WO2017213581A1

WO2017213581A1 - Nanostructured material

Info

Publication number: WO2017213581A1
Application number: PCT/SE2017/050620
Authority: WO
Inventors: Thomas WÅGBERG; Xueen JIA; John Berge
Original assignee: Wågberg Thomas; Jia Xueen
Priority date: 2016-06-10
Filing date: 2017-06-09
Publication date: 2017-12-14

Abstract

A nanostructured material is diclosed comprising a solid substrate surface with a plurality of nonoprotrusions and domains comprising at least one noble metal with simulataneous improvements in conductivity and electromagnetic response by plasniome resonance. Also disclosed are chemical vapor deposition methods and nanoimprining methods to prepare the nanostractured material.

Description

Nanostructured material

Field of the invention

A nanostructured material comprising a solid substrate surface with a plurality of nanoprotrusions and domains comprising at least one noble metal with sknnlataneous improvements in conductivity and

electromagnetic response by plasmonic resonance.

Background of the invention

Detection of pathogenic organisms, hormones, or other medically relevant analytes still demands the development of innovative-analytical -devices with enhanced sensitivity, specificity, precision, speed and usability. Lab-on-a Chip (LOC) Technology which integrates several laboratory functions on a single chip and has several advantages including reduced sample and reagent Consumption, automation, and fast detection times. Though LOC technology leads: to remarkable new biochemical sensors and molecular diagnostic devices, conventional fabrication process of microiiuidic device is time consuming and cost inefficient Concurrently the small sample volumes used in microflnidic cells raise: the requirements of high- sensitivity for the detection method. A multifunctional microiiuidic device that can be used to detect enzymatic and immunoassays optically and/or electrochemically is highly desirable. In order to improve the performance of the mini-lab (and tliereby enable fast testing of relatively small, sample volumes), a plasmonic metal layer should be generated on a multiple: electrode array or in the channel of microfluidics chip, which can be used for a number of potential diagnostic applications, since the biochips can be loaded with corresponding biomarkers, which after "reacting" with certain target molecules in the body fluidics will change the electrochemical or optical response on the device and therefore generate a measurable signal and after piasmonic modification, such. response will be significantly enhanced. For this purpose, new nanostructure arrays are needed which following functionalization admit both an optical response and are operable as an electrode for electrochemical detection. Such features are estimated to improve both safety and accuracy in sensing technologies. The present invention is directed to providing such improved structures. There are numerous examples of nanoarrays, wherein nanosteed tubes are deposited on substrates and functionaiized as sensors. US 2015/0210549 (Johansson et a!) describes carbon nanotubes (CNTs) are grown on or attached to a substrate surface. For example vapor deposition technologies (CVD or PHCVD) are used on surface coated with a buffer layer and a catalyst layer. Such tubes can be former funetionaiized with domains of noble metal or other chemical means. US 2013/0089735, J Zahang et al in Chem. Communi., 2011 , Vol 47.. Pp 668-670; VJ Gozales et al, Carbon, Volume 88, July 2017, pp 51-59; DH Lee at al., Nano Lett., 2009, Vol. 9(4), pp 1427-1432; Beilstein J. Nanotechnol., 2014, Vol. 5, pp 910-918 represent other examples of functionalized carbon nanotubes.

However, technical problems remain to establish sufficient control of the density of such nanostruetures and thereby ultimately the applicability of different sensing technologies for the same nanoarray structure. Description of the invention

The present invention generally relates to a. nanostruetured materia] comprising a solid substrate surface with a plurality of nanoprotrustons and domains comprising at least one noble metal that both exhibits a conducti ty (vertically and horizontally) and supports plasinonic resonance or SERS (Surface Enhanced Raman Scattering) enhancement, in order to be simultaneously suitable for both electrochemical and optical detection methods.

In one general aspect of the invention, the distance between the

nanoportrusions of the nanostructural material is less than 50 nm, preferably 10 to 50 nm; and the conductivity of the .material estimated as vertical resistivity to 1 x 10^-4 Ohm*m and estimated as sheet resistance of 0.1 to .1 kOhm square.

