Dissertations / Theses on the topic 'Ion implantation'

The aim of this work is to analytically treat the dynamic ion behavior during the evolution of the ion matrix sheath, considering the industrial application plasma source ion implantation for both planar and cylindrical targets, and then to de-velop a code that simulates this dynamic ion behavior numerically. If the sepa-ration between the electrodes in a discharge tube is small, upon the application of a large potential between the electrodes, an ion matrix sheath is formed, which fills the whole inter-electrode space. After a short time, the ion matrix sheath starts moving towards the cathode and disappears there. Two regions are formed as the matrix sheath evolves. The potential profiles of these two regions are derived and the ion flux on the cathode is estimated. Then, by us-ing the finite-differences method, the problem is simulated numerically. It has been seen that the results of both analytical calculations and numerical simula-tions are in a good agreement.

This thesis investigates ion energy distributions (IEDs) during plasma immersion ion implantation (PIII). PIII is a surface modification technique where an object is placed in a plasma and pulse biased with large negative voltages. The energy distribution of implanted ions is important in determining the extent of surface modifications. IED measurements were made during PIII using a pulse biased retarding field energy analyser (RFEA) in a capacitive RF plasma. Experimental results were compared with those obtained from a two dimensional numerical simulation to help explain the origins of features in the IEDs. Time resolved IED measurements were made during PIII of metal and insulator materials and investigated the effects of the use of a metal mesh over the surface and the effects of insulator surface charging. When the pulse was applied to the RFEA, the ion flux rapidly increased above the pulse-off value and then slowly decreased during the pulse. The ion density during the pulse decreased below values measured when no pulse was applied to the RFEA. This indicates that the depletion of ions by the pulsed RFEA is greater than the generation of ions in the plasma. IEDs measured during pulse biasing showed a peak close to the maximum sheath potential energy and a spread of ions with energies between zero and the maximum ion energy. Simulations showed that the peak is produced by ions from the sheath edge directly above the RFEA inlet and that the spread of ions is produced by ions which collide in the sheath and/or arrive at the RFEA with trajectories not perpendicular to the RFEA front surface. The RFEA discriminates ions based only on the component of their velocity perpendicular to the RFEA front surface. To minimise the effects of surface charging during PIII of an insulator, a metal mesh can be placed over the insulator and pulse biased together with the object. Measurements were made with metal mesh cylinders fixed to the metal RFEA front surface. The use of a mesh gave a larger ion flux compared to the use of no mesh. The larger ion flux is attributed to the larger plasma-sheath surface area around the mesh. The measured IEDs showed a low, medium and high energy peak. Simulation results show that the high energy peak is produced by ions from the sheath above the mesh top. The low energy peak is produced by ions trapped by the space charge potential hump which forms inside the mesh. The medium energy peak is produced by ions from the sheath above the mesh corners. Simulations showed that the IED is dependent on measurement position under the mesh. To investigate the effects of insulator surface charging during PIII, IED measurements were made through an orifice cut into a Mylar insulator on the RFEA front surface. With no mesh, during the pulse, an increasing number of lower energy ions were measured. Simulation results show that this is due to the increase in the curvature of the sheath over the orifice region as the insulator potential increases due to surface charging. The surface charging observed at the insulator would reduce the average energy of ions implanted into the insulator during the pulse. Compared to the case with no mesh, the use of a mesh increases the total ion flux and the ion flux during the early stages of the pulse but does not eliminate surface charging. During the pulse, compared to the no mesh case, a larger number of lower energy ions are measured. Simulation results show that this is caused by the potential in the mesh region which affects the trajectories of ions from the sheaths above the mesh top and corners and results in more ions being measured with trajectories less than ninety degrees to the RFEA front surface.

Doctor of Philosophy (PhD)
This thesis investigates ion energy distributions (IEDs) during plasma immersion ion implantation (PIII). PIII is a surface modification technique where an object is placed in a plasma and pulse biased with large negative voltages. The energy distribution of implanted ions is important in determining the extent of surface modifications. IED measurements were made during PIII using a pulse biased retarding field energy analyser (RFEA) in a capacitive RF plasma. Experimental results were compared with those obtained from a two dimensional numerical simulation to help explain the origins of features in the IEDs. Time resolved IED measurements were made during PIII of metal and insulator materials and investigated the effects of the use of a metal mesh over the surface and the effects of insulator surface charging. When the pulse was applied to the RFEA, the ion flux rapidly increased above the pulse-off value and then slowly decreased during the pulse. The ion density during the pulse decreased below values measured when no pulse was applied to the RFEA. This indicates that the depletion of ions by the pulsed RFEA is greater than the generation of ions in the plasma. IEDs measured during pulse biasing showed a peak close to the maximum sheath potential energy and a spread of ions with energies between zero and the maximum ion energy. Simulations showed that the peak is produced by ions from the sheath edge directly above the RFEA inlet and that the spread of ions is produced by ions which collide in the sheath and/or arrive at the RFEA with trajectories not perpendicular to the RFEA front surface. The RFEA discriminates ions based only on the component of their velocity perpendicular to the RFEA front surface. To minimise the effects of surface charging during PIII of an insulator, a metal mesh can be placed over the insulator and pulse biased together with the object. Measurements were made with metal mesh cylinders fixed to the metal RFEA front surface. The use of a mesh gave a larger ion flux compared to the use of no mesh. The larger ion flux is attributed to the larger plasma-sheath surface area around the mesh. The measured IEDs showed a low, medium and high energy peak. Simulation results show that the high energy peak is produced by ions from the sheath above the mesh top. The low energy peak is produced by ions trapped by the space charge potential hump which forms inside the mesh. The medium energy peak is produced by ions from the sheath above the mesh corners. Simulations showed that the IED is dependent on measurement position under the mesh. To investigate the effects of insulator surface charging during PIII, IED measurements were made through an orifice cut into a Mylar insulator on the RFEA front surface. With no mesh, during the pulse, an increasing number of lower energy ions were measured. Simulation results show that this is due to the increase in the curvature of the sheath over the orifice region as the insulator potential increases due to surface charging. The surface charging observed at the insulator would reduce the average energy of ions implanted into the insulator during the pulse. Compared to the case with no mesh, the use of a mesh increases the total ion flux and the ion flux during the early stages of the pulse but does not eliminate surface charging. During the pulse, compared to the no mesh case, a larger number of lower energy ions are measured. Simulation results show that this is caused by the potential in the mesh region which affects the trajectories of ions from the sheaths above the mesh top and corners and results in more ions being measured with trajectories less than ninety degrees to the RFEA front surface.

