Method for depositing crystalline titania nanoparticles and films
A one-step and room-temperature process for depositing nanoparticles or nanocomposite (nanoparticle-assembled) films of metal oxides such as crystalline titanium dioxide (TiO 2 ) onto a substrate surface using ultrafast pulsed laser ablation of Titania or metal titanium target. The system includes a pulsed laser with a pulse duration ranging from a few femtoseconds to a few tens of picoseconds, an optical setup for processing the laser beam such that the beam is focused onto the target surface with an appropriate average energy density and an appropriate energy density distribution, and a vacuum chamber in which the target and the substrate are installed and background gases and their pressures are appropriately adjusted.
1. A method for depositing nanoparticles of crystalline TiO 2 or nanocomposite films of crystalline TiO 2 , comprising:
providing a target comprised of a titanium-containing material;
providing a substrate to support the deposited nanoparticles of crystalline TiO 2 or films of crystalline TiO 2 ;
ablating regions of said target with ultrafast laser pulses, wherein an ultrafast pulse width is in the range of about 10 fs to 100 ps, and a fluence of an ultrafast pulse at a surface of said target is in the range of about 0.01 J/cm 2 to 2 J/cm 2 , to create a plume of particles directed toward said substrate, and
depositing said nanoparticles of crystalline TiO 2 or nanocomposite films of crystalline TiO 2 onto said substrate, wherein said depositing step is performed in the absence of substrate heating, at approximately room temperature, and at a background pressure of about 100 Pa or less,
wherein, at said room temperature and at said background pressure of about 100 Pa or less, said method can produce functional nanoparticles or functional nanocomposite films of crystalline TiO 2 which exhibit a thermally stable rutile phase subsequent to deposition at said temperature and said background pressure.
2. The method of claim 1 , wherein said substrate comprises a heat sensitive material, and said step of ablating produces a temperature at the substrate sufficiently low to substantially avoid thermal induced alteration of a substrate property, such that a functional film is formable on the heat sensitive material.
3. The method of claim 1 , wherein said nanoparticles of crystalline TiO 2 have sizes of less than 1 micron.
4. The method of claim 1 , wherein said nanocomposite films are films assembled of nanoparticles of crystalline TiO 2 .
5. The method of claim 1 , wherein said nanocomposite films are composed of a host material embedded with nanoparticles of crystalline TiO 2 .
6. The method of claim 1 , wherein said target includes elemental titanium, and said ablation takes place in an oxygenated atmosphere so that said crystalline TiO 2 is formed subsequent to said ablation.
7. The method of claim 1 , further comprising the steps of:
providing a vacuum chamber containing said target and said substrate, and wherein said ablation step comprises irradiating the target with a laser beam generated by an ultrafast pulsed laser, the said laser beam being processed and focused onto the target by an optical system.
8. The method of claim 1 or 7 , wherein said substrate is a heat sensitive material, including one of glass, paper, plastic and polymer.
9. The method of claim 7 , wherein the ultrafast pulsed laser has a repetition rate of 1 kHz-100 MHz.
10. The method of claim 7 , wherein the optical system processes the intensity distribution of the laser beam from a Gaussian profile to a ‘flat-top’ profile.
11. The method of claim 1 or 7 , wherein said target includes titanium oxide and deposition onto said substrate takes place in vacuum or in background gas(es) containing oxygen.
12. The method of claim 7 , wherein said target includes elemental titanium and the step of performing laser ablation takes place within background gas(es) containing oxygen.
13. The method of claim 1 , wherein said nanoparticles of crystalline TiO 2 have sizes less than 1 μm.
14. The method of claim 1 , wherein said nanocomposite films are assembled from nanoparticles of crystalline TiO 2 .
15. The method of claim 1 , wherein said substrate comprises silicon, said target material comprises titanium oxide, and wherein said target material is ablated with background gas pressure equal to about 0.1 Pa, wherein particles within said crystalline film comprise sizes less than about 1 μm.
16. The method of claim 1 , wherein said substrate comprises glass, said target material comprises titanium metal, and wherein said target material is ablated with background gas pressure equal to about 100 Pa, and particles within said crystalline film comprise sizes less than about 1 μm.
17. The method of claim 1 , wherein crystallinity of said nanoparticles of crystalline TiO 2 or nanocomposite films of crystalline TiO 2 formed at room temperature is characterized by having one or more referenced peaks in an X-ray diffraction (XRD) pattern or electron diffraction pattern.
18. The method of claim 1 , wherein said functional nanoparticles or films are characterized by having catalytic activity associated with the crystallinity of individual nanoparticles.
19. The method of claim 1 , wherein said functional nanoparticles or films produced with said method form a portion of a photocatalyst.
20. The method of claim 1 , wherein said functional nanoparticles or films produced with said method are configured as a portion of a gas sensor, an electrochromic device, a solar cell, and/or a photocatalyst.
21. The method of claim 1 , wherein said method produces functional nanoparticles of TiO 2 or functional films of TiO 2 characterized by having a mixture of primarily said thermally stable rutile crystalline phase, together with an anatase phase, and/or a brookite phase.
22. The method of claim 1 , wherein said thermally stable rutile phase is exhibited as a rutile only phase.
23. The method of claim 22 , wherein said rutile only phase is characterized by having one or more referenced peaks in an X-ray diffraction (XRD) pattern or electron diffraction pattern.