Scientific applications range from analytical and medical instrumentation to the use of vacuum in particle physics, space research, nuclear fusion, material sciences, biology and chemistry. Many of the developments and discoveries made across these sectors simply would not have been possible without vacuum technology. Of course, since the applications and markets are so diverse, each application requires a different vacuum solution and poses different challenges. With this considered, an understanding of the underlying principles that govern vacuum science and the hardware available is essential for all those in the industry.
A vacuum is when the atmospheric pressure falls below the threshold of mbar — corresponding to a value of mbar absolute. On the other hand, one talks about negative pressure when the value exceeds this. Vacuum does not mean vacuum to everyone in the industry. The range below mbar can be broken down even further, beginning with the fine and high vacuum and moving up to the optimal ultra-high vacuum. A perfect vacuum would be able to reach an absolute pressure of 0. Without so-called vacuum pump units, it would not be possible, to reach this range.
When comparing vacuum pumps to compressors, the main difference is in the product results; generating vacuum pressure, or excess pressure, is physically achieved via similar methods. While a compressor compresses the outside air in a pressure tank, blower releases the gases outside, thus evacuating the gas from any sealed room.
Using vacuum blowers is not only limited to air-related industrial tasks, but can also be used with all possible gases. It is also important to know that not every vacuum blower is suitable for numerous applications and processes. Depending on the different properties of gases, and the size of their molecules, the technology has to be synchronised with the desired task. In addition, taking the environmental conditions into account is also an important factor in which a vacuum blower should be used.
Especially in the chemical, pharmaceutical and food industries, difficult production requirements prevail. There are also gases that are aggressive to equipment or even cause health hazards in industrial use. Others are dangerous. For this reason, it is essential that the correct separation of evacuated gases, and their proper disposal, are never neglected.
Depending on the strength of the desired vacuum, AERZEN offers a variety of components that can reach and maintain the precise desired values. Adhering to desired parameters for specific needs in vacuum and high vacuum technology is extremely important.
It is also important to recognise these circumstances beforehand, so the right equipment is used. For example, parameters needed in the steel industry vary immensely from the application of vacuum blowers elsewhere. Depending on the requirements needed, so-called pumping stations work using several levels and, in general, more than two levels are used.
Without such pumping stations, an economical production of a low, fine and high vacuum would not make sense — let alone be possible. The interaction of pre-pumps and rotary blowers signals the use of two-level pumping stations. While the negative pressure can be reached between mbar and mbar absolute at one level, it is well under the threshold for vacuums and a combination of pre-pumps and vacuum rotary blowers is necessary.
Here, the pre-pump already reduces the pressure in the first step in the respective tank or room. Next, the rotary blower can be turned on and can, combined with the pre-pump, produce the desired final vacuum or volume flow that is required for the particular application. In order to plan the vacuum unit correctly, the operator must specify the necessary parameters to the manufacturer. Content from this work may be used under the terms of the Creative Commons Attribution 3. Any further distribution of this work must maintain attribution to the author s and the title of the work, journal citation and DOI.
Vacuum sciences have received wide recognition as a broad research field comprising applied surface science, biointerfaces, electronic materials, nanometre structures, plasma science, surface engineering, surface science, thin films and pure vacuum science. The aim of this review paper is to highlight recent advances in vacuum sciences. Pure vacuum science is focused on outgassing of materials used in vacuum systems, rarified gas dynamics with modelling of complex vacuum systems and vacuum metrology.
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New developments in electron transport near solid surfaces are reviewed. Progress in analysis of carbon-based nanostructures and applications of surface analytical methods in conservation technology of cultural heritage objects will be presented. Indeed, bioimplants, anti-fouling properties, biomedical or diagnostic devices are some of the emerging technologies and applications which need fundamental understanding and knowledge. Ultra-high vacuum UHV -based surface analytical tools are used extensively for research, development and quality control of such biointerfaces, as powerful and reference tools.
A selection of examples is presented, focusing on chemical speciation and quantification of surface functional groups as well as their reactivity, combining XPS and ToF-SIMS measurements. The more challenging aspects in probing biointerfaces lie in in situ characterizations at the solid—liquid interface in atmospheric conditions: existing analytical methods are then coupled to improved or dedicated new techniques, resulting in new approaches and methodologies.