Plasma Immersion Ion Implantation has several unique advantages over conventional implantation, such as low cost, large area capability, non-line-of-sight features and high dose rate implantation. However, it is still far from use in routine production because of problems such as the ability to control the ion depth profile in targets, the ion dose and contamination. In this thesis, a PIII system has been systematically calibrated, and a computer simulation code for PIII has been developed in order to understand more clearly the physics of the PIII process and to optimise the experimental conditions. In the second part of this thesis, a new application of PIII has been explored, where the PIII technique has been used as a high dose-rate implant treatment to form amorphous silicon nitride/oxide films on both crystalline and amorphous silicon substrates. The electrical properties of these films have been characterized. It shows that low dose nitrogen/oxygen implantation leads to the modification of Schottky barrier heights or the introduction of charged defects in the materials. As the ion dose is increased, alloying effects take over, forming silicon nitride/oxide alloys. The a-SiNx:H films synthesized via PIII have electrical characteristics similar to those grown by PECVD, but a-SiOx:H has different electrical properties from a-SiNx:H.

Thesis (BSc. (Hons))--Australian National University, 2002.
Available via the Australian National University Library Electronic Pre and Post Print Repository. Title from title screen (viewed Mar. 27, 2003). "A thesis submitted in part fulfillment of the requirements for the degree of Bachelor of Science (Honours), The Australian National University" "November 2002" Includes bibliographical references.

It was proposed that amorphous alloys may be more resistant to radiation damage than crystalline metals. In crystalline metals neutron induced transmutations lead to the formation of inert gas bubbles. These preferentially nucleate near line defects and result in embrittlement. Amorphous alloys do not contain sites where nucleation can occur preferentially. In this work the growth of argon bubbles in amorphous Cu[50]Zr[50] has been induced by implanting thin specimens with 80keV argon ions at room temperature. The bubble size distribution was obtained over the dose range 5x10[16] to 3x10[17] Ar[+] cm[-2]. Larger bubbles grew in the amorphous alloy than would have been expected to grow in a crystalline metal implanted under the same conditions. It was found that ion bombardment caused surface atoms to be sputtered away from the specimens at a rate of 2.3at.ion[-1]. The sputtering process led to saturation in the amount of argon retained by the material and caused the formation of copper rich near-surface layer. This layer also contained significant amounts of oxygen. Blister formation was induced at the surface of the amorphous alloy by implanting it with 100keV helium ions. At a critical dose of 3x10[17] He[+]cm[-2] a population of very small blisters was formed. These were the result of large bubbles forming just below the specimen surface. As higher doses were used the features joined up to produce large, thin-lidded blisters at a dose of 10[18] He[+] cm[-2]. These observations could not be completely explained in terms of the two popular models of blister formation, where interbubble fracture or lateral stress result in surface deformation.

Secondary ion mass spectrometry (SIMS) has been employed tostudy the spatial distributions resulting from mass transportby diffusion and ion implantation in single crystal siliconcarbide (SiC). By a systematic analysis of this data,fundamental processes that govern these phenomena have beenderived.

The acceptor atoms Al and B are known to be electricallypassivated by H in SiC. By studying the thermally stimulatedredistribution of implanted deuterium (2H) in various acceptordoped structures, it is found that hydrogen forms complexeswith the doping atoms, and also interacts strongly withimplantation induced defects. A comprehensive understanding ofthe formation and dissociation kinetics of these complexes hasbeen obtained. The extracted effective capture radius for theformation of 2H-B complexes is in good agreement with thatexpected for a coulomb force assisted trapping mechanism. Thelarge difference of 0.9 eV in the extracted dissociationenergies for the 2H-Al and 2H-B complexes suggests that theatomic configurations of the two complexes are significantlydifferent. Furthermore, by studying the migration behavior of Hin the presence of built-in electric fields, it is concludedthat all of the mobile H is in the positive charge state inp-type SiC.

A large number of implantations have been performed withrespect to ion mass, energy, fluence, and crystal orientation.The electronic stopping cross sections in the low velocityregime for ions with atomic numbers 1 ≤ Z1 ≤ 15have been extracted from the ion range distributions. Theydisplay both Z1-oscillations and a smaller than velocityproportional stopping for ions with Z1 ≤ 8, in agreementwith previous reports for other materials. Furthermore, thedegree of ion channeling in various major axial and planarchannels of the 6H and 4H-SiC crystal has been explored. Twotypes of ion implantation simulators have been developed. Onebased on a statistical, data-base approach, and one atomisticsimulator, based on the binary collision approximation (BCA).By fitting BCA simulated profiles to the experimental profiles,detailed information about the electronic stopping andimplantation induced damage is extracted. In addition, thevacancy-related damage caused by the implantations has beeninvestigated by positron annihilation spectroscopy (PAS). Twotypes of implantation induced positron traps have been isolatedand are tentatively identified as a Si vacancy (VSi) and a Si-Cdivacancy (VSiVC). The extension of detected VSi is in goodagreement with that predicted by BCA simulations, and forimplantations with heavier ions VSi are revealed at far greaterdepths than the mean projected ion range due to deeplypenetrating channeled ions.

The effects of ion implantation of Al2O3interface to 4H-SiC epitaxial n- and p-type layers are presented. Different fluencies of carbon and nitrogen ions are used, as well as different annealing processes, with the aim to study the effects of implanted ions at the Al2O3/SiC interface. Capacitance-Voltage (C-V) behavior for fabricated MOS capacitors is studied before and after implantation to determine the effect of the implantation. Terman‟s method was employed to extract the density of interface traps (Dit) present at the Al2O3/SiC interface. Effective oxide charges density (Neff), present inside the Al2O3,was also evaluated by comparing the theoretical (ideal) C-V curve with the experimental C-V curves. It is generally known, and also proved by this study, that Al2O3 on n-type 4H-SiC shows significantly higher effective oxide charges density (Neff) and density of interface traps (Dit=3-4×1012 eV-1cm-2) compared to n-type SiO2/SiC MOS capacitors. However, the analysis of the collected data from N and C implanted n-type Al2O3/SiC samples show Dit values around 2-9×1011 eV-1cm-2, i.e., an effective reduction has been achieved by the ion implantation. The values of Neff for N ion implanted n-type Al2O3/SiC is as high as 1013 cm-2 in some cases, but C implanted n-type Al2O3/SiC sample shows exceptionally low Neff =1.8×1011 cm-2, which is comparable to SiO2/SiC based MOS capacitor. This result suggest that using C ion implantation before the formation of the oxide layer could be a promising approach to improving both oxide and interface properties of n-type 4H-SiC MOS capacitors.

