Search

Serendipity plays a major role in scientific progress. Often unintentionally, things lead to consequences which pave road for further developments. Here, we report high thermoelectric figure of merit of a gram-scale synthesized, compositionally graded nanocomposite made by unintentional graphite inclusion in nanocrystalline 2%Al doped ZnO (AZO) hot pressed sample. This facile inclusion has led to significantly high thermoelectric figure of merit of this Al doped zinc oxide system. The hybrid compositionally graded samples obtained using hot uniaxial pressing contained nanosized AZO particles with graphitic carbon inclusions together having density of 4.3 gm/cc i.e. 80% of theoretical density of ZnO. Al has been found to substitute at Zn site in the ZnO lattice as seen from XRD. This led to a giant electrical conductivity of about 600 S/cm. Moreover, the thermopower values are about 50 µV/k which is rather low for pure oxides. Nonetheless, it also showed significantly low thermal conductivity (< 7 W /m.K). Together, all these parameters could give the figure of merit as 0.09 at 1000 K, which is at least two orders of magnitude higher than the values expected of polycrystalline zinc oxides reported in the literature.In the original version of the article supplied to AIP Publishing, the name of Keshav Dabral was misspelled. Additionally, figure 4 did not appear clearly. An updated article, with these issues corrected, was published on 21 January 2021.

Single crystals of pure and Copper (Cu) doped (0.5, 1 and 1.5 mol%) SAP were grown by slow evaporation method at ambient temperature. XRD profile exhibited that all crystals reveals orthorhombic crystal structure. The functional groups existing in the grown crystal were studied by the FTIR analysis. The UV–Vis–NIR study proposes that the optical transmittance is increased with increase of Cu concentration and doped crystals are highly transparent in the region 300–1000 nm. The energy band gap was calculated using the transmittance spectra for all the crystals. In photoluminescence analysis, the green emission at 523 nm was observed. Concentration percentage of the Cu in the grown crystals was confirmed by inductively coupled plasma optical emission spectroscopic analysis. Second harmonic generation efficiency measurements indicate an increase of optical transmittance due to Cu dopant concentration. The thermal stability and decomposition temperature of SAP crystal were found.

Silicon dispersed beta-FeSi2 with different aluminium concentrations are synthesized using eutectoid decomposition of alpha-Fe(2)Si(5-x)A(lx) (

Hysteresis loops exhibited by the thermal properties of undoped and 0.8 at.% W-doped nanocrystalline powders of VO2 synthesized by means of the solution combustion method and compacted in pellets, are experimentally measured by photothermal radiometry. It is shown that: (i) the W doping reduces both the hysteresis loops of VO2 and its transition temperature up to 15 °C. (ii) The thermal diffusivity decreases (increases) until (after) the metallic domains become dominant in the VO2 insulating matrix, such that its variation across the metal-insulation transition is enhanced by 23.5% with W-0.8 at.% doping. By contrast, thermal conductivity (thermal effusivity) increases up to 45% (40%) as the metallic phase emerges in the VO2 structure due to the insulator-to-metal transition, and it enhances up to 11% (25%) in the insulator state when the local rutile phase is induced by the tungsten doping. (iii) The characteristic peak of the VO2 specific heat capacity is observed in both heating and cooling processes, such that the phase transition of the 0.8 at.% W-doped sample requires about 24% less thermal energy than the undoped one. (iv) The impact of the W doping on the four above-mentioned thermal properties of VO2 mainly shows up in its insulator phase, as a result of the distortion of the local lattice induced by the electrons of tungsten. W doping at 0.8 at.% thus enhances the VO2 capability to transport heat but diminishes its thermal switching efficiency.

