WO2019003247A1 - Substrat sers accordable - Google Patents

Substrat sers accordable Download PDF

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Publication number
WO2019003247A1
WO2019003247A1 PCT/IN2018/050422 IN2018050422W WO2019003247A1 WO 2019003247 A1 WO2019003247 A1 WO 2019003247A1 IN 2018050422 W IN2018050422 W IN 2018050422W WO 2019003247 A1 WO2019003247 A1 WO 2019003247A1
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WO
WIPO (PCT)
Prior art keywords
metal
nanowires
substrate
base
list
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PCT/IN2018/050422
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English (en)
Inventor
Siva Umapathy
Navakanta Bhat
Deepak Ranjan NAYAK
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Indian Institute of Science IISC
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Indian Institute of Science IISC
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Publication of WO2019003247A1 publication Critical patent/WO2019003247A1/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons

Definitions

  • the invention generally relates to the field of physical chemistry and particularly to a method for obtaining a substrate for performing surface enhanced Raman spectroscopy.
  • Raman spectroscopy is a powerful technique which provides analyte specific spectra. However, the technique is inadequate in detecting analyte at low concentration.
  • SERS Surface Enhanced Raman Spectroscopy, generally referred to as SERS is a technique capable of obtaining Raman spectra of an analyte, by enhancing the signal more than 4 orders of magnitude, as compared to the normal Raman signal enabled detection of even single analyte molecule.
  • the aforementioned effect is observed when the analyte is at close proximity to a metal nanostructure surface.
  • the incident electromagnetic wave interacts with the metal nanostructure, the free electrons on the metal collectively oscillate giving rise to localized surface plasmons resonance called as LSPR.
  • LSPR results in intense electric field at the metal surface which in turn increases the weak Raman signal of the analyte by orders of magnitude.
  • SERS is performed either in a metal colloidal solution or on metal nanostructures fabricated on top of a base substrate which is termed as SERS substrate.
  • a SERS substrate has the advantage of further integration with lab-on-a-chip systems for potential bio-sensor application. Guillot N.,et.al., Yue. W, et.al., and Das G, et.al., the details of which are incorporated herein by reference, have reported fabrication of SERS substrate using lithography, self-assembly of nanoparticles have been demonstrated by Yap FL, et al., and Lee, W, et al., the details of which are incorporated herein by reference. There have been numerous methods that have shown physical vapor deposition of metalson nanostructures.
  • Controlled nanostructure fabrication with optimal precision and high enhancement factor is obtained by e-beam lithography.
  • large area fabrication and cost is a major disadvantage in lithography.
  • Orientation of structure requires specific placement of substrate with respect to the polarization of incident LASER to achieve high enhancement.
  • the synthesis process includes multiple fabrication steps.
  • FIG.1 shows a schematic representation of the process for obtaining a tunable SERS substrate, according to an embodiment of the invention.
  • FIG.2 shows SEM photographs of various stages of formation of a tunable SERS substrate, according to an embodiment of the invention.
  • FIG.3 shows intensity graphs of standard molecules tested using the tunable SERS substrate.
  • FIG.4 shows SERS intensity peaks of molecules TNT, being detected using the SERS substrate obtained, according to an example of the invention.
  • One aspect of the invention provides a method for obtaining a tunable Sensitive and large area Surface Enhanced Raman Scattering, SERS, substrate.
  • the method includes selecting a base.
  • a layer of a dielectric is deposited on the base through plasma enhanced chemical vapor deposition.
  • a first metal is selected as a catalyst for deposition on the dielectric layer.
  • Nanowires are grown on the deposited metal layer.
  • the nanowires can be formed to obtain various configurations.
  • the nanowires formed are then introduced in a solution of a second metal for varying duration of time to obtain a growth of nanostructures on the nanowires.
  • the nanostructures grown on the nanowire yields a SERS substrate.
  • the duration of contact of the nanowires with the metal solution determines the tunability of the SERS substrate formed.
  • the substrate consists of dense vertical germanium nanowires grown by plasma enhanced chemical vapour deposition.
  • Metals exhibiting plasmon resonance effect such as silver can be grown on the nanowires by galvanic displacement reaction.
  • the reaction results in growth of nanostructures on the tip of the nanowires resulting in formation of hotspots.
  • the hotspots are highly localized at the tips of the nanowire which aids in detection of analyte at low concentration.
  • the sensitivity can be further improved by obtaining SERS signal versus reaction time during the displacement reaction. This enables to define accurate time for the reaction for a specific wavelength.
  • Various embodiments of the invention provide a method for obtaining a tunable SERS substrate.
  • the method includes selecting a base.
  • a layer of a dielectric is deposited on the base through plasma enhanced chemical vapor deposition.
  • a first metal is selected as a catalyst for deposition on the dielectric layer.
  • Nanowires are grown on the deposited metal layer.
  • the nanowires formed are then reacted with a solution of a second metal for varying duration of time to obtain a growth of nanostructures on the nanowires.
