The synthetic system of Fe(SO 3 CF 3 ) 2 and one or two TPA ligands (TPA ) tris(2-pyridylmethyl)amine) affords a series of complexes that demonstrate the complexities of the solid-state and solution coordination chemistry of labile iron(II) even with a multidentate ligand. The low-spin [Fe(TPA)(CH 3 CN) 2 ](SO 3 CF 3 ) 2 (1-OTf) complex forms in acetonitrile, but the high-spin complex Fe(TPA)(SO 3 CF 3 ) 2 (2) forms in chloroform. The methanolbound complex [Fe(TPA)(CH 3 OH) 2 ](BPh 4 ) 2 (3) forms in the presence of the noncoordinating anion, BPh 4 -, and six-coordinate [Fe(TPA) 2 ](SO 3 CF 3 ) 2 (4-OTf) and eight-coordinate [Fe(TPA) 2 ](BPh 4 ) 2 (4-BPh 4 ) form in the presence of excess ligand. Their behavior in solution is explored by studying their magnetic properties and NMR spectra, which indicate the presence of spin and coordination equilibria. The crystal structures of these complexes are reported. Crystallographic parameters are as follows. 1-OTf‚CH 3 CN: C 26 H 27 F 6 FeN 7 O 6 S 2 , monoclinic, P2 1 /n, a ) 12.418(2) Å, b ) 16.192(4) Å, c ) 15.855(2) Å, β ) 92.09(2)°, Z ) 4. 2: C 20 H 18 F 6 FeN 4 O 6 S 2 , monoclinic, P2 1 /c, a ) 17.636(2) Å, b ) 9.659(1) Å, c ) 16.004(2) Å, β ) 113.29 (1)°, Z ) 4. 3‚CH 3 OH: C 69 H 70 B 2 -FeN 4 O 3 , monoclinic, P2 1 /n, a ) 17.525(1) Å, b ) 19.150(2) Å, c ) 17.703(1) Å, β ) 100.36(1)°, Z ) 4. 4-OTf: C 38 H 36 F 6 FeN 8 O 6 S 2 , monoclinic, Pc, a ) 10.236(1) Å, b ) 10.129(1) Å, c ) 19.251(1) Å, β ) 92.27(1)°, Z ) 2. 4-BPh 4 : C 84 H 76 B 2 FeN 8 , monoclinic, P2 1 /n, a ) 12.489(1) Å, b ) 14.189(1) Å, c ) 19.843(1) Å, β ) 102.84-(1)°, Z ) 2.

Spectroscopic ellipsometry was used to characterize the complex refractive index of chemical vapor deposition (CVD) graphene grown on copper foils and transferred to glass substrates. Two ellipsometers, with respective wavelength ranges extending into the ultraviolet and infrared (IR), have been used to characterize the CVD graphene optical functions. The optical absorption follows the same relation to the fine structure constant previously observed in the IR region, and displays the exciton-dominated absorption peak at ∼4.5 eV. The optical functions of CVD graphene show some differences when compared to published values for exfoliated graphene.

The HfO2–Si valence and conduction band offsets (VBO and CBO, respectively) of technologically relevant HfO2/SiO2/Si film stacks have been measured by several methods, with several groups reporting values within a range of ∼1 eV for both quantities. In this study we have used a combination of x-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry to measure the HfO2–Si VBO and CBO of both as-deposited and annealed stacks. Unlike previous XPS based measurements of the HfO2–Si VBO, we have corrected for the effect of charging in the XPS measurement. We find that after correction for charging, the HfO2–Si VBOs are decreased from their typical XPS-measured values, and agree better with values measured by UV photoemission spectroscopy and internal photoemission. We also report values for the rarely reported HfO2–SiO2 and SiO2–Si VBOs and CBOs in HfO2/SiO2/Si stacks. In addition to the band offsets, XPS was used to measure the band bending in the Si substrate of HfO2/SiO2/Si film stacks. Unannealed HfO2 stacks showed downward Si band bending of 0.4–0.5 eV, while annealed HfO2 stacks showed negligible band bending. Finally, we investigated the composition of the SiO2 layer in SiO2/Si and HfO2/SiO2/Si. By decomposing the Si 2p spectra into the spin orbit partner lines of its five oxidation states we observed that the growth of the HfO2 films resulted in the growth of the SiO2 underlayer and an increase by a factor of ∼2.3 in the density of suboxide species of SiO2. Based on the relatively high binding energy of the Si 2p4+ level with respect to the Si 2p0 level and a survey of results from literature, we conclude that the SiO2 layer in the HfO2/SiO2/Si samples we measured does not undergo significant intermixing with HfO2.

The field of plasmonics relies on light coupling strongly to plasmons as collective excitations. The energy loss function of graphene is dominated by two peaks at ∼5 and ∼15 eV, known as π and π + σ plasmons, respectively. We use electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope and density functional theory to show that between 1 to 50 eV, these prominent π and π + σ peaks are not plasmons, but single-particle interband excitations.

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