Angle-dependent X-ray Photoelectron Spectroscopy Research Articles

Surface Dynamics of Polymer Glasses: Sub-Tg Surface Reorganization in End-Functional Polymers

Dynamic water contact angle analysis is applied to characterize the surface reorganization of glassy polystyrenes (PS), terminated with either a fluorosilane or carboxylic acid end group, upon exposure to an atmosphere of saturated water vapor. Fluorosilane end groups are initially adsorbed preferentially at the surface and diffuse away from the surface when exposed to water vapor. Carboxylic acid end groups are initially depleted from the surface and are drawn to the surface when exposed to water vapor. The time dependence of the surface composition during reorganization, determined by application of Cassie’s equation, scales with the square root of time, consistent with a diffusive process. Angle dependent X-ray photoelectron spectroscopy (ADXPS), applied to characterize the surface concentration depth profiles of the fluorosilane-terminated PS before and after exposure to water vapor, indicates that reorganization in the glassy state involves motions on a length scale of about 2 nm. Modified lattice model calculations, assuming that reorganization can occur only over length scales of this magnitude, are found to provide a reasonable representation of ADXPS surface composition depth profiles, supporting the conclusion that the length scale for surface reorganization of end-functional polymers in the glassy state is of the order of a few nanometers. When this length scale is coupled with the dynamic contact angle data, apparent diffusion coefficients in the range of 10–13 to 10–10 cm2/s are obtained. Analysis of the temperature dependence of the apparent diffusion coefficients, found to be an activated process following Arrhenius behavior, yields activation energies of 137 kJ/mol for fluorosilane-terminated PS and 39 kJ/mol for PS terminated with a carboxylic acid end group, considerably lower than experimental values determined from analysis of either polymer–polymer interdiffusion or free surface dynamics. These activation energies are a closer match to those of the β-relaxation of bulk PS than they are to the α-relaxation of either the PS surface or the PS bulk, suggesting that surface reorganization in glassy PS can occur by virtue of short-range motions characteristic of a surface activated β-relaxation occurring over length scales of a few nanometers.

Comparative research on activation technique for GaAs photocathodes

The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs–O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

Monolayer formation of octyltrimethoxysilane and 7-octenyltrimethoxysilane on silicon (1 0 0) covered with native oxide

Modification has been carried out of silicon (100) covered with native oxides with monolayers of octyltrimethoxsilane (C8TMS) and octenyltrimethoxysilane (C8enTMS). Different conditions of adsorption from the organic solvents chloroform, toluene and n-hexane with subsequent exposure to ammonia vapour under ambient atmosphere have been tested for monolayer formation without exclusion of moisture. Thickness of resulting adsorbates has been measured using spectroscopic ellipsometry (SE), water contact angles were measured, and the surface roughness was determined by atomic force microscopy (AFM). If all three results are consistent with the presence of monolayers on the surface, further characterisation has been carried out by angle dependent X-ray photoelectron spectroscopy (XPS). For monolayers, surface roughnesses about <0.3nm were measured, which were mainly determined by the substrate. Thicknesses obtained from SE and XPS agree. Conformational and orientational order of the monolayers determined by attenuated total reflection infrared (ATR-IR) spectroscopy show disordered chains in both cases with nearly isotropic orientation. C8enTMS was found to be partly hydroxylated when treated under alkaline conditions.

Dipole Layer Formation by Surface Segregation of Regioregular Poly(3-alkylthiophene) with Alternating Alkyl/Semifluoroalkyl Side Chains

A regioregular poly(3-alkylthiophene) with alternating alkyl/semifluoroalkyl side chains (P3DDFT) spontaneously segregates on the surface of poly(3-dodecylthiophene) (P3DDT) during a spin-coating process and forms a thin fluoroalkyl layer with a thickness of less than 3 nm. This surface layer is as dense as fluoroalkyl-based self-assembled monolayers (SAMs) on metals, as demonstrated by angle-dependent X-ray photoelectron spectroscopy and water contact angle measurements. The semifluoroalkyl chains aligned at the air/solid interface form a large molecular dipole moment that continuously shifts the ionization energy by as much as +1.8 eV depending on the surface density of P3DDFT. This can be a novel approach to controlling the energy-level alignment at organic/(in)organic interfaces, analogous to the work function shifts of metals induced by the formation of SAMs.