Modified forms of Bi2Te3 system attracts immense importance in thermoelectric generation by providing a green and clean technology for converting low-grade waste heat into electrical energy. Herein, we have explored the potential of a new material graphitic carbon nitride (g-C3N4) for tuning the thermoelectric properties of Bi0·4Sb1·6Te3. The electronic and lattice transport properties of Bi0·4Sb1·6Te3 are effectively decoupled through nanostructuring, modification of carrier concentration through defect engineering and embedding g-C3N4 nanostructures in the bulk material which leads to the synergetic optimization of power factor and suppressed thermal conductivity due to all-scale hierarchical architecture. All the Bi0·4Sb1·6Te3/g-C3N4 nanocomposites exhibit reduction in thermal conductivity and we obtained an ultra-low thermal conductivity of 0.33 W/mK for Bi0·4Sb1·6Te3 nanocomposite with 1% g-C3N4. The simultaneous optimization of electrical and lattice transport properties leads to a marked improvement in figure of merit from 0.295 for pristine Bi0·4Sb1·6Te3 to a peak value of 1.09 for Bi0·4Sb1·6Te3 with 0.50% g-C3N4.

Biosynthesized gold nanoparticles using gymnemic acid (GA), a secondary metabolite of Gymnema sylvestre, are studied. The gymnemic acid reduced gold nanoparticles (GA–AuNPs) were primarily confirmed from the colour change and UV absorption. The reducing potential of GA was computed and free GA was quantified after the biosynthesis of GA–AuNPs using HPLC. The size, charge, shape, crystalline nature and functional groups of GA–AuNPs were studied by TEM, DLS, XRD and FT-IR analysis respectively. The stability of GA–AuNPs in various physiological buffers and pH was examined. The cytotoxicity of GA–AuNPs and the comparative glucose utilization effect of GA and GA–AuNPs were analysed. The GA–AuNPs appeared ruby red in colour and showed UV absorption at 540 nm. The reducing efficiency of GA was found to be 98%. The complete utilization of GA (100%) after the biosynthesis of GA–AuNPs was observed in the HPLC chromatogram. The GA–AuNPs displayed a spherical morphology under TEM analysis. The DLS analysis of GA–AuNPs revealed an average size of 62.93 nm and a zeta potential of −14.9 mV. The XRD data confirmed the nature of GA–AuNPs to be face centered cubic (fcc) crystals and their stability was identified from the FT-IR spectra. The GA–AuNPs showed remarkable stability in the various media and displayed 56.67% cell viability at 1000 μM concentration in 3T3-L1 adipocytes. The adipocytes treated with GA and GA–AuNPs displayed a minimal and a dose-dependent rise in glucose uptake respectively, demonstrating enhanced bioavailability mediated glucose utilization. The study suggests that GA–AuNPs might serve as an effective plant-based oral formulation for the treatment of hyperglycemia.

Aim: Rats fed high dosage of fructose that form a well-known experimental model of the metabolic syndrome also display progressive renal disturbances. The present study evaluates the influence of l-carnitine (CA) administration on oxidant–antioxidant balance, protein damage and lipid levels in kidney of rats administered high dose of fructose. Methods: Adult male Wistar rats were divided into four groups of 10 rats each. Groups I and IV animals received starch-based control diet, while groups II and III rats were fed a high-fructose diet (60 g/100 g). Groups III and IV animals additionally received CA (300 mg/kg/day) for 60 days. The extent of lipid peroxidation, enzymatic and non-enzymatic antioxidants and lipid levels were measured after 60 days. The accumulation of nitrated and oxidatively modified proteins in kidney was also measured by immunohistochemical study with specific antibodies. Results: Fructose-fed rats exhibited increased levels of peroxidation end products, diminished antioxidant status, increased staining for the presence of 4-hydroxy-2-nonenal, 2,4-dinitrophenol and 3-nitrotyrosine protein adducts and lipid accumulation in kidney. CA administration attenuated these pathological renal alterations. Conclusions: The benefits of CA in this model suggest the therapeutic use of CA to counter the kidney changes associated with metabolic syndrome.

