Single-crystal cheinically/isotopically pure synthetic diamond operated at low temperature offers an unusual opportunity for a small transparent optic that may transmit as much as tens to hundreds of megawatts of light , even in the presence of high peak power in the light beam. This property stems from the probable very low absorption of light in such material and the nature of the phonon energy transport at low temperatures.

Pure diamond has excellent mechanical and infra red properties and would make an ideal window material were it readily available. Synthetic diamond films can be grown with good infra red transmission and used as protective coatings. Many coating requirements can already be met using diamond-like carbon films.

Boron doped diamond films were deposited onto (100) orientated Si substrates using a thermal filament CVD method. Boron trioxide was used as a doping source and samples with boron to carbon (B/C) ratios of 0, 10, 100, and 1000 ppm were prepared for the optical measurements. The infrared (IR) results reveal the formation of an ultrathin SiC layer at the interface between Si and diamond. Furthermore, the IR data confirm the resistivity data obtained from electrical measurements. Raman spectroscopy was used to probe the quality and homogeneity of the diamond films. Upon increasing B/C ratio the diamond phonon line shifts to lower frequency and is also broadened revealing a softening of the diamond. In addition, the optical absorption was found to increase strongly with increasing B/c ratio.

The exceptional properties of diamond have stimulated a considerable research effort into the low pressure synthesis of diamond thin films for a diverse range of applications including:-. tribological coatings, semiconductor heat sinks and (as in this work) protective optical coatings. Numerous deposition techniques have been reported in the literature including Microwave Plasma Assisted Chemical Vapour Deposition (MPACVD). This paper briefly describes the MPAC\'D deposition system used at Plessey Research Caswell Limited and outlines the effects of important deposition parameters on the growth morphology of diamond crystallites and thin films. Techniques including SEM, ThM and X-ray diffraction have been used to study the growth mechanisms of MPACVD diamond. JR and Raman spectroscopy have been used to characterise the deposited films and an JR reflection technique is described for studying the infrared properties of the layers. The effect of deposition parameters on the properties of diamond thin films is discussed with regard to the use of these films for protecting JR windows and domes.

A requirement exists for more durable windows for airborne applications to improve their survivability under highly erosive conditions. A range of materials show potential including nitrides, phosphides, carbides and diamond. This paper will address the phosphide materials system and review the various possibilities available. Materials such as gallium phosphide show promise for use In the infrared on the basis of their behaviour in bulk form, with significant lattice absorption bands only apparent at wavelengths beyond l2jnn. Other known phosphides include those of Al, B, Si, Mg, In, Zn, Cd, Rb, Ir, Ni, Go, Y, Sc, Ti, Nb, Mo, W, Th as well as several of the rare earth elements. Ternary systen have also been examined, largely as bulk materials. Recently the potential of phosphide materials for infra-red applications has been highlighted by the deinstration of high durability in amorphous coatings of boron phosphide deposited by plasma assisted chemcal vapour deposition. The levels of durability obtained have exceeded those characteristic of diamond-like carbon, whilst allowing simultaneous transmission of both IR bands and the important 1.O6im wavelength. Here there is significant evidence of the role of non-stoichiometry, with P/B ratios of as high as 7 being typical. Some forms of amorphous phosphorus itself have been known to demonstrate remarkable stability, with samples remaining atomically clean in dry air for significant periods of time. Various other forms of high phosphorus polyphosphides are known, such as those containing alkali metals in a bridging configuration between phosphorus skeletons. These can be produced as thin films and exhibit high levels of stability and adhesion.

Diamondlike a-C:H films have been deposited by decomposition of acetylene. By the combination of Brillouin scattering and the ultralow load indentation technique, the following mechanical properties of the films were studied: the microhardness, H, the Young's modulus, E, the shear modulus, Ii , and the Poisson's ratio, v. From the measured data of mass density, hydrogen concentration and the ratio of sp3/sp2 bonds the f illing factors of these films were calculated. The results show that the hardness,Young's modulus and shear modulus of these films depend stongly on the volume concentration of voids and are directly proportional to the filling factor.

