Ion Implantation In Diamond Research Articles

Molecular dynamics simulation study of nitrogen vacancy color centers prepared by carbon ion implantation into diamond

Nitrogen vacancy (NV) color centers in diamond have useful applications in quantum sensing and fluorescent marking. They can be generated experimentally by ion implantation, femtosecond lasers, and chemical vapor deposition. However, there is a lack of studies of the yield of NV color centers at the atomic scale. In the molecular dynamics simulations described in this paper, NV color centers are prepared by ion implantation in diamond with pre-doped nitrogen and subsequent annealing. The differences between the yields of NV color centers produced by implantation of carbon (C) and nitrogen (N) ions, respectively, are investigated. It is found that C-ion implantation gives a greater yield of NV color centers and superior location accuracy. The effects of different pre-doping concentrations (400–1500 ppm) and implantation energies (1.0–3.0 keV) on the NV color center yield are analyzed, and it is shown that a pre-doping concentration of 1000 ppm with 2 keV C-ion implantation can produce a 13% yield of NV color centers after 1600 K annealing for 7.4 ns. Finally, a brief comparison of the NV color center identification methods is presented, and it is found that the error rate of an analysis utilizing the identify diamond structure + coordination analysis method is reduced by about 7% compared with conventional identification methods.

Study of the effects of focused high-energy boron ion implantation in diamond

Boron-doped diamond is a material with a great technological and industrial interest because of its exceptional chemical, physical and structural properties. At modest boron concentrations, insulating diamond becomes a p-type semiconductor and at higher concentrations a superconducting metal at low temperature. The most conventional preparation method used so far, has been the homogeneous incorporation of boron doping during the diamond synthesis carried out either with high-pressure sintering of crystals or by chemical vapour deposition (CVD) of films. With these methods, high boron concentration can be included without distorting significantly the diamond crystalline lattice. However, it is complicated to manufacture boron-doped microstructures. A promising alternative to produce such microstructures could be the implantation of focused high-energy boron ions, although boron fluences are limited by the damage produced in diamond. In this work, the effect of focused high-energy boron ion implantation in single crystals of diamond is studied under different irradiation fluences and conditions. Micro-Raman spectra of the sample were measured before and after annealing at 1000°C as a function of irradiation fluence, for both superficial and buried boron implantation, to assess the changes in the diamond lattice by the creation of vacancies and defects and their degree of recovery after annealing.

The effect of spin transport on spin lifetime in nanoscale systems

Spintronics use the electron spin as a state variable for information processing and storage. This requires manipulation of spin ensembles for data encoding, and spin transport for information transfer. Because of the central importance of lifetime for understanding and controlling spins, mechanisms that determine this lifetime in bulk systems have been extensively studied. However, a clear understanding of few-spin systems remains challenging. Here, we report spatially resolved magnetic resonance studies of electron spin ensembles confined to a 'spin nanowire' formed by nitrogen ion implantation in diamond. We measure the spin lifetime of the ensemble--that is, its spin autocorrelation time--by monitoring the statistical fluctuations of its net moment, which is in thermal equilibrium and has no imposed polarization gradient. We find that the lifetime of the ensemble is dominated by spin transport from the ensemble into the adjacent spin reservoir that is provided by the remainder of the nanowire. This is in striking contrast to conventional spin-lattice relaxation measurements of isolated spin ensembles. Electron spin resonance spectroscopy performed on nanoscale spin ensembles by means of a novel spin manipulation protocol corroborates spin transport in strong field gradients. Our experiments, supported by microscopic Monte Carlo modelling, provide a unique insight into the intrinsic dynamics of pure spin currents needed for nanoscale devices that seek to control spins.

An upper limit on the lateral vacancy diffusion length in diamond

Ion implantation is widely used to modify the structural, electrical and optical properties of materials. By appropriate masking, this technique can be used to define nano- and micro-structures. However, depending on the type of mask used, experiments have shown that vacancy-related substrate modification can be inferred tens of micrometers away from the edge of the mask used to define the implanted region. This could be due to fast diffusion of vacancies from the implanted area during annealing or to a geometric effect related to ion scattering around the mask edges. For quantum and single-atom devices, stray ion damage can be deleterious and must be minimized. In order to profile the distribution of implantation-induced damage, we have used the nitrogen-vacancy color center as a sensitive marker for vacancy concentration and distribution following MeV He ion implantation into diamond and annealing. Results show that helium atoms implanted through a mask clamped to the diamond surface are scattered underneath the mask to distances in the range of tens of micrometers from the mask edge. Implantation through a lithographically defined and deposited mask, with no spacing between the mask and the substrate, significantly reduces the scattering to ≤5μm but does not eliminate it. These scattering distances are much larger than the theoretically estimated vacancy diffusion distance of ~260nm under similar conditions. This paper shows that diffusion, upon annealing, of vacancies created by ion implantation in diamond, is limited, and the appearance of vacancies many tens of micrometers from the edge of the mask is due to scattering effects.