In one aspect the nanostruetured material comprises on the substrate a buffering layer, a catalyst layer on the buffering layer arid carbon nanotubes prepared by a chemical vapor deposition (CVD) method. The buffering layer, preferably has at least the double thickness of the catalyst layer and the catalyst layer is about 2 to about 15 nm thick. The buffer layer can be a metal film of at least one of Al, Ti , Mo, Ta, Cr, Au, Pt and W, preferably the buffering layer comprises titanium. The buffering layer can have a thickness of 4 to 50 mn. In one exampel, the buffering layer is 10 nm thick, preferably 5 nm thick and the catalyst layer is less than 15 nm thick. In one example, the catalyst layer comprises iron, or an alloy of iron and another metal, preferably an alloy of iron and cobalt. In one example, the catalyst layer can be treated with ammonia gas before perforating the chemical vapor deposition.The nanotubes according this aspect cab have a length of approximately from 100 nm to 50 μm, preferably 100 nm to 1000 nm. The the nanosturtured material generally has a density so the nanotube. to nanotube: distance is less than 50 nm. Nanotubes according this aspect should have wide meaning and include carbon nanofibers (CNF), helical carbon nanofiber (HCNF), multi-walled carbon nanotabes (MWNTs), nitrogen doped multi- walled carbon nanotabes (N-CNTs) single-walled carbon nanotubes (SWCNT), ordered mesoporous carbon or graphefte,. In one example, the nanotubes are multiwalled carbon nanotubes (MWNTs). The nanotubes preferbly are nitrogen doped carbon nanotubes.The nanostructured material according to this aspect can be prepared by providing a solid subsirate, optionally eompnsing an electrode pattern, with a buffering layer and a catalyst layer; growing on die so provided substrate, by chemical vapor deposition a vertically aligned carbon nanosiructure forest of nanotubes and thereby introducing nitrogen functionalities on said nanotubes; and finally anchoring noble metal nanopartic.es to the nanotubes to the nitrogen functionalities. The skilled person can conceive alternative routes to funcionalize the nanotubes and introduce noble metal domains, however, in this aspect of the invention it is one conceivable way to perform chemical vapor deposition by introducing acetylene, pyridine, ammonia and an argon-based earner gas as further described in for example in T. Sharift, et a!., Carbon, 2012, Vol. 50 (10), pp 3535-3541 , It is applicable to use different rations of acetylene and pyridine or use pyridine only as carbon and nitrogen: source. The noble metal domains according to this aspect, can be of gold and/and silver and can be arrayed on the nitrogen doped carbon nanostructures with techniques,, such as thermal evaporation (referred to as physical vapor deposition in high-vacuum systems below) or wet chemical methods, wherein a gold or silver salt is reduced by a reducing agent together with the nitrogen doped carbon nanostructures. As an example the noble metal can be represented by nanoparticles homogenously distributed on the nanostructures.

In this aspect, the nanostmctured. material has the SERS enhancement factors (EF) of at least 9x10⁶ and at least 2,7x 10⁵, for domains of gold and silver, respectively, when calculated by comparing the Raman signal for a 4- ATP adsorbed on the material provided with nitrogen doped carbon nanostructures and NCNT/Au Features and the Raman signal for 4-ATP on a non-piasrnonie silicon dioxide substrate.

In one aspect, the nanostructured material generally described above wi th a high density of nanoprotrusions is be prepared by nanoimprinting

lithography (NIL) by contacting a polymeric material cast on a substrate, optionally comprising an electrode pattern, with a hard mold containing a nanoscale surface relief obtaining a pattern of solid nanopillars on said substrate surface with a. length of 50 to 400 nm, preferably 50 to 200 nm; optionally removing residua! polymeric material; and introducing a noble metal film to provide nanostructured material with the noble metal domains. The noble metal domains can be introduced with methods similar to what has been described above with the carbon nanotubes. hi this the step of contacting the cast with .mold can comprise heating a transparent thermoplastic polymer having a glass transition temperature of 60- 100 °C and applying a pressure of 5 to 60 bar. One example of suitable polymer is polyethylene terephthalaie (PET) and the conditions are requirements for this technology is described further U Guo, 2007, Adv. Mater., Vol 19, pp 495-513. importantly the material of this aspect has SERS enhancement factors (EF) of at least 2.5x10⁵, for noble domains of silver, when calculated by comparing the Raman signal for a 4-ATP adsorbed on the- material and the Raman signal for 4-ATP on a iion-plasmonic silicon dioxide substrate. The materials according to the described aspects are suitable for being included in a multifunctional biociiip with an electrochemical and an optical detection zone and thereby perioral simultaneous and/or comparative measurements. The biochip comprises a substrate comprising an electrode pattern for establishing an electrochemical detection zone, wherein the substrate is provided- with the nanostmetures according to the present invention having domains of noble metal with at least one immobilized biomarker for establishing an optical detection zone, and wherein the biochip has a microfluidic system comprising a port adapted to receive a fluid sample, a first, fluid channel for transporting sample fluid to the electrochemical detection zone and second fluid channel for transporting fluid to the optical detection zone. The biochip can have the micro fluidic system present in a layer added to the substrate, or the microtluidic system can be present in the substrate.

