Atomic Force Microscopy Scratching Research Articles

Superlubricity and Stress-Shielding of Graphene Enables Ultra Scratch-Resistant Glasses.

Glasses, when subjected to scratch loading, incur damages affecting their optical and mechanical integrity. Here, it is demonstrated that silica glasses protected with mechanically exfoliated few-layer graphene sheets can exhibit remarkable improvement in scratch resistance. To this extent, the friction and wear characteristics of silica glasses with exfoliated graphene using atomic force microscopy (AFM) are explored. The friction forces recorded during AFM scratch tests of the graphene-glass surfaces at multiple loads exhibit ∼98% reduction compared to that of the bare silica glass, with the friction coefficient falling in the superlubricity regime. This dramatic reduction in friction achieved by the graphene sheets results in significantly lower wear of the graphene-glass surfaces postscratching. Further investigations employing atomistic simulations reveal that the stress-shielding mechanism is due to the reduced deformation of graphene-glass surfaces, thereby curtailing the overall damage. Altogether, the present work provides a new fillip toward the development of glasses with enhanced scratch resistance exploiting two-dimensional coatings.

Effect of pH of H2O2 solutions on the morphology and wear resistance of human dental enamel: an AFM study

Introduction Teeth whitening is a highly demanded aesthetic dental procedure to remove teeth stains and get a whiter and perfect smile. This type of treatment is usually performed by the application on the teeth surface of hydrogen or carbamide peroxides which diffuse through the external layer of the teeth, enamel [1]. Although whitening treatments improve teeth appearance, they can impair teeth health, due to the eventual degradation of the teeth tissues. This may lead to abnormal wear and weaken the tooth structure. The aim of this work is to study the effect of the pH of 30% H2O2 solutions on the surface of human enamel. Materials and methods Human molars were collected for the study with informed consents of the patients. Teeth were bleached in 30% H2O2 solution with different pH values (2, 4 and 6). All samples were submitted to 11 bleaching sessions of 10 min each with alternate periods (2 min) of exposition to blue light. Microhardness, surface roughness and topography/morphology were characterised by microindentation tests, atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively, before and after the whitening treatments. AFM scratching tests (10 × 10 µm2) were performed, using a diamond probe. After the nanowear tests, topographical images of larger areas (20 × 20 µm2) which include the scratched squares were obtained with a silicon probe. The wear mechanisms were evaluated by SEM. Acceptance of the study protocol was obtained from a local ethics committee. Results The most significant changes on enamel surface were obtained for pH = 2: the microhardness decreases, and the surface roughness significantly increases as confirmed by the SEM image analysis. A higher wear rate was observed for pH = 2 in the AFM scratching tests. SEM observation of the wear zone showed differences in the wear mechanisms, which depend on the pH. Discussion and Conclusions Enamel microhardness, surface roughness and wear resistance are affected by the pH of the bleaching solution: pH = 2 led to the most adverse effects, which was attributed to hydroxyapatite demineralisation. The study of the effect of pH in the bleaching treatments is crucial to optimise this type of procedures and avoids enamel damage.

Towards understanding the machining mechanism of the atomic force microscopy tip-based nanomilling process

Atomic force microscopy (AFM) tip-based nanofabrication is as a powerful method to machine nanostructures. However, the traditional AFM scratching process suffers from low processing efficiency and a low rate of material removal. Thus, an AFM tip-based nanomilling method was previously proposed to improve the machining efficiency and material removal rate; however, the machining mechanism of the nanomilling process, especially on hard-brittle silicon crystals, is not well understood. In this study, we used an AFM tip-based nanomilling approach to machine nanochannels on single-crystal silicon to investigate the machining mechanism (i.e., the material removal state, undeformed chip thickness, the brittle-to-ductile transition, and subsurface damage). For the first time, we established a theoretical model for tip-based nanomilling with a constant normal load to predict the machined depth. Nanochannels fabricated with a wide range of feed directions, crystal orientations, and tip trajectories were obtained, which provided a reference for machining high-quality nanochannels and an in-depth understanding of the nanomilling of single-crystal silicon. The experimental results demonstrated that we could machine a nanochannel without pile-ups by selecting a specific trajectory with a feed smaller than 4 nm in the 0° direction, a normal load no greater than 120 μN, and a crystal orientation at rotation angles of 135°, 157.5°, or 180°. Moreover, transmission electron microscope analysis of the subsurface of the nanochannel revealed a large number of dislocations, stacking faults, and a layer of amorphous silicon. Our findings are of great significance for obtaining high-quality nanochannels with a predicable machined depth and understanding the nanomilling mechanism of hard-brittle materials.