High fructose feeding (60 g/100 g diet) in rodents induces alterations in both glucose and lipid metabolism. The present study was aimed to evaluate whether intraperitoneal carnitine (CA), a transporter of fatty acyl-CoA into the mitochondria, could attenuate derangements in carbohydrate metabolizing enzymes and glucose overproduction in high fructose-diet fed rats. Male Wistar rats of body weight 150-160 g were divided into 4 groups of 6 rats each. Groups 1 and 4 animals received control diet while the groups 2 and 3 rats received high fructose-diet. Groups 3 and 4 animals were treated with CA (300 mg/Kg body weight/day, i.p.) for 30 days. At the end of the experimental period, levels of carnitine, glucose, insulin, lactate, pyruvate, glycerol, triglycerides and free fatty acids in plasma were determined. The activities of carbohydrate metabolizing enzymes and glycogen content in liver and muscle were assayed. Hepatocytes isolated from liver were studied for the gluconeogenic activity in the presence of substrates such as pyruvate, lactate, glycerol, fructose and alanine. Fructose-diet fed animals showed alterations in glucose metabolizing enzymes, increased circulating levels of gluconeogenic substrates and depletion of glycogen in liver and muscle. There was increased glucose output from hepatocytes of animals fed fructose-diet alone with all the gluconeogenic substrates. The abnormalities associated with fructose feeding such as increased gluconeogenesis, reduced glycogen content and other parameters were brought back to near normal levels by CA. Hepatocytes from these animals showed significant inhibition of glucose production from pyruvate (74.3%), lactate (65.4%), glycerol (69.6%), fructose (56.2%) and alanine (63.6%) as compared to CA untreated fructose-fed animals. The benefits observed could be attributed to the effect of CA on fatty acyl-CoA transport.

The intensities of the optical spectral lines emitted from a Ge(1 0 0) surface under Ar + ion bombardment are studied as a function of the ion kinetic energy (1–5 keV) and the partial pressure (5 × 10 −6 –5 × 10 −4 Torr) of either germane or silane. For germane exposures, the Ge (GeI, 265 nm and 304 nm), H Balmer beta (486 nm) and H Balmer gamma (434 nm) optical lines are observed. For silane, additional peaks due to excited neutral Si (SiI, 288 nm) and molecular SiH (A 2 Δ–X 2 Π, 414 nm) are visible. The ion kinetic energy dependence of the GeI photon yields (265 nm and 304 nm) is analyzed in terms of the electron exchange mechanism. The similarity between the measured de-excitation parameters for germane and silane pressure between 5 × 10 −6 and 5 × 10 −4 Torr implies that the de-excitation mechanism does not change significantly. For both germane and silane exposures, the intensities of excited neutral Ge, H beta and H gamma optical lines increase with either larger partial pressures or ion kinetic energy. A similar trend is found for neutral SiI and molecular SiH emission during silane exposures. In contrast, the intensity of the H Balmer alpha transition (656 nm) decreases with increasing incident ion kinetic energy at all measured partial pressures. Both trends are similar to that observed for either silane or germane exposed Si(1 0 0) surfaces under ion bombardment.

The intensities of the optical spectral lines emitted from a Si(1 0 0) surface under Ar + ion bombardment are studied as a function of the ion kinetic energy (1–5 keV) and the partial pressure of germane. In these experiments, the ion flux is held constant while either the bombardment energy or the partial pressure of germane is varied. The excited neutral Si (SiI, 288 nm), neutral Ge (GeI, 265 nm and 304 nm), H Balmer beta (486 nm) and H Balmer gamma (434 nm) optical lines are observed. With increasing germane partial pressure, a broad emission feature develops between 330 and 365 nm and is assigned to excited GeH 2 and/or GeH 3 species. The emission intensities of the excited neutral Si, neutral Ge, H β and H γ optical lines from the bombarded Si(1 0 0) surface increase with greater germane partial pressures and ion kinetic energy in a manner similar to that previously observed for silane exposures. In contrast to the monotonic increase of the above emission lines with higher germane partial pressures and greater incident kinetic energies, the H Balmer alpha (656 nm) optical line exhibits unique behavior. Paralleling the behavior observed for silane exposed surfaces, the intensity of the Balmer alpha transition decreases with increasing incident ion kinetic energy at all measured partial pressures of germane.

