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Dopability in semiconductors plays a crucial role in device performance. Using the first-principles density-functional theory calculations, we investigate systematically the doping properties of layered MX2 (M = Mo, W; X = S, Te) by replacing M or X with the groups III, V and VII elements. It is found that the defect BM is hard to form in MX2 due to the large formation energy originating from the crystal distortion, while AlM is easy to realize compared to the former. In MoS2, WS2 and MoTe2, Al is the most desirable p-type dopant under anion-rich conditions among the group III components. With respect to the doping of the group V elements, it is found that the substitutions on the cation sites have deeper defect levels than those on the anion sites. AsTe and SbTe in MoTe2 and WTe2 are trend to form shallow acceptors under cation-rich conditions, indicating high hole-concentrations for p-type doping, whereas SbS in MoS2 and PTe in WTe2 are shown to be good p-type candidates under cation-rich conditions. In despite of that the substitutions of group VII on X site have low formation energies, the transition energies are too high to achieve n-type MoS2 and WS2. Nevertheless, for MoTe2, the substitutions with the group VII elements on the anion sites are suitable for n-type doping on account of the shallow donor levels and low formation energies under Mo-rich condition. As to WTe2, F is the only potential donor due to the shallow transition energy of FTe. Our findings of filtering out unfavorable and identifying favorable dopants in MX2 are very valuable for experimental implementations.

Penta-hexa-graphene (PHG) is the name given to a novel puckered monolayer of carbon atoms tightly packed into an inerratic mixing pentagonal and hexagonal network. Theoretically, it exhibits excellent electronic properties and can be rolled into penta-hexa-graphene nanotubes (PHGNTs). By using first-principles combined with density functional theory, the PHGNTs with two types of chirality and different diameters were studied. Studies show that not only the nanotubes have intrinsic magnetic properties, but also the magnetic ground state changes with the tube diameter. Interestingly, the nanotubes exhibit semiconducting properties that do not vary with chirality in the antiferromagnetic (AFM) state. And in the ferromagnetic (FM) state, the materials realize the transitions from metal to spin gapless semiconductors (SGS), and to semiconductor with the change of tube diameter. Furthermore, first-principles calculation shows that PHGNTs exhibit diverse electronic properties when the external electrical field is applied, ranging not only from semiconductor to SGS and to metal, but also from semiconductor to half-metal and to metal. Our simulations have an impact on their possible applications in spintronic devices.

Thermal transport across graphene/hexagonal boron nitride (h-BN) nanoribbon interface is investigated using nonequilibrium molecular dynamics method. It is found that the heat current runs preferentially from the h-BN to graphene domain, which demonstrates pronounced thermal rectification behavior in this heterostructure. The observed phenomena can be attributed to the resonance effect between out-of-plane phonon modes of the graphene and h-BN domains in the low frequency region. In addition, we demonstrate that the optimum conditions for thermal rectification include low temperature, large temperature bias, short sample length and small interface densities. More interestingly, an unexpected negative differential thermal resistance (NDTR) behavior is also found at graphene/h-BN (CBN) nanoribbon interface with special edge geometry. Phonon spectra analysis reveals that the transverse acoustic wave plays an important role for the heat transfer at such interface.

The effects of magnetic atom on the band structure of zigzag-edged graphene nanoribbons are investigated by the density functional theory. The results show that for narrow zigzag-edged graphene nanoribbons, the band gap can be opened duo to the spin-up/spin-down charges being re-enriched on the edge sites. However, for the wide zigzag-edged graphene nanoribbons, a spin-up/spin-down half-metallic property can be observed. Moreover, it is found that the Seebeck coefficients in the narrow zigzag-edged graphene nanoribbons are reversed and enlarged, which provides a way to design novel thermoelectric device.

The phonon scattering and thermal conductance properties have been studied in two coupled graphene nanoribbons connected by different bridge atoms by using density functional theory in combination with non-equilibrium Green's function approach. The results show that a wide range of thermal conductance tuning can be realized by changing the chemical bond strength and atom mass of the bridge atoms. It is found that the chemical bond strength (bridge atom mass) plays the main role in phonon scattering at low (high) temperature. A simple equation is presented to describe the relationship among the thermal conductance, bridge atom, and temperature.

