Publications by authors named "Eirini Sarigiannidou"

6 Publications

  • Page 1 of 1

Chemical Synthesis of β-GaO Microrods on Silicon and Its Dependence on the Gallium Nitrate Concentration.

Inorg Chem 2020 Nov 20;59(21):15696-15706. Epub 2020 Oct 20.

Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France.

β-GaO microrods have attracted increasing attention for their integration into solar blind/UV photodetectors and gas sensors. However, their synthesis using a low-temperature chemical route in aqueous solution is still under development, and the physicochemical processes at work have not yet been elucidated. Here, we develop a double-step process involving the growth of α-GaOOH microrods on silicon using chemical bath deposition and their further structural conversion to β-GaO microrods by postdeposition thermal treatment. It is revealed that the concentration of gallium nitrate has a drastic effect on tuning the morphology, dimensions (i.e., diameter and length), and density of α-GaOOH microrods over a broad range, in turn governing the morphological properties of β-GaO microrods. The physicochemical processes in aqueous solution are investigated by thermodynamic computations yielding speciation diagrams of Ga(III) species and theoretical solubility plots of GaOOH(s). In particular, the qualitative evolution of the morphological properties of α-GaOOH microrods with the concentration of gallium nitrate is found to be correlated with the supersaturation in the bath and discussed in light of the standard nucleation and growth theory. Interestingly, the structural conversion following the thermal treatment at 900 °C in air results in the formation of pure β-GaO microrods without any residual minor phases and with tunable morphology and improved structural ordering. These findings reporting a double-step process for forming high-quality pure β-GaO microrods on silicon open many perspectives for their integration onto a large number of substrates for solar blind/UV photodetection and gas sensing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.inorgchem.0c02069DOI Listing
November 2020

Morphology Transition of ZnO from Thin Film to Nanowires on Silicon and its Correlated Enhanced Zinc Polarity Uniformity and Piezoelectric Responses.

ACS Appl Mater Interfaces 2020 Jul 18;12(26):29583-29593. Epub 2020 Jun 18.

Université Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France.

ZnO thin films and nanostructures have received increasing interest in the field of piezoelectricity over the last decade, but their formation mechanisms on silicon when using pulsed-liquid injection metal-organic chemical vapor deposition (PLI-MOCVD) are still open to a large extent. Also, the effects of their morphology, dimensions, polarity, and electrical properties on their piezoelectric properties have not been completely decoupled yet. By only tuning the growth temperature from 400 to 750 °C while fixing the other growth conditions, the morphology transition of ZnO deposits on silicon from stacked thin films to nanowires through columnar thin films is shown. A detailed analysis of their formation mechanisms is further provided. The present transition is associated with strong enhancement of their crystallinity and growth texture along the -axis together with a massive relaxation of the strain in nanowires. It is also related to a prevailed zinc polarity, for which its uniformity is strongly improved in nanowires. The nucleation of basal-plane stacking faults of I-type in nanowires is also revealed and related to an emission line at about 3.326 eV in cathodoluminescence spectra, further exhibiting fairly low phonon coupling. Interestingly, the transition is additionally associated with a significant improvement of the piezoelectric amplitude, as determined by piezoresponse force microscopy measurements. The Zn-polar domains exhibit a larger piezoelectric amplitude than the O-polar domains, showing the importance of controlling the polarity in these deposits as a prerequisite to enhance the performances of piezoelectric devices. The present findings demonstrate the high potential in using the PLI-MOCVD system to form ZnO with different morphologies and polarity uniformity on silicon. They further reveal unambiguously the superiority of nanowires over thin films for piezoelectric devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.0c04112DOI Listing
July 2020

Formation mechanisms of ZnO nanowires on polycrystalline Au seed layers for piezoelectric applications.

Nanotechnology 2019 Aug 29;30(34):345601. Epub 2019 Apr 29.

Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France. Univ. Grenoble Alpes, CNRS, LTM, F-38054 Grenoble Cedex, France. Univ. Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France.

