Low-temperature Thermal Annealing Research Articles

High-Performance Organic Field-Effect Transistors of Liquid Crystalline Organic Semiconductor by Laser Mapping Annealing.

Organic semiconductors (OSCs), especially small molecule semiconductors, have received increasing attention due to their good designability and variability. Phase transitions and interfacial properties have a decisive influence on device performance. Here, 2-Dodecyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-12) devices are treated with low-power laser annealing, which is able to avoid the influence of the dewetting effect on the hole mobility of organic semiconductor materials. Ultraviolet ozone treatment and self-assembled monolayer treatment can improve the performance and stability of the device. Moreover, after low-temperature thermal annealing, the hole mobility of the device can even reach as high as 4.80 cm2 V-1 s-1, and we tested the optical response of the device to the ultraviolet wavelength and found that its maximum optical responsivity was 8.2 AW-1.

UV irradiation assisted low-temperature process for thin film transistor performance improvement of praseodymium-doped indium zinc oxide

Flexible displays have developed rapidly in recent years, low-temperature process to produce high performance amorphous oxide semiconductor devices are significant for the wide application of low-cost flexible display. In this work, praseodymium-doped indium zinc oxide semiconductor deposited by vacuum sputtering was irradiated with UV light before low-temperature thermal annealing. The treated semiconductor retains its characteristics of amorphous and high transparency to visible light. The carrier concentration and oxygen-related defects of the PrIZO films were significant changed under the superposition of UV irradiation and thermal annealing, the effects of UV light and thermal annealing can be well superimposed. The PrIZO-TFT that have been thermally annealed at 200 °C for 1 h after irradiated by UV light with power density of 175 mW cm−2 for 1800 s exhibit an optimal performance (μ sat of 12.34 cm2 V−1·s−1, I on/I off of 3.8 × 108, V th of 0.7 V, SS of 0.15 V/decade) and stability. The device performance broadens the application prospect of AOS TFT in low-cost flexible display.

Tuning the electrical properties of graphene oxide through low-temperature thermal annealing.

During the last fifteen years, the reduction of electrically insulating graphene oxide (GO) through the elimination of oxygen containing functional groups and the restoration of sp2 conjugation yielding its conducting form, known as reduced graphene oxide (rGO), has been widely investigated as a scalable and low-cost method to produce materials featuring graphene-like characteristics. Among various protocols, thermal annealing represents an attractive green approach compatible with industrial processes. However, the high temperatures typically required to accomplish this process are energetically demanding and are incompatible with the use of plastic substrates often desired for flexible electronics applications. Here, we report a systematic study on the low-temperature annealing of GO by optimizing different annealing conditions, i.e., temperature, time, and reduction atmosphere. We show that the reduction is accompanied by structural changes of GO, which affect its electrochemical performance when used as an electrode material in supercapacitors. We demonstrate that thermally-reduced GO (TrGO) obtained under air or inert atmosphere at relatively low temperatures (<300 °C) exhibits low film resistivities (10-2-10-4 Ω m) combined with unaltered resistance after 2000 bending cycles when supported on plastic substrates. Moreover, it exhibits enhanced electrochemical characteristics with a specific capacitance of 208 F g-1 and a capacitance retention of >99% after 2000 cycles. The reported strategy is an important step forward toward the development of environmentally friendly TrGO for future electrical or electrochemical applications.

Low-Temperature Annealing of CdTe Detectors With Evaporated Gold Contacts and Its Effect on Detector Performance

Cadmium telluride (CdTe) detectors are usually subjected to elevated temperatures during postprocessing and bonding them to readout electronics while fabricating imaging arrays. We studied the effects of low-temperature and short duration rapid thermal annealing of CdTe bulk as well as CdTe epitaxial-layer-based detectors with evaporated gold contacts. The detectors were annealed in the temperature range of 100 °C–300 °C, and its effect on the detector dark current, gamma detection property, and response stability was studied. For the bulk-detectors, the detector dark current decreased and gamma detection properties as well as the performance stability improved after annealing. However, such improvements were moderate for epitaxial-layer-based detectors. The study of the metal–semiconductor interface of annealed detectors revealed that diffused gold, elemental oxygen, and tellurium oxide existed and extended deep inside the bulk portion in epitaxial detectors; however, they were confined in the surface regions only in bulk-detectors, which likely be the causes of observed results in these two types of detectors.

