Investigation of self-assembled monolayer treatment on SiO2 gate insulator of poly(3-hexylthiophene) thin-film transistors

We have investigated self-assembled monolayer (SAM) treatment on SiO₂ gate insulator of poly(3-hexylthiophene) (P3HT) thin-film transistor (TFT), and demonstrated a correlation between mobility and surface free energy of the insulator. The device with lower surface free energy shows higher mobility. The docosyltrichlorosilane (DCTS)-treated device exhibits the best performance among the various SAM-treated devices examined. Field-effect mobility, on/off ratio and threshold voltage of the DCTS-treated P3HT TFT were 0.015 cm²/Vs, >10⁵ and −14 V, respectively.     

Energy-dispersive X-ray reflectivity and GID for real-time growth studies of pentacene thin films

We use energy-dispersive X-ray reflectivity and grazing incidence diffraction (GID) to follow the growth of the crystalline organic semiconductor pentacene on silicon oxide in-situ and in real-time. The technique allows for monitoring Bragg reflections and measuring X-ray growth oscillations with a time resolution of 1 min in a wide q-range in reciprocal space extending over 0.25-0.80 Å^− 1, i.e. sampling a large number of Fourier components simultaneously. A quantitative analysis of growth oscillations at several q-points yields the evolution of the surface roughness, showing a marked transition from layer-by-layer growth to strong roughening after four monolayers of pentacene have been deposited.     

Further insights into the photodegradation of poly(3-hexylthiophene) by means of X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to monitor the chemical changes resulting from irradiation (> 295 nm) in air of poly(3-hexylthiophene) (P3HT), polymer which is a good candidate for photovoltaic applications. The formation of carbonyl moieties and the stepwise oxidation of sulphur atoms were characterised. The oxidation and the cleavage of the hexyl side-chain was monitored. It is also shown that sulfur was first converted into sulfoxides, then into sulfones and finally into sulfinate esters. The formation of these ultimate degradation products provoked a disruption of π-conjugation in P3HT, leading to diminished visible absorbance. Based on these results, a mechanism of P3HT photooxidation is proposed. Comparison of XPS data with previously reported infrared and UV-visible spectral analysis showed that the information provided by these techniques is completely consistent.     

XPS and X-ray diffraction studies of aluminum-doped zinc oxide transparent conducting films

Aluminum-doped zinc oxide transparent conducting films are prepared by spray pyrolysis at different dopant concentrations. These films are subsequently characterized by X-ray diffractometric and X-ray photoelectron spectroscopic (XPS) techniques. The results are compared with those obtained from pure zinc oxide films prepared under identical conditions. X-ray diffraction measurements show an increase in lattice parameters (c and a) for aluminum-doped films while their ratio remains the same. This study also indicates that within the XPS detection limit the films are chemically identical to pure zinc oxide. However, a difference in the core-electron line shape of the Zn 2p_3/2 photoelectron peaks is predicted. An asymmetry in Zn 2p_3/2 photoelectron peaks has been observed for aluminium-doped films. The asymmetry parameters evaluated from core-electron line-shape analysis yield a value of the order of 0.04±0.01. The value is found to lie between those obtained for pure zinc oxide and has been attributed to the presence of excess zinc in the films.     

Thermophysical properties of free-standing micrometer-thick Poly(3-hexylthiophene) films

The solution of Poly(3-hexylthiophene) (P3HT) in chloroform is generally adopted for fabricating P3HT thin films or nanofibers. In this work, 4 regular P3HT solution weight percentages, 2, 3, 5 and 7 wt.%, are compounded to fabricate P3HT thin films by using spin-coating technique. Raman spectrum study suggests that the density of the P3HT thin films varies with different P3HT solution weight percentages while X-ray diffraction analysis reveals that the crystal structures are identical for all P3HT thin films. The transient electrothermal technique is employed to measure the thermal diffusivity of the P3HT thin films and an efficient temperature-resistance calibration is performed to cooperatively study the thermal conductivity. When the P3HT weight percentage changes from 2% to 7%, the thermal conductivity varies from 1.29 W/m·K to 1.67 W/m·K and the thermal diffusivity goes down from around 10^− 6 m²/s to 5 × 10^− 7 m²/s. The density of P3HT thin films is also determined from the experimental data. The relationship between the density and thermophysical properties clearly demonstrates that the thermal conductivity increases with density while the thermal diffusivity decreases.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Enhancement of carrier mobility in all-inkjet-printed organic thin-film transistors using a blend of poly(3-hexylthiophene) and carbon nanoparticles

