White Light Interferometer Microscopy Research Articles

Bacteriostatic Poly Ethylene Glycol Plasma Coatings for Orthodontic Titanium Mini-Implants.

Titanium mini-implants are used as anchorage for orthodontic tooth movements. However, these implants present problems due to the infection of surrounding tissues. The aim of this work was to obtain a polyethylene glycol (PEG) layer by plasma in order to achieve a bacteriostatic surface. Titanium surfaces were activated by argon plasma and, after, by PEG plasma with different powers (100, 150 and 200 W) for 30 and 60 min. The roughness was determined by white light interferometer microscopy and the wettability was determined by the contact angle technique. Surface chemical compositions were characterized by X-ray photoelectron spectroscopy (XPS) and cytocompatibility and cell adhesion studies were performed with fibroblast (hFFs) and osteoblast (SAOS-2) cells. Bacterial cultures with Spectrococcus Sanguinis and Lactobacillus Salivarius were performed, and bacterial colonization was determined. The results showed that plasma treatments do not affect the roughness. Plasma makes the surfaces more hydrophilic by decreasing the contact angles from 64.2° for titanium to 5.2° for argon-activated titanium, with values ranging from 12° to 25° for the different PEG treatments. The plasma has two effects: the cleaning of the surface and the formation of the PEG layer. The biocompatibility results were, for all cases, higher than 80%. The polymerization treatment with PEG reduced the adhesion of hFFs from 7000 to 6000 and, for SAOS-2, from 14,000 to 6500, for pure titanium and those treated with PEG, respectively. Bacterial adhesion was also reduced from 600 to 300 CFU/mm2 for Spetrococcuns Sanguinis and from 10,000 to 900 CFU/mm2 for Lactobacillus Salivarius. The best bacteriostatic treatment corresponded to PEG at 100 W and 30 s. As a consequence, the PEG coating would significantly prevent the formation of bacterial biofilm on the surface of titanium mini-implants.

Calibration method of the phase-shifting error for the topography measurement utilizing white light interferometric microscopy

Calibration method of the phase-shifting error for the topography measurement utilizing white light interferometric microscopy

Benefits of Residual Aluminum Oxide for Sand Blasting Titanium Dental Implants: Osseointegration and Bactericidal Effects.

Objectives. The purpose of this work was to determine the influence of residual alumina after sand blasting treatment in titanium dental implants. This paper studied the effect of alumina on physico-chemical surface properties, such as: surface wettability, surface energy. Osseointegration and bacteria adhesion were determined in order to determine the effect of the abrasive particles. Materials and Methods. Three surfaces were studied: (1) as-received, (2) rough surface with residual alumina from sand blasting on the surface and (3) with the same roughness but without residual alumina. Roughness was determined by white light interferometer microscopy. Surface wettability was evaluated with a contact angle video-based system and the surface free energy by means of Owens and Wendt equation. Scanning electron microscopy equipped with microanalysis was used to study the morphology and determine the chemical composition of the surfaces. Bacteria (Lactobacillus salivarius and Streptococcus sanguinis) were cultured in each surface. In total, 110 dental implants were placed into the bone of eight minipigs in order to compare the osseointegration. The percentage of bone-to-implant contact was determined after 4 and 6 weeks of implantation with histometric analysis. Results. The surfaces with residual alumina presented a lower surface free energy than clean surfaces. The in vivo studies demonstrated that the residual alumina accelerated bone tissue growth at different implantation times, in relation to clean dental implants. In addition, residual alumina showed a bactericidal effect by decreasing the quantity of bacteria adhering to the titanium. Conclusions. It is possible to verify the benefits that the alumina (percentages around 8% in weight) produces on the surface of titanium dental implants. Clinical relevance. Clinicians should be aware of the benefits of sand-blasted alumina due to the physico-chemical surface changes demonstrated in in vivo tests.

Effect of the Acid-Etching on Grit-Blasted Dental Implants to Improve Osseointegration: Histomorphometric Analysis of the Bone-Implant Contact in the Rabbit Tibia Model

