Multi-instrument characterization of HiPIMS and DC magnetron sputtered tungsten and copper films

In this work, copper and tungsten were sputtered onto silicon wafers by direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS). The resulting films were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and X-ray diffraction (XRD). By EDX and XPS, all the sputtered films showed only the expected metal peaks. By XPS, the surfaces sputtered by DCMS were richer in oxygen than those produced by HiPIMS. By AFM, the surfaces were quite smooth. The root mean square (RMS) roughness values are as follows: 0.83 nm (W, HiPIMS), 1.10 nm (W, DCMS), 0.85 nm (Cu, HiPIMS), and 1.78 nm (Cu, DCMS). By SEM, the HiPIMS films exhibited smaller grain sizes, which was confirmed by XRD. The crystallite sizes estimated by XRD are as follows: 4 nm (W, body-centered cubic, HiPIMS), 13 nm (W, body-centered cubic, DCMS), 7 nm (W, cubic, HiPIMS), 14 nm (W, cubic, DCMS), 25 nm (Cu, HiPIMS), and 35 nm (Cu, DCMS). By SE, the HiPIMS surfaces showed higher refractive indices, which suggested that they were denser and less oxidized than the DCMS surfaces.     

Dense passivating poly(ethylene glycol) films on indium tin oxide substrates

We describe the formation and characterization of surface-passivating poly(ethylene glycol) (PEG) films on indium tin oxide (ITO) glass substrates. PEG chains with a molecular weight of 2000 and 5000 D were covalently attached to the substrates in a systematic approach using different coupling schemes. The coupling strategies included the direct grafting with PEG-silane, PEG-methacrylate, and PEG-bis(amine), as well as the two-step functionalization with aldehyde-bearing silane films and subsequent coupling with PEG-bis(amine). Elemental analysis by X-ray photoelectron spectroscopy (XPS) confirmed the successful surface modification, and XPS and ellipsometry provided values for film thicknesses. XPS and ellipsometry thickness values were almost identical for PEG-silane films but differed by up to 400% for the other PEG layers, suggesting a homogeneous layer for PEG-silane but an inhomogeneous distribution for other PEG coatings on the molecularly rough ITO substrates. Atomic force microscopy (AFM) and water contact angle goniometry confirmed the different degrees of surface homogeneity of the polymer films, with PEG-silane reducing the AFM rms surface roughness by 50% and the water contact angle hysteresis by 75% compared to uncoated ITO. The ability of the PEG layers to passivate the substrate against the nonspecific adsorption of biopolymers was tested using fluorescence-labeled immunoglobulin G and DNA oligonucleotides in combination with fluorescence microscopy. The results indicate a positive relationship between film density and homogeneity on one hand and the ability to passivate against biopolymer adhesion on the other hand. The most homogeneous layers prepared with PEG-silane reduced the nonspecific adsorption of fluorescence-labeled DNA by a factor of 300 compared to uncoated ITO. In addition, the study finds that the ratio of film thicknesses derived by ellipsometry and XPS is a useful parameter to quantify the structural integrity of PEG layers on molecularly rough ITO surfaces. The findings may be applied to characterize PEG or other polymeric films on similarly coarse substrates.     

Two Routes for Immobilization of a Hyperbranched OH-Terminated Polyester on a Silicon Surface

Summary: Stable thin films of a hyperbranched aromatic-aliphatic OH-terminated polyester (POH) were prepared on silicon substrates. We report on grafting-to processes using macromolecular (PGMA) and bifunctional low-molecular weight coupling agents (BOX). An appropriate annealing procedure was developed for the covalent immobilization. The HBP films were characterized with spectroscopic ellipsometry, drop shape analysis (DSA), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrokinetic measurements. The immobilized films have an uniform surface morphology and are slightly hydrophilic (θ_a = 79°). The grafting process did not influence the chemical composition and the surface properties, which is important for the further application as functional layers in aqueous media.     

