Debabrata Ghose

Saha Institute of Nuclear Physics | SINP · Surface Physics and Materials Science Division

We report on the first time observation of endotaxial growth of size-selected nanoclusters on a patterned substrate when we fabricate highly ordered and partially embedded 3D crystalline Cu nanostructure arrays of controlled size in Si-substrates. For this purpose, we combine low energy cluster deposition on the ripple-patterned substrate with cont...

Nanoscale pattern formation on Ge (001) surface by 500 eV Ar ⁺ bombardment has been studied for a wide range of ion incidence angles at a temperature of 300° C. In the angular regime 0° to 65°, a fourfold symmetric topography forms which shows a remarkable transition into highly regular one-dimensional asymmetric pattern at grazing incidences, know...

Ion sputtering induced nanoscale pattern formation on Ge (001) surface by 500 eV Ar+ bombardment has been investigated for a wide range of ion incidence angles at temperature of 300 deg.C. A fourfold symmetric topography forms in the angular regime 0 - 65 deg. Above 65 deg, they show a remarkable transition into highly regular one-dimensional (1D)...

The evolution of GaAs (001) surface morphology by normal incidence 1 keV Ar⁺ ion sputtering at high temperature has been investigated for different temperature and ion fluence. An anisotropic surface modulation is observed above the substrate recrystallization temperature ∼300°C. With increase of sputtering time, they evolve into highly ordered and...

The effect of low energy irradiation, where the sputtering is imperceptible, has not been deeply studied in the pattern formation. In this work, we want to address this question by analyzing the nanoscale topography formation on a Si surface, which is irradiated at room temperature by Ar þ ions near the displacement threshold energy, for incidence...

The nanoscale pattern formation on Ge(100) surfaces is studied by exposure of uniform Ar⁺ ion beam of energy 500 eV for ion incidence angle 0°–85° at room temperature. Anisotropic ripple nanopatterns with wave-vector along parallel and perpendicular to the ion beam projection are found to evolve at 75° and 85° respectively for fixed ion fluence 1 ×...

Nanoarchitecture by atomic manipulation is considered to be one of the emerging trends in advanced functional materials. It has a gamut of applications to offer in nanoelectronics, chemical sensing, and nanobiological science. In particular, highly ordered one-dimensional semiconductor nanostructures fabricated by self-organization methods are in h...

We have carried out an investigation on nanostructure evolution of GaAs(100) surface due to normal incidence of threshold energy ion irradiation at different elevated temperatures. Well-ordered ripple nanopatterns are observed above 350°C near to surface recrystallization temperature where ripple wave-vector is oriented along 110 crystallographic d...

Self-organized pattern formation by the process of reverse epitaxial growth has been investigated on GaAs (001) surfaces during 1 keV Ar+ bombardment at target temperature of 450 degC for a wide range of incident angles. Highly ordered ripple formation driven by diffusion instability is evidenced at near normal incidence angles. Concurrent sample r...

Topography evolution of Si(100) surface due to oblique incidence low energy ion beam sputtering (IBS) is investigated. Experiments were carried out at different elevated temperatures from 20$^{\circ}$C to 450$^{\circ}$C and at each temperature, the ion fluence is systematically varied in a wide range from $\sim$ 1$\times$10$^{18}$cm$^{-2}$ to 1$\ti...

In recent years, a fast, reproducible and well-controlled way of nanopattern fabrication on material surface is a prime concern in numerous branches of modern science. Through atomic force microscopy study, here we show an investigation on tuning ability of topography formation by low energy ion beam sputtering on Si (100) surface as function of di...

Ripple formation driven by Ehrlich–Schwoebel barrier is evidenced for normal incidence 30 eV Ar ⁺ bombardment of GaAs (001) surface at elevated target temperature. The pattern follows the twofold symmetry of the bombarded crystal surface. The ridges of the ripples are found to align along the direction. The results are described by a non‐linear con...

A dense array of faceted nanostructures evolves on the Ge (001) surfaces for normal incidence hyperthermal ion bombardment at elevated temperatures. There is a narrow window of temperatures, just above the crystal annealing temperature, in which the grown pattern resembles to the checkerboard pattern of alternating mounds and pits as often observed...