Vertical heterostructures of two-dimensional (2D) materials are excellent candidates for designing next-generation electronic devices with superior performance. By using both ab initio electronic calculations and quantum transport simulations, we investigated the electronic and transport properties of InAs/graphene heterostructure. The results reveal that electrons and holes accumulate at different layers after the adsorption of InAs layer, forming the built-in electronic field at the interface. The electrostatic potential energy of InAs layer is higher than that of graphene, and it favors more electrons transferring from InAs to graphene layer. Comparing the comment methods by introducing impurity and carriers' injection, rectifying and negative differential resistance behaviors can also be realized by the combined effects of electron-hole distribution, interfacial hybridization, and contact barrier in InAs/graphene heterostructure device. It shows that the rectifying ration gradually increases with bias voltage, and the negative differential resistance effect happens at either positive or at negative bias voltage regions. Electrostatic potential distribution and contact barrier play important roles in determining transport properties. Increasing interfacial hybridization is helpful for transmission enhancement in the weak interlayer interaction van der Waals heterostructure.

We investigate the phonon thermal transport properties in InAs nanowires with different size and growth directions by using nonequilibrium molecular dynamics methods. The results show a remarkable anisotropy for the thermal conductivity in InAs nanowire. It is found that the thermal conductivity along [110] growth direction is about three times larger than that along [100] or [111] direction. With the increase of temperature, the thermal conductivity along [110] direction decreases significantly. However, the thermal conductivity along other two directions is not sensitive to temperature. Moreover, we find a crossover from ballistic to ballistic-diffusive thermal transport for a certain length of InAs nanowire. A brief physical analysis of these results is given. It is suggested that the anisotropy of thermal conductivity is common for nanowires with zinc blende structures.

The thermal transport properties of graphene nanoribbons (GNRs) with pentagon–heptagon defect (PHD) are studied by using first principles calculations in combination with non-equilibrium Green’s function approach. The results show that the PHD effect on thermal conduction in armchair-oriented GNR is stronger than that in zigzag-oriented GNR. The out-of-plane acoustic mode is almost reflected by the PHD at a particular frequency. When the temperature is larger than 400 K, the thermal conduction ratio is only related to the PHD’s orientation, and insensitive to the width of PHD. These results will be helpful for designing high-performance thermal insulation or thermoelectric device.

The spin transport properties of molecular devices constructed by hydrogen–phthalocyanine and transition metal (TM)–phthalocyanine molecule with zigzag graphene nanoribbon electrodes are investigated by the Keldysh nonequilibrium Green’s function method in combination with the density functional theory. The results show that there exists giant magnetoresistance in both the hydrogen–phthalocyanine and the TM-phthalocyanine systems. The magnetoresistance ratio is much bigger than that found by Schmaus et al. [S. Schmaus, A. Bagrets, Y. Nahas, T. K. Yamada, A. Bork, M. Bowen, E. Beaurepaire, F. Evers, W. Wulfhekel, Nature Nanotechnology 6 (2011) 185–9] in single hydrogen–phthalocyanine-Co electrodes system. Moreover, it is found that the chromium–phthalocyanine molecular device is a good spin filtering device with nearly 100% spin filtering efficiency at a wide bias voltage region. The mechanisms are proposed for these phenomena.

By using first-principles calculations, the magnetic properties of a SnO 2 quantum dot (QD) are investigated. It is found that dangling bonds (DBs) are equated with Co (Ni) dopants, which can induce magnetic moments in SnO 2 QDs. Thus, the QD shows very abundant variation of the magnetic properties by combining dopants with DBs. The changes of magnetic moments can be explained well by a carrier modulation model.

Electronic and magnetic properties of half-bare zigzag silicon carbon nanoribbons (ZSiCNRs) have been studied by using HSE06 hybrid function. The calculation results show that the ZSiCNRs with bare Si edge and terminated C edge are metal with 1.3 μ B magnetic moments per supercell. While the half-bare ZSiCNRs with bare C edge are small band gap semiconductor with 2 μ B magnetic moments per supercell. Stable magnetism of the half-bare ZSiCNRs can be demonstrated by the total energy calculations of different spin configurations. It is found that the magnetic coupling of half-bare ZSiCNRs depends on the bare edge atoms, regardless of the terminated atoms (H or F). Our results indicate that the half-bare ZSiCNRs with turnable electronic and magnetic properties have potential applications in spintronic nanodevices.