Rectifying and non-rectifying contacts were fabricated in n-type 4H-Silicon Carbide. To improve the characteristics of the fabricated contacts various different surface pre-treatments were used. The impact of these pre-treatments on both contacts types was evaluated, and any improvements recorded. The findings report on the improvements made to the specific contact resistance of nickel contacts fabricated to n-type 4H-SiC epilayers. Ohmic contacts with an average value of specific contact resistances as low as 1.15 x 10^-4 Ω cm² following annealing at around 900^oC were created. In addition nickel Ohmic contacts were created with similarly low specific contact resistance, which required no such annealing, a phenomenon never previously reported. Further investigation was conducted into the reasons behind this finding, and a hypothesis developed. Various different surface preparations were also experimented for use in the formation of Schottky contacts. No improvements were seen over the standard cleaning process however. High power Schottky diodes were fabricated using a single nickel Schottky contact that exhibited reverse breakdown voltages of around 600V. This figure was improved upon through the use of boron implantation as an edge termination but at the detriment of the forward I(V) characteristic. Further development of the diodes, using a multiple metal Schottky contact, yielded breakdown voltages of 1kV without the need for any further edge termination. This value is more than 85% of the theoretical value for reverse breakdown. In addition to the work on metal contacts, investigation was also performed into the use of ion implantation for the purpose of semiconductor doping. A database was developed to allow the prediction of implant profiles for both Boron and Nitrogen into SiC. This prediction compared well to experimental results. The damage created by high temperature annealing of SiC and the possible steps to prevent and repair this damage is also investigated.

Ion implantation is used to dope silicon substrates during the manufacture of integrated circuits. Insulating films, inevitably present on the wafer surface during a typical metal-oxide-silicon process, will prevent the charge introduced by the ions from being conducted away. The resultant charge accumulation will produce localised electric fields which can lead to breakdown of the insulator and damage to the devices. In this work an investigation into the underlying charging and charge leakage mechanisms during ion implantation of silicon MOS structures was undertaken, concentrating on charge conduction in silicon dioxide under ion bombardment. A detailed theoretical study of the phenomena that occur as a result of ion implantation indicated that photoconduction, space charge limited current injection, impact ionisation and secondary electrons all have a role in charge conduction through oxide. To distinguish between these various possible types of conduction, X-ray, electron and ion radiations were used for the experiments in this work. The X-ray yield from ion implantation into silicon was measured. From these results and the data in the literature it was deduced that X-ray generated photoconduction in oxide during ion irradiation is insignificant. Electron beam induced conductivity was measured as a function of applied field with various electron energies, electron energy deposition rates, oxide thicknesses and doses. The results of these experiments confirmed the charge conduction mechanisms proposed, i. e. that photoconduction and space charge limited conduction are the main methods of charge conduction through oxide under irradiation. Under ion irradiation the voltage acquired by an aluminium pad on oxide on silicon was measured in real time. The development of the pad potential was measured with various oxide thicknesses, ion species and energies, beam current densities, pad geometries and dose. The major factors determining the pad voltage proved to be the pad area to perimeter ratio and the ions' projected range compared with the oxide thickness. Secondary electrons were also found to contribute to pad potential.

Many doses of ions have been implanted through near-surface AlGaAs/GaAs double-barrier diodes. The first objective of this work was the creation of a resistive layer beneath the diodes in selected areas of the wafer. It is shown that if the damage within the double-barrier diodes could be annealed without removing the resistive layer, the three-dimensional integration of the diodes with a second level of devices beneath the resistive layer could be attained. Implantation-and-annealing to create either a damaged or a chemically-compensated resistive layer has been attempted, where, during both types of process, the damage within the doublebarrier diodes was much less than that below them. After implantation of 5.0x1018 2.0MeV B+ ions cm-2, and anneals at 600° C, near-surface Al0.4Ga0.6As/GaAs double-barrier diodes still had good quality negative differential-resistance. It is shown that if (the smaller and less damaging) 1.2MeV Be+ ions were implanted instead of the 2.0MeV B+ ions, an n+-doped layer beneath the diodes can, in principle, be chemically compensated without destroying the diodes irreparably. This work was the first to successfully carry out the anneal-induced recovery of an ion-implanted electronic device having quantum-length-scale layers. The second objective of this work was the elucidation of the electronic and structural characteristics of the same implanted-and-annealed double-barrier diodes. Before annealing, electron conduction through the ion-implanted diodes was limited primarily by field-enhanced emission of electrons from defect states within the lightly-doped spacer layers. The current of ballistic electrons through the as-grown double-barrier structures was suppressed by implantation-and-annealing; this was probably caused by scattering of these electrons by the remaining defect states. The suppression of the ballistic-electron current within implanted-and- annealed double-barrier diodes is proposed to be the primary cause of their larger-than-as-grown 5K and 77K peak-to-valley current ratios. Multi-stage annealing of defects within the double-barrier diodes has been investigated by electrical measurements. The anneal-induced creation of defect clusters within the device mesas was confirmed by both DC and AC measurements, where these clusters were surrounded by percolation paths of as-grown material. Single-electron switching and resonant tunnelling through donor states have been observed within the percolation paths at 4.2K; these observations indicate that the typical diameter of the paths was probably less than five microns, and possibly less than one micron.

Field emission and breakdown characteristics of high voltage, large area electrodes determine the performance of many vacuum-based electron sources. A corroborative project with the Thomas Jefferson National Accelerator Facility involves studying the behavior of such electrodes after nitrogen ion implantation. A Plasma Source Ion Implantation (PSII) facility is designed and constructed at William and Mary, and used to treat stainless steel electrodes. PSII is a novel implantation technique developed at the University of Wisconsin-Madison. A workpiece is submerged in a quiescent plasma of the species to be implanted. A series of high, negative voltages (30--100 kV) is applied to the workpiece to accelerate the ions in the plasma, implanting them to depths of several hundred Angstroms. to characterize the response of the modified electrodes to high field gradients, fields as high as 20 MV/m are applied between parallel electrodes in a VG ESCALab MKII surface analysis system. XPS, AES, and SEM are used to characterize the surface of the cathodes. The pre-breakdown current from implanted electrodes is compared to that of thin film coated, polished, electron beam treated, and untreated electrodes. Current models to explain anomalous field emission are reviewed and considered as explanation of observed effects.

