Silicon Nanoneedles Research Articles

Integrating Porous Silicon Nanoneedles within Medical Devices for Nucleic Acid Nanoinjection.

Porous silicon nanoneedles can interface with cells and tissues with minimal perturbation for high-throughput intracellular delivery and biosensing. Typically, nanoneedle devices are rigid, flat, and opaque, which limits their use for topical applications in the clinic. We have developed a robust, rapid, and precise substrate transfer approach to incorporate nanoneedles within diverse substrates of arbitrary composition, flexibility, curvature, transparency, and biodegradability. With this approach, we integrated nanoneedles on medically relevant elastomers, hydrogels, plastics, medical bandages, catheter tubes, and contact lenses. The integration retains the mechanical properties and transfection efficiency of the nanoneedles. Transparent devices enable the live monitoring of cell-nanoneedle interactions. Flexible devices interface with tissues for efficient, uniform, and sustained topical delivery of nucleic acids ex vivo and in vivo. The versatility of this approach highlights the opportunity to integrate nanoneedles within existing medical devices to develop advanced platforms for topical delivery and biosensing.

Silicon Nanoneedle-Induced Nuclear Deformation: Implications for Human Somatic and Stem Cell Nuclear Mechanics.

Cell nuclear size and shape are strictly regulated, with aberrations often leading to or being indicative of disease. Nuclear mechanics are critically responsible for intracellular responses to extracellular cues, such as the nanotopography of the external environment. Silicon nanoneedle (SiNN) arrays are tunable, engineered cell culture substrates that permit precise, nanoscale modifications to a cell's external environment to probe mechanotransduction and intracellular signaling. We use a library of four different SiNN arrays to investigate the immediate and downstream effects of controlled geometries of nanotopographical cues on the nuclear integrity/dynamics of human immortalized somatic and renewing stem cell types. We quantify the significant, albeit different, nuclear shape changes that both cell types undergo, which suggest that cellular responses to SiNN arrays are more comparable to three-dimensional (3D) environments than traditional flat cultureware. We show that nanotopography-induced effects on nuclear envelope integrity, protein localization, and focal adhesion complex formation are cell-dependent. Migration is shown to be dramatically impeded for human neural progenitor cells (hNPCs) on nanotopographies compared to flat substrates but not for somatic cells. Our results indicate an additional layer of complexity in cellular mechanotransduction, which warrants closer attention in the context of engineered substrates and scaffolds for clinical applications.

Biodegradable silicon nanoneedles for ocular drug delivery.

Ocular drug delivery remains a grand challenge due to the complex structure of the eye. Here, we introduce a unique platform of ocular drug delivery through the integration of silicon nanoneedles with a tear-soluble contact lens. The silicon nanoneedles can penetrate into the cornea in a minimally invasive manner and then undergo gradual degradation over the course of months, enabling painless and long-term sustained delivery of ocular drugs. The tear-soluble contact lens can fit a variety of corneal sizes and then quickly dissolve in tear fluid within a minute, enabling an initial burst release of anti-inflammatory drugs. We demonstrated the utility of this platform in effectively treating a chronic ocular disease, such as corneal neovascularization, in a rabbit model without showing a notable side effect over current standard therapies. This platform could also be useful in treating other chronic ocular diseases.