Oxidation and nitridation of niobium films by rapid thermal processing

The oxidation and nitridation processes of niobium films in a rapid thermal processing (RTP) – system were investigated. 200 and 500 nm niobium films were deposited via sputtering on sapphire-(1-102)-substrate. At first niobium films were oxidized in molecular oxygen at temperatures ranging from 350 to 500 °C and for times of 1, 2 and 5 min and then nitridated in ammonia at 1000 °C for 1 min using an RTP system. For characterisation of the niobium films complementary analytical methods were used: X-ray diffraction (XRD) for phase analysis, secondary ion mass spectrometry (SIMS) for determining the elemental depth profiles of the films, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for characterisation of the surface morphology of the films. The influence of the substrate, single crystalline sapphire, on the reactivity of the niobium films was studied in dependence of temperature, time of reaction and film thickness. The possibility of existence of niobium oxynitride phase was investigated. According to XRD and SIMS data, there is evidence that an oxynitride phase is formed after oxidation and subsequent nitridation in the bulk of some Nb films. In some of the experiments crack formation in the films or even delamination of the Nb films from the substrates was observed.     

Characterization of self-assembled monolayers of thiols on Au(111)

Self-assembled monolayers (SAMs) of n-butanethiol, n-dodecanethiol and their equimolar mixture on Au(111) were prepared and characterized by ellipsometry, contact angle measurement, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results revealed that these SAMs are oriented ultrathin films with the thickness of nanometer scale, and the SAMs were influenced by the molecular chain length, the lattice orientation and cleanliness of the substrates. The surface of the longer chain SAM is hydrophobic. The thicknesses of three SAMs of n-butanethiol, n-dodecanethiol and their mixture revealed by ellipsometry and XPS are about 0.59 - 0.67nm, 1.60- 1.69 nm and 1.23 - 1.32nm, respectively. AFM images further demonstrated that the SAM formed by the mixture has some microdomains with two different thicknesses.     

Self-assembled monolayers prepared from ω-thiophene-functionalized n-alkyltrichlorosilane on silicon substrates

Self-assembled monolayers (SAMs) of thienyl-functionalized n-alkyltrichlorosilane (11-(3-thienyl)undecyltrichlorosilane [TUTS]) have been prepared by adsorption from solution and characterized by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle measurements, ellipsometry, and scanning electron microscopy (SEM). Using contact angle and SEM measurements, the film preparation protocol was optimized, resulting in reproducible SAM formation with no adverse deposition of polysiloxane particles. XPS and ellipsometry studies confirmed the existence of SAM formation. AFM results show a smooth and homogeneous SAM, with surface roughness of Ra≤0.2 nm, which is slightly higher than the corresponding values for octadecyltrichlorosilane (OTS) SAMs. Such thiophene-based SAM surfaces can be used for surface-initiated polymerization of thiophene. The resulting formed polythiophene layers at non-compatible surfaces offer some practical applications in manufacturing [W. Plieth, A. Fikus, D. Appelhans, H.-J. Adler, German Patent Application No. 2661977 (1998); D. Appelhans, D. Ferse, H.-J. Adler, A. Fikus, W. Plieth, B. Aldolphi et al., J. Electrochem. Soc. (accepted)].     

Dendrimer-functionalized self-assembled monolayers as a surface plasmon resonance sensor surface

We report here a multistep route for the immobilization of DNA and proteins on chemically modified gold substrates using fourth-generation NH(2)-terminated poly(amidoamine) dendrimers supported by an underlying amino undecanethiol (AUT) self-assembled monolayer (SAM). Bioactive ultrathin organic films were prepared via layer-by-layer self-assembly methods and characterized by fluorescence microscopy, variable angle spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). The thickness of the AUT SAM base layer on the gold substrates was determined to be 1.3 nm from ellipsometry. Fluorescence microscopy and AFM measurements, in combination with analyses of the XPS/ATR-FTIR spectra, confirmed the presence of the dendrimer/biopolymer molecules on the multilayer sensor surfaces. Model proteins, including streptavidin and rabbit immunoglobulin proteins, were covalently attached to the dendrimer layer using linear cross-linking reagents. Through surface plasmon resonance measurements, we found that sensor surfaces containing a dendrimer layer displayed an increased protein immobilization capacity, compared to AUT SAM sensor surfaces without dendrimer molecules. Other SPR studies also revealed that the dendrimer-based surfaces are useful for the sensitive and specific detection of DNA-DNA interactions. Significantly, the multicomponent films displayed a high level of stability during repeated regeneration and hybridization cycles, and the kinetics of the DNA-DNA hybridization process did not appear to be influenced by surface mass transport limiting effects.     