Ion implantation in diamond using 30 keV Ga + focused ion beam

Focused ion beam (FIB) technique is a well established technique for processing and modifying materials at micro- and nanoscale. FIB implantation with 30 keV Ga + ions into a single crystal diamond has been studied via a combination of transmission electron microscopy (TEM) imaging and spectroscopy in the attempt to understand the damage formation in diamond. The damage formation has been studied as a function of implantation dose with eight different doses ranging from 6 × 10 14 to 1 × 10 16 ions/cm 2. The TEM studies have revealed different structure of low-dose and high-dose implanted regions. 3.5 nm diamond cap layer was observed in the low-dose implanted layer. TEM analysis has shown volume extension of around 50% in the amorphous region and up to 7% in diamond at the crystal–amorphous interface. The density of amorphous damage layer was measured to be 2.51 g/cm 3 and 2.24 g/cm 3 in the low-dose and high-dose implanted regions, respectively. The amorphisation threshold for ion implantation in diamond at room temperature was determined to be 5.2 × 10 22 vacancies/cm 3.

Spectroscopy and micro-luminescence mapping of Xe-implanted defects in diamond

Ion implantation in diamond creates optically active defects which have emission lines in broad spectral regions and may be used in advanced photonics and optical communication applications. A brief review of the photoluminescence properties of Xe+ ion implanted diamond is presented. The Xe-related center is of particular interest as this center is one of a few centers (Ni, Si, Cr) in diamond having sharp emission lines in the infrared spectral region, specifically at 813 and 794nm. The paper discusses an approach to determine the important and difficult to measure conversion efficiency of implanted ions into emitting optical centers. The method uses micro-luminescence confocal mapping and statistical analysis based on a compound Poisson distribution, accounting for both the implanted centers and the optically excited centers statistics. Results of numerical simulations and experimental measurements are presented.

Engineering single photon emitters by ion implantation in diamond.

Diamond provides unique technological platform for quantum technologies including quantum computing and communication. Controlled fabrication of optically active defects is a key element for such quantum toolkit. Here we report the production of single color centers emitting in the blue spectral region by high energy implantation of carbon ions. We demonstrate that single implanted defects show sub-poissonian statistics of the emitted photons and can be explored as single photon source in quantum cryptography. Strong zero phonon line at 470.5 nm allows unambiguous identification of this defect as interstitial-related TR12 color center.

The essential role of visualization for modeling nanotubes and nanodiamond

Visualization techniques to help understand the structure of carbon and its allotropes have been developed and applied to atomistic simulation projects which model different carbon systems on the nanoscale. Examples from ion implantation in diamond, the diffusion of hydrocarbons in nanotubes and the creation of nanodiamond from amorphous carbon under pressure are given.

Propagation of acoustic phonons across the interfaces in CdTe and Si/CVD-diamond and quasi-two-dimensional phonon wind in CdTe/ZnTe quantum wells

Using a heat-pulse technique we investigated propagation of acoustic phonons in twinned CdTe, ZnTe crystals, in the vicinity of CdTe/ZnTe quantum well, and Si/CVD-diamond structures. Phonon mean free paths in CdTe were estimated. We studied the effect of phonon wind on the luminescence of narrow CdTe quantum well and observed an increase in the total luminescence intensity and the change of the luminescence band shape. We believe that this effect is due to a quasi-two-dimensional lateral propagation of subsurface and interface acoustic phonons in the ZnTe/CdTe structure. Preliminary data obtained on the Si/CVD-diamond interfaces suggest they are strongly damaged. To reduce the thermal boundary resistance of the interface between the material studied and the thin-film phonon detector we developed a buried bolometer based on a graphitized layer produced by ion implantation in diamond.

Irradiating diamond: Aspects of defect generation, accumulation and annealing

It is postulated that for diamond the activation barrier EC that a diffusing point defect has to scale before being trapped, is in general larger than the activation barriers ED that it has to scale during diffusion. By taking this into account, one can explain why the residual damage decreases with increasing target temperature during ion implantation, and why vacancies seem to diffuse “uphill” while being attracted by A-centres in electron irradiated type laA diamonds. The general applicability of this model indicates strongly that the defects formed during ion implantation of diamond are, as in the case of electron-irradiation, primarily individual vacancies and interstitial atoms. Recent results on the properties of interstitials in diamond also give credence to the latter conclusion as well as the postulates on which the Cold-Implantation-Rapid-Annealing (CIRA) routine for ion-beam doping of diamond is based.

