Regimented Charge Transport Phenomena in Semiconductive Self-Assembled Rhenium Nanotubes.

Photoconductivity, a crucial property, determines the potential of semiconductor materials for use in optoelectronic and photocatalytic device applications. The one-dimensional metal-organic nanotube semiconducting material [{Re(CO)3}6(bho)(phpy)6]n (MBT 1, where bho is benzene-1,2,3,4,5,6-hexaoate and phpy is 4-phenylpyridine) reported herein exhibits record photocurrent responses at a broad spectral range. MBT 1 is comprised of a unique nanotube structure that is composed of six rhenium sites, six 4-phenylpyridine ligands, and a benzene-1,2,3,4,5,6-hexaoate unit. The highly organized self-assembled molecular bamboo tube MBT 1 displays semiconducting characteristics with a low activation energy of 1.63 meV. The alternating current (AC) and direct current (DC) conductivities of pellet devices are approximately 10-4 S/cm. For a single-crystal device, DC conductivity was found to be 1.5 S/cm, an unprecedented 10 000 times higher. The bandgap of MBT 1 was determined to be 1.03 eV, consistent with the theoretically estimated value of 1.2 eV. Theoretical calculations suggest that the unique structural architecture of MBT 1 allows for effective charge transport, which is facilitated by the spatial separation of electrons and holes that MBT 1 contains. This also eliminates fast charge recombination. The findings are not only chemically and fundamentally important but also have great potential for applications in innovative nano-optoelectronics.

Functional Groups Assisted Tunable Dielectric Permittivity of Guest-Free Zn-Based Coordination Polymers for Gate Dielectrics.

The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2 ) and electron-withdrawing (R=NO2 ) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1 )(L2 )]n (1) and [Zn(L1 )(L3 )]n (2) [L1 =2-(2-pyridyl) benzimidazole (Pbim), L2 =5-aminoisophthalate (Aip), and L3 =5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2 . Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties.

Dielectric relaxation of the double perovskite oxide Ba2PrRuO6.

Samples of Ba2PrRuO6 were prepared by the solid state reaction method and the structure was characterized by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and dielectric measurements were performed in order to investigate the morphology and electric properties of the ceramics. X-ray diffraction data reveal that the Ba2PrRuO6 samples are of the cubic crystal structure with the space group Fm3̄m at room temperature. The dielectric properties were studied in the range of 20 Hz to 1 MHz in the temperature range from 10 K to 300 K. Strong dispersion in frequency and a rapid increase in ε' are observed when T > 150 K. The observed steps of the ε'(T) curves are correlated with the peaks of the tan δ(T) curves, with the peak temperature shifting to higher values as the frequency increases. Impedance spectroscopy studies indicate the presence of grain and grain boundary relaxations in the sample at high temperatures, while at low temperatures only grain relaxation can be observed. Both grain and grain boundary relaxation times follow the Arrhenius law with activation energies of 0.16 eV and 0.17 eV, respectively.

High-κ Samarium-Based Metal-Organic Framework for Gate Dielectric Applications.

The self-assembly of a samarium-based metal-organic framework [Sm2(bhc)(H2O)6]n (1) in good yield was achieved by reacting Sm(NO3)3·6H2O with benzenehexacarboxylic acid (bhc) in a mixture of H2O-EtOH under hydrothermal conditions. A structural analysis showed that compound 1 crystallized in a space group of Pnmn and adopted a 3D structure with (4,8) connected nets. Temperature dependent dielectric measurements showed that compound 1 behaves as a high dielectric material with a high dielectric constant (κ = 45.1) at 5 kHz and 310 K, which is comparable to the values for some of the most commonly available dielectric inorganic metal oxides such as Sm2O3, Ta2O5, HfO2, and ZrO2. In addition, electrical measurements of 1 revealed an electrical conductivity of about 2.15 × 10-7 S/cm at a frequency of 5 kHz with a low leakage current (Ileakage = 8.13 × 10-12 Amm-2). Dielectric investigations of the Sm-based MOF provide an effective path for the development of high dielectric materials in the future.

Semiconductor Behavior of a Three-Dimensional Strontium-Based Metal-Organic Framework.

The self-assembly of a three-dimensional strontium-based metal-organic framework [Sr(Hbtc)(H2O)]n (1) was achieved through the reaction of Sr(NO3)2 with a 1,2,4-benzenetricarboxylic acid (1,2,4-H3btc) ligand under hydrothermal conditions. This Sr-based metal-organic framework exhibits remarkable semiconducting behavior, as evidenced by theoretical calculations and experimental measurements. Temperature-dependent DC conductivity, near-room-temperature AC conductivity, diffuse reflection spectra, and photoluminescence spectra provide strong proof that compound 1 shows a band gap of 2.3 eV, which is comparable to that for other commonly available semiconducting materials (e.g., CdSe, CdTe, ZnTe, GaP, etc.). The optimized molecular structure and electronic properties (density of states and band gap energy) of 1 were calculated using density functional theory, and the results are consistent with experimental findings. This is the first report on the semiconducting properties of a strontium-based MOF, which will pave the way for further studies in semiconducting MOFs with interesting potential applications in optoelectronic devices.