The intensities of the optical spectral lines emitted from a Si(100) surface under Ar+ ion bombardment are studied as a function of the ion kinetic energy (1–5keV) and the partial pressure of silane. In these experiments, the ion flux is held constant while either the bombardment energy or the partial pressure of silane is varied. The intensities of the spectral lines are normalized with respect to the intensity of the excited neutral silicon (SiI,288nm) optical line emitted from the clean Si surface. The intensities of excited neutral Si (SiI,288nm), molecular SiH (A2Δ–X2Π,414nm), H Balmer beta (486nm) and H Balmer gamma (434nm) optical lines emitted from silane exposed Si surfaces follow a similar increasing trend with respect to increasing partial pressures of silane. During continuous silane exposures, the intensity of these four lines also increases with increasing ion kinetic energy. A qualitative explanation based on the adsorption and decomposition of silane on the Si surfaces can account for this...

The adsorption and surface reactions of ICN, BrCN, and ClCN on the Si(100)−(2×1) surface are studied using ab initio quantum calculations on single- and triple-dimer silicon clusters. These cyanoge...

The adsorption and decomposition of cyanogen halides, XCN (X = Br, Cl), on Si(100) is investigated utilizing X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For submonolayer exposures, XPS indicates that the CN triple bond of XCN remains intact upon adsorption at 100 K. The UPS spectrum contains two peaks assigned to the π-electrons in the CN triple bond. The splitting indicates that some fraction of the XCN molecules adsorbs molecularly at low temperature. XPS analyses of the C 1s photoelectron peak following submonolayer exposure at low temperature suggest a greater fraction of BrCN (60%) adsorbs molecularly than ClCN (40%). XPS and UPS measurements at room temperature show that the X−CN bond breaks, while the CN bond remains intact during room-temperature adsorption on Si(100). Thus, the UPS spectrum of XCN adsorbed at room temperature on Si(100) contains a peak at 6.0 eV due to the unperturbed π electrons of the CN species. Upon annealing a CN-saturated Si(100)...

The adsorption and surface reactions of ICN on the Si(1 0 0)-(2×1) surface are studied using ab initio quantum calculations on model dimer clusters. ICN can physisorb via a dative bond through the N atom. This species can further react to form either a dissociated state through I–CN bond cleavage or a stable side-on intermediate by reacting across the dimer bond. There are two important differences between the ICN adsorption process and that of HCN. Unlike HNC, the INC dative bonded structure is not stable. Next, there is no transition state between the side-on adsorbed ICN and INC species.

The growth of Cu nanostructures on the hydrogen-terminated Si(111) surface was studied by scanning tunnelling microscopy (STM). On the hydrogen-terminated Si(111) surface, small Cu nanostructures scatter mainly on the terraces and a few structures along the steps and domain boundaries at a deposition temperature of ∼310°C: the shape of the nanostructure is round or triangular, and the face is not clear. At ∼340°C, the Cu nanostructures form preferentially at steps and domain boundaries of the substrate: the shape is triangular with truncated corners and the nanostructures have some facets. The top face has an inclination angle of ∼6° and the side face has one of ∼35°. On the top face, mono-atomic steps can be seen ∼0.8 nm apart. From these results, it is concluded that the Cu nanostructure has a {554} facet on top and a {110} facet on the side. Copyright © 2003 John Wiley & Sons, Ltd.

