Production of metal and metal-alloy nanoparticles with high repetition rate ultrafast pulsed laser ablation in liquids

Abstract

Various embodiments include a method of producing chemically pure and stably dispersed metal and metal-alloy nanoparticle colloids with ultrafast pulsed laser ablation. A method comprises irradiating a metal or metal alloy target submerged in a liquid with ultrashort laser pulses at a high repetition rate, cooling a portion of the liquid that includes an irradiated region, and collecting nanoparticles produced with the laser irradiation and liquid cooling. The method may be implemented with a high repetition rate ultrafast pulsed laser source, an optical system for focusing and moving the pulsed laser beams, a metal or metal alloy target submerged in a liquid, and a liquid circulating system to cool the laser focal volume and collect the nanoparticle products. By controlling various laser parameters, and with optional liquid flow movement, the method provides stable colloids of dispersed metal and metal-alloy nanoparticles. In various embodiments additional stabilizing chemical agents are not required.

1 . A method of producing nanoparticle colloids, comprising:
 generating ultrashort pulsed laser beams at a pulse repetition rate greater than 100 kHz, each pulsed laser beam having a pulse with pulse energy in the range from about 1-20 μJ, and a pulse duration up to about 10 picoseconds (ps);   irradiating a target with said pulsed laser beams, said target being disposed in liquid that is substantially transparent at a wavelength of said pulsed laser beams, said target being a source material for production of metal or metal-alloy nanoparticles that result from target material modification; and   imparting relative motion between said pulsed laser beams and said target with at least movement of the pulsed laser beams to limit heat accumulation and to substantially avoid blocking of laser pulses by scattering and absorption from nanoparticle colloids that are formed in said liquid at said repetition rate,   wherein at said repetition rate above 100 kHz a size distribution dominated by nanoparticles results from fragmentation of particles in the laser plume, and highly stable nanoparticle colloids are produced with said steps of generating, irradiating, and imparting.   
     
     
         2 . The method of  claim 1 , wherein said target comprises gold, silver, or copper. 
     
     
         3 . The method of  claim 1 , wherein said target comprises a binary alloy. 
     
     
         4 . The method of  claim 1 , wherein said target comprises a precious metal. 
     
     
         5 . The method of  claim 1 , wherein said liquid comprises de-ionized water. 
     
     
         6 . The method of  claim 5 , wherein said de-ionized water has a resistance greater than 0.05 M Ohm·cm. 
     
     
         7 . The method of  claim 1 , further producing liquid flow relative to a surface of said target, and wherein said liquid flow comprises liquid movement across the target surface. 
     
     
         8 . The method of  claim 1 , wherein said liquid is substantially free of any stabilizing chemical agents. 
     
     
         9 . The method of  claim 1 , wherein imparting said relative motion of said pulsed laser beams comprises guiding said beams with a vibration mirror. 
     
     
         10 . The method of  claim 9 , wherein said guiding comprises operating said vibration mirror at a frequency greater than about 10 Hz, and providing an angular amplitude greater than about 0.1 mrad. 
     
     
         11 . The method of  claim 10 , wherein the vibration mirror guides laser beam movement on the target such that a focal spot moves with speed greater than about 0.1 m/s. 
     
     
         12 . The method of  claim 1 , wherein said pulsed laser beams propagate within said liquid, and said irradiating comprises focusing said pulsed beams on a surface of said target. 
     
     
         13 . The method of  claim 1 , wherein said imparting said relative motion comprises rastering said pulsed beams relative to said target. 
     
     
         14 . The method of  claim 1 , wherein said liquid flow causes cooling a region about said target and transporting of said nanoparticles away from a target region and toward a collection location. 
     
     
         15 . The method of  claim 1 , wherein said colloids are stable for at least one week. 
     
     
         16 . The method of  claim 1 , wherein said colloids are stable for at least about 2 months. 
     
     
         17 . The method of  claim 1 , wherein a pulse duration of a pulsed beam is in the range of about 0.1-10 ps. 
     
     
         18 . The method of  claim 1 , wherein a pulse energy is in the range of about 1-10 micro-Joule. 
     
     
         19 . A laser-based system for nanoparticle generation in liquids, comprising:
 a high-repetition rate source of pulsed laser beams generating pulses at rate greater than 100 kHz, each pulsed laser beam having a pulse with pulse energy in the range from about 1-20 μJ, and a pulse duration up to about 10 picoseconds (ps);   a positioner, including an optical scanner, to produce motion between said target and said pulsed beams;   a circulation system to produce liquid flow about said target;   a collector disposed at a collection location to collect said nanoparticles; and   a controller operatively coupled to at least said source, motion system, and said circulation system.   
     
     
         20 . A product, comprising: colloids that are chemically pure and do not coagulate during a time period of at least one week after production of said colloids, said colloids characterized by having a particle size distribution dominated by nanoparticles. 
     
     
         21 . The product of  claim 20 , made with a method of high-repetition rate, ultrashort laser processing. 
     
     
         22 . The product  claim 20 , wherein stability of said colloids is characterized by absorption spectra information exhibiting nearly identical spectra near a resonance peak. 
     
     
         23 . The product of  claim 20 , wherein said colloids consist of a liquid and nanoparticles, said nanoparticles comprising at least one of a metal and metal alloy. 
     
     
         24 . The product of  claim 20 , wherein said chemically pure colloids are substantially free of any stabilizing chemical agents. 
     
     
         25 . The product of  claim 20 , wherein said colloids are stable for at least about 2 months. 
     
     
         26 . The product of  claim 20 , wherein said colloids consist essentially of gold-water colloids containing water and gold nanoparticles. 
     
     
         27 . The product of  claim 20 , wherein said chemically pure colloids do not coagulate for a period of at least about 2 months. 
     
     
         28 . A product comprising: metal or metal alloy nanoparticles collected from stable and chemically pure colloids.