Chemical structure study of SiO2/4H-SiC (0001) interface transition region by angle-dependent x-ray photoelectron spectroscopy

The chemical structure of SiO2/4H-SiC (0001) interface transition region is investigated using angle-dependent x-ray photoelectron spectroscopy. The relative intensities of various silicon oxycarbides (SiOxCy) components as a function of polar emission angle suggest that SiOC3, SiO2C2, SiO3C, and SiO2 have different depth distributions at the interface. Then a nonabrupt four-layer structure model is proposed. And the relative intensities of various SiOxCy species are fitted based on the model by an electron damping scheme. The well fitted results indicate that the SiO2/4H-SiC (0001) interface transition region can be described by a chemically nonabrupt four-layer structure model well.

Studies of fluorinated methylacrylate copolymer on the surface of cotton fabrics

A fluorine-containing methylacrylate copolymer latex has been synthesized by emulsion polymerization and was used as a water- and oil-repellent agent to treat some pure cotton woven fabrics at different dry and curing temperature. The treated cotton fabric surfaces were investigated by attenuated total reflectance infrared analysis and angle-dependent X-ray photoelectron spectroscopy directly. The analysis results could agree with the fluorine-containing copolymer real situation on the fabrics surface much more, and could indicate, factually, surface properties of treated or modified material rather than copolymer film. It was found that fluorine elements are enriched at the air-polymer interface and fluorine content of the treated cotton fabrics surface decreases with increasing analysis depth, which depends on heating and cooling experience, such as annealing and quenching. Furthermore, the results showed that almost the same effect can be attained using this copolymer curing from 100°C to 175°C; the relatively low curing temperature is very valuable and advantageous for some fabrics which would yellow easily at higher temperatures. The water- and oil-repellency grade of treated cotton fabrics by the fluorine-containing methylacrylate copolymer latex increases with an increase on fluorine content on the surface.

Comprehensive Characterization of Grafted Expanded Poly(tetrafluoroethylene) for Medical Applications

Successful implantation of any biomaterial depends on its mechanical, architectural, and surface properties. Materials with good bulk properties seldom possess the appropriate surface characteristics required for good biointegration. The present study investigates the results of surface modification of a highly porous, fully fluorinated polymeric substrate, expanded poly(tetrafluoroethylene) (ePTFE), with a view to improving the surface bioactivity and hence ultimately its biointegration. Modification involved gamma irradiation-induced graft copolymerization with the monomers monoacryloxyethyl phosphate (MAEP) and methacryloxyethyl phosphate (MOEP) in various solvent systems (water, methanol, methyl ethyl ketone, and mixtures thereof). In order to determine the penetration depth of the graft copolymer into the pores and/or the bulk of the ePTFE membranes, angle-dependent X-ray photoelectron spectroscopy (XPS) and magnetic resonance imaging (MRI) were used. It was found that the penetration depth was critically affected by the choice of monomer and solvent as well as by the technique used to remove dissolved oxygen from the grafting mixture: nitrogen degassing versus vacuum. Difficulties due to the porous nature of the membranes in establishing the lateral position of the graft copolymers were largely overcome by combining data from microattenuated total reflectance Fourier transfer infrared (μ-ATR-FTIR) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging. Results show that the large variation in graft heterogeneity found between different samples is largely an effect of the underlying substrate and choice of monomer. The results from this study provide the necessary knowledge and experimental data to control both the graft copolymer lateral position and depth of penetration in these porous ePTFE membranes.

Epitaxial SiC formation induced by medium energy ions on Si(1 1 1) at room temperature

In the search for silicon technology compatible substrate for III-nitride epitaxy, we present a proof-of-concept for forming epitaxial SiC layer on Si(1 1 1). A C/Si interface formed by ion sputtering is exposed to 100–1500 eV Ar + ions, inducing a chemical reaction to form SiC, as observed by core-level X-ray photoelectron spectroscopy (XPS). Angle dependent XPS studies shows forward scattering feature that manifest the epitaxial SiC layer formation, while the valence band depicts the metal to insulator phase change.

Evolution of surface potential barrier for negative-electron-affinity GaAs photocathodes

The evolution of surface potential barrier for reflection-mode GaAs photocathodes in an ultrahigh vacuum system has been investigated by using spectral response and angle-dependent x-ray photoelectron spectroscopy (ADXPS) measurements at room temperature. The escape probabilities of electrons emitted into vacuum are obtained as a function of the incident electron energy, surface barrier height, and thickness. Based on the new escape probability expressions, we obtain the surface barrier parameters of the reflection-mode negative-electron-affinity (NEA) cathodes from the fit of the spectral response curves by using quantum-efficiency equations. These parameters reveal the evolution of the NEA cathode surface during the degradation process. In addition, the surface layer structure of both the freshly activated and degraded cathodes is calculated from the ADXPS spectra. The calculated results are in fair agreement with the fitted barrier parameters.