Ripple formation driven by Ehrlich-Schwoebel barrier is evidenced for normal incidence 30 eV Ar+ bombardment of GaAs (001) surface at elevated target temperature. The pattern follows the symmetry of the bombarded crystal surface. The results can be described by a non-linear continuum equation based on biased diffusion of adspecies created by ion im...

We have studied scaling behavior of ripple structured mica surfaces. Clean mica (001) surface is sputtered by 500 eV Ar+ ion beam at 400 incidence angle for different time ranging from 28 minutes to 245 minutes to form ripples on it. The scaling of roughness of sputtered surface characterized by AFM is observed into two regime here; one is super ro...

The anisotropic regular patterns are often results during oblique incidence ion beam sputtering (IBS). Simultaneous substrate rotation (SR) during IBS can suppress surface roughening and removes anisotropic nature of surface pattern. Here, the evolution of Si surface morphology as result of with and without SR is studied during oblique incidence...

Nanometer-thickness SiGe alloy layers were synthesized by direct Si ion implantation in Ge (100) wafers at different fluences followed by high temperature annealing. The cross-sectional transmission electron microscopy and secondary ion mass spectrometry reveal the formation of a thin Si-rich crystalline layer in the near-surface region. The micro-...

The hydrophilic mica surface can be made hydrophobic by low energy Ar+ ion sputtering. The ion sput- tering leads to both topographical and physicochemical changes of the surface which are thought to be responsible for the water repelling behavior. The sessile drop method is used to evaluate the wetting properties of the sputtered mica surfaces. It...

We demonstrate that surface ripples with an exceptionally high degree of order can develop when germanium is bombarded with a broad beam of gold ions. In contrast, if silicon is sputtered with an Au+ beam, patches of ripples with two distinct wave vectors can emerge. These types of order can be understood if the coupling between the surface morphol...

Energetic Au ion sputtering of crystalline Ge surface at normal incidence and room temperature can produce nanodot morphology, which has been studied by atomic force microscopy. The cross-sectional transmission electron microscopy of the dot structure reveals that the implanted Au does not form solid solution with Ge, but preferentially segregates...

We have shown that at grazing incident angle the self sputtering of negative Si beam can produce perpendicular mode ripples on the Si without pre-roughening the surface. The energy of mass analyzed Si beam was 26 keV obtained from a low energy negative ion implanter. The threshold fluence for ripple formation is comparatively low for Si than for Ar...

The mechanical properties of 25 - 403 nm Au films deposited on a Si substrate were studied by nanoindentation technique. The film hardness and reduced elastic modulus were measured. The results show that for 25 nm film, hardness value extraction is difficult. For 100 nm and 266 nm film, we get composite hardness up to the film substrate interface....

Irradiation of crystalline muscovite mica samples by 500 eV Ar+ ions at different incident angles can induce significant surface morphological variations. A periodic ripple pattern of nano-dimensions forms in the angle window 47°-70°. On the other hand, tilted conical protrusions develop on the surface at grazing incidence angles around 80°. From t...

We have observed micron size pit formation on Ge surface due to bombardment of 26keV Si− ion at normal incidence in the fluence range 1×1018 and 7×1018ions/cm2. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to follow the evolution of the surface morphology. The pits are of various shapes, e.g., crescent-shaped, kidne...

Site-controlled InP/GaInP quantum dots emitting single photons in the red spectral range Appl. Phys. Lett. 100, 091109 (2012) Micromagnet structures for magnetic positioning and alignment Irradiation of crystalline muscovite mica samples by 500 eV Ar þ ions at different incident angles can induce significant surface morphological variations. A peri...

Investigations dealing with the forecasting techniques of natural calamities like cyclones, thunderstorms, floods, earthquakes and tsunamis have become an important research trend. Among these natural hazards, earthquakes and tsunamis are the most destructive, in terms of loss of life and destruction of property. The present paper deals with the te...

Helium was first observed in the sun and subsequently much later on the earth. Starting from the early days of its discovery, helium continues to be entwined with the Indian scientific scenario in more ways than one. The element thus has a special charm and significance to the currently emerging situation where it is applied to solve problems in th...

Off-normal low energy ion beam sputtering of solid surfaces often leads to morphological instabilities resulting in the spontaneous formation of ripple structures in nanometer length scales. In the case of Si surfaces at ambient temperature, ripple formation is found to take place normally at lower incident angles with the wave vector parallel to t...