The adsorption of cyanogen iodide (ICN) on a silicon (1 0 0) surface is studied by X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and temperature programmed desorption (TPD) spectroscopy. After submonolayer exposures, XPS indicates that the CN triple bond of ICN remains intact upon adsorption at 100 K. The UPS spectrum for submonolayer exposures at 100 K contains two peaks assigned principally to the π electrons in the CN triple bond. The splitting is due to the interaction between the π electrons of the cyanogen and the p electrons of the iodine. These results show that a portion of ICN molecules adsorbed molecularly. Higher exposures result in multilayer molecular ICN film. TPD spectra from both the submonolayer and multilayer films formed at 100 K show a peak at 170 K due to the desorption of adsorbed molecular ICN. In contrast to the low-temperature results, the UPS spectrum of ICN adsorbed at room temperature (RT) on Si(1 0 0) contains only one peak which originates principally from the π electrons in the CN triple bond. The lack of splitting in the RT UPS spectrum is a result of IC bond dissociation upon adsorption on Si(1 0 0). At RT the IC bond breaks while the CN bond remains intact. Upon annealing the Si(1 0 0) surface to higher temperatures, the UPS and XPS spectra indicate that the CN triple bond starts to disappear at ≈470 K. Simultaneous changes in the C 1s and N 1s photoelectron peaks between 470 and 800 K are consistent with the idea that CN bond cleavage in ICN is correlated with silicon carbide and nitride formation. By 800 K, all adsorbed CN species decompose completely into silicon carbide and nitride.

X-ray Photoelectron Spectroscopy (XPS) measurements have been performed on oxygen- and argon-annealed YBa 2 Cu 3 O 7-δ (YBCO) and the results are compared with similar measurements performed on Y 2 O 3. The structural changes in oxygen- and argon-annealed YBCO are reflected in the shift of the Binding Energy (BE) peak positions for the various components existing in the YBCO lattice.

Secondary-ion mass spectrometry (SIMS) and x-ray photo-electron spectroscopy (XPS) studies have been performed on -irradiated (Bi-2212) superconductor. Results have been explained in terms of various phenomena such as changes in the oxidation states of the individual elements of the compound or radiation-induced defects, occurring due to -irradiation.

A comparative study of the secondary ion signals (In+, n = 1,2) for the N2+Ge and N2+Si ion-target combinations under varying bombardment conditions has been undertaken. Only the former reveals anomalous Ge2+ emission I 2+ I + (Ge) > 1) over a wide range of primary energy (E) and target current densities (Jp). A possible explanation has been sought. This work is actually a follow-up of our previous works carried out in search of anomalous emission of multicharged ions for various ion-target combinations.

SIMS signals of embedded primary atoms, + (Ar) and I + (Ne) generated from Si and Ge surfaces have been monitored as a function of bombarding energy ( E ) as well as target current density ( J p ). I + (Am) data supports the predominence of resonance charge transfer phenomenon above the target surface. Under Ne + bombardment, however, it is more likely that in addition to the charge transfer phenomenon, a significant fraction of secondary Ne + ions is produced in close binary encounters between NeSi and NeNe atoms within the solid by molecular orbital electron promotion - a phenomenon which is possible in the low keV region only for light ions. Our results might have some importance in the study of plasma confinement time in nuclear reactors where only light ions are used as initiating fuels.

Primary ion energy variation curves (In+ α E, where E = 3–10 keV; n=1,2) for secondary ions emitted from Si and Ge targets at different target current densities (Jp ≈ 60–400 μA/cm2) have been studied, both under inert (Ar+) and reactive ion (N2+, O2+) bombardment. It is interesting to note that while In+ increases with E under Ar+ bombardment the same parameter under the same bombardment conditions exhibits a steady fall under N2+ or O2+ bombardment, at least for E up to ∼ 5 keV. Not only this, the changes in the slopes of the above curves with Jp in the two cases are also in the opposite direction. In the former case, the increase in the slopes of the curves with Jp can be accounted for by taking into account target current density effects which are now known to occur even for Jp

Very few works till now support the direct emission phenomenon for small clusters (ions or neutrals) from an ion-bombarded surface, and moreover, all such works present only evidences but do not actually probe into the possible processes behind such emission. Our previous work on this line evaluates the experimental conditions under which the direct emission mechanism predominates over recombination phenomena. The experimental results also suggest that the concerned cluster ions are emitted “as such” (directly) from the ion-bombarded surface. The present work is actually a follow-up of the previous work, and strengthens the above concept from a different angle. Moreover, in the light of some very recent concepts, the possible processes leading to such emission are suggested. The phenomenon highlights the importance of evaporation effects from the impact zone at increased target current densities ( J P ) .