Surface engineering deals with the materials science and technology of modifying and improving the surface properties of materials for protection in demanding contact conditions or aggressive environments, as well as designing different functionalities with respect to combination of electrical, optical, thermal, chemical, and biochemical responses, including adaptive and active control of functions. Current hot topics are the synthesis of multifunctional surfaces, including active and adaptive control, the design of interfaces, and implementation of modelling approaches based on density functional theory, molecular dynamics simulations, and finite element methods for materials development, as well as engineered multilayers and nanostructured coatings.
Recent progress in thin films includes the growth of thin film on granulates and hollow microspheres, MAX phases, magnetic and oxide thin films, and nanostructured thin films. We also discuss carrier mobility in organic thin films, quantum dot QD self-assembly, and superlattices investigation using grazing incidence small angle x-ray scattering GISAXS. Current hot topics in plasma science include plasma nanoscience and plasma biomedicine.
Methods for improved hemocompatibility of cardiovascular implants and soaking capacity of wound dressings are presented. Hypotheses on selective destruction of bacteria on body tissues are introduced and a theory on propagation of plasma bullets created by pulsed atmospheric low-frequency discharges is enlightened.
Pure vacuum science is focused on outgassing of materials used in vacuum systems, rarified gas dynamic with modelling of complex vacuum systems and vacuum metrology. Vacuum Science is in general the physics and chemistry of surfaces. The fact that in vacuum the particle density on the surface goes up to ten orders of magnitude higher than in the volume, means the processes on the surface of the wall material are decisive.
The main research and developments in this field are thus documented in surface and applied surface science. The technological scope of pure vacuum science and technology is stimulated and forced by very large projects.
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This installation is the largest vacuum system in the world and the main goal was to establish extremely low pressure in the beam line to avoid collisions during the acceleration of particles. A key issue for vacuum science research was the study of the outgassing behaviour of materials. Among all technical alloys stainless steel SS is the construction material of choice. Its main advantages are: standard machining and welding techniques, it is non-magnetic and chemically inert.
The most disadvantageous property of SS is the outgassing of hydrogen. Since this outgassing of H determines the ultimate pressure of an UHV system the reduction of the outgassing rate is essential. Among different treatments such as bakeout in inert and low hydrogen content atmosphere, formation of adlayers to suppress the rate, high temperature bakeout thermal outgassing in vacuum became the most efficient way to reduce hydrogen outgassing.
Thermal outgassing and in general the cleaning techniques in accelerator applications and in the majority of UHV applications is largely well understood [ 1 — 4 ]. Unfortunately a considerable part of the research work is not published but is shared within the vacuum science community at meetings, workshops [ 5 ] and conferences. These coatings have two main advantages: lower desorption yield compared to materials used for accelerator vacuum chambers such as SS, copper and aluminum, and the coating acts as a virtual vacuum pump of uniformly distributed pumping speed.
Recent results demonstrate well that the NEG coated vacuum chamber, even non-activated, performs better than a baked SS chamber. Being saturated, the NEG coating can be re-activated by electron bombardment. It has been found that the NEG coating morphology is very important for its proper operation [ 8 — 11 ]. Although the thermal outgassing is the main source of gas in the majority of vacuum systems, there is a class of vacuum system where desorption is induced by energetic particle photon, electrons, ions, etc bombarding or irradiating the vacuum chamber walls.
Often this induced or stimulated desorption is a dominant source of gas in a vacuum system. To study different surface treatment to reduce such induced desorption e. Desorption yields were studied for numerous materials and coatings bombarded with different ions of different charge state and different energies and are documented in [ 14 — 17 ].
Presently most of the research activities in vacuum science and technology are focused on the huge fusion project ITER. ITER is a large-scale scientific experiment that aims to demonstrate that it is possible to produce commercial energy from fusion. The scientific goal of the ITER project is to deliver ten times the power it consumes.
During its operational lifetime, ITER will test key technologies necessary for the next step: that it will be possible to capture fusion energy for commercial use. The successful operation of ITER requires the largest, complex vacuum systems yet to be built. The vacuum spaces on ITER are provided by a set of around vacuum pumps of ten different technologies. These are serviced by a network of vacuum lines. All gasses with the potential of being radioactive are routed to the vacuum pumping room in the tritium plant building.
