalyst (water/HCl) and precursor (the bimetallic alkoxide) were as previously described, but 

the two solutions were placed in separate wells of a double well reactor (figure 2) and positioned 

in an ultrasonicator bath operated at 40 kHz. A stream of pure N2 carrier gas at low flow-rate was 

used to drive vapor droplets of the water/acid catalyst over the well containing the BaTi(OR)x 

precursor and to remove the product. The resulting combination of sonication and vapor droplet 

collision significantly accelerated synthesis without affecting the size, crystallinity, high quality 

and virtually quantitative yield of the final product. As an example, 3.6 grams of high quality, 

phase-pure, cubic BaTiO3 nanoparticles were produced within 6 h, including the drying process, 

in contrast to the previously reported time requiring 2 days. We believe that this new method for 

accelerating throughput of synthesis offers several advantages that we will use in designing a 

continuous flow reactor for future scale up of production:

1) Sonication produces small vapor droplets with high surface area and high surface energy; 

sonication also increases evaporation of the solvent, increasing the precursor concentration 

in the reactive droplets;

2) Collision between the highly reactive vapor droplets containing the catalyst (H2O/HCl) and 

those containing the precursor results in rapid hydrolysis and polycondensation to form the 

initial product;

3) Sonication also may accelerate dehydration and crystallization by producing local, 

microscopic hot spots in the liquid.
7

Figure 2. (a) Acceleration of synthesis throughput by sonication and vapor droplet 

collision. (b) XRD spectrum of the final product, showing high crystallinity 

of ca. 6 nm cubic barium titanate. (c) TEM image of the final product. 

(d) High resolution TEM image of the final product, showing 

crystallographic lattices.

3.2 Preparation and Characterization of Uniform BaTiO3 Nanoparticulate Thin-films, 

and Provision to Our Partners at ARL and The Aerospace Corporation

As described at the end of quarter 3, we found that functionalization of the BaTiO3 nanoparticles 

with simple linear organic carboxylic acids, such as oleic acid, provides sufficient Coulombic 

repulsion to prevent aggregation of the particles, permitting complete solubilization in organic 

solvents from which we are able to spin-cast uniform, well-dispersed thin films. We 

characterized the smoothness and uniformity of these films by SEM and cross-sectional TEM, 

profilometry and atomic force microscopy, and provided these films to our partners at ARL and 

The Aerospace Corporation.

Functionalization of the BaTiO3 nanoparticles with oleic acid prevents aggregation of the 

particles, permitting complete solubilization in hexane and similar organic solvents. Uniform, 

well-dispersed films were produced from these solutions by spin-casting on silicon and quartz 

silica. Analyses by SEM and cross-sectional TEM, profilometry and atomic force microscopy 

quantified the smoothness and high density of these films. The absence of cracks in these films 

and their high smoothness confirms the importance of stabilization and dispersion of the 

nanoparticles with surface functionalities compatible with volatile organic solvents.

Two kinds of samples were prepared and sent to The Aerospace Corporation for investigation of 

laser-induced site selective phase transformation in comparison to the results of bulk-heating. 

The first set comprised films produced by layer-by-layer spin coating of pre-functionalized 

BaTiO3 nanoparticles from hexane colloidal solution onto quartz or silicon substrates. The 

second set was identical but annealed at 400 oC for 1 h under air at 2 oC/min heating and cooling 

rates. Measurements by optical profilometry show that layer-by-layer spin coating did not 
8

significantly increase film thickness beyond the first layer; however, annealing consistently 

produced thicker films (~380 nm) than the identical films without heating (~330 nm). This 

observation remains to be explained, and will be investigated in depth in the next quarter.

Samples of the unfunctionalized nanoparticles (as-prepared) also were sent to ARL, for 

investigation of alternative routes to processing for IR detection. Results will be compared to 

those obtained with the thin films described above.

4. Progress by the U.S. Army Research Laboratory (ARL)

4.1 Preparation for Pyroelectric Parameter Measurements

In order to progress with our strategy for using the laser-processed, bio-inspired BaTiO3 thin 

films for uncooled IR detectors applications, we must be characterize the pyroelectric properties 

of the post laser-induced phase transformed films. We are preparing to do these measurements 

and have begun the approval and the procurement process for obtaining the needed 

instrumentation. We will leverage the perovskite thin film research already in progress at the 

Weapons and Materials Research Directorate of ARL. This group already possesses the expertise 

and majority of the instrumentation, consisting of $150K of dielectric measurement 

instrumentation in-house and working, to accomplish most of the dielectric measurements 

required to evaluate the figure of merit (FoM) for pyroelectric uncooled detectors. An additional 

$16K of instrumentation is required as an add-on to the existing equipment in order to measure 

the pyroelectric coefficient, and we have secured the needed approvals for cost sharing between 

SEDD and WMRD to procure this equipment, and the procurement is now awaiting action by the 

Army’s contracts department.