Detailed and exemplifying description of the invention

Fig. 1 depicts Scanning electron microscopy (SEM) images of vertically aligned nitrogen doped carbon nanotubes (NCNTs) grown on a) SiO2 substrate -coated with a Ti buffer layer and a catalyst layer comprising a 1: 1 Fe/Co alloy thin film.

Fig 1b) depicts a SiO2 substrate with a catalyst layer comprising a. 1 :1 Fe/Co alloy thin film but without a buffer layer. The figures show that the NCNT forest prepared with a buffer layer is much denser and more homogeneous compared to the NCNT forest synthesized without buffer layer (note that the scale bar in the images are the same). A buffer layer works like a spacer between catalyst and substrate: avoiding catalyst particles penetrate or escape from the substrate.

Fig 2a and 2b, respectively depicts Scanning electron microscopy (SEM) images with Fig 2a low magnitude (zoom-out perspective and Fig 2b high magnitude (zoom-in perspective) of vertically aligned nitrogen doped carbon nanotubes (NCNTs) grown on SiO2 substrate coated with a Ti buffer layer and a catalyst layer comprising a 1 :1 Fe/Co alloy thin film after depositing and annealing a Ag thin film on top of the NCNTs, The image shows that the Ag nanoparticles are uniformly distributed on the NCNT forest forming suitably sized nanodomains/nanop articles. Note that without NCNTs, in the area outside the NCNTs, the Ag-partieles grow into much larger domains. The presence, morphology and, size of the nanodomains formed on the NCNTs result in two targeted purposes; i) plasmonk resonances for wavelengths in visible range (500-700 run) leading to an enhanced Raman or fluorescence signal, and ii) conducting bridges, leading to a horizontally conducting pathway (percolation path) between tube and tube.

Example 1

According to the present invention, the CNT forests were grown from a catalyst metal layer through a C VD process at 800 °C and a physical vapor deposition (PVD) and annealing processes were applied subsequently for the evaporation and diffusion of noble metal nanoparticles on the forest.

Substrate preparation

Electrodes patterning were made onto the silicon-oxide (SiO2) wafers through the photoiitliography process with and without depositing buffer layer on the Si-surfaces. Photolithography is selected as a process oftransferring geometric shapes on a mask to the surface of a silicon wafer. We prepared our samples in a clean room of ISO 5 standard. Si-wafers were cleaned by soni cation in acetone, ethanot and water for 20 min separately, and then blow dry by N2 blowing and cleaned again by pi asma cleaner with UV and ozone for 25 minutes. A photoresist was added to the surface of each wafer and kept them spinning separately by a spin coater at 4000 rpm: (or 1000 rpm/sec) for one minute. After that each wafer was hot baked in a portable oven at 1 10 °C for 1 minute. A mask aligner was used as a source of radiation which produces a typical mercury spectrum with the highest intensity at the H-line (404.7 nm), see the article "Growing patterned vertically aligned nitrogen-doped carbon nanotubes (VAN-CNTs) by CVD and photolithography, Author: Joakim Ekspong, 2014-06-09, Department of Physics, Umea University, Sweden". The exposure time for the mask aligner was set to 25 seconds. The electrode patterns were pre-printed on an opaque plate which- was used as a photomask for patterning. After exposing a high intensity ultraviolet light to the mask, the electrode patterns were burned into the photoresist on the wafers, see

http^//ualr.edu/systemsengineering/mask-aligner/. Then the wafers with patterns were put separately in a developer solution for 40 and 60 seconds, respecti vely. The exposed parts of the photoresist were taken away by the developer and the different patterns on the surface of the wafers were clearly visible.. The wafers with patterns were then kept in a beaker with distilled water for I minute and then blow-dried with N2.

Deposition of buffering and catalyst layers The buffering layer is found to have critical role with the thickness of catalyst on the density of the NCNT forest production. Generally, it is found herein that the buffermg layer hinders catalysts to partially diffuse into the substrate (silicon) an that it enables forming of appropriate catalyst particles on the silicone substrate, In the present example, first a titanium (Ti) buffering layer with thickness of 10 nm were deposited by physical vapor deposition (Physical vapor deposition (PVD) is a vaporization coating process which is carried out in high vacuum pressure at any temperature between 150 and 500 °C, see

were deposited onto the Ti-film coated silicon wafer by co-evaporation of Co and Fe. The thickness of this film is important in order to obtain NCNTs with homogeneous diameters and high density. We have found that Fe/Co films of 5 nm can be readily pretreated by ammonia (NH3) to form nanocatalyst particles from which the aligned NCNTs can grow.

