A. E. Curzon

X-ray and electron microscopy studies of single-layer TaS2 and NbS2

Abstract Single-molecular-layer suspensions and various restacked forms of the metallic layered compounds TaS 2 and NbS 2 were prepared using the intercalation of hydrogen and water. It was found that the intercalation of water separates the layers by at least 10nm and single-layer X-ray diffraction patterns with only ( hk .0) lines are observed for this system. Single layers in suspension are readily made from the water-intercalated material. Restacked films obtained from dried suspensions appear to have a random layer stacking sequence. Electron microscopy shows evidence of single layers up to 200 nm in lateral size in the suspension. The charge density wave superlattice diffraction pattern which is observed in bulk crystalline TaS 2 below 75 K is not observed in thin platelets obtained from TaS 2 suspensions.

Charge density wave commensurability in 2H-TaS2 and AgxTaS2

Abstract The charge density wave transition in 2H-TaS2near 75 K has been observed to be incommensurate, using electron diffraction, with q ∗ = ( 0.338 ± 0.002 )a ∗ 0 along the 〈10.0〉 directions which, within the experimental uncertainty, remains temperature independent to about 14 K. Incommensurate charge density formation is also observed in AgxTaS2 samples for x⪷ 0.26 with an increase in q∗ to ( 0.347 ± 0.002 )a ∗ 0 when x≅0.26. Within the experimental error q∗ appears to be temperature independent to 25 K.

A simple method for the determination of film thickness from electron image contrast in a scanning electron microscope

Abstract A simple rapid method is described for measuring the thickness of a film on a substrate. The method uses contrast ratios measured with a standard backscatter detector in a scanning electron microscope.

Growth and characterization of BiSrCaCuO whiskers

Abstract Superconducting whiskers grown from BiSrCaCuO powders during a sintering process have been studied as a function of the starting mixture and sintering cycles. Experiments using X-ray diffraction, electron diffraction, EDX, HREM, magnetization and resistance were used to investigate the composition, structure and superconducting properties of these whiskers. They are found to be very homogeneous, free of stacking faults and exfoliations. They also show a full Meissner effect. Under proper conditions layers of the 2223 phase appear to be intercalated in the predominant 2212 phase.

Film thickness and composition determination for binary alloys using backscattered electrons

Abstract A method has been developed to measure the composition and thickness of thin films of binary alloys. It makes use of a scanning electron microscope operating with a Robinson detector for backscattered electrons. The electron-image contrast between a given film and an adjacent uncoated reference substrate depends on the energy of the incident electron beam. This dependence has been measured. Electron beams with low energy were used to determine composition, while higher beam energies were used to penetrate the film, the onset of this penetration being related to the film thickness. In order to test the method, the binary copper-tungsten system was investigated. Atomic composition ratios of the films were determined to within ±5% for films of mass thickness greater than 0.040 mg cm −2 . The thickness could be determined to within ±3% by using a calibration curve.

The use of electron image contrast to measure the thickness and composition of thin films of light binary alloys

Abstract A backscattered electron image detector has been used in a scanning electron microscope to study simultaneously the image intensity If of thin sputtered films of copper-aluminium alloys on single-crystal silicon substrates and the image intensity Ir of an adjacent, bulk copper reference specimen. The contrast ratio k = If/Ir for a given film and the reference sample depends on the energy E of the incident electrons. A graph of k vs. 1/E is used to obtain a characteristic energy Ei called the intercept energy which, in agreement with previous work, depends on the thickness of the film but not on its composition. Another feature of a curve of k vs. 1 E is that k tends to a limit as 1/E increases. This limit depends on the composition of the film to which the curve applies, and thus both thickness and composition can be obtained from a given curve. The present results which cover the low range of atomic numbers (Z = 13−29) are compared with the results obtained for Cu-W films which cover the atomic number range from Z = 29 to Z = 74. It is confirmed that the thicknesses of the light Cu-Al alloys studied in the present experiments and of Cu-W films can be obtained from a single curve of ln(thickness) vs. ln(Ei) and therefore that the method of using electron image contrast to measure thickness is applicable over a wide range of atomic numbers.

A double Faraday cup attachment for relative intensity measurements on an electron microscope

A double Faraday cup attachment has been made for a Philips EM300 electron microscope in order to measure the relative intensities of diffracted beams simultaneously. Preliminary data showing the order-disorder phase transition of silver intercalated into a TaS2 crystal are given.

The attainment of a substrate temperature of 25K in a Philips FM 300 electron microscope

A description is given of how to convert a standard low-temperature specimen rod of a Philips EM 300 electron microscope into a continuous-flow device capable of reaching 25K when liquid helium is used as a refrigerant. The specimen exchange facility is retained. The temperature can be held steady for minutes at a time to 1 or 2K in the range between 25K and room temperature.

A liquid helium stage for the Philips EM 300 electron microscope

A liquid helium stage for the Philips EM 300 electron microscope is described. The stage, which makes use of an external reservoir for liquid helium, enables a temperature of less than 9 K to be obtained at the specimen. The 31/2 1 of liquid helium used to fill the reservoir is sufficient for about 21/2 h of low-temperature operation.

A closed expression for beam heating of thin films

Abstract When an electron beam passes through a thin film, it causes the temperature to rise. A simple expression is developed for the temperature rise which occurs at the centre of a circular beam incident on a square thin film whose edges are thermally anchored. Heat loss is assumed to occur by thermal conduction. The axis of the beam may be incident at any point of the film (not only the centre) but the beam should not strike any of the supporting grid bars. A calculation accuracy of less than 1% can be obtained with the use of three coefficients and this can be improved further by the use of additional coefficients which are tabulated.