Nanostructured Silicon Substrates Research Articles

Dewetting-Assisted Patterning: A Lithography-Free Route to Synthesize Black and Colored Silicon.

We report the use of thermal dewetting to structure gold-based catalytic etching masks for metal-assisted chemical etching (MACE). The approach involves low-temperature dewetting of metal films to generate metal holey meshes with tunable morphologies. Combined with MACE, dewetting-assisted patterning is a simple, benchtop route to synthesize Si nanotubes, Si nanowalls, and Si nanowires with defined dimensions and optical properties. The approach is compatible with the synthesis of both black and colored nanostructured silicon substrates. In particular, we report the lithography-free fabrication of silicon nanowires with diameters down to 40 nm that support leaky wave-guiding modes, giving rise to vibrant colors. Additionally, micrometer-sized areas with tunable film composition and thickness were patterned via shadow masking. After dewetting and MACE, such patterned metal films produced regions with distinct nanostructured silicon morphologies and colors. To-date, the fabrication of colored silicon has relied on complicated nanoscale patterning processes. Dewetting-assisted patterning provides a simpler alternative that eliminates this requirement. Finally, the simple transfer of resonant SiNWs into ethanolic solutions with well-defined light absorption properties is reported. Such solution-dispersible SiNWs could open new avenues for the fabrication of ultrathin optoelectronic devices with enhanced and tunable light absorption.

Ni/Al multilayer reactions on nanostructured silicon substrates

Fast energy release, which is a fundamental property of reactive multilayer systems, can be used in a wide field of applications. For most applications, a self-propagating reaction and adhesion between the multilayers and substrate are necessary. In this work, a distinct approach for achieving self-propagating reactions and adhesion between deposited Ni/Al reactive multilayers and silicon substrate is demonstrated. The silicon surface consists of random structures, referred to as silicon grass, which were created by deep reactive ion etching. Using the etching process, structure units of heights between 8 and 13 µm and density between 0.5 and 3.5 structures per µm2 were formed. Ni and Al layers were alternatingly deposited in the stoichiometric ratio of 1:1 using sputtering, to achieve a total thickness of 5 µm. The analysis of the reaction and phase transformation was done with high-speed camera, high-speed pyrometer, and X-ray diffractometer. Cross-sectional analysis showed that the multilayers grew only on top of the silicon grass in the form of inversed cones, which enabled adhesion between the silicon grass and the reacted multilayers. A self-propagating reaction on silicon grass was achieved, due to the thermally isolating air pockets present around these multilayer cones. The velocity and temperature of the reaction varied according to the structure morphology. The reaction parameters decreased with increasing height and decreasing density of the structures. To analyze the exact influence of the morphology, further investigations are needed.

Полуполярные широкозонные III-N-слои на кремниевой подложке: эпитаксия с контролем свойств структур (обзор)

The experimental results of the recent years on the synthesis of semipolar wide-band III-N layers on a nanostructured silicon substrate are summarized. The idea of synthesis involves the formation of Si(111) side walls on the silicon surface, then the epitaxial nucleation of the layer in the “c” direction of the crystal, followed by the fusion of blocks in the semipolar direction of the surface. Examples of orientation controlling epitaxy of semipolar AlN(10-11), GaN(10-11), GaN(11-22) layers synthesized on nanostructured Si(100), Si(113) substrates by methods of metalorganic vapor phase epitaxy and hydride vapor phase epitaxy are shown. The review presents a summary and the prospects for further developments in the field of optoelectronics based on the platform - semipolar GaN on Si.

