The effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotu... more The effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotube (SWNT) bundles were studied. In addition, a comparative study was made on the effects of O2, Ar and H 2 gases on the field emission properties of SWNT bundles and multiwall carbon nanotubes (MWNTs). We observed that Cs deposition decreases the turn-on field for FE by a factor of 2.1--2.9 and increases the FE current by 6 orders of magnitude. After Cs deposition, the FE current versus voltage (I-V) curves showed non-Fowler-Nordheim behavior at large currents consistent with tunneling from adsorbate states. At lower currents, the ratio of the slope of the FE I-V curves before and after Cs deposition was approximately 2.1. Exposure to N2 does not decrease the FE current, while exposure to O2 decreases the FE current. Our results show that cesiated SWNT bundles have great potential as economical and reliable vacuum electron sources. We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurred after operation in UHV. The higher operating voltages in an O2 environment caused a permanent decrease of FE current and increase in turn-on field of MWNTs. The ratios of the slopes before and after O2 exposure were approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively. SWNTs compared to MWNTs would appear to make more economical and reliable vacuum electron sources.
The structural properties of FeSi2 films grown using Reactive Deposition Epitaxy (RDE) were chara... more The structural properties of FeSi2 films grown using Reactive Deposition Epitaxy (RDE) were characterized using ultrahigh vacuum scanning tunneling microscopy, Auger spectroscopy, Raman spectroscopy and atomic force microscopy. The FeSi2 films were grown by depositing Fe on a Si (100) substrate at a temperature of 400 ^oC. The morphology of the films was investigated as a function of Fe deposition showing the development of a continuous film from an initial island distribution. The properties of the RDE grown films will be compared with those of FeSi2 films grown using molecular beam epitaxy.
We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties ... more We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties of nanostructured carbon films including single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), amorphous carbon, and polycrystalline diamond. Both unpurified and purifed SWNTs are investigated. We find that argon and hydrogen do not significantly affect the FE properties of carbon films. Oxygen temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurs after operation in UHV. An oxygen environment causes a permanent decrease of the FE current and an increase in the turn-on field of MWNTs, amorphous carbon and polycrystalline diamond films.
We report the effects of Cs deposition on the field emission (FE) properties of single-walled car... more We report the effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotube bundles. Cs deposition lowers the turn-on field for field emission by a factor of 2.1 - 2.8, and increases the field emission current by 6 orders of magnitude. At large currents, the FE current versus voltage (I-V) curves show non Fowler-Nordheim behavior consistent with tunneling from adsorbate states. At lower currents, the slope of the I-V curves decreases by a factor of approximately 2.1 after Cs deposition. The FE current does not decrease in ultrahigh vacuum and during exposure to nitrogen, but decreases during exposure to oxygen.
We compare the effects of oxygen, argon and hydrogen gases on the field emission (FE) properties ... more We compare the effects of oxygen, argon and hydrogen gases on the field emission (FE) properties of diamond films and carbon nanotubes. We find that hydrogen does not affect the FE properties of either diamond films or single- and multi-walled carbon nanotubes. Argon slightly degrades the FE properties of diamond films and has no effect of the FE properties of carbon nanotubes. Oxygen degrades the FE properties of both diamond films and carbon nanotubes. The degradation is more significant for diamond films. In addition, we find that diamond films do not field emit after they are heated to 1000 degrees C in ultrahigh vacuum. We propose that this is due to the desorbtion of hydrogen from the surface.
We compare the effects of residual gases on the field emission (FE) properties of sinle-walled an... more We compare the effects of residual gases on the field emission (FE) properties of sinle-walled and multi-walled carbon nanotubes, polycrystalline diamond films, and amorphous carbon films. The different films were exposed to oxygen, hydrogen and nitrogen residual gases at a pressure of 10-6 Torr for varying lengths of time under operating FE conditions. We observe that hydrogen and nitrogen exposure do not significantly affect the FE properties of all the samples. Oxygen exposure degrades the turn-on voltage of all the samples. The carbon nanotubes and diamond films are similarly affected by oxygen exposure. However, since nanotubes field emitt at lower voltages, they would be a better material for FE applications.
β-FeSi2 shows promise as a Si based light emitter operating in ˜ 1.5μm wavelength range. However,... more β-FeSi2 shows promise as a Si based light emitter operating in ˜ 1.5μm wavelength range. However, there exists a number of concerns related to the nature of the bandstructure and the ability to dope the material. In order to determine the effect of Cr and Co dopants, temperature-dependent Hall effect measurements were taken on a series of β-(Fe_1-xCr_x)Si2 , β-(Fe_1-xCo_x)Si2 doped films, grown by MBE. The results show that Cr is a p-type dopant and Co is an n-type dopant in this material system. It is shown that at low temperature, conduction is dominated by defect band conduction, while at higher temperatures valence band conduction prevails. These samples show good conduction properties with typical resistivity of 1Ω-cm at 30K and .05 Ω-cm at 300K.