Aqueous mechano-bactericidal action of acicular aragonite crystals

Nanoneedle structures on dragonfly and cicada wing surfaces or black silicon nanoneedles demonstrate antibacterial phenomena, namely mechano-bactericidal action. These air-exposed, mechano-bactericidal surfaces serve to destroy adherent bacteria, but their bactericidal action in the water is no precedent to report. Calcium carbonate easily accumulates on solid surfaces during long-term exposure to hard water. We expect that aragonite nanoneedles, in particular, which grow on TiO2 during the photocatalytic treatment of calcium-rich groundwater, exhibit mechano-bactericidal action against bacteria in water. Here, we showed that acicular aragonite modified on TiO2 ceramics prepared from calcium bicarbonate in mineral water by photocatalysis exhibits mechanical bactericidal activity against E. coli in water. Unmodified, calcite-modified and aragonite-modified TiO2 ceramics were exposed to water containing E. coli (in a petri dish), and their bactericidal action over time was investigated under static and agitated conditions. The surfaces of the materials were observed by scanning electron microscopy, and the live/dead bacterial cells were observed by confocal laser scanning microscopy. As a result, the synergistic bactericidal performance achieved by mechano-bactericidal action and photocatalysis was demonstrated. Aragonite itself has a high biological affinity for the human body different from the other whisker-sharpen nanomaterials, therefore, the mechano-bactericidal action of acicular aragonite in water is expected to inform the development of safe water purification systems for use in developing countries.

High Aspect Ratio Polymeric Nanoneedle Arrays

AbstractHigh aspect ratio (HAR) nanoneedle arrays can be used to tune the intrinsic properties of substrates such as their wettability and reflectivity. Here, a simple and scalable fabrication method for producing dense arrays of freestanding polyethylene glycol (PEG) nanoneedles with sub 50 nm tips and surface coverage up to 83 needles per µm2 is presented. Two distinct sets of silicon nanoneedle master arrays with base diameters between 15 and 265 nm and heights between 146 and 613 nm are fabricated using block copolymer micelle lithography. Replication of selected silicon masters using photocurable polymers produces HAR PEG nanoneedle arrays with feature base diameters ranging between 15 and 292 nm and heights between 133 and 656 nm. At their maximum, the aspect ratio of the pillars is 4.6. PEG nanoneedle arrays are produced using polymers with two different molecular weights as well as two different photoinitiators, showing the versatility of the process.

Abstract 2857: Digital nanoneedle biosensor technology for proteome-wide biomarker discovery

Abstract Understanding diseases and related biological processes at the proteome level will lead to the discovery of biomarkers for early diagnostics, enable drug development, patient selection, and treatment monitoring. Thus, there is an increasing demand for a more comprehensive and quantitative interrogation of the proteome at higher sensitivity, wider dynamic range, lower cost, and higher throughput than is currently possible by mass spectrometry or traditional immunoassays. NanoMosaic is a digital immunoassay technology that achieves fg/ml level sensitivity, whole-proteome level multiplexing capability and 7 logs of dynamic range. It overcomes the sensitivity and dynamic range limitations posed by traditional protein arrays and mass spectrometry. The NanoMosaic technology is powered by silicon nanoneedle biosensors that are densely integrated on a plate and manufactured with CMOS-compatible nanofabrication processes. Each nanoneedle is a label-free biosensor, functionalized with capture antibodies, and changes its scattering spectrum when an antigen binds to its surface. Each analyte specific sensing area consists a total of ~24k nanoneedles divided into a digital region (~20k nanoneedles), an analog region (~3k nanoneedles) and a fabrication control region (~1k nanoneedles). The colors of all nanoneedles are imaged in a single shot with a low-cost color camera. The digital nanoneedles provide the single molecule sensitivity. Therefore, at ultra-low concentration when antigens captured by the nanoneedles follow Poisson statistics, the number of antigens can be quantitated by counting the presence or absence of color changes of individual nanoneedles in a binary fashion. As the protein concentrations increase, the counts increase accordingly and achieve saturation when all nanoneedles capture more than one protein. Above the saturation concentration, an adjacent section of analog nanoneedles perform quantitative analysis based on the level of color change, thus providing a wider dynamic range beyond the digital counting concentration ranges. We have demonstrated various assays on the NanoMosaic platform, in particular, a tau assay at 50fg/mL sensitivity, which serves as a potential biomarker for Alzheimer's disease. Each single analyte area, including both digital and analog sensors, is less than 500um. Therefore, ultrahigh level multiplex can be achieved by parallelizing the detection in a microarray format, while maintaining the same level of sensitivity and dynamic range. An ultrahigh-multiplex proteome wide assay only requires a ~70mm area with a total of 5 billion nanoneedles. In conclusion, proteome-wide quantification and discovery of biomarkers can be performed in a single experiment, with high levels of multiplex and sensitivity on the NanoMosaic platform. Our technology enables the next frontier in biomarker discovery and proteome-wide interrogation which will lead to early diagnostics and more comprehensive understanding of diseases. Citation Format: Qimin Quan, Joshua Ritchey, Mark Clenow, Joe Wilkinson, John Geanacopoulos, John Boyce. Digital nanoneedle biosensor technology for proteome-wide biomarker discovery [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 2857.