Low contact-resistivity and high-uniformity Ni/Au ohmic contacts on Si nanomembranes grafted to Si substrates via low-temperature rapid thermal annealing

Grafted lattice-mismatched semiconductor heterostructures have the potential to simultaneously achieve low on-resistance and high breakdown performance. These novel semiconductor devices are typically fabricated by grafting single-crystal semiconductor nanomembrane (NM) layers onto a foreign substrate. The optimal temperature for grafting often prevents the use of high temperatures to achieve optimal ohmic contacts. Herein, we present a method to form low temperature Ni/Au ohmic contacts for the anode electrode to a p + Si NM that is grafted to a Si substrate. Ohmic contact resistivity (ρc) and its device-to-device uniformity are characterized against different annealing temperatures and are also compared against contact resistivity of p + SOI structure. Low resistivity ohmic contacts (ρc = 5.92 × 10-6 Ω cm2) and high uniformity were achieved on grafted NM structure. Demonstration of low ρc for NM-transferred layers via a low-temperature metallization scheme achieves an important step towards further developing high performance lattice-mismatched heterostructure-based devices.

18.77 % Efficiency Organic Solar Cells Promoted by Aqueous Solution Processed Cobalt(II) Acetate Hole Transporting Layer

A robust hole transporting layer (HTL), using the cost-effective Cobalt(II) acetate tetrahydrate (Co(OAc)2 ⋅4 H2 O) as the precursor, was simply processed from its aqueous solution followed by thermal annealing (TA) and UV-ozone (UVO) treatments. The TA treatment induced the loss of crystal water followed by oxidization of Co(OAc)2 ⋅4 H2 O precursor, which increased the work function. However, TA treatment differently realize a high work function and ideal morphology for charge extraction. The resulting problems could be circumvented easily by additional UVO treatment, which also enhanced the conductivity and lowered the resistance for charge transport. The optimal condition was found to be a low temperature TA (150 °C) followed by simple UVO, where the crystal water in Co(OAc)2 ⋅4 H2 O was removed fully and the HTL surface was anchored by substantial hydroxy groups. Using PM6 as the polymer donor and L8-BO as the electron acceptor, a record high PCE of 18.77 % of the binary blend OSCs was achieved, higher than the common PEDOT:PSS-based solar cell devices (18.02 %).

18.77 % Efficiency Organic Solar Cells Promoted by Aqueous Solution Processed Cobalt(II) Acetate Hole Transporting Layer

AbstractA robust hole transporting layer (HTL), using the cost‐effective Cobalt(II) acetate tetrahydrate (Co(OAc)2⋅4 H2O) as the precursor, was simply processed from its aqueous solution followed by thermal annealing (TA) and UV‐ozone (UVO) treatments. The TA treatment induced the loss of crystal water followed by oxidization of Co(OAc)2⋅4 H2O precursor, which increased the work function. However, TA treatment differently realize a high work function and ideal morphology for charge extraction. The resulting problems could be circumvented easily by additional UVO treatment, which also enhanced the conductivity and lowered the resistance for charge transport. The optimal condition was found to be a low temperature TA (150 °C) followed by simple UVO, where the crystal water in Co(OAc)2⋅4 H2O was removed fully and the HTL surface was anchored by substantial hydroxy groups. Using PM6 as the polymer donor and L8‐BO as the electron acceptor, a record high PCE of 18.77 % of the binary blend OSCs was achieved, higher than the common PEDOT:PSS‐based solar cell devices (18.02 %).

Characteristic Variabilities of Subnanometer EOT La2O3 Gate Dielectric Film of Nano CMOS Devices.

As CMOS devices are scaled down to a nanoscale range, characteristic variability has become a critical issue for yield and performance control of gigascale integrated circuit manufacturing. Nanoscale in size, few monolayers thick, and less thermally stable high-k interfaces all together cause more significant surface roughness-induced local electric field fluctuation and thus leads to a large device characteristic variability. This paper presents a comprehensive study and detailed discussion on the gate leakage variabilities of nanoscale devices corresponding to the surface roughness effects. By taking the W/La2O3/Si structure as an example, capacitance and leakage current variabilities were found to increase pronouncedly for samples even with a very low-temperature thermal annealing at 300 °C. These results can be explained consistently with the increase in surface roughness as a result of local oxidation at the La2O3/Si interface and the interface reactions at the W/La2O3 interface. The surface roughness effects are expected to be severe in future generations’ devices with even thinner gate dielectric film and smaller size of the devices.