By using nonequilibrium Green’s functions in combination with the density-functional theory, we investigate the electronic transport properties of the molecular device constructed by a single 4,4-(ethene-1,2-diyl) dibenzoic acid sandwiched between carbon nanotube electrodes. The results show that an obvious reversible switching behavior can be observed when the molecular structure changes between E isomerization and Z isomerization by ultraviolet irradiation or visible irradiation. More importantly, the switching ratio can reach to a maximum (about 7000) at 0.28 V and then decrease gradually to a minimum at 0.48 V. It is suggested that the controllable switching behavior is very useful for the design of functional molecular devices.

Since the fixed ejector cannot adjust the optimum high-side pressure, the adjustable ejector is designed and built based on a transcritical CO 2 heat pump system model results. The adjustable ejector is subjected to electrical pulses through the stepper motor which drives needle forward or backward movement to change the nozzle throat area for the optimum high-side pressure. Experimental investigation of the transcritical CO 2 heat pump cycle with adjustable ejector is presented. The effects of the high-side pressure on the system performance are analyzed. A control strategy for maximum COP h is developed by correlating the CO 2 pressure and temperature at the gas cooler exit, yielding the ejector optimum high-side pressure control equation. Experiment results show that there exist maximum values for heating performance coefficient and heat capacity with increasing high-side pressure. The increased high-side pressure has a positive effect on the system performance and outweighs lower ejector efficiencies. The ejector efficiency is mainly distributed within range of 20%–30%.

The micro-arrangement of helium atoms and electronic properties of tritides LaNi5TxHey (x=5, 5.5, 6, 6.5; y=0.5, 1.0) have been systematically investigated by means of the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). Those optimized results indicate that helium atoms prefer to occupy the tetrahedral interstitial sites (6c1) in LaNi5 tritides. From the analysis of the electronic structure, a strong and narrow peak appears in the low energy region (about −4.0 eV), which is due to the contribution of the He–s band. With increasing in the helium content, the empty band in the low energy region gradually moves to the right. Compared with H atoms, the interactions between He atom and La, Ni atoms are quite weaker, which can easily cause the pulverization of the host alloy.

Using nonequilibrium Greenʼs functions in combination with the density functional theory, the spin-dependent electronic transport properties on V-shaped notched zigzag-edged graphene nanoribbons junctions have been calculated. The results show that the electronic transport properties are strongly depending on the type of notch and the symmetry of ribbon. The spin-filter phenomenon and negative differential resistance behaviors can be observed. A physical analysis of these results is given.

A new method to fabricate metal/conducting polymer composite nanowires is presented by taking silver/polypyrrole composite nanowires as an example. A silver (I)-coordinated organogel as template was prepared firstly, and redox-polymerization of pyrrole took place on the gel fiber, giving product of silver/polypyrrole nanowires. The silver/polypyrrole nanowires were characterized by multiple techniques. This strategy could be carried out in one-step procedure at room temperature, and it proves the utility of coordinated organogels in template synthesis of polymer nanostructures.

A simple and general strategy is described for preparing network supported catalyst through a one-pot synthetic procedure using supramolecular gel as template. This procedure directly attaches ligand to support during fabricating the support. Using this strategy, supported CuBr/di-(2-picolyl)amine catalyst with U-shaped fibrillar network was prepared and used in atom transfer radical polymerization of methyl methacrylate. XPS and SEM characterization of the catalyst revealed homogeneous distribution of ligand, sufficient reactive sites, adequate mechanical strength and macroporosity. The polymerization results demonstrated high activity and reusability of such catalyst. This strategy might be extended to other supported catalysts used in column reactors.

New supramolecular hydrogels with the maximal sol–gel transition temperature ( T gel ) of 95 °C were obtained by using gelators formed from 1,3,5-benzenetricarboxylic acid (BTA) and para-hydroxyl pyridine (PHP) or meta-hydroxyl pyridine (MHP). The single crystal structure of the complex formed from BTA and ortho-hydroxyl pyridine (OHP) indicated that the molecules assembled into superstructure via both hydrogen bonds and π–π stacking interaction.

The crystal structures and electronic properties of hydrides LaNi4.5Al0.5H6−xHey ( x = 0 , 0.5 , 1.0 ) have been investigated by means of the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The calculated data indicate that the micro-arrangement of hydrogen atoms in LaNi4.5Al0.5H6 is the same as that of hydride LaNi5H6, which is consistent with the experimental results in terms of the equilibrium desorption isotherms. And we found that once the first He atom locates in the tetrahedral interstitial sites (6m site) near Al atom for LaNi4.5Al0.5H5.5He0.5, then it is difficult for the second He atom to locate in the 6m site again. Therefore, the second He atom would prefer to occupy the middle plane site (6m\ast site) apart from Al atom for LaNi4.5Al0.5H5He. To study the interaction among La, Ni, Al, H and He atoms, the figures referring to the densities of states and contour maps of the electron densities on two different planes are analysed.

