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NC STATE UNIVERSITY UNC-Chapel Hill
Cobalt-bis(Dioxolene) Valence Tautomers: Molecular Properties and
Progress toward Devices
David A. Shultz,*1 Robert D. Schmidt,1 Will Rice,2 Frank Tsui,2 Marco Buongiorno-Nardelli3 and Arrigo Calzolari4
1Department of Chemistry, NC State University, Raleigh, NC
27695-82042Department of Physics, UNC-Chapel Hill
3Department of Physics, NC State University4Department of Physics, University of Modena
NC STATE UNIVERSITY UNC-Chapel Hill
NSF CCI: Center for Molecular Spintronics (CMS)
The CMS is exploring the utility of switchable/bistable paramagnetic molecules and semiconducting oligomers (based on metal complexes of semiquinones) -- as new ways to understand and to control both spin injection and spin-polarized transport. Our approach involves a highly-integrated program consisting of:(1) synthesis and characterization of these molecules and oligomers,(2) detailed surface structure and bonding studies, (3) spin injection and transport measurements, and (4) computational modeling.
NC STATE UNIVERSITY UNC-Chapel Hill
Collaborative Structure to Date
Shultz GroupMolecule and polymer synthesis
You GroupMonolayer synthesis
Tracy GroupNanoparticle synthesis
Tsui GroupValence Tautomer“crystal devices”
Dougherty GroupNanoparticle devices
Rowe GroupDevice characterization
Jones GroupEducation/Outreach
Buongiorno-Nardelli GroupTheory/Computation
NC STATE UNIVERSITY UNC-Chapel Hill
New Valence Tautomersand New Studies of “Old” Valence
Tautomers
NC STATE UNIVERSITY UNC-Chapel Hill
Using Electron Transfer to Affect “Long-Range Exchange” Coupling via Organic Double Exchange
One quartet, one doublet
-15J/4
-3J/4Very weak superexchange across 11 bonds
Intramolecular ET within the mixed-valent SQ-Cat dyad promotes ferromagnetic coupling: double exchange
Hab
2Hab
NC STATE UNIVERSITY
ET
One quartet, one doublet
-15J/4
-3J/4 Very weak superexchange across 11 bonds
ET = f(Hab)Hab Hab
NC STATE UNIVERSITY UNC-Chapel Hill
Using Electron Transfer to Affect“Long Range Exchange Coupling”
c par
aT (e
mu
K m
ol-1)
Temperature (K)
• C2h complex has p-overlap between metal/dyad that C2 complex lacks• J is a direct measure of mixed-valent wavefunction
J = +74 cm-1
(Doublet + Triplet model; 3J gap)
J ≈ +4 cm-1
(Doublet + Triplet model; 3J gap)
NC STATE UNIVERSITY
NC STATE UNIVERSITY UNC-Chapel Hill
> 2 nm
Phenyl ring torsions are ≈15° from SQ and NN ring planes
ORTEPs of C2h Complexes
SQ-NN torsion ≈ 15°
NC STATE UNIVERSITY
> 1.4 nm
CoIIISQ(Cat) formulation with crystallographic inversion center at Co
NC STATE UNIVERSITY UNC-Chapel Hill
cparaT=1.1253-uncorrelated spins
High Temp Limit
cparaT=1.8753-coupled spins
Low Temp Limit
Temperature (Kelvin)
c par
a•T (e
mu
K m
ol-1)
NC STATE UNIVERSITY
Magnetic Susceptibility for
• Only quartet state populated at all temperatures
NC STATE UNIVERSITY UNC-Chapel Hill
cparaT=1.1253-uncorrelated spins
High Temp Limit
cparaT=1.8753-coupled spins
Low Temp Limit
Temperature (Kelvin)
c par
a•T (e
mu
K m
ol-1)
NC STATE UNIVERSITY
Magnetic Susceptibility for
• Quartet and doublet states populated
NC STATE UNIVERSITY UNC-Chapel Hill
A more sophisticated HDvV fit of the magnetic data…
JA (5 bonds)JB (11 bonds)
JC
Results of trimer fit support delocalization of SQ/Cat!
