Engineering topics

Phillips, Harry

Publications and source records attributed to Phillips, Harry.

4 records

DOE OSTI2012

Structural Characterization of Nb Films Deposited by ECR Plasma Energetic Deposition on Crystalline Insulators

An energetic condensation thin film coating technique with an electron cyclotron resonance (ECR) induced plasma ion source is used to deposit Nb thin films on crystalline insulating substrates, such as a-plane and c-plane sapphire (Al2O3) and on magnesium oxide, MgO (100), (110) and (111). Heteroepitaxial Nb films were produced by ECR deposition with regulated substrate temperature. The residual resistance ratio (RRR) of about 1 micron thick films reach unprecedented values (350 - 450) on (11-20) sapphire substrates. The epitaxial relationship of Nb/crystalline substrate is found to be strongly influenced by the substrate bias voltage (adding to the initial Nb+ kinetic energy), the substrate crystalline orientation, and heating conditions. At low substrate temperature, the Nb films demonstrated non-epitaxial crystalline textures, revealed by XRD Pole Figure technique and Electron Backscattering Diffraction (EBSD). The texture might be caused by ?Volmer-Weber? growth mode, i.e. island growth, at low surface adatom mobility. This study shows that the film?s crystal structural character has great impact on its RRR/Tc value, which in turn is related to the electron-mean-free-path of radio-frequency superconductivity. The knowledge learned from this research sheds some light on how to coat low-defect density Nb thin films on SRF cavity-preferred metallic substrates, such as Cu.

Zhao, X.↗

DOE OSTI2012

RF SURFACE IMPEDANCE OF MgB2 THIN FILMS AT 7.5 GHz

The Surface Impedance Characterization (SIC) system in Jefferson Lab can presently make direct calorimetric RF surface impedance measurements on the central 0.8 cm2 area of 5 cm diameter disk samples from 2 to 20 K exposed to RF magnetic fields up to 14 mT at 7.5 GHz. MgB2 thin films from STI/LANL were deposited on 5 cm diameter Nb disks using reactive evaporation technique. We will report the results of measurements on these samples using the SIC system. The data will be interpreted based on BCS theory as the temperature-dependant properties suggest evaluation of the Tc, energy gap, penetration depth, mean free path and coherence length.

Phillips, Harry↗

DOE OSTI2012

SRF MULTILAYER STRUCTURES BASED ON NBTIN

For the past three decades, bulk niobium has been the material of choice for SRF cavities applications. In the recent years, RF cavities performances have approached the theoretical limit for bulk niobium. For further improvement of RF cavity performance for future accelerator projects, an interesting alternative has been recently proposed by Alex Gurevich with the Superconductor-Insulator-Superconductor multilayer approach, using the benefit of the higher critical field Hc2 of higher-Tc superconductors without being limited with their lower Hc1. JLab is pursuing this approach with the development of multilayer structures based on NbTiN via magnetron sputtering and High Power Impulse Magnetron Sputtering (HiPIMS). Insulators such as, AlN, Al2O3 and MgO are being investigated as candidates for the insulator layers. This paper present the preliminary results on the characteristics of NbTiN and insulator layers and a first attempt of a NbTiN-based multilayer structure on bulk Nb and thick Nb films.

Valente, Anne-Marie↗

DOE OSTI2012

Structural Properties of Niobium Thin Films Deposited on Metallic Substrates by ECR

Particle accelerator technologies rely on SRF cavities to create the accelerating gradient for beam lines. Solid niobium cavities are widely employed throughout the community despite high material, fabrication, and operation cost. New thin film technologies are being explored for the suitability of niobium coatings for accelerating cavities. Thin layers of high-quality niobium would be deposited on a base material that has lower material and fabrication cost. Copper is a strong candidate for the cavity base due to availability, cost, machinability, and potentially improved performance characteristics of the niobium SRF surface. Initial results of TEM, EBSD and XRD analyses of niobium thin films grown on copper substrates under controlled conditions are presented to demonstrate the feasibility of the technology and establish lower limits of performance characteristics. Correlation of RRR data with the structure of niobium thin films will demonstrate the importance of thin film structural quality. *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

Spradlin, Joshua↗