Concurrent self-assembly of RGB microLEDs for next-generation displays.

MicroLED displays have been in the spotlight as the next-generation displays owing to their various advantages, including long lifetime and high brightness compared with organic light-emitting diode (OLED) displays. As a result, microLED technology1,2 is being commercialized for large-screen displays such as digital signage and active R&D programmes are being carried out for other applications, such as augmented reality3, flexible displays4 and biological imaging5. However, substantial obstacles in transfer technology, namely, high throughput, high yield and production scalability up to Generation 10+ (2,940 × 3,370 mm2) glass sizes, need to be overcome so that microLEDs can enter mainstream product markets and compete with liquid-crystal displays and OLED displays. Here we present a new transfer method based on fluidic self-assembly (FSA) technology, named magnetic-force-assisted dielectrophoretic self-assembly technology (MDSAT), which combines magnetic and dielectrophoresis (DEP) forces to achieve a simultaneous red, green and blue (RGB) LED transfer yield of 99.99% within 15 min. By embedding nickel, a ferromagnetic material, in the microLEDs, their movements were controlled by using magnets, and by applying localized DEP force centred around the receptor holes, these microLEDs were effectively captured and assembled in the receptor site. Furthermore, concurrent assembly of RGB LEDs were demonstrated through shape matching between microLEDs and receptors. Finally, a light-emitting panel was fabricated, showing damage-free transfer characteristics and uniform RGB electroluminescence emission, demonstrating our MDSAT method to be an excellent transfer technology candidate for high-volume production of mainstream commercial products.

Distinct U-shape efficiency-versus-current curves in AlGaN-based deep-ultraviolet light-emitting diodes.

The efficiency of an AlGaN deep-ultraviolet light-emitting diode with peak emission wavelength of 285 nm is investigated as a function of current over a wide range of temperatures (110 K to 300 K). We find that the efficiency-versus-current curve exhibits unique and distinct features over the entire temperature range including three points of inflection. At low temperatures, the change in slope in the efficiency-versus-current curve is particularly pronounced producing a minimum in the efficiency after which the efficiency rises again. Furthermore, at high current density, the low-temperature efficiency exceeds the room-temperature efficiency. The feature-rich efficiency-versus-current curve is consistent with an enhancement in p-type conductivity by field-ionization of acceptors that occurs in the high-injection regime and is particularly pronounced at low temperatures. Differential conductivity measurements show a marked rise in the high-injection regime that is well correlated to the minimum point in the efficiency-versus-current curve.

Geometric part error and material property profile separation technique of the additively manufactured and post-processed rods.

This paper presents novel surface profilometry for both geometric part error and metallurgical material property distribution measurements of the additively manufactured and post-processed rods. The measurement system, the so-called fiber optic-eddy current sensor, consists of a fiber optic displacement sensor and an eddy current sensor. The electromagnetic coil was wrapped around the probe of the fiber optic displacement sensor. The fiber optic displacement sensor was used to measure the surface profile, and the eddy current sensor was used to measure the change in permeability of the rod under varying electromagnetic excitation conditions. The permeability of the material changes upon exposure to mechanical forces, such as compression or extension and high temperatures. The geometric part error and material property profiles of the rods were successfully extracted by using a reversal method that is conventionally used for spindle error separation. The fiber optic displacement sensor and the eddy current sensor developed in this study have a resolution of 0.286 µm and 0.00359 µr, respectively. The proposed method was applied not only to characterize the rods but also to characterize composite rods.

A monolithic linear motion platform driven by a piezoelectric and fluidic pressure-fed dual mechanism.

This paper presents a novel dual-mode motion mechanism capable of achieving nanopositioning on a monolithic linear motion platform. Unlike conventional dual-mode stages that use piezoelectric (PZT)- and electromagnetic-combined or similar actuation mechanisms comprising two separate motion axes, the dual-mode actuation was developed by combining a PZT for a coarse motion and a fluidic pressure-fed mechanism (FPFM) for a fine motion and was implemented in a monolithic flexure stage fabricated by metal additive manufacturing. The FPFM actuates the flexure stage by pressuring the media in the fluidic channels created inside the flexure spring structures. Experimental tests were performed to investigate the performance of the dual-mode linear motion platform. The stiffness, damping, and frequency response functions of the dual-mode stage were experimentally characterized. The proportional-integral-differential control combined with dual-mode control was employed to control the position of the flexure stage while bidirectionally controlling the flow of compressed air for a fine motion. The FPFM motion showed a good response to 1 nm stepwise input (every 10 psi), and it was implemented to provide up to ∼10 nm fine motion along with the PZT coarse motion (1 µm). The hysteresis characteristics of the FPFM were also characterized and compensated to track the positioning error.

