Carol M. Garland

Amorphous (Mo, Ta, or W)-Si-N diffusion barriers for Al metallizations

M–Si–N and M–Si (M=Mo, Ta, or W) thin films, reactively sputtered from M5Si3 and WSi2 targets, are examined as diffusion barriers for aluminum metallizations of silicon. Methods of analysis include electrical tests of shallow-junction diodes, 4He + + backscattering spectrometry, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and secondary-ion-mass spectrometry. At the proper compositions, the M–Si–N films prevent Al overlayers from electrically degrading shallow-junction diodes after 10 min anneals above the melting point of aluminum. Secondary-ion-mass spectrometry indicates virtually no diffusivity of Al into the M–Si–N films during a 700 °C/10 h treatment. The stability can be partially attributed to a self-sealing 3-nm-thick AlN layer that grows at the M–Si–N/Al interface, as seen by transmission electron microscopy.

Microstructure of polycrystalline CuInSe2/Cd(Zn)S heterojunction solar cells

Abstract Polycrystalline CuInSe 2 /Cd(Zn)S heterojunction solar cells deposited on Corning 7059 or soda-lime glass are characterized structurally and chemically by scanning electron microscopy and transmission electron microscopy in conjunction with energy-dispersive analysis of X-rays. Scanning electron micrographs reveal rough and uneven surfaces and cross-sectional morphologies of the Cd(Zn)S and CuInSe 2 layers. The crystallography and defect structure of the individual Cd(Zn)S, CuInSe 2 and molybdenum layers are examined by conventional and high resolution transmission electron microscopy. The crystal structures for Cd(Zn)S, CuInSe 2 and molybdenum are wurtzite, chalcopyrite and b.c.c. respectively. The Cd(Zn)S layer exhibits stacking faults on hexagonal basal planes. Planar defects such as twins and stacking faults on {112} chalcopyrite planes are identified in the CuInSe 2 layer. The most significant features obtained from these cross-sections are (i) the lateral non-uniformity of the Cd(Zn)S and CuInSe 2 layers, (ii) the intimate bonding between these two layers, and an epitaxial relationship between grains of Cd(Zn)S and CuInSe 2 at the interface ({0001} Cd(Zn)S ∥ {112} CuInSe 2 ), and (iii) the presence of voids and fractures in the CuInSe 2 layer. A correlation between the formation of fractures and voids and the defect structure in CuInSe 2 layer, and the mechanical stresses induced by differential thermal contraction of the substrate/film assembly is discussed.

Unusual decrease in conductivity upon hydration in acceptor doped, microcrystalline ceria

The impact of hydration on the transport properties of microcrystalline Sm(0.15)Ce(0.85)O(1.925) has been examined. Dense, polycrystalline samples were obtained by conventional ceramic processing and the grain boundary regions were found, by high resolution transmission electron microscopy, to be free of impurity phases. Impedance spectroscopy measurements were performed over the temperature range 250 to 650 °C under dry, H(2)O-saturated, and D(2)O-saturated synthetic air; and over the temperature range 575 to 650 °C under H(2)-H(2)O atmospheres. Under oxidizing conditions humidification by either H(2)O or D(2)O caused a substantial increase in the grain boundary resistivity, while leaving the bulk (or grain interior) properties unchanged. This unusual behavior, which was found to be both reversible and reproducible, is interpreted in terms of the space-charge model, which adequately explains all the features of the measured data. It is found that the space-charge potential increases by 5-7 mV under humidification, in turn, exacerbating oxygen vacancy depletion in the space-charge regions and leading to the observed reduction in grain boundary conductivity. It is proposed that the heightened space-charge potential reflects a change in the relative energetics of vacancy creation in the bulk and at the grain boundary interfaces as a result of water uptake into the grain boundary core. Negligible bulk water uptake is detected under both oxidizing and reducing conditions.

Reaction of thin Ni films with (001) 3C-SiC at 700°C

Abstract The reaction layer of a thermally reacted thin Ni film, deposited by electron-beam evaporation on a single crystalline (001) 3CSiC substrate, was investigated after vacuum annealing at 700°C in terms of its morphology and structure by cross-sectional transmission electron microscopy (TEM). Ni2Si and carbon are identified as reaction products. Distinctive dissimilarities with depth in the morphology of the reacted layer are observed. Carbon appears to form isolated clusters in the upper part of the Ni2Si layer and microcolumns in the lower part.

Manipulating the ABCs of self-assembly via low-χ block polymer design

Significance Molecular sequence and interactions dictate the mesoscale structure of all self-assembling soft materials. Block polymers harness this relationship to access a rich variety of nanostructured materials but typically require energetically unfavorable (high-χ) interactions between blocks. Contrary to this convention, we demonstrate that ABC triblock terpolymers featuring low-χ interactions between end blocks can self-assemble into a unique mixed morphology that subverts the demands of chain connectivity. As a consequence of block–block mixing, the characteristic length scales of these self-assembled structures exhibit an unusual trend: As the total polymer size increases, the domain spacing decreases. These developments expand the vocabulary of block polymer design and open additional avenues for manipulating the self-assembly of synthetic macromolecules. Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χij). In this article, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χAC ≲ 0), promotes organization into a unique mixed-domain lamellar morphology, which we designate LAMP. Transmission electron microscopy indicates that LAMP exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM3) with ABCB periods. Complementary small-angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations and predicts that LAMP is thermodynamically stable below a critical χAC, above which LAM3 emerges. Both experiments and theory expose close analogies to ABA′ triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. These conclusions provide fresh opportunities for block polymer design with potential consequences spanning all self-assembling soft materials.

Epitaxial growth of GaAs by solid‐phase transport

(100) GaAs substrates with an Ag film about 45 nm thick were first annealed at 550 °C for 30 min in an Ar‐flowing furnace (preannealing). A 110‐nm‐thick GaAs layer was then deposited on top of the preannealed 〈GaAs〉/Ag samples, followed by an amorphous Ta‐Si‐N film that was deposited over the GaAs layer to serve as a cap layer to minimize the loss of As during the following annealing process. The completed structures were then annealed again at 550 °C for 30 min in flowing Ar. The transport of Ga and As through the Ag layer and an epitaxial growth of GaAs on top of the (100) GaAs substrate are observed by cross‐sectional transmission electron microscopy and MeV 4He backscattering spectrometry. No GaAs epitaxial growth is observed in samples that are not preannealed. Our results demonstrate that epigrowth through a solid transport medium is possible for a III‐V semiconductor as it is for Si and Ge.