Presented ACS 2015 Spring National Meeting, Denver, CO
Elucidating Reaction Pathways for Thermoelectric Materials Fabricated by
Bottom-Up Solution-Phase Solid-State Synthesis
Cameron Holder, Evan Rugen, Daniel Stevens, and Mary E. Anderson*
Introduction
Weigh out stoichiometric amounts of TeO2, Pb(C2H3O2)2, and Bi(NO3)3
Thermoelectrics convert heat to electricity or vice versa
Add salts to 10 mL of solvent Tetraethylene glycol (TEG)
Reduce cost and energy consumption
Sparge solution with nitrogen (N2) for ~15 minutes
Increase efficiency
Combine NaBH4 with 5 mL of TEG and pipet into flask
20
30
EDS Spectra for
PbTe
40
2θ
50
60
Identifies crystal structure
and indicates composition
Store powder under vacuum to dry in order to characterize using SEM/EDS and XRD
Synthetic Method: Modified Polyol Process
Te+4
XRD Pattern
of TeO2
Identifies elemental
composition of sample
Wash by centrifugation three times with ethanol
Methods
X-ray Diffractometry (XRD)
Energy Dispersive
X-ray Spectroscopy (EDS)
Pipet solution of product into centrifuge tubes
Seat Warmers/Coolers, Refrigeration, Deep Space Probes
Pb+2
Scanning Electron
Microscopy (SEM)
Run reaction under N2, for specified temperature and amount of time
Promising applications:
Te+4
Characterization Techniques
Experimental Details
PbTe and Bi2Te3 nanoparticles are classified as thermoelectric materials
Pb+2
Department of Chemistry, Hope College, Holland MI 49423
Experimental Goals
Intermetallic Nanoparticles
Summary
TEG and NaBH4
Te+4
PbTe
Heat
Pb+2
Determine the growth mechanism
of PbTe and Bi2Te3 nanoparticles as
a function of time and temperature
Acknowledgments
•
The PbTe mechanism forms an oxide intermediate, while the Bi2Te3 mechanism
proceeds through a reduction-diffusion process.
•
The growth mechanism for both materials remains unchanged when the reaction
was run for a longer period of time (1 hour). However, growth stages were
observed at lower temperatures.
Lab members: Monica Ohnsorg, Lauren Gentry, Brandon Bowser
Hope College Chemistry Department
NSF
HHMI
Results
Pb0
PbTe
TeO2
PbTeO3
24°C
Bi2Te3
TeO2
PbTe, PbTeO3
PbTeO3, PbTe
PbTe
24°C
270°C
100°C
TeO2
280°C
220°C
200°C
150°C
185°C
Bi2Te3
150°C
100°C
250°C
250°C
Te
220°C
220°C
185°C
200°C
TeO2
200°C
20
200°C
100°C
220°C
24°C
280°C
PbTe
Bi2Te3
PbTeO3
Bi
Pb
150°C
TeO2
40
50
2θ
60
70
20
80
Above: PbTe XRD pattern where reactions were held at the
indicated temperature for 1 minute.
200°C
• Upon the application of heat, the Pb begins to diffuse into the
TeO2 crystal, forming the bulbous PbTeO3 intermediate.
35
40
2θ
45
50
55
60
• Bi2Te3 mechanism begins much like what was observed for
PbTe mechanism with elemental Bi and TeO2 after NaBH4
addition without heating.
220°C
• While PbTe goes through an oxide intermediate, the Bi2Te3
been shown to proceed through a reduction-diffusion process.
• Distinct morphology changes are observed for PbTeO3 before
oxygen is expelled from the crystal to from the final product,
PbTe.
270°C
30
Above: Bi2Te3 XRD pattern where reactions were held at the
indicated temperature for 1 minute.
• At room temperature and after the NaBH4 addition, the Pb
precursor is reduced and the TeO2 is unchanged.