c par
aT (e
mu
K m
ol-1)
Temperature (K)
JA = JB = 234 cm-1
g = 2.0 (fixed)q = -2.06 K
NC STATE UNIVERSITY
234 cm-1Q
DA
DB
0
€
JA + JB + JA2 + JB
2 − JA JB
€
JA + JB − JA2 + JB
2 − JA JB€
J = J0e−α r−r0( )
€
ˆ H Trimer = −2JA ( ˆ S i • ˆ S j ) − 2JB ( ˆ S j • ˆ S k ) − 2JC ( ˆ S i • ˆ S k )
JA ≠ JB ≠ 0; JC = 0
NC STATE UNIVERSITY UNC-Chapel Hill
Matrix elements of interacting doublets formed from local SQPhNN singlet states
nmax = 2Hab
Cat SQ CT band in IR region!
Energy (cm-1)
Double Exchange/Spin-Dependent Delocalization Model…
Electronic Structure/Spin-Dependent Delocalization Approach…
Double exchange:Girerd, et al.. Chem. Rev. 1990, 90, 1359.
• Hab describes delocalization of the mixed-valent dyad one set of quartets and two sets of doublets• HDvV (Heitler-London)Double exchange (Zener)single J only: JB = 0
NC STATE UNIVERSITY
€
) H
ST =32
=−J Hab
Hab −J
€
) H
ST = 12
=
−J Hab2 0 0
Hab2 −J 0 0
0 0 J −Hab2
0 0 −Hab2 J
Cat SQ
NN NNJ
Hab
SQ Cat
NN NNJHab
• vibronic structure• ∆n1/2 less than Hush prediction
• weak solvent dependence• Class II/III or Class III mixed valent
(DELOCALIZED)
NC STATE UNIVERSITY UNC-Chapel Hill
nmax = 2Hab
Cat SQ CT band in IR region!
Energy (cm-1)
Bersuker, et al., Adv. Chem. Phys. 1992, 81, 703.
Double Exchange/Spin-Dependent Delocalization Model…
Electronic Structure/Spin-Dependent Delocalization Approach…
Double exchange:Girerd, et al.. Chem. Rev. 1990, 90, 1359;
Off-diagonal blocks allow for interaction of doublet states six state SDD model
NC STATE UNIVERSITY
€
) H
ST =32
=−J Hab
Hab −J
€
) H
ST = 12
=
−J Hab2 0 3
2 Hab
Hab2 −J 3
2 Hab 0
0 32 Hab J −Hab
23
2 Hab 0 −Hab2 J
NC STATE UNIVERSITY UNC-Chapel Hill
nmax = 2Hab
Cat SQ CT band in IR region!
Energy (cm-1)
QA
DA
QB
DB
DB*
DA*
3500 cm-1
Electronic Structure/Spin-Dependent Delocalization Approach…NC STATE UNIVERSITY
€
J + Hab − J 2 + Hab2 + JHab
€
J + Hab − J 2 + Hab2 − JHab
€
J + Hab + J 2 + Hab2 − JHab
€
J + Hab + J 2 + Hab2 + JHab
2Hab
0
NC STATE UNIVERSITY UNC-Chapel Hill
JA JB
JCKirk, M. L.; Shultz, D. A.; Schmidt, R. D.; Rodriguez, D. H.; Lee, H.; Lee, J. J. Am. Chem. Soc. 2009, 131. 18304.
