NanoTech LLC, SIO2 NAN-OTECH LLC COLLABORATION-Blood percolation into implanted glucose sensors f... more NanoTech LLC, SIO2 NAN-OTECH LLC COLLABORATION-Blood percolation into implanted glucose sensors for diabetics limits sensor lifetime to 3-7 days. Na + mobile ions from blood permanently damage Si-based devices. Ion Beam Analysis (IBA) can detect Na in sensors. However, due to the low atomic number of Na (Z=11) and low mass ratio of Na to Si, Na that has percolated into implanted sensors is difficult to detect via standard 2 MeV 4 He Rutherford backscattering. Nuclear resonance can increase the Na scattering cross-section. This work characterizes a ∼ 4.7 MeV resonance, annotated 23 Na(α,α) 23 Na, between 23 Na atoms and α particles. To increase precision of measurements for resonance energy, width, and factor, ion beam energy is calibrated via 3 signals: 5.486 ± 0.007 MeV emission of α particles by 241 Am, and two nuclear resonances, 4.265 ± 0.055 MeV 4 He with 12 C, and 3.038 ± 0.003 MeV 4 He with 16 O. The 23 Na(α,α) 23 Na nuclear resonance is found to have an energy of 4.696 ± 0.180 MeV and cross-section increase of 41 ± 7.0%. Increase of Na detection in IBA via the studied resonance is statistically significant. Future research can determine if the cross-section increase is sufficient for Na detection in glucose sensors.
Several 1 μm thick, nearly lattice-matched InAsBi layers grown on GaSb are examined using Rutherf... more Several 1 μm thick, nearly lattice-matched InAsBi layers grown on GaSb are examined using Rutherford backscattering spectrometry and X-ray diffraction. Random Rutherford backscattering measurements indicate that the average Bi mole fraction ranges from 0.0503 to 0.0645 for the sample set, and ion-channeling measurements indicate that the Bi atoms are substitutional. The X-ray diffraction measurements show a diffraction sideband near the main (004) diffraction peak, indicating that the Bi mole fraction is not laterally uniform in the layer. The average out-of-plane tetragonal distortion is determined by modeling the main and sideband diffraction peaks, from which the average unstrained lattice constant of each sample is determined. By comparing the Bi mole fraction measured by random Rutherford backscattering with the InAsBi lattice constant for the sample set, the lattice constant of zinc blende InBi is determined to be 6.6107 Å.
Accurate analysis of microliter blood samples can improve patient care during medical testing and... more Accurate analysis of microliter blood samples can improve patient care during medical testing and forensics. Patients can suffer from anemia due to the larger volume required for blood tests, 7 milliliters per vial. Attempts at analysis of nanoliter blood samples by Theranos have systematic errors > 10%, higher than medically acceptable thresholds. Our research aims to analyze composition of microliters of blood. This research investigates accuracy of analyzing blood via HemaDrop™, a patented technique to create a Homogenous Thin Solid Film (HTSF) on super-hydrophilic and hyper-hydrophilic surfaces with 5 microliter droplets of blood. To investigate HemaDrop™’s accuracy, Ion Beam Analysis (IBA) is conducted on dried blood spots (DBS) and HTSFs from congealed blood drops on HemaDrop™-treated samples. HTSFs are observed via optical microscopy to compare uniformity, precipitation, and phase separation. DBSs and HTSFs are compared via optical microscopy for canine blood and human blo...
The growth of PbTi03 films by a metalorganic chemical-vapor-deposition technique has resulted in ... more The growth of PbTi03 films by a metalorganic chemical-vapor-deposition technique has resulted in three-dimensionally epitaxial heterostructures on various single-crystal substrates. These heterostructures consist of PbTi03 films on the (001) surface of the single crystals: potassium tantalate (KTa03), strontium titanate (SrTi03), and magnesium oxide (MgO). It was found that the presence of a structural (ferroelectric) phase transition in PbTi03 leads to a "strain-accommodating" mechanism in which a domain pattern forms as the system cools through the Curie temperature and limits the extension of interfacial strain in the heterostructurethus minimizing the total energy of the heterostructure. For PbTi03/KTa03(001), the interfacial strain is accommodated by the formation of a periodic domain pattern in the overlayer. In PbTi03/Sr Ti03(001), which exhibits an excellent lattice match between respective a lattice parameters, the film exists as a single c domain. The PbTi03/MgO(001) system, having a poor lattice match for both the a and c axes, appears to find the energy minimum by locking into domains of two-dimensional superlattices with the greatest atomic coincidences. It is found that the nature of the domain pattern depends very strongly on both the film thickness and measuring temperature. A theoretical model of the domain-pattern formation has been developed by using linear-elasticity theory and a Landau-Ginzburg-Devonshire-type phenomenological theory for the substrate and the overlayer, respectively. The theoretical predictions and the experimental measurements were in good agreement in both the thickness and temperature dependence of the relative domain population and the spontaneous strains.