Diamondlike amorphous hydrogenated carbon (a-.C:H) films have found widespread use as hard coatings for IR optical applications. The refractive index of these films (n=2) allows the deposition of quarter-wave antireflection coatings on germanium. More complex optical designs, however, require the extension of the range of the optical constants. For this reason we studied amorphous hydrogenated carbon-germanium alloys. The corresponding a-C1 xc3ex H films with 0 < X < 1 were grown by ri-plasma deposition using mixtures of a hydrocarbon gas and germane or tetramethylgermanium (TMG) as precursors. Film composition, refractive index and IR absorption spectra were measured. This material system offers the possibility to adjust. the refractive index between 1 .8 and 4.1 and thus allows the deposition of multilayer thin film systems for IR optical applications. As a result of numerical design calculations, a three layer structure with a hard a-C:H top layer is proposed, which acts as a broadband antireflection coating on germanium substrates for 8-1 2 j.m. We report on the growth and performance of these hard multilayer AR coatings.

The fundamental possibifity to synthesize diamond under low pressure from the gas phase as a metastable carbon allotrope is known nearly as long as the high pressure route to this valuable material. Nevertheless more than twenty years elapsed, befoie research activities were started world-wide aiming atthe development ofdepositionprocesses meeting the demands of technical applications. In this review the present state ofthis work will be surveyed, with an emphasis on those topics which are of critical importance for an eventual success of a diamond technology: Scale-up of deposition processes, low temperature deposition, heteroepitaxy and control ofnucleation, mechanical adhesion, and electrical properties ofdiamond films.

Tin was sputtered from a DC planar magiistrcn target in a confined volume , stabilitywas maintained in the reactive sputtering by controlling the oxygen partial prire throogh observation of this liajit emitted by the oxygen in the -ofthe magnetron. The material deposited on this walls of the chamber was designed to getter this system of imt, The oxygen coisumption at the set point was a good indication oftlis approach to stoichiometiy of tbo film. It was observed that trazspazent oonckxting filnis were prepared at the point where this oxygen comaimption indicated a break from fill izxorporalion into the growing film. Films there had a resistivity of 100 micro ohm-meters for a 600 ohms per sqisze sheet restance, a thickne ofabont 150 naix>.meters. Tlisse filnis showed some o1 absorption in the bhis regkm oftho spectziim. Optically clear filnis required preparation in a greater oxygen rteeane which reckd the rate ofdeposition by a factor c(two. The refractive index was measuied as2.Oat633nm.

High quality dielectric films are required today for various interference optical applications and for planar wave guides in integrated optics. Many inorganic chemical compounds which were difficult to deposit by conventional techniques in form of well adherent, dense, hard and stable low-loss films are now routinly synthesized by reactive gas discharge plasma and energetic ion and/or coating materials atom processes. A survey over such PVD coating technologies and on the resulting film properties is given in this paper.

Silicon nitride films were synthesized in a Balzers BAP 800 coating plant by an plasma enhanced evaporation process. Transparent, stoichiometric films free of hydrogen, oxygen, argon, and heavy metals were obtained. The optical properties, the chemical composition, the microhardness, the structure, and the morphology of the films were investigated.

An empirical relationship between the long wavelength edge of the residual ray band in the IRreflectance of partly ionic compounds and bulk hardness is demonstrated. The group of materials studied includes alkali halides, semi-conductors and some hard compounds, mostly with cubic structure and a few with hexagonal. The correlation is shown for the Young modulus, the melting temperature and also to some extent the indentation hardness. The Young moduli cover a range from 10 to almost 500 GPa and the melting temperatures vary from 600 to 3000°C.

