Reusable Substrate Research Articles

Highly ordered Au-decorated Ag nanorod arrays as an ultrasensitive and reusable substrate for surface enhanced Raman scattering

For surface-enhanced Raman spectroscopy (SERS) substrates, complexity of the fabrication process, sensitivity and stability are factors that need to be considered. We report a simple and novel method for preparing an effective substrate that greatly enhances SERS signals. The SERS substrate is fabricated by selectively electroless deposition of Ag nanoparticles in the highly ordered porous anodized aluminum oxide (AAO) template and then etching it to form Ag nanorod bundles structure, so that the Raman enhancement occurs in the gap between the nanorods and the top of the nanorod bundle, which is verified by finite element analysis. A peculiarity of this method is that this is the first time to synthesize Ag nanorod arrays structure by using it. The results indicated that this prepared substrate has special micro-nano structure and when rhodamine 6 G is selected as the detection reagent, the detection limit is as low as 10−16 M with excellent recyclability. This outstanding array structure has a promising practical application in SERS field.

Ag/ZnO/Au 3D hybrid structured reusable SERS substrate as highly sensitive platform for DNA detection

Ultra-sensitive hybrid Silver/Zinc oxide/Gold (Ag/ZnO/Au) structure based three dimensional (3D) surface enhanced Raman scattering (SERS) substrates have been prepared by three step fabrication process using thermal evaporation, hydrothermal growth, and sputtering techniques. The size and inter-particle (IP) gap of decorated Au nanoparticles (NPs) on ZnO nanorods (NRs) in the sub-nanometer range have been achieved through varying the sputtering time of Au. The superhydrophobic nature, the formation of the Schottky barrier at ZnO/Au interface and the broad optical absorption spectrum facilitated towards higher SERS activity of Ag/ZnO/Au hybrid structures. The higher SERS activity of 3D SERS substrate as compared with two dimensional (2D) SERS substrate has been studied. The good SERS signal reproducibility of 3D hybrid structures have been explored through Raman mapping. Higher SERS enhancement factor (EF) of 1 × 1010 has been achieved with a limit of detection (LOD) up to 10−16 M and 10 ng/μL for Rhodamine-6 G (Rh6G) and lambda DNA (λ-DNA), respectively. The degradation of Rh6G and λ-DNA molecules have been studied through photocatalytic degradation process to explore the reusability of the SERS substrates up to 10 and 4 times, respectively, with maintaining good SERS signal reproducibility. This metal/semiconductor/metal hybrid structure based SERS substrate with reusable capability indicates potential application towards biosensor for the detection of biologically important molecules at very low concentration level.

III–V Solar Cells Grown on Unpolished and Reusable Spalled Ge Substrates

Substrate reuse offers a promising route toward enabling high-efficiency III–V solar cells to become cost-competitive for one-sun terrestrial applications. In this study, Ge films were spalled using an electroplated Ni stressor layer, and the fracture surface was characterized. Initial heteroepitaxial GaAs films grown on spalled Ge substrates by hydride vapor phase epitaxy were found to be single crystal with nearly equivalent growth rates between growth on epi-ready and unpolished spalled Ge substrates. We show the first demonstration of III–V solar cells (GaInAsP, Eg ∼ 1.7 eV) grown on unpolished spalled Ge substrates to assess the viability of substrate reuse. We demonstrate equivalent performance for a solar cell grown on spalled Ge and on a coloaded epi-ready Ge substrate, despite the residual roughness on the spalled Ge substrate and the lack of any substrate surface preparation. This initial demonstration of combining substrate reuse with the ability to grow III–V solar cells using a high growth rate and high throughput deposition process is a promising step toward low-cost III–V photovoltaics.

Fabrication of seeded substrates for layer transferrable silicon films**Project supported by the National Natural Science Foundation of China (Grant No. 11374313) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 11504392).

The layer transfer process is one of the most promising methods for low-cost and highly-efficient solar cells, in which transferrable mono-crystalline silicon thin wafers or films can be produced directly from gaseous feed-stocks. In this work, we show an approach to preparing seeded substrates for layer-transferrable silicon films. The commercial silicon wafers are used as mother substrates, on which periodically patterned silicon rod arrays are fabricated, and all of the surfaces of the wafers and rods are sheathed by thermal silicon oxide. Thermal evaporated aluminum film is used to fill the gaps between the rods and as the stiff mask, while polymethyl methacrylate (PMMA) and photoresist are used as the soft mask to seal the gap between the filled aluminum and the rods. Under the joint resist of the stiff and soft masks, the oxide on the rod head is selectively removed by wet etching and the seed site is formed on the rod head. The seeded substrate is obtained after the removal of the masks. This joint mask technique will promote the endeavor of the exploration of mechanically stable, unlimitedly reusable substrates for the kerfless technology.