Some vacuum spaces such as the cryostat and cryogenic guard vacuum systems are always kept segregated to avoid contamination. Other vacuum spaces such as the torus and neutral beam vessels are frequently connected and form part of the closed fuel cycle. The optimal design of the ITER vacuum system benefits from both a practical and theoretical understanding of gas dynamics over an extreme range of different conditions [ 19 ].
Rarefied gas dynamics became an important part of the design and modelling of large vacuum systems and microsystems [ 18 , 20 — 22 ]. Great efforts were made, therefore, to develop numerical and analytical methods to calculate rarefied gas flows and describe them in appropriate reviews [ 23 — 26 ]. Since in practice, however, one deals more with gaseous mixtures than with a single gas, the mathematical modelling of transport phenomena in gaseous mixtures is one of the present activities [ 19 ]. Gaseous mixture flows are determined by more parameters than single-gas flows.
Besides the parameters for gas rarefaction, pressure, and temperature, mixture flows depend upon the chemical composition and the species composing the mixture. As a result of these complexities, the computational effort to model gaseous mixture flows drastically increases in comparison to that of a single gas.
Several theoretical approaches to numerical calculations of gaseous mixtures over the whole range of Knudsen numbers have been developed [ 27 — 38 ] and the validity tested in benchmark problems [ 39 — 41 ]. Rarified gas dynamics plays an important role in the development of new pumping concepts for Tritium in the ITER vacuum system.
All hydrogen isotopes originating from the torus or the cryopumps, during regeneration, are first pumped by a cryogenic viscous flow compressor CVC. The design of the CVC was first optimized by modelling the gas dynamics and in parallel building and testing prototypes. Modelling of the gas flowing into the pump and through the pre-cooler heat exchanger and freezing tubes was first performed with a computational fluid dynamics CFD code.
Computational investigations of complex geometries of model cryopumps have been performed using rarified gas dynamics with DSMC method. Since the flow close to the cryopanels can be assumed free molecular due to low pressures, the capture coefficient of the cryopanels can be estimated by applying the test particle Monte Carlo method.
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Then, this information can be used as input data to the corresponding DSMC simulations [ 42 ]. Simulation of the true three-dimensional 3D complex geometry of the model cryopump by the newly developed PROVAC3D Monte Carlo code shows in the free molecular regime that the numerical simulation results are in good agreement with the pumping speeds measured. This means that the test particle Monte Carlo simulations in free molecular flow can be used not only for the optimization of the pumping system but also for the supply of the input parameters necessary for the future DSMC in the full flow regime [ 43 ].
Significant increase in the performance of classical pumps such as turbomolecular pumps was also obtained by gas dynamic calculations [ 44 ]. Research and development work in vacuum metrology is basically concentrated to national institutions of standardization. The plan is to develop ultra-precise optical interferometer cavity devices for pressure standards that will be accurate to about 1.
Such devices—initially developed at the size of a small mailing tube—would find immediate applications in commercial aviation, semiconductor SC manufacturing, and military activities, and they would also eliminate persistent difficulties in pressure metrology.
The pressure and temperature of a gas are directly related to its density. Gas density is, in turn, directly related to the refractivity of the gas. An FP cavity is formed by careful alignment of two highly reflective mirrors at each end of an enclosure figure 1. A laser is locked to an FP cavity by tuning its frequency such that an integer number of half-wavelengths fit between the mirrors.
Figure 1. Since the vacuum sections of seven European National Metrology Institutes, supported by five industrial partners and three research grants, have worked together in the consortium EMRP IND 12 'vacuum metrology for production environments' to open up new measurement capabilities for vacuum and to help industry to characterize vacuum in industrial environments.
In the first work package it is investigated how fast vacuum gauges can react on pressure changes in load locks or during fast processes. To accomplish this, a gas expansion is carried out from a small chamber of 0. The mass flow rate can be calculated by gas flow simulation software so that it is possible to predict the pressures and temperatures figure 2 at any time in the small chamber. The aim of the second work package is to improve the knowledge of gas flow through nano- and micro-channels in terms of predictability for different gas species and environmental conditions with the focus on the industrial applications and conditions.
