many challenges remain opening regarding the integration of diamond into electronic devices . in particular , seeding processes are typically harsh on the substrate surface , leading to defect creation and lack of reproducibility . iron - based materials have been used as catalysts in the synthesis of crystalline diamond by high temperature , high - pressure growth [ 1 - 3 ] . yet , it is difficult to fabricate diamond on iron - based materials by chemical vapor deposition ( cvd ) due to the rapid diffusion of carbon into the bulk and high carbon solubility . there have been a number of attempts to grow diamond by forming a thin film of iron on silicon substrates [ 5 - 7 ] . c are attained by depositing a thin layer of iron on silicon substrates , thus suggesting that a high carbon concentration resulting in a saturated carbide layer during the initial stage of nucleation is required for producing diamond nucleation sites . the above - described developments suggest that the fe nanoparticles can be employed as diamond nucleation centers : they have a strong affinity for c atoms and yet they are too small to act as c sinks . feo nanoparticles ( nfeo ) are ideal candidates for this task because the fe nanoparticle is passivated by o , which is then removed by the cvd reactions , leaving the active fe nanoparticle exposed for c trapping and accumulation . microcrystalline diamond particles and films were synthesized using a custom - built hot filament cvd ( hfcvd ) apparatus , which is described in detail elsewhere . the films were grown on 14-mm diameter and 0.5-mm thick mo , si , and quartz substrates . the substrates were cleaned by sonication in methanol and acetone and dried with inert gas . after cleaning , a suspension of nfeo with nominal particle size distribution in the 710 nm range ( integran technologies inc . ) the surface density of nfeo clusters was estimated to be 10 cm by atomic force microscopy and scanning electron microscopy ( sem ) . however , scattered micron - size patches of unseeded substrate remained . a mixture of 2% ch4 in h2with a total flow of 100 sccm was directed over the heated rhenium filament kept at 2,700 k and 10 mm above the substrate . the total pressure was kept constant at values between 20 and 50 torr ( 2.66.6 kpa ) . the substrates were maintained around 700730 c and the deposition time was varied between 30 min and 6 h. the surface morphology of the films was investigated by sem using a jeol jsm 845a model microscope . small portions of the diamond samples were placed on formvar - coated cu grids and uncoated silicon nitride tem grids for energy - filtered transmission electron microscopy ( eftem ) and electron energy - loss spectroscopy ( eels ) using an energy - filtered leo 922 omega microscope operating at an accelerating voltage of 200 kv . the structural phases of the films were characterized by micro - raman spectroscopy ( rs ) using a triple monochromator ( isa jobin - yvon inc . model t64000 ) with 1 cmresolution and the 514.5 nm ar - ion laser line for excitation . the spectra were recorded using an 80 objective that probes an area of about 12 m . the uv raman spectra were measured using a double monochormator ( isa jobin - yvon inc . ) with a resolution of 34 cmand the second harmonic generation of 488 nm radiation ( 244 nm ) from an ar - ion laser . the x - ray diffraction ( xrd ) measurements were taken on a siemens d5000 diffractometer using the cu kline source (  = 1.5405  ) in2configuration . the x - ray photoelectron spectroscopy ( xps ) measurements were taken using a physical electronic system ( model phi5600 esca , mn , usa ) for elemental analysis at room temperature , which was operated in the constant energy pass mode using monochromatic al k x - rays ( h = 1,486.6 ev ) . the average size of the nanoparticles was determined to be around 10 nm using eftem ( fig . these nfeo induced the synthesis of microcrystalline diamond , as shown in the sem images of fig . 2 for different deposition times : 0.5 , 2 , and 6 h. micron - size well - faceted diamond particles are readily observed for a deposition time of 30 min , as shown in fig . the diamond crystallite size increased proportionally for a deposition time of 2 h , and lateral collision of growing particles began forming a film , as shown in fig . 2b . a deposition time of 6 h led to quite continuous films of about 1011 m thickness with a few scattered gaps , as shown in fig . the bragg reflections characteristic of 111 and 400 diamond lattice planes were obtained for all the films ( data not shown ) . control experiments to grow diamond directly on mo , si , and quartz without nfeo or diamond seeding were unsuccessful for deposition times of 6 h , as expected , except for the formation of a moc or a sic surface layer according to xrd . ( a ) x - ray diffractogram of nfeo particles employed to induce diamond growth . the peaks labeled correspond to cubic feo crystal structure . ( b ) eftem image of nfeo showing its particle size in the range of 710 nm sem images of nfeo - induced diamond deposited on mo substrates for : ( a ) 30 min , ( b ) 2 h , and ( c ) 6 h the diamond growth rates were around 1.71.9 m / h , which is substantially high for hfcvd ( typically 0.10.2 m / h ) , and the observed nucleation densities were around 10 cm , corresponding well to the initial nfeo density and similar to those typically obtained by diamond - seeded diamond deposition . in contrast , previous reports of methods involving some