Electrografting of Sterically Bulky Tetramethylaniline Groups on Glassy Carbon Electrodes through Aryldiazonium Chemistry: Reasons for the Formation of Multilayers

AbstractWithin the field of electrografting with aryldiazonium cations, there are various methods available to graft a monolayer of organic groups onto electrode surfaces. One of these relies on the presence of steric groups or constraints on the aryldiazonium cation itself, which prevent multilayers from being formed by blocking access of the free aryl carbons on the grafted layer to the diazonium cations. Here, we investigate the nature of the layer formed from the electrochemical reduction of bulky 2,3,5,6‐tetramethylaniline monodiazonium cations on glassy carbon (GC) electrodes, to form 2,3,5,6‐tetramethylaniline‐modified GC (GC−TMA), which was subsequently characterized by atomic force microscopy scratching, cyclic voltammetry, electrochemical impedance spectroscopy, and X‐ray photoelectron spectroscopy. Despite the bulky structure of the TMA group, GC−TMA was found to exhibit sparse multilayers, owing to the ability of the precursor to undergo its own electropolymerization under the experimental conditions used.

Fluorinated zirconia-based sol-gel hybrid coatings on polycarbonate with high durability and improved scratch resistance

Hard, scratch-resistant and transparent fluoropolymer-based hybrid coatings are successfully prepared through the sol-gel chemistry and investigated, in the attempt to correlate the chemical, physical and surface properties of these materials with the mechanical properties (i.e. hardness and elastic modulus) measured at the nanoscale by atomic force microscopy (AFM). The organic component of these coatings consists in a hydroxyl-functional fluoropolymer resin, which belongs to the class of chlorotrifluoroethylene-vinylether copolymers and exhibits remarkable properties such as easy handling, great weather resistance, good adhesion and flexibility of coatings. A functionalization of this copolymer is also performed using an isocyanate-functionalized silane in order to assure a covalent cross-linking of organic fluorinated resin with inorganic phases. The combination of the silanized chlorotrifluoroethylene-vinylether copolymer with different sols composed of silica and zirconia is used to obtain high scratch resistance and high durability coatings on polycarbonate. A series of three hybrid coatings with different zirconia/silica molar ratios (0.09/0.48) are developed and analyzed by differential scanning calorimetry (DSC), water contact angle measurements, pencil hardness and adhesion tests. AFM scratch hardness, coating wettability and surface composition measured by Fourier transform infrared spectroscopy (FTIR) are regularly monitored over long-term UV–vis light exposure, to assess the durability of the hybrid coatings. Interestingly, the hybrid fluorinated coatings exhibit an improved scratch resistance and a superior long-term stability when exposed to an accelerated weathering, compared to pristine PC substrates. The mixed silica/zirconia hybrid coatings with a low and intermediate zirconia-to-silica ratio also show excellent mechanical strength, high level of hardness and superior integrity after long-term light exposure.