Significantly (roughly, three times as thick) lead to tbe growth of large diameter carbon fibers with low density, while thinner films lead to small diameter tubes with low density, or to no tube growth at all .

The pretreatment step with ammonia (NH3) in the CVD is performed in accordance with T. Sharifi et al. in Carbon, 50, 3535-3541 (2012), used to grow CNTs and NCNTs with uniform diameters on a Si-substrate. Time duration of the NH3 treatment according to the presently exemplified invention is about 20 minutes. Pyridine was used as carbon and nitrogen precursor for the CNT growtli and the height of the forest can be controlled by the growth time (the time at which the precursor is introduced in the CVD oven while maintaining a temperature high enough to decompose the precursor). In the present example below 20 and 60 minutes, were used respectively.

Introduction of noble metal nanoparticles to the CNT forest

Establishing gold or silver nanoparticles anchored on to top, at the sides and at the base of the CNT forest using either thermal evaporation or wet- chemistry methods (by reducing a metal salt). A silver (Ag) film deposition on top of the N-doped CNTs is made by forming a 30 nm Ag layer on top of the CNTs by running a premade recipe in the thermal PVD process in the clean room. For transferring Ag thin film to Ag nanoparticles on the top and along the CNT walls, the Ag-evaporated samples were placed into a quartz tube and annealed at a temperature of 400 0C in the electric oven for 30 minutes. The varigon was kept at a rate of 180 ml/mm during the annealingtime and after the heat treatment the oven was cooled down to 80 °C with keeping the flow of Ar instead at a rate of 180 ml/min. A goid (Au) film deposition on top of the N-doped CNTs is made by a forming 30 mil Au layer- oft top of the CNTs by running a premade recipe in the tfterrnal PVD process in the clean room. For transferring An thin film to An nanopartieles on the top and along the CNT walls, the Au-evaporated samples were placed into a quartz tube and annealed at a temperature of 800°C in the electric oven for 10 minutes. The varigon was kept owing at a rate of 1 80 ml/min during the annealing time and after the heat treatment, the oven was cooled down to 80°C with keeping the flow of Ar instead at a rate of 1 SO ml/min.

Results and SER S enhancement factors (EF)

Scanning Electron. Microscopy (SEM) imaging was employed to

characterize the CNT forest properties and Ag and Au nanoparticle distribution on the CNT forest. The existence of "hot spots" created by the Ag and An nanopartieles through, the surface roughness and plasmonic properties was demonstrated by the SERS, SERS is a surface-sensitivetechnique that enhances Raman scattering, by molecules adsorbed on rough metal surfaces or by nanostructures.[ Xu, X., Li, EL, Hasan, D., Ruoff, R. S., Wang, A. X. and Fan, D. L. (2013), Near-Field Enhanced Plasmonic- Magnetic Bifunctional Nanotubes for Single Cell Bioanalysis. Adv. Funct Mater..] The SERS enhancement factors (EF) were calculated by comparing the Raman signal for a 4-ATP adsorbed on .the functional SERS substrate (the substrate with plasmonic NCNT/Au features) and the Raman signal of 4- ATP on a traditional non-plasmonic substrate. The calculated values of EF from Ag- and Au-coated CNT forests were 9x 10⁶ and 2.7x 10⁵ respectively. Accordingly, the peak intensity at wave number of 1076 cm-1 was picked up from each SERS spectra to establish the Ag- and Ati-trend curves with different concentrations of 4- ATP solutions. [Kazumasa Uetsuki, Prabhat Verma, Peter Nordlander and Satoshi Kawata, Tunable plasmoti resonances in a metallic nanotip-film system, Nanoscale, 201:2, 4, 5931]

Fig. 1a and Fig 1b are SEM images showing that the NCNT forest prepared with buffer layer is much denser and smooth compared to the NCNT forest synthesized without buffer layer (note that the scale bar in the images are the same). A buffer layer works like a spacer between catalyst and substrate avoiding catalyst particles penetrate or escape from the substrate.

The SEM images in Fig. 2a and 2b. show that the Ag nanoparticles are uniformly distributed on the NCNT forest; such plasmonic nanostracture will enhance Raman signal as well as fluorescence signal, also it. works as a perfect bridge between tube and tube, resulting in high conductivity.

