Highlights

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The HfC/a-C nanocomposite structure appears at C content between 58 at.% and 76 at.%.

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The maximum hardness for HfC_x films is up to 34.4 GPa at 30 at.% a-C.

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Film with 52 at.% a-C shows combination of lowest COF of 0.10 and wear rate of 1.10 × 10⁻⁶ mm³/Nm.

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HfC_x films show promise as lubricious wear protective hard coatings.

Abstract

Although point defects are found to exist commonly in non-stoichiometric group-IVB transition metal nitrides, the identification of primary point defects still causes some disagreement. The formation mechanism and influence of primary point defects on electronic structures are not yet well explored. This study finds that the types and formation mechanism of primary point defects in rocksalt hafnium nitride (δ-HfN_x) films can be identified by a combination of first-principles calculations and grazing incidence X-ray diffraction, Raman and high-resolution transmission electron microscopy experiments. It is shown that the primary point defects in sub- and over-stoichiometric δ-HfN_x films are N and Hf vacancies, respectively, which arise preferentially because they are thermodynamically more stable than other types of point defects, such as interstitials and antisites, because they have much lower formation energy and equilibrium formation enthalpy. Furthermore, it is found that the formation of N and Hf vacancies have an important role in changing electronic structures. N vacancies act as donor-like defects and can add extra free electrons to the conduction band at a rate of an electron per N vacancy, while Hf vacancies serve as acceptor-like defects and efficiently reduce free electrons at a rate of two electrons per Hf vacancy. Additionally, the formation of N vacancies can induce two new interband absorption bands centered at ∼0.81 and ∼2.27 eV, while the incorporation of Hf vacancies create an additional interband absorption band at ∼3.75 eV. These new insights are demonstrated by good agreement between calculations and experiments.

Highlights

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A more simple method to prepare TiO₂-RGO nanocomposites was reported.

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The content of GO is much higher than other results.

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The photocatalytic activity of degradation of Rh B is excellent.

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The nanocomposites can even degrade the Rh B in the dark room condition.

Highlights

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The coherent relationship of ${\left\{111\right\}}_{\text{NbN}}{〈110〉}_{\text{NbN}}//{\left\{0002\right\}}_{\text{AlN}}{〈11\overline{2}0〉}_{\text{AlN}}$ forms in multilayer.

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The remarkable hardness enhancement implements at a wide range of modulation periodicity.

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Good wear property appears in multilayers with small modulation periodicity.

Abstract

The field emission from planar graphene sheets is usually limited by the morphological features. To overcome this problem, we grow vertically aligned thin-graphite sheets on graphite-encapsulated Cu particles (VGs/GC) using radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). Field emission measurements show that the insert of Cu particles can substantially improve the field emission properties of the VGs, which can be attributed to the enhanced local fields at the tip of VGs/GC as well as the electron conductivity enhancement due to the existence of Cu particles. The effects of size and inter-particle distance of Cu particles on field emission for the VGs/GC hybrid material have been revealed.

Abstract

We present a simple, low-cost and high-effective method for synthesizing high-quality, large-area graphene using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) on SiO₂/Si substrate covered with Ni thin film at relatively low temperatures (650 °C). During deposition, the trace amount of carbon (CH₄ gas flow rate of 2 sccm) is introduced into PECVD chamber and the deposition time is only 30 s, in which the carbon atoms diffuse into the Ni film and then segregate on its surface, forming single-layer or few-layer graphene. After deposition, Ni is removed by wet etching, and the obtained single continuous graphene film can easily be transferred to other substrates. This investigation provides a large-area, low temperature and low-cost synthesis method for graphene as a practical electronic material.

Abstract

The deformation mechanisms and fracture behavior of TiN coating on a Si(111) substrate, deposited using magnetron sputtering Ti target, is characterized by nanoindentation experiments. The morphologies of the indentations are revealed by scanning electron microscopy, coupled with in situ atomic force microscopy in nanoindentation experiments. The results show that permanent trigonal impressions and radial plastic grooves are confined within the contact regions even though the peak indenter displacement increases to 1500 nm. Local cracks of TiN appear around the indent marks making the edges of the indentations irregular. The cracks increase with an increase of the indenter displacement until the indenter arrives at (or approaches) the Si(1 1 1) substrate at a critical displacement. As the peak indenter displacement increases to 2500 nm, an interfacial fracture between the TiN coating and the Si(1 1 1) substrate is observed using both scanning electron microscopy micrograph and in situ atomic force microscopy images. The diameter of the interfacial fracture determined by scanning electron microscopy micrographs is more accurate than that determined by in situ atomic force microscopy images in nanoindentation experiments. The failure mechanism of the TiN coating is also investigated by means of a standard nanoscratch test.

Abstract

Using the density-functional theory calculations, we have investigated the effect of an in-plane electric field on the electronic properties and the structural stability of the edge-oxygenated armchair graphene nanoribbons (AGNRs). It has been found that the metallic-semiconducting transition and band gap modulation can be realized if a proper in-plane electric field is applied across the edge-oxygenated AGNR. Moreover, the critical strength of the applied electric field for the transition from metallic to semiconducting phase decreases with the width of the AGNR, while the range of the applied electric field required to maintain the semiconducting phase is increased when the width of AGNR decreases.

Abstract

The effects of thermal annealing in vacuum on the bonding structures, optical and mechanical properties for germanium carbide (Ge_1−xC_x) thin films, deposited by radio frequency (RF) reactive sputtering of pure Ge(1 1 1) target in a CH₄/Ar mixture discharge, are investigated. We find that there are no significant changes in the bonding structure of the films annealed below 300 °C. The fraction of Ge–H bonds for the film annealed at temperatures (T_a) above 300 °C decreases, whereas that of C–H bonds show a decrease only when T_a exceeds 400 °C. The out-diffusion of hydrogen promotes the formation of Ge–C bonds at T_a above 400 °C and thus leads to a substantial increase in the compressive stress and hardness for the film. The refractive indices and optical gaps for Ge_1−xC_x films are almost constant against T_a, which can be ascribed to the unchanged ratios of Ge/C and sp²-C/sp³-C concentrations. Furthermore, we also find that the excellent optical transmission for an antireflection Ge_1−xC_x double-layer film on ZnS substrate is still maintained after annealing at 700 °C.

Abstract

The effects of total CH₄/Ar gas pressure on the growth of carbon nanomaterials on Si (1 0 0) substrate covered with CoO nanoparticles, using plasma-enhanced chemical vapor deposition (PECVD), were investigated. The structures of obtained products were correlated with the total gas pressure and changed from pure carbon nanotubes (CNTs) through hybrid CNTs/graphene sheets (GSs), to pure GSs as the total gas pressure changed from 20 to 4 Torr. The total gas pressure influenced the density of hydrogen radicals and Ar ions in chamber, which in turn determined the degree of how CoO nanoparticles were deoxidized and ion bombardment energy that governed the final carbon nanomaterials. Moreover, the obtained hybrid CNTs/GSs exhibited a lower turn-on field (1.4 V/μm) emission, compared to either 2.7 V/μm for pure CNTs or 2.2 V/μm for pure GSs, at current density of 10 μA/cm².

Abstract

Abstract

The (γ′-Fe₄N/Si-N)_n (n: number of layers) multilayer films and γ′-Fe₄N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe₄N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe₄N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe₄N to ɛ-Fe₃N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ɛ-Fe₃N transformed back into γ′-Fe₄N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe₄N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ɛ-Fe₃N.

Abstract