Tip-Based Nanomanufacturing of Nanofluidics Using Atomic Force Microscopy

Presently, nanomanufacturing capabilities limit the commercialization of a broader range of nanoscale structures with higher complexity, greater precision and accuracy, and a substantially improved performance. Atomic force microscopy (AFM)-based nanomachining is a promising technique to address current limitations and is considered a potential manufacturing (MFG) tool for operations such as machining, patterning, and assembling with in situ metrology and visualization. Most existing techniques for fabrication of nanofluidic channels involve the use of electron-beam lithography, which is a very expensive process that requires a lengthy calibration procedure. In this work, atomic force microscopy (AFM) is employed in the fabrication of nanofluidic channels for medical applications. Channels with various depths and widths are fabricated using AFM indentation and scratching. A nanoscale channel is mainly used in the study of the molecular behavior at single molecule level. The resulting device can be used for detecting, analyzing and separating biomolecules, DNA stretching, and separation of elite group of lysosome and other viruses. The nanochannels are integrated between microchannels and act as filters to separate biomolecules. Sharply developed vertical microchannels are produced from deep reaction ion etching. Poly-dimethylsiloxane (PDMS) bonding is performed to close the top surface of the silicon device. An experimental setup is used for testing by flowing fluid through the channels. A cost evaluation shows 47.7% manufacturing-time and 60.6% manufacturing-cost savings, compared to more traditional processes.

The Characterization of CVD-Grown Graphene Modified with Nitrophenyl Groups Using the Diazonium Reduction Method

Graphene, the two-dimensional carbon allotrope, has been attracted much interest since its discovery by Novoselov, Geim and co-workers.1 One of the most promising route for synthesizing a large-area graphene is by chemical vapor deposition (CVD) on catalytic substrate (for example nickel).2 Often the multilayer graphene is formed on the Ni surface by CVD and recently, the morphological properties and electrochemical behavior of multilayer graphene was studied in our research group.3 The modification of carbon substrates via electrochemical reduction of diazonium salts has been an important research area.4 The electrografting has been widely performed in the narrow potential range where the reduction peak of aryldiazonium compound is observed, however the results have shown that the formed aryl layers are rather thin.4 Lately, a special grafting procedure based on diazonium chemistry was used in order to form thick aryl layers on different substrates.5 Recently, anthraquinone layers with high thickness were electrografted on graphene-based substrates using this special modification procedure.6 Considering the fact that the thickness of aryl layer depends on the modification procedure,5,6the main aim of this work was to form thin and thick 4-nitrophenyl (NP) layers on CVD-grown graphene on Ni foil (designated as Ni/Gra) using 4-nitrobenzenediazonium tetrafluoroborate (NBD) and to compare the morphological and electrochemical properties of differently modified Ni/Gra/NP electrodes. To our knowledge, the formation of thick NP films on Ni/Gra electrodes was applied for the first time. For this work, the Ni/Gra electrodes were prepared in the Institute of Physics of the University of Tartu and further characterization of Ni/Gra samples by various surface analytical techniques confirmed the presence of good quality of multilayer graphene on Ni foil.3,7 To form thin and thick NP layers on Ni/Gra electrodes, three modification procedures were applied: (1) one potential cycle in the narrow potential range (0.6 to -0.5 V vs. SCE at a scan rate (ν) of 100 mV s–1), (2) 10 potential cycles in the narrow potential range (0.6 to -0.5 V vs. SCE, ν = 100 mV s–1) followed by holding the electrode at -0.2 V for 10 min and (3) 10 potential cycles in wider potential range (0.6 to -1.4 V vs. SCE, ν = 1 V s–1). All the modifications were carried out in acetonitrile containing 1 mM of NBD and 0.1 M tetrabutylammonium tetrafluoroborate as a base electrolyte. The characterization of NP-modified Ni/Gra electrodes was performed by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy. The experimental results revealed that the electrochemical behavior during electrografting was different when narrow or wider potential range was used.7 The XPS analysis confirmed the presence of NP layers on Ni/Gra surfaces and the Raman spectra revealed a small D peak after electrografting of Ni/Gra samples.7 The AFM images showed that the typical pattern of Ni/Gra was clearly visible in case of using narrow potential range during electrografting. When wider potential range was applied, the Ni/Gra was fully covered with granular structure and the characteristic folds and wrinkles of the underlying material were rarely visible.7 Additionally, the NP layer thickness was determined by AFM scratching method: 5, 20 and 30 nm for the Ni/Gra electrodes modified by procedures (1), (2) and (3).7These results indicate that to obtain thicker NP film on Ni/Gra electrodes, the potential cycling in a wider potential range is more preferable than using narrow potential range. The importance of aryl-modified graphene is generally recognized and we do believe that the results obtained in the present work give further insight into their properties.

