2D-Material-Assisted GaN Growth on GaN Template by MOCVD and Its Exfoliation Strategy.

The production of freestanding membranes using two-dimensional (2D) materials often involves techniques such as van der Waals (vdW) epitaxy, quasi-vdW epitaxy, and remote epitaxy. However, a challenge arises when attempting to manufacture freestanding GaN by using these 2D-material-assisted growth techniques. The issue lies in securing stability, as high-temperature growth conditions under metal-organic chemical vapor deposition (MOCVD) can cause damage to the 2D materials due to GaN decomposition of the substrate. Even when GaN is successfully grown using this method, damage to the 2D material leads to direct bonding with the substrate, making the exfoliation of the grown GaN nearly impossible. This study introduces an approach for GaN growth and exfoliation on 2D material/GaN templates. First, graphene and hexagonal boron nitride (h-BN) were transferred onto the GaN template, creating stable conditions under high temperatures and various gases in MOCVD. GaN was grown in a two-step process at 750 and 900 °C, ensuring exfoliation in cases where the 2D materials remained intact. Essentially, while it is challenging to grow GaN on 2D material/GaN using only MOCVD, this study demonstrates that with effective protection of the 2D material, the grown GaN can endure high temperatures and still be exfoliated. Furthermore, these results support that vdW epitaxy and remote epitaxy principle are not only possible with specific equipment but also applicable generally.

Stability of Graphene and Influence of AlN Surface Pits on GaN Remote Heteroepitaxy for Exfoliation.

Remote epitaxy is a promising technology that has recently attracted considerable attention, which enables the growth of thin films that copy the crystallographic characteristics of the substrate through two-dimensional material interlayers. The grown films can be exfoliated to form freestanding membranes, although it is often challenging to apply this technique if the substrate materials are prone to damage under harsh epitaxy conditions. For example, remote epitaxy of GaN thin films on graphene/GaN templates has not been achieved by a standard metal-organic chemical vapor deposition (MOCVD) method due to such damages. Here, we report GaN remote heteroepitaxy on graphene/AlN templates by MOCVD and investigate the influence of surface pits in AlN on the growth and exfoliation of GaN thin films. We first show the thermal stability of graphene before GaN growth, based on which two-step growth of GaN on graphene/AlN is developed. The GaN samples are successfully exfoliated after the first step of the growth at 750 °C, whereas the exfoliation failed after the second step at 1050 °C. In-depth analysis confirms that the pits in AlN templates lead to the degradation of graphene near the area and thus the alteration of growth modes and the failure of exfoliation. These results exemplify the importance of chemical and topographic properties of growth templates for successful remote epitaxy. It is one of the key factors for III-nitride-based remote epitaxy, and these results are expected to be of great help in realizing complete remote epitaxy using only MOCVD.

Impact of Na Doping on the Carrier Transport Path in Polycrystalline Flexible Cu2ZnSn(S,Se)4 Solar Cells.

It is well-known that the alkali doping of polycrystalline Cu2ZnSn(S,Se)4 (CZTSSe) and Cu(In,Ga)(Se,S)2 has a beneficial influence on the device performance and there are various hypotheses about the principles of performance improvement. This work clearly explains the effect of Na doping on the fill factor (FF) rather than on all of the solar cell parameters (open-circuit voltage, FF, and sometimes short circuit current) for overall performance improvement. When doping is optimized, the fabricated device shows sufficient built-in potential and selects a better carrier transport path by the high potential difference between the intragrains and the grain boundaries. On the other hand, when doping is excessive, the device shows low contact potential difference and FF and selects a worse carrier transport path even though the built-in potential becomes stronger. The fabricated CZTSSe solar cell on a flexible metal foil optimized with a 25 nm thick NaF doping layer achieves an FF of 62.63%, thereby clearly showing the enhancing effect of Na doping.

Flexible High-Efficiency CZTSSe Solar Cells on Diverse Flexible Substrates via an Adhesive-Bonding Transfer Method.

Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells are showing great promise due to using earth-abundant and nontoxic materials and tuning the band gap through the amount of S and Se. Flexible high-efficiency CZTSSe solar cells are one of the outstanding research challenges because they currently require the use of thick glass substrates due to the high-temperature heat treatment process, and for this reason, few flexible CZTSSe solar cells have been reported. Furthermore, most researchers have used thin glass and metal substrates with little flexibility; the power conversion efficiency (PCE or η) values of the solar cells made with them have been slightly lower. To overcome these hurdles, we transferred high-efficiency CZTSSe solar cells formed on a soda-lime glass substrate to flexible substrates via an adhesive-bonding transfer method. Through this method, we were able to achieve the PCE of 5.8-7.1% on completely flexible substrates such as cloth, paper, and poly(ethylene terephthalate) (PET). In particular, we were able to produce a CZTSSe solar cell on a PET substrate with a PCE of 7.1%, which is the highest among fully flexible CZTSSe solar cells currently known to us. In addition, we deeply analyzed the PCE degradation of the flexible CZTSSe solar cell fabricated by the transfer method through a panoramic focused ion-beam image and nanoindentation. From the results of our work, we provide an insight into the possibility of making flexible high-efficiency CZTSSe solar cells using our transfer method.