Fabrication of flower-like surface Ni@Co3O4 nanowires anchored on RGO nanosheets for high-performance microwave absorption

Novel composite microwave absorption (MA) materials with multiple loss mechanism have attracted considerable attention. In this work, flower-like surface Ni@Co3O4 nanowires were designed and fabricated through chemical reduction method induced by magnetic field, followed by in-situ polymerization, low temperature oil bath and thermal annealing. Then, the Ni@Co3O4/RGO composites were prepared through a hydrothermal reaction of the Ni@Co3O4 nanowires and graphene oxide suspension. The electromagnetic properties of different loading content samples (15 wt%, 25 wt% and 35 wt%) were measured to investigate the influence of loading content on the MA performance. For the 35 wt% loading sample, the minimum reflection loss (RLmin) value of −60.0 dB was determined at the thickness of 2.3 mm, and the maximum effective absorption bandwidth (EAB, RL < −10 dB) of 4.62 GHz can be achieved when the thickness is 1.6 mm. This research provides a reference for exploiting high-efficient flower-like surface magnetic-dielectric composites in the field of MA.

The Effect of Annealing on Additive Manufactured ULTEM™ 9085 Mechanical Properties.

Fused filament fabrication (FFF) is increasingly adopted for direct manufacturing of end use parts in an aviation industry. However, the application of FFF technique is still restricted to manufacturing low criticality lightly loaded parts, due to poor mechanical performance. To alleviate the mechanical performance issue, thermal annealing process is frequently utilized. However, problems such as distortion issues and the need for jigs and fixtures limit the effectiveness of the thermal annealing process, especially for low volume complex FFF parts. In this research, a novel low temperature thermal annealing is proposed to address the limitations in conventional annealing. A modified orthogonal array design is applied to investigate the performance of ULTEM™ 9085 FFF coupons. Further, the coupons are annealed with specialized support structures, which are co-printed with the coupons during the manufacturing process. Once the annealing process is completed, multiscale characterizations are performed to identify the mechanical properties of the specimens. Geometrical measurement of post annealed specimens indicates an expansion in the layering direction, which indicates relief of thermal stresses. Moreover, annealed coupons show an improvement in tensile strength and reduction in strain concentration. Mesostructure and fracture surface analysis indicate an increase in ductility and enhanced coalescence. This research shows that the proposed annealing methodology can be applied to enhance the mechanical performance of FFF parts without significant distortion.

Enhanced lattice perfection by low temperature thermal annealing in photoelectric (CH3NH3)PbBr3.

The coupling between the organic CH3NH3+ cations and inorganic perovskite PbBr3- framework in a large single crystal of (CH3NH3)PbBr3 weighting 13 g was studied using neutron diffraction and inelastic neutron scattering. Two lattice incommensurate (ICM) phases were found, one at higher temperatures, marked ICMHT, which appeared between 147 and 135 K. The second one, marked ICMLT, developed below 143 K and remained at 75 K. The transition from the ICMLT to ICMHT phase upon warming gave rise to extremely large lattice shrinking, followed by extremely large lattice expansion of the tetragonal basal plane of the PbBr3 lattice. There was a progressive decrease in the width of the Bragg peaks from the PbBr3 lattice upon warming, which can be described using a critical exponent for each type of Bragg peak to show complete ordering of the atoms into a (CH3NH3)PbBr3 lattice at 194 K. (CH3NH3)PbBr3 exhibits six definitive acoustic-like phonon branches at 75 K. The six branches renormalizes into two at 200 K, with the frequencies of both the transverse and longitudinal modes greatly enhanced. The asymmetric structure of the CH3NH3 ions helps to understand the observed behaviors.

Gold nanoparticle-based eco-friendly ink for electrode patterning on flexible substrates

Au nanoparticles functionalized by short poly(ethylene glycol) chain ligands were suspended in a hydroalcoholic medium. This suspension was then printed by inkjet onto a Kapton® substrate. Gold electrodes consisting of four stacked printed layers exhibited a conductivity of (1 ± 0.1) × 107 S/m, close to that of Au bulk, after low-temperature thermal annealing. The electrochemical behaviour with respect to heterogeneous electron transfer reactions and the reactivity towards thiol chemisorption are identical to those obtained when a conventional polycrystalline Au electrode is used.

