Work function, electron affinity and band bending of zinc oxide surfaces

Jacobi, K.; Zwicker, G.; Gutmann, A.

doi:10.1016/0039-6028(84)90199-7

Cited by 226 publications

(145 citation statements)

References 21 publications

Supporting

Mentioning

109

Contrasting

Order By: Relevance

“…This effect has been reported in several previous reports of FE from ZnO and in some cases leads to nonlinear FN plots, [29][30][31] the interpretation of which is quite uncertain as a result. This hysteresis effect is generally attributed to the effect of adsorbates, and disappears following adequate conditioning of the samples.…”

Section: B Fe Apparatus and Measurementssupporting

confidence: 67%

Field emission in ordered arrays of ZnO nanowires prepared by nanosphere lithography and extended Fowler-Nordheim analyses

McCarthy

Garry

Byrne

et al. 2011

Journal of Applied Physics

View full text Add to dashboard Cite

Screened field enhancement factor for the floating sphere model of a carbon nanotube array J. Appl. Phys. 110, 114311 (2011) Field-emission-assisted approach to dry micro-electro-discharge machining of carbon-nanotube forests J. Appl. Phys. 110, 103305 (2011) The hysteresis phenomenon of the field emission from the graphene film Appl. Phys. Lett. 99, 173104 (2011) Temperature dependence of the field emission from the few-layer graphene film Appl. Phys. Lett. 99, 163103 (2011) Additional information on J. Appl. Phys. A multistage chemical method based on nanosphere lithography was used to produce hexagonally patterned arrays of ZnO vertical nanowires, with 1 lm interspacing and aspect ratio $20, with a view to study the effects of emitter uniformity on the current emitted upon application of a dc voltage across a 250 lm vacuum gap. A new treatment, based on the use of analytical expressions for the image-potential correction functions, was applied to the linear region below 2000 V of the Fowler-Nordheim (FN) plot and showed the most suitable value of the work function / in the range 3.3-4.5 eV (conduction band emission) with a Schottky lowering parameter y $ 0.72 and a field enhancement factor c in the 700-1100 range. A modeled c value of $200 was calculated for an emitter shape of a prolate ellipsoid of revolution and also including the effect of nanowire screening, in fair agreement with the experimental value. The Fowler-Nordheim current densities and effective emission areas were derived as 10 11 Am À2 and 10 À17 m 2 , respectively, showing that field emission likely takes place in an area of atomic dimensions at the tip of the emitter. Possible causes for the observed departure from linear FN plot behavior above 2000 V were discussed.

show abstract

Section: B Fe Apparatus and Measurementssupporting

confidence: 67%

Field emission in ordered arrays of ZnO nanowires prepared by nanosphere lithography and extended Fowler-Nordheim analyses

McCarthy

Garry

Byrne

et al. 2011

Journal of Applied Physics

View full text Add to dashboard Cite

show abstract

“…10,11 The for ZnO and an ionization energy of CuPc were determined to be 4.0 and 4.9 eV, which are consistent with previously reported values within the error margin of our measurements. 9,12 The band alignment between air exposed ZnO and CuPc in Fig. 4͑a͒ is indicative of a typical staggered junction with a positive 0.2 eV for eD due to charge redistribution.…”

Section: -2mentioning

confidence: 94%

“…The of sputter cleaned ZnO ͑3.4 eV͒ is in good agreement with previous results for a Zn terminated ZnO surface ͑0001͒ because oxygen on the surface is preferentially removed by sputtering during the cleaning process. 9 The valence band maximum ͑VBM͒ of ZnO and the HOMO onset position appear at 3.0 eV and 0.7 eV from the Fermi level, respectively. During the subsequent deposition of CuPc on the sputtered ZnO surface, the HOMO onset position is shifted to lower binding energy by 0.3 eV.…”

Section: -2mentioning

confidence: 99%

The effect of ZnO surface conditions on the electronic structure of the ZnO/CuPc interface