form of fe seeding , typically thin fe films , suffered from low growth rates and substantial co - deposition of amorphous carbon ( a  c ) . although there might be a slight effect on the nucleation density due to mechanical polishing of the mo substrates , it does not sufficient to account for the results described above , especially since the quartz and si substrates were not mechanically polished but nevertheless the growth of a microcrystalline diamond film was also successfully induced on them by nfeo . another important difference is the diamond quality of the nfeo - induced diamond films according to their raman spectra . the bonding structure of the material was determined by rs excited with two radiation energies : visible ( 2.4 ev ) and uv ( 5.1 ev ) . the combination of visible and uv raman is an effective approach for probing both kinds of carbon materials because the raman scattering cross - section for sp - bonded carbon in the visible region is 50230 times higher than that of sp - bonded carbon . the stokes - shifted visible and uv raman spectra of the nfeo - induced diamond films are shown in fig . they indicate that there is a relatively small presence of sp - bonded carbon in the nfeo - induced diamond films . ( no plasma etching or any other treatment was performed to enhance the post - deposition diamond quality of the films . ) the deconvolution of the raman spectra was done using a voigt function corresponding to the diamond peak , and five gaussians corresponding to the d and g bands , and the bands centered at 1,285 , 1,490 , and 1,610 cm[17 - 19 ] . the diamond peak fwhm obtained from these simulations is 810 cm , and the diamond quality factor is around 9798% , further indicating the good quality of the films and their similarity to diamond - seeded hfcvd diamond films . the diamond peak is always blue - shifted in the 1,333.51,335.5 cm range , indicating compressive stresses of around 0.61.7 gpa . similar raman spectra , growth rates , xrd diffractograms are obtained for nfeo - induced diamond films deposited on quartz , si , and mo substrates under identical conditions , thus confirming the consistency of the above - described results and ruling out the possibility of an underlying substrate effect . ( a ) representative visible and uv raman spectra of nfeo - induced microcrystalline diamond on mo substrates . ( b ) deconvoluted visible raman spectrum , showing the diamond peak with fwhm of 9 cm and peak position at 1,335 cm energy - filtered transmission electron microscopy and eels were employed to investigate the initial growth phase of nfeo - induced diamond . the high - resolution eftem image shown in fig . 4 shows the aggregation of carbon and formation of lattice planes around a seed nanoparticle ( dark region ) . a fast fourier transform analysis was employed to measure the spacing between the atomic planes , which were found to vary . the lattice spacing in different regions was measured to be 1.1 , 1.16 , 1.24 , and 3.33  0.1  . these values correspond to graphite 006 , 112 , 110 , and 002 interplanar spacing , respectively , and at the same time the 1.1 and 1.24  0.1  values also correspond to diamond 311 and 220 interplanar spacing , respectively . taken altogether , these results point toward the aggregation of graphitic carbon around the seed nanoparticle and the impending formation of diamond . eftem image showing the aggregation of carbon material around the fe nanoparticle ( dark area ) . the zones of eels analyses are labeled as a and b parallel eels core - loss spectra of carbon k - edge and iron l - edge were collected on the area as shown in fig . 4 , and the corresponding spectra for nfeo , a  c , and diamond were also obtained for comparison , as shown in fig . there are features at 285 , 290 , 297 , 305 , and 325 ev in the carbon k - edge spectrum . the peak at 285 ev corresponds to the 0 electronic transition and is thus a signature of sp - bonded carbon . the higher energy features correspond to 0   transitions of diamond - type carbon bonds . the observed broadening and smoothening of the eels features corresponding to diamond - type bonds is due their co  existence with trigonally bonded carbon in the near - seed region . 5b ) , corresponding to the due to transition of electrons from 2p orbitals to unoccupied 3d orbitals , confirming the role of iron nanoparticles as carbon clustering centers . no oxygen signal was detected by eels due to the fact that the hfcvd conditions promote the reaction of surface o with h and c atoms to form ho and co radicals , thus leaving the bare iron particles available to act as c traps . ( a ) carbon k - edge eels obtained from the edge of the dark area ( location b in fig . 4 ) , indicating the presence of sp and sp bonding along with the corresponding reference data for diamond and amorphous carbon . the dashed lines indicate the positions of peaks and shoulders as discussed in the text . ( b ) iron l - edge of the same area ( location b in fig . 4 ) showing the presence of iron l3(2p3/2 ) transition we also studied the average bonding environment of the material by xps . 6 ) indicates the strong presence of tetrahedral carbon ( sp c ) , in agreement with the raman spectra . it also shows a strong oxygen 1s signature and a weak iron 2p signature at 531.5 and 711 ev , respectively . the presence of o on the surface is due to post - deposition adsorbates , while the relatively small fe signature further confirms its saturation with c. 