Glassy carbon is a disordered form of carbon with very high temperature resistance, high hardness and strength and chemical stability even in extreme environments. Glassy carbon is also unaffected by nearly all acids and cannot be graphitized even at very high temperature. Because of these characteristics, there is a possibility that glassy carbon can replace copper, iron, titanium alloys and other materials employed in making canisters used in nuclear waste storage. The modification of glassy carbon due to strontium ions implantation and heat treatment is reported. Glassy carbon (GC) samples were implanted with 200 keV strontium ions to a fluence of 2×1016 ions/cm2 at room temperature. Sequential isochronal annealing was carried out on the implanted samples at temperatures ranging from 200 oC - 900 oC for one hour. The influence of ion implantation and annealing on surface topography was examined by the scanning electron microscopy (SEM), while Raman spectroscopy was used to monitor the corresponding structural changes induced in the glassy carbon. The depth profiles of the implanted strontium before and after annealing were determined using Rutherford Backscattering Spectroscopy (RBS). Compared to SRIM predictions the implanted strontium profiles was broader. After annealing at 300 oC, bulk and surface diffusion of the strontium atoms took place. Annealing at 400 oC- 700 oC not only resulted in further diffusion of strontium towards the surface, the diffusion was accompanied with segregation of strontium on the surface of the glassy carbon substrate. Evaporation of the strontium atoms was noticed when the sample was annealed at 800 oC and 900 oC respectively. These annealing temperatures are higher than the melting point of strontium (~769 oC). The Raman spectrum of the virgin glassy carbon shows the disorder (D) and graphitic (G) peaks which characterize disordered carbon materials. Merging of these two peaks was observed when the virgin sample was implanted with strontium ions. Merging of these peaks is due to damage caused by the implantation of strontium. The Raman spectrum recorded after heat treatment showed that only some of the damage due to implantation was annealed out. Annealing at 20000C for 5 hours resulted in a Raman spectrum very similar to that of virgin glassy carbon indicating that the damage due to the ion implantation was annealed out. SEM showed large differences in the surface topography of the polished glassy carbon surfaces and those of as-implanted samples. Annealing did not significantly change the surface microstructure of the implanted samples.
Dissertation (MSc)--University of Pretoria, 2013.
gm2014
Physics
unrestricted

The systematic study of the formation of β-SiC formed by low energy carbon ion (C-)implantation into Si followed by high temperature annealing is presented. The research is performed to explore the optimal annealing conditions. The formation of crystalline β-SiC is clearly observed in the sample annealed at 1100 °C for a period of 1 hr. Quantitative analysis is performed in the formation of β-SiC by the process of implantation of different carbon ion fluences of 1×1017, 2×1017, 5×1017, and 8×1017 atoms /cm2 at an ion energy of 65 keV into Si. It is observed that the average size of β-SiC crystals decreased and the amount of β-SiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100°C for 1 hr. However, it is observed that the amount of β-SiC linearly increased with the implanted fluences up to 5×1017 atoms /cm2. Above this fluence the amount of β-SiC appears to saturate. The stability of graphitic C-C bonds at 1100°C limits the growth of SiC precipitates in the sample implanted at a fluence of 8×1017 atoms /cm2 which results in the saturation behavior of SiC formation in the present study. Secondly, the carbon cluster formation process in silica and the characterization of formed clusters is presented. Silicon dioxide layers ~500 nm thick are thermally grown on a Si (100) wafer. The SiO2 layers are then implanted with 70 keV carbon ions at a fluence of 5×1017 atoms/cm2. The implanted samples are annealed 1100 °C for different time periods of 10 min., 30 min., 60 min., 90 min., and 120 min., in the mixture of argon and hydrogen gas (96 % Ar + 4% hydrogen). Photoluminescence spectroscopy reveals UV to visible emission from the samples. A detail mechanism of the photoluminescence and its possible origin is discussed by correlating the structural and optical properties of the samples. Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, spectroscopy, photoluminescence spectroscopy, and transmission electron microscopy are used to characterize the samples.

Ion implantation and the subsequent redistribution of manganese atoms in Czochralski Silicon (Cz-Si) and Floating Zone Silicon (Fz-Si) due to thermal annealing between 300 C and 1000 C is studied using Secondary Ion Mass Spectroscopy. The samples ion implanted at 340 C showed multiple peak formation above 900 C. This was not observed for the samples ion implanted at room temperature. Cz-Si and Fz-Si showed similar redistribution profiles.
M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE

There has been great interest in using ion implantation for III-V semiconductor device isolation as an alternative to mesa isolation technique. This is attributed to several advantages that implant isolation has over mesa isolation. Mesa isolation exhibits problems such as over/under etching, repeatability issue of etching depth and nonplanarity of the surface of the semiconductor. However implant isolation is advantageous as the surface planarity is maintained and in general, less intrusion under the mask edges is observed. This thesis presents a study on the isolation of both n and p-type InP and InGaAs layers and n-type InGaAsP layers by ion implantation. Several different ion species such as protons, helium, nitrogen and iron were used to isolate these materials. The n and p-type layers were grown by Solid Source Molecular Beam Epitaxy. Conductive n-type InP layers were also formed using multiple energy silicon implantation to create a uniform dopant distribution throughout the n-type region. The effects of ion mass, implantation temperature, damage accumulation, initial carrier concentration of the conductive layer and post-implant annealing temperature were investigated in detail through electrical and structural characterisation. The major part of the work was to develop recipes for the isolation of the individual InP, InGaAs and InGaAsP layers. The effects of implantation temperature and dose were also examined thoroughly. A parallel resistor model was also created to confirm the reliability of the measurements.

In this study, we used ion implantation technique to synthesize semiconductor (Ge, Si) nanocrystals in SiO2 matrix. Ge and Si nanocrystals have been successfully formed by Ge and Si implantation and post annealing. Implanted samples were examined by characterization techniques such as TEM, XPS, EDS, SAD, SIMS, PL, Raman and FTIR spectroscopy and the presence of Ge and Si nanocrystals in the SiO2 matrix has been evidenced by these measurements. It was shown that implantation dose, implantation energy, annealing temperature, annealing time and annealing ambient are important parameters for the formation and evolution of semiconductor nanocrystals embedded in SiO2 matrix. The size and size distribution of Ge and Si nanocrystals were estimated successfully by fitting Raman and PL spectra obtained from Ge and Si implanted samples, respectively. It was demonstrated that Si implanted and post annealed samples exhibit two broad PL peaks at &
#8764
625 and 850 nm, even at room temperature. Origin of these peaks was investigated by temperature, excitation power and excitation wavelength dependence of PL spectrum and etch-measure experiments and it was shown that the peak observed at &
#8764
625 nm is related with defects (clusters or chain of Si located near the surface) while the other is related to the Si nanocrystals. As an expected effect of quantum size phenomenon, the peak observed at &
#8764
850 nm was found to depend on the nanocrystal size. Finally, the formation and evolution of Ge and Si nanocrystals were monitored by FTIR spectroscopy and it was shown that the deformation in SiO2 matrix caused by ion implantation tends to recover itself much quicker in the case of the Ge implantation. This is a result of effective segregation of Ge atoms at relatively low temperatures.