Abstract 5540: Digital nanoneedle biosensors enable comprehensive monitoring of systemic inflammatory response to immunotherapies

Abstract Cytokine release syndrome (CRS), a systemic inflammatory response observed in some monoclonal antibody drugs and adaptive T-Cell therapies has become a major issue in cancer immunotherapy. CRS can present as a mild reaction requiring minimally invasive supportive care up to a severe systemic response resulting in patient death. Monitoring this response during these therapeutic treatments is non-trivial due to the wide range of biomarker concentrations, small sample volumes, and long assay times. CRS-associated biomarkers including CRP and ferritin vary from 10ng/mL-10mg/mL while other biomarkers (eg, IL6, IFNγ, etc.) vary from 1pg/mL-100ng/mL. At present, no analytical tool, known to us, can provide this large dynamic range simultaneously with the requisite low limit of detection in a single test. NanoMosaic technology has the required sensitivity and dynamic range for the quantification of a large panel of CRS biomarkers in a single assay. The NanoMosaic technology is powered by silicon nanoneedle biosensors that are densely integrated on a plate and manufactured with CMOS-compatible nanofabrication processes. Each nanoneedle is a label-free biosensor, functionalized with capture antibodies, and changes its scattering spectrum when an antigen binds to its surface. Each analyte specific sensing area consists a total of ~24k nanoneedles divided into a digital region (~20k nanoneedles), an analog region (~3k nanoneedles) and a fabrication QC region (~1k nanoneedles). The colors of all nanoneedles are imaged in a single shot with a low-cost color camera. The digital nanoneedles provide the single molecule sensitivity. Therefore, at ultra-low concentration when antigens captured by the nanoneedles follow Poisson statistics, the number of antigens can be quantitated by counting the presence or absence of color changes of individual nanoneedles in a binary fashion. As the protein concentrations increase, the positive counts increase accordingly and achieve saturation when all nanoneedles capture more than one protein. Above the saturation concentration, an adjacent section of analog nanoneedles perform quantitative analysis based on the level of color change, thus providing a wider dynamic range beyond the digital counting concentration ranges. Each single analyte area, including both digital and analog sensors, is less than 500um. Therefore, high level multiplex can be achieved by parallelizing the detection in a microarray format, while maintaining the same level of sensitivity and dynamic range. We have developed various assays on the NanoMosaic platform, including cytokines such as TNF-alpha, IL6, CRP, IFNγ, as well as low-abundance proteins such as Tau proteins at 50fg/mL, in different matrices. Prognostic monitoring of the inflammatory immune response requires simultaneous measurement of multiple cytokines at widely divergent concentrations. NanoMosaic technology provides the sensitivity, dynamic range and multiplexing capacity required to fully integrate patient immune response into therapeutic development and decision making. Citation Format: Qimin Quan, Joshua Ritchey, Mark Clenow, Joe Wilkinson, John Geanacopoulos, John Boyce. Digital nanoneedle biosensors enable comprehensive monitoring of systemic inflammatory response to immunotherapies [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 5540.

