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

MRS Bulletin ◽  
2003 ◽  
Vol 28 (12) ◽  
pp. 918-922 ◽  
Author(s):  
John F. Ankner ◽  
Hartmut Zabel
Keyword(s):  
Thin Films ◽  
Density Profile ◽  
Materials Science ◽  
Kinetic Studies ◽  
Film Plane ◽  
Small Sample ◽  
Neutron Reflectivity ◽  
Nuclear Density ◽  
Essential Difference ◽  
Reflectivity Data

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.

Temperature Dependence of the Morphology of Thin Diblock Copolymer Films as Revealed by Neutron Reflectivity

1989 ◽  
Vol 166 ◽  
Author(s):  
T. P. Russell ◽  
S. H. Anastasiadis ◽  
S. K. Satija ◽  
C. F. Majkrzak
Keyword(s):  
Thin Films ◽  
Temperature Dependence ◽  
Density Profile ◽  
Diblock Copolymer ◽  
Diblock Copolymers ◽  
Decay Length ◽  
Neutron Reflectivity ◽  
Copolymer Films ◽  
Lamellar Morphology ◽  
Oriented Parallel

ABSTRACTThe order-disorder transition in thin films of symmetric diblock copolymers of polystyrene and polymethylmethacrylate has been investigated by neutron reflectivity. At temperatures above the order-disorder temperature, TMST, a surface induced oscillatory segment density profile with an exponential decay length, χ, is observed. The inverse of decay length 1/≤ TMST a lamellar morphology oriented parallel to the surface propagates through the entire specimen.

Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers

2018 ◽  
Vol 51 (6) ◽  
pp. 1556-1563
Author(s):  
Sotirios A. Droulias ◽  
Gunnar K. Pálsson ◽  
Björgvin Hjörvarsson ◽  
Max Wolff
Keyword(s):  
Density Profile ◽  
Optical Model ◽  
Neutron Reflectivity ◽  
Lattice Expansion ◽  
Reflection And Refraction ◽  
Deuterium Concentration ◽  
Kinematic Approximation ◽  
Reflectivity Data

The limitations of a phenomenological fitting approach compared to simulations of the optical model including reflection and refraction at all interfaces are demonstrated using the example of hydrogen loading in ultra-thin vanadium layers. Fe/V superlattices are loaded with deuterium and the lattice expansion and deuterium concentration are extracted from neutron reflectivity data. A noticeable difference is found between the extraction of concentrations and bilayer thicknesses directly from the superlattice peaks and fits of the density profile using the Parratt formalism. The results underline the importance of carefully considering the limitations of phenomenological approaches, in order to obtain robust results. The limitations of the kinematic approximation for the analysis are discussed in detail.

REFLEX: a program for the analysis of specular X-ray and neutron reflectivity data

2019 ◽  
Vol 52 (1) ◽  
pp. 201-213 ◽  
Author(s):  
Guillaume Vignaud ◽  
Alain Gibaud
Keyword(s):  
Physical Properties ◽  
Density Profile ◽  
Scattering Length ◽  
Electron Density Profile ◽  
Neutron Reflectivity ◽  
X Rays ◽  
X Ray ◽  
Spin Polarized ◽  
Reflectivity Data ◽  
Footprint Effect

The use of X-ray and neutron reflectivity has been generalized worldwide for scientists who want to determine specific physical properties (such as electron-density profile, scattering-length density, roughness and thickness) of films less than 200 nm thick deposited on a substrate. This paper describes a freeware program named REFLEX, which is a standalone program dedicated to the simulation and analysis of X-ray and neutron reflectivity from multilayers. This program was first written two decades ago and has been constantly improved since, but never published until now. The latest version of REFLEX covers generalized types of calculation of reflectivity curves including both neutron and X-ray reflectivity. In the case of X-rays, the program can deal with both s and p polarization, which is quite important in the soft X-ray region where the two polarizations can yield different results. Neutron reflectivity is calculated within the framework of non-spin-polarized neutrons. REFLEX has also been designed to include any type of fluid (such as supercritical CO2) on top of the analysed film and includes corrections of the footprint effect for analysis on an absolute scale.