1
1.2
1.4
1.6
1.8
2
0 50 100 150 200 250 300
HDVVDouble Exchange
c paraT
(em
u·K
·mol
-1)
Temperature
CoIII(py)2(SQPhNN)(CatPhNN)
6-State Double ExchangeErrorValue
0.0756-2q289465J
1.44e+058.57e+030.005161.99g
3-State HDVVErrorValue
0.0713-2.06q9.74e+05466J9.73e+05466J'0.0005012g
3-State HDvV
JA 234cm-1
JB 234cm-1
g 1.99q -2.06 K
-J+HAB
2J+Hab/2
2J-Hab/2
QA
DA
QB
DB
Hab/2
-Hab/2
-J-Hab
DB*
DA*
Classical Double ExchangeHDvV
T0J
S 2J
JSQ-Ph-NN
= 100 cm-1
Thermally Accessible Excited
Singlet State
Q
D
0J
-J
D
2J
) ) )ˆ ˆ ˆ ˆ ˆ ˆˆ 2 2 2
, 0; 0
Trimer A i j B j k C i k
A B C
H J S S J S S J S S
J J J
NC STATE UNIVERSITY UNC-Chapel Hill
JA JB
JC
1
1.2
1.4
1.6
1.8
2
0 50 100 150 200 250 300
HDVVDouble Exchange
c paraT
(em
u·K
·mol
-1)
Temperature
CoIII(py)2(SQPhNN)(CatPhNN)
6-State Double ExchangeErrorValue
0.0756-2q289465J
1.44e+058.57e+030.005161.99g
3-State HDVVErrorValue
0.0713-2.06q9.74e+05466J9.73e+05466J'0.0005012g
6-State Double Exchange
J 465 cm-1
Hab 8570 cm-1
g 1.99q -2.00 K
3-State HDvV
JA 234cm-1
JB 234cm-1
g 1.99q -2.06 K
2J+Hab/2
2J-Hab/2
T
Q
D
QA
DA
QB
DB
0J 0J
-J
Hab/2
-Hab/2
-J+Hab
-J-Hab
S 2J D
2J DB*
DA*
JSQ-Ph-NN
= 100 cm-1
Classical Double ExchangeHDvV
Thermally Accessible Excited
Singlet State
QA
DA
QB
DB
DB*
DA*
€
−J + Hab
€
−J − Hab€
− J 2 + Hab2 + JHab
€
− J 2 + Hab2 − JHab
€
J 2 + Hab2 − JHab
Spin-Dependent Delocalization
€
J 2 + Hab2 + JHab
Kirk, M. L.; Shultz, D. A.; Schmidt, R. D.; Rodriguez, D. H.; Lee, H.; Lee, J. J. Am. Chem. Soc. 2009, 131. 18304.
) ) )ˆ ˆ ˆ ˆ ˆ ˆˆ 2 2 2
, 0; 0
Trimer A i j B j k C i k
A B C
H J S S J S S J S S
J J J
NC STATE UNIVERSITY UNC-Chapel Hill
€
12,0, 1
2
€
32,1, 1
2
€
12,1, 1
2
State Energies calculated with J = 465 cm-1
2Hab
HAB/cm-1
Ene
rgy
(cm
-1)
DoubletDoublet
Quartet
Energy (cm-1)
Spectroscopic Hab
NC STATE UNIVERSITY
Evaluating Hab by bothTheory and Spectroscopy
“IVCT” nmax = 2Hab
For Hab > ~1000 cm-1, ∆EQD is constant
NC STATE UNIVERSITY UNC-Chapel HillElectronic Structure/Spin-Dependent Delocalization Approach…
QA
DA
QB
DB
DB*
DA*
0
3500 cm-1
229 cm-1
c par
aT (e
mu
K m
ol-1)
Temperature (K)
J = 580 cm-1
Hab = 1750 cm-1 (fixed)g = 1.99q = -2.06 K
NC STATE UNIVERSITY
€
J + Hab − J 2 + Hab2 + JHab
€
J + Hab − J 2 + Hab2 − JHab
€
J + Hab + J 2 + Hab2 − JHab
€
J + Hab + J 2 + Hab2 + JHab
2Hab
NC STATE UNIVERSITY UNC-Chapel Hill
T
Q
D
QA
DA
QB
DB
0J
DB*
DA*S 2J D
DB*
DA*
Thermally Accessible Excited
Singlet State
JSQ-NN
≈ 500 cm-1
QA
DA
QB
DB
NC STATE UNIVERSITY
• This gap should be larger
• Doublet thermally inaccessible
NC STATE UNIVERSITY UNC-Chapel Hill
J = 580 cm-1
JSQNN = 100 cm-1
NC STATE UNIVERSITY
Strong SQNN exchange in SDD molecule(s) can be explained using VBCI model
Kirk, M. L.; Shultz, D. A.; Schmidt, R. D.; Rodriguez, D. H.; Lee, H.; Lee, J. J. Am. Chem. Soc. 2009, 131. 18304.
