Surface Characterization and Conductivity of Two Types of Lithium-Based Glass Ceramics after Accelerating Ageing

In this study, two different dental ceramics, based on zirconia-reinforced lithium-silicate (LS1) glass-ceramics (Celtra Duo, Dentsply Sirona, Bensheim, Germany) and lithium disilicate (LS2) ceramics (IPS e.max CAD, Ivoclar, Vivadent, Schaan, Liechtenstein) were examined. They were tested prior to and after the crystallization by sintering in the dental furnace. Additionally, the impact of ageing on ceramic degradability was investigated by immersing it in 4% acetic acid at 80 ◦C for 16 h. The degradability of the materials was monitored by Impedance Spectroscopy (IS), X-Ray Powder Diffraction (XRPD), and Field Emission Scanning Electron Microscope (FE-SEM) techniques. It was detected that LS2 (vs. LS1) samples had a lower conductivity, which can be explained by reduced portions of structural defects. XRPD analyses also showed that the ageing increased the portion of defects in ceramics, which facilitated the ion diffusion and degradation of samples. To summarize, this study suggests that the non-destructive IS technique can be employed to probe the ageing properties of the investigated LS1 and LS2 ceramics materials

Impact of Sandblasting on Morphology, Structure and Conductivity of Zirconia Dental Ceramics Material

Over the last decade, zirconia (ZrO2)-based ceramic materials have become more applicable to modern dental medicine due to the sustained development of diverse computer-aided design/computer-aided manufacturing (CAD/CAM) systems. However, before the cementation and clinical application, the freshly prepared zirconia material (e.g., crowns) has to be processed by sandblasting in the dental laboratory. In this work, the impact of the sandblasting on the zirconia is monitored as changes in morphology (i.e., grains and cracks), and the presence of impurities might result in a poor adhesive bonding with cement. The sandblasting is conducted by using Al2O3 powder (25, 50, 110 and 125 µm) under various amounts of air-abrasion pressure (0.1, 0.2, 0.4 and 0.6 MPa). There has been much interest in both the determination of the impact of the sandblasting on the zirconia phase transformations and conductivity. Morphology changes are observed by using Scanning Electron Microscope (SEM), the conductivity is measured by Impedance Spectroscopy (IS), and the phase transformation is observed by using Powder X-Ray Diffraction (PXRD). The results imply that even the application of the lowest amount of air-abrasion pressure and the smallest Al2O3 powder size yields a morphology change, a phase transformation and a material contaminatio

Comparison of the effect of the amino acids on spontaneous formation and transformation of calcium phosphates

Understanding the effect that specific amino acids (AA) exert on calcium phosphate (CaPs) formation is proposed as a way of providing deeper insight into CaPs’ biomineralization and enabling the design of tailored-made additives for the synthesis of functional materials. Despite a number of investigations, the role of specific AA is still unclear, mostly because markedly different experimental conditions have been employed in different studies. The aim of this paper was to compare the influence of different classes of amino acids, charged (aspartic acid, Asp and lysine, Lys), polar (asparagine, Asn and serine, Ser) and non-polar (phenylalanine, Phe) on CaPs formation and transformation in conditions similar to physiological conditions. The precipitation process was followed potentiometrically, while Fourier transform infrared spectroscopy, powder X-ray diffraction, electron paramagnetic spectroscopy (EPR), scanning and transmission electron microscopy were used for the characterization of precipitates. Except for Phe, all investigated AAs inhibited amorphous calcium phosphate (ACP) transformation, with Ser being the most efficient inhibitor. In all systems, ACP transformed in calcium-deficient hydroxyapatite (CaDHA). However, the size of crystalline domains was affected, as well as CaDHA morphology. In EPR spectra, the contribution of different radical species with different proportions in diverse surroundings, depending on the type of AA present, was observed. The obtained results are of interest for the preparation of functionalized CaPs’, as well as for the understanding of their formation in vivo

Precipitation at room temperature as a fast and versatile method for calcium phosphate/TiO2 nanocomposites synthesis

