Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers: Difference between revisions
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The samples with the adhesion layers and 20 nm Au layer were also analyzed. The addition of the adhesion layer had in both cases a profound impact on grain size and orientation of the Au film, as visible in Fig. 7a and 7c. The image shows small grains mainly oriented in the [111] crystal direction, with an average grain size of 40 nm for Ti (Fig. 7b) and 36 nm for Cr (Fig. 7d). During the collection of the TKD maps, only the Kikuchi patterns produced by the electron scattering from the Au layer were recorded and indexed. Cr and Ti layers did not contribute to the pattern formation due to two main reasons: i) they are too thin to produce enough scattered electrons and ii) they are | The samples with the adhesion layers and 20 nm Au layer were also analyzed. The addition of the adhesion layer had in both cases a profound impact on grain size and orientation of the Au film, as visible in Fig. 7a and 7c. The image shows small grains mainly oriented in the [111] crystal direction, with an average grain size of 40 nm for Ti (Fig. 7b) and 36 nm for Cr (Fig. 7d). During the collection of the TKD maps, only the Kikuchi patterns produced by the electron scattering from the Au layer were recorded and indexed. Cr and Ti layers did not contribute to the pattern formation due to two main reasons: i) they are too thin to produce enough scattered electrons and ii) they are | ||
worse electron scattering centers | worse electron scattering centers than Au because they have a lower atomic number. | ||
[[File:Picture8.png|300px|center|thumb|Fig. 7: TKD IPFZ maps of the growth direction and grain size distributions of the 2-Ti/20-Au sample (a-b) and of the 2-Cr/20-Au sample (c-d).]] | [[File:Picture8.png|300px|center|thumb|Fig. 7: TKD IPFZ maps of the growth direction and grain size distributions of the 2-Ti/20-Au sample (a-b) and of the 2-Cr/20-Au sample (c-d).]] | ||
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= Adhesion layer model = | = Adhesion layer model = | ||
Based on the results obtained above, a revised adhesion layer model for Ti/Au and Cr/Au thin-film systems is proposed. The model is intended as an improvement in the description of the layer-layer interaction compared to the model described in Fig. 1, with the aim of helping the thin-film engineering of nanodevices | Based on the results obtained above, a revised adhesion layer model for Ti/Au and Cr/Au thin-film systems is proposed. The model is intended as an improvement in the description of the layer-layer interaction compared to the model described in Fig. 1, with the aim of helping the thin-film engineering of nanodevices. | ||
The adhesion layer model is shown in Fig. 14. The growth of both adhesion layers starts with the deposition of the atoms on the substrate (1) and the subsequent formation of an amorphous layer (2). During the deposition, both Ti and Cr get partially oxidized by oxygen and water molecules present on the substrate surface and in the deposition chamber. The adhesion layer acts as a wetting layer for Au, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to the case where Au is directly evaporated onto the SiO2 surface. The enhanced wetting is due to the formation of Ti-Au and Cr-Au chemical bonds. This leads to the formation of a continuous film having i) monodisperse grain size and ii) the energetically most favorable [111] crystal orientation for Au (3). For the Cr/Au system there is an extra step: the inter-diffusion between Cr and Au to form a Cr-Au alloy (4). Such diffusion is limited to a thickness of 2-3 nm for samples prepared at room temperature. | The adhesion layer model is shown in Fig. 14. The growth of both adhesion layers starts with the deposition of the atoms on the substrate (1) and the subsequent formation of an amorphous layer (2). During the deposition, both Ti and Cr get partially oxidized by oxygen and water molecules present on the substrate surface and in the deposition chamber. The adhesion layer acts as a wetting layer for Au, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to the case where Au is directly evaporated onto the SiO2 surface. The enhanced wetting is due to the formation of Ti-Au and Cr-Au chemical bonds. This leads to the formation of a continuous film having i) monodisperse grain size and ii) the energetically most favorable [111] crystal orientation for Au (3). For the Cr/Au system there is an extra step: the inter-diffusion between Cr and Au to form a Cr-Au alloy (4). Such diffusion is limited to a thickness of 2-3 nm for samples prepared at room temperature. | ||