Charles M. Falco

Thermalization of sputtered atoms

We have calculated the energy distributions of sputtered Nb and Cu atoms ejected from amorphous targets under low‐energy Ar bombardment. A formula based on elementary kinetic gas theory is used to calculate the subsequent energy loss of the ejected atoms due to collisions in the sputtering gas. The energy distributions of the sputtered atoms arriving at the substrate is compared with the distributions obtained using thermal evaporation techniques. This comparison indicates that the preparation of epitaxial metallic films, such as Layered Ultrathin Coherent Structures using sputtering techniques may have fundamental advantages over thermal evaporation.

Superconductivity of Nb/Cu superlattices

Abstract The superconducting transition temperature T c of Nb/Cu superlattices has been investigated as a function of layer thickness. The dependence of T c above 300 A layer thickness agrees well with proximity effect theory with no adjustable parameters. Below 300 A, the data in conjunction with current proximity theory shows that T c of Nb decreases with layer thickness. This is interpreted as changes in the electronic density of states due to a decrease in the mean-free path.

The magnetization and Curie temperature of compositionally modulated Cu/Ni films

We report detailed measurements of the magnetization of Cu/Ni composition modulated foils as a function of temperature, magnetic field, composition wavelength, and composition amplitude. We find a Curie temperature that initially increases rapidly with wavelength but quickly saturates. We also find that the Curie temperature is independent of composition amplitude which we ascribe to the existence of disk‐like Ni clusters.

Structure and physical properties of sputtered metallic superlattices

Abstract The technique of preparing metallic superlattices by sputtering is described as are the results of a calculation of the energy distribution of sputtered atoms. Structural studies by X-ray diffraction, Ion Mill Auger Electron Spectroscopy and Ion Mill Ion Scattering Spectroscopy all indicate well defined layer structure for the Nb/Cu system. The resistivity of Nb/Cu and Nb/Ti and the superconductivity of Nb/Cu are all found to be dependent upon the layered nature of the material.

Superconducting and transport properties of NbTi layered metals

Abstract We report data on the superconducting transition temperature and room temperature resistivity of layered NbTi for thicknesses in the range 7 – 70 A.

Magnetism of iron atoms in superconducting Sc2Fe3Si5

Abstract Mossbauer effect measurements on the ternary superconductor Sc 2 Fe 3 Si 5 in an applied magnetic field show that the magnetic moment on both the iron sites is less than 0.03 μ B .

Superconductivity and magnetism in the series R2Fe3Si5 by Mössbauer and magnetization measurements

Members of the R2Fe3Si5 series become either superconducting or magnetically ordered depending on whether the metal atom R( = rare earth, Y or Sc) is diamagnetic or paramagnetic respectively. We have taken Mossbauer effect and magnetization measurements to determine the magnetic state of the iron and the nature of the superconducting electrons. 57Fe Mossbauer measurements on the Sc, Dy and Er compounds all showed two partially resolved, quadrupole split spectra at all temperatures from 300 K to 1.5 K, indicating that there is no resolvable magnetic interaction at the iron site. No major change in the spectrum of Dy2Fe3Si5 was observed in passing through its antiferromagnetic ordering temperature of ∼4 K. Measurements in an applied field of 5.6 T set an upper limit of 0.03 μB for the iron moment in Sc2Fe3Si5. However, measurements at 4.2 K in fields up to 7 T for the Dy compound gave an internal field ∼9% smaller than the applied field and linear with applied field. This corresponds to an induced moment at the iron site of ∼0.07 μB at 7 T applied field. The 161Dy Mossbauer resonance clearly showed the onset of magnetic order around 4 K and the magnetic moment Dy at 1.5 K was found to be 7.0±0.2 μB consistent with the magnetization measurements. The nature of the superconducting electrons in the R2Fe3Si5 series is discussed in the light of available measurements.

Thermally induced magnetic flux in a superconducting ring

Abstract The thermally induced magnetic flux in a bi-metallic superconducting loop of Nb and Ta has been measured and compared with theory. The predicted logarithmic divergence of the flux near the T c of Ta is found, however the magnitude of the flux is larger than predicted.

Invited Article: High resolution digital camera for infrared reflectography

This paper describes the characteristics of a high resolution infrared (IR) imaging system operating over the wavelength range of 830-1100 nm, based on a modified 8 Mpixels commercial digital camera, with which nonspecialists can obtain IR reflectograms of works of art in situ in a museum environment. The relevant imaging properties of sensitivity, resolution, noise, and contrast are characterized and the capabilities of this system are illustrated with an example that has revealed important new information about the working practices of a 16th century artist.

Transport properties of the compositionally modulation alloy Cu/Ni

We report preliminary transport measurements; electrical resistivity, thermopower, Hall effect and mangetoresistance, of a number of Cu/Ni composition modulated alloy films over the temperature range 10–300 °K and for magnetic field up to 70 kGauss.The results indicate non‐monotonic dependence of the transport properties on the modulation amplitude. The Hall coefficient saturates around 40 kGauss in contrast to the transverse magnetoresistance which does not show evidence for saturation up to 70 kGauss.