ZrB2 Films Research Articles

Interaction of epitaxial silicene with overlayers formed by exposure to Al atoms and O2 molecules.

As silicene is not chemically inert, the study and exploitation of its electronic properties outside of ultrahigh vacuum environments require the use of insulating capping layers. In order to understand if aluminum oxide might be a suitable encapsulation material, we used high-resolution synchrotron photoelectron spectroscopy to study the interactions of Al atoms and O2 molecules, as well as the combination of both, with epitaxial silicene on thin ZrB2(0001) films grown on Si(111). The deposition of Al atoms onto silicene, up to the coverage of about 0.4 Al per Si atoms, has little effect on the chemical state of the Si atoms. The silicene-terminated surface is also hardly affected by exposure to O2 gas, up to a dose of 4500 L. In contrast, when Al-covered silicene is exposed to the same dose, a large fraction of the Si atoms becomes oxidized. This is attributed to dissociative chemisorption of O2 molecules by Al atoms at the surface, producing reactive atomic oxygen species that cause the oxidation. It is concluded that aluminum oxide overlayers prepared in this fashion are not suitable for encapsulation since they do not prevent but actually enhance the degradation of silicene.

Enhanced Thermoelectric Properties and Superlattice Structure of a Bi2Te3/ZrB2 Film Prepared by Ion-Beam-Assisted Deposition

In this study, it was found that a novel superlattice structure can favorably influence the carrier and phonon transport properties of superlattice films. The n-type Bi2Te3/ZrB2 superlattice film was successfully fabricated by simple ion-beam-assisted deposition on a large scale. The composition and microstructure of the films were studied by X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The results show that the multilayered Bi2Te3/ZrB2 film with a modulation period (Λ) of 12 nm is alternately composed of monolithic Bi2Te3 and ZrB2 layers. The Bi2Te3/ZrB2 superlattice film possesses a relatively rough interface and distinct layer structure. The thermoelectric properties, i.e., electrical conductivity (σ), Seebeck coefficient (S), and thermal conductivity (κ), of the Bi2Te3-based films were measured in the in-plane direction. The properties of the Bi2Te3/ZrB2 superlattice film were greatly enhanced in comparison with those of Bi2Te3 and ZrB2 films. The superlattice Bi2Te3/ZrB2 film with a thermoelectric dimensionless figure-of-merit ZT = 1.54 was obtained at room temperature. An in-plane transport mechanism of the superlattice structure was proposed and investigated. Introduction of such a superlattice structure into films is therefore a very promising approach.

Influence of Nitrogen Flow Ratio on the Microstructure, Composition, and Mechanical Properties of DC Magnetron Sputtered Zr–B–O–N Films

Nanocrystalline ZrB2 film and nanocomposite Zr-B-O-N films were prepared by non-reactive as well as reactive magnetron sputtering techniques, respectively. By means of X-ray diffraction analysis, electron probe microanalysis, X-ray photoelectron spectroscopy, and scanning electron microscopy, the influence of nitrogen flow ratio on the film microstructure and characteristics were investigated systematically, including the deposition rate, chemical compositions, phase constituents, grain size, chemical bonding, as well as cross-sectional morphologies. Meanwhile, the hardness and adhesion of above films were also evaluated by micro-indentation method and a scratch tester. With increasing the nitrogen flow ratio, the deposition rate of above films decreased approximately linearly, whereas the contents of N and O in the films increased gradually and tended to saturation. Moreover, the film microstructure was also altered gradually from a fine columnar microstructure to a featureless glass-structure. As the nitrogen flow ratio was 11.7%, the Zr-B-O-N film possessed an typical nanocomposite structure and presented good mechanical properties. During the process of reactive sputtering of metal borides, the introduction of nitrogen can show a pronounced suppression of columnar grain growth and strong nanocomposite structure forming ability.

