Papers by Krish Bharuth-Ram
Physica status solidi (a) , 2023
A double-pulsed laser ablation (DPLA) method has been used to synthesize
crystalline boron nano... more A double-pulsed laser ablation (DPLA) method has been used to synthesize
crystalline boron nanorods (BNRs), boron nanowires (BNWs), and bamboo-like
boron nanotubes (BBNTs) from bulk boron (BKB). A q-switched Nd: YAG laser
operating at the first and second harmonic wavelengths with 1064 and 532nm is
used to ablate a solid composite boron target doped with 1% Ni and 1% Co in a
tube furnace in flowing argon gas. Boron nanostructures in the form of BNRs,
BNWs, and BBNTs are condensed from the hot laser-induced plasma plume at
furnace temperatures of 800, 900, and 1000°C. The morphology and the chemical
and optical nature of the nanostructures are identified from X-ray diffraction,
electron microscopy, energy-dispersive X-ray spectroscopy, Raman, UV–vis, and
photoluminescence (PL) spectroscopies. The results confirm the crystallinity and
phase purity of the boron-nanomaterials and that they are preferentially grown in
the c-axis direction of α-boron. The as-synthesized BNRs, BNWs, and BBNTs are
observed to have lengths of 0.2–1.5μm and widths between 10 and 100nm, and
show respective PL resonance emission peaks at 330, 331, and 333nm, and the
electrical conductivities of 312, 313, and 324 S cm1 at room temperature which
are higher than the electrical conductivity of BKB.
Deleted Journal, Jan 24, 2024
Conversion electron Mössbauer Spectroscopy (CEMS) studies have been conducted on Fe implanted amo... more Conversion electron Mössbauer Spectroscopy (CEMS) studies have been conducted on Fe implanted amorphous and crystalline SiO 2 which were annealed in air up to a temperature of 1000 o C. For both samples, dramatic changes set in after the 1000 o C anneal and the CEM spectra are dominated by strong ferromagnetic sextets. In the amorphous sample, the sextet is characterized by magnetic hyperfine fields of 33T, 31T and 29 T, consistent with the formation α-Fe nanoclusters. In the crystalline sample the ferromagnetic sextet has spectral parameters of δ = 0.38(3) mm/s and B hf = 52.3T, consistent with formation of α-Fe 2 O 3 clusters, reflecting the precipitation of the implanted Fe into such clusters. The line ratios of lines 1, 2 and 3 (and 6, 5 and 4) of the sextet are 3:4:1, reflecting alignment of the magnetic moment of the precipitates normal to the c-axis of the sample surface.
High‐Temperature Laser‐Assisted Synthesis of Boron Nanorods, Nanowires, and Bamboo‐Like Nanotubes
physica status solidi (a)
A double‐pulsed laser ablation (DPLA) method has been used to synthesize crystalline boron nanoro... more A double‐pulsed laser ablation (DPLA) method has been used to synthesize crystalline boron nanorods (BNRs), boron nanowires (BNWs), and bamboo‐like boron nanotubes (BBNTs) from bulk boron (BKB). A q‐switched Nd: YAG laser operating at the first and second harmonic wavelengths with 1064 and 532 nm is used to ablate a solid composite boron target doped with 1% Ni and 1% Co in a tube furnace in flowing argon gas. Boron nanostructures in the form of BNRs, BNWs, and BBNTs are condensed from the hot laser‐induced plasma plume at furnace temperatures of 800, 900, and 1000 °C. The morphology and the chemical and optical nature of the nanostructures are identified from X‐ray diffraction, electron microscopy, energy‐dispersive X‐ray spectroscopy, Raman, UV–vis, and photoluminescence (PL) spectroscopies. The results confirm the crystallinity and phase purity of the boron‐nanomaterials and that they are preferentially grown in the c‐axis direction of α‐boron. The as‐synthesized BNRs, BNWs, and ...