Two-dimensional metamaterials as meta-foams for optimized surface-enhanced solar steam generation

We report on a new class of metamaterials, which consists of meta-foams, optimized for high performance in enhanced solar steam generation. The design of these meta-foams involves precise dimensional control of a periodic two-dimensional micro-pore array. Proof-of-concept of meta-foams efficiency is demonstrated using two fabrication technologies. The first one involves microscale plasma etching onto a nanostructured black silicon substrate. As an alternative low-cost technique, we also use 3D printing of a graphene-containing polymer material. The experimental validation shows that the best evaporation rate reaches 1.34 kg/(h·m2) under 1 sun illumination, in open-air conditions under normal temperature and relative humidity conditions of 20 °C and 58%, an unmatched value so far under similar conditions, while the theoretical limit is estimated at 1.5 kg/(h·m2). This corresponding to a 89% conversion efficiency. Experimental data concur well with the predicted performance obtained by numerical simulations. The proposed model simultaneously accounts for both heat and mass transfer, including photothermal conversion and water phase change, to guide the optimization towards the maximization of the evaporation rate, an important figure of merit in many applications, including solar heat harvesting and solar water purification.

Semipolar III-N Layers Deposited on a Nanostructured Silicon Substrate: Process and Luminescence Specificity

Semipolar III-N Layers Deposited on a Nanostructured Silicon Substrate: Process and Luminescence Specificity

SALDI-MS and SERS Multimodal Imaging: One Nanostructured Substrate to Rule Them Both.

Imaging techniques based on mass spectrometry or spectroscopy methods inform in situ about the chemical composition of biological tissues or organisms, but they are sometimes limited by their specificity, sensitivity, or spatial resolution. Multimodal imaging addresses these limitations by combining several imaging modalities; however, measuring the same sample with the same preparation using multiple imaging techniques is still uncommon due to the incompatibility between substrates, sample preparation protocols, and data formats. We present a multimodal imaging approach that employs a gold-coated nanostructured silicon substrate to couple surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) and surface-enhanced Raman spectroscopy (SERS). Our approach integrates both imaging modalities by using the same substrate, sample preparation, and data analysis software on the same sample, allowing the coregistration of both images. We transferred molecules from clean fingertips and fingertips covered with plasticine modeling clay onto our nanostructure and analyzed their chemical composition and distribution by SALDI-MS and SERS. Multimodal analysis located the traces of plasticine on fingermarks and provided chemical information on the composition of the clay. Our multimodal approach effectively combines the advantages of mass spectrometry and vibrational spectroscopy with the signal enhancing abilities of our nanostructured substrate.

Abstract 5436: Purification and mRNA profiling of extracellular vesicles for early detection of hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is the 4th most common cause of cancer-related deaths worldwide. The poor prognosis of HCC is due to the fact that diagnosis is often made at an advanced stage in disease development. It is crucial to develop a non-invasive liquid biopsy-based diagnostic solution for early detection of HCC. In this study, we developed a covalent chemistry-based nanostructured silicon substrate (“EV Click Chip”) for the isolation of HCC extracellular vesicles (EVs). The EV Click Chip leverages specific click chemistry reactions and sensitive multi-marker cocktail antibody identification of the HCC EVs. The EV Click Chip also allows for the subsequent release of the captured HCC EVs and is optimal for the downstream molecular analysis. A well-validated 10 liver-specific genes were quantified using reverse transcription droplet digital PCR (RT-ddPCR) in HCC EVs purified by the optimized EV Click Chips for the detection of HCC. Our EV Click Chip-based HCC-EV Assay is able to differentiate HCC from non-HCC controls (chronic liver diseases, healthy donors and other cancers) and outperformed clinical AFP test for distinguishing early-stage HCC from at-risk cirrhotic patients. Citation Format: Yi-Te Lee, Na Sun, Ryan Y. Zhang, Rueihung Kao, Pin-Jung Chen, Pai-Chi Teng, Jasmine J. Wang, Yingying Yang, Minhyung Kim, Edwin M. Posadas, Sungyong You, Ju Dong Yang, Vatche G. Agopian, Hsian-Rong Tseng, Yazhen Zhu. Purification and mRNA profiling of extracellular vesicles for early detection of hepatocellular carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5436.