A study on fabrication technique of ZrB2 target

ZrB2 thin film is used as neutron burnable absorbers of nuclear reactor. This paper prepared ZrB2 target by cold isostatic press followed high temperature sintering in order to meet the requirement of preparing thin film by magnetron sputtering. The phase constituent and composition of ZrB2 target was analyzed by X-ray diffraction (XRD) and X-ray energy dispersion spectroscope(EDS). The microstructure of samples was observed by scanning electron microscope(SEM). The density was measured based on Archimedes drainage method; UO2 core was coated by ZrB2 films by magnetron sputtering using as-prepared ZrB2 target. The results indicate that 2000°C could sinter ZrB2 powder. The relative density of sintering product was 71%. The as-prepared ZrB2 might make films on the sample of UO2 surface by magnetron sputtering.

Nanosized zirconium diboride: Synthesis and properties

The thermolysis of Zr(BH4)4 vapor at 573 and 623 K in a vacuum of 1.33 × 10−1 Pa was studied. Nanosized zirconium diboride was produced as an X-ray amorphous powder and a crystalline film. According to electron microscopy data, the X-ray amorphous zirconium diboride powder obtained at 573 or 623 K consists of spherical particles 30–40 nm in diameter, which is in quite a good agreement with the equivalent particle diameter (∼35 nm) calculated from the specific surface area of ZrB2. After annealing at 1273 K, the X-ray amorphous zirconium diboride powder crystallizes into a hexagonal lattice with the unit cell parameters a = 0.3159 nm and c = 0.3527 nm. The coherent scattering length Dhkl is ∼27 nm. The zirconium diboride film produced at 573 or 623 K crystallizes into a hexagonal lattice with the unit cell parameters a = 0.3163−0.3168 nm and c = 0.3524−0.3531 nm. The coherent scattering length Dhkl is ∼14 nm. The thickness of the ZrB2 film on quartz, glass ceramics, and stainless steel is 5–7 μm. The microhardness of the film on a stainless steel substrate under a load of 20 g is 17.8 GPa.

Heat- and radiation-resistant contacts to SiC made on the basis of quasi-amorphous ZrB2 films

The radiation and thermal stability of the Schottky-barrier structures deposited by the magnetron sputtering of zirconium diboride onto the (0001) face of the Lely-grown n-6H(15R)SiC single crystals with the uncompensated-donor concentration of ∼1018 cm−3 was investigated by the methods of the I–V and C–V characteristics combined with the layer-by-layer Auger analysis. It is shown that the use of quasi-amorphous ZrB2 films when manufacturing contacts on n-6H(15R)SiC leads to no changes in the Schottky-barrier characteristics during rapid thermal annealing to 800°C in the range of 60Co γ-ray irradiation doses of 103–107 Gy.

Thermoelastic and Optical Properties of Thick Boride Templates on Silicon for Nitride Integration Applications

We present a comparative study of the structural, thermoelastic, and optical properties of ZrB2 films grown on silicon with the corresponding bulk ZrB2 behavior. Thick ZrB2 films (up to 500 nm) with device quality morphological and structural properties were grown on Si(111) for potential integration of GaN with Si substrates. HR-XRD was used to analyze the thickness and temperature dependence of the films’ strain state. The data indicate that at room temperature a residual tensile strain of ∼0.5% persists in all samples independent of thickness. When the films are heated back to the growth temperature of 900 °C, two distinct behaviors are observed: thinner films (∼200 nm) follow the thermal expansion of the Si substrate, which results in a tensile strain at the growth temperature. Thicker films (∼400 nm) are fully relaxed at 900 °C and thus decoupled from the substrate. These strain behaviors imply that hybrid ZrB2/Si(111) templates are better matched to GaN than any other known substrate. Comparison of ...

Epitaxial semimetallic HfxZr1−xB2 templates for optoelectronic integration on silicon

High quality heteroepitaxial HfxZr1−xB2 (x=0–1) buffers were grown directly on Si(111). The compositional dependence of the film structure and ab initio elastic constants were used to show that hexagonal HfxZr1−xB2 possess tensile in-plane strain (0.5%) as grown. High quality HfB2 films were also grown on strain compensating ZrB2-buffered Si(111). Initial reflectivity measurements of thick ZrB2 films agree with first principles calculations which predict that the reflectivity of HfB2 increases by 20% relative to ZrB2 in the 2–8eV range. These tunable structural, thermoelastic, and optical properties suggest that HfxZr1−xB2 templates should be suitable for broad integration of III nitrides with Si.

