Off-specular Neutron Reflectivity Research Articles

Dewetting Process of Deuterated Polystyrene and Poly(vinyl methyl ether) Blend Thin Films via Phase Separation

We studied the structure development in the dewetting process of deuterated polystyrene (dPS) and poly(vinyl methyl ether) (PVME) thin films, which were prepared by a spin-coating method on a quartz substrate, after the temperature jump into the two-phase region, using time-resolved specular and off-specular neutron reflectivity (NR), specular X-ray reflectivity (XR), light scattering (LS), and optical microscope (OM) measurements. The OM and specular XR measurements showed that there clearly existed an incubation period before dewetting. In the incubation period, composition fluctuations between dPS and PVME were developed due to phase separation. The specular NR results revealed that composition fluctuations began to occur just after the temperature jump along the depth direction over the film, giving rise to the composition gradient heterogeneously over the film. Composition fluctuations were also observed in the in-plane direction by the off-specular NR and LS measurements: the off-specular NR measure...

BioRef: A versatile time-of-flight reflectometer for soft matter applications at Helmholtz–Zentrum Berlin

BioRef is a versatile novel time-of-flight reflectometer featuring a sample environment for in situ infrared spectroscopy at the reactor neutron source BER II of the Helmholtz Zentrum Berlin für Materialien und Energie (HZB). After two years of design and construction phase the instrument has recently undergone commissioning and is now available for specular and off-specular neutron reflectivity measurements. BioRef is especially dedicated to the investigation of soft matter systems and studies at the solid-liquid interface. Due to flexible resolution modes and variable addressable wavelength bands that allow for focusing onto a selected scattering vector range, BioRef enables a broad range of surface and interface investigations and even kinetic studies with subsecond time resolution. The instrumental settings can be tailored to the specific requirements of a wide range of applications. The performance is demonstrated by several reference measurements, and the unique option of in situ on-board infrared spectroscopy is illustrated by the example of a phase transition study in a lipid multilayer film.

Time-resolved specular and off-specular neutron reflectivity measurements on deuterated polystyrene and poly(vinyl methyl ether) blend thin films during dewetting process

We performed time-resolved specular and off-specular neutron reflectivity measurements on blend thin films 42 and 98 nm thick of deuterated polystyrene and poly(vinyl methyl ether) during dewetting process induced by the phase separation in two phase region using a time-of-flight neutron reflectometer. In the specular measurements we found that the phase separation directed to the depth direction occurred near the air interface as well as near the Si substrate during the incubation period before dewetting. In addition we also found that the phase separation occurred asymmetrically at the two interfaces and inhomogeneously in the film plane, showing that the dewetting was induced by the composition fluctuation mechanism. Off-specular reflectivity was analyzed, for the first time, to evaluate kinetics of structure formation in the film plane during the dewetting process. We found in the analysis that the droplets formation in micrometer scale occurred in the late stage of dewetting.

Structure and morphology of Cu/Ni film grown by electrodeposition method: A study of neutron reflectivity and AFM

We present detailed study of structure and interface morphology of an electrodeposited Cu/Ni film using X-ray diffraction, X-ray reflectivity, neutron reflectivity and atomic force microscopy (AFM) techniques. The crystalline structure of the film has been determined by X-ray diffraction, which suggest polycrystalline growth of the film. The depth profile of density in the sample has been obtained from specular X-ray and neutron reflectivity measurements. AFM image of the air–film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks and the relief structure (islands) on the surface in the film, which can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air–film interfaces, the quasi-two-level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. AFM and off-specular neutron reflectivity measurements also show that the morphologies of electrodeposited surface is distinctively different as compared to that of sputter-deposited surfaces in the sample.

Electrochemically controlled pitting corrosion in Ni film: A study of AFM and neutron reflectometry

Electrochemical behavior of pitting corrosion of a Ni film, grown on Si substrate by sputtering, prepassivated in a chloride-free sulfuric acid solution and subsequently exposed to chloride above the pitting potential is reported. Specular and off-specular unpolarized neutron reflectometry and Atomic Force Microscopy (AFM) techniques have been used to determine the depth profile of scattering length density and morphology of as-deposited as well as corroded sample. Specular neutron reflectometry measurement of the film after corrosion shows density degradation along the thickness of film. The density profile as a function of depth, maps the growth of pitting and void networks due to corrosion. The AFM and off-specular neutron reflectivity measurements has suggested that the morphology of the film remains same after exposure of the film in chloride solution.

Lateral length scales of latent image roughness as determined by off-specular neutron reflectivity

A combination of specular and off-specular neutron reflectometries was used to measure the buried lateral roughness of the reaction-diffusion front in a model extreme ultraviolet lithography photoresist. Compositional heterogeneities at the latent reaction-diffusion front has been proposed as a major cause of line edge roughness in photolithographic features. This work describes the experimental observation of the longitudinal and lateral compositional heterogeneities of a latent image, revealing the buried lateral length scale as well as the amplitude of inhomogeneity at the reaction-diffusion front. These measurements aid in determining the origins of line edge roughness formation, while exploring the material limits of the current chemically amplified photoresists.