ABSTRACTPercolation of blood and of interstitial fluids into implantable continuous glucose senso... more ABSTRACTPercolation of blood and of interstitial fluids into implantable continuous glucose sensors (CGS) for diabetics presently limits sensor lifetime between 3 and 7 days. Na+mobile ions in body fluids damage Si-based CGS sensors electronics. The direct detection of Na percolation is investigated by Ion Beam Analysis (IBA) and Proton Induced X-ray Emission (PIXE) in previously used CGS. Based on these results, a new technology called HemaDropTMis then tested to prepare small volume (5-10 µL) of blood for IBA. A species’s detectability by IBA scales with the square of the ratio of element’s atomic numberZto that of the substrate. Because Na has a low atomic number (Z=11), Si signals from sensor substrates can prevent Na detection in Si by 2 mega electron volt (MeV) IBA.Using 4.7 MeV23Na (α, α)23Na nuclear resonance (NR) can increase the23Na scattering cross section and thus its detectability in Si. The NR energy, width, and resonance factor, is calibrated via two well-known alpha ...
The water affinity of Si-based surfaces is quantified by contact angle measurement and surface fr... more The water affinity of Si-based surfaces is quantified by contact angle measurement and surface free energy to explain hydrophobic or hydrophilic behavior of silicone, silicates, and silicon surfaces. Surface defects such as dangling bonds, surface free energy including Lewis acid-base and Lifshitz-van der Waals components are discussed. Water nucleation and condensation is further explained by surface topography. Tapping mode atomic force microscopy (TMAFM) provides statistical analysis of the topography of these Si-based surfaces. The correlation of the above two characteristics describes the behavior of water condensation at Si-based surfaces. Surface root mean square roughness increasing from several Å to several nm is found to provide nucleation sites that expedite water condensation visibly for silica and silicone. Hydrophilic surfaces have a condensation pattern that forms puddles of water while hydrophobic surfaces form water beads. Polymer adsorption on these surfaces alters the water affinity as well as the surface topography, and therefore controls condensation on Si-based surfaces including silicone intraocular lens (IOL). The polymer film is characterized by Rutherford backscattering spectrometry (RBS) in conjunction with 4.265 MeV 12 C(,) 12 C, 3.045 MeV 16 O(,) 16 O nuclear resonance scattering (NRS), and 2.8 MeV elastic recoil detection (ERD) of hydrogen for high resolution composition and areal density measurements. The areal density of hydroxypropyl methylcellulose (HPMC) film ranges from 10 18 atom/cm 2 to 10 19 atom/cm 2 gives the silica or silicone surface a roughness of several Å and a wavelength of 0.16 ± 0.02 m, and prevents fogging by forming a complete wetting layer during water condensation.
The origin of strain-induced, modulated domain structures observed in epitaxial ferroelectric lea... more The origin of strain-induced, modulated domain structures observed in epitaxial ferroelectric lead titanate thin films is discussed using a phenomenological total-energy calculation. Linear elasticity is used to account for the substrate contribution while a free-energy functional of the Landau-Ginzburg-Devonshire type is used to calculate the domain-wall and the polarization contributions from the film. Good agreement between the predictions of this model and the experimental results is found for thickness-dependent properties such as the relative domain population and spontaneous strain.
Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resoluti... more Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resolution depth profiles in polymer blend thin films and is now regarded as a key probe of surface and interfacial segregation in these systems. Segregation phenomena strongly impact blend properties such as adhesion, friction and weatherability. The strengths and limitations of the SIMS polymer profiling technique are
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1999
By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy “seed” species in a l... more By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy “seed” species in a light diluent gas can be aerodynamically accelerated to suprathermal translational energies. Such beams are intense, directional, easily tuneable in energy, and narrowly distributed in energy. They thereby offer the means of selectively promoting activated gas-surface reactions. We report the use of 10% NH3 in He seeded beams to grow GaN and AlN epitaxially on 6H–SiC(0001) and to grow GaN on AlN buffer layers deposited on SiC(0001). The III–N films were grown under a variety of incident energies and angles of the NH3 beam, with the III metal species supplied from an effusive evaporator source. Film thickness and morphology were characterized ex situ with Rutherford backscattering spectroscopy, Auger spectroscopy, transmission electron microscopy, and atomic force microscopy. Of particular relevance to the III–N growth are the following results: (1) Selected energy epitaxial growth was obs...
Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser de... more Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser deposition and investigated with a number of analytical techniques, including electrical and electro-optical measurements. For applications in longitudinal electro-optic modulators, a transparent electrode is required between substrate and electro-optic layers. Suitable electrode materials, which at the same time permit epitaxial growth of KTN, were identified and prepared. The resulting layered samples were not only of good epitaxial and optical quality, but also exhibited the expected maximum of the longitudinal electro-optic effect at temperatures between the phase transitions from cubic to tetragonal and from tetragonal to orthorhombic. However, the maximum achievable electro-optic phase shift was found to be limited to roughly τ/100 for KTN films in the thickness range around 1 μm. Therefore, much thicker films are probably necessary for most practical applications, which requires sig...
The channeling characteristics of helium ions in the polycrystalline semimetal graphite have been... more The channeling characteristics of helium ions in the polycrystalline semimetal graphite have been studied using Rutherford Backscattering Spectrometry in the 1.2–2.4 MeV energy range. Axial channeling is investigated in the geometry where the ion beam is parallel to the highly preferred c-axis direction of a sample of highly-oriented pyrolytic graphite (HOPG). Assuming a Gaussian distribution of crystallite orientations and measuring the energy and angular dependencies of the backscattering yield, it was possible to extract the minimum yield and the critical angle for channeling in single-crystal graphite, and the standard deviation for the spread in c-axis crystallite orientations. An unusual increase of the measured angular width for channeling with depth was observed, and is attributed to the polycrystalline nature of HOPG.
Group II-VI compound semiconductors such as CdTe can be grown epitaxially on III-V materials such... more Group II-VI compound semiconductors such as CdTe can be grown epitaxially on III-V materials such as GaAs. These films possess better physical properties than their bulk-grown counterparts. This work explores the (111) CdTe/(111) GaAs system by means of MeV ion channeling. Good epitaxy is found (backscatter minimum yields of 15%) for a thickness greater than 1000 Å, which is remarkable considering the 14% lattice mismatch between film and substrate. A narrowing of the Cd angular scan suggests Cd atom displacement. A model based on Te vacancies is presented to describe our data.
The metalorganic chemical vapor deposition technique has been successfully applied to the growth ... more The metalorganic chemical vapor deposition technique has been successfully applied to the growth of epitaxial platinum thin films on (100) surfaces of single-crystal potassium tantalate (KTaO3) and strontium titanate (SrTiO3). Platinum thin films grown on KTaO3 (100) at a rate of 70 nm/h showed strong Rutherford backscattering spectroscopy (RBS)/channeling effects with a χmin of 4%. In-plane φ and θ-2θ scan x-ray diffraction analysis demonstrated the three-dimensional epitaxial alignment of the platinum film with the KTaO3 substrate. Transmission electron micrographs viewed in cross section provided additional information regarding the nature of the epitaxial Pt-KTaO3 interface. The room-temperature resistivity of a 60-nm-thick Pt film on KTaO3 (100) was 12.0 μΩ cm. X-ray diffraction and pole-figure analysis showed that in the case of Pt films deposited on either fused quartz or Si (100) surfaces, the resulting films were polycrystalline and were fully textured with <111≳ orienta...
