Energetic condensation growth of Nb thin films

Abstract

This paper describes energetic condensation growth of Nb films using a cathodic arc plasma, whose 60-120 eV ions penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. Heteroepitaxial films of Nb were grown on a-plane sapphire and MgO crystals with good superconducting properties and crystal size (10 mm  20 mm) limited only by substrate size. The substrates were heated to temperatures of up to 700 C and coated at 125 C, 300 C, 500 C, and 700 C. Film thickness was varied from $0:25 m to >3 m. Residual resistivity ratio (hRRRi) values (up to a record hRRRi ¼ 587 on MgO and hRRRi ¼ 328 on a-sapphire) depend strongly on substrate annealing and deposition temperatures. X-ray diffraction spectra and pole figures reveal that RRR increases as the crystal structure of the Nb film becomes more ordered, consistent with fewer defects and, hence, longer electron mean-free path. A transition from Nb(110) to Nb(100) orientation on the MgO(100) lattice occurs at higher temperatures. This transition is discussed in light of substrate heating and energetic condensation physics. Electron backscattered diffraction and scanning electron microscope images complement the XRD data.

A review comparing cathodic arcs and high power impulse magnetron sputtering (HiPIMS)

“…In case of cathodic arc deposition of pure metal coatings (e.g. [6]), one can avoid using process gas and thus deals with vacuum arc plasmas, which usually have higher average ion energies than ions in HiPIMS plasmas. HiPIMS can also be done in vacuum but only in exceptional cases, namely when the sputter yield is very high [157,252] and a means of discharge start is provided.…”

“…[6], known as vacuum arcs [88,91]; most measurements of charge states and ion Unusual but possible for materials of very high selfsputter yields [157,158,252].…”

“…Film synthesis from the plasma phase is sometimes called energetic condensation [1][2][3][4][5][6][7][8] or energetic deposition [9][10][11][12][13] -generally with the same meaning (and here interchangeably used), namely that plasma ions produce a film or coating, with each ion bringing significant kinetic and potential energies to the film growth process. The range of kinetic particle energies includes tens or even hundreds of electron-volts, which often exceed the displacement energy of atoms near the surface.…”

Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications

“…A collaboration led by JLab has been characterizing Nb film growth on a variety of model substrates as a function of substrate preparation and energy of arriving Nb ions [96][97][98][99][100][101][102][103][104][105]. The methods of creating the energetic ions vary from ECR plasma biased extraction, to cathodic arc discharge plasma, to high power impulse magnetron sputtering (HiPIMS) [106] championed by Andre Anders of LBNL.…”

Superconducting cavity material for the European XFEL

“…Niobium is chemically inert (at room temperature, the surface is covered by a protecting pentoxide layer), it can be easily machined and deep drawn, and it is available on the market, in the required amounts, in bulk and sheet material forms. Though the options, competing with bulk niobium, demonstrated evident progress in the last years (for example Nb 3 Sn [6], energetic thin films deposition [7,8], multilayers [9,10]), nevertheless they still cannot be considered as a mature technique for a series cavity production. Therefore, the most of the next accelerator projects (e.g.…”