Fabrication of Block Copolymer Monolayers by Adsorption from Supercritical Fluids: A Versatile Concept for Modification and Functionalization of Polymer Surfaces

We describe a generic method for polymer surface modification and functionalization that is applicable for substrates of arbitrary shape. The method involves the deposition of monolayer and submonolayer films of photoactive block copolymers from supercritical fluids. Poly(styrene-b-tert-butyl acrylate), poly(S-b-tBA), block copolymer monolayers form spontaneously on polystyrene substrates by adsorption from scCO2 when hexane is used as a cosolvent. Atomic force microscopy indicates the films are flat and without pores after modification. Ethylene glycol contact angles increase linearly with deposition pressure until a constant value, equal to that of pure P tBA, is attained at pressures of 18 MPa or greater at 40 degrees C. This trend mimics the change in block copolymer solubility with pressure and indicates that the block copolymer self-assembles and orders at the surface, presenting a P tBA layer at the air interface with the PS block orienting toward the PS substrate. The P tBA layer thickness, determined by angle dependent X-ray photoelectron spectroscopy, reaches a saturated monolayer value of ca. 2 nm for pressures of 18 MPa and higher, consistent with the thickness expected for unperturbed PtBA chains comprising a wet brush. This concept for polymer surface modification initially produces a hydrophobic surface due to surface adsorption of the low surface tension PtBA block, but can also be used to prepare hydrophilic, functional surfaces, either modified or patterned with carboxylic acid groups, by photolytic or acid catalyzed deprotection/hydrolysis of the tert-butyl ester groups.

Highly Efficient Visible-Light-Induced Photocatalytic Activity of Nanostructured AgI/TiO2 Photocatalyst

Nanostructured AgI/TiO(2) photocatalyst was synthesized by a feasible approach with AgNO(3), LiI, and Ti(OBu)(4) and characterized by X-ray diffraction, transmission electron microscopy, angle-dependent X-ray photoelectron spectroscopy, diffusive reflectance UV-vis spectroscopy, Raman spectroscopy, photoluminescence, and the Brunauer-Emmett-Teller technique. The results of characterization reveal that the nanostructured AgI/TiO(2) has a novel core/shell/shell nanostructure of AgI/Ag-I(2)/TiO(2). Compared with TiO(2) (P25) supported AgI, the formation of the nanostructure results in substantial shifting of the absorption edge of AgI to red, enhancement of the absorption intensity, and the appearance of a strong tail absorption above 490 nm, which is assigned to the absorption of I(2) and Ag. Photocatalytic tests show that the nanostructured AgI/TiO(2) photocatalyst exhibited very high visible-light-induced photocatalytic activity for the photodegradation of crystal violet and 4-chlorophenol, which is 4 and 6 times higher than that of P25 titania supported AgI, respectively. The highly efficient visible-light-induced photocatalytic activity of the nanostructured AgI/TiO(2) is attributed to its strong absorption in the visible region and low recombination rate of the electron-hole pair due to the synergetic effect among the components of AgI, Ag, I(20, and TiO(2) in the nanostructured AgI/TiO(2).

“Click-Functional” Block Copolymers Provide Precise Surface Functionality via Spin Coating

There are few existing methods for the quantitative functionalization of surfaces, especially for polymeric substrates. We demonstrate that alkyne end-functional diblock copolymers can be used to provide precise areal densities of reactive functionality on both hard (e.g., glass and silicon oxide) and soft (i.e., polymeric) substrates. Alkyne functionality is extremely versatile because the resultant functional surfaces are reactive toward azide functional molecules by Sharpless click chemistry. Spin-coated films of alpha-alkyne-omega-Br-poly( tert-butylacrylate- b-methylmethacrylate) (poly( tBA-MMA)) spontaneously self-assemble on the aforementioned substrates to present a surface monolayer of PtBA with a thickness in the range of 1 to 9 nm. The PMMA block physisorbs to provide multivalent anchoring onto hard substrates and is fixed onto polymer surfaces by interpenetration with the substrate polymer. The areal density of alkyne functional groups is precisely controlled by adjusting the thickness of the block copolymer monolayer, which is accomplished by changing either the spin coating conditions (i.e., rotational speed and solution concentration) or the copolymer molecular weight. The reactivity of surface-bound alkynes, in 1,3-dipolar cycloaddition reactions or by so-called "click chemistry", is demonstrated by covalent surface immobilization of fluorescently labeled azides. The modificed surfaces are characterized by atomic force microscopy (AFM), contact angle, ellipsometry, fluorescent imaging and angle-dependent X-ray photoelectron spectroscopy (ADXPS) measurements. Microarrays of covalently bound fluorescent molecules are created to demonstrate the approach and their performance is evaluated by determining their fluorescence signal-to-noise ratios.