A review of the effects of carbon self-implantation into amorphous carbon

Abstract Studies carried out on the ion implantation of diamond and amorphous carbon (a-C) in its polymer-like (PAC), tetrahedral (TAC) and diamond-like (DAC) forms have been reviewed. It has been reported that implantation into amorphous carbon results in a re-ordering into a sp 2 -rich state. However, this does not explain the range of optical and electrical results which have been observed. It was shown that the resistivity variation of TAC and DAC films are similar at high doses, although the corresponding band gap data show a significant difference. Based on these data, a model for the increase of electron delocalisation with ion dose within these films is postulated. Also, the role of nascent hydrogen within the films as the ion dose is increased is discussed.

Raman investigation of damage caused by deep ion implantation in diamond

Raman microscopy has been employed to investigate the nature of damage created when natural type-IIa diamond is irradiated with MeV alpha particles. Three features appear in the Raman spectrum due to damage, viz., (i) the first-order diamond Raman line is broadened and downshifted, (ii) broad features appear which are a measure of the vibrational density of states of ion-beam-amorphized diamond, and (iii) the damage causes the appearance of sharp defect-induced Raman peaks at 1490 and 1630 cm-1. For damage below an amorphization threshold, a linear relationship exists between the full width at half maximum and frequency shift, which shows that these are Kramers-Kronig related. The annealing behavior of the sharp Raman feature at 1490 cm-1 suggests that this peak is associated with vacancies with an activation energy for annealing of 4.06 eV, while the 1630-cm-1 peak is due to an interstitial related defect with an activation energy of 1.2 eV. For sub-MeV ion irradiation, damage beyond the critical amorphization level usually leads to relaxation of the diamond structure to graphite upon thermal annealing. However, for MeV ion irradiation, it was found that annealing, even when the ion induced damage level is well above the amorphization threshold, could restore the original diamond structure. We attribute this result to the high internal pressure the damaged layer is subjected to which does not allow relaxation to graphitically bonded structures.

Synchrotron X-ray reticulographic measurement of lattice deformations associated with energetic ion implantation in diamond

A natural diamond plate of thickness 0.55 mm, polished parallel to (110), contained a dislocation-free and unusually distortion-free area into which a beam of fluorine ions of 17 MeV energy had been injected. The beam, the diameter of which was pinhole-limited to ∼3/4 mm, produced a radiation-damaged layer at ∼5 µm depth and uplifted the crystal above to form an optically detectable mesa. Conventional X-ray topography registered lattice distortion strongly at the mesa periphery, but did not disclose the deformation of near-surface lattice layers at the mesa centre. In contrast, reticulography showed directly that the central surface lattice layers were slightly domed outwards. (In reticulography, a fine-scale X-ray absorbing mesh placed between a Laue-reflecting crystal and the topograph-recording plate splits the diffracted beam into individually trackable microbeams, the direction differences of which are measured by recording them at different mesh-to-plate distances.) Reticulographs were recorded in back-reflection, 2θB= 135°, using both symmetric reflection from the (110) surface, reflection 440 dominant, with λ = 0.116 nm, and reflection 331¯, with λ = 0.151 nm. The metrological procedures and geometrical analysis applied are described. The central surface curvature was derived from ten reticulographs recorded under different conditions, which tested the reproducibility of the method. Deviations of individual radius values from the mean were ∼4% for both curvature in (001) and orthogonally in (1¯10), the overall mean being 5 m. Two-beam optical interferometry failed to measure this curvature.

Computer simulation of damage in diamond due to ion impact and its annealing

The structural modifications that a highly damaged region in diamond undergoes upon thermal annealing have been studied by molecular dynamic simulations. We verified our use of the Tersoff potential and our computational methods for describing the thermally driven transition of diamond to graphite by calculating the thermal graphitization of a diamond slab and comparing the results with those of recently published [Alessandro De Vita et al., Nature (London) $379,$ 523 (1996)] ab initio calculations. A deeply buried damage region in diamond was obtained by imparting high momenta (corresponding to a kinetic energy of 416 eV) to up to 12 lattice atoms aimed towards the same point in the crystal. This led to the partial amorphization of a volume of a radius of 1.4 nm. The samples with these damage regions were then annealed, with molecular dynamics, at 3000 K for up to 20 ps. It was found that dislodged carbon atoms in the periphery of the damaged region tended to rearrange as threefold coordinated atoms in a planar graphitic structure oriented along the $〈111〉$ directions of the diamond. Threefold coordinate atoms in the center of the damage region, where the damage density is high, tended to convert to a fourfold coordinated configuration, i.e., regrow to diamond. This behavior was not found for a lightly damaged diamond region, created by the energetic dislodgement of just one C atom. The findings of the present study are in agreement with experimental data on the annealing/graphitization of diamond, damaged by energetic heavy ions as encountered during ion implantation of diamond.