The Association between Macular Thickness and Axial Length in Myopic Eyes.

PURPOSE: To investigate the relationship between macular thickness and axial length (AL) in myopic eyes. METHODS: We included 441 myopic eyes in this study and measured macular thickness at the fovea and in other macular regions, using optical coherence tomography. We got thickness difference indices (TDIs) which by definition are the values of thickness difference obtained by subtracting the foveal thickness from that of each macula sector to evaluate macular contour. We then analyzed the relationships between AL and foveal thickness and AL and the TDIs of each macular sector. RESULTS: In polynomial regression analyses, foveal thickness slope was relatively flat up to an AL of 25.5 mm and began to rise from 25.5-26.0 mm. The TDIs were also relatively flat up to AL of 25.5mm and started to show steepened negative slopes from around AL of 25.5 mm. When grouping myopia participants as high myopia or non-high myopia based on AL of 25.5mm, all macular indices of the high myopia group showed significant correlation with AL (all p values <0.01). But all indices of non-high myopia group had no significant correlation with AL. CONCLUSIONS: Average macular thickness profiles showed that appreciable changes started at an AL of 25.5mm.

Asymmetry of the macular structure is associated with ocular dominance.

OBJECTIVE: We hypothesized that the ocular dominance associated with brain asymmetry would influence macular structure. We assessed the structural asymmetry of the macula by ocular dominance. METHODS: A total of 144 patients with no ophthalmic abnormalities were examined. After classifying eyes as dominant or non-dominant using the hole-in-a-card test, the macular ganglion cell inner plexiform layer and the macular thickness were measured in both groups using spectral domain optical coherence tomography, and we sought associations between ocular dominance and retinal thickness. RESULTS: Ocular dominance was more frequently found in right eyes than in left eyes (68.75% vs 31.25%, respectively; p < 0.001). Using conditioned logistic regression, the right eye and the temporal-to-nasal retinal thickness ratio of the macular ganglion cell inner plexiform layer were selected as a final model for the determination of ocular dominance (p < 0.001, p = 0.013 respectively). CONCLUSIONS: Macular vertical asymmetry was associated with ocular dominance. The macular structure and ocular dominance associated with visual cortex lateralization have functional and structural relationships.

Ganglion Cell-Inner Plexiform Layer, Peripapillary Retinal Nerve Fiber Layer, and Macular Thickness in Eyes with Myopic ß-Zone Parapapillary Atrophy.

Purpose. To assess the correlations of myopic ß-zone parapapillary atrophy (ß-PPA) with the optic nerve head (ONH) and retina. Methods. We selected 27 myopic patients who showed prominent ß-PPA in one eye and no ß-PPA in the other eye. We studied their macula, macular ganglion cell-inner plexiform layer (mGCIPL), peripapillary retinal nerve fiber layer (pRNFL) thickness, and ONH parameters using optical coherence tomography. Results. The average of five out of six sectors and minimum values of mGCIPL thicknesses in eyes with prominent ß-PPA discs were significantly less than those of the control eyes. The results of clock-hour sector analyses showed significant differences for pRNFL thickness in one sector. In the ONH analyses, no significant difference was observed between myopic ß-PPA and control eyes. The macular thickness of the ß-PPA eyes was thinner than control eyes in all sectors. There was a significant difference between the two groups in three sectors (the inner superior macula, inner temporal macula, and inner inferior macula) but there was no significant difference in the other sectors, including the fovea. Conclusions. The myopic ß-PPA eyes showed thinner mGCIPL, parafovea, and partial pRNFL layers compared with myopic eyes without ß-PPA.

Ocular Dominance Is Associated with the Ganglion Cell-Inner Plexiform Layer Thickness Profile in the Macula.