In the third work package, dedicated calibration facilities for quadrupole mass spectrometers QMSs were developed and the factors influencing metrological characteristics of QMS are presently examined. A workshop was organized in April [ 49 ] to gather the latest information from manufacturers and key users of QMSs. In the same work package, traceability and standardized procedures for outgassing rate measurements will be developed as well. With EUV lithography the importance of traceable outgassing rate measurements has considerably increased, since all the components built into such facilities must be carefully checked in order not to affect the reflectivity of the x-ray mirrors.
To this end the community has established the new term 'ultraclean vacuum' which characterizes a high-vacuum environment which is particle and hydrocarbon free. Figure 2. Reproduced with permission from [ 48 ]. Copyright Elsevier. The equivalence of eleven National Standards for leak calibrations was tested in an international comparison [ 52 ] for the first time. By this comparison, industrial laboratories for leak calibrations can be accredited and get international recognition of their certificates.
Applied surface science has recently become one of the most important fields of research stimulating the revolutionary changes in science and technology of our age. Below, examples for some of the latest remarkable achievements are reviewed briefly in three selected subsections: 3. Electron transport near solid surfaces; 3. Surface analysis of carbon-based nanostructures; 3. Applications of surface analytical methods in conservation technology of properties of cultural heritage.
Novel methods, elaborated for describing accurately near-surface energy loss processes and simulating electron, photon and ion-induced electron spectra have predicted new phenomena during surface excitations, as confirmed later by experiments. Applications of these methods for interpretation of electron spectra reveal unknown details of electronic structure of new materials of great practical importance.
The upper part of figure 3 shows a process called the supersurface scattering, not identified before in experimental electron backscattering spectra or in related simulations [ 57 ]. As a consequence of the surface plasmon excitation in vacuum near an Au surface by the incoming or outgoing electrons, their energy and direction is changing slightly, leading to large changes in the probability of electron backscattering near the deep minima in the differential elastic scattering cross section DECS versus scattering angle curve lower part of figure 3.
This phenomenon results in strong oscillations of the angular dependence of the surface excitation probability in vacuum side of the solid and these oscillations are anti-correlated with the changes in the DECS as a function of the scattering angle. The experimental data well reproduce the predictions of simulations accounting for angular deflection of electrons moving in vacuum near the surface [ 57 ]. Posing new challenges to the present assumptions on the surface excitation parameter, this is the first direct observation of surface plasmon excitations by an electron moving in vacuum near surface.
Figure 3. Lower part of the figure; b Average number of surface excitations absolute units as a function of electron emission angle. The solid curve with data points shows the experimental values, the dashed and solid curves the values calculated using Monte Carlo simulations without and with accounting for deflections due to surface excitations, respectively. The curves in the upper part of b are related to the surface excitations while the electrons move in vacuum, the curves in the lower part of b to the surface excitations while the electrons move inside the solid.
Reproduced with permission from [ 57 ]. Copyright American Physical Society. Compared to the case when a photoelectron travels in an infinite solid, the presence of the ionized atom with a suddenly created core hole left behind and the surface surface excitations at surface crossings of the emitted photoelectrons influence decrease the intensity of the photoelectrons emitted from a solid.
Pauly and Tougaard used the dielectric response model for describing the combined effects of the core hole and the surface [ 58 ]. Figure 4 shows the parameter CP XPS accounting for the attenuation of the XPS peak intensity as a function of the emission angle with respect to the surface normal , for different energy photoelectrons, in the case of Si [ 58 ]. Figure 4. The parameter CP XPS accounting for the reduction of the XPS peak intensity—as a consequence of the effect of the core hole left behind and the effect of surface excitations at surface crossing of the photoelectrons—as a function of the emission angle with respect to the surface normal , for different energy photoelectrons, in the case of Si.
Reproduced with permission from [ 58 ]. Complex application of surface analytical methods for studying chemical and structural properties of doped or functionalized carbon nanotubes CNTs or graphene layers lead to the development and production of new, highly effective catalysts of important chemical reactions, as well as to further exciting novel applications of these nanostructures in science and technology. Multiwalled carbon nanotubes MWCNTs , due to their or their modified forms' unique physical and chemical properties are very interesting materials for applications of great significance e.
Before modifications, however, the synthesized MWCNTs need to be purified, removing all contaminations amorphous carbon, traces of catalysts and catalyst's support, defects, etc. It was shown from the consistent results of this complex analysis that the proposed wet chemical purification and modification method effectively removes all impurities originating from the procedure of synthesizing the MWCNTs [ 60 ].