  • the nanostructures grown on the nanowire yields a SERS substrate.
  • the duration of contact of the nanowires with the metal solution determines the tunability of the SERS substrate by increasing the plasmon resonance formed.
  • FIG.1 shows a schematic representation of the process for obtaining a tunable SERS substrate, according to an embodiment of the invention.
  • the method for obtaining a SERS substrate includes selecting a base 101 .
  • base include but are not limited to a glass, a plastic, a ceramic or a metal.
  • silicon substrate is chosen as the base.
  • a dielectric 103 is then chosen to be deposited over the base 101 .
  • dielectric include but are not limited to Si0 2 , Si 3 N 4 ,Hf0 2 , Al 2 0 3 , Ti0 2 and dielectrics of other molecules that is capable or exhibiting similar dielectric properties as that of the above state dielectrics are chosen.
  • Si0 2 is chosen as the dielectric and is deposited as a film of about 30nm thickness by plasma enhanced chemical vapour deposition technique.
  • the base 101 coated with the dielectric layer 103 is then deposited with a metal 105.
  • metal chosen include but are not limted to gold, copper, silver and any metal capable of forming eutectic alloy with the semiconductor chosen for forming nanowires.
  • gold is deposited on the base coated with the dielectric. The deposition of the gold is achieved through any of the known techniques of metal deposition. In one example of the invention, the gold is deposited by sputtering technique onto the base.
  • nanowires 107 of a semiconductor are grown. Examples of semiconductor include germanium or silicon. In one example of the invention, germanium is used as the semiconductor. Germanium in the form of GeH 4 is grown on the dielectric layer through plasma enhanced chemical vapour deposition technique.
  • the nanowires 107 thus formed can be either as a single wire or multiple wires. Further, the nanowires can form either an island or a film.
  • the nanowires of germanium thus formed on the dielectric layer are then reacted with a salt solution of a metal to form nanostructures of the metal on the germanium nanowires.
  • the reaction is achieved through galvanic displacement reaction on the substrate.
  • a typical requirement for the process is to have a substrate with higher reduction potential with respect to the desired metal.
  • all metals with a redox potential lesser than germanium is chosen.
  • silver is chosen in the form of silver nitrate, AgN0 3 for forming nanostructures on the germanium nanowires formed.
  • Other examples of metal selected for growth of nanostructures include but are not limited to copper, gold, palladium, platinum, nickel and aluminium.
  • the duration of reaction of the germanium nanowire with the silver nitrate determines the wavelength at which the intensity of substrate is maximum.
  • the dependency of wavelength of response to the reaction time enables tunability of the substrate towards a wide range of wavelength in the range from about 440 nm to about 830 nm.
  • the formation of nanostructures, as described herein above does not require special environment to achieve the same. Hence, the obtained SERS substrate is robust and has extended life without degradation of the properties of the substrate.
  • FIG.2 shows SEM photographs of various stages of formation of a tunable SERS substrate, according to an embodiment of the invention.
  • the size of the silver nanostructures formed on the tip controls the location of the surface plasmon resonance there by tuning the substrate to a specifc wavelength.
  • Fig.2(d)SEM image cross-sectional view of germanium nanowire treated with silver nitrate for 10 minutes. The image shows the extent of the silver nanostructures on the nanowires which is found to be localised on the tip of the nanowire due to surface tension of the nanowire substrates.
  • FIG.3 shows intensity graphs of standard molecules (4- Mercaptobenzoic Acid) tested using the tunable SERS substrate at 514 nm (FIG.3a) and at 785 nm (FIG.3b). Intensity contour plot from 50 various points are provided in FIG.3c and FIG.3d at 514 nm and 785 nm respectively for reproducibility.
  • FIG.4 shows SERS intensity peaks of molecules TNT and Phenylalanine being detected using the SERS substrate obtained, according to an example of the invention.
  • the invention as described herein above provides a method for fabrication of large area SERS substrate with scalable fabrication steps.
  • the base substrate of germanium nanowires can be stored in a sealed container without degrading the structures.
  • the metal nanostructures can be grown by immersing the nanowire in alkaline or acidic solution of the desired metal, at any desired instance of time, resulting in extended shelf life of the substrate.
  • the extended shelf life of the substrate eliminates the need of additional expensive steps of deposition.
  • the need based growth of nanostructures results in optimization of the reaction time.
  • the optimal reaction time yields various size of the nanostructures for a specific wavelength laser.
  • the varying size of the nanostructures represents high tunability. However, functionalization may increase the sensitivity towards a particular analyte by many folds.
  • the substrate as obtained by the method described herein can be integrated into techniques known in the art for analyte detection resulting in increased sensitivity towards analyte detection.
  • the SERS substrate as obtained can be effectively integrated in a microfluidic device.
  • the microfluidic device can be obtained by integrating the SERS substrate during the design and formation of the microfluidic device.
  • the fabrication process step can provision for a raised chamber height in microfluidics thereby increasing the throughput of such device.