Bioinspired Self‐Propulsion of Water Droplets at the Convergence of Janus‐Textured Heated Substrates

AbstractControlled propulsion of liquid droplets on a solid surface offers viable applications in fog harvesting, heat transfer, microfluidics, and microdevice technologies. A prerequisite for the propulsion of liquid droplets is to break the wetting symmetry of a droplet and contact‐line pinning on the surface by harnessing surface energy gradient. Here, a series of Janus‐textured substrates is constructed to investigate the self‐propulsion of Leidenfrost droplets. It is found that the self‐propulsion of droplets occurs only on two special Janus‐textured substrates. Those are nanostructured silicon substrate bounded by smooth silicon substrate and the nanowire‐decorated microstructured silicon substrate bounded by micropillars with smooth surfaces. The difference in roughness between the two sides of the Janus‐textured substrates creates various numbers and sizes of vapor bubbles. The vapor bubbles cause the droplets to become turbulent, and a pressure gradient is generated. The sufficiently large pressure gradient propels the Leidenfrost droplet to move directionally. The propulsion direction is always toward areas with low roughness.

Covalent chemistry on nanostructured substrates enables noninvasive quantification of gene rearrangements in circulating tumor cells.

Well-preserved mRNA in circulating tumor cells (CTCs) offers an ideal material for conducting molecular profiling of tumors, thereby providing a noninvasive diagnostic solution for guiding treatment intervention and monitoring disease progression. However, it is technically challenging to purify CTCs while retaining high-quality mRNA.Here, we demonstrate a covalent chemistry-based nanostructured silicon substrate ("Click Chip") for CTC purification that leverages bioorthogonal ligation-mediated CTC capture and disulfide cleavage-driven CTC release. This platform is ideal for CTC mRNA assays because of its efficient, specific, and rapid purification of pooled CTCs, enabling downstream molecular quantification using reverse transcription Droplet Digital polymerase chain reaction. Rearrangements of ALK/ROS1 were quantified using CTC mRNA and matched with those identified in biopsy specimens from 12 patients with late-stage non-small cell lung cancer. Moreover, CTC counts and copy numbers of ALK/ROS1 rearrangements could be used together for evaluating treatment responses and disease progression.

Plasmonic optical trapping of pyrene-pendant polymer chains by controlling thermophoretic force

Plasmonic optical tweezers (POT) has a high potential for manipulation of nanomaterials due to an enhanced optical force. However, unfavorable thermal effects induced by plasmon excitation have frequently hindered the manipulation. For this issue, we have recently developed a novel non-plasmonic optical tweezers using a nanostructured silicon substrate (B-Si). We called it “Nano-Structured Semi-Conductor-Assisted Optical Tweezers (NASSCA-OT)”. In the present study, we trapped pyrene-pendant polymer chains homogeneously dissolved in water for POT or NASSCA-OT. We used plasmonic gold nanopyramidal dimer arrays or B-Si in contact with the aqueous polymer solution. During plasmon excitation with a near-infrared laser light, any sign of optical trapping was never detected in fluorescence micro-spectroscopy. By contrast, trapping of the polymer chains was obviously observed for NASSCA-OT. Upon laser irradiation, pyrene excimer fluorescence was dramatically increased at the focal spot. These results indicate that NASSCA-OT is a powerful tool for manipulation of molecular materials.

Surface-Enhanced Raman Spectroscopy of Graphene Integrated in Plasmonic Silicon Platforms with Three-Dimensional Nanotopography