Synthesis of thin dense titania films via an aqueous solution-gel method

Nanostructured titanium dioxide films have been reported to be used in many applications ranging from optics and solar energy devices to gas sensors. This work describes the synthesis of nanocrystalline titania films via an aqueous solution-gel method. The thin films are deposited by spin coating an aqueous citratoperoxo-Ti(IV)-precursor solution onto a silicon substrate. The influence of processing parameters like Ti⁴⁺ concentration and crystallization temperature on the phase formation, crystallite size and surface morphology of the films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, the effect of successive layer deposition on the film thickness of the resulting films is studied by means of cross sectional SEM. SEM and TEM micrographs clearly show that, after optimization of the process parameters, thin, smooth, dense nanocrystalline films are synthesized in a reproducible manner. The films are composed of 15–20 nm grains. At higher crystallization temperatures (600, 650°C) also larger particles (40–70 nm) are present. XRD data reveal that a phase pure anatase film is formed at 450°C. Crystallization temperatures equal to or higher than 600 °C however give rise to the formation of both the anatase and rutile crystalline phases. The smoothness of the films is proved by their very low rms surface roughness (≤1.1 nm) measured by AFM.     

Covalent molecular assembly of multilayer dendrimer ultrathin films in supercritical medium

Ultrathin films containing dendrimers are fabricated on amine- and anhydride-derivatized silicon dioxide surface through alternate layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and poly(amidoamine) (PAMAM) dendrimer in supercritical carbon dioxide (SCCO2) with interlayer linkage established by covalent bonds. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis suggests that the PMDA/PAMAM interlayer covalent bond is established to completion, and functional surfaces for immobilization of the next layer are available after deposition of each layer. UV-visible absorption and ellipsometry revealed layer-by-layer growth of the film. The functional property film as a porous matrix was manifested in the reduction of the refractive index upon introduction of the dendrimer.     

PEGMA/MMA copolymer graftings: generation, protein resistance, and a hydrophobic domain

We synthesized various graft copolymer films of poly(ethylene glycol) methacrylate (PEGMA) and methyl methacrylate (MMA) on silicon to examine the dependency of protein-surface interactions on grafting composition. We optimized atom transfer radical polymerizations to achieve film thicknesses from 25 to 100 nm depending on the monomer mole fractions, and analyzed the resulting surfaces by X-ray photoelectron spectroscopy (XPS), ellipsometry, contact angle measurements, and atomic force microscopy (AFM). As determined by XPS, the stoichiometric ratios of copolymer graftings correlated with the concentrations of provided monomer solutions. However, we found an unexpected and pronounced hydrophobic domain on copolymer films with a molar amount of 10-40% PEGMA, as indicated by advancing contact angles of up to 90 degrees . Nevertheless, a breakdown of the protein-repelling character was only observed for a fraction of 15% PEGMA and lower, far in the hydrophobic domain. Investigation of the structural basis of this exceptional wettability by high-resolution AFM demonstrated the independence of this property from morphological features.     

The effect of Sn dopant on crystal structure and photocatalytic behavior of nanostructured titania thin films

In this study, preparation of Sn doped (0–30 mol % Sn) TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of Sn content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). Surface topography and surface chemical state of thin films were examined by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the Sn dopant. The prepared Sn-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photo-catalytic activity of TiO₂ thin films, and the optimum dopant amount is found to be 15 mol%. The Sn⁴⁺ dopants substituted Ti⁴⁺ in the lattice of TiO₂ and increased surface oxygen vacancies and the surface hydroxyl groups. TEM results showed small increase in planar spacing (was detected by HR-TEM caused by Sn dopants in titania based crystals).     

