Quantitative Study on the Effect of Surface Treatments on the Electric Characteristics of ZnO Nanowires

Xie

Phys. Chem. Chem. Phys.

et al. 2015

Porous ZnO nanocrystalline films have been widely used in optoelectronic and gas-sensing applications. However, the effect mechanisms of the external fields, such as light, heat and atmosphere, are still controversial. In this work, the multi-variable coupling effects of the UV light, heat and oxygen were thoroughly studied by a newly proposed method, the central idea of which was to first isolate each effect of the fields on electron concentration and mobility, and then analyze how the coupling effects were achieved. Our results revealed the important roles of oxygen adsorption-induced interface barriers and photo-assisted thermal ionization first proposed here, because of which the positive coupling effect of UV light/heat and oxygen, as well as the negative coupling effect of UV light and heat was observed. Our work provides inspiration for studies on metal oxides from both the whole idea and the detailed argument.

Section: Isolating the Effects Of Oxygen And Heat In The Darksupporting

confidence: 75%

Assessing multi-variable coupling effects of UV illumination, heat and oxygen on porous ZnO nanocrystalline film through electron concentration and mobility extraction

Xie

Phys. Chem. Chem. Phys.

et al. 2015

“…26,29 Assuming E F moves down to E D at 600 K which is close to the starting value of the high-temperature stage and the defects have mostly ionized from this temperature ( Figure S3, Supporting Information), N D is calculated to be 2.64 × 17 cm −3 based on eq 3, which is comparable with other works (on the order of 10 17 ∼10 18 cm −3 ). 28,30,31 Then the electron concentration at the low-temperature stage can be evaluated by the following equation, if weak ionization is supposed 19 is equal to 63, ≫0.5, which is consistent with the hypothetical condition for eq 4, so the assumption of weak ionization at the low-temperature stage is reasonable. From the above discussion in this section, we can conclude that the conduction electrons are mainly provided by the defect ionization with the ionization energy of 0.3 eV, from weak ionization at the low-temperature stage to almost complete ionization at the high-temperature stage.…”

Section: Resultsmentioning

confidence: 59%

“…According to the related works, the main donor in ZnO is oxygen vacancy, which has the ionization energy (Δ E D ) about 0.3 eV. − From the basic knowledge of semiconductor physics, it could be found that the Fermi level ( E F ) moves down as the ionization goes on, and when E F is equal to E D about 1/3 of the defects have been ionized. Then the defect concentration ( N D ) can be evaluated by the following formula n = N normalC nobreak0em0.25em⁡ exp ( − E C − E F K B T ) = N normalC nobreak0em0.25em⁡ exp ( − E C − E D K B T ) = 1 3 N normalD where N C is equal to 1.92 × 10 15 T 3/2 cm –3 . , Assuming E F moves down to E D at 600 K which is close to the starting value of the high-temperature stage and the defects have mostly ionized from this temperature (Figure S3, Supporting Information), N D is calculated to be 2.64 × 17 cm –3 based on eq , which is comparable with other works (on the order of 10 17 ∼10 18 cm –3 ). ,, Then the electron concentration at the low-temperature stage can be evaluated by the following equation, if weak ionization is supposed n = true( N normalC N normalD 2 true) 1 / 2 …”

Section: Resultsmentioning

confidence: 99%

Synchronously Deriving Electron Concentration and Mobility by Temperature- and Oxygen-Dependent Conductivity of Porous ZnO Nanocrystalline Film

et al. 2014

A simple and effective way to get electron concentration and mobility accurately is significant for the electronic and photoelectric applications of porous ZnO nanocrystalline film. On the basis of the defect ionization and the electron scattering, we proposed here a new temperature-programmed-dependent conductivity-based synchronous derivation method (TPDCBSD) to evaluate electron concentration and mobility of porous ZnO nanocrystalline film independently. The obtained results were consistent with others. Compared with the commonly used Hall-effect measurements, the TPDCBSD method is much more simple, has lower noise, and is convenient to couple external fields. More importantly, the extracted electron concentration and electron mobility are relatively independent. Besides, a series of physical parameters related to the effects of temperature and oxygen partial pressure were obtained, and the coupling effect of temperature and oxygen was discussed in this work, which are inspiring for the applications of porous ZnO nanocrystalline film.

J. Phys.: Condens. Matter

“…Of most interest is the O 1s spectrum as this can reveal details of oxygen associated with hydroxyls, water, surface lattice oxygen and organic molecules. To examine the measured changes the O 1s peak was fitted with two or three Gaussian-Lorentzian components [53,56] which accurately matched the envelope to the raw data.…”

Section: ≡ -Equationmentioning

confidence: 99%

“…[61] The oxygen plasma has the effect of reducing the number of oxygen vacancies and/or increasing Zn vacancies which reduce the carrier concentration near the surface increasing the sample resistivity as shown by the multi-probe transport measurements. [30,51,56,64,65] The O-S peak of the as-received sample originates from a combination and balance of adsorbed surface oxygen ions, H 2 O, hydroxyls and adventitious carbon/hydrocarbons molecules all competing for adsorption sites. The emission associated with hydroxyl groups, or O 2ions in oxygen deficient regions on the ZnO surface, is often considered to be at a BE of ~1 eV nearer to the O-Zn peak than adsorbed H 2 O, O 2and oxocarbons which are generally considered to create a peak at up to ~3 eV greater BE than the O-Zn.…”

Section: ≡ -Equationmentioning

confidence: 99%

Surface sensitivity of four-probe STM resistivity measurements of bulk ZnO correlated to XPS

Lord

Evans

Barnett

et al. 2017

Multi-probe instruments based on scanning tunnelling microscopy (STM) are becoming increasingly common for their ability to perform nano- to atomic-scale investigations of nanostructures, surfaces and in situ reactions. A common configuration is the four-probe STM often coupled with in situ scanning electron microscopy (SEM) that allows precise positioning of the probes onto surfaces and nanostructures enabling electrical and scanning experiments to be performed on highly localised regions of the sample. In this paper, we assess the sensitivity of four-probe STM for in-line resistivity measurements of the bulk ZnO surface. The measurements allow comparisons to established models that are used to relate light plasma treatments (O and H) of the surfaces to the resistivity measurements. The results are correlated to x-ray photoelectron spectroscopy (XPS) and show that four-probe STM can detect changes in surface and bulk conduction mechanisms that are beyond conventional monochromatic XPS.