  xps spectra of nfeo - induced diamond showing the carbon 1s , oxygen 2p , and iron 2p peaks . the inset shows the enlarged iron 2p peak it has been reported that the formation of a very dense amorphous carbon phase can lead to diamond nucleation [ 30 - 32 ] . in this process , sp - bonded c clusters start precipitating by consuming the carbon atoms from the dense amorphous carbon phase . furthermore , there are theoretical studies indicating that diamond nuclei are stable structures when embedded in a  c matrix , and thus the formation of a dense amorphous carbon phase is a plausible route for nucleating diamond . the iron nanoparticle may act as catalyst in decomposing the hydrocarbon under cvd conditions , after oxygen removal from the initial nfeo , leading to active carbon adsorption . since there is no room for diffusion into the interior of the fe nanoparticle and the amount of carbon that the fe nanoparticle can adsorb is limited , there occurs densification of trigonally and tetrahedrally bonded carbon around the iron nanoparticle and the impending formation of diamond bonds . from the above analysis , the synthesis of nfeo - induced microcrystalline diamond films can be summarized as follows : ( a ) iron oxide nanoparticles lose oxygen by chemical vapor reactions that lead to the formation ho and co radicals , creating active nanoscale iron surfaces for the adsorption and decomposition of the incoming carbon - containing species , and thus for the formation of nanoscale c clusters with trigonal and tetrahedral c bonds ; ( b ) as these carbon clusters densify around the iron nanoparticles , diamond - type bonds start precipitating ; and ( c ) diamond film deposition continues to occur under conventional diamond growth conditions of high hydrogen dilution which keep the growing surface hydrogenated and preferentially etch away the trigonal carbon bonds . the iron oxide nanoparticles were employed to induce the formation of diamond nuclei and the synthesis of microcrystalline diamond films . this approach yields relatively high diamond growth rates , low presence of amorphous carbon and can be used for the selective diamond deposition and patterning at the nanoscale through dip pen nanolithography of nfeo followed by chemical vapor deposition . the combined analysis of the various characterization results , indicate that the iron nanoparticles act as nucleation and aggregation sites for carbon and the impending formation of diamond - type bonds . the formation of a dense , mixed c phase around the fe nanoparticles leading to the precipitation of spc bonds is proposed as a plausible explanation for these results . one of the authors ( k.u . ) acknowledges the graduate research fellowship granted by the national science foundation ( grant no . this research project is being carried out under the auspices of the institute for functional nanomaterials ( nsf grant no . this research was also supported in parts by nasa training grant nng05gg78h ( pr space grant ) , nasa cooperative agreement ncc5 - 595 ( pr nasa epscor ) , and nasa grant ncc3 - 1034 ( nasa cnm urc ) .
iron nanoparticles were employed to induce the synthesis of diamond on molybdenum , silicon , and quartz substrates . 
 diamond films were grown using conventional conditions for diamond synthesis by hot filament chemical vapor deposition , except that dispersed iron oxide nanoparticles replaced the seeding . 
 x - ray diffraction , visible , and ultraviolet raman spectroscopy , energy - filtered transmission electron microscopy , electron energy - loss spectroscopy , and x - ray photoelectron spectroscopy ( xps ) were employed to study the carbon bonding nature of the films and to analyze the carbon clustering around the seed nanoparticles leading to diamond synthesis . 
 the results indicate that iron oxide nanoparticles lose the o atoms , becoming thus active c traps that induce the formation of a dense region of trigonally and tetrahedrally bonded carbon around them with the ensuing precipitation of diamond - type bonds that develop into microcrystalline diamond films under chemical vapor deposition conditions . 
 this approach to diamond induction can be combined with dip pen nanolithography for the selective deposition of diamond and diamond patterning while avoiding surface damage associated to diamond - seeding methods .