A simple drug compound, 4-oxo-4-(2-pyridinylamino) butanoic acid (defined as AP), was able to gel water at 4 wt% concentration under various conditions. In the superstructure, AP molecules assembled into fibrous aggregates driving by hydrogen bonds and π–π stacking interaction. The gels with different backbone structures released drug molecules in different speeds.

Using the scattering-matrix method, we investigate the influences of boundary conditions on thermal conductance in quantum wire with structural defect. A comparison between the thermal conductances is made when stress-free, hard-wall, and mixed boundary conditions are applied for acoustic transport leads. The results show that the quantized thermal conductance plateau at very low temperature can be observed only in transport lead with stress-free boundary condition. For hard-wall or mixed boundary conditions, qualitatively different thermal conductance characteristics are found. Moreover, we find that the behavior of the thermal conductance sensitively depend on the geometric parameters and the position of the defect in quantum wire.

A series of new titanium complexes bearing beta-diiminato ligands [(Ph)NC(R-1)CHC(R-2)N(Ph)](2)TiCl2 (4a: R-1 = R-2 = CH3; 4b: R-1 = R-2 = CF3; 4c: R-1 = Ph, R-2 = CH3; 4d: R-1 = Ph, R-2 = CF3) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4a and 4c adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4a-d are active catalysts for ethylene polymerization, and produce high molecular weight polyethylenes. Catalyst activities and the molecular weights of polymers are considerably influenced by the steric and electronic effects of substituents on the catalyst backbone under the same polymerization condition. With the strong electron-withdrawing groups (CF3) at R-1 or/and R-2 position, complexes 4b and 4d show higher activities than complexes 4a and 4c, respectively.

A series of titanium complexes [(Ar)NC(CF 3 )CHC(R)O] 2 TiCl 2 ( 4b : Ar = –C 6 H 4 OMe( p ), R = Ph; 4c : Ar = –C 6 H 4 Me( p ), R = Ph; 4d : Ar = –C 6 H 4 Me( o ), R = Ph; 4e : Ar = α-Naphthyl, R = Ph; 4f : Ar = –C 6 H 5 , R = t -Bu; 4g : Ar = –C 6 H 4 OMe( p ); R = t -Bu; 4h : Ar = –C 6 H 4 Me( p ); R = t -Bu; 4i : Ar = –C 6 H 4 Me( o ); R = t -Bu) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4b , 4c and 4h adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4b – c and 4f – i are active catalysts for ethylene polymerization and ethylene/norbornene copolymerization, and produce high molecular weight polyethylenes and ethylene/norbornene alternating copolymers. In addition, the complex 4c /MMAO catalyst system exhibits the characteristics of a quasi-living copolymerization of ethylene and norbornene with narrow molecular weight distribution.

Rare-earth Ni–Re–P (Re=Ce, Nd) films were prepared by electrodeposition from an aqueous bath using citric acid as a complexing agent on copper substrates. It was found that the percentage of rare earth was as high as 30 wt.%, the structure of all films was amorphous, and the glass temperature of all the films was about 385 °C. The crystallization activation energy of these amorphous films was determined by differential thermal analysis (DTA). The regularity of the amorphous film formation was studied by plotting the two-dimensional Miedema's coordinates Δ ϕ * and Δ n ws −1/3 and the three-dimensional chemical coordinates with the size factor Δ R / R A added. The means of realizing the deposition of rare-earth films from aqueous bath by electrodeposition is discussed.

Hyperbranched poly(amine–ester)s bearing self-complementary quadruple hydrogen bonding units display excellent mechanical and temperature-dependent melt rheological properties, which make them suitable as novel hot-melting materials.

A supramolecular hydrogel (defined as G1) formed from 1,2,4,5-benzene tetracarboxylic acid (BTCA) and 2-amino-3-hydroxypyridine possessed higher Tgel than that of another hydrogel (defined as G2) formed from BTCA and 3-hydroxypyridine. Based on the analysis of their xerogels by 1H NMR, IR and XRD, the higher stability of G1 was attributed to the formation of stronger hydrogen binding enhanced by the ortho amino group of 2-amino-3-hydroxypyridine.