The laser deposition technique has developed into a versatile method for depositing films of the ... more The laser deposition technique has developed into a versatile method for depositing films of the YBaâCuâO/sub x/ material. A brief description of the method and important materials characteristics, such as composition, surface smoothness, crystalline structure, and interactions with substrates, are described. Tc over 93K, Jc in the 10ⶠA/cm² range at 77K, tolerance to high magnetic fields, low temperature deposition (near 650°C) as-deposited superconducting films, epitaxial growth, and very smooth surfaces have been demonstrated. Relevance to practical application is briefly discussed.
Amorphous silicon nitride or silicon carbonitride thin films were deposited on (100) silicon subs... more Amorphous silicon nitride or silicon carbonitride thin films were deposited on (100) silicon substrates by the pyrolysis of ethylsilazane, [CH2CH3SiHNH],, in ammonia or hydrogen in the temperature range 873-1073 K at 0.1 MPa. Studies by means of Auger electron spectroscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis indicated the removal of carbon species present in the precursor to yield silicon nitride when the deposition was carried out in ammonia. Carbon-related bonds were, however, partiaUy ruptured in the precursor when hydrogen was used, resulting in the formation of silicon carbonitride. The hydrogen content was determined by elastic recoil detection to decrease from 18 to 10 f 1 % in silicon nitride and from 21 to 8 f 1% in silicon carbonitride with increasing deposition temperature. Fourier transform infrared spectroscopy analysis showed only Si-H, bonds (n = 1,2,3) in silicon carbonitride and only N-H, bonds (n = 1,2) in silicon nitride. The refractive index increased with the deposition temperature from 1.86 to 2.10 for silicon nitride and from 1.81 to 2.09 for silicon carbonitride. The average deposition rate measured by ellipsometry increased with temperature from 1.9 to 49 nm/min. The apparent activation energiea calculated from the slopes of the Arrhenius plot were equal to 19 and 43 kJ/mol in the mass transport regime and to 181 and 197 kJ/mol in the kinetic regime for silicon carbonitride and silicon nitride, respectively.
NanoTech LLC, SIO2 NAN-OTECH LLC COLLABORATION-Blood percolation into implanted glucose sensors f... more NanoTech LLC, SIO2 NAN-OTECH LLC COLLABORATION-Blood percolation into implanted glucose sensors for diabetics limits sensor lifetime to 3-7 days. Na + mobile ions from blood permanently damage Si-based devices. Ion Beam Analysis (IBA) can detect Na in sensors. However, due to the low atomic number of Na (Z=11) and low mass ratio of Na to Si, Na that has percolated into implanted sensors is difficult to detect via standard 2 MeV 4 He Rutherford backscattering. Nuclear resonance can increase the Na scattering cross-section. This work characterizes a ∼ 4.7 MeV resonance, annotated 23 Na(α,α) 23 Na, between 23 Na atoms and α particles. To increase precision of measurements for resonance energy, width, and factor, ion beam energy is calibrated via 3 signals: 5.486 ± 0.007 MeV emission of α particles by 241 Am, and two nuclear resonances, 4.265 ± 0.055 MeV 4 He with 12 C, and 3.038 ± 0.003 MeV 4 He with 16 O. The 23 Na(α,α) 23 Na nuclear resonance is found to have an energy of 4.696 ± 0.180 MeV and cross-section increase of 41 ± 7.0%. Increase of Na detection in IBA via the studied resonance is statistically significant. Future research can determine if the cross-section increase is sufficient for Na detection in glucose sensors.
Several 1 μm thick, nearly lattice-matched InAsBi layers grown on GaSb are examined using Rutherf... more Several 1 μm thick, nearly lattice-matched InAsBi layers grown on GaSb are examined using Rutherford backscattering spectrometry and X-ray diffraction. Random Rutherford backscattering measurements indicate that the average Bi mole fraction ranges from 0.0503 to 0.0645 for the sample set, and ion-channeling measurements indicate that the Bi atoms are substitutional. The X-ray diffraction measurements show a diffraction sideband near the main (004) diffraction peak, indicating that the Bi mole fraction is not laterally uniform in the layer. The average out-of-plane tetragonal distortion is determined by modeling the main and sideband diffraction peaks, from which the average unstrained lattice constant of each sample is determined. By comparing the Bi mole fraction measured by random Rutherford backscattering with the InAsBi lattice constant for the sample set, the lattice constant of zinc blende InBi is determined to be 6.6107 Å.