Li doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and optical properties

Thin films of ZnO were grown by the sol–gel method using spin-coating technique on (0001) sapphire substrates. The effect of doping after annealing on the structural and optical properties has been investigated by means of X-ray diffraction (XRD), cathodoluminescence (CL) spectrum, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films that were dried at 623 K and then post annealed at 873 K showed (0002) as the predominant orientation. Two emission bands have been observed from CL spectrum. Lithium doped film shows shift in the near band edge UltraViolet emission peak and suppressed defect level emission peak in the visible range. SEM analysis of the films exhibits many spherical shaped nanoparticles. Roughness of the films determined using atomic force microscopy.      

Characterization of Ultrathin Films of Cellulose Esters

The adsorption of cellulose acetate (CA), cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) from solutions prepared in acetone onto silicon wafers led to ultrathin films, which were characterized by ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The polysaccharides films were characterized in the air just after their formation and after annealing at temperatures higher than their glass transition temperature or melt temperature. The films thickness close to 2 nm and surface roughness did not vary significantly upon annealing. AFM images revealed the presence of small clumps dispersed on a homogeneous layer, which covered completely the Si wafers. Such topographic details were also observed after annealing. However, upon annealing the films surfaces changed from hydrophilic to hydrophobic, evidencing molecular re-orientation at the solid–air interface. The adhesion of bovine serum albumin (BSA) and lipase onto the cellulose esters films was quantified in order to evaluate the possibility of applying such films as selective support for biomolecules.     

Operation and application of a new time-of-flight e-gas secondary neutral mass spectrometer (ToF–SNMS)

The low-pressure rf plasma of a secondary neutral mass spectrometer (e-gas SNMS) was connected with a time-of-flight (ToF) mass spectrometer for the first time. As opposed to ToF–SIMS in e-gas SNMS, the primary ion pulse cannot be used for triggering the flight time measurement. Therefore, an extraction pulse is used which at a defined time loads an ion package from the beam of the post-ionised particles into the ToF spectrometer. The newly developed ToF–SNMS system is described, and first experimental results are presented.     

Characterization of the morphology and composition of commercial negative resists used for lithographic processes

We present a spectroscopic and microscopic characterization of the chemical composition, structure, and morphology of two commercial negative resists using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). For this purpose, films of a novolak-based resist (ma-N 2400) and hydrogen silsesquioxane (HSQ) are treated under different conditions (temperature, deep ultraviolet (DUV) exposure, CHF₃ plasma). Topographic AFM images show that both heating and DUV exposure strongly affect the surface morphology of as-prepared ma-N 2400 resist films. These different treatment conditions also lead to decreasing roughnesses, which indicates structural reorganization. Furthermore, the decrease of the photoactive compound (bisazide) in the ma-N 2400 resist films, observed in FTIR spectra, suggests cross-linking of the resist after CHF₃ plasma treatment, heating, or DUV exposure. XPS measurements on different CHF₃ plasma-treated surfaces reveal that a structurally homogeneous fluorine-containing polymer is generated that is responsible for an enhanced etch resistance. FTIR measurements of HSQ films show a correlation between the degree of HSQ cross-linking and baking time.     

Morphology and optical properties of thin silica films containing bimetallic Ag/Au nanoparticles

We have studied the optical spectra in the UV and visible regions, the morphology by scanning electron microscopy (SEM), and the X-ray photoelectron spectra (XPS) of bimetallic Ag/Au nanoparticles incorporated into transparent silicate films in the sol-gel transition stage. The bimetallic nanoparticles, obtained by a combination of photoreduction and thermal reduction, form structures of the alloy or core-shell type. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 348–353, November–December, 2008.     