Visible light emission from silicon nanostructures formed by Si+ ion implantation into a SiO2 matrix and subsequently annealed at high temperatures (mainly 1300°C and 900°C) in various annealing atmospheres has been investigated. Various analyses techniques, such as Rutherford Backscattering Spectroscopy (RBS), Secondary Ion Mass Spectroscopy (SIMS), Photoluminescence (PL), and Transmission Electron Microscopy (TEM) were employed to characterize the structures in terms of their composition and optical properties. RBS and SIMS analyses revealed nitrogen and carbon impurities in the samples which we conclude originate from contamination, such as N2 and CO+ in the ion beam. PL analysis with a 488 nm Ar laser at 300 K showed that there was no visible PL from the samples before Si+ implantation or from the samples after Si+ implantation but before annealing. Also, N+ implantation gave rise to no PL. Si+ implanted samples with 2 x 1017 Si+ cm-2 and 6 x 10 17 Si+ cm-2 exhibited, after annealing at 1300°C for 30 minutes in a nitrogen ambient, strong visible PL, with a broad spectrum at peak wavelengths of 580 nm and 760 nm, respectively. There was a weak dependence of the PL peaks at 580 nm and 760 nm on annealing tune and annealing temperature. However, there was no PL from N+ implanted and annealed samples. Annealing the Si+ implanted samples in forming gas (FG) at lower temperatures (up to 1000°C) increased the PL peak intensity up to a factor of two, however, the PL peak wavelengths were the same. It is concluded that hydrogen annihilates the non-radiative recombination pathways. This effect provides evidence for surface states playing an important role in light emission. From PL analysis, using a short wavelength laser (325 nm), it was found that silica samples showed one broad PL spectrum at a peak wavelength of 440 nm, whereas samples consisting of a 1 mum thick SiO2 film exhibited several peaks which we found to be due to optical interference. Detailed observations of the fine structure in the PL spectra at low temperature (18 K), from the silica samples which were annealed in FG at 900°C revealed strong evidence for interaction between excitons and Si-O vibrations localized in a very small region. TEM analysis showed that there were precipitates after annealing at 1300°C in N2 in a sample implanted at a dose of 2 x 10 17 Si+ cm2 with an energy of 400 keV whilst HTEM analysis showed that the microcrystallites varied in size from 2.5 nm to 7.5 nm. However, TEM failed to show any precipitates in samples which were implanted with the same dose at an energy of 200 keV and have strong PL, and this is also another strong indicator that the PL emission is not simply due to quantum confinement. In this thesis, we propose a luminescent model to describe the mechanism for light emission. Physically the emitting structures are envisaged to have three regions, namely, a Si core (Si precipitate), an interfacial transition region whose composition varies from Si to SiO2, and the surrounding SiO2 matrix. Light emission occurs by a two step process involving generation and confinement of excitons in the Si core, whose band structure is modified from that of bulk crystalline silicon, and radiative recombination through the interaction of excitons and Si-O vibrations within the interfacial transition region. The justification for this model is discussed in this thesis.