The surface sensitivity of the electron spectroscopic methods proved to be greatly helpful in determining quantitatively the surface properties, such as the surface chemical composition of the 'as-received' or modified MWCNTs or in determining the content of the C sp 2 and C sp 3 bonds from the first derivative [ 61 ] of the C KLL Auger spectra [ 60 ]. In the case of various polymers the combined application of electron spectroscopic methods EPES, REELS, XPS and the pattern recognition method to study effects of electron induced degradation resulted in the consistent identification of phenomena as decreasing content of hydrogen and increasing the C sp 2 bond content during irradiation [ 63 ].
These studies provide information on the stability of different polymers against electron induced degradation as well [ 63 ]. Graphene structures are in the focus of the frontline research nowadays because of their unique physical properties and the strong hope to witness soon a spectacular increase of their various important practical applications.
This result—the controllable production of the electric superlattice in graphene—has a fundamental significance for the nano-electro-mechanic systems NEMSs based on graphene [ 64 ]. Figure 5. Lower part: STM line scan showing the magnitude of the ripples. Reproduced with permission from [ 65 ]. Copyright Nature. The number of applications of surface and interface analytical methods in studies of archaeological objects and conservation technology of cultural heritage is steadily increasing. An important field of applications is the study of deteriorating environmental effects—including biodeterioration, bio-degradation and weathering—on cultural heritage artefacts.
Because the surface region of cultural heritage objects can be very complex and heterogeneous, for characterizing the nature, structure and composition of these materials, in most cases a combination of complementary analytical methods are needed. Below, some examples of applications of surface analytical methods for studies and conservation of mosaics, ancient wall paintings and wooden objects are mentioned.
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The study revealed not only the chemical composition and degradation state of the tesserae, but provided information on the procedure of their fabrication and their origin as well [ 65 ]. Surface and bulk techniques, such as XPS, XRF, XRD, laser induced breakdown spectroscopy and ionic chromatography were used for characterizing pieces from the wall matrix sampled at different depths when investigating the degradation of the walls with medieval graffiti in the Chiaramonte Palace in Palermo [ 66 ].
Application of combined surface and bulk analytical methods proved to be very important for improving conservation technology of historical wooden objects as ancient wrecks of battleships buried under the sea [ 67 ]. These studies made clear that iron acted as a catalyst of sulfur oxidation and the origin of sulfur was attributable to the activity of bacteria living in the deep sea and converting the sulfate content pollution into hydrogen sulfide that penetrated into the wooden parts of the ships [ 67 ].
Figure 6 shows XPS spectra taken along an oak core cut from the orlop deck of the ancient shipwreck of the warship Kronan sank in the Baltic Sea [ 68 ]. The spectra indicate the presence of the dominating reduced 'S 8 ' and the oxidized ' ' forms of sulfur the quantity of the latter is increasing close to the surfaces and the presence of the silicon, chloride and phosphate in the core.
These results stimulated further and more detailed research of deteriorating and conservation processes in the case of shipwrecks, including studies of wooden materials exposed to simulated environments [ 67 , 68 ] and on the basis of the analytical results and model experiments, new procedures were proposed for safe long-term conservation of waterlogged wood objects.
Figure 6. XPS spectra of regions along an oak core taken from the orlop deck of the shipwreck of the warship Kronan sank in the Baltic Sea in during a battle. The spectra show the presence of the dominating reduced 'S 8 ' and the oxidized ' ' forms of sulfur the quantity of the latter is increasing close to the surfaces and the presence of the silicon, chloride and phosphate in the core.
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Reproduced with permission from [ 68 ]. Indeed, implants, biomedical or diagnostic devices, biotechnology, personal care, food production, anti-fouling properties, are some of the emerging technologies and applications which need fundamental understanding and knowledge. However, experimental techniques which reveal the details of the solid—liquid processes provide limited information and, in many cases, do not provide information that may be interpreted in a reliable and quantitative manner.
Within this field, many practitioners rely upon the use of vacuum-based methods to understand the nature of the interface before and after events have taken place within a liquid. Thus, UHV-based surface analytical tools are used extensively for research, development and quality control of such biointerfaces, as powerful and reference tools. Another point is that the theme of biointerfaces is transversal and multidisciplinary, thus there is a general consensus that access to historical studies and data is difficult and presents a significant barrier for new researchers in the area.