Effect of nitridation on the growth of GaN on ZrB2(0001)∕Si(111) by molecular-beam epitaxy

The effect of nitridation on the epitaxial growth of GaN on lattice-matched ZrB2(0001) films prepared ex situ and in situ was studied using an ultrahigh-vacuum molecular-beam epitaxy (MBE)-scanning probe microscopy system. The growth of GaN was carried out by rf-plasma-assisted MBE, and epitaxy of wurtzite GaN was observed on both ex situ and in situ prepared ZrB2 samples. The polarity was found to be consistently N-polar regardless of the samples, based on the observation of a series of N-polar Ga-rich reconstructions: (3×3), (6×6), and c(6×12). The nitridation of ZrB2 film was conducted by exposing it to active nitrogen and well-ordered hexagonal-BN (h-BN) formation was observed when the annealing temperature was above 900°C. The partially formed BN layer affected neither the epitaxy nor the polarity of GaN, but when the surface was fully covered with well-ordered h-BN, GaN growth did not occur.

Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

We report the measurements of the temperature dependence of the resistivity, \rho(T), magnetic penetration depth,\lambda(T) the lower, Hc1(T), and upper, Hc2(T), critical magnetic fields, for single crystals of dodecaboride ZrB12, diboride ZrB2 and thin films of diboride MgB2. We observe a number of deviations from conventional behavior in these materials. Although ZrB12 behaves like a simple metal in the normal state, the resistive Debye temperature, 300 K, is three times smaller relative to that (800-1200 K) calculated from the specific heat, C(T), data. We observe predominantly quadratic temperature behavior of resistivity in ZrB12 below 25 K, and in ZrB2 below 100 K, indicating the possible importance of the electron-electron interaction in these borides. Superfluid density of ZrB12 displays unconventional temperature dependence with pronounced shoulder at T/Tc equal to 0.65. Contrary to conventional theories we found a linear temperature dependence of Hc2(T) for ZrB12 from Tc down to 0.35 K. We suggest that both \lambda(T) and Hc2(T) dependencies in ZrB12 can be explained by two band BCS model with different superconducting gap and Tc.

Epitaxial growth of group III nitrides on silicon substrates via a reflective lattice-matched zirconium diboride buffer layer

Growth of metallic and reflecting ZrB2 films is conducted on Si(111) substrates at 900 °C using a single-source unimolecular precursor Zr(BH4)4 in a molecular beam epitaxy chamber. Epitaxial growth of ZrB2(0001) is accomplished despite the very large lattice mismatch between ZrB2 and Si(111). High-resolution cross-sectional transmission electron microscopy images of the sharp ZrB2/Si(111) interface show a heteroepitaxial relationship involving a “magic mismatch” of coincidence lattices. The GaN films grown on the ZrB2/Si(111) template is virtually homoepitaxy because of the very small lattice mismatch, 0.6%, between the in-plane lattice parameters of ZrB2(0001) and GaN(0001).

Remote-plasma chemical vapor deposition of conformal ZrB2 films at low temperature: A promising diffusion barrier for ultralarge scale integrated electronics

High-quality ZrB2 thin films have been deposited at substrate temperatures as low as 300 °C by a new method: remote hydrogen-plasma chemical vapor deposition from the single-source precursor Zr(BH4)4. Carrying out the deposition in the presence of atomic hydrogen generates films with properties that are far superior to those deposited by purely thermal methods; the latter are boron-rich, oxidize readily in air, and adhere poorly to the substrates. In contrast, the films generated at a substrate temperature of 300 °C in the presence of atomic H have a B/Zr ratio of 2, a resistivity of 40 μΩ cm, an oxygen content of ⩽4 at. %, and are fully conformal in deep vias. A 20 nm thick amorphous film of ZrB2 on c-Si(001) prevents Cu indiffusion after 30 min at 750 °C. We propose that the beneficial effects of atomic hydrogen can be attributed to promoting the desorption of diborane from the growth surface.