Domains and domain nucleation in magnetron-sputtered CoCr thin films

1993 ◽  
Vol 51 ◽  
pp. 1046-1047
Author(s):  
B. G. Demczyk
Keyword(s):  
Thin Films ◽  
Domain Structure ◽  
Magnetic Domain ◽  
Domain Size ◽  
Film Plane ◽  
Magnetic Domain Structure ◽  
Perpendicular Magnetization ◽  
Columnar Grains ◽  
Reversal Mechanism ◽  
Lorentz Transmission Electron Microscopy

CoCr thin films have been of interest for a number of years due to their strong perpendicular anisotropy, favoring magnetization normal to the film plane. The microstructure and magnetic properties of CoCr films prepared by both rf and magnetron sputtering have been examined in detail. By comparison, however, relatively few systematic studies of the magnetic domain structure and its relation to the observed film microstructure have been reported. In addition, questions still remain as to the operative magnetization reversal mechanism in different film thickness regimes. In this work, the magnetic domain structure in magnetron sputtered Co-22 at.%Cr thin films of known microstructure were examined by Lorentz transmission electron microscopy. Additionally, domain nucleation studies were undertaken via in-situ heating experiments.It was found that the 50 nm thick films, which are comprised of columnar grains, display a “dot” type domain configuration (Figure 1d), characteristic of a perpendicular magnetization. The domain size was found to be on the order of a few structural columns in diameter.

scholarly journals Strain-stabilized superconductivity

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
J. P. Ruf ◽  
H. Paik ◽  
N. J. Schreiber ◽  
H. P. Nair ◽  
L. Miao ◽  
...  
Keyword(s):  
Thin Films ◽  
Materials Science ◽  
Condensed Matter ◽  
Quantum States ◽  
Low Energy ◽  
Superconducting Transition ◽  
Superconducting Properties ◽  
Detailed Understanding ◽  
Epitaxial Strain ◽  
Promising Strategy

AbstractSuperconductivity is among the most fascinating and well-studied quantum states of matter. Despite over 100 years of research, a detailed understanding of how features of the normal-state electronic structure determine superconducting properties has remained elusive. For instance, the ability to deterministically enhance the superconducting transition temperature by design, rather than by serendipity, has been a long sought-after goal in condensed matter physics and materials science, but achieving this objective may require new tools, techniques and approaches. Here, we report the transmutation of a normal metal into a superconductor through the application of epitaxial strain. We demonstrate that synthesizing RuO2 thin films on (110)-oriented TiO2 substrates enhances the density of states near the Fermi level, which stabilizes superconductivity under strain, and suggests that a promising strategy to create new transition-metal superconductors is to apply judiciously chosen anisotropic strains that redistribute carriers within the low-energy manifold of d orbitals.

Neutron reflectivity study of thin films of hydrogen-bonded polymer blends: influence of annealing on composition profile

1992 ◽  
Vol 25 (10) ◽  
pp. 2619-2623 ◽  
Author(s):  
Lei Jong ◽  
Eli M. Pearce ◽  
T. K. Kwei ◽  
W. A. Hamilton ◽  
G. S. Smith ◽  
...  
Keyword(s):  
Thin Films ◽  
Polymer Blends ◽  
Composition Profile ◽  
Neutron Reflectivity ◽  
Hydrogen Bonded

The Materials Science of “Permeable Polysilicon” Thin Films

2001 ◽  
Vol 687 ◽  
Author(s):  
George M Dougherty ◽  
Timothy Sands ◽  
Albert P. Pisano
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Materials Science ◽  
Single Step ◽  
Process Window ◽  
Silicon Thin Films ◽  
Growth Regime ◽  
Deposition Parameters ◽  
Simple Kinetic Model ◽  
The Relationship

