M. D’Olieslaeger

Disclosure of the nanostructure of MDMO-PPV:PCBM bulk hetero-junction organic solar cells by a combination of SPM and TEM

Abstract The microstructure of MDMO-PPV:PCBM blends as used in bulk hetero-junction organic solar cells is studied by atomic force microscopy (AFM) to image the surface morphology and by means of transmission electron microscopy (TEM) to disclose the bulk nanostructure of the film. Typical thin films, as used for state-of-the-art organic bulk hetero-junction solar cells consist of a 1:4 ratio by weight of MDMO-PPV as electron donating polymer and PCBM, a soluble electron accepting C 60 derivative. For these films it is found, using both TEM an AFM, that phase separation occurs. A two-phase system is observed that consists of PCBM-rich domains that are embedded in a matrix consisting of a mixture of MDMO-PPV and PCBM. By combining planar and cross-sectional views, three-dimensional information is obtained on the phase separated PCBM-rich regions, formed during spincoating. Changing the solvent is found to influence the size of the phase separated PCBM-rich domains. But not only the dimensions of the phase separated regions are affected by changing the solvent. Also the composition of the matrix is found to be determined by the choice of solvent. This was studied by changing the ratio of PCBM compared to MDMO-PPV. Since it is commonly believed that the morphology of the active layer influences electrical properties and photovoltaic performance, the nanostructural information obtained with the presented analytical techniques will attribute to a better understanding and improvement of present organic photovoltaic devices.

Increasing the mean grain size in copper films and features

A new grain-growth mode is observed in thick sputtered copper films. This new grain-growth mode, also referred to in this work as super secondary grain growth (SSGG) leads to highly concentric grain growth with grain diameters of many tens of micrometers, and drives the system toward a {100} texture. The appearance, growth dynamics, final grain size, and self-annealing time of this new grain-growth mode strongly depends on the applied bias voltage during deposition of these sputtered films, the film thickness, the post-deposition annealing temperature, and the properties of the copper diffusion barrier layers used in this work. Moreover, a clear rivalry between this new growth mode and the regularly observed secondary grain-growth mode in sputtered copper films was found. The microstructure and texture evolution in these films is explained in terms of surface/interface energy and strain-energy density minimizing driving forces, where the latter seems to be an important driving force for the observed new growth mode. By combining these sputtered copper films with electrochemically deposited (ECD) copper films of different thickness, the SSGG growth mode could also be introduced in ECD copper, but this led to a reduced final SSGG grain size for thicker ECD films. The knowledge about the thin-film level is used to also implement this new growth mode in small copper features by slightly modifying the standard deposition process. It is shown that the SSGG growth mode can be introduced in narrow structures, but optimizations are still necessary to further increase the mean grain size in features.

Dynamics of electromigration induced void/hillock growth and precipitation/dissolution of addition elements studied by in-situ scanning electron microscopy resistance measurements

Abstract In the present paper it has been shown that the in-situ SEM resistance measurement technique is a powerful technique to study the dynamics of void/hillock growth and precipitation/dissolution of addition elements in a metal line submitted to a temperature/current stress. The power of the in-situ SEM resistance measurement technique is shown with the first results on Al1wt.%Si0.5wt.%Cu metal lines. During the electromigration experiment, performed in a SEM equipped with a heating stage, back scattered electron images are taken continuously over the entire length of the metal line monitoring a.o. the growth, shape variation and motion of voids/hillocks. The dissolution and motion of Al 2 Cu precipitates in the Al1wt.%Si0.5wt.%Cu metal lines can also be monitored since the precipitates appear in the BSE mode as white objects. By comparing the observed electrical resistance drift results with the corresponding SEM micrographs it can be concluded that the resistance changes in the current stressed metal lines are mainly induced by geometrical changes.

Investigation of the formation of M 2 + -molecular ions in sputtering processes

The formation process of M2+ molecular ions sputtered from elementary target materials is investigated. In a previous article it was shown that these molecules can be used to quantitate major elements [1]. The quantitation method was based on the assumption that the M2+ molecular ions are formed by the atomic combination of independently sputtered M and M+ particles above the surface. In this paper this assumption will be investigated using a Monte Carlo model to simulate the formation mechanism. The model is used to calculate the velocity distribution of the M2+ dimers sputtered from three different elementary target materials (Fe, Ge, and Ni). The results are compared with experimental data. Good agreement exists between theory and experiment that supports the Monte Carlo model and hence also the assumed formation mechanism.