Strong anomalies in the concentration of helium, radon and gamma were observed in gases at the geochemical monitoring station, Bakreswar, West Bengal, India, about two weeks before the 7.9 M earthquake at Sichuan, China. The distance between the epicenter of the earthquake and the monitoring site is about 1800 km. This long distance preseismic obse...

In this study we report the growth, morphology, structures, and composition of silver nanocluster films on Si substrates. DC Magnetron discharge is used to generate the clusters inside a liquid nitrogen cooled aggregation tube. The morphology of the films was characterised by Scanning Electron Microscopy attached with Energy Dispersive X-ray Analys...

The development of fine scale nanostructures in polycrystalline metal films by off-normal ion beam sputtering (IBS) follows similar mechanisms to those in random targets, i.e. the pattern results from the interplay of curvature-dependent-roughening and various smoothing processes. By grazing angle IBS of the deposited metal films it is possible to...

Off-normal low energy ion beam sputtering of solid surfaces often leads to morphological instabilities resulting in the spontaneous formation of ripple structures in nanometer length scales. In the case of Si surfaces at ambient temperature, ripple formation is found to take place normally at lower incident angles with the wave vector parallel to t...

In this study, morphologies of as-deposited and rapid thermal annealed films of silver nanoclusters are studied using scanning electron microscope (SEM) and atomic force microscope (AFM). Size-selected silver nanoclusters, containing 5000 atoms in a cluster, produced by the gas condensation method are deposited on Si substrate for a period of 8 min...

Thin films of silver nanoclusters deposited on Si substrates are studied using scanning electron microscopy along with energy dispersive x-ray spectrometry. The nanoclusters are produced by dc magnetron sputtering followed by gas aggregation in a dense buffer gas. The film deposition is performed in a low impact energy regime with mass (size) selec...

The effect of pre-existing random roughness on the evolution of ripple structures in O ₂⁺ sputtered thin Al films has been investigated. The results show that there is a considerable reduction in initial roughness of the film surface at the early stages of sputtering. For large scale surface structures, angle-dependent first o...

We report the investigation of morphology and composition of copper nanocluster films deposited on Si substrates. The nanoclusters are formed in an aggregation tube at room temperature and magnetron sputtering source is used to get negatively charged Cu-clusters' beam which is subsequently mass-filtered to get size-selected cluster on the substrate...

The sputter ripple formation in polycrystalline metal thin films of Al, Co, Cu, and Ag has been studied by 16.7 keV Ar ⁺ and O ₂⁺ ion bombardment as a function of angle of ion incidence. The experimental results show the existence of a critical angle of ion incidence (θ_c) beyond which the ripples of wave...

The damage growth and surface modifications in Si(1 0 0), induced by 25 keV Si_5^- cluster ions, as a function of fluence, phi, has been studied using atomic force microscopy (AFM) and channelling Rutherford backscattering spectrometry (RBS/C). RBS/C results indicate a nonlinear growth in damage from which it has been possible to get a threshold fl...

We report here the influence of initial surface roughness on the development of ion induced Si surface morphology. Surfaces of different initial roughness have been generated chemically and bombarded by 16.7 keV O ₂<sup arrange="stagger">+</sup> ions at an oblique angle. It is observed that surface roughness enhances the initial perturba...

Ion implantation is known to be an effective method for improving the surface mechanical properties of materials, such as hardness, elastic modulus, wear and corrosion resistance. In the present work, we have modified Si(1 0 0) surface by 100 keV Cr implantation at fluences 5×10 and 1×10ions/cm. The near-surface hardness and elastic modulus have be...

Sputtering by off-normal ion bombardment of solid targets frequently leads to the development of periodically modulated structures (ripples) on the eroded surface. The ripple topography provides insight about the nature of diffusion mechanisms in the topography evolution. In the present work, the wavelength and the amplitude of the ripples formed o...