The constantly growing need for advanced bone regeneration materials has motivated the development of calcium phosphates (CaPs) composites with a different metal or metal-oxide nanomaterials and their economical and environmentally friendly production. Here, two procedures for the synthesis of CaPs composites with TiO2 nanoplates (TiNPl) and nanowires (TiNWs) were tested, with the immersion of TiO2 nanomaterials (TiNMs) in corrected simulated body fluid (c-SBF) and precipitation of CaP in the presence of TiNMs. The materials obtained were analyzed by powder X-ray diffraction, spectroscopic and microscopic techniques, Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis, dynamic and electrophoretic light scattering, and their hemocompatibility and ability to induce reactive oxygen species were evaluated. After 28 days of immersion in c-SBF, no significant CaP coating was formed on TiNMs. However, the composites with calcium-deficient apatite (CaDHA) were obtained after one hour in the spontaneous precipitation system. In the absence of TiNMs, CaDHA was also formed, indicating that control of the CaP phase formed can be accomplished by fine-tuning conditions in the precipitation system. Although the morphology and size of crystalline domains of CaDHA obtained on the different nanomaterials differed, no significant difference was detected in their local structure. Composites showed low reactive oxygen species (ROS) production and did not induce hemolysis. The results obtained indicate that precipitation is a suitable and fast method for the preparation of CaPs/TiNMs nanocomposites which shows great potential for biomedical applications

Fleksibilni uređaji bazirani na slojevitim 2D materijalima

Present-day flexible and stretchable electronic devices, such as bendable phones or displays, are mostly built from rigid microscopic components (sensors and transistors), where rigidity ultimately sets limitations to the devices’ mechanics and performances. Due to their atomically thin nature, 2D materials (2DMs) exhibit impressive mechanical attributes which offer, in conjunction with the tunability of their other properties, significant advancements of the next generation of flexible devices. Although there is a massive interest in 2DMs and their applications, many steps are still needed to fully exploit 2DMs for flexible and stretchable devices. Within this thesis, we have investigated MoS_2, borophene, and graphene monolayers as well as MoS_2/graphene heterostructures in view of flexible devices. Different segments which are required for the understanding of physical properties and device implementation of these materials have been investigated. For borophene and heterostructures of MoS2/graphene, the focus was on mechanical manipulation. Graphene monolayers were mainly used for testing of the transfer and transport methods. MoS_2 monolayers and respective devices, as the most advanced systems we constructed, constitute the basis of strain-dependent measurements in our work. More specifically, the first part of our research was dedicated to different device fabrication procedures in order to determine the optimum type of 2DM growth, sample morphology, and method of transfer. In this effort, several experimental techniques have been used: AFM, SEM, Raman and PL spectroscopy, and transport measurements. Large-scale monolayers (>100 μm) proved to be advantageous over smaller isolated flakes. Mechanical stamping method and electrochemical delamination yielded good results for the transfer of 2DMs from the growth substrates to arbitrary ones, with minimum contaminations or damage. E-beam and stencil lithography were used on both rigid and flexible substrates for the fabrication of electrodes of the 2DM-based devices. In the second part of the thesis, strain-dependent measurements with uniaxial bending were conducted, thus enabling the investigation of tensile strain on devices’ performances. For example, our devices did not show any degradation in terms of electrical resistance even after 40 bending cycles at strain values as high as 1%. Also, the photoresponse of MoS_2 can be significantly enhanced by the application of strain, where the increase of photocurrent and broadening of spectral sensitivity have been found. Additionally, we have shown that on encapsulated devices strain has uniformly propagated over the whole surface of 2DMs, while with a transfer of 2DMs on pre-fabricated electrodes, the electrodes are a source of inhomogeneous strain distribution within the 2DM. Overall, the research presented in this thesis provides a new insight into the physical phenomena behind the synthesis and manipulation of 2DMs, and can serve as a guideline for the fabrication of novel devices based on 2DMs. In line with this, the conducted straindependent characterisation brings unique properties of 2DMs closer to real-life applications.Istraživanje provedeno u sklopu ove teze predstavlja nove uvide u fizikalne fenomene u pozadini sinteze i manipulacije 2DM-a, koji mogu služiti kao smjernice za izradu novih uređaja na bazi 2DM-a. Konkretno, pokazali smo kako elektrokemijski transfer može biti korišten za mehaničku manipulaciju osjetljivih materijala poput Bo te kompleksnih materijala poput MoS_2/Gr heterostrukture. Nakon toga detaljno smo istražili svojstva MoS_2 te demonstrirali kako se PDMS transfer te stencil i e-beam litografija mogu primijeniti za konstrukciju uređaja na bazi 2DM-a. Dodatno smo pokazali kako se sa raznim dopiranjima može utjecati na energije kvazičestica te da se MoS_2 može iskoristiti za FET-ove na Si waferima. Poseban naglasak u istraživanju stavljen je na karakterizaciju izrađenih fleksibilnih uređaja MoS_2-a u ovisnosti o naprezanju. Utvrdili smo da granice zrna ne sputavaju prijenos naprezanja unutar large-scale 2DM-a, zatim kako se MoS_2 može iskoristiti za fleksibilne senzore naprezanja i pritiska te u konačnici da se primjenom naprezanja mogu poboljšati performanse fleksibilnih fotodetektora na bazi MoS_2. Ostvareni rezultati značajno približavaju iskorištavanje jedinstvenih svojstava 2DM-a za svakodnevne uređaje otporne na drastične mehaničke deformacije poput rastezanja i savijanja