The influence of annealing on electrochromic properties of Al–B–NiO thin films prepared by sol–gel

Al–B–NiO thin films were prepared using the sol–gel process and deposited on Indium tin oxide (ITO)-coated glass substrates via the dip-coating technique for the purpose of developing high performance electrochromic materials. The influence of the anneal on the structural and electrochromic properties of Al–B–NiO films is reported. Thermogravimetry (TG) and differential thermal analysis (DTA), cyclic voltammetry measurements (CV), UV spectrophotometer, atomic force microscopy (AFM) and X-ray diffraction (XRD) have been used to investigate the structural and electrochromic properties. The thickness of the films was determined by spectrophotometric analysis in 350–1,000 nm wavelength. Results showed that the Al–B–NiO thin films treated at high temperature have both the excellent electrochromic properties and good reversibility. The transmittance change (ΔT) of the film treated at 500 °C reaches still ~50% at the wavelength of 550 nm. The microstructure and the surface morphology were considered to play an important role in the electrochromic properties with different temperatures.     

Surface structure of thin film blends of polystyrene and poly(n -butyl methacrylate)

 Thin films of blends of polystyrene (PS) and poly(n-butyl methacrylate) (PBMA) were prepared by spin-casting onto silicon wafers in order to map the lateral distribution of the two polymers. The surfaces were examined by atomic force microscopy (AFM) secondary ion mass spectroscopy X-ray photoelectron spectroscopy (XPS) and photoemission electron microscopy (PEEM). Films with PBMA contents of 50% w/w or less were relatively smooth, but further increase in the PBMA content produced, initially, protruding PS ribbons and then, for PBMA ≥80% w/w, isolated PS islands. At all concentrations the topmost surface (0.5–1.0 nm) was covered by PBMA, whilst the PBMA concentration in the near-surface region, measured by XPS, increased with bulk content to eventual saturation. PEEM measurements of a PS–PBMA film at the composition at which ribbon features were observed by AFM also showed a PS-rich ribbon structure surrounded by a sea of mainly PBMA. Received: 6 December 1999/Accepted: 5 April 2000     

Stability of monomolecular films of archaebacterial tetraether lipids on silicon wafers: a comparison of physisorbed and chemisorbed monolayers

The monomolecular organisation of symmetric, chemically modified tetraether lipids caldarchaeol-PO(4) was studied using Langmuir film balance, ellipsometry, and atomic force microscopy (AFM). Solid silicon wafer substrates were modified to hydrophobic, hydrophilic, and amino-silanised surfaces; and Langmuir-Blodgett (LB)-films were transferred onto each. LB-caldarchaeol-PO(4) films were subjected to further rinsing with organic solvent and additional physical treatments, to compare their resistance and stability on chemisorbed (amino-silanised) and physisorbed (hydrophobic and hydrophilic) surfaces. The resistance and stability of these monolayer films was characterized by ellipsometry and AFM, and film thickness was determined using ellipsometry. AFM was also employed to observe surface morphology. Monolayer films on hydrophobic surfaces were found to be more resistant to rinsing with organic solvent and additional physical treatments than monolayer films on either amino-silanised or hydrophilic surfaces. The hydrophobic effect with hydrophobic surfaces appears to support the formation of stronger caldarchaeol-PO(4) films on silicon wafer substrates, with increased resistance and stability.     

NHS-ester functionalized poly(PEGMA) brushes on silicon surface for covalent protein immobilization

Poly(PEGMA) homopolymer brushes were developed by atom transfer radical polymerization (ATRP) on the initiator-modified silicon surface (Si-initiator). Through covalent binding, protein immobilization on the poly(PEGMA) films was enabled by further NHS-ester functionalization of the poly(PEGMA) chain ends. The formation of polymer brushes was confirmed by assessing the surface composition (XPS) and morphology (atomic force microscopy (AFM), scanning electronic microscopy (SEM)) of the modified silicon wafer. The binding performance of the NHS-ester functionalized surfaces with two proteins horseradish peroxidase (HRP) and chicken immunoglobulin (IgG) was monitored by direct observation. These results suggest that this method which incorporates the properties of polymer brush onto the binding surfaces may be a good strategy suitable for covalent protein immobilization.