Method of producing compound nanorods and thin films

Abstract

A method of producing compound nanorods and thin films under a controlled growth mode is described. The method involves ablating compound targets using an ultrafast pulsed laser and depositing the ablated materials onto a substrate. When producing compound nanorods, external catalysts such as pre-deposited metal nanoparticles are not involved. Instead, at the beginning of deposition, simply by varying the fluence at the focal spot on the target, a self-formed seed layer can be introduced for nanorods growth. This provides a simple method of producing high purity nanorods and controlling the growth mode. Three growth modes are covered by the present invention, including nanorod growth, thin film growth, and nano-porous film growth.

1 . A method of producing a porous film, comprising:
 using an ultrafast pulsed laser to ablate a solid target material , wherein the target is ablated with ultrafast pulses, at least one pulse providing fluence at least about ten times higher than an ablation threshold fluence of the target material; and   depositing the ablated target material onto a substrate with a close lattice match to the intended material of growth to form a porous thin film, the film comprising a porous surface supported on a substrate, wherein the film is heated during growth and the substrate temperature is between 300° C. and 1000° C.   
     
     
         2 . The method of  claim 1  further comprising: providing a deposition chamber for said target material and said substrate, feeding neutral gases into said chamber, radicalizing said neutral gases by means of a plume of ablated target material, such that said radicalized gases participate in said growth. 
     
     
         3 . The method of  claim 1 , wherein the pulsed laser generates at least one pulse having a pulse duration between 10 fs and 100 ps. 
     
     
         4 . The method of  claim 1 , wherein the target is a compound material and comprises a metal oxide. 
     
     
         5 . The method of  claim 1 , wherein the target is a compound material and comprises a nitride. 
     
     
         6 . The method of  claim 1 , wherein the target material comprises a metal and the growth occurs through reaction with a reactive gas. 
     
     
         7 . The method of  claim 1 , wherein the said ablating and depositing are performed in an environment having a reactive background gas, the reactive gas selected from a group of reactive gases comprising at least one of oxygen, nitrogen, NH 3 , NO, NO 2 , or N 2 O, supplied either in neutral or in plasma form. 
     
     
         8 . The method of  claim 1 , wherein the target is a compound material and comprises arsenide. 
     
     
         9 . The method of  claim 1 , wherein the laser fluence of at least one pulse is chosen to be above the plasma formation threshold F th  of the target material. 
     
     
         10 . The method of  claim 1 , wherein a layered stack of nanoporous films is deposited using different target materials for each layer of said stack. 
     
     
         11 . The method of  claim 1 , wherein the substrate temperature is above 500° C. 
     
     
         12 . The method of  claim 1 , and further comprising feeding neutral gases into a deposition chamber for said target material and said substrate, radicalizing said neutral gases by means of a plume of ablated target material, such that said radicalized gases participate in said growth.