Effect of substrate temperature on vapor-phase self-assembly of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors

Swati Gupta, Pavol Sutta, Dimitrios Lamprou, Helena Gleskova

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

N-octylphosphonic acid (C8PA) monolayer was self-assembled on aluminium oxide (AlOx) from vapour in vacuum, while the substrate temperature was varied between 25 and 150°C. The capacitance, water contact angle measurement, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM) confirmed the presence of C8PA on AlOx for all growth temperatures. However, the structural and electrical properties of such monolayers depend on their growth temperature. The minimum surface roughness of 0.36 nm, the maximum water contact angle of 113.5°±1.4°, the lowest leakage current density of ~ 10-7 A/cm2 at 3 V, and the capacitance of 0.43 µF/cm2 were obtained for AlOx/C8PA bi-layers with C8PA deposited at 25°C. The elevated temperature led to increased surface roughness, decreased water contact angle, increased leakage current, inferior molecular ordering, and lower molecular coverage; while the effect on the chemisorption of the phosphonate was minimal. Methyl and methylene FTIR vibrations associated with C8PA aliphatic tails exhibited similar centre-peak wavenumbers to those observed for C8PA monolayers assembled from solutions, presenting a viable ‘dry’ alternative to the existing solution process.
The substrate temperature applied during C8PA self-assembly also affected the parameters of pentacene thin-film transistors with AlOx/C8PA gate dielectrics. The increase in the growth temperature from 25 to 150°C decreased the field-effect mobility from 0.060 to 0.026 cm2/Vs and increased the threshold voltage from -1.19 to -1.38 V, while maintaining the off-current at or below 10-12 A and the subthreshold slope near 90 mV/decade.

LanguageEnglish
Pages2468–2475
Number of pages8
JournalOrganic Electronics
Volume14
Issue number10
Early online date27 Jun 2013
DOIs
Publication statusPublished - Oct 2013

Fingerprint

Aluminum Oxide
Thin film transistors
low voltage
Self assembly
self assembly
Monolayers
Growth temperature
transistors
Vapors
vapor phases
Contact angle
Aluminum
acids
Oxides
Acids
Electric potential
Substrates
thin films
aluminum oxides
Leakage currents

Keywords

  • self-assembled monolayer (SAM)
  • vapour-phase
  • organic thin-film transistor
  • vacuum growth
  • substrate temperature
  • vapour-phase self-assembly

Cite this

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title = "Effect of substrate temperature on vapor-phase self-assembly of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors",
abstract = "N-octylphosphonic acid (C8PA) monolayer was self-assembled on aluminium oxide (AlOx) from vapour in vacuum, while the substrate temperature was varied between 25 and 150°C. The capacitance, water contact angle measurement, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM) confirmed the presence of C8PA on AlOx for all growth temperatures. However, the structural and electrical properties of such monolayers depend on their growth temperature. The minimum surface roughness of 0.36 nm, the maximum water contact angle of 113.5°±1.4°, the lowest leakage current density of ~ 10-7 A/cm2 at 3 V, and the capacitance of 0.43 µF/cm2 were obtained for AlOx/C8PA bi-layers with C8PA deposited at 25°C. The elevated temperature led to increased surface roughness, decreased water contact angle, increased leakage current, inferior molecular ordering, and lower molecular coverage; while the effect on the chemisorption of the phosphonate was minimal. Methyl and methylene FTIR vibrations associated with C8PA aliphatic tails exhibited similar centre-peak wavenumbers to those observed for C8PA monolayers assembled from solutions, presenting a viable ‘dry’ alternative to the existing solution process. The substrate temperature applied during C8PA self-assembly also affected the parameters of pentacene thin-film transistors with AlOx/C8PA gate dielectrics. The increase in the growth temperature from 25 to 150°C decreased the field-effect mobility from 0.060 to 0.026 cm2/Vs and increased the threshold voltage from -1.19 to -1.38 V, while maintaining the off-current at or below 10-12 A and the subthreshold slope near 90 mV/decade.",
keywords = "self-assembled monolayer (SAM), vapour-phase , organic thin-film transistor , vacuum growth, substrate temperature, vapour-phase self-assembly",
author = "Swati Gupta and Pavol Sutta and Dimitrios Lamprou and Helena Gleskova",
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language = "English",
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journal = "Organic Electronics",
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Effect of substrate temperature on vapor-phase self-assembly of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors. / Gupta, Swati; Sutta, Pavol; Lamprou, Dimitrios; Gleskova, Helena.