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  • Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

La présente invention concerne un procédé d'obtention d'un substrat SERS accordable. Le procédé comprend la sélection d'une base. Une couche d'un diélectrique est déposée sur la base par dépôt chimique en phase vapeur assisté par plasma. Un premier métal est sélectionné en tant que catalyseur pour le dépôt sur la couche diélectrique. Des nanofils sont développés sur la couche métallique déposée. Les nanofils formés sont ensuite introduits dans une solution d'un second métal pendant une durée variable afin de permettre le développement de nanostructures sur les nanofils. Les nanostructures qui se sont développées sur le nanofil produisent un substrat SERS. La durée de contact des nanofils avec la solution métallique détermine l'accordabilité du substrat SERS formé.
PCT/IN2018/050422 2017-06-30 2018-06-27 Substrat sers accordable Ceased WO2019003247A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IN201741023122 2017-06-30
IN201741023122 2017-06-30

Publications (1)

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WO2019003247A1 true WO2019003247A1 (fr) 2019-01-03

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140043605A1 (en) * 2012-08-09 2014-02-13 National Tsing Hua University Sers-active structure, fabrication method thereof, and sers system comprising the same

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140043605A1 (en) * 2012-08-09 2014-02-13 National Tsing Hua University Sers-active structure, fabrication method thereof, and sers system comprising the same

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
NAYAK DR ET AL.: "Impact of ultrathin dielectric spacers on SERS: energy transfer between polarized charges and plasmons", J. MATER. CHEM. C, vol. 5, no. 8, 3 February 2017 (2017-02-03), pages 2123 - 2129, XP055569277 *
PENG M ET AL.: "Reductive self-assembling of Ag nanoparticles on German ium nanowires and their application in ultrasensitive surface-enhanced Raman spectroscopy", CHEM. MATER., vol. 23, 28 June 2011 (2011-06-28), pages 3296 - 3301, XP055569289 *
WANG T ET AL.: "The effect of dielectric constants on noble metal/ semiconductor SERS enhancement: FDTD simulation and experiment validation of Ag/Ge and Ag/Si substrates", SCIENTIFIC REPORTS, vol. 4, no. 1-7, 11 February 2014 (2014-02-11), pages 4052, XP055569285 *

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