Au-Au composites with inverse opal structure for surface-enhanced Raman spectroscopy

Golden inverse opals additionally decorated with 15.5 ± 1.5 nm gold nanoparticles are proposed as reusable substrates for surface-enhanced Raman spectroscopy (SERS). Gold nanoparticles are found to be uniformly distributed making an input of enhancement ability of spectral characteristics with the colloidal system by ten times. This technique is demonstrated to be efficient in spectral features tuning via a combination of different gold derivatives. Two lasers served for resonant, pre-resonance, and non-resonance signal analyses. Reusability of the Au-Au composite films is demonstrated for methylene blue as a stable dye deposited onto the SERS chips using a 632.8-nm resonant laser for exciting. The enhancement factor for methylene blue achieved 108 and for rohodamine 6G was of about 105. It was observed that rinsing of Au-Au nanocomposite SERS films with distilled water and heating up to 100 °C followed by dropping on a new portion of Au colloids onto the platform regenerates the substrates.

Investigation of silver nanorods as reusable SERS-active substrates for trace level detection of 2-MIB volatile organic compound

Silver nanorod arrays deposited on a silicon wafer by employing the DC magnetron sputtering system have been investigated as reproducible and reusable SERS-active substrates. 2-Methylisoborneol (2-MIB) is used as a test molecule to exploit the uniformity, reproducibility and reusability of the fabricated substrates. SERS chips are found to be reusable by simple washing with DI water. Quantitative measurements show a good correlation between the intensity and molar concentration of 2-MIB. SERS chips can detect 2-MIB as low as 1 ppt, limit of detection. The present method is a single package of high SERS performance, large-scale production, ultrasensitive, uniform, reproducible and reusable.

Electrochemical fabrication of pyramid-shape silver microstructure as effective and reusable SERS substrate

The high sensitivity and reproducibility are significant for the routine Surface-enhanced Raman Scattering (SERS) detection. Here, the pyramid-shape silver microstructures has been successfully synthesized using a facile electrochemical deposition method and the reaction with a two-indium tin oxides (ITO) electrode system is carried out by potentiostatic method, where only silver nitrate (AgNO3) and poly (methyl methacrylate) (PMMA) nanospheres are introduced to control the reaction process. Meanwhile, PMMA nanospheres as morphology controlled reagents are used to lead Ag units to grow in the form of pyramid-shape. The prepared pyramid-shape silver microstructures possesses high SERS activity with an average enhancement factor (EF) of 9.1 × 105, which is superior or close to some individual Ag or Au microstructures and Ag composite materials. In addition, an excellent reproducibility is achieved resulting from a relative standard deviation of 7.9%, 8.5%, 7.3%, and 8.7% measured by four Raman shifts of R6G at 612, 772, 1363, and 1650 cm−1, respectively, which is much lower than those of the commonly used SERS substrates. Importantly, the as-prepared pyramid-shape silver microstructures have been evolved as a sensitive SERS substrate for the detection of trace amounts of rhodamine 6G (R6G) and 3-mercaptopropionic acid (3MPA) down to nanomolar and millimolar concentration with excellent recyclability. Therefore, this work offers a simple way to prepare pyramid-shape silver microstructures as an effective SERS substrate and make the SERS more practicable.

HfO2-wrapped slanted Ag nanorods array as a reusable and sensitive SERS substrate for trace analysis of uranyl compounds

SERS has been used for rapid and trace analysis of uranyl compounds due to its fast response and high sensitivity. However, the difficulties in preparing stable and reusable SERS substrate as well as quantitative detection severely restrict its practical application prospects. Herein, HfO2-wrapped slanted Ag nanorods array was used as SERS substrate for sensitive analysis of trace uranyl compounds for the first time. The proposed substrate with uniform surface roughness and well-distributed Ag nanorods showed excellent spectral reproducibility, while the ultrathin HfO2 film fully covering Ag nanorods effectively improved the substrate stability and contributed to its cyclic utilization. Besides, quantitative detection of trace uranyl ions was achieved by using this substrate with an ultra-low detection limit of 8.33 ppb. Most importantly, SERS spectra of varied uranyl hydroxides at different pH values together with in situ SERS spectrum of UO2(CO3)34− were recorded on this substrate, building the correspondence between SERS band position of OUO(ν1) and uranyl species. Thus, SERS technique based on this substrate could be a promising method for both concentration detection of uranyl ions and structure identification of some uranyl compounds in trace level, indicating high potential application prospects in the environmental monitoring.

