Macroporous Semiconductors

Föll, H.; Leisner, Malte; Cojocaru, Ala; Carstensen, Jürgen

doi:10.3390/ma3053006

Cited by 63 publications

(42 citation statements)

References 210 publications

(336 reference statements)

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“…PVM is capable of accurately and reproducibly measuring myocardial velocities in the LV [1]. However, analyzing RV motion is more difficult because of the thinness of the free wall and its asymmetrical geometry.…”

Section: Introductionmentioning

confidence: 99%

Right ventricular (RV) velocity measurements using high resolution spiral myocardial phase velocity mapping (PVM)

Simpson

Keegan

Firmin

2013

Journal of Cardiovascular Magnetic Resonance

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Section: Introductionmentioning

confidence: 99%

Right ventricular (RV) velocity measurements using high resolution spiral myocardial phase velocity mapping (PVM)

Simpson

Keegan

Firmin

2013

Journal of Cardiovascular Magnetic Resonance

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“…11 Even though formation mechanisms of needles generated by anodization of p-type Si are briefly described in, 12,13 no model for their formations has been reported yet. In this work, formation mechanisms of self-organized needles generated by anodic etching of lowly doped (<10 15 atoms/cm 3 ) 14 p-type Si in an aqueous HF solution is investigated in detail. Impacts of current density and substrate resistivity range in the lowly doped region, and electrolyte additives on morphology of surfaces are also discussed.…”

mentioning

confidence: 99%

“…Impacts of current density and substrate resistivity range in the lowly doped region, and electrolyte additives on morphology of surfaces are also discussed. A simple model based on the Current Burst (CB) model, 15 the Zhang model (distribution of the electric field at different regions of a pore), 16 and the Lehmann macro-pore formation model 17 is then presented to describe formation of needles in the transition region.…”

mentioning

confidence: 99%

Formation Mechanisms of Self-Organized Needles in Porous Silicon Based Needle-Like Surfaces

Keshavarzi

Mescheder

Reinecke

2018

J. Electrochem. Soc.

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Formation mechanisms of self-organized Si-needles generated by anodic etching of lowly doped p-type silicon wafers in an aqueous HF solution in the transition region (region between the pore formation and the electropolishing) is studied through surface SEM images taken after different etch times. Impacts of current density, substrate resistivity range in the lowly doped region, and electrolyte additives on morphology of needles are also investigated. A simple model based on pore formation models is presented to describe formation of self-organized needles during anodic etching of lowly doped p-type silicon in an aqueous HF solution in the transition region. Anodization is a well-known technique for porous silicon (PSi) formation or electropolishing of silicon (Si) wafers. Although the technique is known for several decades, it has attracted renewed interest since 1990 resulting from discovery of luminescence properties of PSi.1 The technique has also emerged in micromachining due to its low cost, easy implementation, and compatibility with standard microelectronic processes.2 Usage of the anodization technique to create needle-like Si surfaces for room temperature Si-Si bonding applications has currently attracted attention.3-5 Additionally, the technique has a good potential to easily replace complicated and costly processes, such as inductively coupled plasma reactive ion etching (ICP-RIE), 6 interference lithography combined with Reactive Ion Etching (RIE) technique, 7 metal-assisted etching (MAE) technique, 8 and laser micro/nano-processing, 9 which are commonly used to generate Si needle-like antireflection coating surfaces for visible and (near infrared) NIR applications.Using the anodization technique, needle-like surfaces can be obtained by anodic etching of lowly doped p-type Si in aqueous HF solutions in the so-called transition region, the region between pore formation and electropolishing.3-5 Although formation of PSi and electropolishing of p-type Si are quite well-understood, formation mechanisms of self-organized needles in the transition region, where both pore formation and electropolishing are competing for control over the surface, 10 is still unclear since instabilities in space and time are occurring in this region.11 Even though formation mechanisms of needles generated by anodization of p-type Si are briefly described in, 12,13 no model for their formations has been reported yet. In this work, formation mechanisms of self-organized needles generated by anodic etching of lowly doped (<10 15 atoms/cm 3 ) 14 p-type Si in an aqueous HF solution is investigated in detail. Impacts of current density and substrate resistivity range in the lowly doped region, and electrolyte additives on morphology of surfaces are also discussed. A simple model based on the Current Burst (CB) model, 15 the Zhang model (distribution of the electric field at different regions of a pore), 16 and the Lehmann macro-pore formation model 17 is then presented to describe formation of needles in the transition region. Exp...