In: Organic Electronics, Vol. 14, No. 10, 10.2013, p. 2468–2475.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Effect of substrate temperature on vapor-phase self-assembly of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors

AU - Gupta, Swati

AU - Sutta, Pavol

AU - Lamprou, Dimitrios

AU - Gleskova, Helena

PY - 2013/10

Y1 - 2013/10

N2 - N-octylphosphonic acid (C8PA) monolayer was self-assembled on aluminium oxide (AlOx) from vapour in vacuum, while the substrate temperature was varied between 25 and 150°C. The capacitance, water contact angle measurement, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM) confirmed the presence of C8PA on AlOx for all growth temperatures. However, the structural and electrical properties of such monolayers depend on their growth temperature. The minimum surface roughness of 0.36 nm, the maximum water contact angle of 113.5°±1.4°, the lowest leakage current density of ~ 10-7 A/cm2 at 3 V, and the capacitance of 0.43 µF/cm2 were obtained for AlOx/C8PA bi-layers with C8PA deposited at 25°C. The elevated temperature led to increased surface roughness, decreased water contact angle, increased leakage current, inferior molecular ordering, and lower molecular coverage; while the effect on the chemisorption of the phosphonate was minimal. Methyl and methylene FTIR vibrations associated with C8PA aliphatic tails exhibited similar centre-peak wavenumbers to those observed for C8PA monolayers assembled from solutions, presenting a viable ‘dry’ alternative to the existing solution process. The substrate temperature applied during C8PA self-assembly also affected the parameters of pentacene thin-film transistors with AlOx/C8PA gate dielectrics. The increase in the growth temperature from 25 to 150°C decreased the field-effect mobility from 0.060 to 0.026 cm2/Vs and increased the threshold voltage from -1.19 to -1.38 V, while maintaining the off-current at or below 10-12 A and the subthreshold slope near 90 mV/decade.

AB - N-octylphosphonic acid (C8PA) monolayer was self-assembled on aluminium oxide (AlOx) from vapour in vacuum, while the substrate temperature was varied between 25 and 150°C. The capacitance, water contact angle measurement, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM) confirmed the presence of C8PA on AlOx for all growth temperatures. However, the structural and electrical properties of such monolayers depend on their growth temperature. The minimum surface roughness of 0.36 nm, the maximum water contact angle of 113.5°±1.4°, the lowest leakage current density of ~ 10-7 A/cm2 at 3 V, and the capacitance of 0.43 µF/cm2 were obtained for AlOx/C8PA bi-layers with C8PA deposited at 25°C. The elevated temperature led to increased surface roughness, decreased water contact angle, increased leakage current, inferior molecular ordering, and lower molecular coverage; while the effect on the chemisorption of the phosphonate was minimal. Methyl and methylene FTIR vibrations associated with C8PA aliphatic tails exhibited similar centre-peak wavenumbers to those observed for C8PA monolayers assembled from solutions, presenting a viable ‘dry’ alternative to the existing solution process. The substrate temperature applied during C8PA self-assembly also affected the parameters of pentacene thin-film transistors with AlOx/C8PA gate dielectrics. The increase in the growth temperature from 25 to 150°C decreased the field-effect mobility from 0.060 to 0.026 cm2/Vs and increased the threshold voltage from -1.19 to -1.38 V, while maintaining the off-current at or below 10-12 A and the subthreshold slope near 90 mV/decade.

KW - self-assembled monolayer (SAM)

KW - vapour-phase

KW - organic thin-film transistor

KW - vacuum growth

KW - substrate temperature

KW - vapour-phase self-assembly

U2 - 10.1016/j.orgel.2013.06.005

DO - 10.1016/j.orgel.2013.06.005

M3 - Article

VL - 14

SP - 2468

EP - 2475

JO - Organic Electronics

T2 - Organic Electronics

JF - Organic Electronics

SN - 1566-1199

IS - 10

ER -