Applications of Open Source GMAW-Based Metal 3-D Printing

The metal 3-D printing market is currently dominated by high-end applications, which make it inaccessible for small and medium enterprises, fab labs, and individual makers who are interested in the ability to prototype and additively manufacture final products in metal. Recent progress led to low-cost open-source metal 3-D printers using a gas metal arc welding (GMAW)-based print head. This reduced the cost of metal 3-D printers into the range of desktop prosumer polymer 3-D printers. Consequent research established good material properties of metal 3-D printed parts with readily-available weld filler wire, reusable substrates, thermal and stress properties, toolpath planning, bead-width control, mechanical properties, and support for overhangs. These previous works showed that GMAW-based metal 3-D printing has a good adhesion between layers and is not porous inside the printed parts, but they did not proceed far enough to demonstrate applications. In this study, the utility of the GMAW approach to 3-D printing is investigated using a low-cost open-source metal 3-D printer and a converted Computer Numerical Control router machine to make useful parts over a range of applications including: fixing an existing part by adding a 3-D metal feature, creating a product using the substrate as part of the component, 3-D printing in high resolution of useful objects, near net objects, and making an integrated product using a combination of steel and polymer 3-D printing. The results show that GMAW-based 3-D printing is capable of distributed manufacturing of useful products for a wide variety of applications for sustainable development.

Vertically aligned γ-AlOOH nanosheets on Al foils as flexible and reusable substrates for NH3 adsorption

Vertically aligned γ-AlOOH nanosheets (NSs) have been successfully fabricated on flexible Al foils via a solvothermal route without morphology-directing agents. Three different reaction temperature (25, 80, and 120 ◦C) and time (30 min, 45 min, and 24 h) are discussed for the growth period, which efficiently tune the density and size of the γ-AlOOH NSs. Meanwhile, the growth speed of the nanosheets confirms that dominant growth stage is seen in the initial 45 min. Furthermore, the interlayer of the γ-AlOOH NSs displays an average height of 140 nm and superhydrophilicity. By dynamic adsorption, the assynthesized γ-AlOOH NSs exhibit an outstanding NH3 adsorption capacity of up to 146 mg/g and stably excellent regeneration for 5 cycles. The mechanism of NH3 adsorption on the in-plane of the γ-AlOOH NSs is explained by the Lewis acid/base theory. The H-bond interactions among the NH3 molecules and the edge groups (-OH) further improve the capture ability of the nanosheets.

Metallic carbide nanoparticles as stable and reusable substrates for sensitive surface-enhanced Raman spectroscopy.

We demonstrate for the first time that metallic carbide nanoparticles with a strong localized surface plasmon resonance (LSPR) effect could be used as SERS substrates to detect trace substances. They achieve a noble metal-comparable enhancement factor of 6.4 × 107.

Synthesis of Multi-Au-Nanoparticle-Embedded Mesoporous Silica Microspheres as Self-Filtering and Reusable Substrates for SERS Detection