NC STATE UNIVERSITY UNC-Chapel Hill
New Valence Tautomersand New Studies of “Old” Valence
Tautomers
NC STATE UNIVERSITY UNC-Chapel Hill
N
NO
OCoIII
t-Bu
t-Bu
X
X
O
O
t-Bu
t-BuN
XO
O
t-Bu
t-Bu
CoIIO
Ot-Bu
t-Bu
4Heat
8
X = HX = OMe
X = CN
21
X = Br X = NO2
Buchanan, R. M.; Pierpont, C. G. J. Am. Chem. Soc. 1980, 102, 4951-4957.Schmidt, R. D.; Shultz, D. A.; Martin, J. D. Inorg. Chem. 2010, 49, 3162-3168.
Schmidt, R. D.; Shultz, D. A.; Martin, J. D.; Boyle, P. D. J. Am. Chem. Soc. 2010, 132, 6261-6273.
X = Me
NC STATE UNIVERSITY UNC-Chapel HillNC STATE UNIVERSITY UNC-Chapel Hill
22
High temperature values:Non-active – 0.375 → CoIII(Cat)(SQ)
Low temperature values – 0.375 – Appropriate for CoIII(Cat)(SQ)
Schmidt, R. D.; Shultz, D. A.; Martin, J. D. Inorg. Chem. 2010, 49, 3162-3168; J. Am Chem. Soc. 2010, 132, 6261-6273.
Active – 2.85 – 4.75 → hs-CoII(SQ)(SQ)
Accessibility of metastable state via thermal cycling or irradiation
Thermal Conversion Photoinduced Conversion
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2 4 6 8 10Cycle
c para
·T (e
mu·
K·m
ol-1
)
0
0.2
0.4
0.6
0.8
1
0 5000 10000 15000
Decay % 10KDecay % 20KDecay % 30KDecay % 40KDecay % 50KDecay % 55KDecay % 60KDecay% 80K
Time (s)
c para
·T/c
para
·T(t
=0)
Long-lived kinetic stability
NC STATE UNIVERSITY UNC-Chapel Hill
• Anisotropic lattice distortions implicate C-H•••N and C-H•••O interactions• Totally symmetric Co-L stretching coupled to lattice modes cooperativity ?