Angle-dependent XPS analysis of silicon nitride film deposited on screen-printed crystalline silicon solar cell

In this work silicon nitride (Si 3N 4) film was deposited as an antireflection coating (ARC) on crystalline silicon solar cell (cell♯A) using plasma-enhanced chemical vapor deposition (PECVD). Two solar cells XA and XB of approximately equal area were diced from cell#A and characterized by angle-dependent X-ray photoelectron spectroscopy (XPS). The XPS profiling shows the presence of silicon (Si), nitrogen (N), carbon (C) and oxygen (O) in the Si 3N 4 film. The presence of C and O indicates that organic substances, involved in processing steps were not released completely from the surface and may diffuse in Si 3N 4 ARC during deposition. The XPS spectra corresponding to Si2p, N1s, C1s and O1s were recorded at angles 0° (normal to the surface), 30° and 45°, as angle increases spectra becomes more surface sensitive. Peak positions in Si2p and N1s spectra explain the oxygen contamination in the Si 3N 4 film. The shift in the peak positions of C1s and O1s as angle increases from 0° to 45° explains the surface contamination of carbon and oxygen. The atomic composition of elements Si, N, C and O show more carbon, oxygen concentration and smaller N/Si ratio than stoichiometry, i.e. Si 3N 4 in cell XB. However, cell XA not only show better photovoltaic performance in terms of parameters open-circuit voltage ( V oc), short-circuit current density ( J sc), fill factor (FF) and efficiency ( η) but also have more uniform texturization and regular pyramids on the surface as revealed by scanning electron microscopy (SEM). The presence of higher concentration of impurities (carbon and oxygen), non-uniformity in texturization and in the Si 3N 4 film as well could be responsible for less satisfactory photovoltaic performance of cell XB.

XPS, TOF-SIMS, NEXAFS, and SPR Characterization of Nitrilotriacetic Acid-Terminated Self-Assembled Monolayers for Controllable Immobilization of Proteins

For immobilization of proteins onto surfaces in a specific and controlled manner, it is important to start with a well-defined surface that contains specific binding sites surrounded by a nonfouling background. For immobilizing histidine-tagged (his-tagged) proteins, surfaces containing nitrilotriacetic acid (NTA) headgroups and oligo(ethylene glycol) (OEG) moieties are a widely used model system. The surface composition, structure, and reactivity of mixed NTA/OEG self-assembled monolayers (SAMs) on Au substrates were characterized in detail using X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and surface plasmon resonance (SPR) biosensoring. XPS results for sequential adsorption of NTA thiols followed by OEG thiols showed that OEG molecules were incorporated into an incompletely formed NTA monolayer until a complete mixed SAM was formed. The surface concentration of NTA headgroups was estimated to be 0.9-1.3 molecule/nm2 in the mixed NTA/OEG monolayers, compared to 1.9 molecule/nm2 in pure NTA monolayers. Angle-dependent XPS indicated NTA headgroups were slightly reoriented toward an upright position after OEG incorporation, and polarization-dependent NEXAFS results indicated increased ordering of the alkane chains of the molecules. Nitrogen-containing and OEG-related secondary ion fragments from the TOF-SIMS experiments confirmed the presence of NTA headgroups and OEG moieties in the monolayers. A multivariate peak intensity ratio was developed for estimating the relative NTA concentration in the outermost (10 A) of the monolayers. SPR measurements of a his-tagged, humanized anti-lysozyme variable fragment (HuLys Fv) immobilized onto Ni(II)-treated mixed NTA/OEG and pure NTA monolayers demonstrated the reversible, site-specific immobilization of his-tagged HuLys Fv (108-205 ng/cm2) with dissociation rates (koff) between 1.0 x 10-4 and 2.1 x 10-5 s-1, both depending on the NTA surface concentration and orientation. The monolayers without Ni(II) treatment exhibited low nonspecific adsorption of his-tagged HuLys Fv (<2 ng/cm2).