Fleksibilni uređaji bazirani na slojevitim 2D materijalima

Present-day flexible and stretchable electronic devices, such as bendable phones or displays, are mostly built from rigid microscopic components (sensors and transistors), where rigidity ultimately sets limitations to the devices’ mechanics and performances. Due to their atomically thin nature, 2D materials (2DMs) exhibit impressive mechanical attributes which offer, in conjunction with the tunability of their other properties, significant advancements of the next generation of flexible devices. Although there is a massive interest in 2DMs and their applications, many steps are still needed to fully exploit 2DMs for flexible and stretchable devices. Within this thesis, we have investigated MoS_2, borophene, and graphene monolayers as well as MoS_2/graphene heterostructures in view of flexible devices. Different segments which are required for the understanding of physical properties and device implementation of these materials have been investigated. For borophene and heterostructures of MoS2/graphene, the focus was on mechanical manipulation. Graphene monolayers were mainly used for testing of the transfer and transport methods. MoS_2 monolayers and respective devices, as the most advanced systems we constructed, constitute the basis of strain-dependent measurements in our work. More specifically, the first part of our research was dedicated to different device fabrication procedures in order to determine the optimum type of 2DM growth, sample morphology, and method of transfer. In this effort, several experimental techniques have been used: AFM, SEM, Raman and PL spectroscopy, and transport measurements. Large-scale monolayers (>100 μm) proved to be advantageous over smaller isolated flakes. Mechanical stamping method and electrochemical delamination yielded good results for the transfer of 2DMs from the growth substrates to arbitrary ones, with minimum contaminations or damage. E-beam and stencil lithography were used on both rigid and flexible substrates for the fabrication of electrodes of the 2DM-based devices. In the second part of the thesis, strain-dependent measurements with uniaxial bending were conducted, thus enabling the investigation of tensile strain on devices’ performances. For example, our devices did not show any degradation in terms of electrical resistance even after 40 bending cycles at strain values as high as 1%. Also, the photoresponse of MoS_2 can be significantly enhanced by the application of strain, where the increase of photocurrent and broadening of spectral sensitivity have been found. Additionally, we have shown that on encapsulated devices strain has uniformly propagated over the whole surface of 2DMs, while with a transfer of 2DMs on pre-fabricated electrodes, the electrodes are a source of inhomogeneous strain distribution within the 2DM. Overall, the research presented in this thesis provides a new insight into the physical phenomena behind the synthesis and manipulation of 2DMs, and can serve as a guideline for the fabrication of novel devices based on 2DMs. In line with this, the conducted straindependent characterisation brings unique properties of 2DMs closer to real-life applications.Istraživanje provedeno u sklopu ove teze predstavlja nove uvide u fizikalne fenomene u pozadini sinteze i manipulacije 2DM-a, koji mogu služiti kao smjernice za izradu novih uređaja na bazi 2DM-a. Konkretno, pokazali smo kako elektrokemijski transfer može biti korišten za mehaničku manipulaciju osjetljivih materijala poput Bo te kompleksnih materijala poput MoS_2/Gr heterostrukture. Nakon toga detaljno smo istražili svojstva MoS_2 te demonstrirali kako se PDMS transfer te stencil i e-beam litografija mogu primijeniti za konstrukciju uređaja na bazi 2DM-a. Dodatno smo pokazali kako se sa raznim dopiranjima može utjecati na energije kvazičestica te da se MoS_2 može iskoristiti za FET-ove na Si waferima. Poseban naglasak u istraživanju stavljen je na karakterizaciju izrađenih fleksibilnih uređaja MoS_2-a u ovisnosti o naprezanju. Utvrdili smo da granice zrna ne sputavaju prijenos naprezanja unutar large-scale 2DM-a, zatim kako se MoS_2 može iskoristiti za fleksibilne senzore naprezanja i pritiska te u konačnici da se primjenom naprezanja mogu poboljšati performanse fleksibilnih fotodetektora na bazi MoS_2. Ostvareni rezultati značajno približavaju iskorištavanje jedinstvenih svojstava 2DM-a za svakodnevne uređaje otporne na drastične mehaničke deformacije poput rastezanja i savijanja