We report the effects of O_2, H_2, and Ar exposure on the field emission properties of single and... more We report the effects of O_2, H_2, and Ar exposure on the field emission properties of single and multi-wall carbon nanotubes. The field emission current vs. voltage curves and field emission current vs. time were measured as a function of gas exposure at 10-8 Torr over a period of approximately 8 hours. The data were collected using an automated system running under Labview. We find that H2 and Ar exposure do not significantly affect the field emission properties of either single or multi-walled carbon nanotubes. However, O2 exposure degrades the field emission properties of multi-wall tubes more than those of single-wall tubes. After O2 exposure, the turn-on voltage for multi-wall tubes increased fromm 300 to 500 volts, while the turn-on voltage for single-wall tubes increased from 200 to 250 volts. An explanation of these results will be discussed.
We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties ... more We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). We find that hydrogen and argon gases do not significantly affect the FE properties of SWNTs or MWNTs. Oxygen temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurs after opertation in UHV. The higher operating voltages in an oxygen enviroment cause a permanent decrease of FE current and increase in turn-on field of MWNTs. The ratios of the slopes before and after oxygen exposure are approximnately 1.04 and 0.82 for SWNTs and MWNTs, respectively.
We describe the growth and structural and optical propeties of FeSi2 films grown on Si (100). The... more We describe the growth and structural and optical propeties of FeSi2 films grown on Si (100). The films are grown using a molecular beam epitaxy (MBE) system attached to an ultrahigh vacuum (UHV) scanning tunneling microscopy system (STM). Si and Fe are codeposited at a substrate temperature of 500 ^oC and then annealed at 700 ^oC in UHV. Then, a Si overlayer approximately 0.3 μm thick is grown over the FeSi2 film and the sample is annealed at 900 oC for 15 minutes. The structural properties of the films were analyzed using UHV STM, atomic force microscopy, magnetic force microscopy, and Raman spectroscopy. The photoluminece and magneto-optical properties were also investigated. The results of these experiments will be compared.
We compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-wa... more We compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these
The effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotu... more The effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotube (SWNT) bundles were studied. In addition, a comparative study was made on the effects of O2, Ar and H 2 gases on the field emission properties of SWNT bundles and multiwall carbon nanotubes (MWNTs). We observed that Cs deposition decreases the turn-on field for FE by a factor of 2.1--2.9 and increases the FE current by 6 orders of magnitude. After Cs deposition, the FE current versus voltage (I-V) curves showed non-Fowler-Nordheim behavior at large currents consistent with tunneling from adsorbate states. At lower currents, the ratio of the slope of the FE I-V curves before and after Cs deposition was approximately 2.1. Exposure to N2 does not decrease the FE current, while exposure to O2 decreases the FE current. Our results show that cesiated SWNT bundles have great potential as economical and reliable vacuum electron sources. We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurred after operation in UHV. The higher operating voltages in an O2 environment caused a permanent decrease of FE current and increase in turn-on field of MWNTs. The ratios of the slopes before and after O2 exposure were approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively. SWNTs compared to MWNTs would appear to make more economical and reliable vacuum electron sources.
The structural properties of FeSi2 films grown using Reactive Deposition Epitaxy (RDE) were chara... more The structural properties of FeSi2 films grown using Reactive Deposition Epitaxy (RDE) were characterized using ultrahigh vacuum scanning tunneling microscopy, Auger spectroscopy, Raman spectroscopy and atomic force microscopy. The FeSi2 films were grown by depositing Fe on a Si (100) substrate at a temperature of 400 ^oC. The morphology of the films was investigated as a function of Fe deposition showing the development of a continuous film from an initial island distribution. The properties of the RDE grown films will be compared with those of FeSi2 films grown using molecular beam epitaxy.
We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties ... more We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties of nanostructured carbon films including single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), amorphous carbon, and polycrystalline diamond. Both unpurified and purifed SWNTs are investigated. We find that argon and hydrogen do not significantly affect the FE properties of carbon films. Oxygen temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurs after operation in UHV. An oxygen environment causes a permanent decrease of the FE current and an increase in the turn-on field of MWNTs, amorphous carbon and polycrystalline diamond films.
