Implanted layers composition

Diffusion. Another technique for modifying the electrical properties of siUcon and siUcon-based films involves introducing small amounts of elements having differing electrical compositions, dopants, into substrate layers. Diffusion is commonly used. There are three ways dopants can be diffused into a substrate film (/) the surface can be exposed to a chemical vapor of the dopant at high temperatures, or (2) a doped-oxide, or (J) an ion-implanted layer can be used. Ion implantation is increasingly becoming the method of choice as the miniaturization of ICs advances. However, diffusion is used in... 

Protein diffusivity, however, is not always the main determinant in the composition of adsorbed protein layers. If this were the case, the composition of the adsorbed protein layer would be the same on different materials exposed to the same solution. This condition is not usually observed (Horbett, 1999), indicating that the affinity of each protein is influenced by the surface chemistry of the biomaterial (Horbett and Brash, 1995). Because proteins differ in affinity for various surface chemistries, the competitive protein adsorption process will also differ, leading to unique protein layer compositions upon different materials. Furthermore, the vast majority of protein adsorption studies have been carried out in vitro, assuming that this accurately mimics the in vivo environment. However, differences in implant site (i.e., blood-contacting devices vs solid tissue... 

Figure 20 shows an AES depth profile taken from the N-implanted conventional Cr layer showing film composition as a function of depth, The predominant constituents of the film are O, Cr and N. The outermost layers of the film consist of oxides. The implantation has produced a broad N profile down to 250 nm with a maximum concentration of 33 at. % at a depth of 70 nm. If a higher ion dose were to be implanted, it would result not in a higher concentration but in a broader profile, The composition of the implanted layer does not quite reach the stoichiometry of CrN, which would correspond to 50 at.% N if all Cr were converted into CrN. It seems that in this region a significant amount of Cr is bound to O. 

Figure 20. AES depth profiles obtained from an ion-implanted conventional Cr layer, Composition is shown as a function of depth. Zero depth corresponds to the original surface. Only the most prominent changes in Cr, N and O concentrations are shown. [149].

Studies of the combination of coating and ion implantation have been per-fonned with two kinds of Cr layers, both implanted with N ions. It has been shown that N implantation of both conventional and ABCD films results in an increase in the near-surface hardness of the Cr layers. The extent of this increase was greater for those films of both types that had been annealed at 400 C. AES depth profile analysis showed that the concentration of N in the implanted layer should not exceed 40 at.%. Implantation beyond that amount led to a broadening of the nitrogen profile. Analysis of film composition of the implanted Cr layers showed that the films consisted of Cr, C and N in the case... 

The increasing demand for synthetic biomaterials, especially polymers, is mainly due to their availability in a wide variety of chemical compositions and physical properties, their ease of fabrication into complex shapes and structures, and their easily tailored surface chemistries. Although the physical and mechanical performance of most synthetic biomaterials can meet or even exceed that of natural tissue (see Table 5.15), they are often rejected by a number of adverse effects, including the promotion of thrombosis, inflammation, and infection. As described in Section 5.5, biocompatibility is believed to be strongly influenced, if not dictated, by a layer of host proteins and cells spontaneously adsorbed to the surfaces upon their implantation. Thus, surface properties of biomaterials, such as chemistry, wettability, domain structure, and morphology, play an important role in the success of their applications. 

Implantable prosthetic bearings may be constructed from a composite material having a first layer and a second layer (20). The first layer has an articulating surface defined therein, whereas the second layer has an engaging surface defined therein for engaging either another prosthetic component or the bone itself. The first layer is constructed of a UHMWPE, whereas the second layer is constructed of a copolymer of ethylene and an acrylate. 

Ion implantation also has promise in other tields involv ino surface technology for example, new metallurgical phases w ith prior unknown properties can be I untied. In some eases. Mich as heav y implantations of tantalum irt copper of phosphorus in iron, amorphous or glassy phases can be formed. Or. if the implanted atoms ore mobile, inclusions and precipitates can he formed as. for example, implanted argon and helium atoms are insoluble in metals and may form bobbles. The composition of a surface layer can be changed by differential sputtering caused by the implanted ions. 

Protein Adsorption. The development of medical implant polymers has stimulated interest in the use of ATR techniques for monitoring the kinetics of adsorption of proteins involved in thrombogenesis onto polymer surfaces. Such studies employ optical accessories in which an aqueous protein solution (93) or even ex - vivo whole blood (94-%) can be flowed over the surface of the internal reflection element (IRE), which may be coated with a thin layer of the experimental polymer. Modem FT-IR spectrometers are rapid - scanning devices, and hence spectra of the protein layer adsorbed onto the IRE can be computed from a series of inteiferograms recorded continuously in time, yielding ah effective time resolution of as little as 0.8 s early in the kinetic runs. Such capability is important because of the rapid changes in the composition of the adsorbed protein layers which can occur in the first several minutes (97). 

The scaffolds for implants can be manufactured by mean of solid freeform fabrication (SFF), which relies on a layer-by-layer (LbL) composition of 3D materials. 

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