To enhance the carrier mobility of all-inkjet-printed organic thin film transistors, we fabricated devices that incorporated poly(3-hexylthiophene) (P3HT) and carbon nanoparticles (CNPs). The fabricated devices had an on/off ratio of 10⁴, which is one order less than that of pristine organic thin-film transistors (OTFTs). The maximum carrier mobility as high as 0.053 cm²/V-s was achieved for a CNP/P3HT weight-weight ratio of 7/100. This degree of mobility is 10 times greater than average mobility of pristine P3HT-OTFTs. X-ray diffraction and scanning electron microscopy images reveal that the carrier mobility was enhanced by reducing the injection barrier and enhancing the carrier injection. This work demonstrates the feasibility of all-inkjet-printed OTFT technology.     

Molecular orientation of poly(3-butylthiophene) friction-transferred films

Oriented thin films of regioregular-poly(3-butylthiophene) (P3BT) were prepared by friction transfer method. Molecular orientation of P3BT in the friction-transferred films was investigated with grazing-incidence X-ray diffraction (GIXD), polarized ultraviolet–visible (UV) spectra, and infrared (IR) spectra. Polarized UV spectra showed the polymer backbones were aligned in the friction direction. GIXD measurements suggest that a axis in P3BT film is normal to the substrate, that is, π-stacking direction tends to be parallel to the substrate. This orientation is different from those of friction-transferred poly(3-hexylthiophene) and poly(3-dodecylthiophene).     

Electrical characteristics of poly(3-hexylthiophene) organic thin film transistor with electroplated metal gate electrodes on polyimide

The electroplating of the gate electrode on a flexible polyimide (PI) substrate was successfully applied to the fabrication of inverted-staggered poly(3-hexylthiophene) (P3HT) organic thin film transistors (OTFTs). The Ni gate electrode was electroplated through patterned negative photo-resist (KMPR) masks onto Cu (seed)/Cr (adhesion) layers that had been sputter-deposited on O₂-plasma-treated PI substrates. The electrical measurements of the fabricated OTFTs with the SiO₂ gate insulator indicated non-ideal output characteristics, which are similar to the model of electrical transport by a space-charge limited current (SCLC). The use of a poly(4-vinyl phenol) (PVP) and SiO₂/PVP bilayer gate dielectric produced output characteristics that were closer to the ideal TFT behavior but led to a lower effective mobility and on/off current (I_on/I_off).     

Damage mode tensile testing of thin gold films on polyimide substrates by X-ray diffraction and atomic force microscopy

In situ tensile testing has been performed on thin gold film, 320 nm thick, deposited on polyimide substrates. During the tensile testing, strain/stress measurements have been carried out by X-ray diffraction using the d-sin²ψ method. The X-ray stress analysis suggests crack formation in the films for stresses greater than 670 MPa. The surface of the deformed specimen observed by atomic force microscopy (AFM) exhibits both cracks and two types of straight-sided buckling patterns lying perpendicular to the tensile axis. These buckling patterns can have a symmetrical or asymmetrical shape. The evolution of these two kinds of buckling structures under tensile stress has been observed in situ by AFM and compared to X-ray stress data. The results indicate that symmetrical straight-sided buckling patterns are induced by the compressive stress during unloading, whereas the asymmetrical result from the delamination of the film during the tensile deformation.     