Surface-enhanced Raman-scattering-based (SERS-based) biosensing in biological fluids is constrained by nonspecific macromolecule adsorptions and disposable property of the SERS substrate. Here, novel multi-Au-nanoparticle-embedded mesoporous silica microspheres (AuNPs/mSiO2) were prepared using a one-pot method, which served as reliable substrates for SERS enhancement associated with salient features of self-filtering ability and reusability. The fabrication and physical characterization of AuNPs/mSiO2 microspheres were discussed, and SERS activity of this novel substrate was investigated by using 4-mercaptobenzoic acid (4-MBA) as Raman probe. The responses of our substrates to Raman intensities exhibited a SERS enhancement factor of 2.01 × 107 and high reproducibility (relative standard deviation of 6.13%). Proof-of-concept experiments were designed to evaluate the self-filtering ability of the substrates in bovine serum albumin (BSA) and human serum solution, separately. The results clearly demonstrate that mesoporous SiO2 can serve as a molecular sieve via size exclusion and avoid Raman signal interference of biomacromolecules in biological fluids. Subsequently, feasibility of practical application of AuNPs/mSiO2 microspheres was assessed by quantitative detection of methotrexate (MTA) in serum. The method exhibited good linearity between 1 and 110 nM with the correlation coefficients of 0.996, which proved that the obtained AuNPs/mSiO2 microspheres were good SERS substrates for determination of small biomolecules directly in biological fluids without need of manipulating samples. In addition, the substrate maintained its SERS response during multiple cycles, which was evaluated by recording Raman signals for 4-MBA before and after thermal annealing, thereby demonstrating the high thermostability and satisfactory reusability. These results offered the AuNPs/mSiO2 microspheres attractive advantages in their SERS biosensing.

Bioinspired Synthesis of Mesoporous Gold-silica Hybrid Microspheres as Recyclable Colloidal SERS Substrates

Noble metal nanostructures have been intensively investigated as active substrates for surface-enhanced Raman spectroscopy (SERS) from visible to near-IR wavelengths. However, metal nanoparticle-based SERS analysis in solutions is very challenging due to uncontrollable and irreproducible colloid aggregation. Here we report the templated synthesis of porous gold-silica hybrid microspheres and their application as reusable colloidal SERS substrates. Mesoporous polymer microspheres are synthesized and used as templates for the synthesis of non-aggregated gold nanoparticles, followed by polydopamine-mediated silicification to fabricate mesoporous gold-silica hybrid microspheres. The mesoporous hybrid particles detect crystal violet in the order of 10–8 M and provide the structural durability of the immobilized gold nanoparticles, allowing them to be recycled for repeated SERS analyses for analytes in a solution with the similar sensitivity. This work suggests that the mesoporous gold-silica hybrid microspheres are attractive SERS substrates in terms of reusability, sensitivity, and stability.

Spontaneous delamination via compressive buckling facilitates large‐scale β‐Ga2O3 thin film transfer from reusable GaAs substrates (Phys. Status Solidi A 10∕2017)

Spontaneous delamination via compressive buckling facilitates large‐scale β‐Ga₂O₃ thin film transfer from reusable GaAs substrates (Phys. Status Solidi A 10∕2017)

A multifunctional Ag/PAOCG reusable substrate for p-nitrophenol reduction and SERS applications

We demonstrate a facile galvanic replacement reaction route to direct growth of silver nanoparticles (AgNPs) into porous alumina on conductive glass (PAOCG). Porous Al2O3 layer was prepared by using boehmite as precursor, deposited on conductive glass via spin coating, and followed by a heat treatment. PAOCG was attached firmly with a tiny sheet of steel and was then soaked in AgNO3 solution. Ag+ ions in the nanopores of PAOCG adsorbed by capillarity were automatically reduced to metallic AgNPs, thus forming Ag/PAOCG. The catalytic property of Ag/PAOCG was investigated for p-nitrophenol (PNP) reduction using UV–Vis absorption spectroscopy, and the rate constant was evaluated using the pseudo-first-order kinetic model. This film catalyst could be readily regenerated and reused for up to ten times without significantly depreciate its efficiency. The SERS performance of Ag/PAOCG was investigated using aqueous crystal violet (CV) as a probe molecule. The optimum Ag/PAOCG substrate was capable of detecting as low as 10−10 M aqueous CV. The reusability of Ag/PAOCG was achieved by heating the substrate at 400 °C for 5 min in air. This substrate could be reused for at least five cycles without significantly reduced SERS performance. Therefore, this powerful multifunctional surface can serve as a portable, durable and reusable substrate for PNP reduction and SERS applications.

Laser writing of single-crystalline gold substrates for surface enhanced Raman spectroscopy

Surface enhanced Raman scattering (SERS) spectroscopy, a powerful contemporary tool for studying low-concentration analytes via surface plasmon induced enhancement of local electric field, is of utility in biochemistry, material science, threat detection, and environmental studies. We have developed a simple, fast, scalable, and relatively low-cost optical method of fabricating and characterizing large-area, reusable and broadband SERS substrates with long storage lifetime. We use tightly focused, intense infra-red laser pulses to write gratings on single-crystalline, Au (1 1 1) gold films on mica which act as SERS substrates. Our single-crystalline SERS substrates compare favourably, in terms of surface quality and roughness, to those fabricated in poly-crystalline Au films. Tests show that our SERS substrates have the potential of detecting urea and 1,10-phenantroline adulterants in milk and water, respectively, at 0.01 ppm (or lower) concentrations.