The main issues appear to be that the earliest works are hard to find using modern databases due to patchy coverage; recent studies are published in a wide range of journals and are of a variable quality. Providing the link between surfaces, characterizations and UHV, a dedicated issue of the Surface Science journal published a series of reviews of great interest [ 69 ]. Where, what and how many are fundamental questions which must be systematically answered with regard to the adsorbed biomolecules.
A selection of examples will be presented, focusing on chemical speciation and quantification of surface functional groups as well as their reactivity, combining XPS and ToF-SIMS measurements. Personalized medicine and point of care POC diagnostics are fields of tremendously growing importance in the recent society.
Devices developed for personalized medicine and POC often make use of interfaces engineered on a bio- molecular level. Proper function can be only reached when these interfaces are carefully characterized enabling optimization and trouble shooting. An example of a type of diagnostic device used for personalized medicine and POC is a microarray. Successful microarrays require careful characterization of the interfaces between supports i. For real medical applications and clinical use, biosensors like microarrays have to go through an approval process under control of regulatory authorities e.
A thorough physical—chemical characterization of biointerfaces by surface chemical analysis is of great benefit for a deeper understanding of what really happens at the interfaces mentioned above and to get proper control on them. Such studies result in a more rational design and further optimization in terms of sensitivity and specificity of biosensing devices.
Specifically, microarrays represent a sensor system in the field of medical diagnostics that allows simultaneous screening of a wide range of biomarkers in a patient's serum or other bio matrices using a single chip. Diagnostic microarrays are highly relevant multiplex or high-throughput diagnostic devices. DNA or oligonucleotide arrays are often prepared on amino-terminated supports either by selective covalent binding to the amino NH 2 groups or by unspecific UV cross-linking of the oligonucleotides to the support material. Amino surfaces can be obtained from a number of different vendors.
XPS analysis of such slides demonstrated that the chemical species on the surface might be rather different from that intended and the final performance achieved by a microarray thereon will therefore be less than ideal [ 70 ]. In the same way, the amounts of other nitrogen-containing species can be determined as well and this kind of information is rather useful for quality assessments because only free amines and can be used for the immobilization reactions in the next step of microarray production.
Besides amide, various other species hampering a reproducible DNA attachment can be present on the surface, e. Besides aminated supports, epoxy slides enjoy great popularity for microarray applications due to their broad reactivity towards various functional groups as thiols, amines and alcohols.
Immobilization of many different classes of biomolecules is enabled in this case. Recently successful quantification of reactive epoxy surface groups was demonstrated in a combined XPS and fluorescence approach using Rhodamine as a dye [ 75 ]. On-going research is done to use that dual XPS-fluorescence label approach for quantification of other reactive surface groups, for example, amino groups, using a custom-made Bodipy dye [ 76 ].
Other relevant microarrays are based on carbohydrate-based interactions. Especially for clinical diagnostics, these so-called glycan microarrays play a vital role because carbohydrate-based interactions are involved in many recognition events in a living cell. So it is a challenge for surface chemical analysis to characterize the specific surface chemistry of immobilized sugar molecules on glycan microarrays. A model surface using a dimannose-thiol self-assembled monolayer SAM on gold was prepared in order to identify specific spectral signatures in XPS and ToF-SIMS, which are useful to characterize relevant chemical moieties present on biointerfaces at glycan microarrays [ 77 — 79 ].
High-resolution C 1s XPS of the printed arrays showed component peaks of carbohydrate-specific acetal and C—O moieties allowing imaging and quantification of immobilized carbohydrates in single spots. Figure 7. In a more fundamental approach, simple and versatile design of oligoethylene based SAM using thiolene chemistry, starting from commercially available compounds, and providing high-quality SAM exhibiting adhesive and anti-adhesive patterns, have been demonstrated on metal oxide surfaces: on silicon oxides and particularly glass substrate for cell biology applications but also on biocompatible metals such as titanium [ 80 ].
The C 1s core-level spectra indicate that, in the first step, a robust vinyl-terminated surface C, C—H species was obtained a , in a second step, the adhesive O- 2-Carboxyethyl -O'- 2-mercaptoethyl heptaethylene glycol has reacted b to the previous surface new O—C—O, C—O bonds.