There are increasing demands of surface modification of transpar- ent substrates such as glass and plastics for windows in automobiles as well as houses in view of adding them fascinating optical properties. These properties include surface hardening of plastics, infrared re- flection, ultraviolet absorption, optical switching and birefringence. This paper reviews recent examples of applications of sophisticated thin film processes of plasma treatment and Physical Vapour Deposition (PVD). The novelty of functions by PVD method together with their durability for practical usage are emphasized as areas where the thin film process has a significant impact. Characterization of the modified surface and interface is also included to demonstrate recent advances in surface chemistry. Finally, future challenges for optical modification of transparent substrates in the automobile industry are also discussed.

Infrared transparent amorphous hydrogenated alloys of germanium and carbon (germanium carbide) have been deposited by plasma assisted chemical vapour deposition (PACVD) using germane (GeH4 ) and butane (C 4Hid as the feedstocks and by reactive sputtering of germanium with a CH1g-Ar plasma. The effects of varying various deposition conditions have been assessed on a number of coating properties . Germanium Carbide has good environmental durability and can be deposited in thick layers. Using PACVD it can be deposited with any refractive index in the range 2 to 4 while the sputtering process is limited to indices in the range 3 to 4 . One advantage of the sputtering process is the high deposition rates achievable which can be up to '-lOum/h compared with lum/h for the PACVD process. When used in conjunction with "diamond-like" carbon (a-'C:H) , germanium carbide offers the prospect of rnultilayer antireflection coatings for 8 to 12 urn optics with durabilities which hitherto have been impossible to achieve. Antireflection coatings for zinc sulphide windows which are subject to hostile environmental conditions have been investigated and the performance of the coatings is presented. The factors affecting the practical realisation of these coatings on a production scale are discussed.

Using a parallel plate reactor we optimized a PECVD process and coated Si02-films on CR 39 lenses with layer-thicknesses of 2,5 trn to 5 I_tIn. Besides high transmittance in the VIS-range we obtained refractive indices between n=1.46 and n=1.49 depending on the process parameters. We achieved deposition rates up to 30 A/s and thickness uniformities of 10 %. The abrasion resistance of these layers were tested with different inethodes and gave better results compared with techniques like lAD or lacquering.

The inf1ere of simulated space environment on the prcpert ies of the satel 1 i te temperature-control coat ing --- Optical Sol ar Ref1etor (OSR) is discussed. I kinds of CSR sample are tested in the simu1at1 space environment . The simulat ion i tens include vacuum US? irradi at on, electron and proton i rradiat ion . The surface charge/discharge test is carried out tcx . After the ecron, proton and UV accelerat ive irradiat ion of total dosage equivalent to 7 years at the south or north pale of geosyixthrcrx,us satellite, the solar aI:sorptaire increases from 0 .068 to 0 . 078 for cczxkt ive C , and from 0 . 066 to 0 . 085 for ncn-oonduct ive OSR; the normal ni ttance decreases from 0 .83 to 0.72 for conditive OSR, and from 0.82 to 0.76 for non-conductive OSR. Also, it is shown from the charge/discharge test that the surface charge potential is only I5--40 V for conduct ive CSR, and about 1 --1 0 Ky for non-conduct ive CSR.

The chemical and mechanical stability of tin oxide coated aluminium reflectors have been investigated. The tin oxide has been applied with the pyrolytic spray technique which results in a hard crystalline coating. Tin oxide is a wide bandgap semiconductor and is transparent in the visible part of the spectrum. The visual appearance of tin oxide coated aluminium is therefore similar to the uncoated metal. Interference effects can give a slightly coloured appearance, and owing to the higher refractive index and extinction coefficient of the tin oxide the reflectance is lower than for an anodized aluminium surface. The tin oxide was applied both on electropolished aluminium and on evaporated aluminium films on glass. In both cases an improved resistance both to alcaline and acid solutions was noted. It was found that the chemical stability was better than for an anodized surface. The mechanical stability of the evaporated film was considerably improved. The electropolished samples were also characterized with respect to film hardness and resistance to erosive and abrasive wear. The hardness of the tin oxide was found to be higher than that of the anodized layer while the opposite relation applied for the erosive wear resistance. The abrasive wear resistance was about equal for tin oxide coated and anodized aluminium.