PURPOSE: To investigate the characteristics of macular ganglion cell-inner plexiform layer (GCIPL) thickness profiles associated with ocular dominance. SETTING: Private practice, Seoul, Republic of Korea. DESIGN: Comparative case-control study. METHODS: Both eyes of 199 participants with no ophthalmic abnormalities were included. Participants were imaged by spectral-domain optical coherence tomography, and underwent dominant eye testing using a hole-in-a-card test (sighting dominance) at the same visit. Macular GCIPL, as well as circumpapillary retinal nerve fiber layer (RNFL) thickness were compared for individual patients, according to ocular dominance. RESULTS: Ocular dominance occurred predominantly in the right eye (right vs. left: 72.36 vs. 27.60%; P < 0.001). In the comparison of macular GCIPL thickness, the average (81.27±5.01 µm vs. 80.66±6.31 µm in dominant vs. non-dominant eyes), inferonasal (81.39±5.47µm vs. 80.33±6.82µm, and inferior sectors (77.95±6.05µm vs. 76.97±8.15µm) were significantly different between dominant and non-dominant eyes (P = 0.040, 0.005, and 0.032, respectively). Significant predictors of average GCIPL thickness were spherical equivalent (ß = 1.37, P<0.001), astigmatic power (ß = 1.44, P = 0.009), disc area (ß = 3.90, P < 0.001), average RNFL thickness (ß = 0.22, P<0.001), average cup-to-disc ratio (ß = 5.74, P = 0.002), difference between the inferior and superior quadrant RNFL thicknesses (ß = 0.08, P = 0.024), and ocular dominance (ß = 2.10, P = 0.020). On multivariate regression analysis, ocular dominance was correlated with average GCIPL thickness after adjusting for potential confounders (ß = 1.63, P = 0.048). CONCLUSIONS: Dominant eyes accompanied significantly thicker average macular GCIPL. This information suggests that macular GCIPL thickness may provide an indicator of the relative dominance of an eye.

An elegant route to overcome fundamentally-limited light extraction in AlGaN deep-ultraviolet light-emitting diodes: Preferential outcoupling of strong in-plane emission.

While there is an urgent need for semiconductor-based efficient deep ultraviolet (DUV) sources, the efficiency of AlGaN DUV light-emitting diodes (LEDs) remains very low because the extraction of DUV photons is significantly limited by intrinsic material properties of AlGaN. Here, we present an elegant approach based on a DUV LED having multiple mesa stripes whose inclined sidewalls are covered by a MgF2/Al omni-directional mirror to take advantage of the strongly anisotropic transverse-magnetic polarized emission pattern of AlGaN quantum wells. The sidewall-emission-enhanced DUV LED breaks through the fundamental limitations caused by the intrinsic properties of AlGaN, thus shows a remarkable improvement in light extraction as well as operating voltage. Furthermore, an analytic model is developed to understand and precisely estimate the extraction of DUV photons from AlGaN DUV LEDs, and hence to provide promising routes for maximizing the power conversion efficiency.

Retinal nerve fiber layer thickness profiles associated with ocular laterality and dominance.

Although human anatomy is arranged symmetrically based on a central vertical axis, the majority of persons will use one side of their body more readily than the other. Interestingly, these lateral body dominances including ocular dominance are all rightward. The asymmetry in retinal nerve fiber layer (RNFL) thickness between the right and left eyes in healthy subjects has been reported in several studies, and the reason for this structural difference between right and left eyes is unclear. In the manuscript, we hypothesized that the characteristics of ocular dominance are reflected in the RNFL profile and may be related to inter-ocular structural differences between right and left eyes. In this study, ocular dominance occurred mostly in right eyes (right vs. left: 78.77% vs. 21.22%; P<0.001). According to ocular dominance and laterality, different relationships between the inferior and superior RNFLs were observed. The right eyes had a thicker RNFL, except in the superior quadrant, than the left eyes. Regardless of laterality, inferior RNFL was thicker than superior RNFL in the dominant eyes. To our knowledge, this paper is the first report demonstrating the RNFL characteristics associated with ocular dominance.

The foveal position relative to the optic disc and the retinal nerve fiber layer thickness profile in myopia.

