By controlling the timing and duration of hydrogen exposure in a fixed thermal process, we tuned the diameters of carbon nanotubes (CNTs) within a vertically aligned film by a factor of 2, and tuned the areal densities by an order of magnitude. The CNT structure is correlated with the catalyst morphology, suggesting that while chemical reduction of the catalyst layer is required for growth, prolonged H2 exposure not only reduces the iron oxide and enables agglomeration of the Fe film, but also leads to catalyst coarsening. Control of this coarsening process allows tuning of CNT characteristics.

We report on the growth and properties of nanocrystalline silicon:H films deposited using plasma discharge at 45MHz under varying pressure regimes from 50 to 500mTorr. X-ray diffraction data revealed that the primary orientation in these films was ⟨111⟩. The amount of hydrogen dilution needed to crystallize the films was found to be a strong function of deposition pressure, with a significantly higher hydrogen dilution needed to crystallize films at higher pressures. Langmuir probe data showed that these results could be attributed to the increase in density of low-energy hydrogen ions impinging on the substrate at lower pressures.

The evolution of mechanical stress during Volmer-Weber growth of thin films is complex, often including a reversible stress evolution during interruptions of film deposition. The underlying mechanism for stress evolution during growth interruptions has been extensively debated, but remains unclear. In this work, in situ measurements of stress evolution during growth interruptions of various time scales, film thicknesses, and substrate temperatures were made during deposition of gold and nickel films. It was found that at least two mechanisms lead to the observed stress evolution, one fast (time constant ∼102 s) and one slow (time constant ∼104 s). The fast process is reversible and weakly dependent on the film thickness, while the slow process is irreversible and strongly dependent on the film thickness. It is shown that grain growth during growth interruptions can account for a significant portion of the stress change associated with the slow process. The fast reversible process is likely to be associated with reversible changes of the surface structure.

A component of the compressive stress that develops during deposition of polycrystalline thin films reversibly changes during interruptions of growth. The mechanism responsible for this phenomenon has been the subject of much recent speculation and experimental work. In this Letter, we have varied the inplane grain size of columnar polycrystalline gold films with a fixed thickness, by varying their thermal history. Without a vacuum break, the stress in these films was then measured in situ during growth and during interruptions in growth. Homoepitaxial gold films were similarly characterized as part of this study. The inverse of the in-plane grain size and the corresponding reversible stress change were found to be proportional, with zero reversible stress change observed for infinite grain size (homoepitaxial films). These results demonstrate a clear role of grain size in the reversible changes in gold films.

The system Gd 5 (Si x Ge 1−x ) 4 for 0.4⩽x⩽0.5 has been shown to have an unusual first order, coupled magnetic-structural phase transformation at the Curie temperature. Above the transformation temperature T c , the material is paramagnetic with a monoclinic structure; below T c , it is ferromagnetic with an orthorhombic structure. Another unusual feature of this phase transformation is that an applied magnetic field can increase T c by 5 K per tesla. In this study, the magnetic-structural transformation in single crystalGd 5 Si 2 Ge 2 was triggered by holding the sample at a temperature just above T c , then using an applied field to increase T c beyond the sample temperature, thereby inducing the magnetic-structural transformation. The dynamics of this field-induced phase transformation at various temperatures just above T c were observed by measuring the magnetization as a function of time. This magnetization change is caused by the first order phase transformation which is distinctly different from the magnetization reversal which one observes in conventional magnetic relaxation experiments. The transformation could be modeled as a thermal activation process with a single energy barrier of height4.2±0.2 eV. The system Gd 5 (Si x Ge 1Ϫx ) 4 for 0.4рxр0.5 has been shown to have an unusual first order, coupled magnetic-structural phase transformation at the Curie temperature. Above the transformation temperature T c , the material is paramagnetic with a monoclinic structure; below T c , it is ferromagnetic with an orthorhombic structure. Another unusual feature of this phase transformation is that an applied magnetic field can increase T c by 5 K per tesla. In this study, the magnetic-structural transformation in single crystal Gd 5 Si 2 Ge 2 was triggered by holding the sample at a temperature just above T c , then using an applied field to increase T c beyond the sample temperature, thereby inducing the magnetic-structural transformation. The dynamics of this field-induced phase transformation at various temperatures just above T c were observed by measuring the magnetization as a function of time. This magnetization change is caused by the first order phase transformation which is distinctly different from the magnetization reversal which one observes in conventional magnetic relaxation experiments. The transformation could be modeled as a thermal activation process with a single energy barrier of height 4.2Ϯ0.2 eV. Keywords