the embedding of metal nanocrystals ( ncs ) in dielectric matrix is of considerable interest for the widely potential application in nonlinear optical device and nano - electronics [ 1 - 3 ] . the properties depend on mainly the size and shape of the nanoparticles , the embedding environment , and so on . however , the controllable fabrication of nanostructure remains the daunting challenge for many deposition methods , including sol another attractive method is referred to as a  self - organized  growth , in which the strain force would drive the three - dimensional ( 3d ) island to form in the lattice mismatched growth process . growth process has been performed to fabricate the quantum structure in semiconductor devices successfully , such as inas on gaas , sige on si . to our knowledge , there is seldom report about the self - organization process of metal ncs in oxide matrix . in this work , the laser molecular beam epitaxy ( l - mbe ) was used to embed the ni ncs in the batio3 epitaxial film . the fabrication of the ni - batio3 nanocomposite system is interesting and significant for both fundamental and application aspects . furthermore , another important application for ni - batio3 system is the nano - electronics such as the base - metal - electrode multilayered ceramic capacitors ( bme - mlcc ) . the ni : batio3 epitaxial films were prepared on srtio3 ( 001 ) substrate with batio3/srtio3 buffer layers by l - mbe . the deposition process involved a number of pulses on the ni target in ultra high vacuum , followed by the epitaxial growth of batio3 layer . after the completion of every batio3 layer , the sample was annealed about 30 min in the oxygen ambient pressure . such procedure was repeated up to 8 times to grow 300-nm - thick composite film . during the deposition process , the in situ reflection high - energy electron diffraction ( rheed ) monitoring was performed in anti - bray condition using 25-kev electron beam under a grazing incidence of 13 toward the surface . the microstructure and crystallinity of the nanocomposite films were characterized by transmission electron microscopy ( tem ) and x - ray diffraction ( xrd ) , respectively . figure 1a1d recorded the variation of rheed pattern along the   azimuth in the self - organization course of ni ncs on batio3 ( 001 ) surface . with the increasing of ni deposition pulses , the streak pattern of batio3 disappears gradually , while the spot pattern of ni ncs becomes dominant . it is considered that the ni islands formed on batio3 ( 001 ) surface , giving rising to bulk diffraction spots . due to the large lattice mismatch between ni and batio3 ( > 9% ) , the in - plane lattice of ni is subjected to large tensile strain to match the in - plane lattice of batio3 at the initial stage . with the continuing deposition , the increasing strain energy is reduced by the formation of 3d islands with the enlargement surface . therefore , the strain acts as a source of driving force for the self - organization of ni ncs . in such growth process , 1e represent the diffraction intensities along the horizontal spacing and the vertical spacing , respectively , for fig . 1c . if defining the distance between the ( 0 0 ) , ( 1 0 ) batio3 diffraction orders as b shown in curve i , both the horizontal distance and the vertical distance for the ni bulk diffraction spots equal to 2.25b . this corresponds in real space to a lattice constant of 3.55  in cubic structure , close to the crystal structure of bulk ni metal ( 3.52  ) . as well , the same crystal structure for ni ncs was obtained according to the rheed pattern along the   azimuth . from the patterns along the   and   azimuths , it demonstrates that the ni ncs maintain the ( 001 ) orientation with in - plane ni ncs / batio3 epitaxial relationships of ni bto and ni bto during the growth process in 650 c . evolution of rheed patterns along the < 100 > azimuth during the self - organized of ni ncs process : a batio3 surface ; b 100 pulses ni ; c 300 pulses ni ; d 600 pulses ni ; e the intensity spacing scan for fig . 1c : streakhorizontal line scan ( i ) , spot horizontal line scan ( ii ) , and spot vertical line scan ( iii ) the rheed intensity variation during the batio3 growth on ni ncs layer is displayed in fig . the inserts show that the spotty rheed pattern transforms to the streaky pattern at the initial stage , indicating the recovering of two - dimensional batio3 interface for the subsequent growth . it is evident that the batio3 separation layer continued to grow in a layer - by - layer growth mode with the improving of surface smoothness . the appearance of rheed intensity oscillation provided an effective way for controlling the accurate thickness of separation layer . figure 3 is the cross - sectional tem image of ni : batio3 nanocomposite film . in combination with the tem result , it was determined that one period of oscillation corresponded to the growth of three batio3 unit cells . the batio3 separation layers were grown repeatedly in perfect layer - by - layer mode on the irregular interface of strained ncs layers , which smoothed the irregular growth front formed in the self - assembled process of ni ncs and provided a flat substrate for the next strained ni ncs layer . as fig . 3 shows , the nanocomposite film consists of eight ni ncs layers alternating with batio3 separation layers . the sizes of ni nanocrystals were estimated in the range from 3 to 5 nm . and the batio3 separation layers have the uniform thickness of 30 nm or so . this confirms that the ni ncs were embedded in batio3 matrix , by the alternating of ni ncs self - organization process and batio3 epitaxial growth . since the rheed pattern is very sensitive to the surface microstructure [ 15 - 17 ] , the microstructure and the period of such quantum dot superlattice can be engineered with the in situ monitoring of rheed . rheed intensity oscillations recorded on spot ( curvei ) and streak ( curveii ) , respectively , during the batio3 epitaxial growth . the inserts are the rheed patterns collected at 10 , 30 , and 50 s the cross - sectional tem image of ni : batio3 nanocomposite film . it consists of eight ni ncs layers alternating with batio3 separation layers to identify the growth mechanism of the nanocomposite film , a simple schematic cross - sectional view of ni ncs layer shown in fig . 