Accurate analysis of microliter blood samples can improve patient care during medical testing and... more Accurate analysis of microliter blood samples can improve patient care during medical testing and forensics. Patients can suffer from anemia due to the larger volume required for blood tests, 7 milliliters per vial. Attempts at analysis of nanoliter blood samples by Theranos have systematic errors > 10%, higher than medically acceptable thresholds. Our research aims to analyze composition of microliters of blood. This research investigates accuracy of analyzing blood via HemaDrop™, a patented technique to create a Homogenous Thin Solid Film (HTSF) on super-hydrophilic and hyper-hydrophilic surfaces with 5 microliter droplets of blood. To investigate HemaDrop™’s accuracy, Ion Beam Analysis (IBA) is conducted on dried blood spots (DBS) and HTSFs from congealed blood drops on HemaDrop™-treated samples. HTSFs are observed via optical microscopy to compare uniformity, precipitation, and phase separation. DBSs and HTSFs are compared via optical microscopy for canine blood and human blo...
The growth of PbTi03 films by a metalorganic chemical-vapor-deposition technique has resulted in ... more The growth of PbTi03 films by a metalorganic chemical-vapor-deposition technique has resulted in three-dimensionally epitaxial heterostructures on various single-crystal substrates. These heterostructures consist of PbTi03 films on the (001) surface of the single crystals: potassium tantalate (KTa03), strontium titanate (SrTi03), and magnesium oxide (MgO). It was found that the presence of a structural (ferroelectric) phase transition in PbTi03 leads to a "strain-accommodating" mechanism in which a domain pattern forms as the system cools through the Curie temperature and limits the extension of interfacial strain in the heterostructurethus minimizing the total energy of the heterostructure. For PbTi03/KTa03(001), the interfacial strain is accommodated by the formation of a periodic domain pattern in the overlayer. In PbTi03/Sr Ti03(001), which exhibits an excellent lattice match between respective a lattice parameters, the film exists as a single c domain. The PbTi03/MgO(001) system, having a poor lattice match for both the a and c axes, appears to find the energy minimum by locking into domains of two-dimensional superlattices with the greatest atomic coincidences. It is found that the nature of the domain pattern depends very strongly on both the film thickness and measuring temperature. A theoretical model of the domain-pattern formation has been developed by using linear-elasticity theory and a Landau-Ginzburg-Devonshire-type phenomenological theory for the substrate and the overlayer, respectively. The theoretical predictions and the experimental measurements were in good agreement in both the thickness and temperature dependence of the relative domain population and the spontaneous strains.
ABSTRACTPercolation of blood and of interstitial fluids into implantable continuous glucose senso... more ABSTRACTPercolation of blood and of interstitial fluids into implantable continuous glucose sensors (CGS) for diabetics presently limits sensor lifetime between 3 and 7 days. Na+mobile ions in body fluids damage Si-based CGS sensors electronics. The direct detection of Na percolation is investigated by Ion Beam Analysis (IBA) and Proton Induced X-ray Emission (PIXE) in previously used CGS. Based on these results, a new technology called HemaDropTMis then tested to prepare small volume (5-10 µL) of blood for IBA. A species’s detectability by IBA scales with the square of the ratio of element’s atomic numberZto that of the substrate. Because Na has a low atomic number (Z=11), Si signals from sensor substrates can prevent Na detection in Si by 2 mega electron volt (MeV) IBA.Using 4.7 MeV23Na (α, α)23Na nuclear resonance (NR) can increase the23Na scattering cross section and thus its detectability in Si. The NR energy, width, and resonance factor, is calibrated via two well-known alpha ...