Integrating graphene with plasmonic nanostructures results in multifunctional hybrid systems with enhanced performance for numerous applications. In this work, we take advantage of the remarkable mechanical properties of graphene to combine it with scalable 3D plasmonic nanostructured silicon substrates, which enhance the interaction of graphene with electromagnetic radiation. Large areas of femtosecond laser-structured arrays of silicon nanopillars, decorated with gold nanoparticles, are integrated with graphene, which conforms to the substrate nanotopography. We obtain Raman spectra at 488, 514, 633, and 785 nm excitation wavelengths, spanning the entire visible range. For all excitation wavelengths, the Raman signal of graphene is enhanced by 2-3 orders of magnitude, similarly to the highest enhancements measured to date, concerning surface-enhanced Raman Spectroscopy (SERS) of graphene on plasmonic substrates. Moreover, in contrast to traditional deposition and lithographic methods, the fabrication method employed here relies on single-step, maskless, cost-effective, rapid laser processing of silicon in water, amenable to large-scale fabrication. Finite-difference time-domain simulations elucidate the advantages of the 3D topography of the substrate. Conformation of graphene to the Au-decorated silicon nanopillars enables graphene to sample near fields from an increased number of nanoparticles. Due to synergistic effects with the nanopillars, different nanoparticles become more active for different wavelengths and locations on the pillars, providing broadband enhancement. Nanostructured plasmonic silicon is a promising platform for integration with graphene and other 2D materials, for next-generation applications of large-area hybrid nanomaterials in the fields of sensing, photonics, optoelectronics, and medical diagnostics.

Dielectric and Ferroelectric Properties of PZN-4.5PT Nanoparticles Thin Films on Nanostructured Silicon Substrate for Ferrophotovoltaic and Energy Storage Application

The integration of ferroelectric materials as thin films has attracted considerable attention these last years thanks to their outstanding performances that allow considering new features for the realization of photovoltaic devices. Our study focuses on investigating structural, dielectric and ferroelectric properties of undoped and Mn doped PZN-4.5PT nanoparticles thin films on Silicon substrate. We fabricate very stable PZN-4.5PT nanoparticles thin films deposited on nanostructured silicon substrate with giant relative dielectric permittivity of 2.76 × 104 and 17.7 × 104 for respectively the undoped and Mn doped thin films. These values are very large compared to those found in single crystals and might be explained by the influence of the gel in which nanoparticles were dispersed. The SEM images show the crystallization of new hexagonal phases on the film surface probably coming from interaction between Si and the gel. The hysteresis loops permitted to determine the spontaneous polarization (Ps), remnant polarization (Pr) and coercive field Ec which are equal to 11.73 μC/cm2, 10.20 μC/cm2 and 20 V/cm, respectively for the undoped nanoparticles thin film and 22.22 μC/cm2, 19.32 μC/cm2 and 20 V/cm respectively for the Mn doped one. These values are high and correspond to the best ones found in literature compared to typical ferroelectric thin films.

Effect of Silicon Surface Treatment on the Electrical and Photoelectric Properties of Nanostructured MoOx/n-Si Heterojunctions

The paper presents the results of studies of the effect of silicon surface treatment on the electrical and photoelectric properties of nanostructured MoOx/n-Si heterojunctions. The nanostructured heterojunctions MoOx/n-Si, were prepared by deposition of thin films of molybdenum oxide (n-type conductivity) by reactive magnetron sputtering in the universal vacuum system Leybold Heraeus L560 on the nanostructured silicon substrates (n-type conductivity), which were made by chemical etching with the assistance of silver nanoparticles. Dark and light volt-ampere (I – V) characteristics of the heterojunctions under study were measured, the value of the potential barrier height, the values of the serial Rs and the shunt Rsh resistance at room temperature were determined. It was established that the silicon surface treatment does not affect the potential barrier height, but significantly affects the values of serial Rs and shunt Rsh resistance. The electrical and photoelectric properties of the obtained structures were investigated, the dominant mechanisms of current transfer through the heterostructures under forward bias are well described in the framework of emission-recombination and tunneling models with the presence of interface states. The main mechanism for the charge carrier transport through heterojunctions with the reverse bias is the Frenkel–Pool emission. Investigation of photoelectric properties of heterojunctions MoOx/n-Si was carried out at illumination by white light with intensity Popt = 80 mW/сm2. It was established that the heterostructure No.5 MoOx/n-Si with grown nanowires and etched silver nanoparticles has a maximum open-circuit voltage Voc = 0.17 V, short-circuit current density Isc = 10 mA/cm2. The possibilities of using the obtained heterostructures as photodiodes were analyzed.