The present work focuses on the incorporation of -CH3 radicals in organic SiCO(H) films with low dielectric constant (k = 2.46). The SiCO(H) films were deposited by dielectric barrier discharge plasma method using a mixture of CH4 and Ar gases at different conditions (varying the frequency and pressure). The evolution of the film microstructure was...

b Università degli studio di Trento, 38100 Povo (TN), Italy c Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar, Kolkata 700 064, India The present work focuses on the incorporation of –CH 3 radicals in organic SiCOH films with low dielectric constant k = 2.46. The SiCOH films were deposited by dielectric barrier discha...

Carbon nitride films have been deposited by dielectric barrier discharge with a CH4/N-2 gas mixture at different conditions. Fourier Transform Infrared (FTIR) spectroscopy, X-ray photo electron spectroscopy (XPS), Raman spectroscopy, Atomic force microscopy (AFM) and ellipsometry were used to systematically study chemical composition, bond structur...

Temporal variation of gaseous radon and helium concentrations emanating from thermal springs at Bakreswar (23052’30”N ; 87002’30”E), W.Bengal, India are found to be very sensitive to seismo-tectonic activity. The monitoring springs appear through the intersections of intensive faults and fissures and characterized by the presence of deep seated flu...

Anomalous fluctuations of helium concentration emanating from thermal springs have been observed on several occasions prior to major seismic events such as earthquakes. With a view to probe the scaling properties inherent to the helium time series and to explore the effect of anomalies the method of Detrended Fluctuation Analysis (DFA) has been emp...

Off-normal ion bombardment of solid targets often leads to development of periodically modulated structures on the eroded surface. For tilted incidence (θ{>=}30 deg.) of 16.7 keV Oâ{sup +} ion beam on Al thin films, quasiperiodic ripple topography has been found to develop on the sputtered surface. As predicted by Bradley-Harper theory, below a cr...

Effects of mass analyzed low energy O2+ ion implantation in Al thin films on the hardening and microstrucure have been studied by nanoindenting atomic force microscopy (AFM). The fluence range was 1×1017–1×1018 Oatoms/cm2. A maximum increase of hardness about 90% of the implanted samples is observed. Apparently there is no significant variation in...

Nanosized ripples are formed on Al thin films by oblique angle low energy O2+ ion beam sputtering. Conductive atomic force microscopy (C-AFM) shows that the ripples are composed of periodically spaced thin insulating layers on the metal substrate.

Plethora of seemingly random phenomena on the earth are governed by some complex mechanism and find themselves non-random in statistical sense. It has been established that many apparently random phenomena in nature, such as occurrence of earthquakes, fault system, function of heart and brain besides several other events have ingrained pattern that...

The dynamics of ripple topography on silicon surfaces generated by oxygen ion bombardment with increasing fluences have been investigated by atomic force microscopy (AFM). At the early stages of sputtering, periodic ripples with the wave vector parallel to ion beam direction are developed. At the late stages of sputtering, the ripple structure tend...

A 30 nm Pt thin film evaporated onto a Si wafer was sputtered by 9.7 keV oblique Ar+ bombardment at various ion fluences. The evolution of the modified sputtered films was monitored by atomic force microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The most interesting observation was the formation of mound-like structures o...

We have observed the formation of ripples in a number of thin metal films, e.g. Au, Pt, Ag, Cu and Co under Ar+ ion beam sputtering at grazing incidence. The structures are found to be quite stable under ambient conditions. The results show that the ripple formation in polycrystalline metallic films relies on the erosion-induced surface instability...

The phenomenon of Coulomb sputtering of ultra-thin Pt films due to impact of 20 keV highly charged Arq+ (q=3–8) ions has been investigated. The results show enhanced erosion of the Pt film with the increase of potential energy of the Ar projectile.

Studies of excitation processes in sputtering due to bombardment of an Mg target with saturated oxygen coverage by 3–56 keV ions of various projectiles, namely, krypton, argon, neon, helium, oxygen and nitrogen have been carried out in a low energy ion beam facility developed in the laboratory. It is found that the relative excitation probability o...

Total electron yields and the most probable electron energy have been measured for impact of Oq+ (q=1–7) ions at near-normal incidence on a clean Al(110) single-crystal target. The projectile velocities were varied in the range from 0.08 a.u. to 0.6 a.u. The contributions from potential emission (PE) and kinetic emission (KE) to the total yields ha...

