IN-SITU GROWTH AND CATALYTIC NANOPARTICLE DECORATION OF METAL OXIDE NANOWIRES

Abstract

A method for manufacturing nanoparticle decorated nanowires by a vacuum deposition system having a deposition chamber and an aggregation chamber connected thereto includes: mounting a metal member in the deposition chamber; performing thermal oxidization of the metal member in the deposition chamber in an oxygen atmosphere so as to grow metal oxide nanowires on a surface of the metal member; without breaking vacuum in the vacuum deposition system, generating a vapor of a catalytic metal particles clusters in the aggregation chamber that is connected to the deposition chamber; and without breaking vacuum in the vacuum deposition system, transporting the generated catalytic metal particles clusters to the deposition chamber so as to decorate the metal oxide nanowires with catalytic metal nanoparticles made of the catalytic metal particles.

Claims

1. A method for manufacturing nanoparticle decorated nanowires by a vacuum deposition system having a deposition chamber and an aggregation chamber connected thereto, the method comprising: mounting a metal member in the deposition chamber; performing thermal oxidization of the metal member in the deposition chamber in an oxygen atmosphere so as to grow metal oxide nanowires on a surface of the metal member; without breaking vacuum in the vacuum deposition system, generating a vapor of a catalytic metal particles clusters in the aggregation chamber that is connected to the deposition chamber; and without breaking vacuum in the vacuum deposition system, transporting the generated catalytic metal particles clusters to the deposition chamber so as to decorate the metal oxide nanowires with catalytic metal nanoparticles made of the catalytic metal particles.

2. The method according to claim 1, wherein the metal member is a Cu wire, and metal oxide nanowires are CuO nanowires.

3. The method according to claim 1, wherein the metal member is a pair of Cu patterns, separated from each other with a gap therebetween, formed on a Si substrate, and wherein the step of performing thermal oxidation grows CuO nanowires that bridge said gap between the pair of the Cu patterns on the substrate.

4. The method according to claim 1, wherein the catalytic metal nanoparticles include Pd nanoparticles.

5. The method according to claim 1, wherein the catalytic metal nanoparticles include Ni/Pd bimetallic nanoparticles.

6. The method according to claim 1, wherein the metal member is a Cu wire, and metal oxide nanowires are CuO nanowires, and wherein the catalytic metal nanoparticles include Pd nanoparticles.

7. The method according to claim 1, wherein the metal member is Cu wire, and metal oxide nanowires are CuO nanowires, and wherein the catalytic metal nanoparticles include Ni/Pd nanoparticles.

8. The method according to claim 1, wherein the vapor of the catalytic metal particles clusters is generated in the aggregation chamber by linear magnetron sputtering.

9. A method for manufacturing a sensor device by a vacuum deposition system having a deposition chamber and an aggregation chamber connected thereto, the method comprising: forming a pair of metallic patterns on a substrate, the metallic patterns facing each other with respective edges parallel to each other with a constant gap therebetween; mounting said substrate having the pair of metallic patterns thereon in the deposition chamber; performing thermal oxidization of the metallic patterns in the deposition chamber in an oxygen atmosphere so as to grow metal oxide nanowires bridging the gap between the pair of metallic patterns; without breaking vacuum in the vacuum deposition system, generating a vapor of a catalytic metal particles clusters in the aggregation chamber that is connected to the deposition chamber; and without breaking vacuum in the vacuum deposition system, transporting the generated catalytic metal particles clusters to the deposition chamber so as to decorate the metal oxide nanowires with catalytic metal nanoparticles made of the catalytic metal particles.

10. The method according to claim 9, wherein the metallic patterns are made of Cu, and metal oxide nanowires are CuO nanowires.

11. The method according to claim 9, wherein the catalytic metal nanoparticles include Pd nanoparticles.

12. The method according to claim 9, wherein the catalytic metal nanoparticles include Ni/Pd bimetallic nanoparticles.

13. The method according to claim 9, wherein the metallic patterns are made of Cu, and metal oxide nanowires are CuO nanowires, and wherein the catalytic metal nanoparticles include Pd nanoparticles.

14. The method according to claim 9, wherein the metallic patterns are made of Cu, and metal oxide nanowires are CuO nanowires, and wherein the catalytic metal nanoparticles include Ni/Pd nanoparticles.

15. The method according to claim 9, wherein the vapor of the catalytic metal particles clusters is generated in the aggregation chamber by linear magnetron sputtering.

