Initiation and Formation of Porous GaAs

Schmuki, Patrik; Fraser, J.; Vitus, Carissima M.; Graham, M. J.; Isaacs, H.S.

doi:10.1149/1.1837204

Cited by 170 publications

(121 citation statements)

References 2 publications

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“…Schmuki et al 38 were found to both occur at a potential region that is near −0.8 V vs SCE until all the oxide was reduced. This value corresponds well with the one observed here in the initial part of the transient in Figure 4c, for the reduction of the Fe-rich oxide generated from step 2.…”

Section: Discussionmentioning

confidence: 99%

Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Geng¹,

Liang²,

Podlaha³

2017

J. Electrochem. Soc.

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Fe-Ni-Co nanotips at the end of nanowires are fabricated at the interface of two Fe-Ni-Co regions via a combination of pulse electrodeposition, anodization and chemical etching. The conditions to electrodeposit and anodize the Fe-Ni-Co nanowires in polycarbonate templates were investigated with a rotating cylinder electrode (RCE) to inspect the polarization behavior of the thin film deposition. The wires were fabricated with three, consecutive electrochemical conditions, where first an Fe-Ni-Co wire segment is deposited, followed by an anodic potential to induce growth of an iron oxide thin film, and then followed by an applied, pulse cathodic current density to reduce the oxide and deposit another layer of Fe-Ni-Co. Upon etching, tips formed at the end of the last Fe-Ni-Co region, as evidenced by SEM. Potential transients during the last applied cathodic pulse current step, suggests that both the reduction of the oxide and metal occur, and that TEM/SAED confirm changes in the crystalline Fe-Ni-Co structure at the interfacial region between steps that contributes to the tip formation. Electrodeposition conditions to fabricate nanowires using nanoporous templates have been widely examined for different applications, and several good reviews summarize the vast number of metal and alloy nanowire systems considered.1-4 Different nanowire morphologies have been reported, some directly formed within the templates, such as nanotubes, [5][6][7] and those that are subsequently etched once released from their templates, such as nanogaps, 4,8 and porous nanowires, 9,10 or through subsequent annealing or displacement reactions resulting in interesting structures, such as nanopeapods. 11,12In addition, Geng and Podlaha 13 recently, showed that Cu-Fe-Ni-Co nanowires could be etched in a preferred radial direction, thinning nanowire segments.Nanowires that are shaped into tips at one end, nanotips, have been widely researched due to their application as cantilever tips for high-resolution atomic force microscopy (AFM), 14,15 tip-enhanced near-field optical microscopy, 16 and scanning tunneling microscopy (STM), [17][18][19] and the need has recently expanded to bio/chemical sensors to measure electrical conduction as a new methodology for molecular detection and monitoring. [20][21][22][23] The reported nanotip materials used in AFM/STM are usually W and Pt/Ir, which are prepared through a "drop off" technique, where the tungsten wire is immersed in a KOH solution (etchant) acting as an anodic electrode; the highest etching rate appears just below the air/electrolyte interface, causing necking and eventual "drop off" of the bottom part of the wire, leaving a sharp tip. 14,17,19,24,25 Alternative methods for fabricating nanotips include: focused ion beam (FIB) lithography, 26 vapor-liquidsolid method (VLS), 27,28 and a novel, self-masking technique where SiC nanosized clusters are generated on top of a substrate, followed by a dry etch of the unmasked substrate regions to create nanotips where the SiC clusters reside. 29In this...

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Section: Discussionmentioning

confidence: 99%

Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Geng¹,

Liang²,

Podlaha³

2017

J. Electrochem. Soc.

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“…Anion type and concentration can play a significant role in affecting the pore growth and morphology (6,7). The depth of porous layers and their preferential crystallographic growth directions have been shown to be affected by the substrate type (8), orientation (9) and doping density (10).…”

Section: Introductionmentioning

confidence: 99%

Effect of Electrolyte Concentration on Anodic Nanoporous Layer Growth for n-InP in Aqueous KOH

et al. 2006

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Access to the full text of the published version may require a subscription. The surface morphology and sub-surface porous structure of (100) n-InP following anodization in 1 -10 mol dm -3 aqueous KOH were studied using linear sweep voltammetry (LSV) in combination with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). LSV of n-InP in 10 mol dm -3 KOH showed a single anodic current peak at 0.41 V. As the concentration of electrolyte was decreased, the peak increased in current density and charge and shifted to more positive potentials; eventually individual peaks were no longer discernable. Porous layers were observed in SEM cross-sections following linear potential sweeps and the porous layer thickness increased significantly with decreasing KOH concentration, reaching a maximum value at ~2.2 mol dm -3 . At concentrations less than 1.8 mol dm -3 the layer thickness decreased sharply, pore diameters became wider and pore walls became narrower until eventually, at 1.1 mol dm -2 or lower, no porous layers were observed. It was also observed that the pore width increased and the inter-pore spacing decreased with decreasing concentration. It is proposed that preferential pore propagation occurs along <111> directions, contrary to previous suggestions, and that the resulting nanoporous domains, initially formed, have triangular cross-sections when viewed in one of the {110} cleavage planes, 'dove-tail' crosssections viewed in the orthogonal {110} cleavage plane and square profiles when viewed in the (100) plane of the electrode surface. Rights

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“…The photocurrents of the porous electrode measured in the NaCl electrolyte are plotted in Figure 4(a). In these measurements, the light intensity was set to 2 mW/cm 2 , and the applied voltage, V a , was swept in the positive direction from -0.5 V to 2.5 V. The peaks of anodic current observed at around 0.2 V, which were even observed under the dark condition, are probably caused by the reverse reaction H 2 -> 2H + + 2e -. In contrast to the photocurrents measured in FSI mode, the photocurrents obtained with wavelength of 360 nm showed the smallest values.…”

Section: Photocurrent Measurements Of Gan Porous Structures In Fsi Anmentioning

confidence: 99%

Large photocurrents in GaN porous structures with a redshift of the photoabsorption edge

Sato

Kumazaki

Kida

et al. 2015

Semicond. Sci. Technol.

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Photoresponse and photoabsorption properties of GaN porous structures were investigated by measuring photocurrent and spectroscopic photoabsorption under monochromatic light with various wavelengths. The measured photocurrents on the porous GaN electrode were larger than those on the planar electrodes due to the unique features of the former electrode, such as large surface area and low photoreflectance properties. Moreover, the photocurrents were observed even under illumination with wavelength of 380 nm, corresponding to photon energy of 3.26 eV, which is 130 meV lower than the bandgap energy of bulk GaN. A potential simulation revealed that a high electric field was induced at the pore tips due to modification of the potential in the porous structures. The observed redshift of the photoabsorption edge can be qualitatively explained by the Franz-Keldysh effect.

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Initiation and Formation of Porous GaAs

Cited by 170 publications

References 2 publications

Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Effect of Electrolyte Concentration on Anodic Nanoporous Layer Growth for n-InP in Aqueous KOH

Large photocurrents in GaN porous structures with a redshift of the photoabsorption edge

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