Proteome-wide biomarker quantification and target screening.

e15205 Background: Existing drug development programs are represented by only a few hundred protein targets. A large subset of the ~20,000 proteins encoded by the human genome remain undiscovered. Proteome-wide “druggability” screening may lead to new targets for therapeutics. Methods: The NanoMosaic platform is a digital immunoassay technology that achieves sub-pg/ml level sensitivity, whole-proteome level multiplexing capability, and 7 logs of dynamic range. The platform overcomes the sensitivity and dynamic range limitations of traditional protein arrays and mass spectrometry. Results: The NanoMosaic technology is powered by silicon nanoneedle biosensors that are densely integrated on a plate and manufactured with CMOS-compatible nanofabrication processes. Each nanoneedle is a label-free biosensor, functionalized with capture antibodies. Its scattering spectrum changes when an antigen binds to its surface. Each analyte specific sensing area consists a total of ~23k nanoneedles divided into a digital region (~20k nanoneedles) and an analog region (~3k nanoneedles). The digital nanoneedles provide the single molecule sensitivity. Therefore, at ultra-low concentration when antigens that are captured by the nanoneedles follow Poisson statistics, the number of antigens can be quantitated by counting the presence or absence of color changes of individual nanoneedles in a binary fashion. As the protein concentrations increase, the binding event counts increase accordingly and achieve saturation when all nanoneedles capture more than one protein. Above the digital saturation concentration, an adjacent section of analog nanoneedles perform quantitative analysis based on the level of color change, thus providing a wider dynamic range up to 1ug/ml. Ultrahigh level multiplex can be achieved by parallelizing the detection in a microarray format without loss of the sensitivity and dynamic range. A 20,000-plex proteome-wide study can be achieved with a total of 5 billion nanoneedles on a ~70mm by 70mm chip. Conclusions: In conclusion, proteome-wide biomarker quantification and target discovery can be performed on the NanoMosaic platform at higher sensitivity, wider dynamic range, lower cost and higher throughput than is currently possible by mass spectrometry or traditional immunoassays.

Monitoring of inflammatory response to cancer immunotherapies.

e15199 Background: Inflammation observed in response to some monoclonal antibody drugs and adaptive T-Cell therapies has become a major issue in cancer immunotherapy. Prognostic monitoring of the inflammatory response requires simultaneous measurement of multiple cytokines at widely divergent concentrations. At present, no analytical method, known to us, can provide large dynamic range (> 6 logs), high sensitivity (< 1pg/ml) and high multiplex in a single test. Methods: The NanoMosaic platform is a cytokine quantification technology powered by silicon nanoneedle biosensors that are densely integrated on a plate and manufactured with CMOS-compatible nanofabrication processes. Each nanoneedle is a label-free biosensor, functionalized with capture antibodies. Each analyte specific sensing area consists a total of ~23k nanoneedles divided into a digital region (~20k nanoneedles) and an analog region (~3k nanoneedles), combined to cover the entire range of inflammatory biomarkers from 0.1pg/ml to 1ug/ml. Results: We demonstrated that the digital nanoneedles achieve the single molecule sensitivity. Therefore, at ultra-low concentrations when antigens that are captured by the nanoneedles follow Poisson statistics, the number of antigens can be quantitated by counting the presence or absence of color changes of individual nanoneedles in a binary fashion. As the protein concentrations increase, the binding events increase accordingly and achieve saturation when all nanoneedles capture more than one protein. Above the digital saturation concentration, an adjacent section of analog nanoneedles perform quantitative analysis based on the level of color change, thus providing a wider dynamic range up to 1ug/ml. Each single analyte area, including both digital and analog sensors, is less than 500um. Therefore, high level multiplex can be achieved by duplicating the detection sensor in a microarray format without loss of sensitivity and dynamic range. Conclusions: The CMOS-compatible NanoMosaic technology provides the cost-effectiveness, sensitivity, dynamic range and multiplexing capacity required to fully integrate patient immune response into therapeutic development and decision making.

Size-Tunable Nanoneedle Arrays for Influencing Stem Cell Morphology, Gene Expression, and Nuclear Membrane Curvature.