Fabrication and Characterization of PZN-4.5PT Inorganic Perovskites Nanoparticles Thin Films Deposited on P-Type Silicon Substrate

This work involves an investigation of nanostructures, microelectronic properties and domain engineering of nanoparticles thin layers of Pb(Zn1/ 3Nb2/3)O3-PbTiO3 (PZN-PT) ferroelectric single crystals deposited on nanostructured silicon substrate. In this study, devices made from PZN-4.5PT nanoparticles thin films successfully deposited on silicon substrate have been studied and discussed. SEM images show the formation of local black circles and hexagonal shapes probably due to the nucleation of a new Si-gel component or phase induced by annealing. Micro Xray Fluorescence mapping shows that the high values of Si and B atoms (≅7 and 4 normalized unit respectively) can be explained by the fact that the substrate is p-type silicon. The most interesting result of optical measurements is the very good absorption for all the thin films in UV, Visible and NIR regions with values from 70% to 90% in UV, from 75% to 93% in Visible and NIR. Tauc plots present particularities (rarely encountered behavior) with different segments or absorption changes showing the presence of multiple band gaps coming from the heterogeneity of the thin films (nanowires, gel and nanoparticles). Their values are 1.9 and 2.8 eV for DKRN-Gel, 2.1 and 3.1 eV for DKRN-UD and 2.1 and 3.2 eV for DKRN-D) corresponding respectively to the band gap of nanowires and that of the gel while the last ones correspond to the undoped and doped nanoparticles (3.1 and 3.2 eV respectively).

Self-organized nickel nanoparticles on nanostructured silicon substrate intermediated by a titanium oxynitride (TiNxOy) interface

In this work we report an experimental approach by combining in situ sequential top-down and bottom-up processes to induce the organization of nanosized nickel particles. The top-down process consists in xenon ion bombardment of a crystalline silicon substrate to generate a pattern, followed by depositing a ∼15 nm titanium oxynitride thin film to act as a metallic diffusion barrier. Then, metallic nanoparticles are deposited by argon ion sputtering a pure nickel target, and the sample is annealed to promote the organization of the nickel nanoparticles (a bottom-up process). According to the experimental results, the surface pattern and the substrate biaxial surface strain are the driving forces behind the alignment and organization of the nickel nanoparticles. Moreover, the ratio between the F of metallic atoms arriving at the substrate relative to its surface diffusion mobility determines the nucleation regime of the nickel nanoparticles. These features are presented and discussed considering the existing technical literature on the subject.

The ultraviolet photodetection properties of gallium nitride/ silicon nanoporous pillar array

