Tag Archives: PPP-EFM

Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet

Graphene, since its discovery in 2004 has attracted enormous interest due to its physical and chemical properties, and wide applications. *

Graphene oxide (GO) has emerged as an attractive alternative to graphene due to low cost, large scale production and solution processability. GO is prepared by oxidative exfoliation of graphite.*

The work function is a fundamental electronic property of a material and can be used to interpret the relative position of the Fermi level.*

For efficient transport of electrons or holes in a heterojunction device, the work function of the materials plays a crucial role, since work function determines how the bands will align at the contacts.*

Recently there has been an increased interest in applications of GO for interfacial layers and transparent electrode materials in optoelectronic devices e.g. liquid crystal displays (LCDs), organic light emitting diodes (OLEDs), touch screens, dye-sensitized solar cells (DSSCs) and as supercapacitor electrodes. Tuning the work function of GO is key to achieving high performance devices. *

In the article “Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet” by Avishek Dey, Paheli Ghosh, James Bowen, Nicholas St. J. Braithwaite and Satheesh Krishnamurthy, the authors demonstrate doping graphene oxide (GO) films using a low power atmospheric pressure plasma jet (APPJ) with subsequent tuning of the work function.*

The surface potential of the plasma functionalized GO films could be tuned by 120 ± 10 mV by varying plasma parameters. *

Scanning Kelvin probe microscopy ( SKPM ) also known as Kelvin probe force microscopy ( KPFM ) measurements were carried out to realize changes in work function of the GO films with plasma functionalization.*

NANOSENSORS™ PointProbe® Plus PPP-EFM AFM probes with a platinum iridium coating were used to perform surface potential measurements. *

The Kelvin probe studies showed that the bonding configuration can influence the work function of GO. Pyridinic nitrogen transforms GO to p-type while graphitic nitrogen increases the electron density of GO and transforming it to n type. Pointing to the fact that a low power APPJ can effectively tune the work function of GO and hence the conductivity. *

The findings presented in the article are extremely useful in fabricating heterojunction devices like sensors and optoelectronic devices where band structure alignment is key to device performance when GO is used as a charge transport layer. This technique can be extended to other known 2D systems.*

Fig. 10 (a) from “Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet” by Avishek Dey et al.:

a) KPFM surface potential map of reference GO thin film ( please have a look at https://pubs.rsc.org/image/article/2020/CP/c9cp06174f/c9cp06174f-f10_hi-res.gif for the full figure.)
Figure 10 (a) from “Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet” by Avishek Dey et al.:

a) KPFM surface potential map of reference GO thin film ( please have a look at https://pubs.rsc.org/image/article/2020/CP/c9cp06174f/c9cp06174f-f10_hi-res.gif for the full figure.)

*Avishek Dey, Paheli Ghosh, James Bowen, Nicholas St. J. Braithwaite and Satheesh Krishnamurthy
Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet
Physical Chemistry Chemical Physics, 2020, 22, 7685-7698
DOI: 10.1039/C9CP06174F

Please follow this external link for the full article: https://pubs.rsc.org/en/content/articlehtml/2020/cp/c9cp06174f

Open Access: The article “Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet” by Avishek Dey, logoa, Paheli Ghosh, James Bowen, Nicholas St. J. Braithwaite and Satheesh Krishnamurthy is licensed under a Creative Commons Attribution 3.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/.

Ferroelectricity-free lead halide perovskites

In the recent publication “Ferroelectricity-free lead halide perovskites” Andrés Gómez, Qiong Wang, Alejandro R. Goñi, Mariano Campoy-Quilesa and Antonio Abate describe how they employed direct piezoelectric force microscopy ( DPFM ) to examine whether or not lead halide perovskites exhibit ferroelectricity.*

Their article aims to provide a deeper understanding of the fundamental physical properties of the organic–inorganic lead halide perovskites and solves a longstanding dispute about their non-ferroelectric character: an issue of high relevance for optoelectronic and photovoltaic applications.*

In the course of their research in which besides using DPFM, they also employed piezoelectric force microscopy ( PFM ) and electrostatic force microscopy ( EFM ), they could demonstrate the non-ferroelectricity of lead halide perovskites. *

The PFM images were acquired using a PtIr coated NANOSENSORS PPP-EFM AFM probe.

