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Optical, structural, and electrical properties of thin films in situ grown by activated reactive evaporation
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View: Figures


Image of FIG. 1.
FIG. 1.

(Color online) Schematic representation of the thin film deposition chamber together with the fiber setup to measure in situ the reflection. The film is deposited onto the freshly cleaved fiber surface.

Image of FIG. 2.
FIG. 2.

In situ resistivity measurement for activated reactive evaporation of thin films. Each point in the figure represents another -thick film deposited at the corresponding capillary power (see text). The horizontal line at indicates the resistivity of an ex situ hydrogenated film. Point 1: resistivity of a metallic thin film deposited at . Points 2–7: resistivity at an increasing heating power of the atomic hydrogen source capillary. The resistivity increases from .

Image of FIG. 3.
FIG. 3.

(Color online) Reflectance of Ni, Pd, Mg, Y, and films at an energy of as a function of thickness as measured by a QCM. The beginning of the spectra is characterized by a minimum in reflectance for all the measured elements at a certain thickness. Above a certain thickness the reflectance reaches a constant value and the films become optically closed.

Image of FIG. 4.
FIG. 4.

(Color online) Reflectance as calculated by Eq. (1). The imaginary part of and and the real part of and are shown. It is clear that is constant and negative (this is due to the phase change when reflecting at an interface). is positive and decreases monotonically (as one expects due to the higher absorption in the layer with increasing thickness). The interference of and is destructive for all because the two contributions are out of phase. The destructive interference is obviously largest when has a minimum value.

Image of FIG. 5.
FIG. 5.

(Color online) Reflectance at vs deposited thickness (red curve). The simulated reflectance of a thin film (black curve) and of a thin film (green curve) are also shown. The good agreement between the measured reflectance and simulated reflectance indicates that is synthesized in situ.

Image of FIG. 6.
FIG. 6.

(Color online) Reflection spectrum vs energy for a thin film (red curve). The simulated spectrum of (black curve) indicates that we indeed grow the hydride phase. It is shifted by as compared with the measured spectrum.

Image of FIG. 7.
FIG. 7.

(Color online) Ex situ measured reflection spectrum for an in situ grown thin film without a Pd cap layer (red curve). The spectrum displays a redshift which is also observed in the in situ measured spectrum. The interference pattern of the simulated reflectance is comparable to the interference pattern of the measured reflectance.

Image of FIG. 8.
FIG. 8.

(Color online) Ex situ measured transmission spectrum for an in situ grown thin film without a Pd cap layer (red curve). We observe that the measured transmittance has an optical band gap of and the simulated transmittance has an optical band gap of .

Image of FIG. 9.
FIG. 9.

(Color online) Reflection and transmission spectra at vs hydrogenation time of an as-prepared thin film. At the minimum of the reflectance (blue curve), the transmittance (red curve) is essentially zero, indicating the preferred hydride nucleation at the interface with its maximal absorption.

Image of FIG. 10.
FIG. 10.

(Color online) Reflection and transmission spectra at vs hydrogenation time of a film which was in situ deposited as and then dehydrogenated. At the reflectance minimum (blue curve), the transmittance (red curve) has a finite value of 0.04. This finite value of the transmittance indicates that we can model the layer by a single set of and values during the maximal absorption.

Image of FIG. 11.
FIG. 11.

(Color online) Contour maps of the reflectance and transmittance at for a thin film capped with Pd on quartz. The crossing of the contour plot for transmittance at and the reflectance at (which correspond to the values for a film in the black state) indicates that optically the film can be modeled as a homogeneous layer.

Image of FIG. 12.
FIG. 12.

(Color online) AFM measurements on (a) a thin film covered by of Pd and (b) a thin film prepared by activated reactive deposition.

Image of FIG. 13.
FIG. 13.

(Color online) (a) SEM image of the cross section of an as-deposited . The film shows a clear columnar structure. (b) SEM cross-sectional image of a thin film prepared by activated reactive deposition. The surface of the film is very flat as compared to the film.

Image of FIG. 14.
FIG. 14.

(Color online) Reflectance at as a function of deposited Pd thickness on an in situ grown hydride film. Simulation of the reflectance of a film capped with Pd and capped with are shown together with a metallic film. The developing interference pattern indicates the unloading of the film with the metallic phase forming from the Pd surface downwards. The simulations with Pd and indicates that the film really unloads and that the change in reflectance is not due to the deposited Pd cap layer.

Image of FIG. 15.
FIG. 15.

(Color online) Reflection spectra at during the loading/unloading process at room temperature of an in situ grown thin film. Point 1: Start of the rehydrogenation at of an in situ prepared film which was unloaded after it was capped with Pd. Point 2: Indicating the reduced minimum in reflection. Point 3: Start to unload the thin films in air. Point 4: Start of a rehydrogenation but now at . Point 5: Again the reduced minimum in reflection is observed.

Image of FIG. 16.
FIG. 16.

(Color online) Reflectance at of a postdeposition hydrogen absorption/desorption cycle of an in situ grown thin film capped with Pd. Point 1: Unloaded phase. Point 2: Reduced interference minimum. Point 3: Hydrogen desorption in vacuum. Point 4: Applied atmospherical air environment. The exposure to an air environment catalyzes the dehydrogenation tremendously.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Optical, structural, and electrical properties of Mg2NiH4 thin films in situ grown by activated reactive evaporation