Ion-implantation in diamond and diamond films: doping, damage effects and their applications

Diamond is very special owing to its extremely strong, metastable, sp 3 bonding. The tightness of the diamond crystal makes diffusion-doping of diamond or doping diamond during high-pressure high-temperature growth very difficult, if not impossible. Hence ion-implantation may be the method of choice for doping diamond, in a controlled way, thus opening up the possibility of its use as an electronic material. Ion-implantation in diamond, in CVD diamond or in diamond-like films is, however, complicated by the tendency of broken sp 3 bonds to form the more stable graphite sp 2 bonds which can give rise to non-doping related electrical conductivity. This paper reviews the current status of doping diamond and diamond films by ion-implantation. Special attention is given to ways of avoiding or utilizing ion-beam induced graphitization of diamond, and to attempts of achieving real reproducible n-type doping of diamond.

Modification of diamond films by high-energy ion irradiation: “track channelling” and ion charge fluctuation effects

A model of ion implantation in diamond with an energy of 1 MeV per nucleon is formulated taking into account the two effects: (i) ion channelling through latent tracks, and (ii) ion charge state fluctuations on the basis of a set of the Boltzmann and Fokker–Planck transport equations. Comparison with the experimental data on the implantation of Ni and Xe ions in diamond leads to the conclusion that these effects are essential to the accurate calculation of the depth distributions of impurity and defects at the high energy ion implantation.

Diamond growth by carbon ion implantation of diamond

Abstract Medium energy (5–25 keV) 13 C + ion implantation into diamond (100) to a fluence ranging from 10 16 cm −2 to 10 18 cm −2 was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 × 10 17 to 2 × 10 18 at. cm −2 (with a dose rate of 5 × 10 15 at. cm −2 s −1 at 5 to 25 keV and 800 °C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.

Ion implantation of diamond and diamond films

Abstract Ion implantation is widely employed in semiconductor device manufacture because it offers the possibility of precise control of dopant concentration and depth, and spatially selective doping is readily achievable using masking techniques. However, three major hurdles must be overcome before ion implantation doping of diamond can be practically realized. Firstly, methods must be found for the removal of the residual radiation damage without causing graphitization following the ion implantation. Secondly, the degree of electrical activation of the implanted dopants must be improved and thirdly, a suitable n-type dopant needs to be identified. Novel and innovative approaches designed to overcome these problems have recently been reported. These include pulsed laser annealing of deeply buried ion-implanted layers to achieve very high annealing temperatures while still preventing graphitization, the use of low energy ion-implantation during growth to minimize ion beam damage and maximize dopant incorporation into the diamond lattice, and multiple-step implantation/annealing cycles to improve dopant activation. In addition, fundamental studies examining the ion beam induced conductivity in diamond over a wide range of doses, ion energies and implantation temperatures have provided new insights into the nature of the damage introduced by the ion beam irradiation. In this paper, a brief review of the current status of our understanding of the interaction of ion beams with diamond is provided, with an emphasis on the new results mentioned above. In addition, since it is now clear that n-type doping of diamond films by addition of dopants to the chemical vapour deposition (CVD) growth mixture will not be as easy to achieve as first thought, a review of the work to date on the ion implantation of CVD diamond films is presented and the similarities and differences between the implantation of single crystal diamond and polycrystalline CVD films are discussed. Finally some novel and intriguing nonelectronic applications for ion beam modified diamond are presented.

Infrared emission from selected areas in ion-beam-irradiated diamond

The infrared emission properties of an electrically heated single resistive element produced by ion implantation of diamond is reported. It is found that good contrast can be obtained between the implanted and unimplanted regions of the diamond mainly because of the increased emissivity following implantation. The infrared output is stronger if the diamond is viewed with the implanted surface facing away from the detector. The possible utilization of diamond-based pixels in infrared scene generation is discussed.

Possibilities and limitations of ion implantation in diamond, and comparison with other doping methods

Diamond is a crystal with extremely strong atomic bonds. It is characterised by very low equilibrium parameters of the solubility and diffusion coefficients of impurities. Ion implantation therefore represents a natural alternative doping method. The published experimental results show that p-type and p+-type layers can be formed by boron ion implantation. Implantation of Li+ and C+ produces n-type layers. Diamond films grown in the presence of phosphorus and sodium can also be electrically conducting. The efficiency of this method of introducing electrically active centres varies strongly with the temperature of diamond during implantation and with the conditions during the subsequent annealing.