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“…There are many different types of pores [14,15]. As with any object with such wide variation, a taxonomic system is developed to classify and organize the results.…”

Section: The Second Corner: Architecturementioning

confidence: 99%

“…Here are some of the repeated aspects in the pictures that are readily describable: there are pores with smooth walls (Fig 12.1a) and pores with jagged, craggy edges (Fig 12.1b). Some pores drop vertically down in the material (Fig 12.2a), whilst others sink in diagonally (Fig 12.1c).Pores can be branched or branchless beneath the surface (Fig 12.1d and Fig 12.2a respectively).There are many different types of pores [14,15]. As with any object with such wide variation, a taxonomic system is developed to classify and organize the results.…”

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confidence: 99%

Fabrication and Characterization of a Palladium/Porous Silicon Layer

Lui¹

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Fabrication and Characterization of a Palladium/ Porous Silicon Layer Nicholas LuiA scientific paper can be considered a journey into the logic and mind of the scientist who performed the experiment. This paper, a little unconventional, is written as a reflection of how the author organizes and thinks through his topic. In the telling of it this way, he hopes the journey is as compelling for the reader as it was for him.When porous silicon is plated with a catalytic metal, the two materials can act together as a single entity whose electrical properties are sensitive to its environment -the sensing component of an electrochemical gas sensor. Etching pores into silicon is an electrochemical process; and which type of doped silicon used is one of its key parameters. For nearly all reported porous silicon gas sensors, the silicon has been of the p-doped variety -because pdoped porous etching is better understood and the layers that result from it are more predictable -despite n-doped silicon having potentially significant benefits in ease of fabrication and being more conducive to plating by a catalyst. This experiment is an attempt at creating a palladium plated n-doped porous silicon layer, and an examination into what differentiates this fabrication process and the layers that result from the traditional p-doped type.The porous layers to be plated are to be the same and would ideally have properties that are a close approximation to what a functional gas sensor would require. This experiment defined a process that fabricated this "ideal" layer out of N-type, <100>, double polished silicon wafers with a resistance of 20 Ω cm. The wafers were subjected to the anodic etching method with an HF/ethanol mixture as the electrolyte; and only two (of among many) fabrication parameters were varied: HF concentration of the electrolyte and total etching time. We find that a concentration of 12% HF (by volume) and an etching time of 6 hours result in layers most appropriate to carry into plating. The anodization current density is 15 mA cm -2. Deposition of the catalyst, palladium, is done using the electroless method by immersing the porous layer in a .001M PdCl 2 aqueous bath.Characterization of this Pd/Porous Silicon layer was done by measuring resistivity by four point probe and imaging through Scanning Electron Microscopy. It was found that layers of a v maximum average of 63 ± 6% porosity were created using our fabrication method. There is evidence of palladium deposition, but it is spotty and irregular and is of no improvement despite the n-doping wafer makeup. Resistivity in well-plated regions was measured to be 7-10 Ωcm, while resistivity in regions not well-plated was measured to be 70-140 Ω cm. This is comparable to previous literature values, indicating n-silicon porous silicon can be fabricated and still have potential as a catalytic layer, should metal deposition methods improve.Keywords: Porous Silicon, Electroless Plating, Anodic Etching. vi Chapter 1: IntroductionAt its most general, a porous mate...

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Macroporous Semiconductors

Cited by 63 publications

References 210 publications

Right ventricular (RV) velocity measurements using high resolution spiral myocardial phase velocity mapping (PVM)

Right ventricular (RV) velocity measurements using high resolution spiral myocardial phase velocity mapping (PVM)

Formation Mechanisms of Self-Organized Needles in Porous Silicon Based Needle-Like Surfaces

Fabrication and Characterization of a Palladium/Porous Silicon Layer

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