Previous studies have shown that the most reliable way to evaluate the success of an implant is by bone-to-implant contact (BIC). Recent techniques allow modifications to the implant surface that improve mechanical and biological characteristics, and also upgrade osseointegration. Objective: The aim was to evaluate the osseointegration in rabbit tibia of two different titanium dental implant surfaces: shot-blasted with Al2O3 (SB) and the same treatment with an acid-etching by immersion for 15 s in HCl/H2SO4 (SB + AE). Material and methods: Roughness parameters (Ra, Rt, and Rz) were determined by white light interferometer microscopy. Surface wettability was evaluated with a contact angle video-based system using water, di-iodomethane, and formamide. Surface free energy was determined by means of Owens and Wendt equations. Scanning electron microscopy equipped with X-ray microanalysis was used to study the morphology and determine the chemical composition of the surfaces. Twenty-four grade 4 titanium dental implants (Essential Klockner®) were implanted in the rabbit’s tibia, 12 for each surface treatment, using six rabbits. Six weeks later the rabbits were sacrificed and the implants were sent for histologic analysis. Resonance frequency analysis (RFA) was recorded both at the time of surgery and the end of the research with each device (Osstell Mentor and Osstell ISQ). Results: The roughness measurements between the two treatments did not show statistically significant differences. However, the effect of the acid etching made the surface slightly more hydrophilic (decreasing contact angle from 74.7 for SB to 64.3 for SB + AE) and it presented a higher surface energy. The bone-to-implant contact ratio (BIC %) showed a similar tendency, with 55.18 ± 15.67 and 59.9 ± 13.15 for SB and SB + AE implants, respectively. After 6 weeks of healing, the SB + AE showed an implant stability quotient (ISQ) value of 76 ± 4.47 and the shot-blasted one an ISQ value of 75.83 ± 8.44 (no statistically significant difference). Implants with different surface properties had distinctive forms of behavior regarding osseointegration. Furthermore, the Osstell system was an invasive and reliable method to measure implant stability. Conclusion: Both surfaces of implants studied showed high osseointegration. The SB and SB + AE implants used in our study had similar behavior both in terms of BIC values and RFA. The RFA systems in Osstell Mentor and Osstell ISQ confirmed nearly perfect reproducibility and repeatability.

Influence of curved surface roughness on white light interferometer microscopy

We outline the basic theory behind white light interferometry and the workings of a typical light interferometer microscope. We study WLI images obtained for rough and smooth chrome steel spheres to illustrate the principle that curved rough surfaces can be imaged with such a device as long as the surface roughness is kept within certain limits.

Surface Finishing of Single-Crystal SiC and GaN Wafers Using a Magnetic Tool in H2O2Solution

To remove the microroughness and subsurface damage on the SiC and GaN surface efficiently, a surface finishing technique using a magnetic tool holding iron particles in a hydrogen peroxide solution is developed. This technique utilizes OH radicals generated from the iron catalytic particles in a hydrogen peroxide solution, and can be used to preferentially remove the topmost convex part on the surface, resulting in an atomically smooth surface. We employed this polishing technique to finish the surfaces of 2-inch SiC and 2-inch GaN wafers. The surface roughness before and after finishing was measured by scanning white light interferometric microscopy and atomic force microscopy. In addition, the material removal rate was calculated by weight loss due to the finishing process. The results show that the surface roughness on the SiC and GaN wafers is markedly improved. Moreover, the surface waviness and flatness of these wafers before and after finishing did not deteriorate. Atomic force microscope images indicate that an atomically flat SiC surface with a roughness value below 0.1 nm RMS and a GaN surface with atomic step and terrace structures were achieved. Our proposed finishing technique is effective in improving the surface microroughness of SiC and GaN wafers.

Novel planarization method of single-crystal diamond using 172 nm vacuum-ultraviolet light

We propose a novel planarization method for diamond substrates with 172 nm vacuum-ultraviolet (VUV) irradiation. To demonstrate the effectiveness of the proposed method, a polishing plate made of sapphire was used to polish diamond substrates with and without VUV irradiation under atmospheric conditions at room temperature. To interpret the planarization mechanism of the diamond substrate, the hydrophilic nature, cleanliness, and chemical-bonding state of the polishing plate before and after VUV irradiation were analyzed by a contact angle meter and X-ray photoelectron spectroscopy (XPS). The surface roughness and material removal rate were measured and evaluated by scanning white light interferometric microscopy and atomic force microscopy. The chemical-bonding state on the diamond surface before and after polishing were also analyzed by XPS. The experimental results show that VUV irradiation yields a hydrophilic and OH-terminated surface on the polishing plate, and give the effects in terms of the material removal rate and surface finish. The material removal rate with VUV irradiation (238.1 nm/h) was approximately seven times higher than that without VUV irradiation (33.3 nm/h). An atomically smooth diamond surface with a root-mean-square surface roughness below 0.1 nm can be prepared by polishing with VUV irradiation within 1.5 h.