ZnO nanowires are considered as attractive building blocks for piezoelectric devices, including nano-generators and stress/strain sensors. However, their integration requires the use of metallic seed layers, on top of which the formation mechanisms of ZnO nanowires by chemical bath deposition are still largely open. In order to tackle that issue, the nucleation and growth mechanisms of ZnO nanowires on top of Au seed layers with a thickness in the range of 5-100 nm are thoroughly investigated. We show that the ZnO nanowires present two different populations of nano-objects with a given morphology. The majority primary population is made of vertically aligned ZnO nanowires, which are heteroepitaxially formed on top of the Au (111) grains. The resulting epitaxial strain is found to be completely relieved at the Au/ZnO interface. In contrast, the minority secondary population is composed of ZnO nanowires with a significant mean tilt angle around 20° with respect to the normal to the substrate surface, which are presumably formed on the (211) facets of the Au (111) grains. The elongation of ZnO nanowires is further found to be limited by the surface reaction at the c-plane top facet in the investigated conditions. By implementing the selective area growth using electron beam lithography, the position of ZnO nanowires is controlled, but the two populations still co-exist in the ensemble. These findings provide an in-depth understanding of the formation mechanisms of ZnO nanowires on metallic seed layers, which should be taken into account for their more efficient integration into piezoelectric devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6528/ab1d6eDOI Listing
August 2019

Spontaneous shape transition of thin films into ZnO nanowires with high structural and optical quality.

Nanoscale 2015 Oct;7(40):16994-7003

Université Grenoble Alpes, CNRS, LMGP, F-38000 Grenoble, France.

ZnO nanowires are usually formed by physical and chemical deposition techniques following the bottom-up approach consisting in supplying the reactants on a nucleation surface heated at a given temperature. We demonstrate an original alternative approach for the formation of ZnO nanowire arrays with high structural and optical quality, which is based on the spontaneous transformation of a ZnO thin film deposited by sol-gel process following a simple annealing. The development of these ZnO nanowires occurs through successive shape transitions, including the intermediate formation of pyramid-shaped islands. Their nucleation under near-equilibrium conditions is expected to be governed by thermodynamic considerations via the total free energy minimization related to the nanowire shape. It is further strongly assisted by the drastic reordering of the matter and by recrystallization phenomena through the massive transport of zinc and oxygen atoms towards the localized growth areas. The spontaneous shape transition process thus combines the easiness and low-cost of sol-gel process and simple annealing with the assets of the vapor phase deposition techniques. These findings cast a light on the fundamental mechanisms driving the spontaneous formation of ZnO nanowires and, importantly, reveal the great technological potential of the spontaneous shape transition process as a promising alternative approach to the more usual bottom-up approach.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5nr04394hDOI Listing
October 2015

Selective area growth of well-ordered ZnO nanowire arrays with controllable polarity.

ACS Nano 2014 May 18;8(5):4761-70. Epub 2014 Apr 18.

Univ. Grenoble Alpes, LMGP , F-38000 Grenoble, France.

Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nn500620tDOI Listing
May 2014

Stability of high temperature chemical vapor deposited silicon based structures on metals for solar conversion.

J Nanosci Nanotechnol 2011 Sep;11(9):8318-22

SIMaP Grenoble INP UJF, CNRS, 38402 Saint Martin d'Hères, France.

Highly crystallized silicon layers were grown on metal sheets at high temperature (950 degrees C) by thermal CVD from silane. An intermediate buffer layer was mandatory to prevent interdiffusion and silicide formation but also to compensate lattice parameters and thermal expansion coefficients mismatches between metal and silicon and ideally transfer some crystalline properties (grain size, texture) from the substrate to the silicon layer. After a thermodynamic study, aluminum nitride or titanium nitride diffusion barrier layers were selected and processed by CVD. The structure and the interfaces stabilities of these silicon/nitride/metal stacks were studied by field effect gun scanning and transmission electron microscopy, X-ray diffraction, Raman and energy dispersive X-ray spectroscopy. As a result, TiN deposited by CVD appears to be an efficient material as a buffer layer between steel and silicon.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1166/jnn.2011.5077DOI Listing
September 2011