directly onto TEM grids. Ni grids supporting SiO 2 films (approximately 10 nm thick, Ted Pella) were treated by APTES in the same manner as the SiO 2 /Si substrates, followed by Au particle deposition. The grids were imaged by TEM (Philips CM20, operating voltage 200 keV) before the CVD process to characterize the Au particles, and after the CVD process to characterize the grown nanowires and the particle±wire relationship.Patterned growth: Polymethylmethacrylate (PMMA) was first patterned by electron beam lithography (or photolithography) on a SiO 2 /Si substrate to form 5 î 5 mm wells (Figure 4 a). [11] The substrate was treated with APTES and soaked in a Au colloid solution so that Au particles were deposited into the wells (Figure 4 b). Removal of the PMMA in acetone affords Au particles that are confined in square islands (Figure 4 c). The substrate was then subjected to CVD growth.

No abstract

Laser-ablated uranium atoms have been reacted with CO molecules during condensation with neon at 4 K. Absorptions at 1047.3 and 872.2 cm -1 are assigned to the CUO molecule formed from the insertion reaction that requires activation energy. Isotopic substitution shows that the upper band is largely U-C and the lower band mostly U-O in vibrational character. Absorptions at 2051.5, 1361.8, and 841.0 cm -1 are assigned to the OUCCO molecule, which is formed by the CO addition reaction to CUO and ultravioletvisible photon-induced rearrangment of the U(CO) 2 molecule. The OUCCO molecule undergoes further photochemical rearrangment to the (C 2 )UO 2 molecule, which is characterized by symmetric and antisymmetric OUO stretching vibrations at 843.2 and 922.1 cm -1 . The uranium carbonyls U(CO) x (x ) 1-6) are produced on deposition or on annealing. Evidence is also presented for the CUO -anion and U(CO) x -(x ) 1-5) anions, which are formed by electron capture. Relativistic density functional theoretical calculations have been performed for the aforementioned species, which lend strong support to the experimental assignments of the infrared spectra. It is predicted that CUO is a linear singlet molecule with the shortest U-C bond yet characterized, and it has a U-C triple bond with substantial U 5f character. The theoretical analysis also finds that a distorted tetrahedral geometry of (C 2 )UO 2 lies much lower in energy than either the bent/linear OUCCO structures or the U(CO) 2 uranium dicarbonyl.

A heart of gold: The structure of the Au32− cluster has been elucidated by comparison of the results from photoelectron spectroscopy with those from theoretical calculations. Although DFT calculations suggest a high‐symmetry hollow‐cage structure (Ih, left) to be the lowest in energy at 0 K, the spectrum calculated for a low‐symmetry (C1, right) distorted cage containing three Au atoms inside agrees best with the experimental results.

Among the large Au n - clusters for n > 20, the photoelectron spectra of Au34 - exhibit the largest energy gap (0.94 eV) with well-resolved spectral features, making it a good candidate for structural consideration in conjunction with theoretical studies. Extensive structural searches at several levels of density functional and ab initio theory revealed that the low-lying isomers of Au34 - can be characterized as fluxional core−shell type structures with 4 or 3 inner atoms and 30 or 31 outer atoms, i.e., Au4@Au30 - and Au3@Au31 -, respectively. Detailed comparisons between theoretical and photoelectron results suggest that the most probable ground state structures of Au34 - are of the Au4@Au30 - type. The 30 outer atoms seem to be disordered or fluxional, giving rise to a number of low-lying isomers with very close energies and simulated photoelectron spectra. The fluxional nature of the outer layer in large gold clusters or nanoparticles may have important implications for their remarkable catalytic activities.

We report the observation and characterization of a series of stable bimetallic 18-valence-electron clusters containing a highly symmetric 12-atom icosahedral Au cage with an encapsulated central heteroatom of Group VB transition metals, M@Au(12) (-) (M=V,Nb,Ta). Electronic and structural properties of these clusters were probed by anion photoelectron spectroscopy and theoretical calculations. Characteristics of the M@Au(12) (-) species include their remarkably high binding energies and relatively simple spectral features, which reflect their high symmetry and stability. The adiabatic electronic binding energies of M@Au(12) (-) were measured to be 3.70+/-0.03, 3.77+/-0.03, and 3.76+/-0.03 eV for M=V, Nb, and Ta, respectively. Comparison of density-functional calculations with experimental data established the highly symmetric icosahedral structures for the 18-electron cluster anions, which may be promising building blocks for cluster-assembled nanomaterials in the form of stoichiometric [M@Au(12) (-)]X(+) salts.

Calculations via scalar-relativistic density functional theory (DFT) and ab initio CCSD(T) methodologies are used to explore the possibility of direct interactions between molecular UO2 and Ar atoms. The 3Hg electronic state of UO2, which is an excited state of the isolated molecule, exhibits significant bonding to Ar in the model complexes UO2(Ar) and UO2(Ar)5. The calculated vibrational frequencies of ground-state 3Phiu UO2 and UO2(Ar)5 with an (fphi)1(fdelta)1 electron configuration agree well with the observed frequencies of UO2 in solid neon and solid argon, respectively. The results strongly suggest that the ground electron configuration of UO2 changes from 5f17s1 to 5f2 when the matrix host is changed from neon to argon.

Although ZrO2 and HfO2 are, for the most part, quite similar chemically, subtle differences in their electronic structures appear to be responsible for differing MO2/Si (M = Zr, Hf) interface stabilities. To shed light on the electronic structure differences between ZrO2 and HfO2, we have conducted joint experimental and theoretical studies. Because molecular electron affinities are a sensitive probe of electronic structure, we have measured them by conducting photoelectron spectroscopic experiments on ZrO2(-) and HfO2(-). The adiabatic electron affinity of HfO2 was determined to be 2.14 +/- 0.03 eV, and that of ZrO2 was determined to be 1.64 +/- 0.03 eV. Concurrently, advanced electronic structure calculations were conducted to determine electron affinities, vibrational frequencies, and geometries of these systems. The calculated CCSD(T) electron affinities of HfO2 and ZrO2 were found to be 2.05 and 1.62 eV, respectively. The molecular results confirm earlier predictions from solid state calculations that HfO2 is more ionic than ZrO2. The excess electron in MO2(-) occupies an sd-type hybrid orbital localized on the M atom (M = Zr, Hf). The structural parameters of ZrO2 and HfO2 and their vibrational frequencies were found to be very similar. Upon the excess electron attachment, the M-O bond length increases by ca. 0.04 A, the OMO angle increases by 2-4 degrees, and frequencies of all vibrational modes become smaller, with the stretching modes being shifted by 30-50 cm(-1) and the bending mode by 15-25 cm(-1). Together, these studies unveil significant differences in the electronic structures of ZrO2 and HfO2 but not in their structural or vibrational characteristics.