16. The method according to claim 9, wherein the substrate is a Si substrate.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0043] FIG. 1 shows an experimental setup used for in situ growth and catalytic nanoparticle decoration of metal oxide nanowires. Monometallic, bi-metallic, tri-metallic and alloy nanoparticles of large veracity of materials such as Pd, Pt, Ni, Ag, Fe, Cu, Ta, Ru, Mo, Ti, Co, Si, Ge, Au, etc. can be utilized.

[0044] FIG. 2 shows TEM images of a) CuO nanowires grown by in-situ thermal oxidation of a Cu wire and b) Nanoparticle-decorated CuO nanowire surface.

[0045] FIG. 3 shows TEM images of nanoparticle-decorated CuO nanowire surfaces after in-situ growth and deposition of a) Pd nanoparticles and b) bi-metallic Ni/Pd nanoparticles.

[0046] FIG. 4 shows: a) a low-magnification SEM image of an electrical device based on nanoparticle-decorated CuO nanowires (the inset shows room temperature IV characteristics); b) a SEM image of CuO nanowires bridging the gap between adjacent oxidized Cu structures forming an electrical connection; and c) a high resolution SEM image of nanoparticle-decorated CuO nanowire.

DESCRIPTION OF EMBODIMENTS

[0047] The present disclosure provides a novel method for in-situ metal oxide nanowire growth and decoration with catalytic nanoparticles inside a CMOS compatible nanoparticle deposition system. The present disclosure presents results on CuO nanowires decorated with monometallic nanoparticles (Pd) and bimetallic nanoparticles (PdNi). It is believed that this technology can be used for different types of metal oxide nanowires synthesized by thermal oxidation, such as ZnO (NPL No. 22) or Fe.sub.2O.sub.3 (NPL No. 23). Furthermore, the present disclosure shows the in-situ realization of nanoparticle-decorated CuO nanowire devices on Si substrates, which is a crucial step towards the development of smart electronic nose systems, for example.

[0048] In-situ CuO nanowire growth and nanoparticle decoration were performed in a modified ultra-high vacuum deposition system with a magnetron-sputtering inert gas-condensation cluster beam source as illustrated in FIG. 1. FIG. 1 shows an experimental setup used for in situ growth and catalytic nanoparticle decoration of metal oxide nanowires. Monometallic, bi-metallic, tri-metallic and alloy nanoparticles of large veracity of materials such as Pd, Pt, Ni, Ag, Fe, Cu, Ta, Ru, Mo, Ti, Co, Si, Ge, Au, etc. can be utilized. As shown in FIG. 1, the disclosed process generally includes: mounting a metal member in the deposition chamber; performing thermal oxidization of the metal member in the deposition chamber in an oxygen atmosphere so as to grow metal oxide nanowires on a surface of the metal member; without breaking vacuum in the vacuum deposition system, generating a vapor of a catalytic metal particles clusters in the aggregation chamber that is connected to the deposition chamber; and without breaking vacuum in the vacuum deposition system, transporting the generated catalytic metal particles clusters to the deposition chamber so as to decorate the metal oxide nanowires with catalytic metal nanoparticles made of the catalytic metal particles. In this embodiment, a highly pure Cu wire (Alfa Aesar, diameter 100 ?m, 6N) was mounted in the deposition chamber and used as substrate for CuO nanowire growth. Thermal oxidation experiments were carried out at an oxygen pressure around 25 mbar and a sample heater setpoint temperature of 600? C. for 60 min. Nanoparticles were deposited after the heating stage cooled down to around 200? C. at a pressure of approximately 8?10.sup.4 mbar.

[0049] The fabrication of nanoparticle-decorated CuO nanowire devices comprised the following steps: Two subsequent photolithographic lift-off processes were performed on Si substrates covered with 50 nm of thermal SiO.sub.2 in order to structure electron beam evaporated layers of Ti/Au (contact electrodes; thickness around 5 nm and 200 nm, respectively) and Ti/Cu (substrate for CuO nanowire growth; thickness around 5 nm and 650 nm, respectively). Samples were loaded into the nanoparticle deposition system and oxygen was introduced until a constant pressure of 1000 mbar was reached. Thermal oxidation was performed at a sample heater setpoint temperature of 650? C. for 120 min. The samples were decorated with nanoparticles after the heating stage cooled down to around 100? C. at a pressure of approximately 8?10.sup.4 mbar. Nanoparticles were deposited using an aggregation length of 100 mm and an Ar pressure of 2.5?10.sup.?1 mbar in the aggregation zone. Magnetron powers of 15W and 40W were applied for sputtering of Pd and Ni targets, respectively.