c
b
a
b
NC STATE UNIVERSITY UNC-Chapel Hill
+
T
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+
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Variable Resistor Circuits:Constant applied bias – variable current flow
Photoinduced Thermal-induced
+
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Photoinducedor
Thermal-induced
NC STATE UNIVERSITY UNC-Chapel HillNC STATE UNIVERSITY UNC-Chapel Hill
SiO2 baseelectrode 2electrode 1
VT single crystal or polymer filmCurrent Measurement Devices
NC STATE UNIVERSITY UNC-Chapel Hill
Field Effect Structures for StudyingElectronic Properties of Valence Tautomer
• SiOx/n-Si/Au back gate• Gate capacitance ~0.7 nF
(forward bias)• Crystalline Valence Tautomer
Au contacts without sample Au contacts with sample mounted
• Making contacts via solution• 10 m spacing between contacts
(Van der Pauw)• Forward gate bias to access
HOMO states
100 m 100 m
NC STATE UNIVERSITY UNC-Chapel Hill
L5
L6
L1 (+ Gate)- to C3 on separate sample mount
(contacts back Au)
L8 (- Crystal)
L7
L4 (+ Gate)
L3L2 (+ Crystal)
NC STATE UNIVERSITY UNC-Chapel Hill
Electronic Transport of Tautomer source current vs. gate and source voltages
at room temperature
10
9
87531
Source Voltage Vs (V
)
Gate Voltage Vg (V)
Sour
ce C
urre
nt (1
0-12 A
)
• High threshold voltage (HOMO edge): 7.1 V• Low mobility (hole): 10-6 cm2/V-s
NC STATE UNIVERSITY UNC-Chapel Hill
A More Conductive Valence Tautomer is needed…
NC STATE UNIVERSITY UNC-Chapel Hill
Polymeric Pyrazine-BridgedCobalt Semiquinonate-Catecholate Complex
• Photomechanical polymers that show light-induced transition between different spin states – different geometries
• Potential for functional molecular spintronic devices
• Synthesized (Pierpont, JACS, 1994) but not characterized so far
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
CoIII(N-N)-(DBSQ)(DBCat)Three spin configurations: Paramagnetic Ferromagnetic Antiferromagnetic
Eg(Γ)up = 0.54 eVEg(Γ)dw = 0.25 eV
Metal Semiconductor Semiconductor
Eg(Γ)up = 0.30 eVEg(Γ)dw = 0.30 eV
Dispersive bands indicate possibility for band transport along the polymer axis
Marco Buongiorno-Nardelli and Arrigo Calzolari
NC STATE UNIVERSITY UNC-Chapel Hill
Buongiorno-Nardelli
NC STATE UNIVERSITY UNC-Chapel Hill
New Magnetic Data
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
Conclusions• Electroactive Donor-Bridge-Acceptor biradicals can be used to prepare double exchanged systems that show “long-range electron correlation.”
• This is a general molecular architecture: mixed-valent organic dyad covalently attached to a pair of localized spins.
• Molecular analog of dilute magnetic semiconductors?
• Ongoing studies of valence tautomer-oriented devices
NC STATE UNIVERSITY
NC STATE UNIVERSITY UNC-Chapel Hill
Acknowledgements
$$$National Science Foundation (CHE-0910585 and -0943975)
NC STATE UNIVERSITY
Rob Schmidt Ubie Sullivan
Geoff LewisCooper Dawson Professor Marty Kirk
Diana Habel-Rodriguez Department of Chemistry, University of New Mexico
Professor Marco Buongiorno-NardelliDepartment of Physics, NC State University
Professor Arrigo Calzolari, Trieste
Professor Frank Tsui Will RiceDepartment of Physics, UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
Ground Configuration
Quartet
Excited Configuration A
Quartet
Excited Configuration B
Quartet
NC STATE UNIVERSITY
VBCI model used to explain ferromagnetic exchange in biradical ligand complex suggests stronger ferromagnetic exchange in SDD molecule(s) due to more superexchange pathways
NC STATE UNIVERSITY UNC-Chapel HillNC STATE UNIVERSITY UNC-Chapel Hill
SiO2 baseelectrode 2electrode 1
VT single crystal
Current Measurement Designs
NC STATE UNIVERSITY UNC-Chapel HillNC STATE UNIVERSITY UNC-Chapel Hill
Self Assembled Monolayers of VT and Devices
N
SHAu film
N
NO
OCoIII
CN
CN
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
S
N
NO
OCoIII
S
CN
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
S
CN
t-Bu
t-Bu
O
Ot-Bu
t-BuN
S
N
S
N
S
N
S
N
S
N
S
N
SVT 1
VT 1N
S
N
S
N
S
N
S
O
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
S
N
S
O
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
S
Tet
pyz
Wei YouCoII
O
t-Bu
t-Bu
O O
t-Bu
t-Bu
O
4
Tet
NC STATE UNIVERSITY UNC-Chapel Hill
44
NC STATE UNIVERSITY UNC-Chapel Hill
Preliminary Results1.SAM of Pyridine thiol made;2.Ligand exchange with VT 1 was
attempted; it works!