High-aspect-ratio nanostructures have emerged as versatile platforms for intracellular sensing and biomolecule delivery. Here, we present a microfabrication approach in which a combination of reactive ion etching protocols were used to produce high-aspect-ratio, nondegradable silicon nanoneedle arrays with tip diameters that could be finely tuned between 20 and 700 nm. We used these arrays to guide the long-term culture of human mesenchymal stem cells (hMSCs). Notably, we used changes in the nanoneedle tip diameter to control the morphology, nuclear size, and F-actin alignment of interfaced hMSCs and to regulate the expression of nuclear lamina genes, Yes-associated protein (YAP) target genes, and focal adhesion genes. These topography-driven changes were attributed to signaling by Rho-family GTPase pathways, differences in the effective stiffness of the nanoneedle arrays, and the degree of nuclear membrane impingement, with the latter clearly visualized using focused ion beam scanning electron microscopy (FIB-SEM). Our approach to design high-aspect-ratio nanostructures will be broadly applicable to design biomaterials and biomedical devices used for long-term cell stimulation and monitoring.

Nanoneedle-Mediated Stimulation of Cell Mechanotransduction Machinery.

Biomaterial substrates can be engineered to present topographical signals to cells which, through interactions between the material and active components of the cell membrane, regulate key cellular processes and guide cell fate decisions. However, targeting mechanoresponsive elements that reside within the intracellular domain is a concept that has only recently emerged. Here, we show that mesoporous silicon nanoneedle arrays interact simultaneously with the cell membrane, cytoskeleton, and nucleus of primary human cells, generating distinct responses at each of these cellular compartments. Specifically, nanoneedles inhibit focal adhesion maturation at the membrane, reduce tension in the cytoskeleton, and lead to remodeling of the nuclear envelope at sites of impingement. The combined changes in actin cytoskeleton assembly, expression and segregation of the nuclear lamina, and localization of Yes-associated protein (YAP) correlate differently from what is canonically observed upon stimulation at the cell membrane, revealing that biophysical cues directed to the intracellular space can generate heretofore unobserved mechanosensory responses. These findings highlight the ability of nanoneedles to study and direct the phenotype of large cell populations simultaneously, through biophysical interactions with multiple mechanoresponsive components.

Biointerfaces: Porous Silicon Nanoneedles Modulate Endocytosis to Deliver Biological Payloads (Adv. Mater. 12/2019)

In article number 1806788, Ciro Chiappini, Andrew Shevchuk, Molly M. Stevens, and co-workers show that porous silicon nanoneedles stimulate endocytic activity in mesenchymal stem cells. Endocytic pits localize around the nanoneedles leading to increased uptake of pathway-specific payloads and their endolysosomal trafficking, yet nucleic acids delivered from nanoneedles retain their biological activity, suggesting the overlap of concurrent delivery mechanisms. These findings significantly advance the current understanding of the mechanisms of intracellular delivery by nanoinjection.

Porous Silicon Nanoneedles Modulate Endocytosis to Deliver Biological Payloads.

Owing to their ability to efficiently deliver biological cargo and sense the intracellular milieu, vertical arrays of high aspect ratio nanostructures, known as nanoneedles, are being developed as minimally invasive tools for cell manipulation. However, little is known of the mechanisms of cargo transfer across the cell membrane-nanoneedle interface. In particular, the contributions of membrane piercing, modulation of membrane permeability and endocytosis to cargo transfer remain largely unexplored. Here, combining state-of-the-art electron and scanning ion conductance microscopy with molecular biology techniques, it is shown that porous silicon nanoneedle arrays concurrently stimulate independent endocytic pathways which contribute to enhanced biomolecule delivery into human mesenchymal stem cells. Electron microscopy of the cell membrane at nanoneedle sites shows an intact lipid bilayer, accompanied by an accumulation of clathrin-coated pits and caveolae. Nanoneedles enhance the internalization of biomolecular markers of endocytosis, highlighting the concurrent activation of caveolae- and clathrin-mediated endocytosis, alongside macropinocytosis. These events contribute to the nanoneedle-mediated delivery (nanoinjection) of nucleic acids into human stem cells, which distribute across the cytosol and the endolysosomal system. This data extends the understanding of how nanoneedles modulate biological processes to mediate interaction with the intracellular space, providing indications for the rational design of improved cell-manipulation technologies.