[0050] Nanoparticle-decorated CuO nanowire samples were imaged with a FEI Titan G2 environmental transmission electron microscope (TEM) equipped with a spherical aberration image corrector and a FEI Helios G3 UC scanning electron microscope (SEM). Electrical measurements were performed using tip probe station and a Keithley 2400 SourceMeter.

[0051] <Results>

[0052] <(a) In-situ CuO Nanowire Growth and Nanoparticle Decoration>

[0053] The heat treatment in oxygen atmosphere inside the magnetron sputter gas aggregation system resulted in thermal oxidation of the Cu wire and CuO nanowire growth. FIG. 2a) shows a low magnification TEM image of the sample surface covered with nanoparticle-decorated CuO nanowires. Our in-situ growth results are well comparable in terms of size and crystallinity with literature reports on CuO nanowire synthesis in air (NPL No. 24). As can be seen in FIG. 2b), the CuO nanowire surfaces were successfully decorated with nanoparticles after the magnetron sputter gas aggregation deposition.

[0054] Due to the high degree of deposition parameter control, magnetron sputter gas aggregation is able to produce nanoparticles with well-defined size and structure of a large variety of different materials (NPL Nos. 18, 19, 20, and 21). FIGS. 3a) and b) show nanoparticle-decorated CuO nanowire surfaces after in-situ growth and deposition of Pd and bi-metallic Ni/Pd nanoparticles, respectively. As is known from literature (NPL No. 9), the gas sensitivity as well as selectivity of metal oxide-based gas sensors can be controlled by the catalytic activity of nanoscaled surface additives. Thus the in-situ CuO nanowire growth and nanoparticle decoration results describe herein are an important step towards the efficient realization of sensor devices with specifically tailored gas response.

[0055] <(b) In-situ Realization of Nanoparticle-Decorated CuO Nanowire Devices>

[0056] The above-described in-situ nanowire growth and nanoparticle decoration method were utilized in order to demonstrate the realization of a CuO nanowire device according to an embodiment of the present invention. In this case, Cu microstructures on a Si substrate are used for CuO nanowire growth by thermal oxidation inside the magnetron sputter gas aggregation system. A low magnification SEM image of a representative device is shown in FIG. 4a). Two Cu rectangles (side lengths 20 ?m and 100 m, gap distance before thermal oxidation 2.5 ?m) were connected to two Au electrodes, which can be seen on the left and right side of the image. After thermal oxidation inside the magnetron sputter gas aggregation system, the gap between the Cu rectangles was bridged by multiple CuO nanowires (FIG. 4b), which form an electrical connection between the oxidized Cu microstructures, as shown in the inset of FIG. 4a) that shows room temperature I-V characteristics. FIG. 4c) is a high resolution SEM image of nanoparticle-decorated CuO nanowire. As shown in FIG. 4c), the nanowires were successfully decorated by the nanoparticles.

[0057] A similar device design was reported in (NPL No. 25) and was found to show excellent gas sensor performance. In this disclosure, as described above, CuO nanowire-based gas sensors were demonstrated to be compatible with standard CMOS technology, which is of crucial importance for future integrated, miniaturized sensor devices (NPL No. 26). The presented method enables in-situ CuO nanowire growth and nanoparticle decoration, which allows the efficient fabrication of nanoparticle-decorated sensor devices with minimized surface contamination. As magnetron sputter gas aggregation is a versatile technique for the deposition of various different catalytic nanoparticles, our technology is suitable for the realization of nanoparticle-based smart electronic nose systems.

[0058] Thus, the present disclosure provides in-situ CuO nanowire growth and nanoparticle decoration inside a magnetron sputter gas aggregation system. This method allows nanoparticle decoration with a large variety of nanoparticle materials and enables the efficient realization of electronic devices based on nanoparticle-decorated CuO nanowires. Our fabrication technology is ideally suited for the future development of miniaturized, smart electronic nose systems based on catalytic nanoparticles with well-defined size and structure.

[0059] It will be apparent to those skilled in the art that various modification and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents. In particular, it is explicitly contemplated that any part or whole of any two or more of the embodiments and their modifications described above can be combined and regarded within the scope of the present invention.