Sökning: "Phonons"

Visar resultat 21 - 25 av 70 avhandlingar innehållade ordet Phonons.

  1. 21. Graphene field-effect transistors and devices for advanced high-frequency applications

    Författare :Marlene Bonmann; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; traps; graphene; self-heating; field-effect transistors; remote phonons; carrier transport; saturation velocity; microwave devices; impurities and defects;

    Sammanfattning : New device technologies and materials are continuously investigated, in order to increase the bandwidth of high-speed electronics, thereby extending data rate and range of applications. The 2D-material graphene, with its intrinsically extremely high charge carrier velocity, is considered as a promising new channel material for advanced high frequency field-effect transistors. LÄS MER

  3. 22. Studies of Phonons and Phase Transitions by Time-Resolved X-ray Diffraction

    Författare :Henrik Enquist; Atomfysik; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; synchrotron radiation; ultrashort pulses; material science; phase transition; X-ray diffraction; phonon; X-ray detector;

    Sammanfattning : When light is used to study structures, the wavelength limits the size of the details that can be resolved. Visible light can be used to investigate structures as small as a micrometre in size. To study smaller structures a shorter wavelength is required. LÄS MER

  4. 23. Measurements of phonons in aluminium and lead with a neutron crystal spectrometer

    Författare :Reginald Stedman; Uppsala universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP;

    Sammanfattning : .... LÄS MER

  5. 24. Picosecond X-ray Diffraction Studies of Bulk and Nanostructure Materials

    Författare :Andrius Jurgilaitis; Atomfysik; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; solid-liquid transitions; X-ray diffraction and scattering; nanowires; laser beam impact phenomena; phonons in crystal lattices; Fysicumarkivet A:2012:Jurgilaitis;

    Sammanfattning : Fast phenomena occurring after laser excitation were studied using time-resolved X-ray diffraction (TXRD). In most experiments, a femtosecond laser pulse was used to excite the sample, and X-rays were used as a probe. LÄS MER

  7. 25. Dynamic local structural symmetries and luminescence properties of the yellow emitting phosphor Ce3+-doped Y3Al5O12

    Författare :Yuan-Chih Lin; Chalmers tekniska högskola; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; NATURVETENSKAP; NATURAL SCIENCES; free electron laser; neutron scattering; vibrational spectroscopy; phosphor; light emitting diode; luminescence; thermal quenching; garnet;

    Sammanfattning : This thesis centers on investigations of the local structure and vibrational properties of the oxide garnet Y3Al5O12 (YAG), which when substituted with a few percent of the activator ion Ce3+ to replace Y3+ (Y3−xCexAl5O12, YAG:Ce3+) is one of the most important phosphors for solid state lighting. The study builds on a comprehensive analysis of the nature of the phonons and localized vibrational modes in YAG:Ce3+ and how these depend on the Ce3+ concentration and temperature and how they affect key optical properties, such as the intensity and frequency of the emitted light. LÄS MER