Effects of low‐temperature thermal annealing on interface characteristics in IZO/IGZO dual‐channel thin‐film transistors

Dual-channel thin-film transistors (TFTs) show excellent effective mobility (μ eff ) and reliability, including negative-bias-illumination stability. To enhance the performance of these devices, post-thermal annealing in air is performed for 2 h at the low temperature of 250°C. To investigate the effects of low-temperature thermal annealing, indium–zinc-oxide/gallium–indium–zinc-oxide (IZO/IGZO) dual-channel TFTs with various IZO thicknesses are fabricated and examined. The observed parameters are μ eff, saturation mobility (μ sat ), subthreshold slope (SS), and threshold voltage (V TH ). The interface quality may be improved by low-temperature thermal annealing, which was confirmed by the improvement in μ eff and SS. However, these performance enhancements are intensively observed only in the channels with an IZO thickness below 10 nm. When the IZO thickness becomes 10 nm or more, the improvement in μ eff due to low-temperature thermal annealing hardly occurs. This is because μ eff is greatly influenced by the interface quality due to Coulomb scattering when the IZO thickness is <10 nm. However, for an IZO thickness above 10 nm, as phonon scattering also has a significant effect on μ eff, the improvement in interface quality by thermal annealing is small. This is also supported by low-frequency noise measurements, which are sensitive to interface quality.

Efficient Flexible Inorganic Perovskite Light-Emitting Diodes Fabricated with CsPbBr3 Emitters Prepared via Low-Temperature in Situ Dynamic Thermal Crystallization.

The present study systematically investigates the morphology and crystallization process of inorganic CsPbBr3 perovskite layer films fabricated by thermal coevaporation in conjunction with continuous low-temperature thermal annealing to promote in situ dynamic thermal crystallization. The results confirm for the first time that both the crystal grain size and the compactness of the CsPbBr3 films can be tuned during the thermal coevaporation fabrication process via in situ dynamic thermal crystallization. The performance of the PeLEDs employing the CsPbBr3 films as the emitter layer is investigated in detail with respect to the substrate temperature and deposition rate employed during deposition of the CsPbBr3 film. This study provides guidelines for developing suitable film production processes and highlights future challenges that must be addressed to facilitate the commercial development of large-area, uniform, and flexible perovskite-based optoelectronic devices.

Reducing graphene oxide using hydroiodic acid fumes and low temperature annealing for enhanced electrical conductivity

In this work, a novel hybrid technique for reduction of graphene oxide is explored. The hybrid technique involves chemical reduction of graphene oxide coated over oxidized silicon substrate, by minimal exposure to HI acid fumes followed by low temperature thermal annealing under vacuum environment. Observations have shown improved conductivity as compared to other hybrid techniques and low temperature thermal annealing technique.

Maskless Patterning of Metal Outflow in Alternating Metal/Ceramic Multiple Nanolayers by Femtosecond Laser Irradiation

In this work, solid-state metal transport from internal metal nanolayers onto the surface of metal/ceramic nano-multi-layers (NMLs) has been directed in a controlled way by femtosecond (fs) laser irradiation and subsequent low temperature thermal annealing. Laser irradiation induced modifications of the NML microstructures and stress states can be limited within the first few top nanolayers due to the focused laser energy input at the metal/ceramic interface by exploiting the local plasmonic effect. Accompanied laser peening can further refine the crystallites and introduce compressive stress at the laser-irradiated region, which reduces the activation energies for vacancy formation and migration of metal atoms in the nano-confinement. Patterned Cu surface nanostructures (outflow) appear selectively along the laser path after air annealing at temperatures down to 360 ℃. For the solid-state diffusion of Cu in confinement, in-plane metal transport along the Cu-AlN interfaces is much faster than the outward ...