Effect of Chain Architecture on Surface Segregation in Functional Polymers: Synthesis and Surface Properties of End- and Center-Functional Poly(D,L-lactide)

Poly(d,l-lactide)s with fluorocarbon functional groups located at either the chain end or center are synthesized by the ring-opening solution polymerization of d,l-lactide using monohydroxy or dihydroxy terminated semifluorinated alcohols as co-initiators respectively. The surface composition−depth profiles of the fluorocarbon functional groups are determined by angle dependent X-ray photoelectron spectroscopy (ADXPS) measurements. All polymers exhibit surface segregation of the lower surface tension fluorocarbon functional groups. The extent of surface segregation decreases with molecular weight and, for polymers of equivalent molecular weight, is higher for the end-functional polymers than for center-functional polymers, consistent with the mean field lattice model (MFLM) predictions of O'Rourke-Muisener et al. We find that the MFLM with a single set of bulk and surface interaction parameters provides reasonable predictions of experimental ADXPS concentration depth profiles for all molecular weights and...

Thickness determination of molecularly thin lubricant films by angle-dependent X-ray photoelectron spectroscopy

An angle-dependent X-ray photoelectron spectroscopy (XPS) method used to measure the thickness of molecularly thin lubricants was developed. The method was built based on an island model of patched overlayer on a flat substrate by using the photoemission signal solely from the lubricant film. Typical molecularly thin Zdol films on the CHx overcoat of unused commercial magnetic disks were measured to verify the metrology. The lubricant thickness determined by the metrology was equal to the recent result by thermostatic high vacuum atomic force microscopy. The measured deduction in the thickness of the molecularly thin lubricant films, successively irradiated by the monochromatic source operated at 14kV/250W, was as low as 1Ǻ during the first irradiation hour. XPS spectra showed that no hydrocarbons, water or oxygen were adsorbed over the Zdol outer surfaces in the tested XPS conditions. The inelastic mean free path (IMFP) of C 1s in Zdol or in CHx was found to be independent of take off angle (TOA) when TOA<40°. The IMFP of C 1s in Zdol was ∼63.5Ǻ and the lubricant island thickness was ∼35Ǻ.

Carboxy-Terminated Oligo(ethylene glycol)−Alkane Phosphate: Synthesis and Self-Assembly on Titanium Oxide Surfaces

The surface immobilization of oligo- and poly(ethylene glycol) on solids is a widely used approach to prevent the nonspecific adsorption of proteins, bacteria, and cells. A novel tri(ethylene glycol) derivative, phosphoric acid-mono(22-carboxy-12,15,18,21-tetraoxadocosyl) ester, was synthesized with the aim to produce self-assembled monolayers (SAMs) on metal/metal oxide surfaces. This compound contains two reactive, terminal moieties: the phosphoric acid group as anchor to the surface, and the carboxylic group as linker for further attachment of molecules such as peptides and proteins to be present at the surface. The adsorption on titanium-dioxide-coated substrates was studied quantitatively and the resulting SAMs were characterized by angle-dependent X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS data showed that the monomolecular layer is attached with the phosphate group to the substrate, but not fully ordered. The dry adlayer thickness was determined to be 13.4 A, which is less than expected for a densely packed monolayer. Surface concentration calculated from ellipsometry data resulted in a grafting density of 2.03 molecules/nm2.

Metal Ion Interaction with Phosphorylated Tyrosine Analogue Monolayers on Gold

Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.

Surface Studies on the Ionic Liquid 1-Ethyl-3-Methylimidazolium Ethylsulfate Using X-Ray Photoelectron Spectroscopy (XPS)

Surface studies of ionic liquids are particularly important for all kinds of multiphasic operations employing ionic liquids, e.g. biphasic homogeneous catalysis or supported ionic liquid phase catalysis. Using X-ray photoelectron spectroscopy (XPS), the surface composition of the model system 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtOSO3] was investigated. By comparing two different samples of this ionic liquid from two different origins, we observed a decisive influence of silicon containing impurities on composition and structure of the surface. For the case of the impurities containing ionic liquid, our angle-dependent XPS data are in agreement with a model of a surface layer consisting of highly oriented ionic liquid molecules. From a fundamental point of view, our study may be of general relevance for the understanding of the chemistry of liquid surfaces in general.

Onset of surface segregation controlled by the segment length of the low-energy component of polymers

Films of a series of polymers with variable CF2 segments were studied by angle-dependent X-ray photoelectron spectroscopy (ADXPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The effects of the length of the CF2 segment on the surface composition of the polymers were investigated. ADXPS results indicated that the CF2 segment segregated on the surface of the polymers after thermal annealing at temperatures above their bulk glass transition temperatures when the number of CF2 units was increased to 8. Because of the higher surface sensitivity, ToF-SIMS results showed more CF2 segments at the topmost surface than shown by ADXPS. Copyright © 2006 John Wiley & Sons, Ltd.