AbstractPolycrystalline silicon thin films that are permeable to fluids, known as permeable polysilicon, have been reported by several researchers. Such films have great potential for the fabrication of difficult to make MEMS structures, but their use has been hampered by poor process repeatability and a lack of physical understanding of the origin of film permeability and how to control it. We have completed a methodical study of the relationship between process, microstructure, and properties for permeable polysilicon thin films. As a result, we have determined that the film permeability is caused by the presence of nanoscale pores, ranging from 10-50 nm in size, that form spontaneously during LPCVD deposition within a narrow process window. The unusual microstructure within this process window corresponds to the transition between a semicrystalline growth regime, exhibiting tensile residual stress, and a columnar growth regime exhibiting compressive residual stress. A simple kinetic model is proposed to explain the unusual morphology within this transition regime. It is determined that measurements of the film residual stress can be used to tune the deposition parameters to repeatably produce permeable films for applications. The result is a convenient, single-step process that enables the elegant fabrication of many previously challenging structures.

Model-independent determination of the surface scattering-length-density profile from specular reflectivity data

1992 ◽  
Vol 25 (2) ◽  
pp. 129-145 ◽  
Author(s):  
J. S. Pedersen
Keyword(s):  
Density Profile ◽  
Fourier Transformation ◽  
Scattering Length ◽  
Simulated Data ◽  
Limited Range ◽  
Square Root ◽  
Scattering Length Density ◽  
Angle Scattering ◽  
Specular Reflectivity ◽  
Reflectivity Data

An approach for analysing neutron and X-ray specular reflectivity data from stratified media having variation in the scattering-length density near the surface is described. The method has its origin in small-angle scattering and it is composed of two steps: (i) indirect Fourier transformation [Glatter (1977). J. Appl. Cryst. 10, 415–421] giving the profile correlation function p(z) of the derivative dρ/dz of the scattering-length density; (ii) square-root deconvolution [Glatter (1981). J. Appl. Cryst. 14, 101–108] giving dρ/dz and ρ, the scattering-length-density profile. The only requirement for applying the method is that the scattering-length density varies only in a limited range. In nearly all cases the approach does not require any knowledge of the chemical composition of the surface layer and consequently incorporates a certain degree of objectivity. The method gives the smoothest profile which agrees with the experimental reflectivity data. The method is tested on simulated reflectivity data for a series of different surface profiles and subsequently used for analysing experimental data on fluorocarbon amphiphiles in water and salt solutions. The tests on simulated data show that the indirect Fourier transformation gives correlation functions agreeing very well with the corresponding functions of the original profiles. It is further demonstrated that the square-root deconvolution gives reliable results for the scattering-length-density profiles.

Structural Properties Of Co/Re Superlattices

1991 ◽  
Vol 238 ◽  
Author(s):  
Y. Huai ◽  
R. W. Cochrane ◽  
Y. Shi ◽  
H. E. Fischer ◽  
M. Sutton
Keyword(s):  
Structural Disorder ◽  
Multilayer Films ◽  
Film Plane ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bilayer Films ◽  
Out Of Plane ◽  
Reflectivity Data ◽  
Sharp Interfaces ◽  
Good Agreement

ABSTRACTThe structures of equal-thickness Co/Re multilayer films and several Co/Re bilayer films have been investigated by X-ray diffraction at low and high angles. Analysis of low-angle reflectivity data from bilayer films indicates that interfacial intermixing is limited to three monolayers and that the two interfacial configurations are different. The high-angle X-ray diffraction data show that multilayer films have coherent interfaces and a highly textured structure with hep [002] orientations normal to the film plane for periods 21 Å ≤ Λ ≤220 Å. Detailed structures have been determined by fitting the X-ray spectra to calculated ones using a trapezoidal model. The results indicate that samples with 42 Å≤ Λ ≤220 Å have relatively sharp interfaces, in good agreement with the bilayer results. In addition, an out-of-plane expansion of the Co (002) layer is observed in samples with large Λ and results from structural disorder leading to a reduced atomic density. For Λ <21 Å the interfaces arise from the rougher surfaces of the deposited layers.

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