学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2865号 ; 請求記号: 新制/工/1421 ; 整理番号: 25550
Many conventional methods have been used to modify the wettability of the polymeric surfaces for the biomedical applications of the artificial bionic organ. Those methods are the chemical treatment, the ultraviolet (UV) irradiation, the plasma process and the ion implantation. Many artificial bionic organs, for example, an artificial heart, an artificial blood vessel, a device for prevention of thrombosis stent and an artificial endocranium have been developed for the physical or mental disability. For development of the high function of an artificial bionic organ, the data transmission between the brain neuron cells and the external electrical circuit, and the high biocompatible materials for the interface between brain and electrode are required. It is related to the technology of brain-computer interface (BCI), sometimes called a direct neural interface or a brain-machine interface. In case of the brain-controlled devices, the study of the brain memory is necessary. Then, the artificial pattern network of the brain cells cultured on the surface in vitro for simulation of the brain function is the concerned issue. The arrangement of a lot of neuron on a detection electrode is required. So, a formation method of the artificial neural network that arranged a neuron as technology for this purpose is demanded As for the neuron arrangement, there were the reports about the immobilization of neuron by fabrication of the three-dimension structure, and they could be divided into two methods from their manipulation. One is the arrangement with one-by-one manipulation and the other is the arrangement with self-assembly. The former method is the fabrication of many micro-structures and then arranged a neuron in a desired position with one-by-one manipulation to for a neuron network. For the brain memory stimulation, however, the neuron network from more than 10 millions of neurons is required. So, this method is not suitable. The latter is the fabrication of the carbon nanotube pillar to immobilize the neurosphere with self-assembly adhesion. Although this method could be formed the large neuron network, the neurosphere consists of several 1, 000 cells. So, it is very difficult to analyze the mechanism of data transformation. In contrast, by surface modification even if on the same surface to modify a geometric pattern, the cells can adhere along the modified pattern by using single culture on such surface. The neuron will migrate itself to adhere on the pattern. The self-assembly adhesion occur. This method is very useful for the neuron arrangement method. The surface modification of the polymeric materials to pattern the cell adhesion area as a network has been taken place by using many techniques such as the plasma process, the irradiations of UV and X-ray and the ion implantation. The ion implantation technique into the polymeric-material surface has more advantage than the other techniques since its abilities to control the micro-area, and to break down the tight bonding of polymer material. The ion implantation with positive ion without charge neutralization results in a charge-up problem due to the insulating properties of most polymers. This charge-up problem exerts a bad influence on the implantation control of ion dose and ion energy. The negative-ion implantation occurs almost “charge-up free” even if no external charge compensation. Then, the negative-ion implantation into polymeric surface has a very precise control to obtain very fine pattern. So, it is expected to control the adhesion size of about single cells (about several 10 μm). Since this study will be used for the application in the biomedical fields, the ion element should be considered to be harmless for the living body. Then, carbon is selected since it is main component of polymer materials and more familiar to cells. As above described, in this thesis, I use the carbon negative-ion implantation to modify the polymeric surface to obtain the pattern of the neuron with self-assembly-adhesion. As for the polymeric material in the biomedical fields, I selected polystyrene (PS) and silicone rubber (SR). In this research, the fundamental parameters for cell adhesion on the modified surface by carbon negative-ion implantation were described (Chapters 3, 4 and 5). As for the fundamental issue, the wettability relating to the atomic bonding state of the new functional group and the surface morphology (Chapter 3), the protein adsorption (Chapter 4), and also the adhesion of nerve-like cells on the pattern (Chapter 5) were examined. In these chapters, I clarified the relationship among them and the negative-ion implantation. Then, based on these phenomena, I have developed the new application techniques by negative-ion implantation for the adhesion patterning of neuron (Chapters 6 and 7). In the development of these techniques, I have proposed two methods since the neuronal cells required the special base surface to adhere. One is degradation method of the special base surface by which I tried to make an artificial neuron network (Chapter 6). The other is the patterning of the stem cell adhesion and differentiation into neuron with maintaining the adhesion position. So, the neuron patterns were formed on the pattern (Chapter 7). The obtained results are summarized as the following. In Chapter 3, the surfaces of the PS and SR were implanted by carbon negative ions at the energies of 5 – 20 keV and the doses of 1×1013 – 3×1016 ions/cm2. After the implantation, the change in the physical surface properties, relating to the adsorption properties of adhesive proteins, was described. The new atomic bonding, the surface morphology and the wettability were studied by XPS analysis, AFM and contact angle measurement, respectively. XPS analysis showed the formation of new oxygen function groups of hydroxyl and carbonyl on the implanted surfaces from the adsorption of the oxygen in the residual gas and in the moisture in the air on the ion-induced defects. These new bonds refer to the hydrophilicity for the wettability. The ion implantation sputtered and changed the surface morphology of surface roughness in order of several nm that dose not interfere to the protein adsorption and to cell culture. The wettability properties of the C¯-implanted surfaces of SCPS and SR were evaluated by measuring the change in contact angle. At first, the angles were measured by the water drop method. The contact angles of PS measured by water drop method decreased from 91° to 86° for the non-implantation to the implantation, respectively. Those of SR also decreased from 100° to 86°for the non-implantation to the implantation, respectively, even if the main chain bonds in SR are stronger than that in PS. The hydrophilic surfaces of PS and SR were obtained by carbon negative-ion implantation. Then, the contact angles were measured by the air bubble method. The sample was dipped in the water and the bubbles were injected on the surface. Then, the angle was evaluated from the arc circular of the bubble. After dipping in the water for 24 h, the average value of the angles decreased to 64° and to 52° for PS and SR, respectively. The more clearly hydrophilic properties were observed. In Chapter 4, I checked the adsorption properties of the adhesive protein and the poly-D-lysine (PDL) on the implanted surface. Generally, in the cell adhesion, the adhesive proteins exist between the cell surface and the surface. On the cell membrane, cells have specific receptors that anchor to the specific protein. So, the adsorptions of the adhesive proteins are necessary for the cell adhesion. In nature, protein has both hydrophobic and hydrophilic groups. Thus, the ultra hydrophobic and ultra hydrophilic surfaces are not suitable for protein adsorption. The adhesive proteins for the cell adhesion generally prefer to be adsorbed on the hydrophilic surface, which the contact angle is in the range of 40° – 80°. I evaluated the adsorption properties of adhesive protein such as type-I collagen, fibronectin and laminin and that of PDL on the modified surfaces of PS and SR by detecting the nitrogen atom with using XPS analysis. As a result, the adsorptions of the adhesive protein were almost improved with 1.2 – 3.3 times by carbon negative-ion implantation. In Chapter 5, the nerve-like cells of PC12h (rat adrenal pheochromocytoma) were cultured on the C¯-implanted surfaces of PS and SR to find out the fundamental condition for the neuron network formation. As a results, PC12h cells and their neurite outgrowth showed the self-assembly adhesion along the implanted pattern on both of PS and SR. The suitable condition of the ion implantation for the adhesion patterning of PC12h cells was about 1×1015 – 3×1015 ions/cm2. Almost no effect of energy in the range of 5 – 20 keV on the cell adhesion was observed. The effective minimum line width of the implanted region for the adhesion of single cell-body and single neurite outgrowth were about 5 and 2 μm, respectively. In Chapter 6, the brain neuronal cells require the specific surface culture, such as PDL. So, in this chapter, I used PDL coating on the PS and degraded it by the carbon negative-ion implantation. Two kinds of brain neuronal cells were used. One is newborn mouse brain neuronal cells (1 day) and the other is rat embryo brain cortex neuronal cells (16 – 18 days). As a result, obtained the effective ion dose for degradation of the adhesion at 1×1014 ions/cm2. The adhesion patterning of brain neuronal cells on the unmodified pattern of PDL could be achieved by carbon negative-ion implantation. In Chapter 7, I cultured the adult stem cells of rat mesenchymal stem cells (MSC), which has the multipotential to differentiation into many kinds of cell lines, especially into neuron, on the pattern region of the C¯-implanted surfaces of PS and SR. As a results, MSCs showed the self-assembly adhesion along the implanted pattern of PS and SR. Comparing to the adhesion patterning of PC12h cells, the adhesion patterning of MSCs required a lower ion dose to implant on the polymeric surfaces. By culturing with the culture medium supplementing withβ-Mercaptoethanol (BME) at concentration of 1 mM, the MSCs were induced to differentiate into neuronal cells. The adhesion patterning of the neuron-differentiated cells maintained on the implanted region was observed. By staining with anti-neuron-specific enolase, these differentiated cells were neurons. From all investigation, I clarified the change in the physical surface properties after the carbon negative-ion implantation into the polymeric surface and the mechanisms mentioned above. I showed the surface modification to obtain the hydrophilic surface by the ion-induced effect. This hydrophilic surface improved the protein adsorption properties. By using nerve-like cells, the ion implantation affecting to the cell adhesion were clarified. By the implantation through the micro-pattern mask, the cells adhered along the implanted pattern. The cells could adhere on the implanted area that was smaller than the cell size and their neurite also could adhere on the narrowed implanted area. So, I can obtain the self-assembly separation pattern of cell body adhesion and neurite outgrowth. For the application of patterning of real neuron, I coated the special surface with PDL and degraded it from patterning the negative-charge site on it by using carbon negative-ion implantation through a micro-pattern mask. I could pattern and form the neuron network of the brain neuron on the unmodified PDL. On the other hand, for the MSC, I also achieved the adhesion patterning by using carbon negative-ion implantation through a micro-pattern mask, and I succeeded the patterning of the neuron-differentiated cells from the adhered MSC with maintaining their adhesion pattern. As a conclusion, from all these researches, I achieved the cell-self-assembly adhesion and the patterning of the neuron network formation on the polymeric surfaces by using carbon negative-ion implantation.
Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第13394号
工博第2865号
新制||工||1421(附属図書館)
25550
UT51-2007-Q795
京都大学大学院工学研究科電子工学専攻
(主査)教授 石川 順三, 教授 髙岡 義寛, 教授 小林 哲生
学位規則第4条第1項該当