Several figures of merit have been developed to assess the performance of pyroelectric materials 

for use in thermal detectors. The detection limit of a pyroelectric based detector is limited by the 

thermal noise (Johnson noise) generated in the capacitor elements (3). Therefore, a useful figure 

of merit that weighs the material properties for optimal signal-to-noise ratio is given by: FD

=(p/cv)(εoεr tan δ)

–1/2, where p is the pyroelectric coefficient (representing the amount of electrical 

current that can be generated per temperature change), cv the volume specific heat capacity, εo the 

permittivity of vacuum, εr the relative permittivity and tan δ the dielectric loss (which represent 

the amount of dielectric noise present in the material during modulation). Since both ε and tan δ 

have a strong dependence on frequency, these properties are measured at the frequency range of 

the detector. For bulk detectors, the FD are usually divided by the specific heat of the material, 

but for thin-film detectors it is not included. The above FD provides a convenient metric to 

measure and compare a materials performance for thermal imaging which allows for 

optimization in fabrication and processing. Thus, the pertinent material parameters to be 

measured are p, ε, and tan δ. Our goal is to enhance FD by maximizing the pyroelectric 
9

coefficient and minimizing the permittivity and dissipation factor. Measurements of the complex 

capacitance will be performed with a HP 4194A impedance/gain analyzer. Samples to be 

measured will be fabricated into parallel plate capacitors by evaporating metal electrodes a few 

100-μm in diameter on top of the deposited pyroelectric film. The complex permittivity of a 

dielectric material is given by ε = ε’ - jε’’, where ε’ and ε’’ are the real and imaginary 

components of the frequency dependent permittivity. The dielectric constant is given by εr = 

ε’/εo, where εo is the permittivity of free space and is related to the measured sample capacitance 

by C = ε(A/d), where A is electrode area and d the film thickness. Dielectric loss is given by tan 

δ = ε’’/ ε’.

Pyroelectricity is a phenomenon that occurs in polar materials and refers to a change in the 

orientation of dipole moments (a change in the spontaneous polarization) due to a change in 

temperature. When connected into a circuit, the fluctuation of the dipole moments will generate a 

current given by I = pA(dT/dt), where p is the pyroelectric coefficient, A the electrode area, and 

dT/dt the temperature rate of change with respect to time. Therefore, the pyroelectric coefficient 

can be determined by measuring the current produced during changes in temperature. This 

measurement can be accomplished by integrating the new instrumentation into ARL-WMRD’s 

preexisting electrical characterization scheme. The test station is diagrammed in figure 3 and will 

be used to accurately determine the pyroelectric coefficient in thin-film pyroelectric samples.

Figure 3. Schematic representation of the test station that will be 

used for the pyroelectric coefficient measurements in 

pyroelectric thin-films.

An Agilent 33220A function generator will be used in conjunction with a Maxim-IC power 

driver to modulate the temperature of the Peltier element to a low frequency (f < 1Hz) sine wave. 

This temperature fluctuation will generate a current from the pyroelectric material under test. 

The current will be fed into a Signal Recovery 7265 lock-in amplifier, which contains an internal 

current pre-amplifier, locked onto the reference frequency of the function generator. The 

pyroelectric current will be 90° out-of-phase with the temperature oscillation since it is 

proportional to the time derivative of the driven sine wave. This makes a phase-sensitive lock-in

measurement beneficial since a true pyroelectric current can be determined, while spurious 

temperature-induced DC or in-phase currents are not registered (4). Additionally, a sensitive low-
10

level ammeter, such as a Keithley 6517B electrometer, can be used to digitally record the 

pyroelectric current vs. time during modulation. This can be beneficial in regards to comparing 

the unaltered (frequency unfiltered) pyroelectric signal with the amplitude measured from the 

lock-in amplifier. A

Yokogawa 7651 DC source can be switched into the circuit to allow sample biasing for poling 

optimization experiments. The temperature of the stage will be monitored by platinum RTD 

using a preexisting Agilent 34401A multimeter. The equipment will be connected to a computer 

running LabView allowing computer-based control and datalogging.

To implement the pyroelectric measurements the list of required equipment including pricing is 

given in table 1.

Table 1. Additional pyroelectric equipment to be procured.

Item Model Vendor Cost

Peltier Modules TE Technology, Inc.

60W Peltier modules

TE Technology, Inc. $120.00

Peltier Driver MAX1978evkit Maxim-IC $100.00

Function Generator Agilent 33220A arbitrary 

waveform generator

TestMart $1,269.00

Lock-in Amplifier Signal Recovery Model

7265

Signal Recovery $4,795.00

DC bias source Yokogawa 7651

Programmable DC source

TestMart $2,875.00

DC ammeter Keithley 6517B Keithley Instruments $6,995.00

Total Cost: $16,154.00

4.2 Thin-film Studies

We continued our research into improving the quality of the BaTiO3 thin films. We have 

dispersed BaTiO3 particles into PVA [CH2CH(OH)-]n. PVA is a known film-former used in other 

sol-gel applications. It is a water-soluble insulating polymer, and is resistant to most solvents. 