Example2 The nanoimprinting is made by first, i) heating a polymer film.,

polyethyelene terepthtalate (PET) above its glass transition temperature, roughly 70 °C [Demirel, B.; Yara_s, A.; El_d__cek, FL Crystallization Behavior of PET Materials.Balkesir Universitesi Fen Biiimleri Ensdti Dergisi, 13(1), p. 26-35, 2016] and ii) pressing a. mold into the mold by applying a high pressure (5-60 bar), and then iii) after cooling the polymer substrate below the glass transition temperature withdrawing the mold. The mold can be varied according to the pattern that is desired to press into the polymer substrate. The polymer substrate can be varied as long as the glass transition is suitable (60-100 °C). To obtain the nanopillars a pressure of 30 bar and a temperature of 80 degrees were used. In a scanning electron microscopy (SEM) image of vertically aligned nanopillars, the nanopillars are shown as bright spots protruding from the SiO2 substrate. The pillars are uniform, and are approximately 200 nra high (height can be controlled by varying parameters such as pressure and time), have diameters of 50 nm and have a center-to-center distances of 100 nm. A iianostructured material is estamated to have SER S enhancement factors ( EF) of at. least 2.5 x 10³, for domains of silver, when, calculated by comparing the Raman signal for a 4- ATP adsorbed on the material and the Raman signal for 4-ATP on a non- plasmome silicon dioxide substrate.

Claims

1. A nanostracfured material comprising a solid substrate surface with a plurality of nanoproirusions and domains comprising at least one noble metal, wherein, the distance between the lianoperirusions is less than 50 nm, preferably 10 to 50 nm; and the conductivity of the material estimated as vertical resistivity to I x 10^-4 Ohm*m and estimated as sheet resistance of 0.1 to 1 kOhm square.

2. The material according to claim I , comprising on the substrate a buffering layer, a catalyst layer on the buffering layer and carbon nanotubes prepared by a chemical vapor deposition method (GV D) charcterized in that the buffering layer has at least the double thickness of the catalyst layer and that said catalyst layer is about 2 to about 15 nm thick.

3. The material according to claim 2 and wherein the buffer layer is a metal film of at least one of Al, Ti, Mo, Ta, Cr, An, Pt and W, preferably the buffering layer comprises titanium.

4. The material according to claim 2 or 3, wherein the buffering layer has a thickness of 4 to 50 nm.

5. The material according to any one of claims 2 to 4, wherein the buffering layer is 10 nm thick, preferably 5 nm thick and the catalyst layer is less than 15 nm thick .

6. The material according to any one of claims 2 to 5, wherein the catalyst layer comprises iron or an alloy of iron and another metal, preferably an alloy of iron and cobalt

7. The material according any one of claims 2 to 6, wherein the nanotubes have a length of approximately from 100 nm to 50 pm, preferably the nanotubes are multiwalled carbon nanotubes (MWNTs).

8. The material according to any one of claims 2 to 7, wherein the nanotubes are nirogen doped carbon nanotubes.

9. The material according to any one of claims 1 to 8, prepared by a) providing a solid substrate, optionally comprising an electrode patters,, with a buffering layer and a catalyst layer;

b) growing on the substrate of step a), by chemical vapor deposition a vertically aligned carbon nanostructure forest of nanotubes thereby introducing nitrogen functionalities on said nanotubes;: and

c) anchoring noble metal naiioparticles to the nanotubes;

10. The material according to claim 9, characterized by perforating chemical vapor deposition by introducing acetylene, pyridine, ammonia and an argon- based carrier gas.

1 1. The material according to claims 9 or 10 having the SERS enhancement factors (EF) of at least 9x 10⁶ and at i east 2.7 x10⁵, for domains of gold and silver, respectively, when calculated by comparing the Raman signal for a 4- ATP adsorbed, on the material provided with nitrogen doped carbon nanostructures and NCNT/Au features and the Raman signal for 4-ATP on a non -plasmonic silicon dioxide substrate.

12. The materia.! according to any of claims 2 to 11, comprising txeatiiig the catalyst, layer with ammonia. gas before performing the chemical vapor deposition.

13. The material according to claim 1, prepared by nanoimprinting lithography (NIL) by (a) contacting a polymeric material east on a substrate, optionally

comprising an. electrode pattern, with a hard mold containing a nanoscale surface relief;

(b) obtaining a pattern of solid nanopillars on said substrate surface with a length of 50 to 400 nm optionally removing residual polymeric material; and

(c) introducing a noble metal film to provide nanostractured material with the noble metal domains.

14. The material prepared according to claim 13, having the SERS enhancement factors (EF) of at least. 2.5x10⁵, for noble metal domains of silver, when calculated by comparing the Raman signal for a 4-ATP adsorbed on the material and the Raman signal for 4-ATP on a non- plasmonic silicon dioxide substrate.

15. Tile material prepared according to claim 13 or 14, wherein step (a) comprises heating a transparent themioplastic polymer having a glass transition temperature of 60- 100 °C and applying a pressure of 5 to 60 bar.