The growth of epitaxial graphene on the surfaces of silicon carbide is considered to be one of th... more The growth of epitaxial graphene on the surfaces of silicon carbide is considered to be one of the most promising techniques for obtaining high quality large scale graphene for electronics applications. Although graphene grown on the C-face has high mobility, its growth under vacuum is too fast, not self limited and produces high concentration of crystalline defects. Therefore a precise control over the Si evaporation rate is required. We demonstrate a new method to reduce the growth rate and yield thin graphene layers with excellent thickness uniformity on the C-face of SiC in ultra high vacuum conditions. The sample is capped by another SiC substrate with a rectangular recess of about one micron depth on its surface which forms a partially open cavity between the surfaces. During the growth by high temperature annealing, silicon atoms sublimated from the capped sample are confined inside the cavity between the two substrates. The confined silicon vapor maintains a high partial pre...
In this clinical study, the effect of conventional liposuction on musculocutaneous and fasciocuta... more In this clinical study, the effect of conventional liposuction on musculocutaneous and fasciocutaneous perforator vessels was investigated. The perforator vessels in the abdominal and lateral and medial thigh regions in 7 patients and in the abdominal region in 3 patients (a total of 38 anatomic regions in 10 patients) were marked preoperatively by color Doppler ultrasonography. Following a standard liposuction
The influence of the host-crystal deformation on the acceptor wave-function in a cubic crystal is... more The influence of the host-crystal deformation on the acceptor wave-function in a cubic crystal is considered. The calculations are based on the numerical solution of the Luttinger Hamiltonian for a hole in a complex valence band. The deformation is taken into account using Bir-Pikus Hamiltonian for the deformation. The results can be used for the interpretation of the STM images in strained cubic crystals.
Cross-sectional scanning tunneling microscopy ͑STM͒ measurements on molecular beam epitaxy grown ... more Cross-sectional scanning tunneling microscopy ͑STM͒ measurements on molecular beam epitaxy grown Mn doped GaAs͑110͒ at 5 and 77 K are presented. The enhanced mechanical stability of the STM at low temperature allows a detailed study of the electronic contrast of Mn atoms in the GaAs͑110͒ surface. According to reproducible and distinguishable contrast patterns of single Mn atoms, we present statistical evidence for a layer by layer identification of Mn atoms embedded in the first few monatomic layers of the crystal. A comparison with a bulklike theoretical approach reveals a semiquantitative agreement with the measurements. Remaining differences between theory and experiment indicate the influence of the surface as an important factor to understand the contrast of impurities close to the surface. Furthermore, we report the injection of transition-metal atoms into the surface. Finally, reproducible complexes consisting of a surface Mn and an adsorbate atom are found and manipulated.
ABSTRACT Cleavage induced rows of linear vacancy structures on p-doped ZnTe (110) surface are stu... more ABSTRACT Cleavage induced rows of linear vacancy structures on p-doped ZnTe (110) surface are studied at room temperature by using cross-sectional scanning tunneling microscopy (X-STM). The oscillating contrast superimposed on the Te-driven occupied states neighboring to the vacancy cores are characterized at the atomic scale in order to determine the type of the missing component on the ZnTe surface matrix. We identify three major intensity distributions associated with different vacancy states. The X-STM images of three possible configurations comprising Zn only, Te only, and ZnTe binary vacancy structures on the ZnTe surface are modeled by using ab initio density functional theory calculations. The comparison of the X-STM measurements of each individual vacancy state to the corresponding theoretical simulation showed that unlike the Te vacancy, which leads to a local depression, the absence of Zn only or ZnTe binary gives rise to hillock features on the neighboring Te states of the ZnTe (110) cleaved surface. The theoretical STM images calculated for an undoped ZnTe crystal imply that possible doping-related effects on vacancy-induced features can be disregarded for interpreting the experimentally observed vacancy structures in our samples.
... Once created, the QDs are subsequently capped, a step which is required for any device applic... more ... Once created, the QDs are subsequently capped, a step which is required for any device application. Although a lot of effort has been dedicated to understand the QD growth mechanism, there are relatively few studies focused on the effect of the capping process. ...
The effect of the degree of Si confinement on the thickness and morphology of UHV grown epitaxial... more The effect of the degree of Si confinement on the thickness and morphology of UHV grown epitaxial graphene on (0 0 0 −1) SiC is investigated by using atomic force microscopy and Raman spectroscopy measurements. Prior to the graphene growth process, the C-face surface of a SiC substrate is capped by another SiC comprising three cavities on its Si-rich surface with depths varying from 0.5 to 2 microns. The Si atoms, thermally decomposed from the sample surface during high temperature annealing of the SiC cap /SiC sample stack, are separately trapped inside these individual cavities at the sample/cap interface. Our analyses show that the growth rate linearly increases with the cavity height. It was also found that stronger Si confinement yields more uniform graphene layers.
We demonstrate a technique to produce thin graphene layers on C-face of SiC under ultra high vacu... more We demonstrate a technique to produce thin graphene layers on C-face of SiC under ultra high vacuum conditions. A stack of two SiC substrates comprising a half open cavity at the interface is used to partially confine the depleted Si atoms from the sample surface during the growth. We observe that this configuration significantly slows the graphene growth to easily controllable rates on C-face SiC in UHV environment. Results of low-energy electron diffractometry and Raman spectroscopy measurements on the samples grown with stacking configuration are compared to those of the samples grown by using bare UHV sublimation process.