Flexible elastomer patch with vertical silicon nanoneedles for intracellular and intratissue nanoinjection of biomolecules.

Vertically ordered arrays of silicon nanoneedles (Si NNs), due to their nanoscale dimension and low cytotoxicity, could enable minimally invasive nanoinjection of biomolecules into living biological systems such as cells and tissues. Although production of these Si NNs on a bulk Si wafer has been achieved through standard nanofabrication technology, there exists a large mismatch at the interface between the rigid, flat, and opaque Si wafer and soft, curvilinear, and optically transparent biological systems. Here, we report a unique methodology that is capable of constructing vertically ordered Si NNs on a thin layer of elastomer patch to flexibly and transparently interface with biological systems. The resulting outcome provides important capabilities to form a mechanically elastic interface between Si NNs and biological systems, and simultaneously enables direct imaging of their real-time interactions under the transparent condition. We demonstrate its utility in intracellular, intradermal, and intramuscular nanoinjection of biomolecules into various kinds of biological cells and tissues at their length scales.

Tunable growth of semiconductor nanostructures by Plasma Enhanced Chemical Vapor Deposition - Synthesis, morphological and Raman studies

Gold (Au) catalyst assisted Silicon nanowires (SiNWs) and Silicon nanoneedles (SiNNs) were grown with Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor using VLS methodology. The influential process parameter was the growth temperature, and its effect on the morphology of the structures was studied. FESEM images revealed the growth of high density SiNNs with diameter ranging from 45 to 160 nm and length as much as 5.66 ± 0.2 mm. The superior crystallinity was obtained by Raman measurements. The excellent features of these results propose that our regular method may form a basis for the temperature mediated tunable growth of Silicon nanostructures suitable for optoelectronic devices.

(Invited) Wearable and Flexible Bio-Electronics Enabled By 'crack'-Driven Transfer Printing Methods

Emerging transfer printing methods provide means to build a range of mechanically flexible and wearable bioelectronics, opening up a new prospect in the field of biomedical technologies. The mechanical flexibility allow the devices to intimately integrate with biological systems such as biological cells, tissues, and/or the skin at their length scale. The embedded semiconducting nanomaterials provide the electronic functionalities that can monitor and/or stimulate them with spatial and temporal controls. This presentation will talk about a novel class of transfer printing method by exploiting controlled “crack” that is capable of liberating various nanoelectronics from their native wafer over large scale. The liberated nanoelectronics can be then thinly placed onto an arbitrary surface of biological systems of interest including cells and tissues, and therefore can provide the desired electronic functionalities at the intimate interface. A multiscale computational model that incorporates atomistic debonding mechanisms into macroscale interface delamination reveals the underlying working mechanisms and provide a quantitative guidance for controllable cracking process. The knowledge obtained from these studies provides important insights to improve the manufacturability in terms of scalability, controllability, and reproducibility. System-level demonstrations include skin-mountable sensors and cell-injectable silicon nano-needles, which can validate their utility in wearable healthcare systems and intracellular drug delivery platform. Discussions about the results of detailed experimental and theoretical studies will follow to reveal the essential attributes of the materials, devices, and fabrication process.

Tissue Engineering and Repair of the Damaged Heart490Transplantation of adipose mesenchymal cells overexpressing telomerase and myocardin preserved cardiac function and promoted tissue repair in murine myocardial infarction491Targeting the hippo signalling pathway to enhance the therapeutic potential of iPS-derived cardiomyocytes492Porous silicon nanoneedles for localised in situ gene transfer for cardiac therapy

Tissue Engineering and Repair of the Damaged Heart490Transplantation of adipose mesenchymal cells overexpressing telomerase and myocardin preserved cardiac function and promoted tissue repair in murine myocardial infarction491Targeting the hippo signalling pathway to enhance the therapeutic potential of iPS-derived cardiomyocytes492Porous silicon nanoneedles for localised in situ gene transfer for cardiac therapy

Tunable morphological evolution of in situ gold catalysts mediated silicon nanoneedles