250°C
25
• There comes a point where rate of reduction exceeds rate of
the Bi-Te reaction and Te nanorods are observed (220°C).
Pb(C2H3O2)2
30
All scale bars are 10 µm.
All scale bars are 10 µm.
45
50
55
60
Std.
Open
Cl2
NO3
PbTe
PbTeO3
5 μm
5 μm
Pb
TeO2
Te
20
5 μm
5 μm
PbCl2
250°C
Left: Morphologies observed at each stage of the Bi2Te3 1 minute
growth mechanism. From the top to bottom, the following are the
EDS percentages for Bi and Te, respectively, for each growth
stage: 24°C: 20%, 80%; 100°C: 45%, 55%; 150°C: 42%, 58%;
200°C: 26%, 74%; 220°C: 16%, 84%; 250°C: 36%, 64%.
40
2θ
Closed
• The formation of Bi2Te3 nanoplatelets is complete at 250°C.
Left: Morphologies observed at each stage of the PbTe 1 minute
growth mechanism. The following are the EDS percentages for
each growth stage, from top to bottom, referring to Pb and Te,
respectively: 24°C: 62%, 38%; 175°C: 12%, 88%; 200°C: 36%,
64%; 220°C: 43%, 57%; 250°C: 49%, 51%; 270°C: 51%, 49%.
35
PbTeO3
Pb(NO3)2
Te
220°C
All scale bars are 10 µm.
Te
TeO2
20
30
• Reduction of TeO2 investigated to
determine its role in formation of Bi2Te3.
• Distinct morphological transitions are
observed in SEM images (left) from 200°C
to 220°C, which are also seen for Bi2Te3.
• Representative XRD patterns (above) show
progression of TeO2 reduction as a function
of temperature.
100°C
24°C
200°C
25
150°C
175°C
175°C
TeO2
Te
Te
Bi0
5 μm
All scale bars are 10 µm.
5 μm
30
40
50
2θ
60
70
80
• Formation of PbTeO3 was dependent on
conjugate anion of Pb starting salt containing
oxygen atoms as observed in both the SEM
images (left) and the XRD patterns (above).
• It was determined that formation of PbTeO3
was independent of atmospheric conditions.
Reactions were run under a static (closed) and
dynamic (std) N2 environment in addition to
being run open to the atmosphere (open).
Presented ACS 2015 Spring National Meeting, Denver, CO [selected for Sci-Mix, students won COLL best student poster award]
Foundational Layer Formation of Metal-Organic Coordinated Thin Films
Monica L. Ohnsorg, Brandon H. Bowser, Lauren K. Gentry, Christopher K. Beaudoin and Mary E. Anderson*
Department of Chemistry, Hope College, Holland MI 49423
Introduction
Layer-by-Layer Deposition of Metal-Organic Multilayers vs. Frameworks
SPM Images
Layer-by-Layer Deposition Methods
Cu-TMA 25˚C
1
O
This research explores layer-by-layer (LBL) assembly for two types of metal-organic coordinated thin films, multilayers (ML)
and frameworks (MOF). Controlled step-wise assembly defines the resulting film structure, presenting an opportunity to design
these materials for specific applications, such as sensing and gas storage. Towards this realization, both films are fabricated by
alternating, sequential solution-phase deposition. Both systems were synthesized beginning with a 16-mecaptohexadecanoic
acid (MHDA) self-assembled monolayer on gold. ML were composed of α,ω-mercaptoalkanoic acids and Cu (II) ions forming
a conformal film. MOF were composed of 1,3,5-benzenetricarboxylic acid and Cu (II) ions (HKUST-1) yielding a porous,
crystalline framework. Both films were characterized using ellipsometry to measure film thickness and scanning probe
microscopy (SPM) to map topographical morphology of film growth LBL. Using image analysis software, quantitative data
regarding the growth of these thin films based on the images was procured. Ellipsometry suggests both ML and MOF form
continuous, conformal layers that are each about 2 nm thick, respectively. However, SPM images elucidate two distinct
systems, one that forms a semi-continuous film with distinct “islanding” (ML) and one that forms a rough surface of nucleating
crystallites (MOF). The effects of deposition conditions, such as temperature and solution concentration, have been
investigated in order to tailor film morphology for specific applications. Preliminary findings will be presented for utilizing
surface IR for gas absorption within the MOFs. Future work includes observing continued MOF growth to observe at what
point it becomes continuous and to investigate how the film forms beyond the threshold of complete surface coverage. Further
studies will investigate other metal-organic coordinated thin film systems to understand the chemical and physical processes by
which different film morphologies arise.