Fig. 5 from “Ferroelectricity-free lead halide perovskites” by Andrés Gómez et al.: Scheme of the three AFM modes DPFM (a), EFM (b) and PFM (c) with the measurement results of the MAPbI3 perovskite at a film thickness of 152 nm ((i): scanning from left to right, and (ii): scanning from right to left for DPFM measurements; and (iii) and (iv) for EFM and PFM measurements, respectively), 218 nm ((v): scanning from left to right, and (vi): scanning from right to left for DPFM measurements; and (vii) and (viii) for EFM and PFM measurements, respectively), and 400 nm ((ix): scanning from left to right, and (x): scanning from right to left for DPFM measurements; and (xi) and (xii) for EFM and PFM measurements, respectively). Insets given in (iii), (vii), and (xi) are the topography channel of EFM images of the samples.

*Andrés Gómez, Qiong Wang, Alejandro R. Goñi, Mariano Campoy-Quilesa, Antonio Abate
Ferroelectricity-free lead halide perovskites
Energy Environ. Sci., 2019, Advance Article
doi: 10.1039/C9EE00884E

Please follow this external link to the full article: https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee00884e#!divAbstract

Open Access: The article “Ferroelectricity-free lead halide perovskites” by Andrés Gómez, Qiong Wang, Alejandro R. Goñi, Mariano Campoy-Quilesa and Antonio Abate is licensed under a Creative Commons Attribution 3.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. To view a copy of this license, visit https://creativecommons.org/licenses/by/3.0/

Optical control of polarization in ferroelectric heterostructures

“In the ferroelectric devices, polarization control is usually accomplished by application of an electric field.”* In the article “Optical control of polarization in ferroelectric heterostructures” Tao Li et al. demonstrate optically induced polarization switching in BaTiO3-based ferroelectric heterostructures utilizing a two-dimensional narrow-gap semiconductor MoS2 as a top electrode.

NANOSENSORS PPP-EFM PtIr coated AFM probes were used to perform the KPFM and PFM measurements mentioned in the article cited below.

Figure 1 from “Optical control of polarization in ferroelectric heterostructures”: Electrically induced polarization switching in the MoS2/BaTiO3/SrRuO3 junction. a, b PFM phase (a) and amplitude (b) images after application of a negative voltage pulse (−5 V, 0.5 s) to the MoS2 flake. The 12-u.c.-thick BTO film underneath the MoS2 flake is fully switched to the upward polarization, Pup. c, d PFM phase (c) and amplitude (d) images after application of several positive voltage pulses (+5 V, 0.5 s) to the MoS2 flake. BTO underneath the MoS2 flake is fully switched to downward polarization, Pdown. The polarization state of the bare BTO film (at the lower right corner) is not affected by the electrical bias. e, f The I–V characteristics of the same junction measured in the dark and during illumination. The tunneling current for the OFF state (Pup) is largely increased under illumination. Silicon AFM probes with Pt/Ir conductive coating and nominal stiffness of 3 N m−1 (PPP-EFM, NANOSENSORS) were used to perform the KPFM and PFM measurements.
Figure 1 from “Optical control of polarization in ferroelectric heterostructures”:
Electrically induced polarization switching in the MoS2/BaTiO3/SrRuO3 junction. a, b PFM phase (a) and amplitude (b) images after application of a negative voltage pulse (−5 V, 0.5 s) to the MoS2 flake. The 12-u.c.-thick BTO film underneath the MoS2 flake is fully switched to the upward polarization, Pup. c, d PFM phase (c) and amplitude (d) images after application of several positive voltage pulses (+5 V, 0.5 s) to the MoS2 flake. BTO underneath the MoS2 flake is fully switched to downward polarization, Pdown. The polarization state of the bare BTO film (at the lower right corner) is not affected by the electrical bias. e, f The I–V characteristics of the same junction measured in the dark and during illumination. The tunneling current for the OFF state (Pup) is largely increased under illumination

*Tao Li, Alexey Lipatov, Haidong Lu, Hyungwoo Lee, Jung-Woo Lee, Engin Torun, Ludger Wirtz, Chang-Beom Eom, Jorge Íñiguez, Alexander Sinitskii, Alexei Gruverman
Optical control of polarization in ferroelectric heterostructures
Nature Communications, volume 9, Article number: 3344 (2018)
DOI: https://doi.org/10.1038/s41467-018-05640-4

Please follow this external link to read the full article: https://rdcu.be/bdFYw

Open Access:  The article “Optical control of polarization in ferroelectric heterostructures” by Tao Li et. Al. is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.