Design of a dynamic biofilm imaging cell for white-light interferometric microscopy

In microbiology research, there is a strong need for next-generation imaging and sensing instrumentation that will enable minimally invasive and label-free investigation of soft, hydrated structures, such as in bacterial biofilms. White-light interferometry (WLI) can provide high-resolution images of surface topology without the use of fluorescent labels but is not typically used to image biofilms because there is insufficient refractive index contrast to induce reflection from the biofilm’s interface. The soft structure and water-like bulk properties of hydrated biofilms make them difficult to characterize in situ, especially in a nondestructive manner. We build on our prior description of static biofilm imaging and describe the design of a dynamic growth flow cell that enables monitoring of the thickness and topology of live biofilms over time using a WLI microscope. The microfluidic system is designed to grow biofilms in dynamic conditions and to create a reflective interface on the surface while minimizing disruption of fragile structures. The imaging cell was also designed to accommodate limitations imposed by the depth of focus of the microscope’s objective lens. Example images of live biofilm samples are shown to illustrate the ability of the flow cell and WLI instrument to (1) support bacterial growth and biofilm development, (2) image biofilm structure that reflects growth in flow conditions, and (3) monitor biofilm development over time nondestructively. In future work, the apparatus described here will enable surface metrology measurements (roughness, surface area, etc.) of biofilms and may be used to observe changes in biofilm structure in response to changes in environmental conditions (e.g., flow velocity, availability of nutrients, and presence of biocides). This development will open opportunities for the use of WLI in bioimaging.

Planarization of GaN by tribochemical polishing

In recent years, GaN is expected as a next generation power semiconductor material. However, GaN is known to a high hardness material that is difficult to machine. In order to realize the high precision and high efficiency polihing, tribochemical polishing of GaN substrate under the atmospheric condition was investigated. In this study, four different types of polishing plates, such as a sapphire, quartz glass, borosilicate glass and soda-lime glass, were used to polish the GaN substrate. The material removal rate (MRR) and the microroghness of GaN substrate was evaluated by scanning white light interferometric microscopy and atomic force microscopy. As a result, we concluded that for improving the MRR and the microroghness of the GaN substrate in tribochemical polishing technique, soda-lime glass was the most suitable among all the selected materials of the polishing plates. Obtained results show that the surface roughness of GaN is markedly improved from 0.375 nm Rms to 0.063 nm Rms and the MRR is 1746 nm/h.

Study of the aggregation and adsorption of asphaltene sub-fractions A1 and A2 by white light interferometry: Importance of A1 sub-fraction in the aggregation process

In the present work we show the application of white light interferometric microscopy to study the adsorption of asphaltene on to glass surfaces. Asphaltenes, isolated from two different crude oils and dissolved in chloroform, were studied. The adsorption behavior of the total asphaltene and two sub-fractions is presented and the adsorption behavior is correlated with the solubility of each sub-fraction in different solvents. The existence of nanoaggregates of asphaltenes, even in a good solvent such as chloroform, is presented. The importance of each asphaltene sub-fraction in the aggregation and subsequent deposition is clearly shown. The characteristics of the adsorbed film illustrate differences in the average molecular structures of each sub-fraction and their impact on the solute–solute interaction and consequently the solubility. The results demonstrate, for the first time, the importance of A2, the asphaltene sub-fraction which is soluble, in the impact in the aggregate adsorption.

Comparison of two experimental methods for the mechanical characterization of thin or thick films from the study of micromachined circular diaphragms

The purpose of this study was to compare two experimental methods and evaluate the effectiveness of a set of analytical models in order to measure the initial stress and the Young's modulus value of thin and thick film materials. Two types of experiments were performed on micromachined circular diaphragms: bulge testing and vibrometry. The range of validity and accuracy of the analytical models with respect to the vibration of the diaphragms was discussed from the finite element simulations. It was shown that the a/t ratio should be considered carefully to determine the value of the Young's modulus by vibrometry with an acceptable error. A relative error of approximately ±10% on E was obtained for a/t ≤ 750. For 750 ≤ a/t ≤ 1000, the value of the dimensionless parameter k must also be considered. It has been shown that the residual stress value can be obtained with an accuracy of 10% or less, given that k > 12. As an illustration, experimental methods and models were applied to the characterization of a thick electroplated gold film and a sputter-deposited Inconel thin film. Circular structures were defined by vertical sidewalls etched on the back of a Si wafer using the deep reactive ion etching technique. In addition to analytical models, parametric finite element simulations and a design optimization technique were used to determine the material's mechanical properties. The static deflections of the diaphragms were measured as a function of the applied pressure. The resonant frequencies and mode shapes of the vibrating structures were observed under vacuum by white-light interferometric microscopy. For gold, it was found that E = (53 ± 20) GPa and σ(0) = (180 ± 10) MPa. For Inconel, it was found that E = (157 ± 14) GPa and σ(0) = (172 ± 5) MPa.