The water affinity of Si-based surfaces is quantified by contact angle measurement and surface fr... more The water affinity of Si-based surfaces is quantified by contact angle measurement and surface free energy to explain hydrophobic or hydrophilic behavior of silicone, silicates, and silicon surfaces. Surface defects such as dangling bonds, surface free energy including Lewis acid-base and Lifshitz-van der Waals components are discussed. Water nucleation and condensation is further explained by surface topography. Tapping mode atomic force microscopy (TMAFM) provides statistical analysis of the topography of these Si-based surfaces. The correlation of the above two characteristics describes the behavior of water condensation at Si-based surfaces. Surface root mean square roughness increasing from several Å to several nm is found to provide nucleation sites that expedite water condensation visibly for silica and silicone. Hydrophilic surfaces have a condensation pattern that forms puddles of water while hydrophobic surfaces form water beads. Polymer adsorption on these surfaces alters the water affinity as well as the surface topography, and therefore controls condensation on Si-based surfaces including silicone intraocular lens (IOL). The polymer film is characterized by Rutherford backscattering spectrometry (RBS) in conjunction with 4.265 MeV 12 C(,) 12 C, 3.045 MeV 16 O(,) 16 O nuclear resonance scattering (NRS), and 2.8 MeV elastic recoil detection (ERD) of hydrogen for high resolution composition and areal density measurements. The areal density of hydroxypropyl methylcellulose (HPMC) film ranges from 10 18 atom/cm 2 to 10 19 atom/cm 2 gives the silica or silicone surface a roughness of several Å and a wavelength of 0.16 ± 0.02 m, and prevents fogging by forming a complete wetting layer during water condensation.
The origin of strain-induced, modulated domain structures observed in epitaxial ferroelectric lea... more The origin of strain-induced, modulated domain structures observed in epitaxial ferroelectric lead titanate thin films is discussed using a phenomenological total-energy calculation. Linear elasticity is used to account for the substrate contribution while a free-energy functional of the Landau-Ginzburg-Devonshire type is used to calculate the domain-wall and the polarization contributions from the film. Good agreement between the predictions of this model and the experimental results is found for thickness-dependent properties such as the relative domain population and spontaneous strain.
Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resoluti... more Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resolution depth profiles in polymer blend thin films and is now regarded as a key probe of surface and interfacial segregation in these systems. Segregation phenomena strongly impact blend properties such as adhesion, friction and weatherability. The strengths and limitations of the SIMS polymer profiling technique are
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1999
By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy “seed” species in a l... more By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy “seed” species in a light diluent gas can be aerodynamically accelerated to suprathermal translational energies. Such beams are intense, directional, easily tuneable in energy, and narrowly distributed in energy. They thereby offer the means of selectively promoting activated gas-surface reactions. We report the use of 10% NH3 in He seeded beams to grow GaN and AlN epitaxially on 6H–SiC(0001) and to grow GaN on AlN buffer layers deposited on SiC(0001). The III–N films were grown under a variety of incident energies and angles of the NH3 beam, with the III metal species supplied from an effusive evaporator source. Film thickness and morphology were characterized ex situ with Rutherford backscattering spectroscopy, Auger spectroscopy, transmission electron microscopy, and atomic force microscopy. Of particular relevance to the III–N growth are the following results: (1) Selected energy epitaxial growth was obs...
Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser de... more Thin films of potassium tantalate niobate (KTN) were prepared by means of pulsed excimer-laser deposition and investigated with a number of analytical techniques, including electrical and electro-optical measurements. For applications in longitudinal electro-optic modulators, a transparent electrode is required between substrate and electro-optic layers. Suitable electrode materials, which at the same time permit epitaxial growth of KTN, were identified and prepared. The resulting layered samples were not only of good epitaxial and optical quality, but also exhibited the expected maximum of the longitudinal electro-optic effect at temperatures between the phase transitions from cubic to tetragonal and from tetragonal to orthorhombic. However, the maximum achievable electro-optic phase shift was found to be limited to roughly τ/100 for KTN films in the thickness range around 1 μm. Therefore, much thicker films are probably necessary for most practical applications, which requires sig...