The growth of epitaxial graphene on the surfaces of silicon carbide is considered to be one of th... more The growth of epitaxial graphene on the surfaces of silicon carbide is considered to be one of the most promising techniques for obtaining high quality large scale graphene for electronics applications. Although graphene grown on the C-face has high mobility, its growth under vacuum is too fast, not self limited and produces high concentration of crystalline defects. Therefore a precise control over the Si evaporation rate is required. We demonstrate a new method to reduce the growth rate and yield thin graphene layers with excellent thickness uniformity on the C-face of SiC in ultra high vacuum conditions. The sample is capped by another SiC substrate with a rectangular recess of about one micron depth on its surface which forms a partially open cavity between the surfaces. During the growth by high temperature annealing, silicon atoms sublimated from the capped sample are confined inside the cavity between the two substrates. The confined silicon vapor maintains a high partial pre...
In this clinical study, the effect of conventional liposuction on musculocutaneous and fasciocuta... more In this clinical study, the effect of conventional liposuction on musculocutaneous and fasciocutaneous perforator vessels was investigated. The perforator vessels in the abdominal and lateral and medial thigh regions in 7 patients and in the abdominal region in 3 patients (a total of 38 anatomic regions in 10 patients) were marked preoperatively by color Doppler ultrasonography. Following a standard liposuction
The influence of the host-crystal deformation on the acceptor wave-function in a cubic crystal is... more The influence of the host-crystal deformation on the acceptor wave-function in a cubic crystal is considered. The calculations are based on the numerical solution of the Luttinger Hamiltonian for a hole in a complex valence band. The deformation is taken into account using Bir-Pikus Hamiltonian for the deformation. The results can be used for the interpretation of the STM images in strained cubic crystals.
Cross-sectional scanning tunneling microscopy ͑STM͒ measurements on molecular beam epitaxy grown ... more Cross-sectional scanning tunneling microscopy ͑STM͒ measurements on molecular beam epitaxy grown Mn doped GaAs͑110͒ at 5 and 77 K are presented. The enhanced mechanical stability of the STM at low temperature allows a detailed study of the electronic contrast of Mn atoms in the GaAs͑110͒ surface. According to reproducible and distinguishable contrast patterns of single Mn atoms, we present statistical evidence for a layer by layer identification of Mn atoms embedded in the first few monatomic layers of the crystal. A comparison with a bulklike theoretical approach reveals a semiquantitative agreement with the measurements. Remaining differences between theory and experiment indicate the influence of the surface as an important factor to understand the contrast of impurities close to the surface. Furthermore, we report the injection of transition-metal atoms into the surface. Finally, reproducible complexes consisting of a surface Mn and an adsorbate atom are found and manipulated.
ABSTRACT Cleavage induced rows of linear vacancy structures on p-doped ZnTe (110) surface are stu... more ABSTRACT Cleavage induced rows of linear vacancy structures on p-doped ZnTe (110) surface are studied at room temperature by using cross-sectional scanning tunneling microscopy (X-STM). The oscillating contrast superimposed on the Te-driven occupied states neighboring to the vacancy cores are characterized at the atomic scale in order to determine the type of the missing component on the ZnTe surface matrix. We identify three major intensity distributions associated with different vacancy states. The X-STM images of three possible configurations comprising Zn only, Te only, and ZnTe binary vacancy structures on the ZnTe surface are modeled by using ab initio density functional theory calculations. The comparison of the X-STM measurements of each individual vacancy state to the corresponding theoretical simulation showed that unlike the Te vacancy, which leads to a local depression, the absence of Zn only or ZnTe binary gives rise to hillock features on the neighboring Te states of the ZnTe (110) cleaved surface. The theoretical STM images calculated for an undoped ZnTe crystal imply that possible doping-related effects on vacancy-induced features can be disregarded for interpreting the experimentally observed vacancy structures in our samples.
... Once created, the QDs are subsequently capped, a step which is required for any device applic... more ... Once created, the QDs are subsequently capped, a step which is required for any device application. Although a lot of effort has been dedicated to understand the QD growth mechanism, there are relatively few studies focused on the effect of the capping process. ...
The effect of the degree of Si confinement on the thickness and morphology of UHV grown epitaxial... more The effect of the degree of Si confinement on the thickness and morphology of UHV grown epitaxial graphene on (0 0 0 −1) SiC is investigated by using atomic force microscopy and Raman spectroscopy measurements. Prior to the graphene growth process, the C-face surface of a SiC substrate is capped by another SiC comprising three cavities on its Si-rich surface with depths varying from 0.5 to 2 microns. The Si atoms, thermally decomposed from the sample surface during high temperature annealing of the SiC cap /SiC sample stack, are separately trapped inside these individual cavities at the sample/cap interface. Our analyses show that the growth rate linearly increases with the cavity height. It was also found that stronger Si confinement yields more uniform graphene layers.
We demonstrate a technique to produce thin graphene layers on C-face of SiC under ultra high vacu... more We demonstrate a technique to produce thin graphene layers on C-face of SiC under ultra high vacuum conditions. A stack of two SiC substrates comprising a half open cavity at the interface is used to partially confine the depleted Si atoms from the sample surface during the growth. We observe that this configuration significantly slows the graphene growth to easily controllable rates on C-face SiC in UHV environment. Results of low-energy electron diffractometry and Raman spectroscopy measurements on the samples grown with stacking configuration are compared to those of the samples grown by using bare UHV sublimation process.
Uploads
Papers by C. Çelebi