Nano-mechanical properties of starch and gluten biopolymers from atomic force microscopy

An original method based on atomic force microscopy (AFM) in contact mode was developed to abrade progressively the surface of tablets made of starch or gluten polymers isolated from wheat. The volume of the material removed by the tip was estimated from the analysis of successive topographic images of the surface, and the shear force was measured by keeping a constant normal force. Our data together with a simple tribological model provide clear evidence for a higher hardness and shear strength of starch compared to gluten. Gluten appears to have mechanical properties close to soft materials, such as talc, whereas starch displays higher hardness close to calcite. Our results are in a better agreement with structural properties of gluten (complex protein network) and starch (granular and semi-cristalline structure) than earlier studies by micro-indentation. This work shows that the AFM scratching method is relevant for the characterization of any polymer surface, in particular in application to materials made of different polymers at the nano-scale.

Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates.

This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone.

Molecular Adsorption on ZnO(101̅0) Single-Crystal Surfaces: Morphology and Charge Transfer

While ZnO has excellent electrical properties, it has not been widely used for dye-sensitized solar cells, in part because ZnO is chemically less stable than widely used TiO(2). The functional groups typically used for surface passivation and for attaching dye molecules either bind weakly or etch the ZnO surface. We have compared the formation of molecular layers from alkane molecules with terminal carboxylic acid, alcohol, amine, phosphonic acid, or thiol functional groups on single-crystal zinc oxide (1010) surfaces. Atomic force microscopy (AFM) images show that alkyl carboxylic acids etch the surface whereas alkyl amine and alkyl alcohols bind only weakly on the ZnO(1010) surface. Phosphonic acid-terminated molecules were found to bind to the surface in a heterogeneous manner, forming clusters of molecules. Alkanethiols were found to bind to the surface, forming highly uniform monolayers with some etching detected after long immersion times in an alkanethiol solution. Monolayers of hexadecylphosphonic acid and octadecanethiol were further analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. AFM scratching shows that thiols were bound strongly to the ZnO surface, suggesting the formation of strong Zn-S covalent bonds. Surprisingly, the tridentate phosphonic acids adhered much more weakly than the monodentate thiol. The influence of organic grafting on the charge transfer to ZnO was studied by time-resolved surface photovoltage measurements and electrochemical impedance measurements. Our results show that the grafting of thiols to ZnO leads to robust surfaces and reduces the surface band bending due to midgap surface states.

Assessment of Coating Adhesion Degradation by Atomic Force Microscopy Scratching

Abstract The effects of environmental exposure on polymer coating degradation were studied using atomic force microscopy (AFM) scratching. Adhesion was assessed by the coating removal rate during controlled-force contact mode scratching in the AFM. Low-carbon steel coupons were coated with an ultra-high molecular weight epoxy resin and exposed to environments with high relative humidity and exposure to ultraviolet light. AFM scratching was performed both in air and in water to assess the effect of water on adhesion degradation. The average coating removal rate increased when samples were first degraded by environmental exposure and by scratching in water. AFM scratching is shown to be a quantitative method for the assessment of adhesion and adhesion degradation for coatings less than about 4 μm in thickness.

A novel bio‐functionalization of AlGaN/GaN‐ISFETs for DNA‐sensors

AbstractAlGaN/GaN pH sensitive devices were functionalized and passivated for the use as selective biosensors. For the passivation, a multilayer of SiO2 and SiNx is proposed, which stabilizes the pH‐sensor, is biocompatible and has no negative impact on the following bio‐functionalization. The functionalization of the GaN‐surface was achieved by covalent bonding of 10‐amino‐dec‐1‐ene molecules by a photochemical process. After exposure to ultraviolet light, islands of TFAAD are growing on the sensor surface. After 3 h exposure one monolayer is completed. Further exposure results in thicker films as a consequence of polymerization. The bonding to the sensor surface was analyzed by x‐ray photo electron spectroscopy, while the thickness of the functionalization was determined by atomic force microscopy scratching experiments. These functionalized devices based on the pH‐sensitive AlGaN/GaN ISFET will establish a new family of adaptive, selective biomolecular sensors such as selective, reusable DNA sensors. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of a Novel Process Chain Based on Atomic Force Microscopy Scratching for Small and Medium Series Production of Polymer Nanostructured Components

