Investigation of structural and optical properties of Ag nanoclusters formed in Si(100) after multiple implantations of low energies Ag ions and post-thermal annealing at a temperature below the Ag-Si eutectic point

摘要

Multiple low energies (78 keV, 68 keV and 58 keV) of Ag ions with different fluences up to 1 ×10~(16) atoms/cm~2 were sequentially implanted into Si(100) to create a distribution of different sizes and densities of buried metal nanoclusters (NC) at the near-surface layers. These structures have applications in fields involving plasmonics, optical emitters, photovoltaic, and nano-electronics. The dimension, location and concentration of these NCs influence the type of the applications. The implantation profiles were simulated by utilizing the widely used Stopping and Range of Ions in Matter (SRIM) code as well as a dynamic-TRIM code, which accounts for surface sputtering. The implanted samples were subsequently annealed either in a gas mixture of 4% H_2 + 96% Ar or in vacuum at a temperature ~500 °C up to 90 minutes. The annealing was carried out below the eutectic temperature (~ 841 °C) of Ag-Si to preferentially synthesize Ag NCs in Si rather than silicide. In order to study the size, concentration and distribution of the Ag NCs in Si, the samples were characterized by Rutherford Backscattering Spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) in combination with Ar-ion etching, and Transmission Electron Microscopy (TEM) techniques. The annealed samples showed a preferential distribution of the Ag NCs' sizes up to 10 nm either near the surface region (< 25nm) or at deeper layers (60-80 nm) closer to the interface of the implanted layer with the crystalline Si substrate. Ag NCs of larger diameters (up to 15 nm) were seen in the annealed sample near the peak concentration positions (~35-55 nm) of the implanted Ag ions. We have investigated the optical absorption properties due to these nano-structures in Si. The multiple energy implanted samples annealed in a gas mixture of 4% H_2 + 96% Ar show enhancements in the optical absorption in the visible range.