2
4
3
5
10
16
20
25
30
Cu2+
(a)
ML
HS
25°C
Metal-organic multilayers form as a conformal continuous film covering the underlying substrate completely. After 1 deposition cycle, a foundational and conformal layer covers the grain structure of the
underlying Au substrate observed. Then islands begin to form and coalesce throughout the next few deposition cycles. At ~5 cycles, the film takes on a unique morphology but surface roughness is essentially the
same as the underlying substrate. Graph (a) shows linear growth of 1.8 nm per layer and fairly consistent, low roughness measurements are shown in Graph (c).
1
Cu2+
3
2
4
5
8
7
6
9
200 nm
10
50 nm
(b)
25°C
HKUST-1 SurMOF - small crystallites are present on the surface after 1 cycle of deposition; and the crystallites double in number from 1 to 2 cycles. The crystallites continue to nucleate, grow in size increasing
surface coverage (Graph (b)), and coalesce with one another (9 and 10 cycles). Graph (a) shows growth comparable to that of the ML. Roughness increases with deposition cycle (Graph (c)).
1
Cu2+
4
3
2
5
6
8
7
9
2.00 µm
10
50 nm
(c)
50°C
OH
OH
O
OH
O
OH
O
O
2) Copper (II) Perchlorate Hexahydrate (1 mM, 15 min)
OH
O
1) 16 - Mercaptohexadecanoic Acid (1 mM, 1 hr)
Increasing deposition temperature from 25˚C to 50˚C resulted in nucleation of smaller and more numerous crystallites that appear to almost fully cover the surface at 10 cycles of deposition.
Depositions increase roughness up to cycle 6 (Graph (c)). The thickness of the film is comparable to the 25˚C data up to 5 cycles of deposition, after which the film increases in thickness at a faster rate.
Applications:
Lithography
Au
OH
O
S
S
S
S
Au
Anderson et al., Adv Mater, 2006, 18, 1020.
OH
OH
O
S
1
Zn2+
S
OH
O
S
S
OH
O
S
S
S
S
O
S
OH
S
OH
O
S
OH
O
OH
O
S
OH
O
OH
O
S
OH
O
OH
O
S
O
OH
O
S
OH
O
S
2
3
6
Preliminary data for substituting the metal ion in the SurMOF system with Zn2+ resulted in the formation of platelet-like crystallites on the surface, resulting in roughness measurements much lower than the
Cu SurMOF systems (Graph (c)). The thickness of the film, shown in Graph (a), was approximately half that of the 25˚C deposition of the Cu SurMOF film.
Tracking Gas Adsorption
IR Spectra
0.010
HO
O
OH
O
O
0.04
0.02
0.020
0.010
H2O +
-OH of COOH
0.030
Cu-HKUST
Cu-HKUST +
NH3
0.006
0.004
0.002
3500
3100
1700
1300
Wavenumbers (cm-1)
3500
3100
1700
1300
Wavenumbers (cm-1)
http://www.moftechnologies.com/MOFs.html
http://http://www.sigmaaldrich.com
S
S
S
S
S
S
S
1700
S
Scanning Probe Microscopy
Laser
Electronics
Tip
Ellipsometry
Particle Analysis
1500
1450
1400
1350
3600 3400 3200 3000 2800 1800 1600 1400 1200 1000 800
Subtracted
Background
Original
Particle Count
Particle Size
Percent Coverage
Particle
Outline
Particle
Threshold
Absorbance spectra for deposited layers
elucidates chemical composition of the
films and monitors layer growth by
measuring intensity changes in the
observed functional group peaks.
