Shallow thermal donors (STDs), generated in Czochralski silicon, annealed at 470°C in a hydrogen plasma, and detected by their infrared (IR) electronic absorption, have ground states that shift slightly (∼0.1 ${\mathrm{cm}}^{-1\mathrm{}}$) to smaller binding energies, when deuterium is introduced instead of hydrogen, demonstrating the presence of a hydrogen atom in the donor core. No other IR spectrum is detected apart from that from neutral double thermal donors (TDs). The same optical transitions are observed in three annealed samples given a preheat treatment in water vapor. These latter samples show the NL10 electron-paramagnetic-resonance (EPR) spectrum, recently attributed to hydrogen passivated TDs. The relative strengths of the EPR NL10 spectra correlate with those of the STD IR spectra, providing a strong indication that both spectra arise from the same defects.

Laser irradiation of a mixture of single-element micro/nanomaterials may lead to their alloying and fabrication of multi-element structures. In addition to the laser induced alloying of particulates in the form of micro/nanopowders in ambient atmosphere (which forms the basis of the field of additive manufacturing technology), another interesting problem is the laser-induced alloying of a mixture of single-element nanoparticles in liquids since this process may lead to the direct fabrication of alloyed-nanoparticle colloidal solutions. In this work, bare-surface ligand-free Ag and Pd nanoparticles in solution were prepared by laser ablation of the corresponding bulk target materials, separately in water. The two solutions were mixed and the mixed solution was laser irradiated for different time durations in order to investigate the laser-induced nanoparticles alloying in liquid. Nanoparticles alloying and the formation of AgPd alloyed nanoparticles takes place with a decrease of the intensity of the surface-plasmon resonance peak of the Ag nanoparticles (at ∼405 nm) with the irradiation time while the low wavelength interband absorption peaks of either Ag or Pd nanoparticles remain unaffected by the irradiation for a time duration even as long as 30 min. The nanoalloys have lattice constants with values between those of the pure metals, which indicates that they consist of Ag and Pd in an approximately 1:1 ratio similar to the atomic composition of the starting mixed-nanoparticle solution. Formation of nanoparticle networks consisting of bimetallic alloyed nanoparticles and nanoparticles that remain as single elements (even after the end of the irradiation), joining together, are also formed. The binding energies of the 3d core electrons of both Ag and Pd nanoparticles shift to lower energies with the irradiation time, which is also a typical characteristic of AgPd alloyed nanoparticles. The mechanisms of nanoparticles alloying and network formation are also discussed.

Laser ablation of bulk target materials in liquids has been established as an alternative method for synthesis of nanoparticles with unique and novel properties. Ablation of single element targets can lead to the synthesis of compound nanoparticles due to the interaction of the ablation plasma plume species with the species which are produced by the liquid decomposition. The additional compression which the plasma plume experiences by the liquid may result in the formation of nanoparticles which are characterized by metastable material phases, difficult or impossible to be produced by other methods. In this work laser ablation of a bulk Cr target in DI water, ethanol, acetone or toluene was carried out for the production of nanoparticle colloidal solutions. Mostly spherical nanoparticles are obtained in all four liquids with sizes ranging from 2 nm and up to a progressively smaller maximum diameter of 120, 50, 30 and 23 nm from DI water to toluene. Their size distribution follows a log-normal function with a median diameter of 6.8, 11.2, 6.0 and 5.3 nm for the four liquids, respectively. Graphitic as well as amorphous carbon is found on the nanoparticles synthesized in the hydrocarbon liquids. Nanoparticles synthesized in DI water are a mixture of Cr₃O₄, Cr₂O₃ and CrO₃, in ethanol they are a mixture of Cr₃O₄, Cr₇C₃ and of the metastable phase Cr₃C_2−x, while in acetone or toluene nanoparticles of the metastable phase Cr₃C_2−x are produced.