Surface analysis of bismuth‐based high‐Tc superconductors, like Bi2Sr2CaCu2O8+δ (Bi‐2212) and Bi2Sr2Ca2Cu3O10+δ (Bi‐2223) has been carried out by secondary ion mass spectrometry and x‐ray photoelectron spectroscopy techniques. The results have been compared with that of similar measurements on Bi2O3, CuO, and CaCO3 samples so as to have detailed information about the surface binding energy as well as the chemical nature of the various individual components that exist inside these high‐Tc compounds.

Acetaminophen (APAP)-induced liver damage is one of the most common problems among the population. Therefore, the study was aimed to investigate the hepatoprotective effect of celery leaves on APAP-induced toxicity in a freshwater fish, Pangasius sutchi. Fish were divided into four experimental groups of 6 fish each. Group 1 served as control. Group 2 fish were exposed to APAP (500 mg/kg) for 24 h. Groups 3 and 4 fish were exposed to APAP + celery leaf powder (CE) (500 mg/kg) and CE for 24 h, respectively. The severity of liver damage, hepatic lipid, glycogen, ions status and histological alterations was examined. The characterization of CE extract was also performed. APAP-exposed fish showed elevated levels of both circulating and tissue hepatotoxic markers (AST, ALT and ALP), reduced hepatic glycogen and lipid contents (TG and cholesterol), increased tissue lipid peroxidation markers (TBARS, LHP and PCO), altered tissue levels of enzymatic (SOD, CAT, GPx and GST) and non-enzymatic (GSH) antioxidants and cellular thiol levels (T-SH, P-SH and NP-SH), and reduced hepatic ions (Na(+), K(+) and Ca(2+)) and abnormal liver histology. The abnormalities associated with APAP exposure were reversed on treatment with CE. The TLC separation and HPLC quantification of petroleum ether/acetone extract of CE showed the peaks for highly efficient flavonoids such as rutein, quercetin and luteolin. The observed hepatoprotective effect of CE might be due to its rich flavonoids.

Secondary emission of the ion types Si n+ , Ge n+ and Al n + ( n = 1−3) from 3 to 10 keV Ar + bombarded pure polycrystalline Si, Ge and Al samples at target current densities J p (= l p /A) in the range 60–830 μA cm −2 has been studies in detail. In most cases, the l n+ αl p curves were found to correspond to our proposed semi-empirical formula given by l n+ = C n+ l p +D n+ l p 2 . ( c n + , D n + are constants for a fixed value of primary energy, E.) However, for E p > 16 μ A, a higher order enhancement effect could be persistently recorded in the case of multiply charged ions only, which appears to be very interesting, particularly because E is low. The impact of this enhancement effect is also reflected in the l n + / l + αl p curves at low values of E . Our results suggest that microscopic beam heating effects become important at increased values of J p particularly if E is low and under such conditions that thermodynamic models of secondary ion emission gain prominence.

Kinetic energy distributions of secondary ions emitted from Cs+-bombarded oxygen annealed and argon annealed YBa2Cu3O7−δ (YBCO) samples and Ar+-bombarded Y2O3 have been measured. Surface binding energy of yttrium (Y) and copper in the YBCO sample is found to be influenced by the structural changes and they are compared with that of Y in Y2O3. Difference in the secondary ion emission from the two types of YBCO samples are explained in the light of their known structures.

Target current density effects in secondary emission of positively-charged sputtered clusters from an ionbombarded polycrystalline aluminium surface have been investigated for various primary Cd + ion energies. For each cluster type, at medium target current densities (J p : 0-350 μA/cm 2 ), apart from the presence of the expected linear term in the I s + α J p curves, there is a square law term, depicting that some fraction of the preemitted neutral clusters gets ionized in vacuum above the target surface. Thus, a sum of these two terms constitutes the total cluster ion current which shows a non-linear dependence on the target current density. At higher target current densities (350 μA cm −2 -1.05 mA cm −2 ), in addition to the parabolic effect, a higher order non-linearity comes into play and the net cluster ion current I s + , measured as a function of target current density within the I p range concerned, can be expressed in terms of our previously proposed semi-empirical formula I s + = C.I p + D.I p 2 + F.I p n , which was earlier found to be applicable in case of single and double charged secondary monomers

