Ti-based Films Research Articles

Topological Insulator Films for Terahertz Photonics.

We discuss experimental and theoretical studies of the generation of the third terahertz (THz) frequency harmonic in thin films of Bi2Se3 and Bi2-xSbxTe3-ySey (BSTS) topological insulators (TIs) and the generation of THz radiation in photoconductive antennas based on the TI films. The experimental results, supported by the developed kinetic theory of third harmonic generation, show that the frequency conversion in TIs is highly efficient because of the linear energy spectrum of the surface carriers and fast energy dissipation. In particular, the dependence of the third harmonic field on the pump field remains cubic up to the pump fields of 100 kV/cm. The generation of THz radiation in TI-based antennas is obtained and described for the pump, with the energy of photons corresponding to the electron transitions to higher conduction bands. Our findings open up possibilities for advancing TI-based films into THz photonics as efficient THz wave generators and frequency converters.

Growth and characterization of Ti-based films obtained from two selected precursors: H2O, TiCl4, Ti(N(CH3)2)4 or Al2(CH3)6 by the ALD method

Ti-based films are extensively studied as a prospective material for several applications - for UV-protection, antibacterial coating and effective photocatalytic activity. This is because Ti-based TiO2 shows relatively high reactivity and chemical stability under ultraviolet light (λ < 387 nm), whose energy exceeds the band gap (in the range 3–4 eV) of the anatase crystalline phase. However, the efforts are focused on development of photocatalytic materials exhibiting high reactivity under visible light (λ > 400 nm). Such materials should utilize the main part of the solar spectrum, and if efficient, they should work even under poor illumination, for example upon interior lighting. In this work, we concentrated on optimization of Ti-based films. Films with different chemical compositions were deposited using the atomic layer deposition (ALD) method. These films were prepared using chemical reactions between listed precursors: H2O, TiCl4, Ti(N(CH3)2)4 and Al2(CH3)6. The selection of precursors and, consequently, the modification of the ALD Ti-based process allowed the deposition of thin films with quite different structural, optical and electrical properties.

Alloying effects on the microstructure and mechanical properties of nanocrystalline Ti-based alloyed thin films

Ti-based films alloyed with various Ta or Zr contents were deposited on a Si (100) substrate by magnetron sputtering. Transmission electron microscopy observations suggested that the solute Ta and Zr atoms distributed uniformly in the matrix Ti, refining the grain size. The microstructure transformed from single phase α-Ti to the coexistence of (α + β)-Ti when the Ta addition was increased to 18.2 at%. Hardness and strain rate sensitivity of the Ti-based alloyed films were evaluated by nanoindentation experiments, to show the effects of constituents and their contents. The hardness was found to change non-monotonously within the studied Ta or Zr range, which could be explained by alloying dependence of the strengthening mechanisms, including partial dislocation mechanism emanating from grain boundaries, solid solution strengthening, and solution pinning strengthening. Furthermore, a mechanistic model based on partial dislocation inhomogeneous nucleation was employed to describe the composition-dependent strain rate sensitivity of the alloyed Ti films.

TI-Based Superconducting Films Prepared by Spray Pyrolysis and Vacuum Evaporation

TI-based films were prepared by the 2-step procedure. First, Ba-Ca-Cu-O precursors were deposited either from an aerosol or by thermal evaporation on MgO substrates. Thallination of precursors was then performed at 850 °C in flowing oxygen with annealing time up to 30 min. Films were characterized by Tc and X-ray measurements, and their depth profiles (RBS), surface morphology (SEM) and oxygen Raman modes were also investigated. The aerosol deposited films gave Tc = 94−103.5 K. Films grown by thermal evaporation revealed unusual Tc and structural changes during their 20-months storage in laboratory surroundings. Their Tc has increased from 94 to 106 K.

Formation of high temperature phases in sputter deposited Ti-based films below 100 °C

This article reports on the sputtering of pure Ti and Ti-based alloy films onto substrates where the temperature Ts was kept below 100 °C, using the magnetron sputter ion plating process. It was found that while the pure Ti film is a hexagonal low-temperature phase film (h–αTi), the Ti–Cr, and Ti–Fe alloy films, containing a relatively small amount of Cr or Fe of about 10 wt %, are cubic high-temperature beta phase Ti alloy films [c-βTi(Cr) or c-βTi(Fe)]. This finding is of immense importance both scientifically and practically. The conditions under which high-temperature phases are formed in alloy films sputtered at substrate temperatures below 100 °C, which is much lower than the temperature necessary to form these high-temperature phases (Thtp) according to the equilibrium phase diagram, will be discussed in detail. X-ray diffraction analyses of these films will also be presented.

Production of Ti films with controlled texture

This paper investigates the effects of (i) the substrate bias; (ii) the mixing of one or several additional elements with Ti; (iii) plasma nitriding of the presputtered film; and (iv) the film deposition rate on the structural properties of pure Ti and Ti-based films. The Ti-based films investigated were: Ti−SS (stainless steel), Ti−6A1-4V, Ti−Cu and Ti−Cr. The films were sputtered onto steel and glass substrates using a d.c. magnetron. The negative substrate bias Us used in the magnetron sputter ion plating process varied over a very wide range from 0 to −1500 V. The structural properties of the films were characterized by means of X-ray diffraction. Dramatic differences in the development of the crystal orientation with increasing negative bias for pure Ti and Ti-based films were found. While the pure Ti films were polycrystalline for all values of Us, the Ti-based films were formed not only as polycrystalline but also as amorphous or nanocrystalline substances, characterized by very broad (FWHM up to 10°) reflection lines with very low intensities. The formation of nanocrystalline films is strongly dependent on the type and quantity of additional elements with Ti. Additionally, it was found that at a certain threshold value of the deposition rate the preferred orientation of pure Ti film switches from (002) to (010). This abrupt change in the film texture shows that there is a physical constraint on the maximum deposition rate if the resultant films are to have the same structural properties.

Production of Ti films with controlled texture

This paper investigates the effects of (i) the substrate bias; (ii) the mixing of one or several additional elements with Ti; (iii) plasma nitriding of the presputtered film; and (iv) the film deposition rate on the structural properties of pure Ti and Ti-based films. The Ti-based films investigated were: Ti−SS (stainless steel), Ti−6A1-4V, Ti−Cu and Ti−Cr. The films were sputtered onto steel and glass substrates using a d.c. magnetron. The negative substrate bias U s used in the magnetron sputter ion plating process varied over a very wide range from 0 to −1500 V. The structural properties of the films were characterized by means of X-ray diffraction. Dramatic differences in the development of the crystal orientation with increasing negative bias for pure Ti and Ti-based films were found. While the pure Ti films were polycrystalline for all values of Us, the Ti-based films were formed not only as polycrystalline but also as amorphous or nanocrystalline substances, characterized by very broad (FWHM up to 10°) reflection lines with very low intensities. The formation of nanocrystalline films is strongly dependent on the type and quantity of additional elements with Ti. Additionally, it was found that at a certain threshold value of the deposition rate the preferred orientation of pure Ti film switches from (002) to (010). This abrupt change in the film texture shows that there is a physical constraint on the maximum deposition rate if the resultant films are to have the same structural properties.