Hyperfine Interactions, 2004
Detection of explosives by neutron scattering
Physical Review C, 1987
The angular distribution of deuterons from the Zr(n, d)' Y reaction at E"=22 MeV has been measure... more The angular distribution of deuterons from the Zr(n, d)' Y reaction at E"=22 MeV has been measured with a spectrometer consisting of three multiwire proportional counters followed by a curved plastic scintillator. Spectra were obtained with an energy resolution full width at half maximum, of about 0.7 MeV and an angle resolution full width at half maximum of about 4'. Two prominent peaks were observed in the spectra corresponding to transitions to the ground state and to two states at-1.6 MeV excitation in Y. Distorted wave Born approximation analysis of the angular distributions yielded spectroscopic factors of 1.7(5), 1.8(5), and 0.8(4), respectively, for the transitions to the ground state, the 1.51 MeV state, and the 1.75 MeV state. The results are compared with previous measurements and model predictions.
Lattice sites of Li in CdTe
Journal of Crystal Growth, 1996
... Images Images, Journal/Book title, Volume, Issue, Page, Search tips. ... M. Restle a , Corres... more ... Images Images, Journal/Book title, Volume, Issue, Page, Search tips. ... M. Restle a , Corresponding Author Contact Information , E-mail The Corresponding Author , K. Bharuth-Ram a , 1 , H. Quintel a , C. Ronning a , H. Hofsäss a , U. Wahl b , SG Jahn and The ISOLDE Collaboration ...
Absence of ferromagnetic behaviour in Mn implanted ZnO
Hyperfine Interactions
Crystals, Jul 4, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
the ISOLDE Collaboration: Detection of substitutional and interstitial Fe in silicon by Mössbauer spectroscopy
Hyperfine Interactions, 2019
We have conducted conversion electron Mössbauer spectroscopy (CEMS) studies of Fecarbides produce... more We have conducted conversion electron Mössbauer spectroscopy (CEMS) studies of Fecarbides produced in Fe implanted highly oriented pyrolytic graphite (HOPG) and CVD diamond substrates. The samples were implanted at room temperature with 57 Fe ions with 40 keV and 60 keV, respectively, and corresponding fluences of 1.0•10 16 /cm 2 and 5•10 15 /cm 2. The formation of magnetic structures in the spectra was monitored with CEMS measurement after annealing the samples at temperatures up to 700°C. After the high temperature annealing, the main components in the spectra were sextets whose line shapes displayed strong, asymmetric distortions, consistent with those due the formation of nanoclusters. The hyperfine magnetic fields B hf = 21.6 T, 20.0 T and 18 (1) T were in good agreement with those observed previously for Fe 3 C nanoclusters 10-20 nm in size.
Applied Surface Science, 2019
The properties and performance of TiN thin films are closely related to the concentration and mob... more The properties and performance of TiN thin films are closely related to the concentration and mobility of lattice defects in the thin film structures of TiN. This makes a local atomic scale study of TiN thin films an ever-growing demand. Emission 57 Fe Mössbauer spectroscopy (eMS) is a powerful tool in this regard, which we apply here to study an ultrathin TiN film epitaxially grown on MgO (100). With the help of theoretical calculations, our results show that most implanted Fe ions adopt a 2 + valence state and locate at the Ti sublattice in the bulk-like single crystalline grains, with the rest Fe residing at the grain boundaries as interstitials. A small percentage of nitrogen point defects (vacancy VN and interstitial NI) are observed in the bulk-like crystalline grains. A temperature-dependent, interstitial NI mediated siteexchange between NI and VN inside the crystal grain are deduced via a N2 dimmer like diffusion of NI through the crystal grains in the temperature range of 540-620 K. This is interesting in the perspective of exploring the catalytic property of TiN nanostructures. The titanium vacancy (VTi) is only detected at the grain boundaries. Annealing up to 813 K, both the VN and NI are annihilated in the crystalline grains and the VTi is fully recovered with healing of the grain boundaries. However, no evidence of ferromagnetism due to dilute implantation of 57 Mn/ 57 Fe and or structural defects in the film is obtained. This suggests that the so far reported dilute magnetism and defect-induced ferromagnetism in TiN nanostructures requires a further systematic investigation.