200nm
Thickness: 6.75 nm
Rq: 14.4 nm
Cu-TMA 25˚C
Deposition on
Template
Stripped Au
3
50 nm
2µm
20 nm
Comparison of the Cu- and Zn-HKUST systems.
Spectra above represent samples fabricated by
5 deposition cycles. Key peaks are identified,
supporting the chemical composition of the film.
Thickness: 8.02 nm
Rq: 20.5 nm
2
1
Wavenumbers (cm-1)
Investigate other SURMOF systems
Cu-Jungle Gym System
MOF-5, Jungle Gym
Understand fundamentals of framework formation
Explore crystal face expression and formation
Develop growth mechanism
Tailor film structure via deposition variables
Test variables such as time, temperature, solvent, and concentration
Introduce functionality into films
Dope MOFs for post-synthetic functionalization
Induce conductive or magnetic properties
Cu2+
Preliminary integration into smart interfaces
ITO-PET
Track absorption of gases into framework
Funding:
20 nm
50nm
50nm
2.00µm
2.00µm
Zn-HKUST Post-NH3
Cu-HKUST Post-NH3
Future Investigations
Grazing Angle FT-IR
Plane polarized light of interacts with the surface. The ratio
of change from plane to elliptically polarized light estimates
film thickness and optical properties.
1550
Wavenumbers (cm-1)
Computer
In SPM images,
bright areas indicate
taller features while
dark areas represent
lower regions.
1600
Film growth can be qualitatively and
quantitatively investigated throughout the
deposition of the Cu-HKUST SurMOF system.
Interactions between the scanning
probe and surface renders a
topographic, qualitative image of
film morphology on the nanoscale.
Cantilever
Sample
1650
Wöll et al., Angew. Chem. Int. Ed. 2009, 48, 5038.
Characterization Methods
Detector
4
4
S
10
Thickness: 2.85 nm
Rq: 7.76 nm
0.010
0.000
0.000
S
5
500 nm Cu-TMA 25˚C
NOTE: Regions with fewer crystallites
were selected in order to investigate
background substrate morphology.
0.020
N—H
Absorbance
0.030
0.008
Zn-HKUST
Zn-HKUST +
NH3
0.00
Biomedical – Drug
Storage, Delivery
2
2.00 µm
The underlying, rippled morphology
of the substrate remains consistent
through 10 cycles of deposition,
indicating minimal disruption of the
preliminary SAM.
N—H
OH
HO
OH
O
O
Cu-HKUST
Zn-HKUST
1,3,5- sub benzene
HO
O
O
0.06
0.040
Absorbance
O
OH
OH HO
OH
O
O
O
TMA match
HO
O
O
HO
O
OH
O
OH
O
HO
O
O
OH HO
OH
O
OH
OH
O
OH
O
Hydrocarbon
Separations
HO
OH HO
HO
O
OH HO
OH
O
O
HO
O
O
benzene
HO
O
Absorbance
O
OH
O
COO- assym
0.08
Layer 1
Layer 2
Layer 3
Layer 4
Layer 5
Layer 6
Layer 7
Layer 8
Layer 9
Layer 10
COO- sym
3) Organic Ligand: Benzene-1,3,5-tricarboxylic acid (0.1 mM, 1 hr)
Characterization and Comparison
COO- sym
Watching the SURMOF Grow
COO- assym
benzene
TMA match
2) Metal Ion: Copper (II) Acetate or Zinc (II) Acetate (1mM, 30 min)
O
1
Au
1) 16 - Mercaptohexadecanoic Acid (1 mM, 1 hr)
O
10
25°C
Metal-Organic Framework (MOF)
Applications:
Gas Storage
9
8
7
2.00 µm
50 nm
Evans et al., JACS, 1991, 113, 5866
Carbon Capture and
Sequestration
5
4
-CH2 (SAM)
Electronic and
Nanofluidic
Devices
Zn-TMA 25˚C
20 nm
Metal-Organic Multilayer (ML)
Chemical
Functionality
Cu-TMA 50˚C
ML
OH
ABSTRACT
200nm
200nm
Thermally Deposited Au
Template Stripped Au with MOF
nano-crystallites
Investigate effects of
grain boundaries on
crystallite nucleation.
