TY - JOUR
T1 - Measuring Dipole Inversion in Self-Assembled Nano-Dielectric Molecular Layers
AU - Zeng, Li
AU - Turrisi, Riccardo
AU - Fu, Bo
AU - Emery, Jonathan D.
AU - Walker, Amanda R.
AU - Ratner, Mark A.
AU - Hersam, Mark C.
AU - Facchetti, Antonio F.
AU - Marks, Tobin J.
AU - Bedzyk, Michael J.
N1 - Funding Information:
This research was supported by the Northwestern University MRSEC (NSF DMR-1121262). XSW and XRR measurements were performed at 33BM-C of the Advanced Photon Source (APS) of Argonne National Lab, supported by the DOE under grant number DE-AC02-06CH11357. A.F. thanks the Shenzhen Peacock Plan project (KQTD20140 630110339343) and AFOSR (FA95501510044) for financial support. We also gratefully acknowledge the computational resources from the Quest high performance computing facility at Northwestern University and the Extreme Science and Engineering Discovery Environment (XSEDE) program, which is supported by National Science Foundation grant number ACI-1053575. We thank Dr. Chian Liu and Dr. Bing Shi from the APS Optics Group for the deposition of Si/Mo multilayer substrates.
PY - 2018/2/21
Y1 - 2018/2/21
N2 - A self-assembled nanodielectric (SAND) is an ultrathin film, typically with periodic layer pairs of high-k oxide and phosphonic-acid-based π-electron (PAE) molecular layers. IPAE, having a molecular structure similar to that of PAE but with an inverted dipole direction, has recently been developed for use in thin-film transistors. Here we report that replacing PAE with IPAE in SAND-based thin-film transistors induces sizable threshold and turn-on voltage shifts, indicating the flipping of the built-in SAND polarity. The bromide counteranion (Br-) associated with the cationic stilbazolium portion of PAE or IPAE is of great importance, because its relative position strongly affects the electric dipole moment of the organic layer. Hence, a set of X-ray synchrotron measurements were designed and performed to directly measure and compare the Br- distributions within the PAE and IPAE SANDs. Two trilayer SANDs, consisting of a PAE or IPAE layer sandwiched between an HfOx and a ZrOx layer, were deposited on the SiOx surface of Si substrates or periodic Si/Mo multilayer substrates for X-ray reflectivity and X-ray standing wave measurements, respectively. Along with complementary DFT simulations, the spacings, elemental (Hf, Br, and Zr) distributions, molecular orientations, and Mulliken charge distributions of the PAE and IPAE molecules within each of the SAND trilayers were determined and correlated with the dipole inversion.
AB - A self-assembled nanodielectric (SAND) is an ultrathin film, typically with periodic layer pairs of high-k oxide and phosphonic-acid-based π-electron (PAE) molecular layers. IPAE, having a molecular structure similar to that of PAE but with an inverted dipole direction, has recently been developed for use in thin-film transistors. Here we report that replacing PAE with IPAE in SAND-based thin-film transistors induces sizable threshold and turn-on voltage shifts, indicating the flipping of the built-in SAND polarity. The bromide counteranion (Br-) associated with the cationic stilbazolium portion of PAE or IPAE is of great importance, because its relative position strongly affects the electric dipole moment of the organic layer. Hence, a set of X-ray synchrotron measurements were designed and performed to directly measure and compare the Br- distributions within the PAE and IPAE SANDs. Two trilayer SANDs, consisting of a PAE or IPAE layer sandwiched between an HfOx and a ZrOx layer, were deposited on the SiOx surface of Si substrates or periodic Si/Mo multilayer substrates for X-ray reflectivity and X-ray standing wave measurements, respectively. Along with complementary DFT simulations, the spacings, elemental (Hf, Br, and Zr) distributions, molecular orientations, and Mulliken charge distributions of the PAE and IPAE molecules within each of the SAND trilayers were determined and correlated with the dipole inversion.
KW - DFT
KW - X-ray standing waves
KW - dipole inversion
KW - dipole moment
KW - organic thin film transistor
KW - self-assembled monolayer
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U2 - 10.1021/acsami.7b16160
DO - 10.1021/acsami.7b16160
M3 - Article
C2 - 29378110
AN - SCOPUS:85042532024
VL - 10
SP - 6484
EP - 6490
JO - ACS applied materials & interfaces
JF - ACS applied materials & interfaces
SN - 1944-8244
IS - 7
ER -