The continuing trend for producing novel micro- and nanostructured devices and components in a broad range of materials is a major motivating factor driving the research in the micro- and nanomanufacturing sector toward developing innovative process chains. Some of such chains enable the serial production of micro- and nanostructured parts in polymer material by combining innovatively and optimizing simultaneously master making and replication technologies. For producing features at the nanoscale, the master making processes that are currently commonly employed rely on complex lithography-based pattern transfers and/or on beam-based direct write processes. Unfortunately, the required equipment to perform these techniques are often capital intensive and necessitate particular operating temperatures or vacuum conditions. At the same time, during the development phase of new or improved nanotechnology-enabled products, it is beneficial to produce rapidly polymer prototypes to test the functionality of components with nanoscale features. Thus, the technologies currently available for nanostructuring replication masters do not comply with the low cost requirements typically associated with the production of small batches of components for prototyping purposes. As a result, this could restrict the successful development of products with functional features at the nanoscale. In this research, a new process chain is presented for the fabrication of nanostructured components in polymer that relies on a simple and cost-effective master making technology. In particular, atomic force microscopy scratching is employed as an alternative technique for nanostructuring replication masters for microinjection molding. The conducted experimental study demonstrated the potential of this approach for small and medium series production of nanostructured devices in thermoplastic materials. In addition, the effects of different scratching parameters on the achievable surface roughness and depth of the patterned structures were analyzed by employing the design of experiments approach.

A comparison study of scratch and wear properties using atomic force microscopy

The patterning technique that uses an AFM (atomic force microscopy) tip as a scratch tool, also known as AFM scratching, has been a vital technique for nanofabrication because of its low cost and potential to reach a resolution into the sub-nanometer domain. The AFM scratching technique was first used to study the scratch characteristics of silicon, with an emphasis on establishing its scratchability or the nanoscale machinability. The effects of the scratch parameters, including the applied tip force and number of scratches, on the size of the scratched geometry were specifically evaluated. The primary property that measures the scratchability was identified and assessed. To illustrate its suitability and reliability, the value of the scratchability, based on the present Si scratching experiments, was compared with the values based on the data available in the literatures for different scratching conditions or for materials other than Si. Since AFM scratching is in some aspects similar to the nanoscale wear test, the scratchability property identified is also compared with two major wear resistance indicators, wear coefficient and hardness. All comparison results indicate that the scratchability property identified, the scratch ratio, is an appropriate manufacturability indicator for measuring the degree of the ease or difficulty of a material scratched by an AFM tip and more suitable than the wear coefficient and hardness to gauge the nanoscale AFM scratchability.

Characterization of optical fiber end-plane machining with atomic force microscopy scratching

Characterization of optical fiber end-plane machining with atomic force microscopy scratching

Surface growth processes induced by AFM debris production. A continuum picture

Recent ultra-high vacuum (UHV) scratching atomic force microscopy (AFM) experiments showed the formation of small clusters, larger aggregates or regular patterns on the surface being scanned. In this paper, we suggest a theory that should capture the basic mechanisms that produce the formation of such structures. Such cluster structures, generally self-organized in regular structures, are mainly produced by the flux of adatoms generated by the AFM tip stripping off adatoms during the continuous passage of the probe tip on the surface being analysed. We assume that surface diffusion is the dominant transport mechanism of mass and a nonequilibrium thermodynamics framework for the self-organized growth process is developed. The accurate knowledge of such growth structures is important for two main reasons: it is possible to have an indirect measurement of the incidence of the wear basic mechanisms involved during the AFM scratching test while analysing the structures generated and the patterned structures produced could be used as a base (precursor factor) for mature surface growth processes. Despite granular structure of atom-by-atom nature of the debris, our theory uses a continuum approach for the description of the surface growth induced during the wearing passage of the probe tip.