We report the effects of Cs deposition on the field emission (FE) properties of single-walled car... more We report the effects of Cs deposition on the field emission (FE) properties of single-walled carbon nanotube bundles. Cs deposition lowers the turn-on field for field emission by a factor of 2.1 - 2.8, and increases the field emission current by 6 orders of magnitude. At large currents, the FE current versus voltage (I-V) curves show non Fowler-Nordheim behavior consistent with tunneling from adsorbate states. At lower currents, the slope of the I-V curves decreases by a factor of approximately 2.1 after Cs deposition. The FE current does not decrease in ultrahigh vacuum and during exposure to nitrogen, but decreases during exposure to oxygen.
We compare the effects of oxygen, argon and hydrogen gases on the field emission (FE) properties ... more We compare the effects of oxygen, argon and hydrogen gases on the field emission (FE) properties of diamond films and carbon nanotubes. We find that hydrogen does not affect the FE properties of either diamond films or single- and multi-walled carbon nanotubes. Argon slightly degrades the FE properties of diamond films and has no effect of the FE properties of carbon nanotubes. Oxygen degrades the FE properties of both diamond films and carbon nanotubes. The degradation is more significant for diamond films. In addition, we find that diamond films do not field emit after they are heated to 1000 degrees C in ultrahigh vacuum. We propose that this is due to the desorbtion of hydrogen from the surface.
We compare the effects of residual gases on the field emission (FE) properties of sinle-walled an... more We compare the effects of residual gases on the field emission (FE) properties of sinle-walled and multi-walled carbon nanotubes, polycrystalline diamond films, and amorphous carbon films. The different films were exposed to oxygen, hydrogen and nitrogen residual gases at a pressure of 10-6 Torr for varying lengths of time under operating FE conditions. We observe that hydrogen and nitrogen exposure do not significantly affect the FE properties of all the samples. Oxygen exposure degrades the turn-on voltage of all the samples. The carbon nanotubes and diamond films are similarly affected by oxygen exposure. However, since nanotubes field emitt at lower voltages, they would be a better material for FE applications.
β-FeSi2 shows promise as a Si based light emitter operating in ˜ 1.5μm wavelength range. However,... more β-FeSi2 shows promise as a Si based light emitter operating in ˜ 1.5μm wavelength range. However, there exists a number of concerns related to the nature of the bandstructure and the ability to dope the material. In order to determine the effect of Cr and Co dopants, temperature-dependent Hall effect measurements were taken on a series of β-(Fe_1-xCr_x)Si2 , β-(Fe_1-xCo_x)Si2 doped films, grown by MBE. The results show that Cr is a p-type dopant and Co is an n-type dopant in this material system. It is shown that at low temperature, conduction is dominated by defect band conduction, while at higher temperatures valence band conduction prevails. These samples show good conduction properties with typical resistivity of 1Ω-cm at 30K and .05 Ω-cm at 300K.
We report the effects of O_2, H_2, and Ar exposure on the field emission properties of single and... more We report the effects of O_2, H_2, and Ar exposure on the field emission properties of single and multi-wall carbon nanotubes. The field emission current vs. voltage curves and field emission current vs. time were measured as a function of gas exposure at 10-8 Torr over a period of approximately 8 hours. The data were collected using an automated system running under Labview. We find that H2 and Ar exposure do not significantly affect the field emission properties of either single or multi-walled carbon nanotubes. However, O2 exposure degrades the field emission properties of multi-wall tubes more than those of single-wall tubes. After O2 exposure, the turn-on voltage for multi-wall tubes increased fromm 300 to 500 volts, while the turn-on voltage for single-wall tubes increased from 200 to 250 volts. An explanation of these results will be discussed.
We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties ... more We compare the effects of oxygen, argon and hydrogen gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). We find that hydrogen and argon gases do not significantly affect the FE properties of SWNTs or MWNTs. Oxygen temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurs after opertation in UHV. The higher operating voltages in an oxygen enviroment cause a permanent decrease of FE current and increase in turn-on field of MWNTs. The ratios of the slopes before and after oxygen exposure are approximnately 1.04 and 0.82 for SWNTs and MWNTs, respectively.
We describe the growth and structural and optical propeties of FeSi2 films grown on Si (100). The... more We describe the growth and structural and optical propeties of FeSi2 films grown on Si (100). The films are grown using a molecular beam epitaxy (MBE) system attached to an ultrahigh vacuum (UHV) scanning tunneling microscopy system (STM). Si and Fe are codeposited at a substrate temperature of 500 ^oC and then annealed at 700 ^oC in UHV. Then, a Si overlayer approximately 0.3 μm thick is grown over the FeSi2 film and the sample is annealed at 900 oC for 15 minutes. The structural properties of the films were analyzed using UHV STM, atomic force microscopy, magnetic force microscopy, and Raman spectroscopy. The photoluminece and magneto-optical properties were also investigated. The results of these experiments will be compared.
We compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-wa... more We compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these
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