Silicon-depth profiling with Rutherford backscattering in photoresist layers; a study on the effects of degradation

The reaction of a silicon-containing vapor with a photoresist layer, as used in some dry developable lithographic processes, was studied with Rutherford backscattering spectrometry. Degradation of the polymer layer under ion beam irradiation was observed, but it was found that this had no influence on the shape of the Si-depth profile and the total areal density. The RBS measurements were also verified with secondary ion mass spectrometry measurements. To describe the degradation process that occurs in polymeric layers upon ion beam exposure, elastic recoil detection measurements were carried out on polystyrene layers. Only one dose-independent cross section for carbon and only one for hydrogen were needed to describe the degradation behavior

A rotating molecular ruler : determining nanometer-scale particle-particle distances in an optomagnetic cluster assay

We investigate a fast and sensitive optomagnetic biomarker detection technology based on magnetic particles. Antibody-coated superparamagnetic particles capture biomarker molecules and form clusters with a biomarker molecule sandwiched between two particles. The particle clusters are actuated using a rotating magnetic field, which induces an oscillating light scattering cross-section (see Fig. 1a). Sub-picomolar biomarker concentrations can be resolved by the light scattering signals [Ranzoni et al, Nanoletters 2011; ACS Nano 2012]. In this paper we report a method to quantify inter-particle distances with nanometer resolution. The light scattering data show high-frequency signal components (see Fig. 1b). Simulations show that high-frequency components hold detailed information about the geometry of the particle clusters, including a strong dependence on the inter-particle distance (see Fig. 1c). We will report the simulation results and experimental data of corresponding model cluster assays

Hydrogen incorporation in silicon (oxy)nitride thin films

Hydrogen in low-pressure chemical vapor deposited oxynitride films was measured using elastic recoil detection with 2 MeV He ions. A distinction between N- and Si-bonded hydrogen could be made for films deposited from ND3 instead of NH3. The analyses reveal that on an average three times as much hydrogen is incorporated as NH relative to SiH, and that a maximum in this ratio is present in oxynitride with a composition around O/N=0.3. This optimum coincides with a maximum in total hydrogen content in the film of 3.2 at.¿%. Hydrogen desorption occurs in a narrow temperature interval around 950¿°C and proceeds virtually in an identical way for both binding types

Hydrogen incorporation in silicon (oxy)nitride thin films

Hydrogen in low-pressure chemical vapor deposited oxynitride films was measured using elastic recoil detection with 2 MeV He ions. A distinction between N- and Si-bonded hydrogen could be made for films deposited from ND3 instead of NH3. The analyses reveal that on an average three times as much hydrogen is incorporated as NH relative to SiH, and that a maximum in this ratio is present in oxynitride with a composition around O/N=0.3. This optimum coincides with a maximum in total hydrogen content in the film of 3.2 at.¿%. Hydrogen desorption occurs in a narrow temperature interval around 950¿°C and proceeds virtually in an identical way for both binding types

Magnetic force driven dissociation kinetics in case-mixed protein interaction assays

We quantify dissociation kinetics in assays with mixed specific and non-specific protein interactions. Ligand coupled superparamagnetic particles are incubated on surfaces coated with a mixture of specific receptors and non-specifically interacting proteins. Consequently, a case mixed population of surface bound particles is formed with different binding strengths. Magnetic field gradients were used to apply translational forces on the bound complexes, either constant or increasing in time (applying a loading rate). Using a multi-component dissociation analysis, we observe case-dependent dissociation mechanisms of the particles. The classical Bell and Evans model successfully describes bond dissociation from the deep potential well of a specific bond. Bond characteristics in terms of rate constants, energy barriers and minima’s in the dissociation pathway are revealed for the anti-biotin/biotin and streptavidin/biotin bond; and are in good agreement with values from SPR, other force clamp techniques, and molecular dynamics calculations. The particles bind non-specifically via interactions that show a force induced dissociation mechanism distinctly different from that of the specifically bound particles. The ability to rapidly differentiate and characterize specific and non-specific protein interactions in parallel, and affinity-rank different protein-ligand interactions on the basis of their binding pocket characteristics, will find various applications

Simulations with a dynamic reaction-diffusion model of the polymer grating preparation by patterned ultraviolet illumination

Simulations of volume fraction profiles formed during the lithographic preparation of polymer gratings are made with a reaction/diffusion model, based on the Flory–Huggins theory. Monomer migration is driven by a gradient in the chemical potential rather than a gradient in the concentration. If the chemical potential is used as the driving force, monomer migration is not only driven by a difference in concentration, or volume fraction, but also by other entropic effects: the differences in monomer length and the degree of crosslinking of a polymer network. The monomer volume fractions are simulated as a function of position for different ultraviolet intensities and various grating pitches. Profound edges of the monomer volume fractions caused by the fact that the reaction rate is high compared to the diffusion rate are both measured and simulated. An excellent agreement with nuclear microprobe measurements on the polymer gratings is obtaine

Diffusion enhancement in on/off ratchets

We show a diffusion enhancement of suspended polystyrene particles in an electrical on/off ratchet. The enhancement can be described by a simple master equation model. Furthermore, we find that the diffusion enhancement can be described by a general curve whose shape is only determined by the asymmetry of the ratchet repeat unit. The scaling of this curve can be explained from an analytical expression valid for small off-times. Finally, we demonstrate how the master equation model can be used to find the driving parameters for optimal particle separation. (C) 2013 American Institute of Physics

Imaging of n-hexane in zeolites by positron emission profiling (PEP)

Positron Emission Profiling (PEP) has been used for in-situ measurement of the surface coverage of H-mordenite by n-hexane, as a function of hexane partial pressure, at the elevated temperatures typically used for hydroisomerization by monitoring the retention time of an injected radio-labelled pulse of n-hexane. The labelled molecules ((CH3C5H11)-C-11) were produced via a two-step alkene homologation reaction in which C-11, produced using a cyclotron, was added to 1-pentene. The PEP method described is similar to the ''tracer pulse technique'' however it has the significant advantage of in-situ imaging of the puls

A BGO detector for catalysis studies with positron emitters

A detector for measurement of the activity distribution of positron emitters in a catalyst reactor has been designed and built. The detector consists of two banks of each ten BGO scintillation crystals. The activity distribution is measured as a function of time and position along the reactor. The attainable position resolution along the reactor is 3 mm and the minimum sampling time for the measurement of an activity profile is 1 second. The detector has a high sensitivity and the flexibility to be used with catalyst reactors of different types and size