Secondary emission of the ion types M n q + ( M = Si or Al ; q = 1, 2; n = 1–3) from 3–10 keV Ar + bombarded polycrystalline Si and Al samples at target current densities ( J p ) in the range of 60–800 μ A cm 2 has been studied in detail. For each projectile, the yield ratio of the cluster ions with respect to the singly-charged monomers ( I n + I 1 + ) is observed to be steady only for primary energies ( E ) > 9 keV. Below this energy, the ratio rapidly increases in more or less an exponential manner with I p , the effect being most prominent at the lowest E value. This increase in yield ratio with target current density appears to be rather inconsistent with the recombination model, but can be, to some extent, explained within the framework of the direct emission model. Briefly speaking, our results, at least at high J p and low E values are in apparent contradiction to the standing notion that emission of small clusters is best understood within the framework of the recombination model proposed by Konnen.

Positive secondary ion signals of the type Si n O + m ( n = 1–3, m = 1, 2) from a polycrystalline Si target under O + 2 bombardment in high vacuum at primary energies in the range 3–10 keV have been monitored as a function of target current density J p ( I p / A , where I p is the target current and A the spot area). Most of the secondary ion clusters (but not the monomers) show pronounced chemical enhancement effects with an increase in I p . Moreover, the intensity ratios of the higher oxygen content clusters, e.g. SiO + /Si + or SiO + /Si 2 O + , also showed a marked increase under the same conditions. Our results suggest that reactive primary atoms are gradually accumulated at the target surface under energetic ion bombardment at increased target current densities. The phenomenon stands rather in contradiction to the theoretical concepts where the surface stoichiometry is not expected to change with target current density once steady state is attained. Our observation also gives an insight into the cluster emission process at increased target current densities. It appears that our current ideas regarding the emission of small clusters need to be modified, at least in the high target current density regime.

The superconducting compound YBa2Cu3O7−x (YBCO) and oxides of copper (CuO and mixture of CuO and Cu2O) have been examined by secondary‐ion‐mass spectrometry (SIMS). The results support the fact that two kinds of copper (from the consideration of bonding and valence state) exist in YBCO—one in the basal planes of charge reservoir layers and the other in the conduction layers. The bonding of Cu‐O in the CuO2 conduction layer unit is similar to that in CuO. No Cu+++ secondary ions could be detected in the SIMS spectrum, in agreement with electron spectroscopy for chemical analysis, extended x‐ray‐absorption fine structure, and electron probe microanalysis measurements reported earlier. A plausible explanation has been given for this.

Secondary emission of singly and multiply charged positive atomic ions (Isn+) from 3– keV Ar+ -bombarded Si and Ge targets at target current densities (Jp) in the range 0–820 μA cm−2 has been studied in detail, both as functions of primary ion energy (E) and target current density J p = I p A (A = constant ) . While I s + I s + (Si) at a fixed value of E is found to correspond to the usual experimental results (∼1%), I s 2+ I s + (Ge) is observed to be > 1, which is rather anomalous at such low bombarding energies. The Is2+vsIp curves, however, clearly indicate that, in both cases, the charge transfer process in vacuum (ionization of neutrally sputtered particles by projectile ions) plays a dominant part in the secondary ionization phenomena, especially at increased target current densities. The excessive yield for Ge2+ ions is attributed to near-resonance conditions for the charge-transfer process, that are satisfied for the Ge2+ ions only, at such low kiloelectronvolt energies. Again, a surprisingly high fraction of Ge3+ ions ( I s 3+ I s + ∼ 0.6–1.0) is also observed in the SIMS spectra. In this case, it is, however, suggested that there probably exists an excited state into which electron capture can occur with nearly exact resonance so that at the energies concerned, the near-adiabatic region is attained. Both Is3+ (Ge) vsIpandIs3+ (Ge) vsE curves support this idea.