Park

Kim

Cho

et al. 2011

Applied Physics Letters

View full text Add to dashboard Cite

The interfacial electronic structures of zinc oxide ͑ZnO͒/copper-phthalocyanine ͑CuPc͒ were investigated by in situ x-ray and ultraviolet photoelectron spectroscopy ͑UPS͒ to determine the effects of air contamination on the ZnO substrate. UPS spectra showed that the 0.2 eV of the interface dipole is generated at the interface of the air exposed ZnO/CuPc while the interface of the annealed ZnO/CuPc generated Ϫ0.2 eV. In both cases, no band bending was observed. On the other hand, band bending at 0.3 eV and an interface dipole of 0.2 eV were observed at the interface of the sputter cleaned ZnO/CuPc. The energy offset between the conduction band maximum of ZnO and the highest occupied molecular orbital of CuPc was determined to be 0.6-0.7 eV for the contaminated ZnO interface while the offset was 1.0 eV for the cleaned ZnO interface. Contaminating moisture has little effect on the offset while the charge transfer was blocked and the offset was decreased in the presence of hydrocarbons. © 2011 American Institute of Physics. ͓doi:10.1063/1.3555440͔In recent years, organic photovoltaic ͑OPV͒ devices have attracted considerable attention due to their low cost, ease of fabrication, and their flexibility. 1 Many research groups have reported on attempts to improve their performances in terms of efficiency and stability. In particular, to overcome the weakness of organic materials, which include short exciton diffusion length and air instability, organicinorganic hybrid structures are generally considered to be promising applications. 2 In this respect, zinc oxide ͑ZnO͒ is the most widely used inorganic semiconductor in this type of hybrid device because of its high transparency, nontoxicity, the ease of fabrication of thin films and nanostructure properties. In addition, ZnO/organic hybrid photovoltaic devices with inverted structures show a more stable performance in air than other organic-only devices. 3 However, this hybrid device is usually contaminated at the organic/inorganic interface, as the result of the ex situ process associated with the different deposition methods between ZnO and the organic material. The presence of this contaminant may lead to interfacial states and the development of a tunneling barrier. 4 Although some concerns exist regarding this type of hybrid device due to the ex situ process used, a detailed understanding of the interfacial electronic structure with organic molecules in hybrid applications of ZnO is not available while the electronic structure and chemical bonding of organic molecules with single crystalline ZnO particles has been investigated. 5 A number of studies regarding the preparation of OPVs using copperphthalocyanine ͑CuPc͒ haves been reported because of the appropriate band gap and desirable absorption properties of CuPc.In this letter, we report on a study of the electronic structure and energy level alignments of the ZnO/CuPc interface using x-ray and ultraviolet photoemission spectroscopy ͑XPS and UPS͒ during the stepwise deposition of CuPc on each ZnO films. The sample...

show abstract

“…The physical properties of non-polar ZnO surfaces were investigated theoretically [4][5][6][7] and experimentally by low energy electron diffraction (LEED), [8][9][10] scanning tunneling microscopy (STM) and/or spectroscopy (STS), [11][12][13] and other surface sensitive techniques. [14][15][16][17] It is generally accepted that non-polar ð11 20Þ and ð10 10Þ ZnO surfaces exhibit a 1 Â 1 surface unit cell, where the surface oxygen atom relaxes slightly outward, while the surface zinc atom becomes more sp 2 hybridized. This relaxation is combined with a charge transfer from Zn to O, but the resulting electronic properties are strongly debated: Some calculations predict that the intrinsic surface states are outside of the fundamental bulk bandgap, 4,5 while a newer calculation suggests intrinsic surface states within the fundamental bandgap, at least for the ð10 10Þ surface.…”

mentioning

confidence: 99%

“…Work function measurements are inconclusive too, as some suggest a flat band situation 14 and thus the absence of intrinsic surface states in the fundamental bandgap, whereas others suggest a band bending at the ð10 10Þ surface. 16 Angular-resolved photoemission 18 and electron energy loss spectroscopy experiments 17 find no surface states within the fundamental bandgap. Over all, the electronic properties of non-polar ZnO surfaces are unclear.…”

mentioning

confidence: 99%

Intrinsic bandgap of cleaved ZnO(112¯) surfaces

Sabitova

Ebert

Lenz

et al. 2013

Applied Physics Letters

View full text Add to dashboard Cite

The existence of intrinsic surface states, the position of the Fermi level, and the size of the surface bandgap of the non-polar ZnO(112¯0) cleavage surfaces were investigated by scanning tunneling microscopy and spectroscopy. The comparison of spectroscopic measurements performed on atomically flat and stepped surfaces reveals the absence of intrinsic surface states within the fundamental bulk bandgap, but shows the occurrence of step-induced gap states. These states lead to a pinning of the Fermi level at the surface within the bandgap and generate a significant defect-related tunnel current, narrowing the measured apparent bandgap.

show abstract

Work function, electron affinity and band bending of zinc oxide surfaces

Cited by 226 publications

References 21 publications

Field emission in ordered arrays of ZnO nanowires prepared by nanosphere lithography and extended Fowler-Nordheim analyses

Field emission in ordered arrays of ZnO nanowires prepared by nanosphere lithography and extended Fowler-Nordheim analyses

The effect of ZnO surface conditions on the electronic structure of the ZnO/CuPc interface

Intrinsic bandgap of cleaved ZnO(112¯) surfaces

Contact Info

Product

Resources

About