Comparative inter diffusion study among Ag and AuAg thin film grown on reconstructed Si(5 5 12) substrate

Investigations about various aspects of thin film growth for metal (Au, Ag) deposition on single crystal Si substrate encompass significant importance for interconnects in Si-based technology besides importance of AuAg alloys for their interesting properties, such as templates for surface enhanced Raman spectroscopy. The reconstructed surface of Si(5 5 12) with its one-dimensional wire like structures provides a typical patterned surface for the growth of bilayers. Considering Ag (35.5 monolayer (ML)) and sequential AuAg (22 ML Au after 35.5 ML Ag) growth on reconstructed Si(5 5 12) substrate near at room temperature with subsequent stepwise annealing up to 600 °C in ultra-high vacuum condition, we have comparatively studied various growth aspects viz. crystallographic characteristic, morphology and compositional depth profile. In-situ RHEED measurements explore gradual crystallographic orientation of crystallites along a preferred direction due to anneal at higher temperature, for both kind of thin film. In course of stepwise annealing, for Ag growth RHEED pattern is changed from three dimensional spotty to two dimensional streaky alike as substrate temperature is changed from 380 to 520 °C indicating significant reduction of particle density. But for AuAg growth, 3D spotty like RHEED pattern doesn’t change even after anneal at 600 °C. Resulting morphology is consisted of well-shaped particle with its density ~ 1.5 × 10 3 times larger for AuAg growth than Ag growth. Subsequent annealing process causes significant sublimation from grown Ag thin film, and remnant material is extensively inter diffused inside Si matrix. In comparison, for AuAg thin film sublimation is much less significant for Ag and negligible for Au. For detection of crystal violet molecule with low concentration ~ 5 × 10 –7 M, self-assembled AuAg nanostructures as well as thin film with comparatively smaller enhancement factor, have been utilized for competent SERS substrate.