Low energy ion beam sputtering of magnesium exhibits rich and intense optical spectrum containing a number of Mg(I) and Mg(II) lines. It has been found that the emission intensities of Mg(I) and Mg(II) behave differently against the backfilled oxygen pressure. No single explanation can be given for the two different oxygen dependences observed. Con...

We report in this article our present activities on the study of various aspects of surface and interface physics carried out at Surface Physics Division of Saha Institute of Nuclear Physics. These include growing of materials and their characterization using techniques available at the institute. For growing materials, we have a magnetron sputteri...

The light emission from a polycrystalline FeNi alloy by 6 keV Kr+ ion beam sputtering in presence of oxygen has been studied. Measurements of decay features in spectral lines of Fe I and Ni I indicate that there is a preferential oxidation of Fe in oxygen ambient substantiating the results obtained by other surface analytical techniques. The presen...

An inexpensive simple controller unit using readily available ICs has been designed and developed for automated and normalized data recording useful in the study of ion–solid interaction phenomena and other fields. The performance of the unit has been tested by measuring the Doppler profile of spectral lines during ion beam sputtering of a Si(100)...

Light emission from a BeCu sample under 6 keV O2+ bombardment is studied. BeI, BeII and CuI spectral lines show transient at beam-off conditions. At the base pressure of rest gas, the transients are relatively strong, especially for BeII. When the target chamber is backfilled with oxygen at high pressure, the transients become weak for BeII and CuI...

Ion bombardment of solid surfaces gives rise to a number of elastic and inelastic collision processes. The elastic energy losses experienced by the incident projectile are responsible for the displacement of target atoms and the formation of a collision cascade. The inelastic collisions also require the active participation of electrons and are the...

The optical line emission from excited Si atoms following SF+5 and Ne+ ion bombardment of a Si(100) surface was studied. Transients in the photon yield due to oxygen pressure variation have been observed. The results show evidence of nonlinear sputtering of adsorbed oxygen atoms due to the impact of polyatomic ions.

The most popular way to explain the enhancement of photon yield due to oxygen in metals is to assume the development of an oxide-like band structure with a large band gap at the metal surface. We examine the band-gap model by studying the light emission from a copper target both due to oxygen and argon ions bombardment.

The intensities of optical spectral lines from excited sputtered atoms under Kr+ ion bombardment of a Si target have been measured as a function of oxygen and nitrogen partial pressure. Si I lines are found to be quite sensitive to the presence of O2 as expected, but not to N2 up to the pressure of about 10−5 mbar. Above 10−5 mbar light intensities...

Gal spectral lines originating from the sputtering of GaAs under 6–10 keV Ar+ ion bombardment have been studied. Results of the measurements on the target position, beam current and projectile energy dependences of 4172, 4033 and 2944 Å lines are presented. It is found that the secondary photon emission yields can be well described by the model pro...

Temperature dependence of total sputtering yield of GaAs(100) was studied by mass analyzed (sup 40)Ar(sup + ) at 30 keV. Result showed that at about 240deg C sputtering yield is minimum and with further increase in target temperature, the yield becomes higher. These findings are discussed in the light of ion channeling and thermal spike effect with...

The surface topography development on a Cu sheet and a Si(111) wafer was studied after being sputtered in a Penning ionization gauge (PIG) ion source using Ar gas. In the case of Cu, a high density of conical structure was developed on the surface. The most striking feature was that the individual cones, relatively large in size, were often coated...

The surface topography of aluminium after bombardment with a mass-separated obliquely incident Ar+ beam while simultaneously supplying gold or tungsten seeds, as well as under unseeded conditions, was studied by scanning electron microscopy. The sputtered topography was characterized mainly by cones. It was noted that seeding did not necessarily al...

The angular dependence of physical sputtering yields of Ge and Ag was investigated for 30 keV Ar + and Kr + ion bombardment. It is found that Ag exhibits a weaker angular dependence, though its sputtering yield is higher than that of Ge. The results are compared to the existing theoretical and empirical formulas.

Sharp oblique cones are only formed on polished germanium surfaces by 30 keV Ar+ bombardment, in the presence of tungsten seed atoms; substantiating Wehner's hypothesis that higher melting point seed material is the crucial factor for come formation. The morphology of the cone is characterized by the formation of a sloped ridge, consistent with the...