Quantitation of Major Elements With Secondary Ion Mass Spectrometry by Using M2+-Molecular Ions

A new quantitation method, based on the detection of M2+ molecular ions, is presented. It has been shown that M2+ molecular ions are formed by a recombination process between independently sputtered M and M+ particles. Based on this formation mechanism, it will be demonstrated that M2+ molecular ions can be used to quantitate major elements. The method will be used for quantitation of an AlxGa1−xAs multilayer. Furthermore, it will be shown that some matrix effects can be explained by the energy dependence of instrument transmission.

Investigation of the formation process of MCs+-molecular ions during sputtering

In secondary ion mass spectrometry, the detection of MCs+ clusters (with M an element of the specimen) under a Cs bombardment is frequently used for the quantification of major elements. Despite some very good results obtained by this method, some problems still remain. In order to gain some more insight into these problems, the formation mechanism of the MCs+ clusters is investigated using a Monte Carlo model. It is shown that the majority of the constituent particles of the formed clusters are initially first or second neighbor atoms at the surface and that the velocity distribution of the MCs+ clusters becomes broader and peaked at higher velocities with increasing surface binding energy of the M atom. In addition, it is demonstrated that the interaction potential between the M and Cs+ particle has no influence on the velocity distribution of the MCs+ clusters. On the other hand, the cluster formation probability, defined as the probability that a sputtered M and Cs+ particle will form a MCs+ cluster, is extremely sensitive to this interaction potential. It is also shown that the cluster formation probability decreases with increasing surface binding energy. Finally, a good correspondence is obtained between the calculated and experimental velocity distributions of MCs+ clusters sputtered from different monoatomic materials. As a consequence, the Monte Carlo model and the discussed results can be validated.

Theoretical Description of the Growth and Stability of Helium Platelets in Nickel

A static computer simulation is performed in order to study the nucleation and the two-dimensional growth mode of helium-filled aggregates in nickel. The results indicate that a helium-filled aggregate expels neighbouring atoms at its outer edges. These atoms are displaced in the direction of a nearest octahedral position and they are bound to the cluster.The helium-filled aggregate grows in a planar way and an interstitial loop is formed by the emitted atoms. The two dimensional growth occurs parallel with the close-packed planes. To explain the collapse of the platelets into clusters of smaller aggregates, a theoretical model is developed to describe the total energy of a platelet. It is based partly on the results of the simulations. The variation of the total energy gives information regarding the platelet stability and is calculated in both a numerical and an analytical way. It is shown that small platelets are stable and that, once a critical radius is attained, the platelet becomes unstable and a transformation into a group of smaller aggregates takes place. The theoretical model can also explain the fact that two-dimensional helium aggregates are observed to be more stable in bcc than in fcc structures.

A new method for the analysis of high-resolution SILC data

IMOMEC, IMEC Div, B-3590 Diepenbeek, Belgium. IMEC, B-3001 Heverlee, Belgium. Limburgs Univ Ctr, Inst Mat Res, B-3590 Diepenbeek, Belgium.Aresu, S, IMOMEC, IMEC Div, Wetenschapspk 1, B-3590 Diepenbeek, Belgium.

Statistical aspects of the degradation of LDD nMOSFETs

Limburgs Univ Ctr, Inst Mat Res, B-3590 Diepenbeek, Belgium. XPEQT, B-3980 Tessenderlo, Belgium. IMEC, B-3001 Heverlee, Belgium. Chartered Semicond Mfg Ltd, Singapore 738406, Singapore.Andries, E, Limburgs Univ Ctr, Inst Mat Res, Wetenschapspk 1, B-3590 Diepenbeek, Belgium.

High-resolution SILC measurements of thin SiO2 at ultra low voltages

IMOMEC, IMEC Div, B-3590 Diepenbeek, Belgium. Limburgs Univ Ctr, Mat Res Inst, B-3590 Diepenbeek, Belgium. IMEC, B-3001 Heverlee, Belgium.Aresu, S, IMOMEC, IMEC Div, Wetenschapspk 1, B-3590 Diepenbeek, Belgium.