Electroless deposition of CoPtWP magnetic thin films

CoPtWP magnetic thin films were prepared by electroless deposition. The influence of bath pH, deposition temperature and bath composition on the deposition speed, alloy content, microstructure, and magnetic properties of CoPtWP thin films were investigated. It was found that deposition speed increased gradually with the bath pH and deposition temperature. The cobalt content in the CoPtWP thin films varied from 77 at.% to 85 at.% by controlling the bath pH. The microstructure of CoPtWP thin films was dependent on bath pH and deposition temperature: two mixed structures, face centered cubic (fcc) and hexagonal close packed (hcp), were observed at low pH values and low deposition temperature. With the increase of pH values and deposition temperature, the intensity of fcc (111) peak suppressed gradually. The surface morphology was markedly influenced by bath pH, deposition temperature and bath composition. VSM and MFM measurements revealed that perpendicular coercivity had been increased with the bath pH. Unique hard magnetic properties of CoPtWP thin films with large perpendicular magnetic anisotropy were obtained at 90 °C and bath pH 13.0.     

A transport study on as-grown and cast films of electrogenerated poly(3-hexylthiophene)

Two kinds of poly(3-hexylthiophene) films with identical chemical compositions are prepared. One of the films is obtained by electropolymerization of 3-hexylthiophene (as-grown film) and the other is prepared by casting a solution dissolving the as-grown film (cast film). A clear difference is found in the mobility vs. doping level plots between the as-grown and cast films and its reason is discussed.     

Transmission electron microscopy and X-ray diffraction studies of quantum wells

A series of In _x Ga_1?x As (x=0·47) quantum wells with InP barrier layers have been grown on InP substrates by metalorganic vapour phase epitaxy (MOVPE) at 625°C. The nominal well widths were defined during growth at (i) 25 Å, 39 Å, 78 Å and 150 Å for one sample and (ii) 78 Å for all 4 wells in another sample. The InP barrier widths have been kept constant at 150 Å. These layers have been characterized by X-ray diffraction (XRD) which from simulation gave the nominally 78 Å well width as 84 Å and the nominally 150 Å barrier width as 150·5 Å. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been carried out on etched and ion-milled samples for direct measurement of well and barrier widths. The well widths found from TEM are 25 Å, 40 Å, 75 Å and 150 Å. TEM micrographs revealed that, while the InP barrier layer is of good quality and the growth is confirmed to be epitaxial, dipoles are detected at the interface and the quantum well has some small disordered regions. These thickness measurements are in good agreement with earlier photoluminescence (PL) and secondary ion mass spectrometry (SIMS) studies.     

Microdisk laser emission and electrical properties of composite films based on poly(3-hexylthiophene)s with different stereoregularity

The optical and electrical properties of composite thin films of poly(3-hexylthiophene)s (PAT6s), processing different stereo-regularity originating from side-chain regio orders have been studied. The laser emission properties of PAT6 composite thin films in microdisk structure have been observed by pulsed photopumping. From the electrical and optical measurements, the electrical conductivity and the quantum efficiency of the PAT6 composite films were estimated. The emission and conductivity depending on the mixture ratios were discussed by taking the stereo-regularity of the molecular structure into consideration.     

Raman spectroscopy and X-ray diffraction studies of stress effects in PbTiO3 thin films

A systematic study of domain structure and residual stress evolution with film thickness and of phase transition in c/a epitaxial PbTiO(3)/LaAlO(3) films using X-ray diffraction and Raman spectroscopy is reported. Both techniques revealed that the films are under tensile residual stress in the film plane and that a-domains are more stressed than c-domains. The two components of the large A(1)(TO) Ramanmodes are associated with a- and c-domains and their intensity ratio correlates to the volume fraction of a-domains. The evolution of the Raman signature with temperature revealed that the spectrum of a-domains disappears around 480 degrees C, whereas c-domains present an anomaly in their spectrum at 500 degrees C but maintain a well-defined Raman signature up to 600 degrees C.     