Transistors based on layered 2D materials and their heterostructures

Sagledavajući izazove napretka tehnologije izvjesno je da je silicijska tehnologija na zalasku svojih mogućnosti te da će u bliskoj budućnosti biti potrebno razviti nove materijale koji će svojim svojstvima kvalitetno odgovoriti na potrebe za daljnjim razvojem tehnologije. Riješenja mnogih izazova nudi grafen, koji predvodi čitavu klasu slojevitih 2D materijala. Unatoč nizu prednosti, zbog velike mane grafena u obliku nedostataka procjepa između vodljive i valentne vrpce, daljnja intenzivna istraživanja usmjerena su prema 2D materijalima koji u intrinzičnom obliku, ili u međusobnim kombinacijama slojeva posjeduju poluvodički procjep pogodan za tehnologiju u elektroničkim i sličnim uređajima. Jedni od prvih kandidata u tom smislu su MoS2 i WS2, koji su zbog dobivenih rezultata mobilnosti μ = 200cm2V -1s -1 i omjera struja paljenja/gašenja Ion / Ioff > 108 vrlo obećavajući. U ovome radu osmišljen je sistem izrade tranzistora na jednoslojnim strukturama MoS2 koristeći sjenaste maskirne folije obradene kratkim laserskim impulsima na mikro-skali. Takvim pristupom se izbjegava upotreba raznih polimera i kemikalija koji se u tradicionalnim poluvodičkim tehnologijama sustavno koriste za izradu tranzistora pomoću optičke ili elektronske litografije. U sklopu rada napravljena je aparatura koja omogućuje transportna mjerenja na mikro-skali, ali prva mjerenja do sada sintetiziranih struktura MoS2 ukazuju na pojave proboja naboja prije postizanja struje paljenja, zbog disipacije struje u sloj dielektrika koji je oslabio prilikom sinteze MoS2. U radu je korišten i skeniraju ći tuneliraju ći mikroskop sa 4 kontaktna vrška koji omogućuju mjerenja na nano-skali. Izmjerena je vodljivost gornjeg sloja sintetiziranih struktura MoS2 σ ≈ 10 -5 S/m2. Varirajući parametar međusobne udaljenosti vrškova pokazana je očekivana 2D vodljivost. Mjerenja na ovom uredaju dodatno su omogućila uočavanje pukotina u MoS2 slojevima na mikro-skali, koje su vjerojatno nastale uslijed brzog hlađenja uzoraka nakon sinteze.Looking into the future advances of technology it’s obvious that silicium technology is at decay of its possibilities and that in near future it will be necessary to develop new materials that will adequately answer needs for future development of technology. One of the answers for those challenges can be found in graphene, which is leader of whole class of layered 2D materials. With whole set of advantages that it offers, one but major flaw in form of lack of bandgap between conducting and valent band, leads the direction of intense research towards 2D materials that have bandgap in theirs intrinsic or combined form, so they could be used in electronic devices. One of the first candidates in that sense are MoS2 and WS2, who are considered very promising because of first results of mobility μ = 200cm2V -1s -1 and on/off ratio Ion / Ioff > 108. In this master thesis we developed system for fabrication of transistors on single layered structures of MoS2 using stencil lithography. With that approach usage of different chemicals and polymers is avoided, which are common in traditional semiconductor technology for fabrication of transistors using optical and electronical lithography. In this thesis we constructed vacuum chamber that enables transport measurements on micro-scale, but first measurements done on synthesized structures of MoS2 indicate on dielectric breakdown before achieving on current, because of dissipation of electricity in dielectric layer that was weakened during synthesis of MoS2. We used STM with 4 tips that provides us with ability for measurements on nano-scale. We measured sheet conductivity of MoS2 σ ≈ 10 -5 S/m2 and varying parameter of tip distance we showed expected 2D conductivity. Additionally while using SEM we have spotted cracks in MoS2 layers, which are probably result of fast cooling after synthesis of MoS2 on samples