Cervicofacial Flap: Can We Save Patient's Sideburns?

BACKGROUND: The conventional cervicofacial flap may cause the aesthetic problem of sideburns with a mismatched shape and arrangement. We developed a modified method with the goals of minimizing the destruction of the shape and arrangement of the sideburns and minimizing complications in comparison with the conventional method. METHODS: The incision line was designed to descend just in front of the sideburns, without passing through them, and then to ascend with the sideburns posteriorly when a cervicofacial flap is performed, unlike the conventional method. Patients in whom this method was applied (group B) and patients who underwent surgery using the conventional method (group A) were investigated in a retrospective study. The method was evaluated by assessing changes in the arrangement of the sideburns and patients' satisfaction, and differences in the complication rate. RESULTS: In group A, 23 of the 31 patients experienced changes in the arrangement of their sideburns. Most patients who experienced a change in the arrangement of their sideburns were dissatisfied with the change. The patients in group B did not experience such changes, and the defects were well reconstructed. Most of them were satisfied with the final sideburn arrangement. CONCLUSION: A novel method was used to preserve the sideburns while performing a cervicofacial flap. As a result, the appearance of the sideburns was well preserved and the satisfaction of patients was also high. Moreover, this technique could also prove useful for reconstruction without any increase in complications compared to the conventional method.

Post-Traumatic Peripheral Giant Osteoma in the Frontal Bone.

Osteomas are benign, slow-growing tumors that most frequently occur in the craniomaxillofacial region. These tumors are mostly asymptomatic and are generally found incidentally. A giant osteoma is generally considered to be greater than 30 mm in diameter or 110 g in weight. A 35-year-old female presented to us with complaints of a firm mass that showed continuous growth on the forehead following trauma. A hairline incision was made to expose the osteoma. Biopsy of the tumor confirmed a osteoma. There were no complications after surgery. Postoperative computed tomography revealed that the tumor was completely removed. Because a peripheral giant osteoma of the frontal bone with a history of trauma is a rare finding, thorough history-taking, physical examination, and preoperative imaging tests are needed for patients with a history of trauma to rule out a giant osteoma.

The Relationship between the Size and the Invasion Depth of Tumors in Head and Neck Cutaneous Squamous Cell Carcinoma.

BACKGROUND: Cutaneous squamous cell carcinoma (SCC), which occurs in keratinocytes of the epidermis and is the second most common skin cancer, has a more invasive growth pattern and higher potential to metastasize than basal cell carcinoma. Total excision of the primary tumor is the treatment of choice. For clear excision of the tumor, invasion depth is one of the most important factors. This study was conducted to clarify the relationship between the size and the invasion depth of cutaneous SCC. METHODS: Twenty-six cases were collected for this prospective study. Frozen biopsies were examined after complete resection of the tumor, followed by histological confirmation by pathological examination. The major and minor axis lengths of the tumor, the invasion depth, and the level of invasion were measured. Recurrence or metastasis was recorded through regular follow-up. RESULTS: The Pearson correlation coefficient was used for statistical analysis. Significant results were observed for the relationship between the major and minor axis lengths and the invasion depth of the tumor (0.747, 0.773). No cases of recurrence or metastasis were observed. CONCLUSIONS: In head and neck cutaneous SCC, the invasion depth of the tumor is closely related to the major and minor axis lengths of the tumor. Therefore, the invasion depth of the tumor can be estimated by measuring the size of the tumor, and a standard vertical safety margin for head and neck cutaneous SCC can be established, which could be helpful in the development of a preoperative reconstruction plan.

The Versatility of Cheek Rotation Flaps.

BACKGROUND: The cheek rotation flap has sufficient blood flow and large flap size and it is also flexible and easy to manipulate. It has been used for reconstruction of defects on cheek, lower eyelid, or medial and lateral canthus. For the large defects on central nose, paramedian forehead flap has been used, but patients were reluctant despite the remaining same skin tone on damaged area because of remaining scars on forehead. However, the cheek flap is cosmetically superior as it uses the adjacent large flap. Thus, the study aims to demonstrate its versatility with clinical practices. METHODS: This is retrospective case study on 38 patients who removed facial masses and reconstructed by the cheek rotation flap from 2008 to 2015. It consists of defects on cheek (16), lower eyelid (12), nose (3), medial canthus (3), lateral canthus (2), and preauricle (2). Buccal mucosa was used for the reconstruction of eyelid conjunctiva, and skin graft was processed for nasal mucosa reconstruction. RESULTS: The average defect size was 6.4 cm2, and the average flap size was 47.3 cm2. Every flap recovered without complications such as abnormal slant, entropion or ectropion in lower eyelid, but revision surgery required in three cases of nasal side wall reconstruction due to the occurrence of dog ear on nasolabial sulcus. CONCLUSION: The cheek rotation flap can be applicable instead of paramedian forehead flap for the large nasal sidewall defect reconstruction as well as former medial and lateral canthal defect reconstruction.