Removal Method of Nano-Cut Debris for Photomask Repair Using an Atomic Force Microscopy System

Recently, photomask repairing techniques by scratching fabrication using an atomic force microscopy (AFM) system have been developed. However, the machining method using AFM produces cut debris during photomask repair, which induces problems and errors in photolithography. Here, we describe a novel removal method for cut debris produced in an AFM photomask repair process. The removing method is based on electrophoretic migration. A small amount of aqueous solution is dropped on a cantilever, then two electrodes placed on both sides of the cantilever form an electric field gradient around the cantilever under the liquid condition. Under the condition, the particles of cut debris produced by AFM scratching are dispersed and become spontaneously charged in the liquid, and then the particles can be consequently removed by electrophoresis migration. In particular, smaller cut particles produced by ultrasonic scratching, that is, scratching with probe oscillation, are very suitable for the removal method owing to the ease of electrophoresis migration. These techniques would be very effective in the AFM photomask repair process.

A comparative study of titanium nitrides, TiN, TiNbN and TiCN, as coatings for biomedical applications

A strategy used to reduce wear of the ultra high molecular weight polyethylene (UHMWPE) component of orthopedic joint implants has been to coat the metallic part with a hard ceramic layer. The advantage of this procedure is to reduce both wear and ion release of the metal while keeping a high mechanical resistance. In the present study, the performance of three titanium nitride coatings: TiN, TiNbN, and TiCN for biomedical applications was assessed in terms of their surface properties and cytotoxicity. The morphology, chemical composition, and wettability were determined through atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and contact angle measurement, respectively. The tribological behaviour of the coatings rubbing against UHMWPE in lubricated conditions was investigated using a pin-on-disk apparatus. Albumin adsorption on the three coatings was studied with a quartz crystal microbalance with dissipation (QCM-D) and AFM scratching. Cytotoxicity was determined both in direct or indirect contact of the cells with the coating materials. The results demonstrate that the three coatings have similar surface properties and are not cytotoxic. TiNbN seems to have the best tribological performance in the presence of albumin, although albumin adsorption is slightly higher on TiN.

Characterization of Head Overcoat for 1 Tb/in$^{2}$ Magnetic Recording

To achieve a 1 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> system, diamond-like carbon (DLC) on head and disk have to meet the criteria of corrosion- and wear-resistance at thicknesses of less than 2 nm. This paper will assess the performance of head and disk overcoat for a 1 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> system and beyond, with focus on the influence of DLC forming technologies, thickness, and substrate materials. To evaluate DLC film, sp <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> fraction was measured by X-ray photoelectron spectroscopy (XPS). It was shown that DLC films fabricated by filtered cathodic vacuum arc (FCVA) would have less sp <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> fraction with decreasing thickness. To evaluate corrosion- and wear-resistance, coverage and critical loads were measured by XPS and atomic force microscopy scratch test. XPS revealed that DLC films prepared by both FCVA and ion-assisted sputtering had sufficient coverage at thickness of down to 1 nm. Atomic force microscopy scratch test showed that critical load depends on substrate materials and DLC thickness, not on DLC forming methods.

A novel functionalization of AlGaN/GaN-pH-Sensors for DNA-sensors

AbstractAlGaN/GaN pH sensitive devices were functionalized and passivated for the use as selective bio-sensors. For the passivation, a multilayer of SiO2 and SiNx is proposed, which stabilizes the pH-sensor, is biocompatible and has no negative impact on the following bio-functionalization. The functionalization of the GaN-surface was achieved by covalent bonding of 10-amino-dec-1-ene molecules by a photochemical process. After two different surface preparations islands of TFAAD are growing on the sensor surface by exposure with UV-light. In dependence on the surface pre-treatment and the illumination wavelength the first monolayer is completed after 3 h or 7 h exposure time dependent on the pre-treatment and illumination wavelength. Further exposure results in thicker films as a consequence of cross polymerization. The bonding to the sensor surface was analyzed by X-ray photoelectron spectroscopy, while the thickness of the functionalization was determined by atomic force microscopy scratching experiments. These functionalized devices based on the pH-sensitive AlGaN/GaN ISFET will establish a new family of adaptive, selective biomolecular sensors such as selective, reusable DNA sensors.