Organic semiconductors have great promise in the field of electronics due to their low cost in term of fabrication on large areas and their versatility to new devices, for these reasons they are becoming a great chance in the actual technologic scenery. Some of the most important open issues related to these materials are the effects of surfaces and interfaces between semiconductor and metals, the changes caused by different deposition methods and temperature, the difficulty related to the charge transport modeling and finally a fast aging with time, bias, air and light, that can change the properties very easily. In order to find out some important features of organic semiconductors I fabricated Organic Field Effect Transistors (OFETs), using them as characterization tools. The focus of my research is to investigate the effects of ion implantation on organic semiconductors and on OFETs. Ion implantation is a technique widely used on inorganic semiconductors to modify their electrical properties through the controlled introduction of foreign atomic species in the semiconductor matrix. I pointed my attention on three major novel and interesting effects, that I observed for the first time following ion implantation of OFETs: 1) modification of the electrical conductivity; 2) introduction of stable charged species, electrically active with organic thin films; 3) stabilization of transport parameters (mobility and threshold voltage). I examined 3 different semiconductors: Pentacene, a small molecule constituted by 5 aromatic rings, Pentacene-TIPS, a more complex by-product of the first one, and finally an organic material called Pedot PSS, that belongs to the branch of the conductive polymers. My research started with the analysis of ion implantation of Pentacene films and Pentacene OFETs. Then, I studied totally inkjet printed OFETs made of Pentacene-TIPS or PEDOT-PSS, and the research will continue with the ion implantation on these promising organic devices.

Organic semiconductors have great promise in the field of electronics due to their low cost in term of fabrication on large areas and their versatility to new devices, for these reasons they are becoming a great chance in the actual technologic scenery. Some of the most important open issues related to these materials are the effects of surfaces and interfaces between semiconductor and metals, the changes caused by different deposition methods and temperature, the difficulty related to the charge transport modeling and finally a fast aging with time, bias, air and light, that can change the properties very easily. In order to find out some important features of organic semiconductors I fabricated Organic Field Effect Transistors (OFETs), using them as characterization tools. The focus of my research is to investigate the effects of ion implantation on organic semiconductors and on OFETs. Ion implantation is a technique widely used on inorganic semiconductors to modify their electrical properties through the controlled introduction of foreign atomic species in the semiconductor matrix. I pointed my attention on three major novel and interesting effects, that I observed for the first time following ion implantation of OFETs: 1) modification of the electrical conductivity; 2) introduction of stable charged species, electrically active with organic thin films; 3) stabilization of transport parameters (mobility and threshold voltage). I examined 3 different semiconductors: Pentacene, a small molecule constituted by 5 aromatic rings, Pentacene-TIPS, a more complex by-product of the first one, and finally an organic material called Pedot PSS, that belongs to the branch of the conductive polymers. My research started with the analysis of ion implantation of Pentacene films and Pentacene OFETs. Then, I studied totally inkjet printed OFETs made of Pentacene-TIPS or PEDOT-PSS, and the research will continue with the ion implantation on these promising organic devices.

Rapid Thermal Annealing has been used to study the electrical activation of a range of donor and acceptor species in ion-implanted GaAs. By varying the time and temperature of the post implant anneal, it was found that the activation processes for most implants can be characterised in terms of two distinct regions. The first of these occurs at short annealing times, where the electrical activity is seen to follow a time-dependent behaviour. At longer annealing times, however, a time-independent saturation value is reached, this value being dependent on the annealing temperature. By analysing the data from Be, Mg, S and Se implants in GaAs, a comprehensive model has been evolved for the time and temperature dependence of the sheet electrical properties. Application of this model to each of the ions studied suggests that the activation processes may be dominated by the extent to which ions form impurity-vacancy complexes. An analysis of the time-dependent regime also shows that, at short annealing times, the mobile species is more likely to be the substrate atoms (or vacancies) rather than the implanted impurities. In the time-dependent region, the values of diffusion energy were found to be between 2.3 to 3.0 eV for all ions, these values corresponding to a diffusion of Ga or As vacancies (or atoms). In the saturation region, activation energies of 0.3 to 0.4 eV and 1.0 to 1.2 eV were obtained for the activation processes of interstitial or complexed impurities respectively.

Thesis (Ph. D.)--University of Sydney, 2004.
Title from title screen (viewed 5 May 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Degree awarded 2004; thesis submitted 2003. Includes bibliographical references. Also available in print form.