The Effect of Deformation Speed on Frictional Behavior by Tip Test

In this study, a tip test was carried out under various ram velocities of 0.01 mm/s, 0.1 mm/s, 1.0 mm/s, and 5.0 mm/s to investigate the effect of deformation speed on friction using the commercially available AL6061-O. For experiments, four different lubrication conditions with grease, corn oil, VG100, and VG32 were used to investigate the lubrication characteristics. During the test, temperature was measured in the specimen by a K-type thermocouple to determine the temperature increase induced by heat generation due to plastic deformation. In the present investigation, the linearity between tip distance and experimentally measured maximum load was consistently observed in spite of different orders of ram velocity and types of lubrication. As the ram velocity increased, loads were reduced for liquid lubricants and increased for grease. To better understand such a lubrication phenomenon, white-light interferometer microscopy and laser confocal microscopy were used to observe and compare surface topographies on the bottom and circumferential side of the deformed specimens at various experimental conditions, which formed lubrication pockets incurring hydrodynamic pressure of liquid lubricants. Finally, the effect of deformation speed on the level of shear friction factors at the punch and die interfaces was characterized by the finite element simulations and was determined to be expressed as an exponential function depending on the lubricant. This investigation demonstrates the capability of the tip test to experimentally characterize the effect of deformation speed on the frictional behavior for practical use.

High reflection mirrors for pulse compression gratings

We report an experimental investigation of high reflection mirrors used to fabricate gratings for pulse compression application at the wavelength of 1.053microm. Two kinds of mirrors are studied: the mixed Metal MultiLayer Dielectric (MMLD) mirrors which combine a gold metal layer with some e-beam evaporated dielectric bilayers on the top and the standard e-beam evaporated MultiLayer Dielectric (MLD) mirrors. Various samples were manufactured, damage tested at a pulse duration of 500fs. Damage sites were subsequently observed by means of Nomarski microscopy and white light interferometer microscopy. The comparison of the results evidences that if MMLD design can offer damage performances rather similar to MLD design, it also exhibits lower stresses; being thus an optimal mirror substrate for a pulse compression grating operating under vacuum.

Full-field evaluation of the onset of microplasticity in a steel specimen

This work deals with the study of the local onset of microplasticity in a steel specimen under tensile test through the use of a full-field strain measurement method at the micrometric scale. The kinematic measurements were performed by the so called grid method. In order to produce the gratings, direct interferential photolithography was used. The gratings were digitized through the use of a white-light interferometric microscope. An adapted image stitching algorithm, applied to the phase maps, has been developed and implemented in order to extend the size of the region of interest. With this method, and by paying a particular attention to the conduct of the mechanical tests, the strain resolution obtained ranges from 1 to 2 × 10 −3 for a spatial resolution of about 20 μ m. In this paper, the method was applied to the study of the onset of local elasto-plastic strains in a ferritic steel coupon. The results show that the method is well suited to study small localized strains, for which few alternatives exist. To the best knowledge of the authors, it is the first time that white-light interferometric microscopy is used to measure full-field strains. The technique is reasonably easy to set up although a number of limitations exist. The paper is concluded by some considerations about further work required to extend the range of applicability of the method.

Metal particles produced by laser ablation for ICP–MS measurements

Pulsed laser ablation (266 nm) was used to generate metal particles of Zn and Al alloys using femtosecond (150 fs) and nanosecond (4 ns) laser pulses with identical fluences of 50 J cm −2. Characterization of particles and correlation with inductively coupled plasma mass spectrometer (ICP–MS) performance was investigated. Particles produced by nanosecond laser ablation were mainly primary particles with irregular shape and hard agglomerates (without internal voids). Particles produced by femtosecond laser ablation consisted of spherical primary particles and soft agglomerates formed from numerous small particles. Examination of the craters by white light interferometric microscopy showed that there is a rim of material surrounding the craters formed after nanosecond laser ablation. The determination of the crater volume by white light interferometric microscopy, considering the rim of material surrounding ablation craters, revealed that the volume ratio (fs/ns) of the craters on the selected samples was approximately 9 (Zn), 7 (NIST627 alloy) and 5 (NIST1711 alloy) times more ablated mass with femtosecond pulsed ablation compared to nanosecond pulsed ablation. In addition, an increase of Al concentration from 0 to 5% in Zn base alloys caused a large increase in the diameter of the particles, up to 65% while using nanosecond laser pulses. When the ablated particles were carried in argon into an ICP–MS, the Zn and Al signals intensities were greater by factors of ∼50 and ∼12 for fs versus ns ablation. Femtosecond pulsed ablation also reduced temporal fluctuations in the 66Zn transient signal by a factor of 10 compared to nanosecond laser pulses.