EXAFS studies of enhancement of L21-B2 chemical disorder induced by ball milling in martensitic Ni50Mn36Sn14 pseudo-Heusler alloy

Chemical disorders in L21-B2-type structure, naturally occurred in 57Fe-doped Ni50Mn36Sn14 pseudo-Heusler alloy or enhanced in milled material, were systematically investigated using local probe methods: 57Fe Mössbauer spectroscopy (MS) and extended X-ray absorption fine structure (EXAFS). 57Fe Mössbauer studies show two Fe configurations: paramagnetic (singlet) and ferromagnetic (magnetic distribution) with approximately a 1:1 ratio. Fe atoms in singlet configuration are replacing Ni or Sn sites, where a near zero or magnetically frustrated state occurs. The magnetic distribution component is due to Fe magnetically coupled to Mn atoms. The singlet fraction is 100% after 220 s of milling. Low temperature thermal annealing easily recovers the original magnetic component and its initial ratio. Ni and Mn K-edges EXAFS spectra suggest that the milled material still displays the long range crystalline ordering, but with an enhancement of the local disorder due to Mn atoms occupying Sn sites and Mn-distance changes (D-sites of the L21 structure: Mn–Sn). While Mn–Mn distances seem to reduce slightly from 2.91 Å to 2.89 Å after the milling, the chemical disorder parameter (σ2) enhanced 29%. No change in Mn–Ni distances was observed; a condition necessary for observation of structural transition inside of crystalline grain. The structural transition properties change due to the increase of σ2-parameters of Mn–Ni (enhanced to 38%) and Mn–Sn (increased to 29%). EXAFS spectra of annealed sample indicate an improvement of the D-site symmetry, which is confirmed by a distance value of 2.92 Å for the Mn–Mn and Mn–Sn in the L21 structure as well as a large reduction (between 40% and 80%) of the σ2 parameter value. The chemical order improvement of the L21-structure favors Mn–Mn ferromagnetic order, indirectly measured by 57Fe MS that probed a magnetic hyperfine field component.

Plasma-jet-assisted maskless, erasable, extreme wetting-contrast patterning on stretchable carbon nanotubes film

We present a mask-free approach to fabricate patterned surfaces with extreme wetting-contrast on carbon nanotubes/polydimethylsiloxane films using atmospheric micro-plasma jet, merely through exploiting surface hierarchical roughness for superhydrophobic background and oxygenic functional groups for superhydrophilic patches in sequence. Such high-contrast wetting behavior can be fast erased upon low-temperature thermal annealing and recovered by direct plasma jet writing in atmosphere for five cycles. The superwettable patterns also exhibit rather excellent mechanical stability against tensile strain up to 100% and 1000 cyclic stretching under 50% strain. These appealing features endow their versatile potential in liquid manipulation and self-assembly applications towards flexible/stretchable device.

Incorporation of Pt Nanoparticles on the Surface of TeO₂-Branched Porous Si Nanowire Structures for Enhanced Room-Temperature Gas Sensing.

A new gas sensor working in room temperature, which is compatible with silicon fabrication technology is presented. Porous silicon nanowires (NWs) were synthesized by metal-assisted chemical etching method and then TeO₂ NWs branches were attached to their stem by thermal evaporation of Te powders in the presence of air. Afterwards TeO₂ branched porous Si NWs were functionalized by Pt via sputtering followed by low temperature thermal annealing. Scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy collectively confirmed successful formation of TeO₂ branched porous Si NWs functionalized by Pt nanoparticles. Their gas sensing properties in the presence of CO, C6H6 and C7H8 were tested at room temperature, for Si wafer, pristine porous Si NWs, pristine TeO₂ branched porous Si NWs, and Pt functionalized TeO₂ branched porous Si NWs sensors. Pt functionalized TeO₂ branched porous Si NWs have higher responses to all tested gases than the other sensors. The origin of high response is discussed in detail. This new room temperature gas sensor can open a new aperture for development of gas sensors with minimum energy consumption which are compatible with silicon fabrication technology.

Accurate analytical model for effective carrier mobility of fully hydrogenated poly-si TFTs under White light illumination

The effect of illumination on the effective carrier’s mobility of fully hydrogenated polycrystalline silicon TFT is investigated theoretically as well as experimentally. The polysilicon layers are deposited by LPCVD technique in the amorphous state and then crystallized by a low temperature thermal annealing. Experimental data show that the illumination affects the channel mobility only in the subthreshold region. Based on this, an analytical effective mobility model under illumination is established. The results show that the mobility under illumination follows the Meyer–Neldel rule (MNR). The proposed model is verified with the experimental data. A good agreement is obtained.