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Measuring Dipole Inversion in Self-Assembled Nano-Dielectric Molecular Layers

Journal Article · · ACS Applied Materials and Interfaces
 [1];  [2];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Univ. of Milano-Bicocca (Italy)
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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. In this paper 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.
Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Organization:
National Science Foundation (NSF); Shenzhen Peacock Plan; US Air Force Office of Scientific Research (AFOSR)
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1432885
Journal Information:
ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 7 Vol. 10; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
ENGLISH

Figures / Tables (5)

Figure 1(p. 8)figure Figure 1
Figure 2(p. 12)figure Figure 2
Figure 3(p. 13)figure Figure 3
Table 1(p. 15)table Table 1
Figure 4(p. 17)figure Figure 4

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Related Subjects

36 MATERIALS SCIENCE
DFT
X-ray standing waves
dipole inversion
dipole moment
organic thin film transistor
self-assembled monolayer