Numerous parameters are being explored, such as the molecular weight of the PVA (we have 

used low: 13000–23000, medium: 50000–85000, and high: 120000 molecular weight solutions), 

the percentage alcohol-to-water in the solution, the curing temperature (ranging from room 

temperature to just below the boiling point of water), and the spin speed. We began this study by 

spinning PVA without nanoparticles, to determine whether the alcohol would adhere to the Si 

substrate (it does), whether it needed heat treatment (films are slightly higher quality if heated to 

about 90 °C), and if it would form a smooth crack-free film (yes!). In a parallel study with

Antimony Telluride (Sb2Te3) particles for an ongoing thermoelectric materials research project, 

we found that the PVA tended to sink below the particles and act as glue between the particles 
11

and the substrate, leaving nearly bare Sb2Te3 particles on the surface. Since PVA decomposes 

above 200°C, we are hopeful that the remaining organic in the film will dissipate during the laser 

treatment.

During this quarter we received films consisting of BaTiO3 particles functionalized with oleic 

acid onto TiPt:Si substrates from the ICB. These films are much improved in terms of 

smoothness and adherence to the substrate. We are currently setting up capacitance 

measurements for these samples.

In yet another approach, we are investigating the possibility of depositing films without first 

forming nanoparticles. ARL has successfully used low-temperature metal organic solution 

deposition (MOSD) to grow barium strontium titanate (BST) on Pt:Si substrates (5). The MOSD 

technique is an industry standard for film deposition over large area substrates with high 

chemical purity, strict control over chemical stoichiometry and low overhead cost. For our 

experiment, we have the added luxury using the same commercially-available, inexpensive 

precursor used for the bio-inspired nanoparticles growth at ICB. Having this precursor will save 

us numerous steps in the MOSD process.

The MOSD process for BST uses a home-made carboxylate-alkoxide precursor, glacial acetic 

acid, and 2-methoxyethanol. Since ARL has successfully grown multilayered films with this 

MOSD process, we expect that growing a single BaTiO3 film to be very feasible.

5. Plans and Goals for Year 2 Quarter 1

In the coming quarter, we will continue to expand our nanomaterial synthesis capabilities, laser 

processing techniques and PFM phase conversion studies, and perovskite thin-film 

characterization efforts. We also intend to initiate and pursue several new areas of focus: ICB: 

investigate the deposition of thicker (> 500-nm) BaTiO3 thin films while maintaining film quality 

and crystallinity and initiate explorations into doping of the BaTiO3 nanoparticles with candidate 

photosensitizers for selective laser absorption; Aerospace: initiate testing of the static UV laser 

exposure SHG detection scheme and begin modifications to laser systems for wavelengthdependent studies of the pyroelectric phase conversion process; ARL: perform electrical 

characterization measurements on ICB-provided functionalized BaTiO3 thin-films and 

investigate the use of complementary MOSD techniques for the preparation of BaTiO3 thinfilms.
12

6. References

1. Sarney, W. L.; Little, J. W.; Morse, Daniel E.; Livingston, Frank E. Improved Sensitivity 

Low-cost Uncooled Infrared (IR) Focal Plane Arrays; ARL-TR-4721; U.S. Army Research 

Laboratory: Adelphi, MD, February 2009.

2. Sarney, Wendy L.; Little, John W.; Morse, Daniel E.; Tao, Andrea; Ould-Ely, Teyeb; Niesz, 

Krisztian; Livingston, Frank E. Progress in Biologically-Inspired Pyroelectric Materials 

Growth for Improved Sensitivity, Lower-Cost Uncooled IR Detector Focal-Plane Arrays;

ARL-TR-4770; U.S. Army Research Laboratory; Adelphi, MD, April 2009.

3. Muralt, P. Micromechanical Infrared Detectors Based on Pyroelectric Thin Films. Rep. 

Prog. Phys. 2001, 64, 1339–1388.

4. Dias, C.; Simon, M.; Quad, R.; Das-Gupta, D. K. Measurement of the Pyroelectric

Coefficient in Composites Using a Temperature-modulated Excitation. J. Phys. D: Appl. 

Phys. 1993, 26, 106–110.

5. Cole, M. W.; et al. The Fabrication and Material Properties of Compositionally Multilayered

BaSrTiO3 Thin Films for Realization of Temperature Insensitive Tunable Phase Shifter 

Devices. J. Appl. Phys. 2007, 102, 034104.
13

List of Symbols, Abbreviations, and Acronyms

AFM atomic force microscopy

ARL U.S. Army Research Laboratory 

BaTiO3 Barium Titanium Oxide

BST barium strontium titanate

CCD charge-coupled device

FOM figure of merit

ICB Institute for Collaborative Biotechnologies

IR infrared

LiNbO3 Lithium Niobate

MOSD metal organic solution deposition

PFM piezoelectric force microscopy

PVA polyvinyl alcohol

Sb2Te3 Antimony Telluride

SHG second harmonic generation

UV ultraviolet

XRD x-ray diffraction

Y1Q4 year one, quarter four
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