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High-fluence femtosecond laser pulses can induce physical and chemical changes in materials that are unrealizable under standard laboratory conditions. The exact nature of these changes can depend strongly on the gaseous environment in which the material is irradiated since near-surface chemical reactions can occur between the two materials. Surface modifications of silicon are of particular interest due to its significance in semiconductor-based applications. Specifically, the formation of silicon nitride (Si3N4) structures is desirable for multiple applications due to its high stability and low dielectric constant. Herein, we report on femtosecond laser-induced morphological and chemical modifications of silicon in a nitrogen atmosphere. We observed an extremely fast chemical reaction in the silicon-nitrogen system. The presence of crystalline Si3N4 was confirmed using high-resolution transmission electron microscopy, representing the first reported synthesis of Si3N4 nanocrystals through femtosecond laser-based methods. In addition, the surface was found to contain alternating layers of amorphous and crystalline silicon. Provided are plausible mechanisms for the formation of each of these structures. Taken together, these findings on surface modification of silicon using femtosecond laser irradiation may provide new pathways for manufacturing of nanoscale devices. 

Single electron transistors (SET) featuring metal (Ni) electrodes and silicon nitride dielectric barriers prepared by atomic layer deposition are fabricated and tested. Electrical characterization of the devices reveals electrostatic energy parameters consistent with the parameters of the designed tunnel junctions. In addition, an analysis of temperature dependence of conductance confirms the formation of metal-insulator-metal (MIM) junctions with negligible in-series contribution of any surface native metal oxide. However, the fabricated devices exhibit a very high level of electrical noise, far exceeding the commonly observed shot noise. Experimental investigation reveals the random telegraph signal (RTS) nature of the observed excess noise. The RTS noise in electronic devices is commonly associated with charging of external traps that are electrostatically coupled to the SET island. In the devices under study, however, the defects that result in the observed RTS noise are demonstrated to reside within the tunnel junctions. Our results also indicate the critical importance of interface states and surface preparation for achieving good performance of the SETs fabricated using ALD to form the tunnel barrier.