Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

This time I introduce using for generating one-dimensional nanostructure. The main advantage of this technique is that you can trace nano-wire, a long temperature under mild conditions with simple wet chemistry operations. First in a four-milliliter vial, dissolve 10 milligrams of hydrogen tetrachloroauric trihydrate in one milliliter of deionized water.

By PET 0.197 milliliters of this 2.5 millimolar chloroauric acid stock solution into a 50-milliliter round bottom flask equipped with a stir bar. Add 19.7 milliliters of deionized water to the flask and stir to obtain a 0.025-millimolar chloroauric acid solution. Then in another four-milliliter vial, dissolve 10 milligrams of trisodium citrate dihydrate in one milliliter of deionized water.

Add 0.147 milliliters of this 0.1-gram-per-milliliter sodium citrate stock solution to the diluted chloroauric acid solution while stirring. Next in a third four-milliliter vial dissolve 2.3 milligrams of sodium borohydride and 0.6 milliliters of deionized water to obtain a 0.1-molar solution which should be used within a few minutes. Ensure that the pale yellow reaction mixture is stirring vigorously.

Quickly pipette the sodium borohydride solution into the vigorously stirring mixture which will immediately become bright orange. Continue stirring the mixture for 10 minutes to obtain the gold nanoparticles as indicated by a gradual color change to reddish-orange. The nano articles can be stored for up to a week.

To synthesize gold nanowires, first cut a five-milliliter-by-five-milliliter piece from a 0.5 milliliter-thick silicon wafer. Sonicate this substrate for 15 minutes each in deionized water and ethanol in sequence. Wipe off the clean substrate and allow it to dry in air.

Then treat the substrate with oxygen plasma at 29.6 watts and 220 volts for 20 minutes. During the plasma treatment, in a 20-milliliter vial, dissolve 11.1 milligrams of APTES in 10 milliliters of a one-to-one by volume mixture of deionized water and ethanol to obtain a 5-millimolar solution. When the plasma treatment has finished, soak the substrate in the APTES solution for 30 minutes.

Then thoroughly rinse the substrate with about 20 milliliters each of ethanol and deionized water in sequence. Soak the substrate in the gold nanoparticle solution for two hours to allow the seed nanoparticles to absorb onto its surface. Then prepare 10 milliliters each of a 1.65-millimolar solution of 4-MBA and ethanol.

Add 5.10 millimolars solution of chloroauric acid in a one-to-one mixture of deionized water and ethanol Add a 12.3 millimolar solution of L-ascorbic acid in deionized water. Combine 0.5 milliliters each of the chloroauric acid solution and the 4-MBA solution in a 10-milliliter vial. Shake the vial to mix the solutions.

Next pick up the seeded substrate with tweezers and wash it with 20 milliliters of deionized water to remove unabsorbed gold nanoparticles. Immerse the seeded substrate in the mixture of chloroauric acid in 4-MBA. Then add 0.5 milliliters of the ascorbic acid solution to the mixture.

Gently shake the vial to evenly mix the solutions. Leave the substrate soaking in the mixture undisturbed for 15 minutes. The air ascorbic acid must be added after the mixing of 4-MBA and chloroauric acid otherwise it will cause immediate homogeneous nucleation and the nanowires will not grow.

Monitor the formation of bubbles during the growth process. The substrate surface will change from shiny gray to reddish-brown in appearance. Then remove the substrate from the mixture and rinse it with ethanol and deionized water.

Allow it to air dry afterwards. The substrate surface will become a golden appearance as it dries. To synthesize gold nanowires with alternating segments of different thicknesses, first seed gold nanoparticles on a silicon substrate as previously described.

Also prepare 10 milliliters each of a 1.65-millimolar 4-MBA solution, a 5.10-millimolar chloroauric acid solution, and a 12.3-millimolar ascorbic acid solution as previously described. Then dilute 0.1 milliliters of the 1.6-millimolar 4-MBA solution, 20-fold with ethanol to make two milliliters of a 0.083-millimolar 4-MBA solution. In a 10-milliliter vial, combine 0.5 milliliters each of the 1.65-millimolar solution of 4-MBA, the chloroauric acid solution and the ascorbic solution.

Vortex the mixture to form growth solution A.In another 10-milliliter vial, combine 0.5 milliliters each of the 0.083-millimolar solution of 4-MBA, the chloroauric acid, and the ascorbic acid solution. Vortex the mixture to obtain growth solution B.Soak the gold nanoparticle seeded substrate and growth solution B for about one minute. Rapidly transfer the substrate to the container of growth solution A and allow it to soak for two minutes.

Repeat the soaking sequence once being careful not to let the substrate dry as it is moved between vials. Finally rinse the substrate with 50 milliliters of ethanol and 50 milliliters of deionized water. Gold nanoparticle with diameters of three to five nanometers, 15 nanometers, and 40 nanometers were all successfully seeded on silicon wafer substrates.

Substrate-bound gold nanowires were then grown from these seeds with 4-MBA as the ligand. Gold nanowires were also successfully grown on alumina, strontium titanate, lanthanum aluminate, glass, indium tin oxide, and fluorine-doped tin oxide surfaces. Nanowires with alternating thick-thin segments were grown by alternately immersing the substrate in growth solutions with different ligand concentrations.

And nanoflowers were grown by quickly drying the growth solution on the silicon substrate. The nanowire structures could also be changed by varying the ligand. Using 4-MPAA, 2-naphthalenethiol, or 3-MBA as the ligand, yielded ultra-thin nanowires arrays.

Using mixtures of 4-MBA and 3-MBA in various proportions yielded tapered nanowires. After watching this video, you should have a good understanding of how to grow growth nanowires from a foreign substrate with at the surface growth mechanism.