We present a systematic theoretical study on the mechanism of half-metallicity and ferromagnetism for one-dimensional (1-D) sandwich molecular wires (SMWs) constructed with altering cyclopentadienyl (Cp) and first-row transition metal (Mt). It is unveiled for the first time that, in (MtCp) infinity, one valence electron would transfer from the Mt to the Cp ring, forming Cp (-) and Mt (+) altering structures. This electron transfer not only makes them more stable than the benzene analogues (MtBz) infinity but also leads to completely different half-metallic and ferromagnetic mechanisms. We analyze such unusual half-metallicity and ferromagnetic behaviors and explain each SMW magnetic moment quantitatively. Finally, we indicate that a Peierls transition does not occur in these 1-D SMWs.

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Articles you may be interested inOn the induced microstructure changes of the amorphous carbon nitride films during annealing Plasma enhanced metalorganic chemical vapor deposition of amorphous aluminum nitride Effects of microwave power on the structural and emission properties of hydrogenated amorphous silicon carbide deposited by electron cyclotron resonance chemical vapor depositionWe have investigated the growth of a-Si 1Ϫx C x :H using the electron cyclotron resonance chemical vapor deposition ͑ECR-CVD͒ technique, under the conditions of high microwave power and strong hydrogen (H 2 ) dilution. The microwave power used is 900 W and a gas mixture of CH 4 and SiH 4 diluted in H 2 is varied to give carbon ͑C͒ fractions x ranging from 0 to 1. We aim to understand the effects of these deposition conditions on the characteristics of ECR-CVD grown a-Si 1Ϫx C x :H films at different x. Their microstructure and optical properties are investigated using infrared absorption, Raman scattering, UV-visible spectrophotometry, and photothermal deflection spectroscopy. Information on the atomic fraction x is obtained with Rutherford backscattering spectrometry. The B parameter in the Tauc relation is found to decrease and the Urbach energy E u increase with x, which are indicative of a higher degree of disorder with C incorporation. At intermediate x, the presence of SiuC bonds can be clearly seen from the IR absorption and Raman scattering results. The T peak around 1200 cm Ϫ1 is observed in the Raman spectra of the C-rich samples, with a redshift noted at increasing x. This suggests an increased presence of sp 3 CuC bonds in these films, which is attributed to the high microwave power and strong H 2 dilution that enhance C sp 3 bonding and indirectly limit the number of C sp 2 sites. This accounts for the large E 04 gaps of more than 3.2 eV observed in such films, which are nearly saturated at large x, instead of exhibiting a maximum at an intermediate x as are commonly reported. Blue photoluminescence ͑PL͒ is observed, and the PL peak energies (E PL ) are correlated to the E 04 gap. The full width at half maximum of the PL are also correlated to the Urbach energy E u . These results support that the PL broadening is attributed to the disorder broadening arising from the broad band tails.

Results of structural characterization by Fourier transform infrared spectroscopy, x-ray diffraction, and specular x-ray reflectivity measurements are employed for the interpretation of electrical measurement data and the deconvoluted distribution of electron states, N(E) of carbon doped hydrogenated silicon oxide (SiOCH) low-k dielectric films. Atomic structure of the films is identified as a mixture of a dominant and totally amorphous SiO2-like phase with a partially polycrystalline SiC phase. The n-type dc conductivity that dominates in this material points to the principal role of the SiC-like phase in the dc transport of the SiOCH material. The deep level transient spectroscopy technique is applied for the N(E) shape studies in the energy range up to 0.7 eV below the conduction band bottom. Typical N(E) values lie in the 1010–1014 eV−1 cm−3 range for films deposited at different ratios of tri-methyl-silane to oxygen flow rate. No correlation between the N(E) shape and the film deposition conditions have been found in this case. The Fermi level position usually lies at 0.18–0.4 eV below conduction band bottom. For the SiOCH films prepared at different levels of rf power densities, the N(E) in the whole studied range increases nearly monotonically with increasing rf power, which is attributed to the SiC-like phase fraction increment. An N(E) peak at 0.25–0.35 eV below conduction band bottom has been found in the films. The possible origin of the peak appearance is discussed.

Using density functional theory calculations, we demonstrate that one-dimensional bimetallic molecular ferromagnets (FeCpMCp)(infinity) (M = Sc, Ti, V, Cr and Mn, Cp = cyclopentadienyl) exhibit significant enhancement in local and global atomic magnetic moments as well as relatively large spin-polarization energy as compared to their monometallic counterparts. These yield an unusual charge configuration for one of the wires: (Fe(0)Cp(-1)V(+2)Cp(-1))(infinity). Hückel's rule and double-exchange interaction model are used to illustrate the details of local charge transfer and long-range ferromagnetic order. We then propose a growth mechanism for V(n)(FeCp(2))(n+1) (n = 1-4) clusters, which is supported unambiguously with time-of-flight mass spectroscopy data.

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