Fleksibilni uređaji bazirani na slojevitim 2D materijalima

Present-day flexible and stretchable electronic devices, such as bendable phones or displays, are mostly built from rigid microscopic components (sensors and transistors), where rigidity ultimately sets limitations to the devices’ mechanics and performances. Due to their atomically thin nature, 2D materials (2DMs) exhibit impressive mechanical attributes which offer, in conjunction with the tunability of their other properties, significant advancements of the next generation of flexible devices. Although there is a massive interest in 2DMs and their applications, many steps are still needed to fully exploit 2DMs for flexible and stretchable devices. Within this thesis, we have investigated MoS_2, borophene, and graphene monolayers as well as MoS_2/graphene heterostructures in view of flexible devices. Different segments which are required for the understanding of physical properties and device implementation of these materials have been investigated. For borophene and heterostructures of MoS2/graphene, the focus was on mechanical manipulation. Graphene monolayers were mainly used for testing of the transfer and transport methods. MoS_2 monolayers and respective devices, as the most advanced systems we constructed, constitute the basis of strain-dependent measurements in our work. More specifically, the first part of our research was dedicated to different device fabrication procedures in order to determine the optimum type of 2DM growth, sample morphology, and method of transfer. In this effort, several experimental techniques have been used: AFM, SEM, Raman and PL spectroscopy, and transport measurements. Large-scale monolayers (>100 μm) proved to be advantageous over smaller isolated flakes. Mechanical stamping method and electrochemical delamination yielded good results for the transfer of 2DMs from the growth substrates to arbitrary ones, with minimum contaminations or damage. E-beam and stencil lithography were used on both rigid and flexible substrates for the fabrication of electrodes of the 2DM-based devices. In the second part of the thesis, strain-dependent measurements with uniaxial bending were conducted, thus enabling the investigation of tensile strain on devices’ performances. For example, our devices did not show any degradation in terms of electrical resistance even after 40 bending cycles at strain values as high as 1%. Also, the photoresponse of MoS_2 can be significantly enhanced by the application of strain, where the increase of photocurrent and broadening of spectral sensitivity have been found. Additionally, we have shown that on encapsulated devices strain has uniformly propagated over the whole surface of 2DMs, while with a transfer of 2DMs on pre-fabricated electrodes, the electrodes are a source of inhomogeneous strain distribution within the 2DM. Overall, the research presented in this thesis provides a new insight into the physical phenomena behind the synthesis and manipulation of 2DMs, and can serve as a guideline for the fabrication of novel devices based on 2DMs. In line with this, the conducted straindependent characterisation brings unique properties of 2DMs closer to real-life applications.Istraživanje provedeno u sklopu ove teze predstavlja nove uvide u fizikalne fenomene u pozadini sinteze i manipulacije 2DM-a, koji mogu služiti kao smjernice za izradu novih uređaja na bazi 2DM-a. Konkretno, pokazali smo kako elektrokemijski transfer može biti korišten za mehaničku manipulaciju osjetljivih materijala poput Bo te kompleksnih materijala poput MoS_2/Gr heterostrukture. Nakon toga detaljno smo istražili svojstva MoS_2 te demonstrirali kako se PDMS transfer te stencil i e-beam litografija mogu primijeniti za konstrukciju uređaja na bazi 2DM-a. Dodatno smo pokazali kako se sa raznim dopiranjima može utjecati na energije kvazičestica te da se MoS_2 može iskoristiti za FET-ove na Si waferima. Poseban naglasak u istraživanju stavljen je na karakterizaciju izrađenih fleksibilnih uređaja MoS_2-a u ovisnosti o naprezanju. Utvrdili smo da granice zrna ne sputavaju prijenos naprezanja unutar large-scale 2DM-a, zatim kako se MoS_2 može iskoristiti za fleksibilne senzore naprezanja i pritiska te u konačnici da se primjenom naprezanja mogu poboljšati performanse fleksibilnih fotodetektora na bazi MoS_2. Ostvareni rezultati značajno približavaju iskorištavanje jedinstvenih svojstava 2DM-a za svakodnevne uređaje otporne na drastične mehaničke deformacije poput rastezanja i savijanja