WE PROPOSE TO DEVELOP A NOVEL NORMAL-INCIDENCE X-RAY MIRROR FOR E0.5 KEV USING MULTILAYER COATING. THIS IS THE ENERGY OF THE ELUSIVE OXYGEN VII LINE EMITTED BY WARM CIRCUMGALACTIC GAS HALOS -- ONE OF THE MAJOR "DISCOVERY AREAS" IDENTIFIED BY THE 2020 ASTROPHYSICS DECADAL SURVEY. OUR MIRROR WOULD REFLECT IN A NARROW (FEW-EV) ENERGY INTERVAL, AND, FOR EXAMPLE, HELP SEPARATE THE FAINT REDSHIFTED OVII LINE FROM THE MUCH BRIGHTER, BUT NOT REDSHIFTED, OVII LINE ORIGINATING IN THE MILKY WAY. FOR INCIDENCE ANGLES CLOSE TO 90 DEG (SIMILAR TO OPTICAL TELESCOPES), SUCH A MIRROR CAN HAVE FEW-ARCSECOND ANGULAR RESOLUTION OVER A SIGNIFICANT FIELD OF VIEW, POTENTIALLY PROVIDING SHARP, NARROW-BAND IMAGING AT LOW COST. THE COATING WOULD CONSIST OF MANY LAYERS OF CONTRASTING-DENSITY MATERIALS THAT MUST BE VERY SHARP TO ACHIEVE A USEFUL BRAGG REFLECTIVITY. WHILE NORMAL-INCIDENCE MULTILAYER MIRRORS HAVE BEEN BUILT FOR FAR UV AND VERY LOW-ENERGY X-RAYS (E0.1 KEV), IT HAS NOT BEEN POSSIBLE TO GO TO HIGHER ENERGIES, BECAUSE THE LAYER PERIOD BECOMES VERY SMALL -- 1.1NM FOR OUR ENERGIES OF INTEREST, THE SIZE OF A FEW ATOMS. WE WILL EMPLOY ATOMIC LAYER DEPOSITION (ALD) -- A TECHNIQUE THAT IS CURRENTLY EXPERIENCING FAST DEVELOPMENT IN MANY INDUSTRIES -- TO DEPOSIT LAYERS OF THE REQUISITE SHARPNESS. ALD IS A SELF-LIMITING CHEMICAL REACTION THAT RESULTS IN DEPOSITING STRICTLY ONE MOLECULAR LAYER OF THE MATERIAL ON THE SURFACE, FREE OF THE RANDOM-SHOT ERROR OF THE TRADITIONAL TECHNIQUES THAT BECOMES INTOLERABLE FOR THE SMALL LAYER THICKNESS THAT WE NEED. OUR PRELIMINARY TRIALS HAVE BEEN ENCOURAGING, BUT MORE MATERIAL PAIRS AND ALD VARIANTS MUST BE TRIED. WE PROPOSE TO PURSUE SEVERAL ALD METHODS IN-HOUSE AND USE COMMERCIAL EXPERTISE WHERE EFFICIENT. THE TEAM INCLUDES SCIENTISTS FROM GODDARD AND UNIVERSITY OF TEXAS.