Applied Surface Science, 2015
The formation of Fe silicides in surface ripple patterns, generated by erosion of a Si surface wi... more The formation of Fe silicides in surface ripple patterns, generated by erosion of a Si surface with keV Ar and Xe ions and simultaneous co-deposition of Fe, was investigated with conversion electron Mössbauer spectroscopy, atomic force microscopy and Rutherford backscattering spectrometry. For the dot and ripple patterns studied, we find an average Fe concentration in the irradiated layer between 6 and 25 at.%. The Mössbauer spectra clearly show evidence of the formation of Fe disilicides with Fe content close to 33 at.%, but very little evidence of the formation of metallic Fe particles. The results support the process of ion-induced phase separation toward an amorphous Fe disilicide phase as pattern generation mechanism. The observed amorphous phase is in agreement with thermodynamic calculations of amorphous Fe silicides.
Hyperfine Interactions, 2016
Emission Mössbauer Spectroscopy (eMS) measurements, following low fluence (<10 12 cm −2) implanta... more Emission Mössbauer Spectroscopy (eMS) measurements, following low fluence (<10 12 cm −2) implantation of 57 Mn (t 1/2 = 1.5 min.) into ZnO single crystals preimplanted with Ar and C ions, has been utilized to test the sensitivity of the 57 Fe eMS technique to the different types of defects generated by the different ion species. The dominant feature of the Mössbauer spectrum of the Ar implanted ZnO sample was a magnetic hyperfine field distribution component, attributed to paramagnetic Fe 3+ , while that of the This article is part of the Topical Collection on
Hyperfine Interactions, 2016
Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope 57 Mn... more Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope 57 Mn * (t½ = 1.5 min) at ISOLDE/CERN show that a large fraction of 57 Fe atoms produced in the 57 Mn beta decay are trapped as paramagnetic Fe 3+ with relatively long spin-lattice relaxation times in ZnO. We have extended this study to eMS studies on ZnO pre-implanted with 56 Fe to fluences of 210 13 , 510 13 and 810 13 ions/cm 2 , in order to investigate the dependence of the paramagnetic relaxation rate with fluence. The spectra in the present samples are also dominated by magnetic features displaying paramagnetic relaxation effects. The extracted spin-lattice relaxation rates show a slight increase with increasing ion fluence at corresponding temperatures and the area fraction of Fe 3+ at room temperature reach a maximum contribution in studied fluence range.
Hyperfine Interactions, 2016
An AlN thin film grown on sapphire substrate was implanted with 45 keV 57 Fe and 56 Fe ions at se... more An AlN thin film grown on sapphire substrate was implanted with 45 keV 57 Fe and 56 Fe ions at several energies to achieve a homogeneous concentration profile of approximately 2.6 at.%. in the AlN film. Conversion electron Mössbauer Spectroscopy data were collected after annealing the sample up to 900 • C. The spectra were fitted with three components, a single line attributed to small Fe clusters, and two quadrupole split doublets attributed to Fe substituting Al in the wurtzite AlN lattice and to Fe located in implantation induced lattice damage. The damage component shows significant decrease on annealing up to 900 • C, accompanied by corresponding increases in the singlet component and the substitutional Fe.
CEMS Study of 57Fe Implanted in Diamond
Hyperfine Interactions (C), 2002
Conversion electron Mossbauer (CEMS) measurements have been made on a diamond sample implanted wi... more Conversion electron Mossbauer (CEMS) measurements have been made on a diamond sample implanted with 70 keV 57Fe to a dose of 5 × 1014 cm−2. CEMS spectra were collected in the as-implanted state and after annealing the diamond up to 1470 K. The lower temperature spectra were consistently fitted with three symmetric doublets. With annealing the areal fractions of two of the doublets increased to 44% and 48 %, respectively, while that of the third doublet decreased to be replaced by a single line component with isomer shift δ = 0.0 mm/s. Comparison of the observed isomer shifts with recent in-beam Mossbauer measurements and theoretical calculations allow us to attribute the singlet to interstitial Fe and one of the doublets to Fe close to perturbed substitutional sites.