4 , with a dislike ni island strained on the batio3 matrix . after the relaxation of lattice strain for ni ncs , the in - plane lattice of ni on region b is stretch near to that of batio3 , whereas the in - plane lattice of ni on region c is relaxed to that of bulk ni metal . the average in - plane lattice strain at the island surface ( region b ) is less than the region c away from the island , thus the layer is considered to be uniformly strained . if further growth of batio3 layer , the lattice of the batio3 layer is then distorted above region c , while it is less of distortion above region a ( batio3 natural surface ) and region b. the epitaxial growth of batio3 in layer - by - layer mode occurs more rapidly above region a and region b with less lattice strain , then forms an atomically flat interface for the subsequent epitaxial growth . only the relaxation of lattice strain above the well - developed 3d ni islands is significant , while above the other islands , the strain relaxation is less . therefore , the 2d growth of batio3 was sustained although the local growth was perturbed by the ni islands . a schematic diagram of a strained ni ncs on flat batio3 surface showing the variation of in - plane lattice strain occurring near the growth surface figure 5 compares the structural characterizations of the pure batio3 epitaxial film and the ni : batio3 nanocomposite films by xrd . besides the ( 00 l ) peaks for the srtio3 substrate , fig . 5a consists of two peaks corresponding to batio3 ( 001 ) and batio3 ( 002 ) , respectively , meaning a single phase in the pure batio3 film . in fig . 5b and 5c , the observed systematic shift of the ( 00 l ) peaks toward to the lower diffraction angles indicates an increasing of the out - of - plane parameter of batio3 due to the embedding of ni ncs . the elongating of the out - of - plane lattice is caused by the large compressive strain at the ni : batio3 interface for the in - plane lattice match . the stronger strain was introduced for the higher ni ncs concentration with the more obvious shift of the ( 00 l ) peaks in fig . 5c . furthermore , the extra(h00)peaks exhibit in fig . 5b and 5c , which is a typical polydomain pattern containing the c domains with the c axis normal to the surface and the a domains with the a axis normal to the surface . the domain formation in batio3 epitaxial films is a mechanism that relaxes the total strain energy as a result of the great lattice mismatch . the angles between the surface normal   of ( 001 ) oriented domains and   of ( 100)-oriented domains is defined as  angle ,  = { 2arctan(c / a)90 } , where a and c denote the lattice parameters of the a and c axes . the total internal angles of a / c domains were estimated to be approximately 1.19 and 1.34 for fig . 5b and 5c , respectively . both the values are larger than the theoretical value for the strain - relaxed batio3 powder ( 0.7 ) , which illustrates that the c / a / c / a polytwin relieved the internal strain only partially . the xrd characterization confirmed the rheed result that the epitaxial growth of batio3 was not hindered by the embedding of ni ncs . however , the strain from the lattice mismatch between ni and batio3 altered the microstructure of such nanocomposite film . xrd -2 scans of batio3 film , filled square correspond to diffraction peaks from srtio3 ( 001 ) substrates . a pure batio3 film ; b ni : batio3 nanocomposite film ( 300 ni pulses per layer ) ; c ni : batio3 nanocomposite film ( 600ni pulses per layer ) ; d an expand view around the 002 batio3 peak with the circle label in fig . 5b ; e an expand view around the 002 batio3 peak with the circle label in fig . 5c magnifying the labeled broad peak , a weak peak was observed beside the batio3 ( 002 ) peak shown as the inserts in fig . 5d and 5e , which was supposedly the ni ( 111 ) peak . in comparison with the in situ rheed results , there is a transformation of the preferred out - of - plane orientation for ni ncs from nibto to nibto after annealing . the fcc metal tends to exhibit preferential crystallographic orientation with ( 111 ) , its closet packed plane , achieving minimum surface energy . the ni ncs were speculated to remain metallic , which may be attributed to be well protected by the batio3 separation layer . moreover , jiang et al . found that oxygen atoms in nio intermediate layer migrated to the batio3 layer at 800c . those results suggest that the co - exist system of metal and orientation - preferred ferroelectric oxides was available by the self - organized growth of metal ncs in ferroelectric oxides . in summary , the ni ncs formed in the epitaxial batio3 film by l - mbe . the alternate growth of ni ncs layer and epitaxial batio3 film was well controllable for the desired quality by the monitoring of rheed . for the large lattice mismatch between ni and batio3 , the strain drived the self - organization growth of ni ncs . and the batio3 remained the layer - by - layer growth on the strained ni ncs layer . the strain was relaxed only partially by the emergence of the ( 001)/(100 ) polydomain structure in the batio3 epitaxial film with the elongating of c axis . this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .
ni nanocrystals ( ncs ) were embedded in batio3 epitaxial films using the laser molecular beam epitaxy . 
 the processes involving the self - organization of ni ncs and the epitaxial growth of batio3 were discussed . with the in situ monitoring of reflection high - energy electron diffraction , the nanocomposite films were engineered controllably by the fine alternation of the self - organization of ni ncs and the epitaxial growth of batio3 . 
 the transmission electron microscopy and the x - ray diffraction characterization confirmed that the composite film consists of the ni ncs layers alternating with the ( 001)/(100)-oriented epitaxial batio3 separation layers .