The channeling characteristics of helium ions in the polycrystalline semimetal graphite have been... more The channeling characteristics of helium ions in the polycrystalline semimetal graphite have been studied using Rutherford Backscattering Spectrometry in the 1.2–2.4 MeV energy range. Axial channeling is investigated in the geometry where the ion beam is parallel to the highly preferred c-axis direction of a sample of highly-oriented pyrolytic graphite (HOPG). Assuming a Gaussian distribution of crystallite orientations and measuring the energy and angular dependencies of the backscattering yield, it was possible to extract the minimum yield and the critical angle for channeling in single-crystal graphite, and the standard deviation for the spread in c-axis crystallite orientations. An unusual increase of the measured angular width for channeling with depth was observed, and is attributed to the polycrystalline nature of HOPG.
Group II-VI compound semiconductors such as CdTe can be grown epitaxially on III-V materials such... more Group II-VI compound semiconductors such as CdTe can be grown epitaxially on III-V materials such as GaAs. These films possess better physical properties than their bulk-grown counterparts. This work explores the (111) CdTe/(111) GaAs system by means of MeV ion channeling. Good epitaxy is found (backscatter minimum yields of 15%) for a thickness greater than 1000 Å, which is remarkable considering the 14% lattice mismatch between film and substrate. A narrowing of the Cd angular scan suggests Cd atom displacement. A model based on Te vacancies is presented to describe our data.
The metalorganic chemical vapor deposition technique has been successfully applied to the growth ... more The metalorganic chemical vapor deposition technique has been successfully applied to the growth of epitaxial platinum thin films on (100) surfaces of single-crystal potassium tantalate (KTaO3) and strontium titanate (SrTiO3). Platinum thin films grown on KTaO3 (100) at a rate of 70 nm/h showed strong Rutherford backscattering spectroscopy (RBS)/channeling effects with a χmin of 4%. In-plane φ and θ-2θ scan x-ray diffraction analysis demonstrated the three-dimensional epitaxial alignment of the platinum film with the KTaO3 substrate. Transmission electron micrographs viewed in cross section provided additional information regarding the nature of the epitaxial Pt-KTaO3 interface. The room-temperature resistivity of a 60-nm-thick Pt film on KTaO3 (100) was 12.0 μΩ cm. X-ray diffraction and pole-figure analysis showed that in the case of Pt films deposited on either fused quartz or Si (100) surfaces, the resulting films were polycrystalline and were fully textured with <111≳ orienta...
The laser deposition technique has developed into a versatile method for depositing films of the ... more The laser deposition technique has developed into a versatile method for depositing films of the YBaâCuâO/sub x/ material. A brief description of the method and important materials characteristics, such as composition, surface smoothness, crystalline structure, and interactions with substrates, are described. Tc over 93K, Jc in the 10ⶠA/cm² range at 77K, tolerance to high magnetic fields, low temperature deposition (near 650°C) as-deposited superconducting films, epitaxial growth, and very smooth surfaces have been demonstrated. Relevance to practical application is briefly discussed.
Amorphous silicon nitride or silicon carbonitride thin films were deposited on (100) silicon subs... more Amorphous silicon nitride or silicon carbonitride thin films were deposited on (100) silicon substrates by the pyrolysis of ethylsilazane, [CH2CH3SiHNH],, in ammonia or hydrogen in the temperature range 873-1073 K at 0.1 MPa. Studies by means of Auger electron spectroscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis indicated the removal of carbon species present in the precursor to yield silicon nitride when the deposition was carried out in ammonia. Carbon-related bonds were, however, partiaUy ruptured in the precursor when hydrogen was used, resulting in the formation of silicon carbonitride. The hydrogen content was determined by elastic recoil detection to decrease from 18 to 10 f 1 % in silicon nitride and from 21 to 8 f 1% in silicon carbonitride with increasing deposition temperature. Fourier transform infrared spectroscopy analysis showed only Si-H, bonds (n = 1,2,3) in silicon carbonitride and only N-H, bonds (n = 1,2) in silicon nitride. The refractive index increased with the deposition temperature from 1.86 to 2.10 for silicon nitride and from 1.81 to 2.09 for silicon carbonitride. The average deposition rate measured by ellipsometry increased with temperature from 1.9 to 49 nm/min. The apparent activation energiea calculated from the slopes of the Arrhenius plot were equal to 19 and 43 kJ/mol in the mass transport regime and to 181 and 197 kJ/mol in the kinetic regime for silicon carbonitride and silicon nitride, respectively.
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Papers by B.J. Wilkens