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Fabrication of millimeter-long structures in sapphire using femtosecond infrared laser pulses and selective etching
摘要： This paper analyzes laser and etching parameters to fabricate open and continuous microchannels and stacks of such microchannels in the bulk of crystalline sapphire (??-Al2O3). The structures are produced using a two-step method consisting of laser irradiation and selective etching. Infrared femtosecond laser pulses are focused in the bulk to locally render the crystalline material into amorphous. The amorphous material is, then, selectively etched in hydrofluoric acid. Amorphous sapphire shows a high etching selectivity in comparison to its crystalline state, which makes this material very attractive for a use with this technique. However, some of its properties make the processing challenging, especially during the laser-induced amorphization phase. This paper studies the effect of laser parameters by a step-by-step approach to fabricate long structures (longest dimensions up to millimeters) of different shapes inside the bulk of sapphire. The minimum cross-sectional dimensions of the resulting structures (microchannels) vary from few hundreds of nanometers for the smallest channels to tens of micrometers for the largest stacks of microchannels. The effect of the variation of repetition rate, pulse energy and channel-to-channel distance on the microchannels and stacks of microchannels is studied. SEM micrographs of polished cross-sections are used for performing a quantitative and qualitative analysis of the morphology of the structures after laser irradiation and, subsequently, after selective wet chemical etching.
关键词： Selective etching,Laser processing,Microchannels,Femtosecond laser,Sapphire
更新于2025-09-23 15:21:01
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Guidelines for establishing an etching procedure for dislocation density measurements on multicrystalline silicon samples
摘要： With multicrystalline silicon becoming the main material used for photovoltaic applications and dislocations being one of the main material limitations to better solar cell efficiency, etch pit density measurements are gaining more importance. Traditionally, etch pit density measurements are based on selective etching of silicon samples. The majority of the etchants have been developed for monocrystalline samples with known orientation, while those developed for multicrystalline samples have been investigated and might need some optimization. In this study, we use and compare the PVScan tool, which provides a quick way to assess dislocation density on selectively etched samples, and microscope image analysis. We show how the etching methods used for dislocation density measurements can affect the results, and we suggest how to optimize the Sopori etching procedure for multicrystalline silicon samples with high dislocation densities. We also show how the Sopori etchant can be used to substitute Secco while maintaining a high precision of dislocation density measurements, but without the toxic hexavalent chromium compounds.
关键词： Photovoltaic,Etch pit density,Silicon,Secco,Selective etching,EPD,Dislocations,Sopori
更新于2025-09-23 15:21:01
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Two-Dimensional Hydroxyl-Functionalized and Carbon-Deficient Scandium Carbide, ScC <sub/><i>x</i> </sub> OH, a Direct Bandgap Semiconductor
摘要： Two-dimensional (2D) materials have attracted intensive attention in nanoscience and nanotechnology due to their outstanding properties. Among these materials, the emerging family of 2D transition metal carbides, carbonitrides, and nitrides (referred to as MXenes) stands out because of the vast available chemical space for tuning materials chemistry and surface termination, offering opportunities for property tailoring. Specifically, semiconducting properties are needed to enable utilization in optoelectronics, but direct bandgaps are experimentally challenging to achieve in these 2D carbides. Here, we demonstrate the fabrication of 2D hydroxyl-functionalized and carbon-deficient scandium carbide, namely ScCxOH, by selective etching of a layered parent ScAl3C3 compound. The 2D configuration is determined as a direct bandgap semiconductor, with an experimentally measured bandgap approximated to 2.5 eV. Furthermore, this ScCxOH based device exhibits excellent photoresponse in the ultraviolet-visible light region (responsivity of 0.125 A/W@360 nm/10 V, and quantum efficiency of 43%). Thus, this 2D ScCxOH direct-bandgap semiconductor may find applications in visible-light detectors, photocatalytic chemistry, and optoelectronic devices.
关键词： DFT calculation,photodetector,electronic properties,two-dimensional material,selective etching,MXene
更新于2025-09-19 17:15:36
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Selective Wet-Etching of Polymer/Fullerene Blend Films for Surface- and Nanoscale Morphology-Controlled Organic Transistors and Sensitivity-Enhanced Gas Sensors
摘要： Surface and nanoscale morphology of thin poly(3-hexylthiophene) (P3HT) ?lms are e?ectively controlled by blending the polymer with a soluble derivative of fullerene, and then selectively dissolving out the fullerene from the blend ?lms. A combination of the polymer blending with fullerene and a use of diiodooctane (DIO) as a processing additive enhances the molecular ordering of P3HT through nanoscale phase separation, compared to the pristine P3HT. In organic thin-?lm transistors, such morphological changes in the blend induce a positive e?ect on the ?eld-e?ect mobility, as the mobility is ~5–7 times higher than in the pristine P3HT. Simple dipping of the blend ?lms in butyl acetate (BA) causes a selective dissolution of the small molecular component, resulting in a rough surface with nanoscale features of P3HT ?lms. Chemical sensors utilizing these morphological features show an enhanced sensitivity in detection of gas-phase ammonia, water, and ethanol.
关键词： selective etching process,morphology,polymer blend,chemical sensor,organic thin-?lm transistor
更新于2025-09-19 17:13:59
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Transformation of single Ag nanowires into super-large AgAu elliptic rings via a water/oil interface-oriented asymmetrical etching
摘要： Nanoring as one of fascinating geometries exhibits unique size-dependent physical-chemistry properties endowed by its circular feature. However, to the best of our knowledge, super-large elliptical nanorings cannot be fabricated by the existing techniques. Herein, we successfully fabricate super-large elliptical AgAu nanorings creatively by splitting single Ag nanowires along their longitudinal axes involving oil/water interfacial self-assembly of Ag nanowires and the galvanic replacement between interfacial Ag nanowires and AuCl4? located in the water phase. The formation of AgAu nanoring is mainly attributed to the local nanomasking of Au atoms and asymmetrical etching on interfacial Ag nanowire. Additionally, as-prepared super-large elliptical AgAu nanorings with rough surfaces exhibit enhanced catalytic performance towards the reduction of p-nitrophenol due to the combination of the composition and structure effects. This strategy, without doubt, provides a convenient way for precisely carving nanoparticles, and has the potential for processing other metallic or non-metallic nanoparticles.
关键词： Ag nanowire,selective etching,AgAu nanoring,galvanic replacement,self-assembly
更新于2025-09-09 09:28:46
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From the Bottom-Up: Toward Area-Selective Atomic Layer Deposition with High Selectivity
摘要： Bottom-up nanofabrication by area-selective atomic layer deposition (ALD) is currently gaining momentum in semiconductor processing, because of the increasing need for eliminating the edge placement errors of top-down processing. Moreover, area-selective ALD offers new opportunities in many other areas such as the synthesis of catalysts with atomic-level control. This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area-selective ALD processes can be improved. A general cause for the loss of selectivity during deposition is that the character of surfaces on which no deposition should take place changes when it is exposed to the ALD chemistry. A solution is to implement correction steps during ALD involving for example surface functionalization or selective etching. This leads to the development of advanced ALD cycles by combining conventional two-step ALD cycles with correction steps in multistep cycle and/or supercycle recipes.
关键词： surface functionalization,semiconductor processing,area-selective atomic layer deposition,catalysts synthesis,selectivity,bottom-up nanofabrication,selective etching,ALD
更新于2025-09-04 15:30:14