Results followed average
trends and crystallites
nucleate independent of
etch pit boundaries and
Au grains.
Conclusions
4
50nm
ML form conformal film with unique and stable morphology emerging after 5 deposition cycles,
having surface roughness equal to underlying substrate.
LBL deposition at 25˚C for Cu-TMA SurMOF resulted in a crystallite-rich surface different from the ML system.
Increased deposition temperature for SurMOF increased surface coverage of particles which were more numerous and
smaller in size - resulting in greater surface coverage, increased thickness, and lower roughness.
2.00µm
Changing the metal ion results in new crystallite structure and decreased roughness.
10
50nm
Nucleation of crystallites from Cu-TMA SurMOF deposited at 25˚C is independent of grain boundaries on Au substrate.
IR showed layer growth for Cu-TMA SurMOF as functional group intensities increased.
NH3 absorption was observed using IR. SPM showed SurMOF morphology had been disrupted by the gas.
2.00µm
ACS – PRF
Arnold and Mabel Beckman Foundation
NSF-MRI Grant No. CHE-1126462
Hope College Chemistry Department
Group Members:
Allie Benson
Evan Rugen
Dan Stevens
Meagan Elinski
Cameron Holder
Presented ACS 2013 Spring National Meeting, New Orleans, LA [selected for Sci-Mix]
Qualitative and Quantitative Analysis of Metal-Organic Coordinated Multilayers
Meagan B. Elinski, Alexandra S. Benson, Mary E. Anderson*
Department of Chemistry, Hope College, Holland MI 49423
Introduction
Results
Particle Induced X-Ray Emission (PIXE)
10000
Bottom-up Assembly of Multilayer Films
Cu+X
Cu+X
Cu+X
Cu+X
Cu Au
0.004
Au
Cu+X
Cu+X
Cr
Cu
400
200
300
Channel/Energy
100
0.002
0.000
Energy
0
10
20
30
Layer
600
500
400
300
200
100
0
5
0L
2 Cu: 1 molecule
10 15 20
# of Layers
25
Fitting Cu peak suggests
2-to-1 Cu-to-molecule ratio
30
Average density per layer:
2.21 x1014 molecules/cm2
5L
1000
10L
15L
100
10
1 Cu: 1 molecule
Film Thickness
0
10000
Linear increase in Cu concentration 15-30 layers
Cu+X
10
1
1E15 atoms/cm2
Counts
Au Au
Si
100
0.006
Counts
How does the morphology and roughness change with
increasing number of multilayers?
Are there trends observed to glean insight into film formation?
Count
s
Cr
Au
1000
30 Layer
Si
What is the average areal density of individual layers?
What is the topography of the multilayer films?
Rutherford Backscattering Spectrometry (RBS)
Cu/Au
What is the composition and structure within the films?
What is the binding ratio between metal ions and molecules?
20L
455
460
465
Channel/Energy
470
Fitting shift in front Au edge
shows increase in film thickness
Standard monolayer density:
4.5x1014 molecules/cm2
Cu+X
Atomic Force Microscopy (AFM)
3: 2nd layer
Evans, et. al. J. Am. Chem. Soc. 1991, 113, 5866-5868.