Low temperature growth mechanism of zirconium diboride films synthesised in flowing microwave Ar–BCl3 post-discharges

Zirconium diboride films are synthesised at 460°C by a flowing microwave Ar–BCl3 post-discharge CVD process to coat Zircaloy-4 substrates. As a zirconium tetrachloride flow is of no use to synthesise these films, they are grown by a mechanism which consists of a diffusion step. To identify how this step occurs, characteristics of the films are compared with those that could be expected when three different diffusion processes are considered: boron diffusion, zirconium diffusion and BCl3 diffusion. As the last process requires a high porosity of the film (about 50%) to occur, it cannot be referred to describe the ZrB2 synthesis mechanism. The physico-chemical and structural characteristics of ZrB2 films do not help to distinguish the two processes involving a diffusion step in solid state. Only a profilometric study of the film growth direction has shown that zirconium diffuses into the Zircaloy-4 substrate from the core to the solid–gas interface. This mechanism implies that zirconium tetrachloride is also synthesised at the surface of the film. The influence of this mechanism on the behaviour of the Zircaloy-4 alloying elements has also been analysed. A precise description of the tin behaviour is provided and its consequences on adhesion of ZrB2 films are examined.

Microstructure and properties of nitride and diboride hard coatings deposited under intense mild-energy ion bombardment

The concept of low or mildly energetic but intense ion bombardment was applied to coatings based on the nitrides and diborides of the transition metals titanium and zirconium. Coatings were deposited using non-reactive unbalanced d.c. magnetron sputtering. Films were bombarded by means of argon ions with varying energy (Ei) and intensity (ion/atom flux ratio Ji/Ja). Fracture cross-sections revealed the existence of the transition zone (zone T) structure for all coatings. TiN and ZrN coatings, which are exposed to low energetic bombardment, revealed a preferred growth on (111) lattice planes. Mildly energetic and intense bombardment resulted in a shift of the preferred orientation to (200). TiB2 and ZrB2 films grow more or less randomly under low energetic and less intense bombardment. However, they displayed a preferred (001) orientation with increasing intensity of the ion irradiation. The hardness of the coatings increased by the effect of both mildly energetic and intense ion bombardment, mainly as a result of reduced film porosity and to a lesser extent due to reduced crystal size and increasing film stresses.

Diffusion Barrier Characteristics of Zirconium Diboride Films Grown by Remote Plasma CVD

AbstractLow resistivity and fully conformal ZrB2 thin films are deposited by remote plasma chemical vapor deposition using zirconium tetrahydroborate, Zr(BH4)4. The problems with thermal CVD using this precursor – excess B incorporation, oxygen contamination, and high resistivity – are eliminated by injecting atomic hydrogen from a remote microwave plasma source onto the substrate. Using this technique, the films are stoichiometric, have ∼ 40 μΩ-cm resistivity, < 4 at.% oxygen contamination, and are fully conformal in deep trenches and vias. We show that a 50 nm thick ZrB2 film on c-Si (100) prevents Cu in-diffusion after 1 hour annealing at 650°C.

The behaviour of ZrB x (0 ≤x ≤ 2) thin films deposited on si substrate as a function of annealing treatment

Thin films of ZrB x (0 ≤x ≤ 2) have been deposited on Si substrates by dc magnetron sputtering. The effects of annealing the films have been studied as a function of film composition by sheet resistance measurements, supplemented by Rutherford backscat-tering, Auger electron spectroscopy and x-ray diffraction. Significant departures of film composition from stoichiometric ZrB2 can result in an accompanying Zr-Si reaction cou-ple during annealing treatment which influences the overall film behaviour. These ef-fects are discussed with respect to the possible usefulness of ZrB2 films for VLSI metalli-sation and barrier layer applications.

Optical Properties of Thin Films of Zirconium Diboride

The optical constants of the intermetallic compound ZrB2 were obtained at different angle of incidences over the wavelength range 100–600 nm. These were calculated using a computer code based on the Fresnel equations which solves for n and k from reflectance at two angles of incidence and by the well-known Kramers-Kronig relation. Opaque thin films of about 3000 Å were deposited on quartz substrates employing electron-beam melting technique under a vacuum of 10−7 Torr. The material used was very high-purity ZrB2 powder. Although the samples were exposed to air briefly before measurement, precautions were taken to observe the growth, if any, of an oxide-type layer on the ZrB2 films. No such layer growth was observed. The real and imaginary parts of the dielectric constant, and the energy loss function were calculated from n and k. The significant features of the dispersion curves and the energy loss function are discussed.