Nanostructured Au(111)/Oxide Epitaxial Heterostructures with Tailoring Plasmonic Response by a One-Step Strategy

Abstract

In this work we present a strategy for developing epitaxial incommensurate nanostructured-Au/oxide heterostructures with tuneable plasmonic response. Previously high quality single phase and oriented α-Fe2O3(0001) thin films were achieved, which have been used as a template for the noble metal epitaxial deposition. The complex systems have been grown by pulsed laser deposition on two different type of oxide substrates: α-Al2O3(0001) and SrTiO3(111). A one-step procedure has been achieved tailoring the isolated character and the morphological features of Au nanostructures through the substrate temperature during the Au growth, without altering the structural characteristics of the hematite layer that is identified as single iron oxide phase. The epitaxial character and the lattice coupling of Au/oxide bilayers are mediated through the sort of oxide substrate. Single oriented Au(111) islands are disposed with a rotation of 30º between their crystallographic axes and those of α-Fe2O3(0001). The Au(111) and SrTiO3(111) lattices are collinear while a rotation of 30º happens respect to the α-Al2O3(0001) lattice. The crystallographic domain size and crystalline order of hematite structure and Au nanostructured-layer are dependent on the substrate type and the Au growth temperature respectively. Besides, the functional character of the complex systems has been tested. The localized surface plasmons related to Au nanostructures are excited and controlled through the fabrication parameters, tuning the optical resonance with the degree of Au nanostructuring.

Improving the CO and CH4 Gas Sensor Response at Room Temperature of α-Fe2O3(0001) Epitaxial Thin Films Grown on SrTiO3(111) Incorporating Au(111) Islands

“…It should be pointed out that some Kiessig fringes around layer Bragg peaks can be noted, indicating the occurrence of high quality and smooth surfaces and abrupt α-Fe2O3/STO substrate and Au/α-Fe2O3 interfaces. These results are in agreement with those previously reported in [28]. Out-of-plane and in-plane lattice parameters were calculated from the positions at several diffraction peaks in reciprocal space respect to the STO(111) substrate obtaining for α-Fe2O3 layers: cα-Fe2O3/STO = 13.72(6) Å, cAu/α-Fe2O3/STO = 13.72(3) Å, aα-Fe2O3 = bα-Fe2O3 = 5.08(4) Å and aAu/α-Fe2O3/STO = bAu/α-Fe2O3/STO =5.07 (1) Å and for Au layer: cAu/α-Fe2O3/STO = 7.04 (2) Å and aAu/α-Fe2O3/STO = bAu/α-Fe2O3/STO = 2.89 (2) Å. Additionally, the in-plane domain sizes were calculated to be around 25 nm for the epitaxial α-Fe2O3 layer and Au/α-Fe2O3 system and around 17 nm for the epitaxial Au, in agreement with a previous work [28].…”

“…This type of growth is induced during the Au growth when keeping the sample substrate at a temperature of 250 ºC, as was identified previously in [28], inducing an island-type growth of Au that is promoted by the surface diffusion. The phenomenon is attributed to a dewetting process by a one-step procedure [26][27][28] instead of the usual methodology based on the post-annealing of the metallic film [22][23][24]29,34]. Specifically, here the α-Fe2O3 surface presents a particulated character with a discontinuous profile which generates a more heterogeneous stress distribution than in a flat surface.…”

“…α-Fe2O3 thin films and Au nanoparticles/α-Fe2O3 heterostructures were grown on SrTiO3 (STO)(111) substrates by pulsed laser deposition according to a previous work [28]. The growth was performed by using an ultraviolet pulsed laser source (355 nm) of high power (1 W) to obtain the plasma, with a base pressure of 10 −9 mbar.…”

“…A common and interesting approach that allows covering large surfaces with functional nanoparticles is the solid state dewetting [22][23][24][25]. Based on this processing method, a one-step strategy has been reported in which noble metal nanostructures are prepared on an oxide support by the deposition of metallic material with the substrate at a specific temperature [26][27][28]. This approach avoids a subsequent annealing process after the deposition of a metallic film [22][23][24]29] and to the best of our knowledge it has been used to obtain Au and Pt nanoparticles on iron oxide surfaces [26,28] and Al nanostructures on Si and glass substrates [27].…”

“…Based on this processing method, a one-step strategy has been reported in which noble metal nanostructures are prepared on an oxide support by the deposition of metallic material with the substrate at a specific temperature [26][27][28]. This approach avoids a subsequent annealing process after the deposition of a metallic film [22][23][24]29] and to the best of our knowledge it has been used to obtain Au and Pt nanoparticles on iron oxide surfaces [26,28] and Al nanostructures on Si and glass substrates [27]. Using this methodology, recently we have investigated the effect of the substrate temperature and the type of the substrate in the preparation of Au nanostructures on α-Fe2O3 surfaces, reporting a precise control of the morphological characteristics of the noble metal nanostructures tuning accurately the growth parameters [28].…”