The topography of Si surfaces after 30 keV Ar+ bombardment at oblique incidence is studied with and without seeding of high-melting-point W atoms. In both cases, the sputtered Si surfaces exhibit intense corrugated terrace morphology, the dimension of which increases with increasing ion dose. Also, a few cones characteristics for oblique ion incide...

Surface topography of a Cu (110) single crystal has been studied after sputtering with 30 keV Ar+ ions. W-impurities were simultaneously introduced intentionally during sputtering to investigate the role of impurity in the seeding of cones. The results show only etch pits in the sputtered surface, strongly faceted with a twofold rotational symmetry...

Formation of a very large exfoliation has been observed under SEM on the reverse unbombarded surface of a tungsten foil of thickness comparable to the projected range of 30 MeV alpha particles incident on the sample. Blister parameters like skin thickness, diameter or size, height of the surface layer from the base, pressure etc. are estimated usin...

Formation of a very large exfoliation has been observed under SEM on the reverse unbombarded surface of a tungsten foil of thickness comparable to the projected range of 30 MeV alpha particles incident on the sample. Blister parameters like skin thickness, diameter or size, height of the surface layer from the base, pressure etc. are estimated usin...

This chapter presents the fundamental aspects of ion-solid interactions; the ion bombarded surface modifications in the form of cones, faceting, and blistering; and the progress of the subject in recent years. In specific, fast ion bombardment modifies the topography of solid surfaces as a result of a number of different effects, the most important...

The sputtering yields of GaAs(100) bombarded at normal incidence by mass analyzed 40Ar+, 84Kr+ and 132Xe+ ions obtained from an electromagnetic isotope separator are determined in the energy range 15-35 keV. The experimental values of the sputtering yield obtained by the method of weighing the collected sputtered material are compared with the tota...

The shadow cones for 998 eV Li+--> Ag and 2 keV Na+--> Cu are calculated by classical scattering theory using Thomas-Fermi-Molière potential, universal potential of Ziegler et al. and the Born-Mayer potential. It is found that the Born-Mayer potential with the parameters calculated by Andersen and Sigmund also predicts well the shape of the shadow...

The sputtering yields of a GaAs single crystal with (100) orientation bombarded by 15-35 kev**4**0Ar** plus for normal incidence are determined. The yield values are compared with different modifications of P Sigmund's sputtering yield formula in the elastic collision region. The atomic surface binding energy of GaAs is estimated using the measured...

Topographical changes in the surfaces of GaAs (100) crystal by Ar⁺ beam sputtering at various temperatures are studied. It is found that the bombarded surface remains almost featureless in contrast to similar sputtering of metal targets where conical protrusions always appear. However, cones do appear at high temperature with simultaneou...

A cold cathode PIG discharge ion source is used for direct end extraction of negative ions. Optimal operating conditions for the production of H−, O− and O2− ions are determined with various source parameters. Production mechanisms of the negative ions in the source are discussed. The total collision cross-sections of H− in H2, O2, Ar and CO2 in th...

Angular distributions of sputtered atoms have been determined for a Ag target under bombardment with 20 and 30 keV 20Ne+, 40Ar+, 84Kr+ and 132Xe+ ions both at normal and oblique angles of incidence. At normal ion incidence the distribution is symmet with respect to the target normal, while at oblique ion incidence the distribution is asymmetric in...

The morphological evolution of cones on 30 keV 40Ar+ bombarded Ag (111) and (100) surfaces, as a function of consecutive doses from 1 × 1019 to 1.54 × 1020 ions/cm2 has been studied. The main observations are: (a) The cone density is orientation dependent, (b) Cones are not an equilibrium structure consistent with the observations of Auciello et al...

Sputtering yields of Ge bombarded by 15 to 35 keV 40Ar+, 84Kr+, and 132Xe+ ions are measured. The data are discussed on the basis of Sigmund's linear collision cascade theory taking into account the different reduced nuclear stopping cross-section functions as suggested by different authors. For Ar and Kr ions the theory with the stopping cross-sec...

Conical protrusions observed in the scanning electron microscope on surfaces of copper which have been eroded by 20.5‐keV Ar⁺ ion bombardment are studied for various doses of ions. The critical dose and the cone apex angle are determined, and the results discussed in the light of the existing theories show the importance of secondary and...