Achieving tunable growth of high quality Silicon (Si) nanoneedles (NNs) is challenging. We report the optimized morphology of in situ gold (Au) catalysts assisted SiNNs grown via very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The vapor-liquid-solid (VLS) mechanism mediated morphological evolution is tuned using hydrogen (H2) and silane (SiH4) gas flow. Au-coated Si(100) substrates are treated using H2 plasma to create in situ Au nanoparticles (NPs) with high catalytic activity. FESEM images manifested the existence of mono-dispersed Au NPs and high yield of SiNNs having diameter ranging from 80 to 140nm and lengths up to 2.31±0.3µm. Furthermore, these NNs gradually became thinner to form sharp tips of diameter as small as 4nm. XRD pattern confirmed the diamond (cubic) crystalline phases of SiNNs. HRTEM images revealed the occurrence of Au NPs at the crystalline SiNNs tips. Raman spectrum of as-grown SiNNs exhibited the TO phonon mode accompanied by a red-shift (~23.59cm−1). Synthesized SiNNs displayed extremely low reflectance (~8%) at short wavelengths (λ<700nm), indicating excellent antireflection properties. Our controllable and optimized growth method may constitute a basis to achieve high quality SiNN arrays, which are beneficial for various applications.

Pressure dependent tailored attributes of silicon nanoneedles grown by VHF plasma technique

Gold (Au) catalysts assisted well-aligned silicon nanoneedles (SiNNs) are synthesized using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The tailored morphology and the optical reflectance of such NNs are inspected as a function of varying reactor pressure (200–800 mTorr). FESEM images revealed the growth of high density SiNNs with diameter ranging from 45 to 600 nm and length as much as 5.66 ± 0.2 μm. Overall morphology of these NNs are found to be highly sensitive to the pressure variation, where appreciably aligned thinner NNs are achieved at 600 mTorr pressure. The presence of globule at the NNs tip authenticated their VLS mechanism mediated growth. The reactor pressure sensitivity of the aspect ratio, lattice parameters, Raman modes, and reflectance are demonstrated. XRD patterns manifested SiNNs cubic crystalline phase with preferred orientation along 〈111〉 direction. The occurrence of NNs high crystallinity is further supported by the Raman and HRTEM data. The reflectance of SiNNs grown at 600 mTorr exhibited remarkable reduction (∼6.3%) than those obtained at other pressures. This reactor pressure dependent significant modification in the physical properties of synthesized SiNNs may be prospective for the development of optoelectronics.

VHF-PECVD grown silicon nanoneedles: Role of substrate temperature

Achieving highly aligned and dense silicon (Si) nanoneedles (NNs) is ever demanding for optoelectronics. We report the substrate temperature assisted Au-catalyzed SiNNs synthesis via very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) technique. The effects of varying substrate temperatures (350–550 °C) on the growth process are examined. The maximum density of SiNNs (∼10 NN/μm2) is obtained at the optimum temperature of 550 °C. These NNs have diameters ranging from 38 to 87 nm and the lengths are extended up to 2.96 ± 0.09 μm. Furthermore, the sample prepared at 350 °C is totally devoid of any SiNNs. The axial NNs growth rate increased from 35.3 ± 2.3 nm/min (at 400 °C) to 138.8 ± 8.9 nm/min (at 550 °C). XRD analysis demonstrated the SiNNs cubic structure with preferred orientation along <111>. The NNs prepared at 550 °C displayed better crystallinity than those obtained at other temperatures. This enhanced crystallinity is further supported by Raman measurements. High resolution transmission electron microscopy (HRTEM) confirmed that these NNs are composed of crystalline Si core with an oxide shell. Sample grown at 400 °C revealed a reflectance of 28.642% in the visible region. However, the highly dense SiNNs grown at 550 °C showed a noticeable suppression in the reflectance (15.787%), indicating excellent anti-reflection attributes. The excellent features of the presented results suggest that our systematic method may constitute a basis for the temperature mediated tunable growth of SiNNs suitable for optoelectronics devices.