PURPOSE: To evaluate retinal nerve fiber layer (RNFL) thickness profiles according to the foveal position relative to the optic disc in myopia METHODS: In 164 eyes of 164 healthy myopic subjects, the disc-foveal angle was defined as the angle between a horizontal line through the disc center and the line connecting the fovea and disc center in fundus photographs overlaid on Cirrus-HD optical coherence tomography (OCT) images. The quadrant/clock-hour based peripapillary RNFL thickness and differences between the inferior and superior (I-S) quadrant RNFL thicknesses were measured with OCT. RNFL thickness profiles were determined according to the disc-foveal angle and axial length (AL). RESULTS: As the disc-foveal angle increased (i.e., the fovea becomes more inferior to the optic disc), the superior RNFL decreased significantly (P = 0.003), whereas the inferior RNFL and I-S difference increased (P = 0.010 and P < 0.001, respectively). As the AL increased, the average and temporal RNFLs increased significantly (P = 0.013 and P < 0.001, respectively), and I-S difference was not affected (P = 0.231). The disc-foveal angle was significantly decreased with the distance between the fovea and the optic disc (P = 0.033). In multiple linear regression analysis, the disc-foveal angle was found to be a significant factor related to I-S differences, superior and inferior RNFL (all, P < 0.05) after adjusting for age, disc area, and AL. CONCLUSIONS: The intrinsic foveal position relative to the optic disc was an essential determinant of normal RNFL thickness in myopia. In particular, it was associated with the vertical asymmetry of RNFL distribution.

Base curves of therapeutic lenses and their effects on post Epi-LASIK vision and pain: a prospective randomized clinical trial.

PURPOSE: To compare the efficacy of bandage contact lenses with two different base curves in promoting epithelial healing after epithelial laser in situ keratomileusis (epi-LASIK). METHODS: A prospective, observer-masked study was conducted in 27 patients. Each patient randomly received one bandage contact lens with an 8.4-mm base curve in one eye and one with an 8.8-mm base curve in the fellow eye. Corneal epithelial status, pain score, spherical equivalent, and uncorrected visual acuity (UCVA) were examined during the first postoperative month. RESULTS: Corneal epithelial status, postoperative pain, and spherical equivalent were similar for both lenses during the first postoperative month. The eyes with lenses with an 8.8-mm base curve had better UCVA on postoperative day (POD) 4, but there was no significant difference in UCVA after POD 7. In the patients with preoperative low to moderate myopia and low keratometric values (<43.0 D), there was no significant difference in the postoperative UCVA between the lenses. On the other hand, in patients with preoperative high myopia and high keratometric values (> or =43.0 D), UCVA was better in eyes with lenses with an 8.8-mm base curve on POD 4. CONCLUSIONS: These findings suggest that the base curves of bandage contact lenses affect visual rehabilitation after epi-LASIK, particularly in patients with a steep cornea and high myopia.

Clinical application of a Scheimpflug system for lens density measurements in phacoemulsification.

PURPOSE: To evaluate the relationship between lens density measured using the Pentacam Scheimpflug system and phacodynamics (phacoemulsification time, phacoemulsification energy, and balanced salt solution [BSS] use) in patients with age-related nuclear cataract. SETTING: Department of Ophthalmology and Visual Science, Kangnam St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea. METHODS: This prospective observer-masked study was of eyes with age-related nuclear cataract. Objective lens density (0 to 100 points) was determined using the Scheimpflug system. Subjective grading was by the Lens Opacities Classification System III (LOCS III). The correlations between lens density values and phacoemulsification time, phacoemulsification energy, and BSS use were analyzed prospectively. RESULTS: Fifty-three patients (60 eyes) were evaluated. The mean Scheimpflug-measured lens nuclear density was 14.71 +/- 6.12 (SD). There was a positive linear correlation between the Scheimpflug-measured lens nuclear density and the LOCS III grading scores for nuclear opalescence (NO) and nuclear color (NC) (r = 0.734 and 0.719, respectively; both P<.05). The Scheimpflug-measured lens nuclear density correlated with torsional amplitude, time, and cumulated dissipated energy (CDE) (P<.05), but not with BSS use (P = .195). The CDE was more strongly correlated with Scheimpflug-measured lens nuclear density (r = 0.797) than with LOCS III NO or NC scores (r = 0.614 and r = 0.637, respectively). CONCLUSIONS: Scheimpflug-measured lens nuclear density correlated with phacoemulsification time and energy. The Scheimpflug system enabled quantitative cataract grading and may help predict phacodynamics in cataract surgery.