Conical recessed gold microelectrode arrays produced during photolithographic methods: Characterisation and causes

In this work, surface imaging techniques such as scanning Kelvin nanoprobe (SKN), scanning electron microscopy (SEM) and white light interferometer microscopy show that conical recessed electrodes with gradient potential along the recessed walls are formed during standard photolithographic methods for producing microelectrode arrays. The experimental behaviour of these electrode arrays fits very well with the numerical solution using optimal quasi-conformal mappings proposed recently by Amatore and co-workers [C. Amatore, A. Oleinick, I. Svir, J. Electroanal. Chem. 597 (2006) 69; C. Amatore, A. Oleinick, I. Svir, J. Electroanal. Chem. 597 (2006) 77]. The possible reasons for the formation of conical recesses are discussed.

Influence of metal stress on RF MEMS capacitive switches

The electrical and mechanical response of radio frequency (RF) microelectromechanical systems (MEMS) switches depends critically on the profile of the released structure. Stress gradients within the material can significantly alter the structural profile thereby changing the spring constant and the resulting switch release times. To investigate the influence of metal stress on spring constant and release time, a series of RF MEMS electrostatically actuated capacitive microswitches was fabricated with varying beam metallizations. The total thickness of the beam was fixed at 700 nm consisting primarily of Au while thin (5 nm or 20 nm thick) Ti layers were inserted at different positions within the beam. Changes in the location of the Ti layer within the bridge thickness resulted in distinct structural profiles across both the width and length of the released microswitches. Profile differences were quantified using white light interferometric microscopy. As the Ti layer moved toward the bottom of the tri-layer stack, beam deformation increased, spring constants increased, and release times decreased. Results demonstrated that release times could be reduced by an order of magnitude when compared to all Au switches.

Influencia del proceso de esterilización en la mojabilidad del titanio modificado superficialmente

El objetivo de este trabajo es estudiar el cambio en las propiedades energéticas de muestras de
 titanio comercialmente puro debido a distintos tratamientos superficiales y a distintos métodos de
 esterilización; con la finalidad de entender cómo afectan estos cambios a los procesos biológicos de
 los implantes de titanio.
 Los distintos tratamientos superficiales utilizados fueron: la formación de rugosidad mediante la
 proyección de partículas abrasivas, el granallado, y la esterilización mediante autoclave, óxido de
 etileno o radiación gamma.
 Tanto el nivel de rugosidad generada como la naturaleza de las partículas del granallado influyen
 en el carácter energético de las muestras; incrementando el carácter hidrofóbico con el aumento de la
 rugosidad y con la utilización de alúmina. Los contaminantes debidos al proceso de autoclave
 hidrofobizan las superficies; contrariamente a la esterilización por óxido de etileno que disminuye el
 valor del ángulo de contacto.
 La modificación de las superficies tratadas fue examinada con una serie de técnicas analíticas
 superficiales que incluyen el microscopio electrónico de barrido (SEM), la interferometría óptica y la
 medición del ángulo de contacto para poder realizar una caracterización topográfica, cualitativa y
 cuantitiva, y una caracterización energética, respectivamente. The aim of this work is to study the energetic properties of commercially pure titanium samples due
 to different surface treatments and different sterilization methods; with the purpose to understand
 how these changes affect to the biological processes of titanium implants.
 The different surface treatments were: roughness obtained by shot blasting, and sterilization by
 steam autoclaving, ethylene oxide or gamma radiation.
 Roughness level and the nature of the abrasive particles of shot blasting influence energetically
 the samples; increasing the hydrophobic behaviour with the increase of the surface roughness and
 the alumina use. The contamination due to steam autoclaving hydrophobizes the surface; contrary to
 sterilization by ethylene oxide, which reduces the contact angle value.
 The modification of treated surfaces was examined with a series of surface analytical techniques
 that include the scanning electron microscopy (SEM), the white light interferometer microscopy and
 the static contact angle measurement in order to determine a qualitative and quantitative topographic
 characterization and an energetic characterization.