Atomic Force Microscopy
Peakforce tapping mode to map topography
Herein used to study surface morphology as a function of
layer deposition and annealing temperature
Particle Induced X-ray Emission (PIXE)
Ion beam: protons (H+), 2.9 MeV particle accelerator
Detects emitted X-rays
Determines elemental composition in ppm
Rutherford Backscattering Spectroscopy (RBS)
Ion beam: alpha particles (He1+), 2.9 MeV particle accelerator
Detects energy loss of backscattered particles
Determines elemental composition: based on nuclear collisions
Calculates thickness (atoms/cm2): based on electronic collisions
incident particles
multilayers Au Cr
backscattered
particles
SiO2
Roughness Analysis:
Nonlinear curve fit (Ws)
Roughness Analysis: Image analysis software (Rq)
1L
0L
Rq: 1.52 nm
Ws: 1.59 nm
2L
Rq: 1.60 nm
Ws: 1.69 nm
3 Layer
3L
Rq: 1.93 nm
Ws: 1.95 nm
10 L
4L
5L
Rq: 2.21 nm
Ws: 2.29 nm
Rq: 2.00 nm
Ws: 2.04 nm
20 L
25 L
16 L
Rq: 1.54 nm
Ws: 1.59 nm
30 L
Each image is 500x500 nm
Chris Beaudoin, Cameron Holder, Evan Rugen, Kyle Alexander
Dr. Graham Peaslee, Dr. Paul DeYoung, Dr. Jennifer Hampton
Hope College Chemistry Department
National Science Foundation
Howard Hughes Medical Institute
NSF-MRI Grant No. CHE-1126462
3L film: greater height
deviation within
smaller areas (boxes);
short range disorder
30L film: same overall
roughness as 3L;
exhibited over
larger areas
Length of Box (µm)
Rq: 1.50 nm
Ws: 1.62 nm
Rq: 1.67 nm
Ws: 1.74 nm
Rq: 1.53 nm
Ws: 1.62 nm
Rq: 1.99 nm
Ws: 2.20 nm
Rq: 1.67 nm
Ws: 1.79 nm
Heating in situ (1 x 1 μm scans of 3 Layer Multilayer Sample)
Images are labeled with the sample stage temperature and measured surface roughness (Rq)
Controlled heating from room temperature to 200°C and subsequent cooling to ambient temperature
25°C
75°C
100°C
150°C
200°C
100°C
25°C
side view
Acknowledgments
30 Layer
3 Layer Growth
30 Layer Growth
Roughness (nm)
2+ metal ions
Cu
2:
1: MHDA:
(16-mercaptohexadecanoic acid)
Two methods of roughness analysis were compared
Numbers represent deviation in height from a mean value over a specified region
Rq: 1.65 nm
Rq: 1.47 nm
Multilayer film SPM images
before and after
ex situ annealing to 100 °C.
Rq: 1.21 nm
Rq: 0.968 nm
Pre3L
Rq: 3.04 nm
Rq: 2.53 nm
Post-annealing
Pre-
3L
30L
Rq: 2.36 nm
Post-annealing
30L
Each scan is 500 x 500 nm
Rq: 1.97 nm
Rq: 1.62nm
Rq: 1.78 nm
Rq: 1.80nm
Conclusions and Future Work
What is the composition and structure within the films?
Cu concentration increases linearly with film growth
Binding ratio of Cu to MHDA is approximately 2:1
Average density per layer similar to SAM
What is the topographical structure of the films?
Foundational layers conformal with underlying substrate
Film takes on unique morphology upon reaching five layers
Surface roughness increases with initial layers, but
decreases to that of underlying substrate
Next steps:
Examine island sizes as multilayers form
Study temperature range in which transformation
occurs (75ºC-125ºC) using a tip more appropriate for
imaging organic films
Investigate other metal-organic coordinated systems
Multilayers: e.g. alkylphosphonic acids and Zr4+ or Zn2+
Metal-organic frameworks: e.g. trimesic acid and Cu2+