Control parameters on the fabrication of ZnO hollow nanocolumns

Cembrero, J.; Busquets-Mataix, D.; Rayón, E.; Pascual, María Luisa Vázquez de Ágredos; Pérez-Puig, Miguel Angel; Marı́, B.

doi:10.1016/j.mssp.2012.04.014

Cited by 6 publications

(7 citation statements)

References 13 publications

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“…Several examples of electrochemical ZnO growth perpendicular to the surface with columnar or tube-shaped morphologies from baths containing only chlorides can be found in the literature. 31,33 The EDX analysis reveals that the doping of Cl atomic concentration ranges from 0.7% to 5% for a pure perchlorate electrolyte to pure chloride electrolyte. The detection of chlorine in the material, even if no ZnCl 2 is added to the electrolyte, shows that perchlorate ions can also act as a source of chloride.…”

Section: Resultsmentioning

confidence: 99%

Effective Electrochemical n-Type Doping of ZnO Thin films for Optoelectronic Window Applications

Cembrero-Coca

Mollar

Singh

et al. 2013

ECS J. Solid State Sci. Technol.

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An effective n-type doping of ZnO thin films electrochemically synthetized was achieved by varying the chloride ion concentration in the starting electrolyte. The ratio between chloride and zinc cations was varied between 0 and 2 while the zinc concentration in the solution was kept constant. When the concentration of chloride in the bath increases an effective n-type doping of ZnO films takes place. n-type doping is evidenced by the rise of donors concentration, obtained from Mott-Schottky measurements, as well as from the blueshift observed in the optical gap owing to the Burstein-Moss effect.ZnO with low resistivity, high transmittance down to the UV spectral range, and good chemical stability under strong reducing environments is a promising transparent conductive oxide (TCO) to be used as transparent electrode for photovoltaic solar cells and electrodes on flat panel displays. 1 This role is presently reserved to conventional TCOs like FTO (Fluorine-doped tin oxide) and ITO (Indium tin oxide). Nevertheless, one of the advantages of ZnO is that can be electrochemically deposited on practically any conductive substrate. Unintentionally doped ZnO thin films are always n-type due to the presence of native donors. 2 However, for some applications a greater conductivity is required and then n-type doping has to be boosted by increasing the concentration of shallow donors. In ZnO, additional ntype doping can be attained by using group III metal elements such as Al, Ga or In, which substitute Zn. The conductivity increase depends upon the nature and amount of the ions incorporated. Up to now, metal elements like Al, 3,4 Ga, 5,6 Ba, 7 Sc, 7 Sn 8 and In 8 have been widely used for this purpose. On the other hand, elements of 1B group (Cu, Ag, Au) act as acceptors when substituting Zn. Recently, p-type behavior has been reported in Cu-doped ZnO films. 9 Further, the substitution of ZnO lattice anions can also result in an increase of the conductivity even though this option has been less explored. Substituting O by VII group elements, such as F or Cl, also results in an effective n-type doping. There are a few studies where fluor 10,11 or chlorine 12-15 replace oxygen. It is always found the doping with extrinsic ions increases conductivity and decreases transparency of films. However, the use of non-metal dopants in substitution to O was suggested as a better way to achieve high carrier concentration and mobility while keeping good transparency, due to the weaker perturbation of the ZnO conduction band expected in this configuration. 12,16 Until now, most of the research on the deposition methods has mainly been focused on vapor-phase techniques. 17 A common characteristic of these kinds of techniques is the high temperature. Temperatures around 900-1100 • C are the most frequently used in vapor−liquid−solid processes, 18,19 while lower temperatures of 400−500 • C are used in free-catalyst and more sophisticated techniques such as metal−organic chemical vapor deposition. 20 Electrochemical deposition of ZnO nanowire a...

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Section: Resultsmentioning

confidence: 99%

Effective Electrochemical n-Type Doping of ZnO Thin films for Optoelectronic Window Applications

Cembrero-Coca

Mollar

Singh

et al. 2013

ECS J. Solid State Sci. Technol.

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“…It is known that a typical spectrum of ZnO films has two characteristic peaks: a UV near-bandedge (NBE) whose peak emission is around 377 nm [19,22,23], and a deep-level (DL) emission, also known as green-band or red-band depending on if they are centred around 500 or 600 nm. A sharp NBE emission peak results from excitons and its position and structure is an indication of crystal quality.…”

Section: Figures 2a and 2bmentioning

confidence: 99%

“…A sharp NBE emission peak results from excitons and its position and structure is an indication of crystal quality. The green band is related to transitions involving defects and several point defects, such as oxygen vacancy (VO), zinc vacancy (VZn), interstitial zinc (Zni), interstitial oxygen (Oi) and antisite oxygen (OZn) [22,23], have been proposed as responsible for this emission in ZnO.…”

Section: Figures 2a and 2bmentioning

confidence: 99%

“…etching produces defects causing a deterioration of the surface and bulk quality of ZnO. Then etching, not only changes the surface morphology of the films [22], but also increases the rate of defects or impurities existing in the material generating preferentially the ones that shift PL bands towards the red. Moreover, when the temperature increases, the emission reflects the expected behaviour, i.e.…”

Section: Figures 2a and 2bmentioning

confidence: 99%

“…This last step was required just in case the second step was too aggressive giving hollow nanocolumns but very irregular in shape. Details of the procedure to deposit ZnO nanotubes can be found elsewhere [22]. After growth of both, ZnO nanocolumns and nanotubes samples were further annealed in air at 400ºC.…”

Section: Introductionmentioning

confidence: 99%

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Photoluminescent properties of electrochemically synthetized ZnO nanotubes

Jimenez

Cembrero

Mollar

et al. 2016

Materials Characterization

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ZnO nanotubes were prepared by a sequential combination of electrochemical deposition, chemical attack and regeneration. ZnO nanocolumns were initially electrodeposited on conductive substrates and then converted into nanotubes by a process involving chemical etching and subsequent regrowth. The morphology of these ZnO nanocolumns and derived nanotubes was monitored by Scanning Electron Microscopy and their optical properties was studied by photoluminescence spectroscopy. Photoluminescence were measured as a function of temperature, from 6 to 300 K, for both nanocolumns and nanotubes. In order to study the behaviour of induced intrinsic defect all ZnO films were annealed in air at 400 ºC and their photoluminescent properties were also registered before and after annealing. The behaviour of photoluminescence is explained taking into account the contribution of different point defects. A band energy diagram related to intrinsic defects was proposed to describe the behaviour of photoluminescence spectra.

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