Physics Procedia, 2015
A 460 nm thick amorphous SiO 2 layer, formed on a Si (100) surface by air-annealing the Si substr... more A 460 nm thick amorphous SiO 2 layer, formed on a Si (100) surface by air-annealing the Si substrate at 1100 o C for 24 h, was implanted with 57 Fe to a fluence of 1 x 10 16 /cm 2 at room temperature and annealed at temperatures up to 1000 o C. The implanted and annealed samples were studied by conversion electron Mössbauer spectroscopy (CEMS) and magnetization measurements. The CEMS spectra up to an annealing temperature of 600 o C showed the presence of a singlet due to dispersed Fe ions and paramagnetic doublets with hyperfine parameters characteristic of Fe 2+ and Fe 3+. The spectrum after the 1000 o C annealing was dominated (> 80%) by ferromagnetic sextets, the main components of which were sextets with a hyperfine field of 320(20) kOe and 264(20) kOe, showing the formation of Fe 0 clusters, in agreement with previous observations. Magnetization measurements (m(H)) on the sample after the 1000 o C annealing showed a small hysteresis at 4 K and saturation magnetization with zero hysteresis at room temperature, reached with application of small external field. The CEMS measurement on this sample was repeated after storing the sample under ambient conditions for a period of 6 months. The spectrum showed complete disappearance of the ferromagnetic sextets and the presence only of paramagnetic doublets due to Fe 2+. Evidently progressive oxidation of the Fe clusters had occurred. Magnetization results confirm the paramagnetic transformation of the Fe clusters.
Journal of Magnetism and Magnetic Materials, 2016
The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe... more The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe ions in GaN and AlN were investigated by emission Mössbauer spectroscopy following the implantation of radioactive 57 Mn + ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV γ-rays from the 57 Fe Mössbauer state (populated from the 57 Mn β − decay) reveal that the majority of the Fe ions are in the 2+ valence state nearly substituting the Ga and Al cations, and/or associated with vacancy type defects. Emission Mössbauer spectroscopy experiments conducted over a temperature range of 100-800 K show the presence of magnetically-split sextets in the "wings" of the spectra for both materials. The temperature dependence of the sextets relate these spectral features to paramagnetic Fe 3+ with rather slow spin-lattice relaxation rates which
Exotic Nuclei, 2014
We give an overview on the historical development and current program for lattice location studie... more We give an overview on the historical development and current program for lattice location studies at CERN's ISOLDE facility, where the EC-SLI (Emission Channeling with Short-Lived Isotopes) collaboration maintains several setups for this type of experiments. We illustrate that the three most decisive factors for the success of the technique are access to facilities producing radioactive isotopes, position-sensitive detectors for the emitted decay particles, and reliable simulation codes which allow for quantitative analysis.
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Papers by Krish Bharuth-Ram
crystalline boron nanorods (BNRs), boron nanowires (BNWs), and bamboo-like
boron nanotubes (BBNTs) from bulk boron (BKB). A q-switched Nd: YAG laser
operating at the first and second harmonic wavelengths with 1064 and 532nm is
used to ablate a solid composite boron target doped with 1% Ni and 1% Co in a
tube furnace in flowing argon gas. Boron nanostructures in the form of BNRs,
BNWs, and BBNTs are condensed from the hot laser-induced plasma plume at
furnace temperatures of 800, 900, and 1000°C. The morphology and the chemical
and optical nature of the nanostructures are identified from X-ray diffraction,
electron microscopy, energy-dispersive X-ray spectroscopy, Raman, UV–vis, and
photoluminescence (PL) spectroscopies. The results confirm the crystallinity and
phase purity of the boron-nanomaterials and that they are preferentially grown in
the c-axis direction of α-boron. The as-synthesized BNRs, BNWs, and BBNTs are
observed to have lengths of 0.2–1.5μm and widths between 10 and 100nm, and
show respective PL resonance emission peaks at 330, 331, and 333nm, and the
electrical conductivities of 312, 313, and 324 S cm1 at room temperature which
are higher than the electrical conductivity of BKB.