The accurate detection of ultraviolet light (UV) has been playing important roles in a variety of fields such as industrial and agricultural production, environmental monitoring and protection, defense and aerospace industries. Semiconductor materials have been widely used in fabricating various photodectors. As a representative of the first generation semiconductor materials, silicon has been applied to fabricate UV photodetector for a long time. For example, the first solid UV detectors were based on UV-enhanced silicon photodiode. Nevertheless, silicon-based photodiodes usually exhibit responses to visible light, which will cause serious disturbances for the detection of UV. Furthermore, crystal silicon is an indirect bandgap semiconductor, which decides that its conversion efficiency and therefore responsivity during the optoelectronic process would be low. All these shortcomings make the effort on developing novel UV photodetectors being both important and necessary. In the past years, great progresses have been achieved in preparing high-quality compound semiconductors with direct and wide bandgaps, and this provides a good opportunity for developing high-performance UV photodectors. As a III-V compound semiconductor with a direct and wide bandgap (~3.4 eV), gallium nitride (GaN) possesses the properties of high electronic mobility and heat conductivity, good chemical and thermal stability, and excellent anti-irradiation capability, and therefore is thought to be one of the most suitable materials for preparing UV detectors. Currently, high-quality GaN thin films are usually prepared by heteroepitaxy technology utilizing sapphire wafers as substrates. However, sapphire is an insulator, which can be used only as a mechanical support instead of a functional substrate and might bring additional technical difficulty in device integration. Such a problem might be solved by using silicon substrate, provided that the large lattice and thermal mismatch between silicon and GaN can be conquered, or it will cause serious problems relating to the device performance and operation stability. A proved method is through introducing nanostructured silicon substrates to construct GaN/Si heterojunction, by which the mismatches could be greatly diminished through a three-dimensional stress release mode at the GaN and silicon interface. Silicon nanoporous pillar array (Si-NPA) is a silicon hierarchical structure characterized by a regular array of well separated, micron-sized and highly nanoporous silicon pillars, and it has been proved an ideal template for preparing silicon-based heterstructures with high-quality interfaces. Here we will report that utilizing Si-NPA as substrates, GaN/Si-NPA nanoheterojunctions were prepared by growing GaN nanocrystallites using a chemical vapor deposition method. Through changing the deposition time, the surface morphology, chemical constitution, and electrical and photoluminescent properties of GaN/Si-NPA can be tuned effectively, and this provided a solid foundation for optimizing the device performance of the subsequently developed UV photodetectors. Through preparing ITO top transparent electrodes and silver back electrodes on these nanoheterojunctions, prototype UV photodectors with a device structure of ITO/GaN/Si-NPA/ sc -Si/Ag were prepared and the photodetection properties were studied. It was shown that high-quality UV detection can be realized without applying any bias, with the response and recovery time being ~0.12 s and ~0.24 s, respectively. For the monochromatic UV light with a wavelength of 340 nm, a responsivity of ~0.15 mA/W was achieved. These results might have provided a novel route for developing Si-based GaN UV photodetectors.

Nanostructured Silicon Substrate for Desorption/Ionization on Silicon Mass Spectrometry Coupled with Titanium Oxide and Zinc Oxide Coated Magnetic Nanoparticles for Phosphopeptide Analysis

Nanostructured Silicon Substrate for Desorption/Ionization on Silicon Mass Spectrometry Coupled with Titanium Oxide and Zinc Oxide Coated Magnetic Nanoparticles for Phosphopeptide Analysis

Silicon Nanowire Photocathodes for Photoelectrochemical Hydrogen Production.

The performance of silicon for water oxidation and hydrogen production can be improved by exploiting the antireflective properties of nanostructured silicon substrates. In this work, silicon nanowires were fabricated by metal-assisted electroless etching of silicon. An enhanced photocurrent density of −17 mA/cm2 was observed for the silicon nanowires coated with an iron sulphur carbonyl catalyst when compared to bare silicon nanowires (−5 mA/cm2). A substantial amount of 315 µmol/h hydrogen gas was produced at low bias potentials for the silicon nanowires coated with an iron sulphur carbonyl catalyst.

Preparation of large-area controllable patterned silver nanocrystals for high sensitive and stable surface-enhanced Raman spectroscopy

A novel and facile method for fabricating large-area patterned silver nanocrystals was introduced and the investigation on the high sensitive and stable surface-enhanced Raman spectroscopy(SERS) of the nanocrystals was carried out. Nanostructured silicon substrate was processed by laser interference and used as a template for growing silver nanocrystals via galvanic battery reaction method. The substrate with large area for violent chemical reaction was tailored into a nanocell array. The limited reaction area hindered the growth of silver nanocrystals and made their size uniform and controllable. The size and gaps of the nanocrystals could be controlled by template period and ratio, which were easily reproduced by laser interference. Taking 10–8 to 10–11 mol/L Rh6G for example, the optimized silver arrays exhibited great potential for ultrasensitive molecular sensing in terms of its high SERS enhancement ability, favorable stability, and excellent reproducibility.

Photonic and Plasmonic Guided Modes in Graphene–Silicon Photonic Crystals

We report the results of systematic studies of plasmonic and photonic guided modes in large-area single-layer graphene integrated into a nanostructured silicon substrate. The interaction of light with graphene and substrate photonic crystals can be classified in distinct regimes of plasmonic and photonic modes.