Combined Experimental and Theoretical Investigation on Formation of Size-Controlled Silver Nanoclusters under Gas Phase

Metallic nanoclusters (NCs) have been predicted to achieve the best Surface-Enhanced Raman Scattering (SERS) due to the controllable amount of atoms and structures in NCs. The Local Surface Plasmon Resonance (LSPR) effect on silver metal NCs (Agn) enables it to be a promising candidate for manipulating the LSPR peak by controlling the size of NCs, which in turn demands a full understanding of the formation mechanism of Agn. Here, we apply an extended Smoluchowski rate equation coupled with a fragmentation scheme to investigate the growth of size-selected silver NCs generated via a modulated pulsed power magnetron sputtering (MPP-MSP). A temperature-dependent fragmentation coefficient D is proposed and integrated into the rate equations. The consistency between the computational and experimental results shows that in relative low peak power (Pp≤800 W), the recombination of cation and anion species are the dominant mechanism for NC growth. However, in the higher Pp region (≥800 W), the fragmentation mechanism becomes more impactful, leading to the formation of smaller NCs. The scanning electron microscopy observation shows the Ag36 is successfully soft-landed and immobilized on a strontium titanate crystal, which facilitates the application of the Agn/STO to the SERS research.

Structural characterization, reactivity, and vibrational properties of silver clusters: a new global minimum for Ag16

In the present work, the lowest energy structures and electronic properties of Agn clusters up to n = 16 are investigated using a successive growth algorithm coupled with density functional theory calculations (DFT).

A SELF-CONSISTENT-CHARGE DENSITY-FUNCTIONAL TIGHT-BINDING THEORY BASED MOLECULAR DYNAMICS SIMULATION OF A ZWITTERIONIC GLYCINE IN AN EXPLICIT WATER ENVIRONMENT

A zwitterionic glycine (zGLY) is adopted as an example to study the impact of water environment (310 H2O molecules) on the molecular structure and energetics using a self-consistent-charge density-functional tight-binding theory based molecular dynamics (SCC-DFTB/MD) method. It is found that maximal eight hydrogen bonds could be formed simultaneously between eight water molecules and the zGLY. The ability of the COO- terminal to adsorb water molecules is stronger than the [Formula: see text] terminal with respect to hydrogen bonding with more water molecules and exhibits lower adiabatic adsorption energies. The zGLY's intramolecular hydrogen bond appeared unpredictably, without involving any proton transfer and generally helpful for enhancing the system stability. Water molecules play an important role to stabilize the zwitterionic amino acids and restrain the proton migration from the [Formula: see text] to the COO− group. Our results show that the SCC-DFTB/MD method could successfully describe geometry dynamical evolutions and energetics of biomolecules in a nanoscale simulation with the presence of a large number of water molecules. Our study not only verified the feasibility of a QM level methodology for describing the aqueous states of biochemical molecules, but also gave a clear evidence for the impact of water environment on amino acids.

STRUCTURE AND STABILITY OF $CLOSO-B_{n}H_{n-1}N_{2}^{-} (n=5-12)$

[Formula: see text], framework-isoelectronic to [Formula: see text], have been investigated at the B3LYP/6-311+G** level of theory. The most stable positional isomers of individual [Formula: see text] are similar to those of [Formula: see text] and [Formula: see text] in framework configuration. The energy analysis reveals that the cage [Formula: see text] with the icosahedron framework, [Formula: see text] with the octahedron framework and [Formula: see text] with the bicapped square antiprism framework are, in order, the most stable in the [Formula: see text] system. Furthermore, three-dimensional aromaticity of all [Formula: see text] is characterized. The most stable cages, [Formula: see text], [Formula: see text] and [Formula: see text], also have relatively large aromaticity. All the predicted N–N stretching frequencies (2127–2303 cm−1) of the most stable positional isomers in the [Formula: see text] system are lower than the computational N–N stretching frequency (2445 cm−1) of free N2 at the same level, which results from the σ donation of N2 to B frameworks. The stretching frequencies of N–N in the [Formula: see text] cages increase with the decrease of N–N distances or the increase of B–N distance. In addition, B n−1 H n−1 fragment has larger affinity for group CH than that for group BNN, namely, it favors to form the [Formula: see text] rather than the [Formula: see text].