In the last years, there is a rise of interest in investigation and fabrication of nanometer sized magnetic structures due to their various applications (e.g. for data storage or micro sensors). Over the last several decades ion beam implantation became an important tool for the modification of materials and in particular for the manipulation of magnetic properties. Nanopatterning and implantation can be done simultaneously using focused-ion beam (FIB) techniques. FIB implantation and standard ion implantation differ in their beam current densities by 7 orders of magnitude. This difference can strongly influence the structural and magnetic properties, e.g. due to a rise of the local temperature in the sample during ion implantation. In previous investigations both types of implantation techniques were studied separately. The aim of the current research was to compare both implantation techniques in terms of structural changes and changes in magnetic properties using the same material system. Moreover, to separate any possible annealing effects from implantation ones, the influence of temperature on the structural and magnetic properties were additionally investigated. For the current study a model material system which is widely used for industrial applications was chosen: a 50 nm thick non-ordered nano-crystalline permalloy (Ni81Fe19) film grown on a SiO2 buffer layer based onto a (100)-oriented Si substrate. The permalloy films were implanted with a 30 keV Ga+ ion beam; and also a series of as-deposited permalloy films were annealed in an ultra-high vacuum (UHV) chamber. Several investigation techniques were applied to study the film structure and composition, and were mostly based on non-destructive X-ray investigation techniques, which are the primary focus of this work. Besides X-ray diffraction (XRD), providing the long-range order crystal structural information, extended X-ray absorption fine structure (EXAFS) measurements to probe the local structure were performed. Moreover, the film thickness, surface roughness, and interface roughness were obtained from the X-ray reflectivity (XRR) measurements. Additionally cross-sectional transmission electron microscope (XTEM) imaging was used for local structural characterizations. The Ga depth distribution of the samples implanted with a standard ion implanter was measured by the use of Auger electron spectroscopy (AES) and Rutherford backscattering (RBS), and was compared with theoretical TRIDYN calculation. The magnetic properties were characterized via polar magneto-optic Kerr effect (MOKE) measurements at room temperature. It was shown that both implantation techniques lead to a further material crystallization of the partially amorphous permalloy material (i.e. to an increase of the amount of the crystalline material), to a crystallite growth and to a material texturing towards the (111) direction. For low ion fluences a strong increase of the amount of the crystalline material was observed, while for high ion fluences this rise is much weaker. At low ion fluences XTEM images show small isolated crystallites, while for high ones the crystallites start to grow through the entire film. The EXAFS analysis shows that both Ni and Ga atom surroundings have a perfect near-order coordination corresponding to an fcc symmetry. The lattice parameter for both implantation techniques increases with increasing ion fluence according to the same linear law. The lattice parameters obtained from the EXAFS measurements for both implantation types are in a good agreement with the results obtained from the XRD measurements. Grazing incidence XRD (GIXRD) measurements of the samples implanted with a standard ion implanter show an increasing value of microstrain with increasing ion fluence (i.e. the lattice parameter variation is increasing with fluence). Both types of implantation result in an increase of the surface and the interface roughness and demonstrate a decrease of the saturation polarization with increasing ion fluence. From the obtained results it follows that FIB and standard ion implantation influence structure and magnetic properties in a similar way: both lead to a material crystallization, crystallite growth, texturing and decrease of the saturation polarization with increasing ion fluence. A further crystallization of the highly defective nano-crystalline material can be simply understood as a result of exchange processes induced by the energy transferred to the system during the ion implantation. The decrease of the saturation polarization of the implanted samples is mainly attributed to the simple presence of the Ga atoms on the lattice sites of the permalloy film itself. For the annealed samples more complex results were found. The corresponding results can be separated into two temperature regimes: into low (≤400°C) and high (>400°C) temperatures. Similar to the implanted samples, annealing results in a material crystallization with large crystallites growing through the entire film and in a material texturing towards the (111) direction. The EXAFS analysis shows a perfect near-order coordination corresponding to an fcc symmetry. The lattice parameter of the annealed samples slightly decreases at low annealing temperatures, reaches its minimum at about ~400°C and slightly rises at higher ones. From the GIXRD measurements it can be observed that the permalloy material at temperatures above >400°C reaches its strain-free state. On the other hand, the film roughness increases with increasing annealing temperature and a de-wetting of the film is observed at high annealing temperatures. Regardless of the material crystallization and texturing, the samples annealed at low temperatures demonstrate no change in saturation polarization, while at high temperatures a rise by approximately ~15% at 800°C was observed. The rise of the saturation polarization at high annealing temperatures is attributed to the de-wetting effect.

Thesis (M.S.)--University of Wisconsin--Madison, 1990.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 56-60).

The search for alternative methods of synthesizing cubic boron nitride (cBN), one of the hardest known materials, at low thermo-baric conditions has stimulated considerable research interest due to its great potential for numerous practical industrial applications. The practical applications are motivated by the material’s amazing combination of extraordinarily superior properties. The cBN phase is presently being synthesized from graphite-like boron nitride modifications at high thermo-baric conditions in the presence of catalytic solvents or by ion–beam assisted (chemical and physical) deposition methods. However, the potential and performance of cBN have not been fully realized largely due to central problems arising from the aforementioned synthesis methods. The work reported in this dissertation is inspired by the extensive theoretical investigation of the influence of defects in a ecting the transformation of the hexagonal boron nitride (hBN) phase to the cBN phase that was carried out by Mosuang and Lowther (Phys Rev B 66, 014112 (2002)). From their investigation, using an ab-initio local density approach, for the B, C, N, and O simple defects in hBN, they concluded that the defects introduced into hBN could facilitate a low activation–energy hexagonal-to-cubic boron nitride phase transformation, under less extreme conditions. We use ion implantation as a technique of choice for introducing ‘controlled’ defects into the hot–pressed polycrystalline 99.9% hBN powder samples. The reasons are that the technique is non–equilibrium (not influenced by dilusion laws) and controllable, that is the species of ions, their energy and number introduced per unit area can be changed and monitored easily. We investigate the structural modifications of hBN by ion implantation. Emphasis is given to the possibilities of influencing a low activation–energy hBN-to-cBN phase transformation. The characterization of the structural modifications induced to the hBN samples by implanting with He+ ions of energies ranging between 200 keV and 1.2 MeV, at fluences of up to 1.0 1017 ionscm2, was accomplished by correlating results from X-Ray Di raction (XRD), micro-Raman (-Raman) spectroscopy measurements, and two-dimensional X-Y Raman (2D-Raman) mapping measurements. The surface to pography of the samples was investigated using Scanning Electron Microscopy (SEM). E orts to use Surface Brillouin Scattering (SBS) were hampered by the transparency of the samples to the laser light as well as the large degree of surface roughness. All the implantations were carried out at room temperature under high vacuum. 2D-Raman mapping and -Raman spectroscopy measurements done before and after He+ ion irradiation show that an induced hBN-to-cBN phase transformation is possible: nanocrystals of cBN have been observed to have nucleated as a consequence of ion implantation,the extent of which is dictated by the fluences of implantation. The deviationof the measured spectra from the Raman spectra of single crystal cBN is expected, has been observed before and been attributed to phonon confinement e ects. Also observed are phase transformations from the pre-existing hBN modification to: (a) the amorphous boron nitride (aBN), (b) the rhombohedral boron nitride (rBN) modifications, (c) crystalline and amorphous boron clusters, which are a result of the agglomeration of elementary boron during and immediately after ion implantation. These transformations were observed at high energies. Unfortunately, the XRD measurements carried out could not complement the Raman spectroscopy outcomes probably because the respective amounts of the transformed materials were well below the detection limit of the instrument used in the former case.