Proceedings of the workshop “Probing Dynamics at Interfaces–Options for Inelastic Neutron Reflectometry”

Dynamic phenomena in solid matter can show drastically different behaviour if the system dimensions are reduced. Diffusion and fluctuations in confined structures or at interfaces can be decreased by orders of magnitude, the damping effectively changing the interaction with surrounding media, or even enhanced as found in low dimensional magnetic structures. Up to now neutrons have been used to investigate the dynamics in such systems mainly by classical inelastic time of flight spectroscopy, e.g. the analysis of water diffusion in layered systems, or by applying off-specular neutron reflectivity to elucidate fluctuations in layered systems such as polymer layers, smectic liquid crystals or phospholipid membranes. The application of neutron reflectometry to study not only the structure and lateral organisation of layered systems and interfaces but also the dynamic features have been so far restricted, mainly due to the low flux of current neutron sources. One possibility to do so, neutron spin echo reflectometry, has gained new interest as an option to study the structure and dynamic in layered systems and at interfaces (see recent work by Rekveldt [1,2], Pynn [3] and Felcher [4]). It was proposed to exploit Larmor precession techniques to extract dynamic information by neutron reflectometry and the feasibility of this approach was demonstrated in very recent experiments at HMI and ILL [3–6]. In addition, a first neutron spin echo reflectometry-like measurement of the dynamics in smectic liquid membranes has been recently successfully carried out on IN15 at ILL [7]. It should be mentioned that the principal possibility to perform neutron reflectometry measurements with a classical inelastic time of flight spectroscopy set-up was acknowledged some years ago in Dubna [8]. Inelastic neutron reflectometry would open up a complete new field in the analysis of dynamic phenomena by neutron techniques in various fields such as magnetic multilayers, polymer layers, biomembranes, solid–liquid interfaces and any interface-related system. It would provide new and complementary information to methods like X-ray photoelectron correlation spectroscopy, EXAFS and NMR. Dedicated instruments for inelastic neutron reflectometry could be implemented within the planned instruments at the new neutron

Fast swelling kinetics of thin polystyrene films

In situ the swelling of thin polystyrene (PSd) films by toluene is investigated with specular and off-specular neutron reflectivity. Due to the very high time resolution of 30 s, the initial stages of swelling as well as the fast swelling are detected. Followed by a slow swelling and final stages, in total four different regimes are identified until equilibrium with respect to a homogenously swollen PSd film is reached. Film instabilities are avoided in the absence of any motor movements in the time-of-flight mode of the neutron reflectometer D17.

A new polarized neutron reflectometer at Dhruva for specular and off-specular neutron reflectivity studies

A polarized neutron reflectometer for vertical sample geometry has been installed in the guide tube laboratory of Dhruva reactor at Trombay, India. The instrument uses a monochromatic neutron beam of 2.5 Å in a step scan mode with a linear position s

Applications of Neutron Reflectivity Measurements to Nanoscience: Thin Films and Interfaces

AbstractNeutron reflectivity has matured in recent years from an exotic method used only by a few experts to an essential tool for the investigation of thin films and interfaces on the nanoscale. In contrast to x-ray reflectivity, which provides electron density profiles, neutron reflectivity reveals the nuclear density profile. This is an essential difference when exploring hydrogenous materials such as polymers, Langmuir–Blodgett films, and membranes. Furthermore, neutrons carry a magnetic moment that interacts with the magnetic induction of the film, revealing, in addition to the nuclear density profile, the magnetic density profile in layers and superlattices. Recent developments in the analysis of off-specular neutron reflectivity data enable the characterization of chemical and magnetic correlations within the film plane on nanometer to micron length scales. A new generation of pulsed neutron sources, featuring flux enhancements of factors of 10–100 over existing sources, will make these types of measurements even more exciting, while kinetic studies, pump-probe, and small-sample experiments will become feasible, opening new windows onto nanoscale materials science.

Interaction between magnetostatic waves and neutrons in magnetic thin films

Magnetic dipolar coupling leads to low-energy excitations in magnetic materials named as magnetostatic waves (MSW). The typical energy of these excitations is of the order of a few tens of μeV. We show that working in grazing incidence in a reflectivity geometry makes it possible to study these very low-energy excitations. We present a neutron set-up which allows to study these excitations. The studied samples were permalloy thin films. The MSW were either thermally excited or induced by a microwave (MW) field and the off-specular neutron reflectivity was measured. We have not been able to measure any inelastic scattered signal, even with a large MW excitation (1 W input).

Specular and Off-Specular Neutron Reflectivity of a Low Molecular Weight Polystyrene Surfactant at the Air-Water Interface

Neutron reflectivity measurements were made on films at the air-water interface of a highly characterized low molecular weight polystyrene surfactant, with a single hydroxyl end group. The II-A isotherm is consistent with collapse of a classical fluid surfactant monolayer to a trilayer structure at high compressions. Before the collapse point, reflectivity measurements indicated a decrease in the average tilt angle of the molecules to the surface normal as the layer was compressed. After the collapse point, the film structure was time dependent and was best represented by a monolayer of constant thickness at the water interface, covered by a bilayer whose thickness increased with time and a time-dependent diffuse layer above the bilayer. Multidetector reflectivity profiles showed only specular reflection for surface pressures below the collapse point, but in the collapse region, some off-specular reflection was clearly present, indicating the presence of surface texture on the micron length scale in the plane of the interface. This is believed to be the first observation of well-developed off-specular neutron reflection from a Langmuir film.