Spontaneous delamination via compressive buckling facilitates large‐scale β‐Ga2O3 thin film transfer from reusable GaAs substrates

The fabrication and transfer via spontaneous delamination of large‐area, high‐quality β‐Ga2O3 nanoscale thin films with centimeter‐scale dimensions is demonstrated via thermal oxidation of reusable GaAs substrates. The films are characterized by using X‐ray diffraction, energy dispersive spectroscopy, Raman spectroscopy, and scanning electron microscopy. The film demonstrates good mechanical flexibility facilitating reliable transfer. The β‐Ga2O3 film's optical band gap and Schottky barrier height with gold are 4.8 and 1.03 eV, respectively. Electrical and optical properties of the transferable β‐Ga2O3 thin films exhibit a potential for application in solar‐blind photodetectors. The scale of the β‐Ga2O3 films transferred herein exceeds what the research community has reported to‐date by more than four orders of magnitude. The macroscopic dimensions of the transferred films may offer a remedy for the low thermal conductance of β‐Ga2O3 via transfer onto substrates with high thermal conductivity.

The Influence of Cellular Debris on Cell Guidance and Implications for Incorporating Silicon Based Micropatterns

ABSTRACTDetermining what external stimuli influence cell differentiation, morphology, and growth continues to be a focus on many research groups to meet the healthcare Grand Challenges. While prior work has shown the influence of stiffness, surface chemistry and topography, these parameters often change in tandem, making it difficult to delineate the role of an individual component. This study examined the possible incorporation of microelectronic processing to produce reusable substrates for cell guidance studies. Subsequent plating of substrates cleaned with methods common in a microelectronic fabrication process showed complex responses including migration. Optical characterization of surfaces after cleaning showed remaining cellular debris that could be removed through the incorporation of a piranha solution. The micro patterned substrates did allow controlled comparison between dental pulp stem cells and osteoblast cells. The dental pulp cells did not show any cell alignment or cell proliferation (as indicated by cell density) with the isotropic or anisotropic micropatterns on the initial plating. The osteoblast cells (control) only aligned with the lines and not any of the other patterns (dots, holes or hexagons).

Ultrafast Growth of High-Quality Monolayer WSe2 on Au.

The ultrafast growth of high-quality uniform monolayer WSe2 is reported with a growth rate of ≈26 µm s-1 by chemical vapor deposition on reusable Au substrate, which is ≈2-3 orders of magnitude faster than those of most 2D transition metal dichalcogenides grown on nonmetal substrates. Such ultrafast growth allows for the fabrication of millimeter-size single-crystal WSe2 domains in ≈30 s and large-area continuous films in ≈60 s. Importantly, the ultrafast grown WSe2 shows excellent crystal quality and extraordinary electrical performance comparable to those of the mechanically exfoliated samples, with a high mobility up to ≈143 cm2 V-1 s-1 and ON/OFF ratio up to 9 × 106 at room temperature. Density functional theory calculations reveal that the ultrafast growth of WSe2 is due to the small energy barriers and exothermic characteristic for the diffusion and attachment of W and Se on the edges of WSe2 on Au substrate.

Fabrication of silicon films from patterned protruded seeds.

Thin, flexible silicon crystals are starting up applications such as light-weighted flexible solar cells, SOI, flexible IC chips, 3D ICs imagers and 3D CMOS imagers on the demand of high performance with low cost. Kerfless wafering technology by direct conversion of source gases into mono-crystalline wafers on reusable substrates is highly cost-effective and feedstock-effective route to cheap wafers with the thickness down to several microns. Here we show a prototype for direct conversion of silicon source gases to wafers by using the substrate with protruded seeds. A reliable and controllable method of wafer-scaled preparation of protruded seed patterns has been developed by filling liquid wax into a rod array as the mask for the selective removal of oxide layer on the rod head. Selectively epitaxial growth is performed on the protruded seeds, and the voidless film is formed by the merging of neighboring seeds through growing. And structured hollows are formed between the grown film and the substrate, which would offer the transferability of the grown film and the reusability of the protruded seeds.