Origin on amorphization of Co-Mo magnetic thin films: Experiments and thermodynamic calculation

Amorphisation of Co-Mo magnetic thin films has been studied by using X-ray diffraction technique, and thermodynamic calculation based on Miedema's semi-empirical model has been used to clarify the nature of amorphisation in this binary alloy system. The transition composition from the hexagonal cubic packed structure to the amorphous (H/A) is about 19 at.%Mo when the Co-Mo thin films are deposited at room temperature (RT) under a working Ar pressure of 0.2 Pa and a deposition rate of about 0.7 Å/s, but increases up to about 23 at.%Mo when deposited at 300 °C. The calculated transition composition at RT based on the Miedema's model or the thermodynamically assessed parameters is 18.7 at.%Mo or 16.1 at.%Mo, respectively, well consistent with the experimental value of ~ 19.0 at.%Mo. Higher deposition rate and lower pressure shift the H/A transition composition to a higher Mo content.     

A study of structural transition in nanocrystalline titania thin films by X-ray diffraction Rietveld method

Structural and microstructural analyses of nanocrystalline titania thin films prepared by pulsed laser deposition have been carried out. At lower oxygen partial pressures (≤10⁻⁴ mbar), rutile films were formed, whereas at 1.2 × 10⁻³ mbar of oxygen partial pressure, the thin films contained both rutile and anatase phases. At 0.04 and 0.05 mbar of oxygen partial pressure, the film was purely anatase. Addition of oxygen has also shown a profound influence on the surface morphology of the as deposited titania films. Modified Rietveld method has been used to determine crystallite size, root mean square strain and fractional coordinates of oxygen of the anatase films. The influence of crystallite size and strain on the rutile to anatase phase transition is investigated.     

In-situ energy-dispersive X-ray diffraction of metal sulfide assisted crystallization of strongly (001) textured photoactive tungsten disulfide thin films

Highly (001) textured tungsten disulphide (WS₂) thin films were grown by rapid metal (Ni, Pd) sulfide assisted crystallization of amorphous reactively sputtered sulfur-rich tungsten sulfide (WS_3 + x) and by metal sulfide assisted sulfurization of tungsten metal films. The rapid crystallization was monitored by real-time in-situ energy dispersive X-ray diffraction (EDXRD). Provided that a thin nickel or palladium film was deposited prior to the deposition of WS_3 + x or W, the films crystallized very fast (about 20 nm/s) at temperatures above the metal sulfide eutectic temperature. After crystallization, isolated MeS_x crystallites are located on the surface of the WS₂ layer, which was proved by scanning electron microscopy. The metal sulfide assisted crystallized WS₂ layers exhibit a pronounced (001) orientation with large crystallites up to 2 µm. The in-situ EDXRD analysis revealed distinct differences of the two crystallization routes from tungsten and from amorphous, sulfur-rich WS_3 + x precursors, respectively. The crystallized WS₂ films showed photoactivity. Combined with the high absorption coefficient of 10⁵ cm^− 1 and a indirect band gap of 1.8 eV these properties make such films suitable for absorber layers in thin film solar cells.     

并五苯薄膜的AFM及XRD研究

报道了以热氧化硅片为衬底,用溶液溶解和真空蒸镀两种方法制备有机半导体材料并五苯薄膜.用原子力显微镜(AFM)分析了薄膜的形貌,用X射线衍射仪(XRD)分析了薄膜的晶体结构,讨论了诸多因素对薄膜的影响以及两种方法制备的并五苯薄膜的相结构.     

Comparative determination of the α/β phase fraction in α+β-titanium alloys using X-ray diffraction and electron microscopy

A comparison is made between the measured α/β phase fractions in Ti-6246 using X-ray diffraction (XRD) and electron microscopy. Image analysis of SEM and TEM images was compared to the phase fraction estimate obtained using electron backscattered diffraction, lab and high-energy synchrotron XRD. There was a good agreement between the electron microscopic and diffraction techniques, provided that the microstructural parameters of grain size and texture are estimated correctly when using quantitative Rietveld refinement.