Binding and Structure of Acetonitrile on Si(111)-7 × 7

Patterns of Reacted Adatoms in Adsorption of Acetonitrile on Si{111}-(7 × 7)

We report on the covalent binding of acetonitrile (CH3CN) on Si{111}-(7 × 7) at ∼300 K studied by scanning tunneling microscopy, thermal desorption spectroscopy, and first-principles theoretical calculations. The site-specific study makes it possible to unravel the site-by-site and step-by-step kinetics. A polarized CH3CN prefers to adsorb on the faulted half more frequently compared to on the unfaulted half. Moreover, a molecular CH3CN adsorbs four-times more preferably on the center adatom-rest atom (CEA-REA) pair than on the corner adatom-rest atom (COA-REA) pair. Such site selectivity, the number ratio of reacted-CEA/reacted-COA, depends on the number of reacted adatoms in the half-unit cell. The site selectivity and the resulting reacted-adatom patterns are understood well by considering a simple model. In this simple model, the molecular adsorption probability changes step-by-step and site-by-site with increasing reacted adatoms. Furthermore, our theoretical calculations are overall consistent with the experimental results. The site-selectivity of the adsorption of CH3CN on Si{111}-(7 × 7) is explained well by the chemical reactivity depending on the local conformation, the local density of states, and the interaction between polarized adsorbates.

A Novel Time-Saving Synthesis Approach for Li-Argyrodite Superionic Conductor

The wet-chemical synthetic approach for Li-argyrodite superionic conductors for all-solid-state batteries (ASSBs) is promising as it saves time, energy, and cost, while achieving scalable production. However, it faces certain commercialization issues such as byproduct generation, nucleophilic attack of the solvent, and long processing times. In this study, a facile and time-saving microwave-assisted wet synthesis (MW-process) approach is proposed for Li6 PS5 Cl (LPSC), which is completed in 3 h at the precursor-synthesis stage. The LPSC crystal obtained from the MW-process presents various advantages such as fast-PS4 3- generation, high solubility of LiCl, and low adverse effects from solvent molecules. These features help in achieving a high Li-ion conductivity (2.79 mS cm-1 ) and low electric conductivity (1.85×10-6 mS cm-1 ). Furthermore, the LPSC crystal is stable when reacting with Li metal (2000 h at 0.1 mA cm-2 ) and exhibits superior cyclability with LiNi0.6 Co0.2 Mn0.2 (NCM622) (145.5 mA h g-1 at 0.5 C, 200 cycles with 0.12% of capacity loss per cycle). The proposed synthetic approach presents new insights into wet-chemical engineering for sulfide-based solid-electrolytes (SEs), which is crucial for developing ASSBs from a commercial-scale perspective.

Adsorption of Acetonitrile on Si(111)-(7 × 7)

The adsorption of acetonitrile (CH₃CN) on Si(111)-(7 × 7) at a room temperature has been investigated using scanning tunneling microscopy (STM) and first-principles calculations. The site-specific information on adsorption enables us to understand the site-by-site and step-by-step adsorption mechanism. From theoretical simulations, the most stable configuration of CH₃CN on Si(111)-(7 × 7) is found to be a molecularly chemisorbed CH₃CN with the carbon and nitrogen atoms of CN bonded to the rest atom and adatom on the Si surface, respectively. Some chemisorption-induced features in the STM topographic image are assigned based on the theoretical calculations.

Binding of glycine and L-cysteine on Si(111)-7 x 7

The adsorption of glycine and l-cysteine on Si(111)-7 x 7 was investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The observation of the characteristic vibrational modes and electronic structures of NH3+ and COO- groups for physisorbed glycine (l-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of nu(Si-H), nu(Si-O), and nu(C=Omicron) and the absence of nu(O-H) clearly indicate that glycine and l-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7 x 7. XPS results further verified the coexistence of two chemisorption states for each amino acid, corresponding to a Si-NH-CH2-COO-Si [Si-NHCH(CH2SH)COO-Si] species with new sigma-linkages of Si-N and Si-O, and a NH2-CH2-COO-Si [NH2CH(CH2SH)COO-Si] product through the cleavage of the O-H bond, respectively. Glycine/Si(111)-7 x 7 and l-cysteine/Si(111)-7 x 7 can be viewed as model systems for further modification of Si surfaces with biological molecules.

Binding Mechanisms of Methacrylic Acid and Methyl Methacrylate on Si(111)-7×7Effect of Substitution Groups

The interaction of methacrylic acid and methyl methacrylate with Si(111)-7 x 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). While methacrylic acid chemisorbs dissociatively through O-H bond cleavage, methyl methacrylate is covalently attached to the silicon surface via a [4+2] cycloaddition. The different reaction pathways of these two compounds on Si(111)-7 x 7 demonstrate that the substitution groups play an important role in determining the reaction channels for multifunctional molecules, leading to the desired flexibility in the organic modification of silicon surfaces.

Selective bonding of pyrazine to silicon(100)-2×1 surfaces: The role of nitrogen atoms

The covalent binding of pyrazine on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS) and x-ray photoelectron spectroscopy. Experimental results clearly suggest that the attachment occurs exclusively through the bonding of the two para-nitrogen atoms with the surface without the involvement of the carbon atoms, as evidenced from the retention of the (sp2) C-H stretching mode in HREELS and a significant down shift of 1.6 eV in the binding energy of N 1s. The binding mechanism for pyrazine on Si(100) demonstrates that reaction channels for heteroatomic aromatic molecules are strongly dependent on the electronic properties of the constituent atoms.