3.XPS of surfaces were carried out; it seems that pyridine thiol was not making satisfactory SAM; new molecule was proposed and to be synthesized
N
O
HS
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
NC STATE UNIVERSITY UNC-Chapel Hill
CMS Concept Chart (Phase I)
NC STATE UNIVERSITY UNC-Chapel Hill
Valence Tautomer PolymerSynthesis
72%
30 %
75%
93%
95%
NC STATE UNIVERSITY UNC-Chapel Hill
A
CoIII
CoII
CoIII
I
Voltage, Temperature
TemperaturePressure
Light
Cat SQ SQSQCoIII CoII
NC STATE UNIVERSITY UNC-Chapel Hill
SemiQuinone Conjugated/Conducting Polymer Synthesis
NC STATE UNIVERSITY UNC-Chapel Hill
Purpose: Investigation into carrier/spin transport mechanisms and spin valve properties of magnetic polymers when placed between source and drain.Note: The current backbone is the ortho-polymer, but future work could focus on other topologies (i.e., para and/or meta)
SemiQuinone Conjugated/Conducting Polymer Synthesis(pending)
NC STATE UNIVERSITY UNC-Chapel HillNC STATE UNIVERSITY UNC-Chapel Hill
Self Assembled Monolayers of VT and Devices
N
SHAu film
N
NO
OCoIII
CN
CN
t-Bu
t-Bu
O
Ot-Bu
t-Bu
CoIIO
t-Bu
t-Bu
O O
t-Bu
t-Bu
O
4
N
S
N
NO
OCoIII
S
CN
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
S
CN
t-Bu
t-Bu
O
Ot-Bu
t-BuN
S
N
S
N
S
N
S
N
S
N
S
N
SVT 1
VT 1
VT 2
NO
OCoIII
S
t-Bu
t-Bu
O
Ot-Bu
t-BuN
O
OCoIII
S
t-Bu
t-Bu
O
Ot-Bu
t-BuN
S
N
S
N
S
N
S
N
S
N
S
N
S
O
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
S
N
S
O
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
NO
OCoIII
t-Bu
t-Bu
O
Ot-Bu
t-Bu
N
SVT 2
nTP
LBL
Wei You
NC STATE UNIVERSITY UNC-Chapel HillNC STATE UNIVERSITY UNC-Chapel Hill
FerromagnetX X X X X X X X
PEDOT:PSSTop Electrode
B
V
Ferromagnetic nanoparticle
VT molecules
Bottom Electrode
Future & Ultimate Goal
NC STATE UNIVERSITY UNC-Chapel Hill
Electronic and Magnetic Properties of Molecular Materials
NC STATE UNIVERSITY UNC-Chapel Hill
Will RiceDavid Harris and Michelle Labrecque (Undergraduates)
Prof. Frank TsuiPhysics UNC-Chapel Hill
• Electronic states and transport of valence tautomer− Collaborators: Prof. David Shultz and Rob Schmidt
(Chemistry NCSU)• Tunneling and spin dependent transport through SAMs of
organic molecules (e.g. alkanedithiols) − Collaborators: Prof. Wei You and Jeremy Niskala
(Chemistry UNC-CH)
NC STATE UNIVERSITY UNC-Chapel Hill
• Overcome challenge of attaching 4 terminals to the crystals for measurements in Van der Pauw geometry
• Explore temperature and field dependent transport parameters
• Investigate electronic states, including band gap, mobility, density of states
• Examine effects of light exposure
What’s Next
Image of layered valence tautomer crystal
NC STATE UNIVERSITY UNC-Chapel Hill
CoIII(SQ)(Cat) CoII(SQ)(SQ)
D. A. Shultz, et al., J. Am. Chem. Soc. 2005, 127, 5328
SQSQ
CoIICat SQ
CoIIICat SQ
CoIII